U.S. patent application number 10/718728 was filed with the patent office on 2004-06-17 for exposure apparatus, exposure method using the same, and method of manufacture of circuit device.
This patent application is currently assigned to Nikon Corporation. Invention is credited to Kiuchi, Toru, Nishi, Kenji.
Application Number | 20040114121 10/718728 |
Document ID | / |
Family ID | 27309588 |
Filed Date | 2004-06-17 |
United States Patent
Application |
20040114121 |
Kind Code |
A1 |
Nishi, Kenji ; et
al. |
June 17, 2004 |
Exposure apparatus, exposure method using the same, and method of
manufacture of circuit device
Abstract
A reflective member is fixedly or movably provided near the
pupil plane of a projection optical system with which a projection
exposure apparatus is equipped. A collimated measuring beam with an
exposure wavelength is incident from the object plane side or image
plane side of the projection optical system, and the intensity of
the beam reflected by the reflective member is detected
photoelectrically to measure a value corresponding to the
attenuation factor (transmissivity or reflectivity) of the
projection optical system or the variation with time of the
attenuation factor (transmissivity or reflectivity) of the
projection optical system. In accordance with the measurement
results, the exposing conditions when a photosensitive substrate is
exposed are corrected to avoid the deterioration of the exposure
control precision due to the variation of the attenuation factor
(transmissivity variation or reflectivity variation) which is
caused in the projection optical system and illumination optical
system of a projection exposure apparatus which uses ultraviolet
illumination light.
Inventors: |
Nishi, Kenji; (Tokyo,
JP) ; Kiuchi, Toru; (Tokyo, JP) |
Correspondence
Address: |
WESTERMAN, HATTORI, DANIELS & ADRIAN, LLP
Suite 700
1250 Connecticut Avenue, N.W.
Washington
DC
20006
US
|
Assignee: |
Nikon Corporation
Tokyo
JP
|
Family ID: |
27309588 |
Appl. No.: |
10/718728 |
Filed: |
November 24, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10718728 |
Nov 24, 2003 |
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09908563 |
Jul 20, 2001 |
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09908563 |
Jul 20, 2001 |
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09420000 |
Oct 18, 1999 |
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6414743 |
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09420000 |
Oct 18, 1999 |
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PCT/JP98/01776 |
Apr 17, 1998 |
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Current U.S.
Class: |
355/67 |
Current CPC
Class: |
G03F 7/7085 20130101;
G03F 7/70066 20130101; G03F 7/70941 20130101; G03F 7/70241
20130101; G03F 7/70258 20130101; G03F 7/70058 20130101; G03F
7/70225 20130101; G03F 7/70558 20130101; G03F 7/70358 20130101;
G03F 7/70591 20130101 |
Class at
Publication: |
355/067 |
International
Class: |
G03B 027/54 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 18, 1997 |
JP |
101954/1997 |
Apr 22, 1997 |
JP |
104978/1997 |
Aug 28, 1997 |
JP |
233109/1997 |
Claims
1. An exposure apparatus having: an irradiation means for
irradiating a pattern formed on a mask with an exposing energy
having a wavelength of 250 nm or less; and a projection optical
system for projecting an image of the pattern of the mask at a
predetermined position on a substrate; characterized by a
reflecting member, disposed at least a portion in a Fourier
transform plane formed between an object plane and an image plane
of the projection optical system or in a plane in the vicinity
thereof, having reflecting properties relative to the exposing
energy incident from an object plane side of the projection optical
system or the exposing energy incident from an image plane side of
the projection optical system; wherein an exposing condition for
the substrate is set on the basis of intensity of a reflected
energy reflected from the reflecting member, in order to reduce
deterioration in precision for controlling an exposure amount
resulting from a variation in an attenuation factor of the
projection optical system.
2. An exposure apparatus having: an irradiation means for
irradiating a pattern formed on a mask with an exposing energy
having a wavelength of 250 nm or less; and a projection optical
system for projecting an image of the pattern of the mask at a
predetermined position on a substrate; characterized by a
reflecting member, disposed at least a portion in a Fourier
transform plane formed between an object plane and an image plane
of the projection optical system or in a plane in the vicinity
thereof, having reflecting properties relative to the exposing
energy incident from an object plane side of the projection optical
system or the exposing energy incident from an image plane side of
the projection optical system; a beams irradiation means which
irradiate measuring beams in a state that the exposing energy is
nearly collimated, toward the reflecting member from an object
plane side or an image plane side of the projection optical system;
a detection means which detect an energy reflected by the
reflecting member and output a detection signal in accordance with
the reflected energy; and an exposure control means which set an
exposing condition for the substrate on the basis of the detection
signal from the detection means, in order to reduce deterioration
in precision for controlling an exposure amount resulting from a
variation in an attenuation factor of the projection optical
system.
3. The exposure apparatus as claimed in claim 2, wherein the
reflecting member is disposed at a generally central portion, a
peripheral portion or at an entire area in the Fourier transform
plane of the projection optical system or in the plane in the
vicinity thereof.
4. The exposure apparatus as claimed in claim 3, wherein the
irradiation means comprises a pulse laser light source which
radiates ultraviolet pulse light having a wavelength of 200 nm or
less as the exposing energy, and an exposing illumination system
which irradiates the ultraviolet pulse light toward a predetermined
illumination region set on the mask; and the beam irradiation means
comprises a beam generating optical system which generates the
measuring beams based on the ultraviolet pulse light from the pulse
laser light source.
5. The exposure apparatus as claimed in claim 4, wherein the beam
generating optical system is disposed on the object plane side of
the projection optical system and the detection means, which detect
the reflected energy, is disposed on the object plane side of the
projection optical system.
6. The exposure apparatus as claimed in claim 4, wherein the beams
generating optical system is disposed on the image plane side of
the projection optical system and the detection means is disposed
on the image plane side of the projection optical system.
7. The exposure apparatus as claimed in claim 3, wherein the
reflecting member has a reflecting plane for deflecting the
reflected energy from a projection light path in the projection
optical system, and the detection means is disposed outside the
projection light path.
8. The exposure apparatus as claimed in claim 3, further comprising
a movable mechanism for supporting the reflecting member so as to
enter the reflecting member in the Fourier transform plane of the
projection optical system or in the plane in the vicinity thereof,
or evacuate it therefrom, wherein the reflecting member enters a
projection light path when the measuring beams are irradiated into
the projection optical system and is evacuated therefrom when the
pattern of the mask is projected and exposed to the substrate.
9. The exposure apparatus as claimed in claim 2, wherein the
projection optical system is of a catadioptric type in which a
refractive optical element is combined with a reflective optical
element.
10. A method for scanning and exposing an entire image of a pattern
of a mask to a substrate being exposed, which is carried out by:
irradiating a portion of the pattern of the mask with an exposing
energy having a wavelength of 250 nm or less; and scanning the mask
and the substrate relative to a vision field of the projection
optical system, while projecting a partial image of the pattern
thereof onto the substrate through a projection optical system;
characterized by the steps of: irradiating the exposing energy onto
a reflecting member prior to starting the scanning exposure, the
reflecting member being disposed at least at a portion in a Fourier
transform plane formed between an object plane and an image plane
of the projection optical system or in a plane in the vicinity
thereof, and detecting intensity of a reflected energy reflected
from the reflecting member; and setting an exposing condition for
transcribing the entire image of the pattern thereof onto the
exposing substrate at a predetermined exposure amount in accordance
with the intensity detected.
11. The exposure method as claimed in claim 10, wherein the
exposing energy to be irradiated on the reflecting member passes
through the object plane side or the image plane side of the
projection optical system in a substantially collimated state and
is substantially converged on the reflecting member.
12. The exposure method as claimed in claim 11, wherein during the
scanning and exposing, when the mask is transferred to at least one
of a position at which the scanning of the mask relative to a
vision field of the projection optical system is started or a
position at which the scanning of the mask relative to the vision
field thereof is terminated, the exposure energy is shaped into
measuring beams being generally parallel to each other and
irradiated onto the reflecting member from the object plane side or
the image plane side of the projection optical system, and then the
intensity of the reflected energy reflected from the reflecting
member is detected.
13. The exposure method as claimed in claim 12, wherein when the
exposing condition is set, at least one of an illuminance of the
exposing energy to be irradiated on the mask during the scanning
and exposing, a width of the energy in the scanning direction to be
irradiated on the mask, and a velocity for scanning the mask and
the substrate during the scanning and exposing is adjusted on the
basis of a result of detection of the intensity of the exposing
energy to be irradiated on the mask for scanning exposure, a result
of detection of the intensity of the reflected energy which is
reflected by the reflecting member by irradiation of the measuring
beams and a target exposure amount to be provided on the
substrate.
14. The exposure method as claimed in claim 12, wherein the
reflecting member is formed at a portion of a refractive optical
element or a reflective optical element located in the Fourier
transform plane of the projection optical system or in the plane in
the vicinity thereof.
15. The exposure apparatus as claimed in claim 10, wherein the
projection optical system is of a catadioptric type in which the
refractive optical element and the reflective optical element are
combined with each other.
16. A manufacturing method for forming a circuit device on a
substrate, which is carried out by a lithographic process
comprising; irradiating a circuit pattern formed on a mask with an
exposing energy; and exposing the circuit pattern thereof to each
of plural positions on the substrate sequentially through a
projection optical system; characterized by the steps of: detecting
an intensity of the exposing energy passing through a projection
light path, including a portion of a variation in an attenuation
factor of the projection optical system, through a reflecting
member disposed at least at a portion in a Fourier transform plane
formed in the projection light path of the projection optical
system or in a plane in the vicinity thereof; and setting an
exposing condition for exposing the substrate at a target exposure
amount in accordance with the intensity of the exposing energy
detected, in order to reduce deterioration in precision for
controlling the exposure amount resulting from the variation in the
attenuation factor of the projection optical system.
17. The manufacturing method for forming the circuit device as
claimed in claim 16, wherein the reflecting member is formed at a
portion of a refractive optical element or a reflective optical
element located in the Fourier transform plane of the projection
optical system or in the plane in the vicinity thereof.
18. The manufacturing method for forming the circuit device as
claimed in claim 17, wherein during the step for setting the
exposing condition, at least one of an illuminance of the exposing
energy to be irradiated on the mask and a period of time for
continuing irradiation of the exposing energy on the mask is
adjusted on the basis of a result of detection of the intensity of
the exposing energy to be irradiated on the mask, a result of
detection of the intensity of the reflected energy which is
reflected at the reflecting member, and the target exposure amount
to be provided on the substrate.
19. The method as claimed in claim 16, wherein the reflecting
member has an area covering a substantially whole area of the
Fourier transform plane in the projection optical system, and
wherein during the step for detecting the intensity of the exposing
energy passing through the projection light path, the projection
optical system is irradiated by the exposing energy from an
exposing illumination system for exposing a pattern of the mask to
the substrate, and the reflected energy reflected from the
reflecting member covering the substantially whole area of the
Fourier transform plane is detected.
20. The method as claimed in claim 16, wherein the reflective
optical element is also used as the reflecting member when the
projection optical system is composed of a catadioptric type having
the reflective optical element disposed in the vicinity of the
Fourier transform plane.
21. An exposure apparatus having: an illumination optical system
for irradiating a pattern formed on a mask with an exposing energy
having a wavelength of 250 nm or less; and a projection optical
system for projecting an image of the pattern of the mask at a
predetermined position on a substrate; characterized by a
reflecting member, disposed at least at a portion in a Fourier
transform plane formed between an object plane and an image plane
of the projection optical system or in a plane in the vicinity
thereof, for reflecting exposing energy incident from the object
plane side of the projection optical system through the
illumination optical system; wherein an exposing condition for
exposing the substrate is set on the basis of the intensity of the
reflected energy reflected from the reflecting member, in order to
reduce a deterioration in precision for controlling the exposure
amount resulting from a variation in an attenuation factor of the
illumination optical system and the projection optical system.
22. An exposure apparatus having: an illumination optical system
for irradiating a pattern formed on a mask with an exposing energy
having a wavelength of 250 nm or less; and a projection optical
system for projecting an image of the pattern of the mask at a
predetermined position on a substrate; characterized by a
reflecting member, disposed at least at a portion in a Fourier
transform plane formed between an object plane and an image plane
of the projection optical system or in a plane in the vicinity
thereof, having reflecting properties relative to the exposing
energy incident from the object plane side of the projection
optical system through the illumination optical system; a beam
irradiation means which irradiates the exposing energy as measuring
beams in a substantially collimated state toward the reflecting
member from the object plane side of each of the illumination
optical system and the projection optical system; a detection means
which detects the reflected energy reflected by the reflecting
member and returning through the illumination optical system and
which output a detection signal in accordance with the reflected
energy; and an exposure control means which sets an exposing
condition for exposing the substrate based on the detection signal
from the detection means, in order to reduce a deterioration in
precision for controlling the exposure amount resulting from a
variation in an attenuation factor of the illumination optical
system and the projection optical system.
23. A projection exposure apparatus having: an illumination optical
system for irradiating a pattern formed on a mask with an exposing
energy having a wavelength in an ultraviolet range; and a
projection optical system for projecting an image of the pattern of
the mask at a predetermined position on a substrate; characterized
by a first detection means, disposed in a vision field of the
projection optical system outside an image projection region in
which an image of the pattern of the mask is projected, which
receives at least a portion of the exposing energy passing through
the projection optical system and travelling toward the substrate
and output a detection signal in accordance with an intensity of
the exposing energy received; a second detection means which
detects an intensity of the exposing energy in a predetermined
position in a light path extending from a light source disposed in
the illumination optical system to the mask and which output a
detection signal in accordance with the intensity of the exposing
energy detected; a variation detection means which detects a
variation in an attenuation factor with respect to the exposing
energy, which occurs in a light path of the irradiation means or in
a light path of the projection optical system; and an exposure
control means which corrects an exposing condition for exposing the
substrate so as to provide the substrate with a desired exposure
amount, when such a variation in the attenuation factor is detected
by the variation detection means.
24. The projection exposure apparatus as claimed in claim 23,
wherein the first detection means further comprises a reflecting
member disposed at a top end on the image plane side of the
projection optical system and outside the image projection region;
and a photoelectric element for photoelectrically detecting a
portion of the exposing energy reflected with the reflecting
member.
25. The projection exposure apparatus as claimed in claim 24,
wherein the reflecting member is composed of a full reflection
mirror plane so as to block an arrival at the substrate of the
exposing energy passed through outside of the image projection
region.
26. The projection exposure apparatus as claimed in claim 23,
wherein the exposure control means is to correct at least one of an
intensity of the exposing energy emitting from the light source, an
attenuation factor of an attenuator disposed in the irradiation
means, and an irradiation time for irradiating the exposing energy
to the substrate, in accordance with the variation in the
attenuation factor detected.
27. The projection exposure apparatus as claimed in claim 23,
wherein the light source comprises an ultraviolet laser light
source for radiating a light in a wavelength width set so as to
avoid an absorption band of oxygen in a wavelength region shorter
than 250 nm.
28. The projection exposure apparatus as claimed in claim 23,
further comprising: a movable stage mechanism for moving in a plane
parallel to the image plane of the projection optical system in a
state in which the substrate is loaded thereon; and a third
detection means, disposed in the movable mechanism, for detecting
an illuminance of the exposing energy obtained in an image
projection region on the image plane side of the projection optical
system; wherein the exposure control means is to correct the
exposing condition on the basis of a result of detection by the
variation detection means and the third detection means.
29. The projection exposure apparatus as claimed in claim 23,
wherein the variation detection means further comprises an
operation processing circuit for sequentially saving data
corresponding to a ratio of each detection signal by the first
detection means to each detection signal by the second detection
means at every predetermined time and for computing a periodical
change rate of the variation in the attenuation factor on the basis
of the data saved.
30. The projection exposure apparatus as claimed in claim 23,
wherein the variation detection means further comprises a fourth
detection means disposed in a space between the projection optical
system and the substrate so as to enter in an image pattern region
in a vision field of the projection optical system or to be
evacuated therefrom; and the variation in the attenuation factor is
detected by irradiating a transparent portion around a pattern
region of the mask with the exposing energy and photoelectrically
detecting the light passed through the transparent portion of the
mask, when the fourth detection means is inserted into the image
projection region.
31. The projection exposure apparatus as claimed in claim 30,
wherein the exposure control means is to calibrate a detection
signal corresponding to the variation in the attenuation factor to
be detected by the first detection means on the basis of a signal
detected by the fourth detection means.
32. A projection exposure apparatus for scanning an entire image of
a pattern of a mask and exposing the entire pattern thereof onto a
substrate by scanning the mask and the substrate relative to a
vision field of a projection optical system, the apparatus having:
an irradiation means for irradiating an exposing energy having an
ultraviolet wavelength range, a projection optical system for
projecting an partial image of the pattern formed on the mask by
irradiating a portion of the pattern to be formed on the mask with
the exposing energy from the irradiation means; and a scanning
mechanism for scanning the mask and the substrate relative to the
vision field of the projection optical system; characterized by a
restriction means which restricts an image projection region, in
which a partial image of the pattern of the mask is projected, to a
polygonal or arc-shaped region extending in a direction
intersecting with a relative scanning direction in a vision field
of the projection optical system; a detection means, disposed in a
region outside the image projection region relating to the
relatively scanning direction in the vision field of the projection
optical system, which receives at least a portion of the exposing
energy passed through the projection optical system and travelling
toward the substrate and outputs a detection signal in accordance
with the intensity of the energy; and an exposure control means
which sets an exposing condition for transcribing the entire image
of the pattern thereof on the substrate at a predetermined exposure
amount on the basis of the detection signal and for controlling
scanning exposure in accordance with the exposing condition.
33. The projection exposure apparatus as claimed in claim 32,
wherein the restriction means is provided with an illumination
vision field stop which is disposed in a position substantially
conjugated with the mask in a light path of the irradiation means
and which has a linearly slit-shaped or rectangular opening
extending in a direction intersecting with a direction of the
relative scanning.
34. The projection exposure apparatus as claimed in claim 33,
wherein the detection means further comprises a reflecting member
disposed between the projection optical system and the substrate
and a photoelectric element for receiving a portion of the exposing
energy reflected by the reflecting member, wherein the reflecting
member is disposed in a region within the vision field of the
projection optical system and outside the image projection region
relating to the relative scanning.
35. The projection exposure apparatus as claimed in claim 34,
wherein the exposing energy to be detected by the photoelectric
element through the reflecting member passes through a small
opening portion formed at a portion of the illumination vision
field stop and irradiates through the irradiation means, the
transparent portion around the pattern region of the mask, and the
projection optical system.
36. The projection exposure apparatus as claimed in claim 34,
wherein the detection means is to detect the exposing energy
through the reflecting member while the mask is located at an
approach run start position for relatively scanning each of plural
shot regions when the scanning mechanism scans the mask and the
substrate relative to each of the plural shot regions on the
substrate.
37. A method for scanning and exposing an entire image of a pattern
of a mask to a substrate being exposed, which is carried out by:
irradiating a portion of the pattern of the mask with an exposing
energy of an ultraviolet region having a wavelength of 250 nm or
less; and scanning the mask and the exposing substrate relative to
a vision field of a projection optical system, while projecting a
partial image of the pattern thereof onto the substrate through the
projection optical system; characterized by the steps of:
restricting an image projection region in which the partial image
of the pattern thereof is projected to a polygonal or arc-shaped
region extending in a direction intersecting with a relative
scanning direction in the vision field of the projection optical
system upon scanning exposure; detecting an intensity of at least a
portion of the exposing energy passing through a region outside the
image projection region relating to the relative scanning direction
in the vision field of the projection optical system, at the time
of starting the scanning exposure; and setting an exposing
condition for transcribing the entire image of the pattern thereof
on the substrate at a predetermined exposure amount on the basis of
the intensity of the exposing energy detected, before starting the
scanning and exposing.
38. The exposure method as claimed in claim 37, wherein a result of
detection of the exposing energy passing through the region outside
the image projection region relating to the relative scanning in
the vision field of the projection optical system is calibrated on
the basis of an illuminance of the exposing energy measured in
advance in the image projection region, when the exposing condition
is set.
39. The exposure method as claimed in claim 37, wherein, when the
exposing energy which passes through the region outside the image
projection region relating to the relative scanning direction in
the vision field of the projection optical system is detected, the
intensity of the exposing energy is detected individually in each
of the plural positions outside the image projection region, and an
irregularity of an attenuation factor in a light path through which
the exposing energy passed is measured on the basis of the result
of detection.
40. The exposure method as claimed in claim 37, wherein the
exposing energy comprises pulse light from a narrow-banded ArF
excimer laser light source so as to avoid an absorption band of
oxygen.
41. The exposure method as claimed in claim 40, wherein, when the
exposing energy which passes through the region outside the image
projection region relating to the relatively scanning direction in
the vision field of the projection optical system is detected, a
peripheral transparent portion around the pattern region on the
mask is located in the vision field on the object side of the
projection optical system and outside the image projection region,
and the exposing energy is detected through the peripheral
transparent portion of the mask.
42. A manufacturing method for forming a circuit device on a
substrate, which is carried out by a lithographic process for
projecting and exposing a circuit pattern formed on a mask to be
irradiated with an exposing energy of an ultraviolet region having
a wavelength of 250 nm or less to each of plural positions on a
substrate through a projection optical system; characterized by the
steps of: detecting a variation in an intensity of the exposing
energy resulting from a variation in an attenuation factor of the
projection optical system by detecting at least a portion of the
exposing energy passed through an outer region of an image
projection region in a vision field of the projection optical
system and travelling toward the substrate side at a position close
to an image plane of the projection optical system, the image
projection region being a region in which an image of the circuit
pattern of the mask is formed; and setting an exposing condition
for transcribing the circuit pattern onto the substrate at a
predetermined exposure amount on the basis of the variation in the
intensity of the exposing energy detected; wherein a deterioration
in precision for controlling the exposure amount due to the
variation in the attenuation factor of the projection optical
system is reduced, and the variation in the attenuation factor
occurs when the image of the circuit pattern is projected and
exposed sequentially onto the substrate.
43. The manufacturing method for forming the circuit device as
claimed in claim 42, wherein a first detector is disposed at a top
end portion on the image side of the projection optical system in
order to detect a variation in the intensity of the exposing energy
resulting from the variation in the attenuation factor of the
projection optical system.
44. The manufacturing method for forming the circuit device as
claimed in claim 43, wherein a second detector for detecting the
intensity of at least a portion of the exposing energy passing
through the image projection region is disposed on a movable stage
for holding the substrate thereon and for transferring the
substrate in a two-dimensional way; and a result of detection by
the first detector is calibrated on the basis of a result of
detection by the second detector.
45. The manufacturing method for forming the circuit device as
claimed in claim 43 or 44, wherein the exposing energy is
irradiated on a peripheral portion outside the circuit pattern
region of the mask and the exposing energy passed through the
peripheral portion the projection optical system is detected, upon
detecting the exposing energy by the first detector or the second
detector.
46. A projection exposure apparatus for transcribing a transcribing
pattern on a mask onto a photosensitive substrate by irradiating
the transcribing pattern on the mask with illumination light of an
ultraviolet wavelength region and projecting the transcribing
pattern on the mask onto the photosensitive substrate through a
projection optical system; comprising: a sensor for measuring a
variation in an attenuation factor of the projection optical system
resulting from irradiation with the illumination light of a
ultraviolet wavelength region; and a control unit for maintaining
an illuminance of the illumination light on the photosensitive
substrate at a substantially constant level during exposure on the
basis of an output of the sensor.
47. The projection exposure apparatus as claimed in claim 46,
wherein the sensor receives at least a portion of the reflected
light reflected from the photosensitive substrate.
48. The projection exposure apparatus as claimed in claim 46,
further comprising a light receipt element for receiving a portion
of the illumination light incident to the mask, and the control
unit uses an output of each of the sensor and the light receipt
element.
49. The projection exposure apparatus as claimed in claim 46,
wherein the illuminance of the illumination light on the
photosensitive substrate comprises at least an average illuminance
in the exposure region of the projection optical system or an
irregularity of illuminance in the exposure region of the
projection optical system.
50. The projection exposure apparatus as claimed in claim 46,
further comprising a drive unit for transferring the mask and the
photosensitive substrate in synchronization with each other
relatively to the projection optical system.
51. The projection exposure apparatus as claimed in claim 50,
wherein the projection optical system comprises an
equal-magnification optical system having a first object section
and a light axis turn section with a concave mirror installed
therein, and a reduced projection system having a light axis
deflection section and a second object section.
52. A projection exposure apparatus for transcribing a transcribing
pattern on a mask onto a photosensitive substrate sequentially by
irradiating the transcribing pattern on the mask with illumination
light of an ultraviolet wavelength region and projecting the
transcribing pattern on the mask onto the photosensitive substrate
through a projection optical system; comprising: a sensor for
detecting a variation in an imaging characteristic of the
projection optical system on the basis of a variation in an
attenuation factor of the projection optical system resulting from
irradiation with the illumination light of the ultraviolet
wavelength region; and a control unit for controlling the imaging
characteristic on the basis of an output of the sensor.
53. A projection exposure apparatus for transcribing a transcribing
pattern on a mask onto a photosensitive substrate subsequently by
irradiating the transcribing pattern on the mask with illumination
light of an ultraviolet wavelength region and transferring the mask
and the photosensitive substrate in synchronization with a
projection optical system relatively to a projection optical
system; comprising: an adjustment device for adjusting at least one
of an intensity of the illumination light on the photosensitive
substrate, a velocity for scanning the photosensitive substrate,
and a width of an illumination region of the illumination light
relating to a scanning direction of the photosensitive substrate,
on the basis of a variation in an attenuation factor of the
projection optical system resulting from irradiation with the
illumination light of the ultraviolet wavelength region.
54. The projection exposure apparatus as claimed in claim 53,
wherein the illumination light of the ultraviolet wavelength region
is pulse light; and the adjustment device adjusts at least one of a
frequency of oscillation of the pulse light, the intensity of the
illumination light, the velocity for scanning the photosensitive
substrate, and the width of the illumination region.
55. The projection exposure apparatus as claimed in claim 53,
wherein the projection optical system comprises an
equal-magnification optical system having a first object section
and a light axis turn section with a concave mirror installed
therein, and a reduced projection system having a light axis
deflection section and a second object section.
56. A manufacturing method for manufacturing a micro device,
including a photolithography process for irradiating a device
pattern with an illumination light of an ultraviolet wavelength
region and exposing an image of the device pattern to a substrate,
characterized by the step of: detecting at least one of an
illuminance of the illumination light on the substrate, an
irregularity of illuminance, and an image characteristic of the
device pattern, on the basis of a variation in an attenuation
factor resulting from irradiation of the illumination light of the
ultraviolet wavelength region, during the exposure.
57. An exposure method for irradiating a mask with an illumination
light through an illumination optical system and exposing a
photosensitive substrate to the illumination light through a
projection optical system; characterized by the steps of: supplying
gas having less absorption of the illumination light at least a
portion of the illumination optical system and the projection
optical system; and changing an exposing condition for the
photosensitive substrate in accordance with a variation in
transmittance or in reflectance of at least one of the illumination
optical system and the projection optical system, resulting from
irradiation of the illumination light.
58. The exposure method as claimed in claim 57, wherein an image
characteristic of the pattern on the mask is further adjusted in
accordance with a variation in an imaging characteristic of the
projection optical system attendant upon the variation in
transmittance or reflectance.
59. A projection exposure apparatus for irradiating a mask with an
illumination light through an illumination optical system and
exposing a photosensitive substrate to the illumination light;
comprising: a projection optical system disposed between the mask
and the photosensitive substrate, which is filled with gas having
less absorption of the illumination light; and an adjustment device
for adjusting an exposing condition of the photosensitive substrate
in accordance with a variation in transmittance or in reflectance
of the projection optical system resulting from irradiation with
the illumination light.
Description
TECHNICAL FIELD
[0001] The present invention relates to an exposure apparatus for
use in a lithography process in a production line for manufacturing
semiconductor devices, liquid crystal display devices and an
exposure method using such exposure apparatus. The present
invention also relates to a method for manufacturing circuit
devices for use in forming electronic circuit devices on a
semiconductor substrate (wafer), glass substrate, and so on.
BACKGROUND TECHNOLOGY
[0002] Recently, at plants for manufacturing semiconductor devices
such as super LSIs and so on, developments for mass-producing
D-RAMs (memory chips), processor chips and the like, having a
degree of integration and a fineness of a class of 256 Mbits on a
large scale have been carried out extensively with great effort. As
developments advance, exposure apparatuses for use in a
next-generation lithography process (representatives being
processes for coating a resist, exposing, developing resist, etc.)
are also required to have a higher precision of alignment, a high
resolution and a higher throughput.
[0003] At current times, at plants for manufacturing semiconductor
devices, a reduced projection exposure apparatus of a
step-and-repeat type has been used extensively, which uses i-rays
having a wavelength of 365 nm, among emission line mainly from a
mercury discharge lamp as illumination light for exposing. The
projection exposure apparatus of this type is configured such that
i-rays are irradiated as illumination light onto a reticle (a mask
substrate) disposed on the object plane side of a projection
optical system having a 1/5-fold reduction rate and a circuit
pattern formed on the reticle is transcribed on a resist layer on a
semiconductor wafer by means of a projection optical system.
Further, the projection exposure apparatus of a step-and-repeat
type is configured such that a stage with the wafer loaded thereon
is transferred in a stepwise and two-dimensional manner in order to
allow a sequential transcription of an image of a circuit pattern
of the reticle in plural positions (shot regions) on the wafer.
[0004] Further, as a trend in these years, in order to avoid that a
vision field of the projection optical system should become
extremely large attendant upon enlarging a size (a chip size) of a
circuit device to be formed on the wafer, a reduced projection
exposure apparatus of a step-and-scan type draws attention, which
step-and-scan type is to scan and expose an entire image of the
circuit pattern of the reticle to the wafer by scanning the reticle
in the vision field on the object plane side of the reduced
projection optical system in a one-dimensional direction at an
equal velocity and at the same time scanning the wafer in the
vision field on the image plane side of the reduced projection
optical system in a one-dimensional direction at an equal
velocity.
[0005] Moreover, projection exposure apparatuses of a
step-and-repeat type or of a step-and-scan type have been
developed, which use ultraviolet pulse light having a wavelength of
248 nm from a KrF excimer laser light source as an exposing
illumination light, and they have been begun being launched into
production lines on a large scale. As such an excimer laser light
source, an ArF excimer laser light source having a shorter
wavelength (having a central wavelength of 193 nm) is now being
developed, and it is promising in the future as an exposing light
source.
[0006] In particular, in the case where such an ArF excimer laser
light source is used for exposuring, it is required to narrow
wavelength characteristics of pulse light to a wavelength that can
avoid several absorption bands of oxygen that exist within the
wavelength band in a naturally oscillating state of the pulse
light. Further, it is required to replenish a majority of an
illumination light path extending from the light source to the
reticle and a projection light path extending from the reticle to
the wafer with inert gases (such as nitrogen gas, helium gas,
etc.), in order to provide an environment where oxygen is contained
in the least possible amount in both of the such illumination light
path and projection light path. An example of the projection
exposure apparatus using such an ArF excimer laser light source is
disclosed, for example, in U.S. Pat. No. 5,559,584 (Japanese Patent
Application Laid-Open Nos. 6-260,385 and 6-260,386).
[0007] As an optical glass material for practical use having a
desired transmittance for ultraviolet pulse light (wavelength of
250 nm or less) from the such excimer laser light source, there are
currently known only two, one being quartz (SiO.sub.2) and the
other being fluorite (CaF.sub.2). As a matter of course, although
there are known other optical glass materials such as magnesium
fluoride, lithium fluoride, and so on, they require to solve
various problems with processing, durability, and so on before they
are applied practically as an optical glass material for use with
the projection exposure apparatus.
[0008] Moreover, in the case of use of quartz and fluorite for the
projection exposure apparatus, achromatism in the projection
optical system becomes difficult upon using illumination light.
Therefore, a narrow-banded laser light source is preferred from the
point of view of easiness of performing achromatism in the
projection optical system.
[0009] It should be noted herein, however, that a band of such an
excimer laser light is originally a broad band, so that a
narrow-banded laser light source has its oscillating spectrum
narrowed by injection locking, etc. From these reasons, the
narrow-banded laser light source suffers from the disadvantages
that a laser output is lowered as compared with a broad-band laser
light source, and its life is shorter and its costs of production
is more expensive than the broad-band laser light source.
Therefore, the broad-banded laser light source is more favored in
terms of the laser output, life and costs of production than the
narrow-banded laser light source. Recently, attempts have been made
to use a broad-banded laser light source for a projection optical
system having a structure in which achromatism can be done
easily.
[0010] There are known several types of projection optical systems
to be mounted on the projection exposure apparatus. Among them, the
types of the projection optical systems for exposure apparatuses
which are used for large-scale commercial production lines can be
divided into two major types, one being a dioptric type that is
composed of a plurality of refractive optical elements (lens
elements) only and the other being a catadioptric type that is
composed of a combination of such refractive optical elements with
reflective optical elements (particularly a concave mirror).
[0011] In the case of using a reflection-refraction optical system
as of a catadioptric type, the concave mirror is free from
chromatic aberration, so that achromatism can be effected easily by
locating the concave mirror in a group of refractive lenses. As a
result, a broad-banded laser light source can be used which is
advantageous in terms of the laser output, life, etc. On the other
hand, in the case of using a refractive optical system only as of a
dioptric type, too, a broad-banded laser light source can be used
because a range of achromatism can be widened by making a rate of
fluorite contained in the entire refractive lenses larger.
[0012] In a current situation, however, even which type of the
projection optical system is adopted, the refractive optical
elements (light-transmitting optical elements) have to be used.
Therefore, at this point of time, there is no way but using two
kinds of glass materials, i.e. quartz and fluorite, for the
refractive optical elements. Further, each of the refractive
optical elements and the reflective optical elements is produced so
as to achieve a desired performance as a single optical element by
forming a multi-layer membrane such as a reflection preventive
layer, a protective layer, etc. by deposition etc. on a surface of
each element. The performance to which attention should be paid
herein is how large an absolute value of transmittance or
transmissivity of the single lens element or an absolute value of
reflectance or reflectivity of the single reflective optical
element can be set.
[0013] For instance, in the case of the single lens element, it is
arranged so as to make transmittance as high as possible by coating
a reflection preventive layer, etc. on both surfaces of the
element, i.e. the incident surface to which the light is entered
and the leaving surface from which the light leaves. In a
high-precision imaging optical element of this kind, as much as
20-30 sheets of lens elements are to be used for achieving a high
correction of various aberration characteristics. In such a case, a
transmittance of the entire projection optical elements is reduced
to a large extent even if a slight reduction in transmittance would
occur in each lens element. In addition, it is required to make a
reflectance of each reflective element larger even for the
projection optical system containing a large number of reflective
optical elements in a similar manner.
[0014] For instance, suppose that an imaging light path of the
projection optical system is composed of 25 sheets of the lens
elements and the transmittance is set to be 96% for each lens
element, the transmittance .epsilon. for the entire projection
optical system becomes approximately 36% (0.96 to the 25th power).
If it is assumed that a transmittance of each single lens element
would be decreased by 1%, the transmittance .epsilon. of the entire
projection optical system is reduced to approximately 27.7% (0.95
to the 25th power).
[0015] In the case where the transmittance of the projection
optical system is low, this can be improved by increasing the
intensity (energy) of illumination light for exposing a circuit
pattern image of a reticle onto a semiconductor wafer (a
photosensitive substrate) and developing a photoresist for
ultraviolet rays having a higher degree of photosensitivity. If
such improvements could not be made, a throughput will be decreased
due to an increase in a longer period of time for exposure. A
decrease in throughput is unacceptable, because it results in
higher costs for the production of devices. Therefore, it may be a
one of possible solution to prepare an excimer laser light source
having a higher output.
[0016] As a result of experiments for various exposure by a
projection exposure apparatus having a relatively large field size
using an excimer laser light source, however, a new phenomenon has
been discovered in that a transmittance of an optical element or a
coating material (for example, a thin membrane, such as a
reflection preventive membrane, etc.) for the optical element in
the projection optical system fluctuates in a dynamic mode by
irradiation of illumination light of an ultraviolet wavelength
region (a KrF excimer laser having a wavelength of 248 nm, an ArF
excimer laser having a wavelength of 193 nm, etc.). This phenomenon
has been found to occur for an optical element in an illumination
optical system for illuminating a reticle and a reticle (a quartz
plate) itself, too, in the same manner as described above, as well
as for the optical element in the projection optical system.
[0017] It is considered that such phenomenon is caused by, for
instance, attachment or penetration (floating) of impurities
contained in gases (air, nitrogen gas, etc.) present in a space
within the projection light path or the illumination light path,
gaseous molecules of organic substances to be caused to generate
from adhesive or the like to be used for fixing the optical element
to the barrel, or impurities (for example, water molecules,
hydrocarbon molecules or other substances for dispersing the
illumination light) to be caused to generate from the inner wall of
the barrel (for example, a coated wall surface for prevention of
reflection, etc.) to the surface of the optical element or in the
illumination light path.
[0018] As a consequence, severe problems may occur that the
transmittance of the projection optical system or the transmittance
of the illumination optical system may fluctuate to a great extent
for a relatively short period of time. Such a great fluctuation of
the transmittance results in a decrease in a precision for
controlling the exposure amount to be provided on the
photosensitive substrate, thereby deteriorating a fidelity of
transcription of a fine pattern having a design line width of 0.25
to 0.12 micron to be transcribed on the substrate.
[0019] The projection exposure apparatus of a conventional type as
disclosed, for example, in Japanese Patent Application Laid-Open
No. 2-135,723 (U.S. Pat. No. 5,191,374) is configured such that the
optical intensity of illumination light is detected at an
appropriate portion in a light path in the illumination optical
system and the intensity (energy per one pulse) of the pulse light
from an excimer laser light source is adjusted so as to achieve an
optimal exposure amount on the basis of the detected optical
intensity. Therefore, the such conventional projection exposure
apparatus suffers from the disadvantage in that no accurate control
of the exposure amount can be performed because no fluctuation in
the transmittance of the illumination optical system and the
projection optical system behind the portion in the illumination
light path is added thereto whatsoever, the portion in the
illumination light path being the place where the intensity of the
illumination light has been detected for controlling the exposure
amount.
[0020] In addition, for the causes as described above, there is no
assurance that the fluctuation in the transmittance of the
projection optical system and the illumination optical system
occurs in a uniform manner in the vision field on the image plane
side of the projection optical system, so that there is the risk
that irregularities of illuminance (or irregularities of the
exposure amount) will occur against the projection optical system
within the projection region of the pattern image conjugated with
the illumination region of the illumination light on the reticle.
Furthermore, there is the concern about an occurrence of the
disadvantage that imaging characteristics (e.g., distortion,
spherical aberration, astigmatism, coma aberration, etc.) of the
projection optical system may vary to a subtle extent, attendant
upon an occurrence of such irregularities of illuminance or
otherwise.
SUMMARY OF THE INVENTION
[0021] Therefore, the present invention has the object to provide
an exposure apparatus that can reduce deterioration in precision
for controlling the exposure amount resulting from a fluctuation of
illuminance or irregularities of illuminance on a photosensitive
substrate or on a mask (reticle) which may occur due to a variation
in transmittance or transmissivity of the projection optical system
or the illumination optical system. The present invention has
another object to provide an exposure apparatus can detect a
variation in transmittance of the projection optical system or the
illumination optical system at a semi-real time, even during a
period of time of operations of exposure to the photosensitive
substrate.
[0022] In another aspect, the present invention has a further
object to provide an improved measurement method for measuring a
transmittance in an image projection region of the projection
optical system or measuring an average illuminance or an
irregularity of illuminance in the image projection region of the
projection optical system. In a further aspect, the present
invention has a still further object to provide a method for
manufacturing a circuit device that can form a pattern image of a
circuit device on the substrate always at an appropriate amount of
exposing light and in a favorable imaging state.
[0023] In a still further aspect, the present invention has an
object to provide an exposure apparatus of a scanning type and an
exposure method using the same, which can always provide the
photosensitive substrate with an appropriate amount of exposing
light, even if transmittance of the projection light path or the
illumination light path would fluctuate during scanning the mask
(reticle) and the photosensitive substrate in synchronism with the
projection optical system.
[0024] A first mode of the present invention can be applied to an
exposure apparatus comprising an irradiation means (a laser light
source, a condenser lens system, etc.) for irradiating a pattern
formed on a mask (reticle) with an exposing energy (excimer laser,
fluorine laser, SOR rays having a wavelength of 50 nm or less,
etc.) and a projection optical system for projecting an image of
the pattern on the mask at a given position on a photosensitive
substrate (wafer). The exposure apparatus is characterized by a
reflecting member disposed in a Fourier transform plane or in at
least a part of a plane in the vicinity thereof between an object
plane and an image plane of the projection optical system, and
which reflects the exposing energy incident from the object plane
side of the projection optical system or an exposing energy
incident from the image plane side of the projection optical
system; a beam irradiation means which irradiates the exposing
energy as measuring beams in a nearly collimated state from the
object plane side or the image plane side of the projection optical
system toward the reflecting member; a detection means which
detects the energy reflected by the reflecting member and outputs a
detection signal in accordance with the reflected energy; and an
exposure control means (a processor, a light source control system,
a main control system, etc.) which sets an exposing condition for
the photosensitive substrate based on the detection signal from the
detection means in order to reduce deterioration in a control
precision for an amount of exposing light resulting from a
variation in an attenuation factor (a variation in transmittance or
in reflectance) of the projection optical system.
[0025] In another mode, the present invention is applied to a
method for scanning-exposing an entire image of the pattern of a
mask or reticle (R) on a substrate (wafer) to be exposed, which is
carried by scanning the mask (reticle) and the substrate relative
to the vision field of the projection optical system, while
irradiating a portion of the pattern of the mask (reticle) with an
exposing energy (ultraviolet laser light, etc.) having a wavelength
of 250 nm or less and projecting a partial image of the pattern
onto the substrate (a wafer) through a projection optical system.
The method is characterized by the steps of; irradiating the
exposing energy onto the reflecting member disposed in a Fourier
transform plane formed between the object plane and the image plane
of the projection optical system or at least at a portion in a
plane in the vicinity of the Fourier transform plane prior to
starting scanning exposure, and then detecting the intensity of an
energy reflected from the reflecting member; and setting an
exposing condition (updating database at step 328) for transcribing
the entire image of the pattern of the mask on the substrate at a
predetermined exposure amount in accordance with the intensity
detected.
[0026] Further, the present invention is applied to a manufacturing
method for forming a circuit device on the substrate by practicing
a lithography process in which the circuit pattern of the mask
(reticle) is irradiated with an exposing energy having a wavelength
of 250 nm or less and then exposing the circuit pattern to each of
plural positions on the substrate (wafer) one after another through
the projection optical system while projecting the exposing energy.
The method is characterized by the steps of; detecting the
intensity of the exposing energy passing through a projection light
path, including a portion of a variation by a transmittance of the
projection optical system, through a reflecting member disposed in
a Fourier transform plane formed in the projection light path of
the projection optical system or at least at a portion in a plane
in the vicinity of the Fourier transform plane; and setting an
exposing condition (updating database at step 328) for exposing the
substrate at a target exposure amount in order to reduce
deterioration in precision for controlling the exposure amount
resulting from a variation in an attenuation factor (a variation in
transmittance or a variation in reflectance) of the projection
optical system in accordance with the energy intensity
detected.
[0027] In the first mode of the present invention, the exposure can
be controlled so as to provide the photosensitive substrate always
with an optimal exposure amount with a variation added thereto,
even if the transmittance of the refractive (light-passing) optical
elements constituting the irradiation system and the projection
optical system would vary with time during the exposure
operation.
[0028] Moreover, the present invention is configured such that the
exposing energy reflected at the Fourier transform plane (pupil
plane) of the projection optical system for projecting the pattern
of the mask onto the photosensitive substrate can be detected in a
photoelectric mode, so that, upon exposing a plurality of shot
regions on the photosensitive substrate one after another, a
portion of the exposing energy (monitoring beams for measuring)
which underwent a variation in an attenuation factor (a variation
in transmittance or a variation in reflectance) can be detected in
a photoelectric mode in a short time during subsequent exposure of
the shot regions.
[0029] The variation in the attenuation factor (the variation in
transmittance or in reflectance) of the illumination optical system
and the projection optical system can appear in a remarkable way,
in particular when an ultraviolet light having a wavelength of 200
nm or less is used. It is also known that an ArF excimer laser
light source, F.sub.2 (fluorine) laser light source, etc. can be
included in that category of the light. Therefore, in a projection
exposure apparatus using such a laser light source, an error in
controlling the exposure amount may occur due to a variation in the
transmittance of the illumination optical system and the projection
optical system. In the present invention, however, the reflecting
member is disposed at a portion of the Fourier transform plane of
the projection optical system, and a portion of the exposing energy
passed through the projection optical system is allowed to be
detected in a photoelectric mode at a nearly real time, thereby
enabling reduction of an error due to the variation in the
transmittance upon controlling the exposure amount.
[0030] One of the causes of an occurrence of a variation in the
attenuation factor (a variation in transmittance or in reflectance)
in the ultraviolet region below a wavelength of 200 nm or less is
because of the physical properties of an optical glass material
itself. Another cause is considered to be due to molecules of
impurities to be attached to (or deposited on) such an optical
glass material. Among those causes, in particular, the molecules of
the impurities to be attached to the surface of the optical glass
material may cause a decrease in an attenuation factor
(transmittance or reflectance) in a monotonous way, if they are
left non-removed and stayed as they are. However, once the exposing
energy is irradiated, they would be caused to be decomposed
chemically and to disperse in a space. As a consequence, the
attenuation factor (transmittance or reflectance) is allowed to
rise to its original value.
[0031] This means to cause the entire attenuation factor
(transmittance or reflectance) of the projection optical system and
the illumination optical system to fluctuate, each being
incorporated with a number of optical elements, and it is difficult
to monitor a history of irradiation and the like and to predict
characteristics of a variation in the attenuation factor
(transmittance or reflectance). In accordance with the present
invention, however, the variation in transmittance can be detected
in an accurate way without effecting complicated computation
processing for conducting such a prediction. Therefore, the control
of the exposure amount can be conducted in a precise manner on the
basis of the detection.
[0032] Moreover, the exposing energy reaching the Fourier transform
plane of the projection optical system from the illumination
optical system through the projection optical system can be
detected, so that the variation in the attenuation factor (the
variation in transmittance or the variation in reflectance) of the
entire system including both of the illumination optical system and
the projection optical system can be detected in an accurate mode,
thereby enabling the accurate control of the exposure amount.
[0033] A second mode of the present invention can be applied to a
projection exposure apparatus comprising the irradiation means for
irradiating the pattern formed on the mask (reticle) with the
exposing energy (pulse light from the excimer laser light source)
having a wavelength in an ultraviolet range; and the projection
optical system for projecting an image of the pattern of the mask
to a predetermined positions on the photosensitive substrate
(wafer). The projection exposure apparatus is characterized by a
first detection means which is disposed in the vision field of the
projection optical system outside the image projection region
(illumination region) on which the image of the pattern of the mask
is projected, and which receives at least a portion of the exposing
energy (a monitoring light) directed to the side of the
photosensitive substrate through the projection optical system and
outputs a detection signal in accordance with the intensity
thereof; a second detection means which detects the intensity of
the exposing energy in the predetermined positions in a light path
extending from the light source disposed in the irradiation means
and outputs detection signal in accordance with the intensity
thereof; a variation detection means (a control processor) which
detects a variation in an attenuation factor (transmittance or
reflectance) for the exposing energy on the basis of the detection
signal from each of the first detection means and the second
detection means, the variation occurring at a light path in the
irradiation means or at a light path in the projection optical
system (PL); and an exposure control means (an exposure control
unit containing a processor) which corrects an exposing condition
so as to provide the photosensitive substrate with a desired
exposure amount, when the variation in the attenuation factor
(transmittance or reflectance) is detected by the variation
detection means.
[0034] Further, a second mode of the present invention can be
applied to a projection exposure apparatus for subjecting an entire
image of the pattern of the mask on a photosensitive substrate by
exposing and scanning them relative to each other, which is
comprised of the irradiation means for irradiating the exposing
energy (e.g., pulse light from the excimer laser light source)
having a wavelength in an ultraviolet region, the projection
optical system for projecting a partial image of the pattern onto
the photosensitive substrate (wafer) by irradiating a portion of
the pattern formed on the mask (reticle) with the exposing energy
from the irradiation means, and the scanning mechanism (a stage, a
drive control unit) for scanning the mask and the photosensitive
substrate relative to the vision field of the projection optical
system. The projection exposure apparatus is characterized by a
restriction means (a reticle blind mechanism) which restricts an
image pattern region (within an illumination region) where a
partial image of the pattern of the mask is projected to a
polygonal or arc-shaped region extending in a direction
intersecting with a relative scanning direction in the vision field
of the projection optical system; a detection means which is
disposed in the vision field of the projection optical system and
in a region outside the image projection region (illumination
region) relating to the relatively scanning direction and which
receives at least a portion of the exposing energy (a monitoring
light) directed to the photosensitive substrate side through the
projection optical system and outputs a detection signal in
accordance with the intensity thereof; and an exposure control
means (a main control system, an exposure control unit) which sets
an exposing condition (an intensity of illumination light, a
scanning velocity, an opening width of a blind, etc.) and controls
the scanning exposure in accordance with the exposing
condition.
[0035] The present invention further provides the exposing and
scanning method which is characterized by the steps of: restricting
the image projection region (defined by the illumination region) on
which a partial image of the pattern is projected, upon scanning
exposure, to a polygonal or arc-shaped region (set by the reticle
blind mechanism) extending in a direction intersecting with the
relative scanning direction within the vision field of the
projection optical system; detecting the intensity of at least a
portion of the exposing energy passing through a region outside the
image projection region (corresponding to the illumination region)
relating to the relative scanning direction in the vision field of
the projection optical system prior to the start of the scanning
exposure; and setting the exposing condition (the intensity of the
illumination light, the scanning velocity, the opening width of the
blind, etc.) for transcribing an entire image of the pattern on the
substrate to be exposed at a desired exposure amount (an operation
by the exposure control unit) prior to the start of the scanning
exposure on the basis of the detected intensity thereof.
[0036] Furthermore, another mode of the present invention is
applied to a manufacturing method for forming the circuit device on
the substrate by practicing the lithography process involving
projection exposing the circuit pattern formed on the mask
(reticle) to each of plural positions (shot regions) on the
substrate (wafer) one after another through the projection optical
system by irradiating the circuit pattern with the exposing energy
(for example, ultraviolet pulse laser) of an ultraviolet region
having a wavelength of 250 nm or less; in which an deterioration in
a precision of controlling the exposure amount by a variation in
the attenuation factor (a variation in transmittance or a variation
in reflectance) of the projection optical system, which may occur
during projection exposing the image of the circuit pattern on the
substrate one after another, can be reduced by carrying out the
step for detecting a variation in the intensity of the exposing
energy resulting from the variation in the attenuation factor (the
variation in transmittance or the variation in reflectance) of the
projection optical system, by detecting at least a portion of the
exposing energy (a monitoring light) travelling toward the
substrate side through an outer region of the image projection
region (defined by the illumination region) in which the image of
the circuit pattern of the mask to be formed within the vision
field of the projection optical system, and the step (the operation
processing by the exposure control unit) for setting the exposing
condition (an intensity of illumination light, a scanning velocity,
an opening width of a blind, etc.) for transcribing the circuit
pattern onto the substrate at a given exposure amount on the basis
of the variation in the detected intensity thereof.
[0037] In the second embodiment of the present invention, even if
the attenuation factor (transmittance or reflectance) of a number
of the light-transmitting optical elements and reflecting optical
elements constituting the illumination system and the projection
optical system would fluctuate during the exposing operation, the
exposure can be controlled so as to provide the photosensitive
substrate always with an optimal exposure amount, with the such
fluctuation added thereto. Further, in this embodiment, the
exposing energy can be detected in a photoelectric mode outside the
image projection region on which the pattern of the mask is to be
projected. With this configuration, the present invention can
potoelectrically detect the portion of the exposing energy (the
monitoring light) which is subjected influences from the variation
of the attenuation factor (variation in transmittance or variation
in reflectance) during a short period of time during which the
plural shot regions on the photosensitive substrate are being
exposed one after another.
[0038] It is known that the variation in the attenuation factor
(variation in transmittance or variation in reflectance) of the
illumination system and the projection optical system occurs to a
remarkable extent, particularly when ultraviolet light having a
wavelength of 200 nm or less is used, and that an ArF excimer laser
light source is one of such light sources having such a wavelength
region. Therefore, a conventional projection exposure apparatus
using such an ArF laser light source has an error which may occur
in controlling the exposure amount due to a variation in the
attenuation factor (variation in transmittance or variation in
reflectance) of the illumination system and the projection optical
system. In the embodiment of the present invention, however, it is
modified so as to reduce an error that may be caused by such a
variation in the attenuation factor (variation in transmittance or
variation in reflectance) by photoelectrically detecting the
exposing energy passed through the projection optical system at a
nearly real time.
[0039] With those configuration, like the first embodiment as
described above, the second embodiment of the present invention can
detect the variation in the attenuation factor (variation in
transmittance or variation in reflectance) in a precise mode and
perform an accurate control of the exposure amount even without
conducting a complex prediction computation.
[0040] In the third embodiment of the present invention, the
projection exposure apparatus for transcribing a transcribing
pattern on a mask onto a photosensitive substrate by irradiating
the transcribing pattern with an illumination light in an
ultraviolet wavelength region and projecting the transcribing
pattern onto the photosensitive substrate through the projection
optical system, which is characterized by a sensing means for
sensing a variation in an attenuation factor (variation in
transmittance or variation in reflectance) of the projection
optical system, which depends upon irradiation of the illumination
light of an ultraviolet wavelength region, and by a control unit
that can maintain an illuminance of the illumination light on the
photosensitive substrate at a nearly constant level during exposure
on the basis of an output from the sensor.
[0041] In this embodiment, a sensor (604A) for sensing the
variation in the attenuation factor (variation in transmittance or
variation in reflectance) of the projection optical system as the
sensing menas is disposed, so that an occurrence of a variation in
illuminance or irregularity of illuminance on the photosensitive
substrate due to the variation in the transmittance can be
prevented.
[0042] Further, such a sensor for sensing the variation in the
attenuation factor (variation in transmittance or variation in
reflectance) is preferably configured such that it can receive a
portion of light reflected from the photosensitive substrate. The
sensor of such a type can sense a variation in illuminance of the
illumination light on the photosensitive substrate during
exposure.
[0043] Moreover, it is preferred to provide a light receipt element
for receiving a portion of the illumination light having an
ultraviolet wavelength region incident to the mask, and to use an
output from each of the light receipt element and the sensor (604A)
for the control unit. This configuration can correct an error in
the exposure amount on the photosensitive substrate which may occur
due to the variation in the attenuation factor (variation in
transmittance or variation in reflectance) as described above,
based on the output of the sensor (604A), upon controlling the
accumulated light quantity on the photosensitive substrate to an
optimal dose amount on the basis of the output from the light
receipt element.
[0044] Moreover, in this embodiment of the present invention, it is
desired to measure an average illuminance (i.e., an accumulated
exposure amount) at least in the exposure region of the projection
optical system or an irregularity of illuminance values in the
exposure region of the projection optical system as an illuminance
of the illumination light on the photosensitive substrate. This
allows an appropriate control of the exposure amount in the
exposure region on the projection optical system to an optimal
value.
[0045] In another mode of this embodiment of the present invention,
the projection exposure apparatus for transcribing a transcribing
pattern on a mask onto a photosensitive substrate by irradiating
the transcribing pattern on the mask with the illumination light of
the ultraviolet wavelength region, and for projecting the
transcribing pattern onto the photosensitive substrate through the
projection optical system, which is characterized by a sensor
(604A) for sensing a variation in an imaging characteristic (for
example, a magnification of projection, a focal position and at
least one of five aberrations of Seidel) of the projection optical
system on the basis of the variation in the attenuation factor
(variation in transmittance or variation in reflectance) of the
projection optical system, which depends upon the irradiation of
the illumination light of the ultraviolet wavelength region, and by
a control unit for controlling the imaging characteristic of the
projection optical system on the basis of an output from the
sensor.
[0046] With the configuration of the sensor (604A) for sensing the
variation in the imaging characteristics of the projection optical
system in the manner as described above, the present invention can
prevent a variation in the imaging characteristics of the
projection optical system to be caused due to the variation in the
attenuation factor (variation in transmittance or variation in
reflectance) as described above.
[0047] In a further mode of this embodiment of the present
invention, the projection exposure apparatus for transcribing a
transcribing pattern on a mask sequentially onto a photosensitive
substrate by irradiating the transcribing pattern with the
illumination light of an ultraviolet wavelength region and by
transferring the mask and the photosensitive substrate in
synchronization with the projection optical system, which is
characterized by an adjustment device for adjusting at least one of
an intensity of the illumination light on the photosensitive
substrate, a scanning velocity for scanning the photosensitive
substrate, and a width of the illumination region of the
illumination light involved in the scanning direction of the
photosensitive substrate, on the basis of the variation in the
attenuation factor (variation in transmittance or variation in
reflectance) of the projection optical system depending upon the
irradiation of the illumination light of the ultraviolet wavelength
region.
[0048] With the configuration as described above, the present
invention can always provide the photosensitive substrate with an
optimal exposure amount even if the attenuation factor (variation
in transmittance or variation in reflectance) of the projection
optical system would fluctuate during the movement of the mask and
the photosensitive substrate in synchronism with each other.
[0049] In this embodiment of the present invention, when the
illumination light of the ultraviolet wavelength region is pulse
light, it is preferred to adjust at least one of a frequency of
oscillation of the pulse light, the intensity of the illumination
light, the scanning velocity for scanning the photosensitive
substrate, and the width of the illumination region.
[0050] In another embodiment of the present invention, the method
for the production of micro devices (for example, semiconductor
elements, image pickup elements (CCDs, etc.), liquid crystal
display elements, or thin film magnetic heads) is carried out by a
method for the production of the micro devices, including a
photolithography process in which a device pattern is irradiated
with an illumination light of an ultraviolet wavelength region and
an image of the device pattern to be projected by the projection
optical system is exposed to a substrate, which is characterized by
detecting an illuminance of the illumination light on the
substrate, and an irregularity of illuminance and an image
characteristic of the device pattern (for example, a magnification,
focal position and at least one of the five aberrations of Seidel)
on the basis of the variation in the attenuation factor (variation
in transmittance or variation in reflectance) of the projection
optical system which may be caused by the irradiation of the
illumination light of the ultraviolet wavelength region during
exposure.
[0051] With the configurations as described above, the present
invention can expose the image of the device pattern to the
substrate always at an optimal exposure amount and in a good
imaging state, thereby enabling the production of the micro devices
without reducing a yield rate of production, even if the
transmittance of the projection optical system would vary.
BRIEF DESCRIPTION OF THE DRAWINGS
[0052] FIG. 1 is a view showing an entire construction of a
projection exposure apparatus suitable for use in practicing the
first embodiment of the present invention.
[0053] FIG. 2 is a view showing the principle for explaining a
measuring light path in the projection optical system in an
embodiment of the present invention, upon measuring a transmittance
of the projection optical system.
[0054] FIG. 3 is a plan view showing the structure of a transparent
plate with a reflecting plate disposed in the vicinity of a pupil
plane of the projection optical system.
[0055] FIG. 4 is a view in section showing a central portion of the
transparent plate as shown in FIG. 3.
[0056] FIG. 5 is a view showing a specific configuration in the Y-Z
plane of a transmittance measuring means to be applicable to the
projection exposure apparatus of FIG. 1.
[0057] FIG. 6 is a view showing the configuration in the X-Z plane
as shown in FIG. 5.
[0058] FIG. 7 is a perspective view showing details of a reticle
stage, as shown in FIG. 1, and a state thereof during transmittance
measurement.
[0059] FIG. 8 is a partially sectional view of a wafer stage for
explaining a specific configuration of a transmittance measuring
means in accordance with the second embodiment of the present
invention.
[0060] FIG. 9 is a plane view showing the construction of a light
shielding plate to be disposed in the transmittance measuring means
of FIG. 8 and an example of the disposition of the light shielding
plate.
[0061] FIG. 10 is a view showing an example of an optical system
for producing measuring beams to be projected during measurement of
an attenuation factor (transmittance).
[0062] FIG. 11 is a view showing the construction of a processing
circuit for processing a photoelectric signal from each of
photoelectric detectors to be disposed on the transmittance
measuring means as shown in FIGS. 5, 6, 8 and 9.
[0063] FIG. 12 is a flowchart indicating a flow of a calibration
program to be executed by means of a processor in FIG. 11, in order
to calibrate an output from an integrator sensor for controlling an
exposure amount.
[0064] FIG. 13 is a graph for explaining a measurement method for
measuring the exposure amount upon scanning exposure under
illumination of pulse emission.
[0065] FIG. 14 is a flowchart indicating a flow of a transmittance
measurement program for executing the measurement operation by each
of the transmittance measuring means as shown in FIGS. 5, 6, 8 and
9.
[0066] FIG. 15 is each a graph showing an example of a variation
characteristic between a value corresponding to the transmittance
measured and a correction coefficient for correcting an exposing
condition.,
[0067] FIG. 16 is a view showing another construction of the
reflecting member to be disposed in the vicinity of the pupil plane
of the projection optical system and a detector for receiving
reflected beams.
[0068] FIG. 17 is a view showing another construction of the
reflecting member to be disposed in the vicinity of the pupil plane
of the projection optical system and a projection optical
system.
[0069] FIG. 18 is a view showing the construction of the
transmittance measuring means in a third embodiment of the present
invention.
[0070] FIG. 19 is each a view showing a brief configuration of
various projection optical systems loadable on a projection
exposure apparatus to which the present invention is
applicable.
[0071] FIG. 20 is a view showing an entire configuration for an
example of a scanning projection exposure apparatus in a second
embodiment of the present invention.
[0072] FIG. 21 is a view for schematically explaining a light path
for both of the illumination optical system and the projection
optical system and a light path for monitoring light for
transmittance measurement for use with the projection exposure
apparatus as shown in FIG. 20.
[0073] FIG. 22 is each a plane view showing an example of the
positional relationship between a reticle and a vision field of the
projection optical system for use in measuring transmittance.
[0074] FIG. 23 is a graph showing an example of characteristics of
a variation in transmittance by both of the illumination optical
system and the projection optical system.
[0075] FIG. 24 is a view in section for explaining a modification
of a photoelectric detection means disposed on the bottom surface
of the projection optical system for measuring transmittance.
[0076] FIG. 25 is a circuit block diagram showing details of a
circuit construction for an exposure control unit as shown in FIG.
20.
[0077] FIG. 26 is a view showing the construction of an illuminance
detector on the side of a wafer stage to be added as an example in
the second embodiment of the present invention.
[0078] FIG. 27 is each a view for explaining the position of a
reticle, upon measuring the transmittance for both of the
illumination optical system and the projection optical system by
the illuminance detector of FIG. 26 and calibrating a detector for
use in measuring the transmittance as shown in FIGS. 20 and 24.
[0079] FIG. 28 is a view showing the construction of a
photoelectric detector for use in transmittance measurement by
another example in the second embodiment of the present
invention.
[0080] FIG. 29 is a view showing a brief configuration in an
example for practicing a scanning projection exposure apparatus in
the third embodiment of the present invention.
[0081] FIG. 30 is a longitudinally sectional view showing the
configuration of a projection optical system PL as shown in FIG.
29.
[0082] FIG. 31 is each a view for explaining the relationship
between an illumination region and an exposure region of the
projection optical system PL as shown in FIG. 30 and a variation in
the exposure region.
[0083] FIG. 32 is a partially sectional view showing the
configuration of an alignment sensor 528 of an off-axis type as
shown in FIG. 29.
[0084] FIG. 33 is a partially sectional view showing the
configuration of a multi-point AF sensor as shown in FIG. 29.
[0085] FIG. 34 is a plan view showing the relationship between a
laser interferometer on the wafer side and the projection optical
system as shown in FIG. 29.
[0086] FIG. 35 shows a portion of a sample table; in which (a) is a
side view of the sample table 521 of FIG. 34, when looked in the
+X-direction, and (b) is a perspective view showing triaxial laser
beams incident to a moving mirror 524mY.
[0087] FIG. 36 is a longitudinally sectional view showing the
configuration of a reflecting light detection system 530 for
receiving light reflected from a reference pattern member as shown
in FIG. 29.
BEST MODES FOR CARRYING OUT THE INVENTION
[0088] A description will be made of the overall construction of a
projection exposure apparatus suitable for practicing the first
embodiment of the present invention with reference to FIG. 1. FIG.
1 shows a projection exposure apparatus of a step-and-scan type
which is so adapted as to scan a semiconductor wafer W relative to
a reticle R while projecting a circuit pattern of the reticle R
onto the semiconductor wafer W through an projection optical system
PL using an ArF excimer laser light source 1 which is narrowed so
as to avoid an absorption band of oxygen between ranges of
wavelengths of 192 nm to 194 nm.
[0089] As shown in FIG. 1, the main body of the ArF excimer laser
light source 1 is equipped through a vibration proofing table 2 on
a floor portion FD inside a clean room, or outside the clean room
in some cases, of a semiconductor manufacture plant. The main body
of the ArF excimer laser light source 1 is provided with a light
source control system 1A for exclusive use, including an input unit
such as, for example, a keyboard, a touch panel and so on, and a
display 1B. The light source control system 1A is so designed as to
automatically control the central wavelength of oscillation of
pulse light rays generated from the excimer laser light source 1,
the trigger of pulse oscillation, gases in a laser chamber, and so
on.
[0090] Ultraviolet pulse light rays narrowed to be generated from
the ArF excimer laser light source 1 is transmitted through a light
shielding bellows 3 and a pipe 4 to a movable mirror 5A disposed
inside a beam matching unit (BMU) that matches the position of a
light path with the main body of the exposure apparatus, and the
ultraviolet pulse light rays are reflected by the movable mirror 5A
and then transmitted through a light shielding pipe 7 to a beam
splitter 8 for use in detecting the quantity of light. The beam
splitter 8 allows a majority of the quantity of light to pass
therethrough and a slight portion of the light (for example, about
1%) to be reflected toward a light quantity detector 9.
[0091] The ultraviolet pulse light rays passed through the beam
splitter 8 are then incident to a variable light extinction system
10 that can adjust the intensity of the ultraviolet pulse light
rays as well as arrange for the sectional shape of the beam. The
variable light extinction system 10 is so configured as to contain
a drive motor and adjust a light extinction rate of the ultraviolet
pulse light rays in a stepwise or non-stepwise mode in accordance
with an instruction from a main control system, although not shown
in FIG. 1.
[0092] The movable mirror 5A is so arranged as to adjust a
direction of a reflective plane in a two-dimensional manner by an
actuator 5B. In this embodiment, the actuator 5B is subjected to a
feed-back or feed-forward control on the basis of a signal from a
detector 6 that receives beams for monitoring the position of the
beams in which the beams are generated coaxially with the
ultraviolet pulse light rays emitted from a visible laser light
source (e.g., semiconductor laser, He--Ne laser, or the like) built
in the excimer laser light source 1.
[0093] In order to adapt the movable mirror 5A to the situation as
described above, the movable mirror 5A is configured such that it
has a high transmittance or transmissivity with respect to the
wavelength of the beam for use in monitoring the position of the
beams and a high reflectance with respect to the wavelength of the
ultraviolet pulse light rays. On the other hand, the detector 6 may
comprise a four-part split sensor, CCD image pickup element or the
like, which can photoelectrically detect a variation in the
position of receiving the beams for monitoring the position which
has passed through the movable mirror 5A. The actuator 5B for
inclining the movable mirror 5A may be driven in response to a
signal from an acceleration sensor or a position sensor, each being
so adapted as to detect the vibration of the main body of the
exposure apparatus with respect to the floor portion FD, in place
of the signal from the detector 6.
[0094] The ultraviolet pulse light rays passed through the variable
light extinction system 10 may be irradiated on the reticle R
through an illumination optical system. The illumination optical
system may comprise a fixed mirror 11 disposed along a
predetermined light axis AX, a condenser lens 12, a first fly-eye
lens 13A acting as an optical integrator (homogenizer), a vibration
mirror 14 for decreasing coherency, a condenser lens 15, a second
fly-eye lens 13B, an exchangeable space filter 16 for shifting a
distribution of light source images, a beam splitter 17, a first
imaging lens system 22, a reticle R blind mechanism 23 containing a
vision field stop opening 23A for shaping an illumination area on
the reticle R onto a rectangular slit, a second imaging lens system
24, a reflective mirror 25, and a main condenser lens system
26.
[0095] The ultraviolet pulse light rays emitted from the space
filter 16 and passed through the beam splitter 17 may be received
in the amount of approximately several percentage by a
photoelectric detector 19 through an optical system 18 including a
light condenser lens and a dispersing plate. In this embodiment,
basically, a signal detected in a photoelectric mode by the
photoelectric detector 19 is subjected to operation processing (a
detailed description will be made with reference to FIG. 10) with a
processing circuit for controls of the quality of exposure light,
and conditions for exposure at the time of the scanning exposure
will be determined on the basis of the results of the operation
processing.
[0096] As shown in FIG. 1, a light condensing lens system 20 and a
photoelectric detector 21, which are disposed on the left-hand side
of the beam splitter 17, photoelectrically detect the reflected
light of the illumination light for exposure irradiated onto the
wafer W as the quality of light through the main condenser lens
system 26 from the projection optical system PL. The reflectivity
of the wafer W is detected on the basis of the photoelectric
signal.
[0097] With the configuration as described above, the incident
plane of the first fly-eye lens 13A, the incident plane of the
second fly-eye lens 13B, the plane of the vision field stop opening
23A of the reticle R blind mechanism 23, and the pattern plane of
the reticle R are conjugated optically with one another. The light
source plane formed on the leaving plane side of the first fly-eye
lens 13A, the light source plane formed on the leaving plane side
of the second fly-eye lens 13B, and a Fourier transform plane (the
leaving pupil plane) of the projection optical system PL are set so
as to be conjugated optically with one another. These elements
comprises a Koehler illumination system. Therefore, the ultraviolet
pulse light rays are converted into an illumination light having a
uniform intensity distribution by the plane of the vision field
stop opening 23A in the reticle blind mechanism 23 and the pattern
plane of the reticle R. At least one of the first fly-eye lens 13A
and the second fly-eye lens 13B may be disposed to act as a rod
integrator which has the incident plane set so as to be conjugated
optically with the Fourier transform plane of the projection
optical system PL or otherwise, and the leaving plane set so as to
be conjugated optically with the pattern plane of the reticle R or
otherwise.
[0098] The vision field stop opening 23A in the blind mechanism 23
in this embodiment is disclosed, for example, in Japanese Patent
Application Laid-Open No. 4-196,513 (U.S. Pat. No. 5,473,410). The
vision field stop opening is shown therein to extend in a linear
slit form or a rectangular form in a direction perpendicular to the
scanning exposure direction at a center of a circular vision field
of the projection optical system PL. Further, the blind mechanism
23 is provided with a movable blind for making the width of the
illumination region from the vision field stop opening 23A variable
in the scanning exposure direction on the reticle R. The movable
blind can serve as reducing strokes at the time of
scaning-transferring the reticle R and decrease the width of a
light shielding band on the reticle R, as disclosed in Japanese
Patent Application Laid-Open No. 4-196,513.
[0099] The ultraviolet pulse illumination light rays, the intensity
of which have been distributed in a uniform mode by the vision
field stop opening 23A of the blind mechanism 23, is incident to
the main condenser lens system 26 through the imaging lens system
24 and the reflective mirror 25. The ultraviolet pulse illumination
light rays uniformly irradiate a portion of the circuit pattern
region on the reticle R in a form that resembles the slit-shaped or
rectangle-shaped opening section of the vision field stop opening
23A.
[0100] As shown in FIG. 1, the illumination optical system
extending from the beam splitter 8 to the main condenser lens
system 26 is disposed in an illumination system housing (not shown)
in which the inside is set airtight against the air outside the
housing. The illumination system housing is mounted on a support
column 28 disposed standing on a portion of a base 49 for locating
the main body of the exposure apparatus on the floor portion FD.
The illumination system housing may be filled with clean and dried
gases, such as nitrogen, helium, or the like, so as to reduce the
concentration of the air (oxygen) to several percentages or less,
preferably less than 1%.
[0101] On the other hand, the reticle R is adsorbed on a reticle R
stage 30 and fixed thereto, and the reticle R stage 30 is disposed
such that it is transferred by a drive unit 34 including a linear
motor and so on in a one-dimensional way at a given velocity Vr in
a light-and-right direction (a Y-direction) in FIG. 1 at the time
of the scanning exposure, while the position of the reticle R stage
30 is measured on a real time basis by a laser interferometer 32.
The laser interferometer 32 can measure a variation in position and
rotation in a non-scanning direction (an X-direction) on a
real-time basis, in addition to a variation in the position in the
direction (Y-direction) of scanning the reticle R stage 30, and a
drive motor (a linear motor, a voice coil motor, etc.) can drive
the reticle R stage 30 so as to sustain the variation in the
position and rotation in a given state, to be measured at the time
of the scanning exposure.
[0102] The reticle R stage 30, the laser interferometer 32, and the
drive unit 34 are each mounted above a support column 31A of the
main body of the exposure apparatus. On a top end portion of the
support column 31A to which the drive unit 34 (a stator of a linear
motor) is to be fixed, an actuator is mounted. The actuator is so
disposed as to absorb a reaction force in the scanning direction
which may occur during the period of time for acceleration or
during the period of time for deceleration at the time of
transferring the scanning of the reticle R stage 30. The stator of
the actuator 35 is fixed to a support column 36B standing on a
portion of the base 49 through a mounting member 36A.
[0103] As the reticle R is irradiated with ultraviolet pulse
illumination light rays, the light passed through an irradiation
portion of the circuit pattern of the reticle R is incident to the
projection optical system PL. An image of a portion of the circuit
pattern is imaged on a center of the circular vision field on the
image plane side of the projection optical system PL through the
slit-shaped or rectangle-shaped (polygon-shaped) member whenever
the ultraviolet pulse illumination light rays are irradiated on the
circuit pattern of the reticle R. Such a projected partial image of
the circuit pattern is then transcribed on a resist layer on the
surface in a one shot region out of plural shot regions on the
wafer W disposed on the imaging plane of the projection optical
system PL.
[0104] An image distortion correction plate (quartz plate) 40 is
disposed on the reticle R side of the projection optical system PL
so as to reduce dynamic distortion aberration, particularly random
distortion features, which may occur at the time of the scanning
exposure. The surface of the correction plate 40 is polished
locally in the order of wavelength so as to minutely deviate main
light rays of a partially imaging light flux in a projection
field.
[0105] The projection optical system PL is provided with actuators
41A and 41B which can automatically adjust imaging features (e.g.,
projection magnification or a certain kind of distortion) on the
results of various detection by transferring a particular inner
lens element in a direction parallel to the optical axis or
inclining it at a very minute angle, such detection including
detection of a distorted state of the shot region on the wafer W to
be exposed, detection of a variation in temperature of a medium (an
optical element or gases to be filled therein) present in a
projection light path, and detection of a variation in an inner
pressure in the projection optical system PL with a variation in
atmospheric pressure.
[0106] Moreover, the projection optical system PL in this
embodiment may comprise only a refractive optical element (quartz
lens or fluorite lens), and the side of an object (reticle R) and
the side of an image (wafer W) are both of a telecentric
system.
[0107] The wafer W is adsorbed on and fixed to a wafer stage 42
that may be disposed so as to be transferred in a two-dimensional
way along an X- and Y-plane parallel to an image plane of the
projection optical system PL. The position of the wafer stage 42 is
measured on a real-time basis by a laser interferometer 46 for
measuring a variation in position of a moving mirror Ms fixed to a
portion of the wafer stage 42 with respect to a reference mirror Mr
fixed to the bottom end of a mirror cylinder of the projection
optical system PL. The wafer stage 42 is transferred in a
two-dimensional way on a stage base plate 31D on the basis of the
results of measurement by a drive unit 43 including a plurality of
linear motors.
[0108] The stator of the linear motor constituting the drive unit
43 is mounted on the base 49 through a support frame discrete from
the base plate 31D so as to transmit a reaction force directly to
the floor portion FD, rather not to the base plate 31D, which
reaction force may occur during the period of time of acceleration
or deceleration in transferring the wafer stage 42. Therefore, no
reaction force is applied whatsoever to the main body of the
exposure apparatus upon transferring the wafer stage 42 at the time
of the scanning exposure, so that vibration or stress occurred in
the main body of the exposure apparatus can be reduced to a greater
extent.
[0109] It is to be noted herein that the wafer stage 42 is
transferred at an equal velocity Vw in a right-and-left direction
(Y-direction) in FIG. 1 during the period of time of the scanning
exposure and transferred in a stepwise way in X- and Y-directions.
On the other hand, the laser interferometer 46 measures the
variation in position in the X-direction and a rotational direction
of the wafer stage 42 on a real-time basis, in addition to the
variation in position in the Y-direction of the wafer stage 42, and
the drive motor (linear motor, etc.) of the drive unit 34 is
operated so as to servo-drive the wafer stage 42 so as to bring the
variation in the such positions to be measured during the period of
time for scanning exposure into a given state.
[0110] Information on the variation in the rotation of the wafer
stage 42 measured by the laser interferometer 46 may be transmitted
to the drive unit 34 of the reticle R stage 30 through a main
control system on a real-time basis. An error of the variation in
the rotation on the wafer side can be controlled so as to
compensate for controls of rotation on the reticle R side.
[0111] It is to be noted herein that four corners of the stage base
plate 31D are supported on the base 49 through vibration-proofing
tables 47A and 47B (neither 47C nor 47D being indicated in FIG. 1)
each including an active actuator. A column 31C is disposed on each
of the vibration-proofing tables 47A and 47B (47C and 47D), on
which a column 31B is disposed in turn, which fixes a flange FLG
fixed to an outer wall of the barrel of the projection optical
system PL. Moreover, the support column 31A is mounted on the
column 31B.
[0112] With the construction as described above, each of the
vibration-proofing tables 47A and 47B (47C and 47D) can transfer
the Z-directional positions of the stage base plate 31D and the
support column 31C separately and discretely by the feed-back
controls and the feed-forward controls in response to a signal from
a posture detection sensor for monitoring a variation in the
posture of the main body of the exposure apparatus with respect to
the floor portion FD so as to make the posture of the main body of
the exposure apparatus always stable regardless of a variation in
gravity of the main body thereof in association with the movement
of the reticle R stage 30 and the wafer stage 42.
[0113] Although not shown in FIG. 1, each of the drive units,
actuators and so on of the main body of the exposure apparatus can
be controlled in a collective mode by the main control system. In
addition, an intermediate control unit system is equipped under the
main control system in order to allow specific controls of the
individual drive units and actuators. Representative examples of
such intermediate control unit systems may include, among others,
for example, a reticle R side control unit and a wafer side control
unit. The reticle R side control unit can be arranged to manage
various information on the position, the transferring velocity, the
acceleration of movement, and the position offset of the reticle R
stage 30, among others. Likewise, the wafer side control unit can
be arranged to manage various information on the position, the
transferring velocity, the acceleration of movement, and the
position offset of the wafer stage 42, among others.
[0114] The main control system can make controls of the reticle R
side control unit and the wafer side control unit in
synchronization with each other so as to maintain the transferring
velocity Vr of the Y-directional movement of the reticle R stage 30
and the transferring velocity Vw of the X-directional movement of
the wafer stage 42 at a velocity ratio in accordance with a
projection magnification (a 1/5-fold or 1/4-fold) of the projection
optical system PL, particularly at the time of the scanning
exposure.
[0115] The main control system is further so arranged as to send an
instruction to controlling the movement of each blade of the
movable blind disposed in the blind mechanism 23 in synchronization
with the movement of the reticle R stage 30 at the time of the
scanning exposure. Moreover, the main control system is so arranged
as to execute an optimal exposure sequence in association with an
exposure control device for controlling the light source control
system 1A of the excimer laser light source 1 and the variable
light extinction system 10 thereof as well as to set various
exposing conditions for scanning exposing the shot regions on the
wafer W by an appropriate exposure amount (a target exposure
amount).
[0116] In addition to the constructions as described above, a
reticle alignment system 33 for alignment of the initial position
of the reticle R in this embodiment is disposed outside an
illumination light path between the reticle R and the main
condenser lens system 26 to photoelectrically detect a mark formed
outside a circuit pattern region enclosed by a light shield band on
reticle R. A wafer alignment system 52 of an off-axis type for
photoelectrically detecting an alignment mark formed in each of
shot regions on the wafer W is disposed on the lower side of the
column 31B.
[0117] An actuator 60 of a non-contact type for maintaining
stability of the position between the light axis of the
illumination optical system (the light axis of the main condenser
lens system 26) and the light axis of the projection optical system
PL is interposed between a support column 28 supporting the
illumination system housing and the column 31A as a part of the
main body of the exposure apparatus. The actuator 60 may comprise,
for example, a voicex coil generating a Lorentz thrust, an E-core
type electromagnet generating a thrust by magnetically repulsive
force and attractive force, or the like, and be driven so as to
allow a signal from a sensor for sensing a variation in distance
between the support column 28 and the column 31A to become
constant.
[0118] In the entire space (spaces among plural lens elements)
inside a barrel of the projection optical system PL as shown in
FIG. 1, there is filled an inert gas (e.g., dry nitrogen gas,
helium gas, etc.) that has an oxygen content reduced to an
extremely small amount, like the illumination system housing. The
inert gas is supplied to the barrel thereof at a flow rate small
enough to compensate for leakage therefrom. It is to be noted
herein, however, that the supply of the inert gas is not required
to be performed so often once the air inside the barrel has been
replenished thoroughly with the inert gas, when air tightness is
high inside the tube body of the irradiation system housing and the
projection optical system PL.
[0119] It is required, however, to remove molecules of impurities
composed of various materials (such as, for example, glass
material, coating material, adhesive, paint, metal, ceramics
material, etc.) present in the light path by means of a chemical
filter or an electrostatic filter while forcing the inert gas whose
temperature is controlled to flow in the light path, when a
variation in transmittance is taken into consideration, which is
caused by attachment of water molecules, hydrocarbon molecules or
the like derived from the various substances present in the light
path to the surface of the optical elements.
[0120] The entire construction as shown in FIG. 1 is made of a
dioptric type in which the projection optical system PL is composed
only of refractive optical elements, however, it is also possible
to make the entire construction of a catadioptric type in which the
refractive optical elements are combined with a concave mirror (or
a convex mirror). In each type, it is preferred that each of the
side of an object plane of the projection optical system PL and the
side of an image plane be of a telecentric type.
[0121] The system for controlling the pulse emission in the case
where the excimer laser light source is utilized for projection
exposure of a scanning type is disclosed, for example, in Japanese
Patent Application Laid-Open No. 6-132,195 (U.S. Pat. No.
5,477,304), Japanese Patent Application Laid-Open No. 7-142,354
(U.S. Pat. No. 5,534,970), or Japanese Patent Application Laid-Open
No. 2-229,423. It is to be noted herein that the technology
disclosed in these patents and patent publications may be utilized,
if needed, as they are or as they are modified to some extent.
Moreover, for example, Japanese Patent Application Laid-Open No.
2-135,723 (U.S. Pat. No. 5,307,207) discloses a type of controlling
the exposure amount by adjusting energy of pulse illumination light
from the excimer laser light source by means of the variable light
extinction system 10 or adjusting the intensity (peak value) of
oscillation itself of the excimer laser light source 1 to a minute
extent. The technology disclosed in this patent and patent
publication may also be applied to the embodiment of the present
invention, if needed, as it is or as it is modified to some
extent.
[0122] Furthermore, the illumination optical system as shown in
FIG. 1 may be provided with the first fly-eye lens 13A and the
second fly-eye lens 13B. The illumination system in which such two
fly-eye lenses (an optical integrator) are disposed in tandem is
disclosed, for example, in Japanese Patent Application Laid-Open
No. 1-235,289, and the technology disclosed herein can be likewise
applied to the embodiment of the present invention.
[0123] To the reticle R stage 30 as shown in FIG. 1 can be applied
a type as disclosed in Japanese Patent Application Laid-Open No.
8-63,231, which adopts a construction in which the reaction force
generating from the acceleration or deceleration at the time of the
scanning exposure is offset on the basis of the law of conservation
of momentum.
[0124] To the wafer stage 42 can be applied a type as disclosed in
Japanese Patent Application Laid-Open No. 8-233,964, which adopts a
construction in which a stator of a linear motor is disposed in a
following movable stage member in order to reduce the weight of the
main body of the movable stage member that can move in a
two-dimensional mode.
[0125] Although not shown in FIG. 1, the embodiment of the present
invention includes a transmittance measurement means for detecting
the intensity of reflected light in a photoelectric mode by
irradiating measuring beams made from the ultraviolet pulse
illumination light onto the reflecting member disposed on the
Fourier transform plane of the projection optical system PL or a
plane in the vicinity thereof, in order to measure the intensity of
the ultraviolet pulse illumination light (exposing energy) at a
substantially real time, with the variations in transmittance of
both of the illumination optical system and the projection optical
system PL added thereto. A detailed description will be made
hereinafter of the transmittance measuring means.
[0126] In this embodiment of the present invention, as
schematically shown in FIG. 2, a reflecting member Re is disposed
at the center in the Fourier transform plane (hereinafter referred
to also as "pupil plane") EP of the projection optical system PL,
and measuring beams B1 or B2 are irradiated onto the reflecting
member Re. The reflecting member Re is made of a thin metal film
formed in a generally circular form at a central portion of a
transparent quartz substrate CP disposed on the pupil plane EP by
deposition, and has a high reflectance or reflectivity (for
example, 80% or higher) for the measuring beams B1 or B2 (a portion
of the ultraviolet pulse illumination light transmitted from the
light source 1).
[0127] Plural sheets of lens elements are incorporated in the
projection optical system PL having a flange FLG. FIG. 2 indicates
only representative lens systems GA and GB among them. Further,
FIG. 2 shows an object plane of the projection optical system PL on
which the pattern plane of the reticle R is situated as reference
symbol PF1 and an imaging plane of the projection optical system PL
on which the surface of the wafer W is situated as reference symbol
PF2.
[0128] Moreover, when the projection optical system PL is
telecentric on both ends, each of main light rays MLa and MLb (as
indicated by broken line) of imaging light fluxes LBa and LBb by
the ultraviolet pulse illumination light from each of object points
Pa and Pb on the object plane PF1 is incident to the projection
optical system PL in a mode parallel to the light axis AX of the
projection optical system PL, and then passes through a central
point (a point passing through the light axis AX) inside the pupil
plane EP of the projection optical system PL, thereafter advancing
again from the projection optical system PL toward each of
corresponding image points Pa' and Pb' on the imaging plane PF2 in
parallel to the light axis AX.
[0129] A ratio of a number of openings NAr for the imaging light
fluxes LBa and LBb on the side of the object plane PF1 to a number
of openings NAw therefor on the side of the projection imaging
plane PF2, i.e., a ratio (NAr/NAw), is equal to a magnification of
projection of the projection optical system PL. When the number of
the openings NAw therefor on the side of the projection imaging
plane PF2 is supposed to be 0.8 and the magnification of projection
thereof is supposed to be 1/4, the number of the openings NAr
therefor on the side of the object plane PF1 is 0.2. The numbers of
the openings NAr and NAw are determined substantially on the basis
of the effective size of the pupil plane EP of the projection
optical system PL and the focal distance of the projection optical
system PL. When the effective size of the pupil plane EP becomes
larger, the numbers of the openings NAr and NAw increase and as a
consequence improve a resolving power to that extent.
[0130] In the projection optical system PL, one space between the
object plane PF1 and the pupil plane EP and other space between the
pupil plane EP and the projection imaging plane PF2 constitute an
extremely precise Fourier transform system (or an inverse Fourier
transform system). With this configuration, when the measuring
beams B2 (parallel light flux) collimated from the side of the
object plane PF1 of the projection optical system PL are incident
to the projection optical system PL in parallel to the light axis
AX, the measuring beams B2 are converged at the central point of
the pupil plane EP. Likewise, when the measuring beams B1 (parallel
light flux) collimated from the side of the projection imaging
plane PF2 of the projection optical system PL are incident to the
projection optical system PL in parallel to the light axis AX, the
measuring beams B1 are converged at the central point of the pupil
plane EP.
[0131] In this embodiment, the reflecting member Re is disposed at
the center of the pupil plane EP, so that the measuring beams B2
from the side of the object plane PF1 are reflected there at an
angle symmetrical to the light axis AX to form reflected beams B2',
returning to the side of the object plane PF1 as a parallel light
flux. Likewise, the measuring beams B2 from the side of the
projection imaging plane PF2 are reflected there at an angle
symmetrical to the light axis AX to form reflected beams B1', which
in turn are returned to the side of the projection imaging plane
PF2 as a parallel light flux.
[0132] Therefore, when the intensity of the measuring beams B2
irradiating from the object plane PF1 side to the projection
optical system PL is compared with the intensity of the reflected
beams B2' reflected on the pupil plane EP of the reflecting member
Re and returning to the object plane PF1 side, a transmittance in
the light path extending between the object plane PF1 of the
projection optical system PL and the pupil plane EP thereof and a
variation thereof can be detected. On the other hand, when the
intensity of the measuring beams B1 irradiating from the projection
imaging plane PF2 side to the projection optical system PL is
compared with the intensity of the reflected beams B1' reflected on
the pupil plane EP of the reflecting member Re and returning to the
projection imaging plane PF2 side, a transmittance in the light
path extending between the projection imaging plane PF2 of the
projection optical system PL and the pupil plane EP and a variation
thereof can be detected.
[0133] The measuring beams B1 and B2 are separately from the
irradiation of exposing illumination light (the ultraviolet pulse
illumination light passing through the system ranging from the
fly-eye lens system 13A to the main condenser lens system 26), and
are formed from a portion of the excimer laser light emitted and
divided from the excimer laser light source 1 of FIG. 1, for
example, at a reflecting mirror 11 as shown in FIG. 1,
respectively. A shutter or other -appropriate means can be disposed
in order to separate the irradiation of the exposing illumination
light from the irradiation of the measuring beams B1 and B2.
[0134] The reflecting member Re may be configured in a specific
manner as shown in FIGS. 3 and 4. FIG. 3 shows a flat plane of the
quartz substrate (parallel flat plate) CP from which the reflecting
member Re is formed, and FIG. 4 shows a partially sectional plane
of the quartz substrate CP. The quartz substrate CP may be of a
circular form having a diameter larger than the effective diameter
(as indicated by broken line) of the pupil plane EP of the
projection optical system PL, and the reflecting member Re is
formed at a center of the quartz substrate CP by deposition in a
circular form having a sufficiently smaller diameter.
[0135] In the case of this embodiment, the quartz substrate CP is
disposed in the projection optical system PL in a fixed manner, so
that the reflecting member Re acts as a shielding member against a
pattern imaging light flux upon projecting a pattern of the reticle
R onto the wafer W at the time of the scanning exposure. However,
if the pattern imaging light flux distributing in the pupil plane
EP of the projection optical system PL would have some diameter
range to some extent at the central portion of the pupil plane EP,
no big influence will be exerted on the resolving power and the
quality of an image even if the such pattern imaging light flux
would be shielded thereon.
[0136] In order to avoid the influence therefrom, the diameter of
the reflecting member Re is set to amount to approximately
{fraction (1/10)} to 1/5 of the effective diameter of the pupil
plane EP. It is preferred as a matter of course that the diameter
of the reflecting member Re is extremely small in a region where a
sufficient shielding area can be ensured with respect to the
measuring beams B1 and B2. It is to be noted herein that FIGS. 3
and 4 show each a case where the reflecting member Re is formed
only on one side of the quartz substrate CP, however, it can be
formed on both sides thereof. Moreover, it is preferred that the
reflecting member Re are not permeable to the measuring beams B1
and B2. In addition, the quartz substrate CP may be composed of a
lens element located in the vicinity of the pupil plane EP of the
projection optical system PL, although the quartz substrate CP is
shown therein as being composed of such parallel flat plates. In
this case, the reflecting member Re may be deposited at the center
on the surface of the such lens element.
[0137] Now, a description will be made of an example of the
specific construction of the transmittance measuring means
applicable to the device of FIG. 1 with reference to FIGS. 5 and 6.
FIG. 5 shows a system ranging from the blind mechanism 23 to the
main condenser lens system 26 in the system of the illumination
optical system of FIG. 1. A transmittance measuring means 80 is
configured such that the measuring beams B2 is irradiated toward
the main condenser lens system 26 and the projection optical system
PL through a semi-permeable portion formed at a part of the mirror
25 disposed between the imaging lens system 24 and the main
condenser lens system 26 and that the reflected beams B2' reflected
on the reflecting member Re of the pupil plane EP and returning up
to the main condenser lens system 26 are received through the
semi-permeable portion of the mirror 25.
[0138] As previously described above, the reticle blind mechanism
23 is provided with the fixed blind 23A with a rectangle-shaped
slit-like opening and with a pair of the movable blades 23C and 23D
that can make variable the scanning-directional width of the
rectangle-shaped slit-like illumination light to be irradiated onto
the reticle R. The movable blades 23C and 23D are driven in
association with the positions varying in scanning the reticle R in
the Y-axial direction at the time of the scanning exposure by means
of driving motors 23B1 and 23B2, respectively, as disclosed in
Japanese Patent Application Laid-Open No. 4-96,513 (U.S. Pat. No.
5,473,410).
[0139] The fixed blind 23A and the movable blades 23C and 23D are
disposed close to and along the light axis AX and set so as to
become conjugated with the object plane PF1 (the pattern plane of
the reticle R) of the projection optical system PL by means of the
combination system with the imaging lens system 24 and the main
condenser lens system 26 combined together. Therefore, a plane EP1
(a Fourier transform plane) conjugate with the pupil plane EP of
the projection optical system PL is formed in the vicinity of the
mirror 25 between the imaging lens system 24 and the main condenser
lens system 26.
[0140] With the configuration as described above, parallel beams
from the excimer laser light source 1 branched, for example, at the
mirror (beam splitter) 11, as shown in FIG. 1, is incident to the
transmittance measuring means 80 as the measuring beams B2. The
measuring beams B2 are divided at the beam splitter 82 into two
beams, one being referred to as permeated beams and the other being
referred to as reflected beams. The permeated beams are received by
a photoelectric detector 86A for measuring the beam intensity on
the light transmission side. On the other hand, the reflected beams
from the beam splitter 82 are converged at the plane EP1 through
the lens system (a Fourier transform lens) 84, followed by
permeating through the mirror 25 and reaching the condenser lens
system 26 to convert again into the parallel beams B2 parallel to
the light axis AX, thereafter passing the object plane PF1 of the
projection optical system PL in a perpendicular direction.
[0141] It is to be noted herein that, FIG. 5 shows the measuring
beams B2 leaving from the condenser lens system 26 in a form in
which they are superimposed over the light axis AX of the
projection optical system PL. They, however, are actually
decentered from the light axis AX as shown in FIG. 6. FIG. 6
indicates the construction of the transmittance measuring means 80,
the mirror 25 and the condenser lens system 26 of FIG. 5, when
looked from the right side in FIG. 5. In FIG. 6, the measuring
beams B2 reflected at the beam splitter 82 are set to be decentered
and incident to the lens system 84.
[0142] With this configuration, the measuring beams B2 leaving from
the condenser lens system 26 advances eccentrically with its right
side of the X-axial direction (a non-scanning direction) with
respect to the light axis AX, when looked on a Z-X plane as shown
in FIG. 6. Therefore, as described above in connection with FIG. 2,
the measuring beams B2 are incident to the projection optical
system PL in a collimated state, and the beams B2' reflected at the
reflecting member Re disposed on the pupil plane EP of the
projection optical system PL return to the object plane PF1 side of
the projection optical system PL.
[0143] At this time, the reflected beams B2' travels along the
light path symmetric to the measuring beams B2 with respect to the
light axis AX from the condenser lens system 26, the mirror 25 and
the lens system 84 in this order, and they are received by a
photoelectric detector 86B after transmittance through the beam
splitter 82. Detection signal SS2 from the photoelectric detector
86B is subjected to operation processing by a processing circuit
(will be described in more detail with reference to FIG. 10),
together with detection signal SS1 from the photoelectric detector
86A as a standard, and is used as measuring a transmittance between
the object plane PF1 and the pupil plane EP of the projection
optical system PL or a variation thereof.
[0144] The measurement of the transmittance by the photoelectric
detectors 86A and 86B is basically effected by determining a ratio
lr (SS2/SS1) of the intensity of the signal SS1 to the intensity of
the signal SS2 output at the time of emitting one pulse from the
excimer laser light source 1. On the other hand, a variation of the
transmittance can be obtained by calculating a ratio (lr/lr') of
the intensity ratio lr to the intensity ratio lr' saved before a
predetermined period of time.
[0145] It is to be noted herein, however, that the transmittance
(the intensity ratio lr) measured by the photoelectric detectors
86A and 86B is a relative value and does not represent an absolute
value. Therefore, when an absolute value of the transmittance is to
be determined, some calibration should be made. From the point of
view of improvements in precision of control over the exposure
amount, however, it is not so needed to determine the absolute
transmittance, and it is rather significant to learn a periodical
variation in the measured intensity ratio lr (a measured
transmittance) or a variation characteristic of the measured
transmittance occurring during a period of time, for example, when
one sheet of wafer has been exposed to light or when a lot of
wafers has been exposed to light, or a tendency thereof.
[0146] With the construction of the transmittance measuring means
80 as shown in FIGS. 5 and 6, the measuring beams B2 and the
reflected beams B2' passing through the object plane PF1 are set so
as to pass through a rectangle-shaped slit-like region of exposing
illumination light defined in a vision field on the object plane
PF1 side of the projection optical system PL, and the transmittance
for the light path of the pattern imaging light flux from the
reticle R passing actually inside the projection optical system PL
can be accurately measured upon projection exposure.
[0147] In FIGS. 5 and 6, the measuring beams B2 and the reflected
beams B2' are set so as to run in a state eccentric symmetrically
to the light axis AX on the object plane PF1 side of the projection
optical system PL. It is to be noted herein, however, that the
setting of them is not restricted to such and that the measuring
beams B2 and the reflected beams B2' can be set so as to travel
coaxially with the light axis AX. In this case, the measuring beams
B2 are set so as to pass through the center of the lens system 84
in FIG. 6, so that this construction can provide the feature that
the lens system 84, the beam splitter 82 and other elements in the
transmittance measuring means 80 can be made compact in size.
[0148] Further, when the measuring beams B2 and the reflected beams
B2' are set so as to pass coaxially with the light axis AX, the
diameter (a sectional area at a portion where a light flux is
parallel) of the measuring beams B2 can be made as large as the
size of the lens system 82 so that they can be allowed to pass
through a larger light path inside the projection optical system PL
and the measured transmittance can be averaged to a higher
extent.
[0149] It should be noted herein that the measuring beams B2 from
the transmittance measuring means 80 as shown in FIGS. 5 and 6 and
the reflected beams B2' from the reflecting member Re of the pupil
plane EP of the projection optical system PL are set so as to pass
through an opening portion 30H formed in the reticle R stage 30
without being blocked by the reticle R, for example, as shown in
FIG. 7. FIG. 7 is a perspective view schematically showing the
construction on the reticle R stage 30, and the reticle R is
adsorbed and supported on four adsorbing members 30K disposed at
the four corners of the reticle R stage 30.
[0150] A moving mirror 32a and corner mirrors 32b and 32c are
mounted on the reticle R stage 30. The moving mirror 32a reflects
beams IBa from an interferometer 32 for measuring the position of
the stage in the non-scanning direction (the X-axial direction),
which is disposed extending in the scanning direction (the Y-axial
direction). The corner mirrors 32b and 32c reflect beams IBb and
Ibc from the interferometer 32 for measuring the position of the
stage in the scanning direction (the Y-axial direction) and the
yawing (rotational) direction, respectively.
[0151] With this construction, the rectangle-shaped slit-like
illumination light from the exposing illumination system is set so
as to extend in the X-axial direction at the center of a lenses
group GA defining the vision field on the object plane PF1 side of
the projection optical system PL, during a period of time when a
pattern region PS on the reticle R is subjected to scanning
exposure on the wafer. Generally, the circuit pattern region PS on
the reticle R is located in the position deviated by a
predetermined approach-run distance in the Y-axial direction from
an illumination region of the exposing illumination light before
the start of a one-dimensional movement upon scanning exposure.
[0152] FIG. 7 shows the state in which the reticle R is set at the
position of starting the approach run. The measuring beams B2 from
the transmittance measuring means 80 in the approach-run start
position are incident to the lenses group GA of the projection
optical system PL through the opening portion 30H of the reticle R
stage 30 without being blocked by the reticle R, and the reflected
beams B2' from the projection optical system PL are returned to the
transmittance measuring means 80 through the opening portion
30H.
[0153] Therefore, a precise measurement of the transmittance can be
effected without undergoing an influence of partially shielding a
pattern of the pattern region PS as well as an influence of light
shielding at a pellicle frame on the reticle R. It should be noted
herein, however, that when a relatively large space (a transparent
portion) is provided in the scanning direction outside the circuit
pattern region PS on the reticle R, the measuring beams B2 and the
reflected beams B2' can be set so as to pass through the space
portion. In this case, the transmittance of the portion of the
reticle R including the transparent portion can be measured.
[0154] In the construction as shown in FIG. 7, the opening portion
30H of the reticle R stage 30 is formed only on one side in the
scanning direction. When a stroke of transferring the reticle R
stage 30 in the Y-axial direction can be ensured, however, an
opening portion can also be likewise provided on the side of each
of the corner mirrors 32b and 32c in FIG. 7. When the opening
portion 30H is disposed on the both sides of the reticle R stage 30
in the scanning direction in the manner as described above, the
transmittance can be measured even if the direction of starting the
approach run of the reticle R stage 30 would be +Y-axial direction
or -Y-axial direction, thereby presenting the advantage in that the
freedom of measuring timing and the freedom of a measuring sequence
can be improved.
[0155] Then, a description will be made of means for measuring the
transmittance within the light path extending from the pupil plane
EP of the projection optical system PL to the projection imaging
plane PF2 with reference to FIGS. 8 and 9. FIG. 8 shows a sectional
structure of a part of the projection optical system PL and a part
of the wafer stage 42, and FIG. 9 indicates an example of the
relationship of a planar disposition of a vision field IF on the
projection imaging plane PF2 side of the projection optical system
PL with a light shielding member 94 on the wafer stage 42. It
should be noted herein, however, that in FIG. 8 lenses groups GB
and GC for subjecting the pattern imaging light flux from the
reticle R to inverted Fourier transformation are located under the
quartz substrate CP (the reflecting member Re) disposed on the
pupil plane EP of the projection optical system PL.
[0156] Inside the wafer stage 42, there are provided a pinhole
plate 90, a lens system 91, and a mirror 92, the pinhole plate 90
being disposed to horizontally receive beams LB0 emitting from the
excimer laser light source 1 in a parallel mode, the lens system 91
being disposed to receive divergent light rays from the pinhole
plate 90 as the measuring beams B1 and collimate them into a
parallel light flux, and the mirror 92 being disposed to bend the
measuring beams B1 in the Z-axial direction (a perpendicular
direction). On top of the wafer stage 42, a light shielding plate
94 is mounted, the light shielding plate 94 being provided with a
window 94A through which the perpendicularly bent beams B1 are
transmitted upwardly above the wafer stage 42.
[0157] As shown in FIG. 9, the light shielding plate 94 is shaped
in a rectangular form in which one pair of its parallel sides
extends in the X-axial direction (the non-scanning direction). As
the light shielding plate 94 is located in a predetermined
measuring position (the state in FIG. 9) on the X-Y plane by
transferring the wafer stage 42, the measuring beams B2 from the
window 94A (in a sectionally circular form in this embodiment) are
located at the position apart in the X-direction by a predetermined
distance from the central point (the point through which the light
axis AX passes) of the vision field IF, when looked on the X-Y
plane. In FIG. 9, a rectangle-shaped region EIA extending in the
X-direction (the non-scanning direction) within the vision field IF
represents an effective projection region in a shape analogous to a
distribution of intensity of the illumination light from the
exposing illumination system.
[0158] The measuring beams B1 leaving in the direction
perpendicularly from the window 94A of the light shielding plate 94
are converged toward the center of the pupil plane EP by the lenses
groups GB and GC disposed inside the projection optical system PL
as shown in FIG. 8 and then reflected by the reflecting member Re
disposed therein. The reflected beams B1' are then returned as a
parallel light flux through the lenses groups GC and GB to the
light shielding plate 94. While they pass through the lenses groups
GC and GB, the reflected beams B1' travel through the light path
symmetrical with respect to the light axis AX to the light path
through which the measuring beams B1 have traveled up to the
reflecting member Re.
[0159] A window 94B as shown in FIG. 9 is provided at the position
on the light shielding plate 94 at which the reflected beams B1'
are returned to reach. A photoelectric detector 96B for detecting
the light intensity or light quantity of the reflected beams B1' is
disposed right under the window 94B. Detection signal SS4 from the
photoelectric detector 96B is transmitted to a processing circuit
and used for measuring transmittance between the pupil plane EP of
the projection optical system PL and the object plane PF1 thereof
and a variation in transmittance between them.
[0160] In order to set the intensity of the measuring beams B1 as a
standard, a beam splitter 89 for reflecting a portion of the beams
LB0 (approximately several %) and a photoelectric detector 96A for
detecting the intensity or quantity of the light reflected are
provided, and detection signal SS3 from the photoelectric detector
96A is transmitted to a processing circuit. Upon measuring the
transmittance and a variation of the transmittance, a ratio
(SS4/SS3) of the detection signal SS4 from the photoelectric
detector 96B to the detection signal SS3 from the photoelectric
detector 96A is calculated.
[0161] As shown in FIGS. 8 and 9, the transmittance measuring means
may be composed of the beam splitter 89, the pinhole plate 90, the
lens system 91, the mirror 92, and the photoelectric detectors 96A
and 96B. In this embodiment, the transmittance measuring means is
located on the wafer stage 42, so that it is required to align the
wafer stage 42 in the state as shown in FIGS. 8 and 9 upon
measuring.
[0162] When the light shielding plate 94 is disposed with respect
to the vision field IF as shown in FIG. 9, the reflected beams B1'
return in an accurate way within the window 94B of the light
shielding plate 94. If the light shielding plate 94 is aligned in
such a way that it is deviated from that disposition, for example,
toward the right side by a distance .DELTA.X, the reflected beams
B1' are deviated by 2.DELTA.X toward the left side with respect to
the window 94B. In other words, in this embodiment, the position of
the reflected beams B1' inside the vision field IF is located
always in a point-symmetrical relationship with the measuring beams
B1 with respect to the point through which the light axis AX
passes.
[0163] Therefore, in the case where the measuring beams B1 are
located on the X-axis on which the light axis AX passes as shown in
FIG. 9, the X-directional distance from the light axis AX to the
center of the measuring beams B1 becomes larger than the initial
value, so that the X-directional distance from the light axis AX to
the center of the reflected beams B1' becomes larger than the
initial value by that increased distance. The size of the window
94B on the light shielding plate 94 can be determined with a scope
larger than twice the error of alignment of the wafer stage 42
added to the size of a sectional shape of the reflected beams
B1'.
[0164] When the measuring beams B1 and the reflected beams B1' are
arranged so as to travel through the different light paths inside
the lenses groups GB and GC on the projection imaging plane PF2
side rather than the pupil plane EP of the projection optical
system PL as in the construction as shown in FIG. 8, a variation in
transmittance at a wider portion within the lenses groups GB and GC
can be measured, like in the case of FIGS. 5 and 6 above.
[0165] It is also possible to transmit the measuring beams B1 to
the projection optical system PL coaxially with the reflected beams
B1', when the mirror 92 in FIG. 8 is replaced with a beam splitter
and the photoelectric detector 96B is disposed below the beam
splitter. In this case, however, it is needed to align the window
94A of the light shielding plate 94 leaving in the direction
perpendicularly from the measuring beams B1 right under the light
axis AX upon measuring transmittance.
[0166] Further, when the mirror 92 in FIG. 8 is replaced with the
beam splitter, the photoelectric detector 96A for use as a standard
can be disposed on the left-hand side of the beam splitter, so that
the beam splitter 89 can be omitted and the light quantity of the
beams LB0 from the excimer laser light source 1 can be utilized in
a more effective mode.
[0167] It can also be noted herein that the measuring beams B2 as
shown in FIGS. 5 and 6 and the measuring beams B2 as shown in FIGS.
8 and 9 may be obtained, as shown in FIG. 10, by arranging the
mirror 11 so as to work as a beam splitter in the portion composed
of the variable light extinction system 10, the mirror 11 and the
lens system 12 in the illumination optical system as shown in FIG.
1 and by passing an excimer laser light transmitted through the
mirror 11 to a concave lens 104 after passage through a wholly
reflecting mirror 102 and a convex lens 103.
[0168] With this construction, in order to selectively shift
between the supply of the illumination light upon exposure and the
supply of the illumination light upon measuring the transmittance,
a shutter 101A that can be opened and shut off by a drive system
100A is interposed between the mirror (beam splitter) 11 and the
lens system 12 and the other shutter 101B that can be opened and
shut off by the other drive system 100B, behind the concave mirror
104. Further, the shutters 101A and 101B are disposed so as to
offset with each other. Moreover, the drive systems 100A and 100B
are driven by an instruction from a processor disposed in the
processing circuit in FIG. 11 as will be described hereinafter.
[0169] Furthermore, the convex lens 102 and the concave lens 104 in
FIG. 10 are not restricted to particular ones and they may be of
any system that can reduce the beam size to a state of a parallel
light flux and that can collimate and send out the measuring beams
B1 and the measuring beams B2 or that can expand the beam size
thereof and send out them.
[0170] Now, a description will be made of the configuration of the
processing circuit for processing information relating to the
transmittance on the basis of each signal from the photoelectric
detectors 86A, 86B, 96A and 96B as the transmittance measuring
means, with reference to FIG. 11. The processing circuit of FIG. 11
mainly comprises high-speed sample-hold circuits (hereinafter
referred to each as an "S/H circuit") 120A to 120E, inclusive, and
analog-digital converters (each hereinafter referred to as "ADC")
124A and 124B. The S/H circuits detect the light quantity of pulse
light accurately in response to a pulse light having a duration as
extremely short as approximately 10 to 20 ns, which is emitted from
the excimer laser light source 1. The ADC convert the signal
voltage in accordance with the hold light quantity to a digital
value.
[0171] First, the detection signal SS1 from the photoelectric
detector 86A is applied to the S/H circuit 120A including an
amplifier circuit, and the area (light quantity) of a pulse wave
form of the signal SS1 amplified is sampled and held in response to
a timing signal from a timing circuit 128, thereafter being applied
to a multiplexer 122A. Likewise, the detection signal SS3 from the
photoelectric detector 96A is applied to the S/H circuit 120B
including an amplifier circuit, and the area (light quantity) of a
pulse wave form of the signal SS3 amplified is sampled and held in
response to a timing signal from the timing circuit 128, thereafter
being applied to the multiplexer 122A.
[0172] Each of the detection signals SS2 and SS4 from the other
photoelectric detectors 86B and 96B is applied to the S/H circuits
120C and 120D each including an amplifier circuit, and the area
(light quantity) of each pulse wave form of the signals SS2 and SS4
amplified is sampled and held in response to a timing signal from
the timing circuit 128, respectively, thereby being applied to a
multiplexer 122B.
[0173] Moreover, a photoelectric signal from the photoelectric
detector 19 as shown in FIG. 1 is likewise applied to a high-speed
sample-hold circuit 120E. The signal amplified by the circuit is
sampled and held in response to the timing signal from the timing
circuit 128, thereafter being applied to the multiplexer 122B. With
this configuration, the multiplexer 122A selects either one of the
values of the light quantities of the held signals SS1 and SS3 in
response to an instruction from the processor 126, while the other
multiplexer 122B selects either one of the values of the light
quantities of the held signals SS2 and SS4 and the light quantities
of signals from the detector 19 in response to an instruction from
the processor 126.
[0174] One light quantity value selected out of the light quantity
values by the multiplexer 122A is applied to the ADC 124A, while
one light quantity value selected therefrom by the other
multiplexer 122B is applied to the ADC 124B. The light quantities
are then converted into digital values by each of the ADCs 124A and
124B, respectively, and each data converted into the digital value
is read by the processor 126. Then, the processor 126 performs
providing the instruction to the timing circuit 128, generating a
shift signal for selection to the multiplexer 122A or 122B, reading
data from each of the ADCs 124A and 124B, and associating between
the control system 1A of the excimer laser light source 1 and the
main control system of the main body of the exposure apparatus.
[0175] With the configuration as described above, the processor 126
provides three main functions, including a transmittance measuring
program for detecting and updating a variation of transmittance and
the tendency of such a variation at each time interval by the
photoelectric detectors 86A, 86B, 96A and 96B; an exposing
condition specifying program for setting various exposing
conditions (including an applying voltage (or charging voltage) of
the excimer laser light source 1, the extinction rate of the
variable light extinction system 10, the speed of scanning each of
the stages, a slit width of the blind mechanism 23, etc.) on the
basis of the exposure amount (an accumulated light quantity) to be
measured by the photoelectric detector 19 upon controls of the
exposure amount; and a calibration program for calibrating in
advance the relationship between the exposure amount measured by
the photoelectric detector 19 and the actual exposure amount
provided on the wafer.
[0176] Now, a description will be made of an example of the
calibration program with reference to FIG. 12. Upon the calibration
operation, a reference illuminance meter is mounted on a given
portion on the wafer stage 42, which can measure an absolute
exposure amount (unit mJ).or an illuminance (mW/cm), as shown at
step 300. The reference illuminance meter is adapted to measure an
illuminance value and the exposure amount of a single pulse light
ray or an accumulated exposure amount of plural pulse light rays
with a measuring precision of .+-.0.5% or less with respect to the
absolute value.
[0177] Then, as shown at step 302, standard exposing conditions for
calibration are set for the main control system of the exposure
apparatus. The standard exposing conditions are determined by the
product obtained by multiplying an average illuminance value i
(light quantity) of one pulse light required to provide an
appropriate exposure amount (mJ) on a resist on a wafer to be used
by the number (N) of pulse light accumulated at each point on the
wafer.
[0178] It is noted herein that, as this embodiment assumes scanning
exposure, the number N (a positive integer) of the pulse light
accumulated at each point of the wafer can be set by the formula:
N=f.times.(Dap/Vws), where f (in Hz) is the oscillating frequency
of the excimer laser light source 1.; Dap (in mm) is the width
relating to the scanning direction of an effective projection
region EIA (as shown in FIG. 9) on the wafer; and Vws (in mm/s) is
the velocity at which to scan the wafer.
[0179] Thus, it can be understood that the number N is the number
of pulses to be oscillated during a period of time during which the
wafer is being transferred in the scanning direction by the width
Dap portion of the effective projection region EIA and as a rule it
is required that an integer without any fraction can be obtained by
the operation of the above formula. As a practical procedure, the
number N of the pulse light is determined roughly by a variation
(.+-..alpha.%) in the intensity of the pulse light from the excimer
laser light source 1 and a control precision (.+-.A%) of the
exposure amount exposed to the wafer and set to satisfy the
relationship: A>(.alpha./({square root}N).
[0180] As the number N is set to, for example, N=40 in the manner
as described above, the scanning velocity Vws can be determined
from existing values of the width Dap and the frequency f. Suppose
that the width Dap=8 mm and the frequency f=800 Hz, the velocity
Vws is given as 160 mm. Among those figures, the number N can be
made larger than the initial value, but it cannot be made smaller
therefrom, in order to ensure the precision for controlling the
exposure amount. On the other hand, the width Dap can also be made
smaller than its initial value due to the size (diameter) of the
vision field IF of the projection optical system PL, but it cannot
be made larger than the initial value thereof.
[0181] In each case, the light quantity (illuminance value i) per
pulse light is adjusted so as to set the relationship to satisfy
the formulas: A>(.alpha./({square root}N) and
N=f.times.(Dap/Vws). At this end, the light extinction rate by the
variable light extinction system 10 in FIG. 1 or the discharging
voltage (in high volt) within the excimer laser light source 1 is
to be adjusted.
[0182] When the standard exposing conditions have been set in the
manner as described above, a dummy exposure operation is carried
out in a manner as shown at step 304 in FIG. 12. Upon the dummy
exposure operation, the reticle R is removed from the reticle R
stage 30 and the wafer stage 42 is aligned so as to locate a light
receipt window of the reference illuminance meter on the wafer
stage 42 right under the projection optical system PL.
[0183] Upon measurement of illuminance on the image plane side of
the projection optical system PL, the way of measurement can be
selected from the dynamic measurement of illuminance for scanning
and transferring the wafer stage 42 in accordance with the standard
exposing conditions and the static measurement of illuminance in
which the illuminance is measured in a state in which the wafer
stage 42 is stayed still. The static measurement of illuminance is
of a type in which the wafer stage 42 is exposed to light in a
still state under exposing conditions excluding the scanning
velocity Vws set under the standard exposing conditions, while the
light receipt window of the reference illuminance meter is stayed
still within the effective projection region EIA.
[0184] Although the device according to the present invention can
utilize each of both dynamic illuminance measurement and static
illuminance measurement, the dummy exposure operation at step 304
is set so as to use the dynamic illuminance measurement. Therefore,
at step 304, the wafer stage 42 is transferred with scanning at the
velocity Vws so as to cause the light receipt window of the
reference illuminance meter to cross in the Y-axial direction right
under the effective projection region EIA.
[0185] As the scanning and transferring of the wafer stage for the
dummy exposure operation has been finished, a measured value of the
reference illuminance meter is confirmed as shown at step 306. The
measured value represents an exposure amount provided at each point
on the wafer by scanning the wafer stage 42 in a one direction.
Then, at step 308, it is decided to determine whether the measured
exposure amount is equal to a target exposure amount to be
determined by a sensitivity to the resist.
[0186] When it is decided that the target exposure amount was not
obtained at step 308, then the operator corrects the exposing
conditions as shown at step 312. The correction usually includes an
alteration of a high volt value of the excimer laser light source 1
or an alteration of the light extinction rate by the variable light
extinction system 10. However, in some cases the slit width Dap of
an exposing illumination light, the scanning velocity Vws or the
oscillating frequency f also can be altered.
[0187] Once the exposing conditions have been corrected, the
processes from step 304 are repeated until the decision at step 308
becomes YES. Then, when it is decided at step 308 that the measured
value coincides with the target exposure amount within a
predetermined acceptable scope (for example, .+-.0.2%), the process
advances to step 310 at which the target exposure amount provided
on the wafer is allowed to correspond to an output of an integrator
sensor (the measured value of the accumulated light quantity by the
photoelectric detector 19 in FIG. 1).
[0188] The process at step 310 is to determine a proportional
relationship between the accumulated light quantity and the
exposure amount, the accumulated light quantity being obtained by
the photoelectric detector 19 for the pulse illumination light
having the pulse number N and oscillating during a period of time
during which the wafer stage 42 has been transferred by the width
portion Dap in the scanning direction of the effective projection
region EIA upon the scanning exposure, and the exposure amount
being defined by the reference illuminance meter. At this end, a
software-type running window is set in the processor 126 in FIG.
11, which can always monitor the accumulated light quantity of the
pulse illumination light having pulses N, in synchronization with
the oscillation of the pulse illumination light from the excimer
laser light source 1.
[0189] The running window can be operated in a manner as shown in
FIG. 13 which shows an example of oscillation characteristics of
pulse illumination light by representing the time t on the X-axis
and the illuminance (or light quantity) value i of the pulse
illumination light on the Y-axis. As shown in FIG. 13, the
intensity of the pulse illumination light from the excimer laser
light source 1 may cause a deviation for each pulse, even if it is
oscillated at a constant frequency.
[0190] Therefore, the number of pulses N (the pulse number N being
set herein to be N=12 for brevity of illustration in the drawing)
determined as the width of the running window under the exposing
conditions, and each of the accumulated light quantities P1, P2,
P3, . . . , Pj, are calculated and saved in order in the running
window, wherein the accumulated light quantity P1 is the
accumulated light quantity from pulse 1 to pulse N of the pulse
illumination light, the accumulated light quantity P2 is the
accumulated light quantity from pulse 2 to pulse (N+1), the
accumulated light quantity P3 is the accumulated light quantity
from pulse 3 to pulse (N+2), and the subsequent accumulated light
quantities being obtained in the like way as described immediately
above.
[0191] At this time, the processor 126 as shown in FIG. 11 reads
data of the illuminance value (the light quantity value) i for each
of the pulse illumination light one after another through the
photoelectric detector 19, the S/H circuit 120E, the multiplexer
122B, and the ADC 124B, and adds the data of the illuminance value
(the light quantity value) i corresponding to the number N within
the running window, followed by storing the data therein. Each
value of the accumulated light quantities P1, P2, P3, . . . , Pj
should be present within the acceptance scope (for example,
.+-.0.4%) for the target exposure amount, when a variation in
oscillation of the excimer laser light source 1 is included within
a standard and the exposing conditions are set in a favorable
manner, that is, when the decision at step 308 is made YES.
[0192] It should be noted herein, however, that it is difficult to
compare each value of the accumulated light quantities P1, P2, P3,
. . . , Pj measured by the photoelectric detector 19 directly with
the value of the target exposure amount defined by the reference
illuminance meter, because measuring sensors to be used each
therefor is different completely from each other. Therefore, at
step 310, when the target exposure amount is obtained on the wafer
side, the accumulated light quantities P1, P2, P3, . . . , Pj are
determined in a manner as shown in FIG. 13, and an average value
Pav (=.SIGMA.[Pn]) of the accumulated light quantities P1, P2, P3,
. . . , Pj is computed as an output value of the integrator sensor,
and a proportional constant k for the arget exposure amount at that
time and the output value Pav of the integrator sensor is computed
and then saved.
[0193] The constant k is one factor that is the basis for
controlling the exposure amount hereinafter. Once the constant k
can be determined accurately, then the accurate control over the
exposure amount can be feasible on the basis of a value
(corresponding to each of the accumulated light quantities P1, P2,
P3, . . . , Pj in FIG. 13) obtained by accumulating signals from
the photoelectric detector 19 in a running window type, and the
constant k. The running window type referred to herein is to
transfer a window in a software mode, in synchronization with the
pulse emission of the excimer laser light source 1, however, it
allows the operator to specify the start timing (to designate which
start pulse is set to be pulse 1) optionally by the processor 126
in FIG. 11 on the basis of an instruction from the operator or an
instruction on a program.
[0194] As the calibration program of FIG. 12 has been finished in
the manner as described above, the absolute exposure amount
provided on the wafer and the accumulated light quantity value
measured by the photoelectric detector 19 are associated with the
constant k. Therefore, when the operator sets a new target exposure
amount Ed on the wafer, the exposing conditions, for example, for
setting an accumulated light quantity value Pn measured in a
running window type so as to satisfy k.times.Ed (or Ed/k), can be
set automatically or manually through the exposing condition
designating program in the processor 126.
[0195] Then, an example of the transmittance rate measuring program
to be executed by the processor 126 in FIG. 11 will be described
with reference to a flow chart of FIG. 14. The measurement
operation of FIG. 14 is executed in response to an instruction from
the main control system that controls the device in a comprehensive
way at an appropriate time during operation of the exposure
apparatus, i.e., at every appropriate time interval, for example,
after operation for exchanges reticles R, at the time of starting
the exposure processing for wafers of one lot, at the time of
starting the exposure processing for one sheet of a wafer, at the
time of appropriate shot exposure during exposure of one sheet of a
wafer, during operation for exchanges wafers or reticles, and
during a standby status of the device.
[0196] Further, the program of FIG. 14 is executed automatically
immediately after the execution of the calibration program of FIG.
13 as described above, and a flag may be set in advance for
selecting a way of measurement from the measurement of a variation
in transmittance between the object plane side PF1 and the pupil
plane EP of the projection optical system PL (the measurement of
transmittance on the reticle side) by means of the transmittance
measurement means of FIGS. 5 and 6 and the measurement of a
variation in transmittance between the image plane PF2 and the
pupil plane EP (the measurement of transmittance on the wafer side)
thereof by means of the transmittance measurement means of FIGS. 8
and 9.
[0197] Once the program of FIG. 14 has been executed, it is decided
at step 320 to determine whether this execution has been started
immediately after the calibration operation of FIG. 13. If it is
decided that the program of FIG. 14 has been executed immediately
after the execution of the calibration operation, a flag is set so
as to execute the measurement of transmittance both for the reticle
side and the wafer side, and a transmittance measurement routine
between the object plane and the image plane using the measurement
means of FIGS. 5 and 6 is executed in a manner as shown at step
322. A detailed description of this routine will be made
hereinafter.
[0198] As the routine at step 322 has been finished, then it is
decided to determine whether the transmittance has been measured
for the reticle side only as shown at step 324. When it is decided
at step 320 as having been executed immediately after calibration,
then the flag is set so as to make measurements for both the
reticle side and the wafer side, so that the process advances to
step 326 at which a transmittance measurement routine between the
image plane and the pupil plane is executed using the measurement
means of FIGS. 8 and 9. A detailed description will be made of the
operation of the routine in more detail.
[0199] Finally, at step 328, database of a history of variations in
transmittance is renewed or updated on the basis of data relating
to the transmittance obtained by the measurement of transmittance
on the reticle side at step 322 and data relating to the
transmittance obtained by the measurement of transmittance on the
wafer side at step 326. The database saves a history of variations
in transmittance of the projection optical system PL during a
period of time ranging from a certain point of time in the past to
the current point of time as well as a history of correction
coefficients for controlling the exposure amount in accordance with
such variations in transmittance. Such correction coefficients can
be calculated on the basis of the variations in transmittance and
are each an operator that acts directly on a part of the exposing
conditions.
[0200] On the other hand, when it is decided at the previous step
320 that the timing of executing the program of FIG. 14 is not
immediately after calibration, then the process advances to step
330 at which the contents of setting the flag are checked. When the
flag is set so as to perform the measurement of transmittance for
both the reticle side and the wafer side, the processes at steps
322, 324, 326 and 328 are executed. On the other hand, when it is
decided at step 320 that no measurement of transmittance for both
sides is set, then it is decided to determine if the flag is set
for the measurement of transmittance for the wafer side only as
shown at step 332.
[0201] Then, at step 332, it is decided that the measurement for
transmittance is only for the wafer side, then the processes at
steps 326 and 328 are to be executed. On the other hand, when it is
decided at step 332 that the measurement is not made for the wafer
side only (in other words, the measurement for transmittance for
the reticle side only), then the processes at the steps 322, 324,
and 328 are to be executed. The processes as described above then
conclude the operation of the transmittance measurement
program.
[0202] Next, a description will be made of the transmittance
measurement routine at step 322 in FIG. 14. In this measurement
routine, the reticle R stage 30 is first set at an appropriate
position as indicated in FIG. 7, and the shutter 101A is shut off
while the other shutter 101B is opened, as shown in FIG. 10. Then,
the light extinction rate of the variable light extinction system
10 in FIGS. 1 and 10 is set to be a value suitable for the
measurement for transmittance.
[0203] Then, the excimer laser light source 1 is triggered on the
basis of an instruction from the processor 126 in FIG. 11, and
pulses are oscillated by an appropriate number of pulses. The
processor 126 reads a wave-shaped level (illuminance) of the signal
SS1 from the photoelectric detector 86A in FIG. 11 through the S/H
circuit 120A, the multiplexer 122A and the ADC 124A, in synchronism
with the triggering, and at the same time a wave-shaped level
(illuminance) of the signal SS2 from the photoelectric detector 86B
through the S/H circuit 120C, the multiplexer 122B and the ADC
124B.
[0204] At this time, when the wave-shaped level of the signal SS1
read from the ADC 124A is referred to as I1j (j being a number of
pulse light) and the wave-shaped level of the signal SS2 read from
the ADC 124B is referred to as I2j, the processor 126 obtains a
value Irn corresponding to the transmittance sequentially in
accordance with the formula: Irn=I2j/I1j, whenever each pulse light
is emitted. As the pulse emission has been finished, the processor
126 calculates an averaged value Ir (=[.SIGMA.(Irn)]/n) obtained by
averaging the value Irn corresponding to the transmittance obtained
for each of the pulse light number n as a transmittance or
transmissivity between the object plane side PF1 and the pupil
plane EP of the projection optical system PL. The value Ir for the
transmittance is saved in database at step 328 in FIG. 14.
[0205] Likewise, in the transmittance measurement routine at step
326 in FIG. 14, the wafer stage 42 is first set at an appropriate
position as shown in FIGS. 8 and 9, and the shutter 101A is shut
off while the shutter 101B is opened, as shown in FIG. 10. Then,
the light extinction rate of the variable light extinction system
10 in FIGS. 1 and 10 is set to be a value appropriate for the
measurement of transmittance.
[0206] Then, the excimer laser light source 1 is triggered on the
basis of an instruction from the processor 126 in FIG. 11, and
pulses are oscillated by am appropriate number of pulses. The
processor 126 reads a wave-shaped level (illuminance) of the signal
SS3 from the photoelectric detector 96A in FIG. 11 through the S/H
circuit 120B, the multiplexer 122A and the ADC 124A, in synchronism
with the triggering, and at the same time a wave-shaped level
(illuminance) of the signal SS4 from the photoelectric detector 96B
through the S/H circuit 120D, the multiplexer 122B and the ADC
124B.
[0207] At this time, when the wave-shaped level of the signal SS3
read from the ADC 124A is referred to as I3j (j being a number of
pulse light) and the wave-shaped level of the signal SS4 read from
the ADC 124B is referred to as I4j, the processor 126 obtains a
value Iwn corresponding to the transmittance sequentially in
accordance with the formula: Iwn=I4j/I3j, whenever each pulse light
is emitted. As the pulse emission has been finished, the processor
126 calculates an averaged value Iw (=[.SIGMA.(Iwn)]/n) obtained by
averaging the value Iwn corresponding to the transmittance obtained
for each of the pulse light number n as a transmittance rate or
transmissivity between the image plane PF2 and the pupil plane EP
of the projection optical system PL. The value Iw for the
transmittance rate is saved in database at step 328 in FIG. 14.
[0208] It is to be noted herein, however, that although the
averaged pulse number n is set with the purpose to improve
deterioration in an error of measurement due to a fluctuation in
detection mainly upon photoelectric detection, the values Ir and Iw
of transmittance may be obtained by emission of one pulse, if such
a fluctuation in detection can be disregarded.
[0209] Further, the processor 126 determines a correction
coefficient at the time of controlling the exposure amount by
operation on the basis of the values Ir and Iw of transmittance
obtained in the manner as described above, upon renewal of database
in FIG. 14. In this case, when it was decided at step 320 in FIG.
14 that the calibration program has been executed immediately
beforehand, the values Ir and Iw of transmittance obtained are
saved as initial values IrO and IwO of transmittance, respectively,
in the database.
[0210] Therefore, the correction coefficient at the time of
controlling the exposure amount is computed, up to the next
execution of the calibration program, using as a reference a
proportional constant k for the target exposure amount saved at the
time of execution of the calibration program at this time and the
output value Pav (the average accumulated light quality obtained at
step 310 in FIG. 12) of the integrator sensor, and the initial
values, IrO and IwO, of transmittance obtained by the transmittance
measurement program to be executed concurrently therewith.
[0211] More specifically, when the values Ir and Iw of
transmittance are to be obtained by executing the transmittance
measurement program at step 322 or step 326 in FIG. 14 after some
time has elapsed from the execution of the calibration program, the
processor 126 gives a correction coefficient Ve at the time of
controlling the exposure amount by the following formula:
Ve=(Ir/IrO).times.(Iw/IwO).
[0212] The correction coefficient Ve is Ve=1, as a matter of
course, when there is no variation in transmittance. When
transmittance varies to some extent in accordance with an elapse of
time after the time of execution of the calibration program, the
correction coefficient Ve gives an integer other than 1. Although
the correction coefficient Ve is less than 1 in many cases, it can
give the numeral larger than 1 due to the state of use of the
exposure apparatus, the timing of execution of the calibration
program, and so on. Further, the correction coefficient Ve means
that an actual exposure amount provided on the wafer causes an
error by (Ve-1) with respect to the target value, even if the
exposure amount is controlled so as to make the output value of the
integrator sensor equal to the value Paw corresponding to the
target exposure amount.
[0213] Therefore, in this case, the exposure amount can be
controlled so as to make the output value of the integrator sensor
equal to a value (Pav/Ve) in order to bring the actual exposure
amount into agreement with the target value. It is to be noted,
however, that as the actual value of the target exposure amount can
be altered optionally by the input from the operator, the exposure
amount may be controlled so as to make the output value (an average
value of the accumulated light quantity) of the integrator sensor
equal to a value (Eg/k.times.Ve), upon exposure to the wafer, when
the target exposure amount provided on the wafer is set to be Eg,
because the relationship of Eg=k.times.Pav is established by the
proportional constant k obtainable by the calibration program.
[0214] Therefore, when both the calibration program in FIG. 12 and
the transmittance measurement program in FIG. 14 are both executed
at steps 322 and 326, respectively, upon updating the database as
shown at step 328 in FIG. 14, the proportional constant k and the
correction coefficient Ve are both updated to latest values. When
only the transmittance measurement program in FIG. 14 is executed,
the correction coefficient Ve is updated to a latest value. It is
to be noted herein, however, that the values Ir and Iw (IrO and
IwO) of transmittance measured are saved in database for a period
of time of one day, one week or one month, together with
information on the measuring time and measuring timing, and they
are utilized for analysis and prediction of the feature or tendency
of the variations in transmittance.
[0215] Now, a description will be made of an example of variations
in transmittance of the projection optical system PL with reference
to FIG. 15. FIG. 15(A) is a graph in which time t is given on the
X-axis and the values Ir and Iw of transmittance measured are given
on the Y-axis. FIG. 15(B) is a graph in which time t is given on
the X-axis and the value of the correction coefficient Ve is given
on the Y-axis.
[0216] In FIG. 15(A), a period of time from time T1 to time T2 is a
period of time is a period of time during which lots are exchanged
or reticles are exchanged after the previous processing by exposure
has been finished and during which the exposing illumination light
does not pass through the projection optical system PL. As
molecules of impurities floating in the barrel of the projection
optical system PL may be attached or deposited gradually to or on
the surface of an optical element during this period of time, there
is the tendency that the transmittance values Ir and Iw become
gradually smaller when the transmittance is measured at an
appropriate time interval between times T1 and T2.
[0217] The period of time between times T2 to T3 in FIG. 15(A) is a
period of time during which plural sheets (a representative lot
comprising 25 sheets) of wafers in a new lot are processed
continually by exposure processes, and the exposing illumination
light continues passing through the projection optical system PL,
excluding a period of time required for exchanging wafers (for
example, from 15 to 30 seconds) by work in exchanging one sheet of
a wafer, aligning a wafer, etc. At this end, the molecules of
impurities deposited on the surface of each optical element within
the projection optical system PL are released gradually in a space
by a cleaning action of ultraviolet rays by irradiation of the
exposing illumination light, and there is the tendency that the
values Ir and Iw for the transmittance rate of the projection
optical system PL become gradually larger.
[0218] When the calibration program of FIG. 12 is executed at the
time of starting the lot exposure processing at time T2 and at the
same time the transmittance measurement program of FIG. 14 is
executed, the correction coefficient Ve determined at time T2 is
renewed to 1, as shown in FIG. 15(B). Thereafter, as the
transmittance measurement program is executed each at an
appropriate time interval during the lot exposure processing to
give the transmittance values Ir and Iw and the correction
coefficient Ve is computed, the correction coefficient Ve tends to
become gradually larger because there is the tendency that the
transmittance rate of the projection optical system PL becomes
gradually larger during the period of time from time T2 to time
T3.
[0219] Then, when the lot exposure processing has been completed at
time T3, the transmittance rate of the projection optical system PL
becomes smaller gradually in the case of the period of time between
time T1 to time T2. When the transmittance measurement program is
executed at every appropriate time interval until time T4 when the
next lot exposure processing starts and the transmittance rate
values Ir and Iw are given, the correction coefficient Ve is
computed as a value that has the tendency to become smaller
gradually.
[0220] Immediately before the start of executing the next lot
exposure processing at time T4, the calibration program of FIG. 12
and the transmittance measurement program of FIG. 14 are executed
again, so that the correction coefficient Ve is reset again to 1 at
time T4. It should be noted herein, however, that when the
calibration program of FIG. 12 and the transmittance measurement
program of FIG. 14 are executed at time T3 in FIG. 15, the
correction coefficient Ve is shifted in a parallel mode to a
correction coefficient Ve' in FIG. 15(B).
[0221] As shown in FIG. 15, the correction coefficient Ve (or Ve')
represents a variation characteristic of a transmittance rate of
the projection optical system PL at the point of time, as a
reference, when the calibration program has been executed. When the
progress of the correction coefficient Ve (or Ve') is associated
with various timings of the exposure processing operations and the
resulting data is saved as a history on database, the data can
present the advantage in that it can be confirmed immediately
whether defects are caused from a poor control of the exposure
amount or not, in the case where such defects are found during an
inspection step of inspecting a line width or an image quality of a
pattern on the wafer which has been subjected to exposing
processes.
[0222] In FIG. 15(A), the values Ir and Iw for transmittance are
set so as to vary in a generally equal characteristic mannfer. It
can be noted herein, however, that they are not limited to the mode
that they always vary in such an equal characteristic manner and
that there may be the case where either one can vary to an
extremely slow extent, due to the construction or disposition of
optical lens elements in the projection optical system PL or kinds
of a glass material therefor. In this case, it is also possible to
disregard the transmittance value that varies to a very slow extent
from the viewpoint of a precision required for controlling the
exposure amount. In other words, in this case, it is possible to
measure either one of a variation in transmittance from the object
plane to the pupil plane of the projection optical system PL and a
variation in transmittance from the pupil plane to the image plane
by either one of the transmittance measuring means of FIGS. 5 and 6
as well as the transmittance measuring means of FIGS. 8 and 9.
[0223] Then, a description will be made of another embodiments
applicable to the present invention with reference to FIGS. 16 and
17. First, FIG. 16 shows a construction of a projection optical
system PL corresponding to the projection optical system PL as
shown in FIG. 2. This construction has the feature in a structure
of a reflecting member (a transparent plate CP) disposed on the
pupil plane EP, in particular in a passage for use in measuring
transmittance within a projection light path extending from the
object plane side PF1 to the pupil plane EP. In other words, as
shown in FIG. 16, measuring beams B2 incident from the object plane
side PF1 side are reflected in a transverse direction by a small
reflecting member Re' disposed obliquely on the transparent plate
CP at the center of the pupil plane EP of the projection optical
system PL and then received by a photoelectric detector 86'
disposed in the barrel of the projection optical system PL or on an
outer wall of the barrel thereof.
[0224] The photoelectric detector 86' can be used in place of the
photoelectric detector 86B as shown in FIGS. 5 and 6, and can
measure a transmittance value Ir on the basis of its photoelectric
signal in the same manner as above. In the construction as shown in
FIG. 16, the reflected beams reflected from the reflecting member
Re' are not returned to the object plane side PF1 side, so that the
transmittance measuring means as shown in FIGS. 5 and 6 can be
provided simply with a system for irradiating the measuring beams
B2. Therefore, this construction is advantageous in terms of its
compact structure.
[0225] Although FIG. 16 shows the construction in which the
reflecting oblique member Re' is disposed only on the upper side of
the transparent plate CP, however, it should be noted herein that
the reflecting member Re' may also be disposed on the lower side of
the transparent plate CP. In this case, the measuring beams B1
incident from the projection imaging plane PF2 side of the
projection optical system PL can be reflected in a transverse
direction in the vicinity of the pupil plane EP thereof and then
detected in a photoelectric way, so that this construction presents
the advantage in that the structure of the transmittance measuring
means as shown in FIGS. 8 and 9 can be made compact in size.
[0226] Now, turning to FIG. 17, this embodiment is shown therein to
have the construction of the projection optical system PL
corresponding to the projection optical system PL as shown in FIG.
2 above. The projection optical system PL according to this
embodiment is characterized by the structure of a reflecting member
Re (a transparent plate CP) disposed on the pupil plane EP thereof.
In particular, the projection optical system PL is characterized by
a path for use in measuring transmittance within a projection light
path extending from the object plane side PF1 to the pupil plane EP
thereof. In other words, as shown in FIG. 17, main light rays are
incident to the projection optical system PL in a-direction oblique
to the light axis AX, although the measuring beams B2 incident from
the object plane side PF1 side are a parallel light flux. With this
construction, the measuring beams B2 reaching the pupil plane EP of
the projection optical system PL are allowed to converge at a
position in the vicinity of the pupil plane EP thereof.
[0227] Therefore, in this embodiment, the plates CPa and CPb on
which the reflecting member Re is formed are disposed detachably at
a peripheral portion of the pupil plane EP, each of the plates CPa
and CPb is disposed so as to be movable by means of respective
drive mechanisms DKa and DKb in order to allow the reflecting
member Re to be inserted in the position through which the
measuring beams B2 pass at the peripheral portion of the pupil
plane EP upon measuring the transmittance. With this configuration,
the reflected beams B2' from the pupil plane EP have the main light
rays advance in an oblique direction with respect to the light axis
AX upon passage through the object plane side PF1, however, they
can maintain a collimated state.
[0228] This embodiment can provide the advantages in that the
transparent plate CP as large in size as covering the entire area
of the pupil plane EP of the projection optical system PL is not
required any more and that a quality of a pattern projection image
can be sustained in the highest state and a loss of the exposure
amount provided on the wafer can be reduced because no barrier
exists for the pupil plane EP even during a period of time during
which a pattern of a reticle is exposed by projection.
[0229] It should be noted herein, however, that for the
construction as shown in FIG. 17, as a matter of course, the
movable reflecting member Re can also be formed on the lower side
of each of the plates CPa and CPb and that a reflecting surface can
be disposed for the measuring beams B1 from the image plane PF2. In
this case, the measuring beams B1 are incident to the projection
optical system PL in a direction oblique to the light axis AX while
they are maintained in a state in which they stay collimated.
[0230] It also should be noted herein that, when this construction
assumes the provision of the drive mechanisms Dka and DKb, the
similar effects can also be achieved by a construction in which the
movable reflecting member Re is formed on the transparent plate CP
so as to cover the entire area of the pupil plane EP of the
projection optical system PL and the transparent plate CP in its
entirety is inserted into or retracted from the projection optical
system PL. In this case, when the transmittance measurement program
is to be executed, the transparent plate CP can be moved by sliding
in the vicinity of the pupil plane EP and, when the measurement for
the transmittance has been finished, the transparent plate CP can
be moved by sliding outside the projection light path.
[0231] With the configuration as described above, the movable
reflecting member Re can also function as a shutter for blocking
the entirety of the pupil plane EP of the projection optical system
PL, so that this construction can provide the advantage in that an
unnecessary exposure by a slight amount of stray light can be
prevented to a full extent upon irradiating the measuring beams B2
from the object plane side PF1 side of the projection optical
system PL, even if the wafer W would be located right under the
projection optical system PL.
[0232] It should also be noted herein that a variation in
transmittance may occur likewise in the illumination optical system
as well as in the projection optical system PL. For example, for
the exposure apparatus as shown in FIG. 1, the photoelectric
detector 19 of FIG. 1 is used for controlling the exposure amount,
so that an error portion in the exposure amount cannot be measured
the photoelectric detector 19 on a real time basis, the error
occurs due to an influence of a variation in transmittance within
an illumination light path extending from the beam splitter 17 to
the main condenser lens system 26, the beam splitter 17 being
dividing a part of the exposing illumination light for the
photoelectric detector 19.
[0233] When each of the programs as shown in FIGS. 12 and 14 is
executed by means of the transmittance measuring means as described
in FIGS. 5 and 6 as well as FIGS. 8 and 9, such an error in the
control of the exposure amount can be corrected which might be
caused by a variation in transmittance of the illumination optical
system, however, a variation in transmittance in the illumination
optical system itself cannot be measured. Therefore, a description
will be made of a type for correcting the control of the exposure
amount with reference to FIG. 18, while measuring a variation in
transmittance for both the illumination optical system and the
projection optical system PL.
[0234] FIG. 18 shows a configuration of the correction type, in
which the measuring beams B2 from the transmittance measuring means
as shown in FIGS. 5 and 6 are supplied through an exposing
illumination optical system (composed of a system ranging from the
beam splitter 17 to the main condenser lens system 26 in this
embodiment). Further, as shown in FIG. 18, the elements
constituting the exposing illumination optical system, including
the second fly-eye lens 13B, the beam splitter 17, the condensing
lens system 22, the reticle blind mechanism 23, the imaging
condensing lens system 24, the mirror 25, and the condenser lens
system 26, are disposed in substantially the same manner as shown
in FIG. 1.
[0235] In this embodiment, however, the transmittance monitor
system (including the lens system 20 and the photoelectric detector
21) as shown on the left side of the beam splitter 17 in FIG. 1 is
omitted, and instead there may be installed therein an irradiation
system for producing the measuring beams B2 for measuring
transmittance and a light recipient system for photoelectrically
detecting the reflected beams B2' from the pupil plane EP of the
projection optical system PL.
[0236] More specifically, the measuring beams B2 collimated by a
beam shaping optical system as shown in FIG. 10 are incident to a
beam splitter 140 in FIG. 18, and the beam intensity of a part of
the beams reflected at the beam splitter 140 is detected
photoelectrically by means of the photoelectric detector 86D to
give the signal SS1 as a reference. On the other hand, the
measuring beams B2 passing through the beam splitter 140 are
converted by a lens system 142 into a converging light flux which
in turn is reflected one reflecting plane of a prism mirror 144 and
reaches the center of a pupil plane EP3.
[0237] The pupil plane EP3 is located at the position corresponding
to a secondary light source plane formed on the leaving plane side
of the second fly-eye lens 13B, and is a plane that is conjugated
with the pupil plane EP of the projection optical system PL.
Therefore, when the measuring beams B2 are set so as to pass
through the center of the pupil plane EP3 in a state inclining at
an angle with respect to the light axis AX and to converge at the
center of the pupil plane EP3, the measuring beams B2 can be
converged just at the pupil plane EP of the projection optical
system PL toward the reflecting member Re, as shown in FIG. 2.
[0238] The measuring beams B2 passed through the pupil plane EP3
are converted into a nearly parallel light flux by the condensing
lens system 22 and then converted into a parallel light flux,
again, through an opening portion of the reticle blind mechanism 23
by means of the imaging lens system 24, the mirror 25, and the
condenser lens system 26, the resulting parallel light flux being
incident to the projection optical system PL. On the other hand,
the reflected beams B2' from the reflecting member Re disposed in
the vicinity of the pupil plane EP of the projection optical system
PL pass along a light path symmetrical to the measuring beams B2
with respect to the light axis AX common with the projection
optical system PL and the illumination optical system, through the
main condenser lens system 26, the imaging lens system 24, the
reticle blind mechanism 23 and the condensing lens 22 in this
order, thereby being converged at the central portion of the pupil
plane EP and then allowed to disperse.
[0239] Moreover, the reflected beams B2' from the condensing lens
system 22 are reflected with the other reflecting plane of the
prism mirror 144 and then received by the photoelectric detector
86C. A level of a signal SS5 from the photoelectric detector 86C
undergoes influences from the transmittance of both the
illumination optical system and the projection optical system PL,
and a variation in transmittance by both the illumination optical
system and the projection optical system PL can be given by
calculating a periodical variation in a ratio (SS5/SS1) of the
level of the signal SS5 to the signal SS1 from the photoelectric
detector 86A.
[0240] The embodiments as described above enable an accurate
measurement for a transmittance value (corresponding to the value
Ir), in which the illumination optical system subsequent to the
beam splitter 17 branching a part of the illumination light to an
integrator sensor (the photoelectric detector 19) to be used for
controls over the exposure amount is combined with the projection
light path extending up to the pupil plane EP of the projection
optical system PL, and for a transmittance variation characteristic
(corresponding to the correction coefficient Ve). Therefore, this
construction can provide the advantage that an accurate management
for a control precision at the time of the control over exposure
can be fulfilled by adding an influence from a variation in
transmittance of the illumination optical system. Further, this
construction does not require the provision of the mirror 25 with a
partially permeable portion in the illumination optical system,
unlike in the case as shown in FIGS. 5 and 6, so that this
construction can present the advantage that no loss is caused
thereby for the exposing illumination light.
[0241] Moreover, in the case where there can be adopted a movable
reflecting member Re (a movable transparent plate CP) having an
area that can cover the entirety of the pupil plane EP of the
projection optical system PL, as described in connection with FIG.
17, the measurement of transmittance can be made in substantially
the same manner as above by using the exposing illumination light,
even if the measuring beams B2 collimated could not particularly be
formed as shown in FIG. 18. More specifically, when the
transmittance measurement program is to be executed, the movable
reflecting member Re is inserted in the vicinity of the pupil plane
EP of the projection optical system PL in a state in which no
reticle is loaded, the exposing pulse illumination light is
irradiated in the such state toward the projection optical system
PL through the second fly-eye lens 13B as shown in FIG. 1.
[0242] It is possible to easily measure a transmittance value or a
variation in transmittance or the correction coefficient Ve, with
both of the illumination optical system and the projection optical
system PL added thereto, by determining a ratio (i qb/i qa) i qb of
an illuminance value (light quantity) per pulse light to be
detected with the photoelectric detector 21 for the reflectance to
an illuminance value (light quantity) i qa per pulse light to be
detected with the photoelectric detector 19 for monitoring the
integrator sensor as shown in FIG. 1.
[0243] With this configuration, a system extending from the excimer
laser light source 1 to the second fly-eye lens system 13B as shown
in FIG. 1 can also be used as the irradiation system of the
measuring beams at the time for measuring the transmittance, and a
reflectance monitor system extending from the beam splitter 17 to
the photoelectric detector 21 as shown in FIG. 1 can also be used
as a light recipient system at the time for measuring the
transmittance, so that this construction does not require the
transmittance measuring means as shown in FIGS. 5 and 6 and in FIG.
18 as well as the beam shaping optical system as shown in FIG. 18
to be used any more. Therefore, this device construction can
achieve remarkable effects that the structure of the device can be
made compact in size as a hole and costs for production can be
reduced to a great extent.
[0244] It should be noted herein, however, that when the exposing
illumination light from the second fly-eye lens system (an optical
integrator) 13B is also used as measuring beams at the time for
measuring the transmittance in the manner as described above, the
exposing illumination light becomes a light flux accompanying a
certain number of openings (NA) at the object plane side PF1 of the
projection optical system PL because they are supplied so as to
become an image of a light source having an area at the pupil plane
EP of the projection optical system PL. Therefore, when the
exposing illumination light from the second fly-eye lens system 13B
are utilized as measuring beams, the measuring beams are not
present in a collimated state at the object plane side PF1.
[0245] Although each of the embodiments according to the present
invention has been described above, it should be noted herein that
the present invention can be applied in the same manner as
described above not only to an exposure apparatus having a
projection optical system composed only of refractive optical
elements (transparent elements such as lenses, etc.) made of quartz
or fluorite as a optical glass material, but also to an exposure
apparatus with a projection optical system of a catadioptric type
equipped in which the such refractive optical elements are combined
with reflective optical elements (particularly a concave mirror).
In some cases, the present invention can be likewise applied to an
exposure apparatus with a full reflective projection system
composed only of plural sheets of reflective optical elements.
[0246] When the exposure apparatus is equipped with an optical
element system of the such catadioptric type or full reflective
projection type, a reflectance or reflectivity at each of the
reflective optical elements may vary with an amount of particles of
impurities attached or deposited on the surface of each of the
reflective optical elements, and an attenuation factor (a
transmittance or a reflectance) of the entirety of the projection
optical system may be caused to vary thereby. Therefore, in the
case of the projection optical systems including the reflective
optical elements, a value corresponding to the attenuation factor
(transmittance or reflectance) or a variation in the attenuation
factor (a variation in the transmittance or in the reflectance) can
also be obtained in the thoroughly same manner as described
above.
[0247] Then, a description will be made briefly of some examples of
projection optical elements of a catadioptric. type, with reference
to FIG. 19.
[0248] FIG. 19(A) shows a condensed projection optical system in
which refractive optical elements (lens system) GS1 to GS4,
inclusive, and a concave mirror MRs are combined with a beam
splitter PBS. The feature of this system resides in that an imaging
light flux from the reticle R is reflected at the concave mirror
MRs through a large-sized beam splitter PBS and returned again to
the beam splitter PBS, thereby focusing an image on the projection
imaging plane PF2 (on the wafer W) at a given reduction rate by
means of the refractive lens system GS4. A detailed description is
disclosed in Japanese Patent Application Laid-Open No. 3-282,527
(U.S. Pat. No. 5,220,454).
[0249] Moreover, the transparent plate CP with the reflecting
member Re for reflecting the measuring beams (exposing illumination
light) formed thereon at the time of measuring transmittance is
fixedly or detachably disposed in the vicinity of the pupil plane
between the beam splitter PBS and the refractive lens system GS4.
In the case of the projection optical system as shown in FIG.
19(A), the pupil plane may be created inside the beam splitter PBS.
In this instance, the reflecting member Re may also be formed
directly on the leaving plane on the side of the lens system GS4 of
the beam splitter PBS.
[0250] FIG. 19(B) shows a condensed projection optical system in
which refractive optical elements (lens systems) GS1 to GS4,
inclusive, and a small-sized mirror MRa are combined with the
concave mirror MRs. The feature of this system resides in that an
imaging light flux from the reticle R is arranged so as to form an
image on the projection image plane PF2 (on the wafer W) through a
first imaging system PL1 of a nearly equal magnification, composed
of the lens systems GS1 and GS2 and the concave mirror MRs, a
small-sized mirror MRa disposed in an eccentric way, and a second
imaging system PL2 having a nearly desired reduction rate, composed
of the lens systems GS3 and GS4. A detailed description is
disclosed in Japanese Patent Application Laid-Open No. 8-304,705
(U.S. Pat. No. 5,691,802).
[0251] Moreover, in this embodiment, the transparent plate CP with
the reflecting member Re for reflecting the beams for measuring
transmittance (exposing illumination light) formed thereon is
fixedly or detachably disposed in the vicinity of the pupil plane
to be formed in the second imaging system PL2. In the case of the
projection optical system as shown in FIG. 19(B), an intermediate
imaging plane PF4 is formed between the first and second imaging
systems PL1 and PL2, respectively, so that the system may be
configured such that the measuring beams collimated are irradiated
from the position of the intermediate imaging plane toward the
reflecting member Re on the transparent plate CP and then the
reflected beams can be detected photoelectrically by returning the
reflected beams from the reflecting member to the reticle R.
[0252] FIG. 19(C) is a projection optical system of an equal
magnification, in which the refractive optical element (lens
system) GS1 is combined with the concave mirror MRs. The feature of
this system resides in that an imaging light flux from the reticle
R is arranged so as to form an image on the projection imaging
plane PF2 (on the wafer W) as an erect image of an equal
magnification through a first Dyson imaging system PL1 and a second
Dyson imaging system PL2, each composed of a prism reflecting
mirror MRe, the lens system GS1, and the concave mirror MRs. This
system is disclosed in more detail in Japanese Patent Application
Laid-Open No. 7-57,986 (U.S. Pat. No. 5,729,331).
[0253] In the case of the projection optical system as shown in
FIG. 19(C), the intermediate imaging plane PF4 having a
magnification nearly equal to an illumination region on the reticle
R is formed between the first and second Dyson imaging systems PL1
and PL2, and the pupil plane as the projection optical system is
formed in the vicinity of the position of the concave mirror MRs of
each of the Dyson imaging systems. Therefore, in the case of FIG.
19(C), the concave mirror MRs can also be used as a reflecting
member for the measuring beams at the time of measuring the
transmittance.
[0254] Further, for the projection optical system as shown in FIG.
19(C), a plane mirror (preferably a double-sided mirror) is
inserted at a position of the intermediate imaging plane PF4 in a
direction parallel to the plane PF4 at the time of measuring
transmittance, and the measuring beams (or the exposing
illumination light) incident from the reticle R side are reflected
to a full extent at the intermediate imaging plane PF4 by means of
the plane mirror and returned to the reticle side. Then, the
measuring beams are detected in a photoelectric manner. Likewise,
the measuring beams (the measuring beams B1 leaving vertically from
the wafer stage 42 as shown in FIG. 8) incident from the imaging
plane PF2 (wafer) side can also be detected in a photoelectric
manner by reflecting them to a full extent at the intermediate
imaging plane PF4 by means of the plane mirror and returning them
to the imaging plane PF2 side.
[0255] With the configuration as described above, the exposure
apparatus equipped each with the projection optical system as shown
in FIGS. 19(A), (B) and (C) can also execute the calibration
program and the transmittance measurement programs as described
above in an equal manner.
[0256] It is to be noted herein, too, that, among the projection
optical systems as shown in FIG. 19, the projection optical system
of FIG. 19(A) has a circular vision field, and the projection
optical systems of FIGS. 19(B) and (C) have each a generally
semi-circular vision field. Further, each of the projection optical
systems as shown in FIG. 19 is so adapted as to utilize the
effective projection region EIA having a rectangle-shaped slit-like
area in the vision field. However, in some cases, an arc-shaped
slit-like projection region may also be set for each of the
projection optical systems.
[0257] In that case, a shape of distribution of intensity of the
illumination light for illuminating the reticle R may be set to
assume an arc-shaped slit-like form or an arc-shaped transmission
slit may be disposed in the intermediate imaging plane PF4.
However, when the fact that the illuminating light is a pulse light
is taken into account, it is not advisable to make the width of the
arc-shaped slit-form illuminating light or arc-shaped transmission
slit too small as disclosed in prior art literature (SPIE, Vol.
1088, pp. 424-433 (1989)). The width should be rather wide to some
extent.
[0258] For example, when it is supposed that the width Dap of the
arc-shaped slit on the wafer extending in the scanning direction is
set to be 1 mm, the number Nm (an integer) of pulse light to be
oscillated during a movement of the wafer by the width portion of
the slit during scanning is set to be 20 pulses, and the maximum
frequency fp of the pulse oscillation of the illuminating light is
set to be 1,000 Hz (as required by the standard of a laser light
source), the transferring velocity Vws of the wafer at which the
wafer is being moved during the scanning exposure of a one shot
region on the wafer can be calculated by the following formula:
Vws=Dap/(Nm/fp), to give 50 mm/second. From this result, it can be
found that the larger the slit width Dap the higher the throughput
can be improved.
[0259] Therefore, even when the arc-shaped slit-like illumination
light or the arc-shaped transmission slit is used, it is needed to
adopt a width greater than a conventional type, for example, a
width on the wafer being from about 3 mm to 8 mm. At that time,
however, it is preferred that the inner arc inside the arc-shaped
slit be not concentric with the outer arc outside it and that the
width of the arc-shaped slit for scanning exposure is set so as to
assume a similar crescent-shaped form at any position in the
non-scanning direction of the arc-shaped slit.
[0260] In the first embodiment of the present invention, even if a
transmittance of a large number of refractive (or transmitting)
optical elements constituting the illumination system or the
projection optical system or reflectance of reflective optical
elements would vary or fluctuate with time during the exposure
operation, the present invention can control the exposure so as to
always provide an appropriate exposure amount on the photosensitive
substrate (the resist layer) by adding such a variation or
fluctuation thereto.
[0261] Moreover, as an exposing energy reflected at the Fourier
transform plane (pupil plane) of the projection optical system for
projecting a pattern of the mask onto the photosensitive substrate
is arranged so as to be detected in a photoelectric manner, it is
possible to photoelectrically detect a portion (measuring beams) of
the exposing energy that undergoes an influence from a variation in
transmittance for a short period of time during exposure to each
shot upon exposing plural shot regions sequentially on the
photosensitive substrate.
[0262] In particular, the present invention is favorable for a
projection exposure apparatus using an ultraviolet laser light
source having a wavelength of 200 nm or less or an other light
source having a shorter wavelength (e.g., energy rays having a
wavelength of 50 nm or less from SOR or the like), in the case
where a variation in transmittance is caused in the illumination
optical system or the projection optical system due to an influence
from molecules of impurities or for other reasons.
[0263] Further, the present invention has the reflecting member
disposed fixedly or movably at least at a portion of the Fourier
transform plane of the projection optical system, so that a portion
(measuring beams) of the exposing energy passed through the
projection optical system can be photoelectrically detected on a
nearly real time basis during the exposure processing of the
photosensitive substrate. Therefore, the present invention performs
the effect that an occurrence of an error at the time of
controlling the exposure amount to be caused by a variation in
transmittance can be suppressed with high precision.
[0264] Moreover, the present invention can detect the exposing
energy passed through the projection optical system from the
illumination optical system and then reaching the Fourier transform
plane of the projection optical system, so that a variation in
transmittance of a generally entire system including both of the
illumination optical system and the projection optical system can
be detected in an accurate way. Therefore, the present invention
can effect the accurate control of the exposure amount in the
manner as described above.
[0265] Next, a description will be made of the construction of a
projection exposure apparatus suitable for the practice of the
second embodiment of the present invention with reference to FIGS.
20 and 21. FIG. 20 shows the entire construction of the projection
exposure apparatus of a step-and-scan type in which a reticle R and
a semiconductor wafer W are scanned relative to each other, while a
circuit pattern of the reticle R is being projected onto the
semiconductor wafer W through a projection optical system PL, by
using an ArF excimer laser light source 401 narrowed so as to avoid
an absorption band of oxygen between wavelengths of 192 to 194 nm,
in substantially the same manner as in the first embodiment as
shown in FIG. 1.
[0266] In FIG. 20, reference numeral 401 denotes the ArF excimer
laser light source, reference numeral 403 denotes a beam matching
unit (BMU) including a movable mirror and so on, reference numeral
405 denotes a light-shielding pipe, and reference numeral 406
denotes a variable light extinction device as a light attenuator.
The variable light extinction device 406 includes a drive motor and
can adjust an extinction rate of an ultraviolet pulse light in a
stepwise or non-stepwise manner in accordance with an instruction
from an exposure control unit 430.
[0267] The ultraviolet pulse light passed through the variable
light extinction device 406 is incident to a first illumination
optical system 407 including a beam splitter 408, a first fly-eye
lens system 410 or a beam shaping optical system or otherwise, each
disposed along a given light axis AX. The beam splitter 408
reflects the ultraviolet pulse light passed therethrough by several
percentage toward a photoelectric detector 409. In this embodiment,
a photoelectrically detected signal from the photoelectric detector
409 is processed by the exposure control unit 430, thereby
determining exposing conditions at the time of the scanning
exposure.
[0268] In the embodiment as described above, the ultraviolet pulse
light leaving from the first illumination optical system 407
travels to a second fly-eye lens system 411 and then to a space
filter 412 for a variable illumination, followed by passing through
a reflective mirror 413 and a condenser lens system 414 to
distribute the intensity hereof in a uniform way and then reaching
a fixed irradiation vision field stop (a fixed blind) 415 in a
reticle blind mechanism 416.
[0269] Then, the ultraviolet pulse illumination light having its
intensity distributed in a uniform mode with the fixed blind 415 of
the reticle blind mechanism 416 are incident to a main condenser
lens system 419 through an imaging lens system 417 and a reflecting
mirror 418 and irradiate uniformly a portion of a circuit pattern
region on the reticle R in a form resembling a slit-shaped or
rectangle-shaped opening of the fixed blind 415. Each of the
opening planes of the fixed blind 415 or a movable blind in the
reticle blind mechanism 416 is disposed so as to be nearly
conjugated with a pattern plane of the reticle R by a combination
system in which the lens system 417 is combined with the main
condenser lens system 418.
[0270] In FIG. 20, reference numeral 420 denotes a reticle stage,
and reference numeral 422 denotes a drive control unit including a
laser interferometer. The reticle stage 420 and the drive control
unit 422 have each the construction generally equal to those as
shown in FIG. 1.
[0271] On the other hand, as shown in FIG. 20, reference numeral
424 denotes a wafer stage, and reference numeral 425 denotes a
drive control unit including a laser interferometer. The wafer
stage 424 and the drive control unit 425 have each the construction
generally equal to those as shown in FIG. 1.
[0272] Information on a rotational displacement of the wafer stage
424 measured by the laser interferometer of the drive control unit
425 is transmitted at a real time to the drive control unit 424 for
the reticle stage 420 through the main control system 427, and an
error in the rotational displacement on the wafer side is
controlled so as to be compensated for by the control of rotation
on the reticle side.
[0273] The main control system 427 is arranged to control each of
the drive control units 422 and 425 in synchronism with each other
so as to allow a transferring velocity Vr in the X-axial direction
of the reticle stage 420 and a transferring velocity Vw in the
X-axial direction of the wafer stage 424 to maintain a velocity
rate in accordance with a projection magnification (for example, a
1/5-fold or 1/4-fold magnification) of the projection optical
system PL at the time of the scanning exposure.
[0274] Further, the main control system 427 executes an optimal
exposure sequence in association with the exposure control unit 430
for controlling the excimer laser light source 401 and the variable
light extinction device 406 by setting a variety of exposing
conditions for subjecting shot regions on the wafer W to scanning
exposure at an appropriate exposure amount.
[0275] In addition to the constructions as described above, the
present invention in this embodiment can measure an exposing energy
at a nearly real time, with a variation in transmittance of both of
the illumination optical system and the projection optical system
PL, by locating photoelectric detectors 432A and 432B at the
positions close to an image plane (on the wafer W) of the
projection optical system PL, receiving a portion of exposing
ultraviolet pulse illumination light passed through the projection
optical system PL, and sending a photoelectric signal in accordance
with the intensity of the ultraviolet pulse illumination light
selectively through a shift circuit 433 to the exposure control
unit 430.
[0276] At this end, in this embodiment, an optical configuration on
the tip side (on the wafer W side) of the projection optical system
PL is modified to a special one so as to allow a monitoring light
of the ultraviolet pulse light for monitoring a variation in an
attenuation factor (a variation in transmittance or a variation in
reflectance) occurs at both of the illumination optical system and
the projection optical system PL to reach the projection optical
system PL through a small opening disposed in the fixed blind 415
in the reticle blind mechanism 416. The measurement of such a
monitoring light and a variation in transmittance by the
photoelectric detectors 432A and 432B will be described hereinafter
in more detail with reference to FIGS. 21 to 25, inclusive.
[0277] Further, the apparatus in this embodiment uses the ArF
excimer laser light source 401 in substantially the same manner as
the apparatus as shown in FIG. 1, so that a sub-chamber 435 is
disposed so as to shut off a light path extending from the pipe 405
to the variable light extinction device 406, the first illumination
optical system 407 and the second illumination optical system
(including a system ranging from the second fly-eye lens system 411
to the main condenser lens system 419) from the outside air. To the
entire space of the sub-chamber 435 are fed dry nitrogen (N.sub.2)
gases so as to control the oxygen content inside to an extremely
low level through a pipe 436. Likewise, dry nitrogen gases are fed
through a pipe 437 to the entire space (gaps among plural lens
elements) inside the barrel of the projection optical system
PL.
[0278] Although the entire configuration of FIG. 20 is set to be of
a dioptric type in which the projection optical system PL is
composed of refractive optical elements only, it is also possible
to be of a catadioptric type in which refractive optical elements
are combined with a concave mirror (or a convex mirror). In each
type, the object end and the image end of the projection optical
system PL are of a telecentric type,
[0279] Next, a description will be made of details of the
construction of the first embodiment of the device for detecting a
variation in transmittance with reference to FIGS. 21 and 22. FIG.
21 schematically shows a light path extending from the reticle
blind mechanism 416 to the wafer W as shown in FIG. 20, and FIG. 22
schematically shows a positional relationship of the vision field
on the object side of the projection optical system PL with the
reticle R. First, as shown in FIG. 21, ultraviolet pulse
illumination light with its intensity distributed in a uniform mode
by the condenser lens system 414 in FIG. 20 is irradiated on the
fixed blind 415 in the reticle blind mechanism 416.
[0280] The fixed blind 415 is provided with a slit-shaped or
rectangle-shaped opening 415A through which the illumination light
is illuminated onto the circuit pattern region on the reticle R at
the time of the scanning exposure and small openings 415B and 415C
on both sides in the scanning direction (X-axial direction) of the
opening 415A, through which a monitoring light LBm passes for
detecting a variation in transmittance. In the state as shown in
FIG. 21, the monitoring light LBm passed through the small opening
415C only out of the small openings 415B and 415C on the both sides
is incident to the imaging lens system 417 and the main condenser
lens system 419 without being blocked by movable blades 416A and
416B of a movable blind and then reaches the reticle R.
[0281] The movable blades 416A and 416B are controlled by drive
motors 416C and 416D, respectively, so as to move in the
X-direction at a velocity in synchronization with the movement in
the X-direction of the reticle stage 420 at the time of starting
and finishing the scanning movement of the reticle R, as disclosed
in Japanese Patent Application Laid-Open No. 4-196,513 (U.S. Pat.
No. 5,473,410).
[0282] In FIG. 21, when the shielding of light by the movable blade
416A is released, ultraviolet pulse illumination light ILP passed
through the rectangle-shaped opening 415A of the fixed blind 415 is
irradiated on the reticle R by limiting the width Da of the
scanning direction (the X-direction) to a slit-shaped or
rectangle-shaped illumination light through the imaging lens system
417 and the main condenser lens system 419. Main light rays (as
indicated by broken line) LEa and LEb defining the width Da are
light rays from edge portions on the both ends defining a width in
an X-axial direction of the opening 415A.
[0283] The main light rays LEa and LEb are crossed at a pupil plane
(a Fourier transform plane) epo formed between the imaging lens
system 417 and the main condenser lens system 419, and then are
projected from the main condenser lens system 419 parallel to the
light axis AX and then are incident to a lens element (a
light-transmitting element) GL1 on the side closest to the object
plane of the projection optical system PL. Further, the main light
rays LEa and LEb advances to the center (a point through which the
light axis AX passes) in the leaving pupil plane EP of the
projection optical system PL and are crossed at the center thereof,
followed by passing through a lens element GL2 and a
light-transmitting optical element GL3, each located in the
position closest to the image plane of the projection optical
system PL, then advancing again in a direction parallel to the
light axis AX, and reaching the wafer W.
[0284] Further, as shown in FIG. 21, the reticle R is located in
the position in which the approach run starts at the time of the
scanning exposure, and it is deviated from a slit-shaped or
rectangle-shaped exposing illumination region having a width Da.
Therefore, the monitoring light LBm passed through the small
opening 415C of the fixed blind 415 is arranged so as to pass
through a transparent portion on the right-hand side far on the
right-hand side of a light shield band SBR defining a circuit
pattern region on the reticle R in FIG. 1 and then reaching and
entering in the projection optical system PL.
[0285] The monitoring light LBm arrived at the light-transmitting
optical element GL3 disposed at the bottommost portion through the
center of the pupil plane EP of the projection optical system PL is
reflected toward the side at the full reflection portion GMa
disposed at a portion (an outer region in the X-direction of a
slit-shaped or rectangle-shaped image projection region) of the
light-transmitting optical element GL3, which is provided so as to
fail to block a projection light path for the main light rays LEa
and LEb. Light rays LBm' reflected at the full reflection portion
GMa travel in the transverse direction and advance from an edge
portion of the light-transmitting optical element GL3. Then, the
light rays LBm' are received by a photoelectric detector 432A, and
a photoelectric signal Sa is output to the shift circuit 433 in
accordance with the intensity of the light rays LBm'.
[0286] Likewise, when the reticle R is located in the approach run
start position on the right-hand side in FIG. 21, the movable
blades 416A and 416B are disposed so as to allow only the
monitoring light RBm from the small opening portion 415B of the
fixed blind 415 to pass, and the monitoring light RBm is incident
to the projection optical system PL through a transparent portion
on the left-hand side far from the left-hand light shielding band
SBL defining a circuit pattern region on the reticle R. Then, the
monitoring light RBm passed through the projection optical system
PL is reflected toward the side at a full reflection portion GMb
disposed at a portion (an outer region in the X-direction of a
slit-shaped or rectangle-shaped image projection region) of the
light-transmitting optical element GL3 at its top end portion,
which is provided to fail to block a projection light path for the
main light rays LEa and LEb. The light reflected at the full
reflection portion GMb advances in the transverse direction and is
received by a photoelectric detector 432B, and a photoelectric
signal Sb is output to the shift circuit 433 in accordance with the
intensity of the light received by the photoelectric detector
432B.
[0287] In the configuration as shown in FIG. 21, the small opening
portions 415B and 415C of the fixed blind 415 are disposed so as to
be nearly conjugated with the pattern plane of the reticle R, and
each image of the small opening portions 415B and 415C is formed
within the transparent portions on the left-hand and right-hand
ends of the reticle R. Further, the imaging magnification from the
fixed blind 415 to the reticle R comprises an about 2-fold extended
system. A further description will be omitted herein because the
operation of the movable blades 416A and 416B is disclosed in
detail in Japanese Patent Application Laid-Open No. 4-196,513 (U.S.
Pat. No. 5,473,410).
[0288] Then, a description will be made of the state of
illumination of the monitoring light LBm and RBm on the reticle R
through the small opening portions 415B and 415C of the fixed blind
415, respectively, with reference to FIG. 22. FIG. 22(a) is a plan
view showing a positional relationship in the state of FIG. 21 of
the reticle R with the vision field IFo on the object side of the
projection optical system PL. In this figure, the X- and Y-
coordinate axes are set with the central point (the light axis AX)
of the circular vision field IFo as an original point.
[0289] A slit-shaped or rectangle-shaped illumination region 415A'
to be irradiated with a width Da in the scanning direction in the
circular vision field IFo is formed on the reticle R as an image of
the opening portion 415A of the fixed blind 415. Edges Ea and Eb of
the illumination region 415A', each extending in the Y-direction,
correspond to the respective positions of the main light rays LEa
and LEb in FIG. 21, and the light shield bands SBR and SBL
extending in the Y-direction to the left and right of the circuit
pattern region PA of the reticle R are disposed to be parallel to
each other. Further, the edges Ec and Ed defining the length in the
Y-direction of the illumination region 415A' are set so as to agree
with the positions of the light shield bands defining the upper and
lower portions of the circuit pattern region PA of the reticle
R.
[0290] In the state of FIG. 22(A), the opening portion 415A of the
fixed blind 415 is shut off by the action of the movable blades
416A and 416B, so that the ultraviolet pulse illumination light is
not irradiated within the illumination region 415A' even if the
excimer laser light source 401 is oscillated.
[0291] Moreover, it is supposed that a central point Cr of the
circuit pattern region PA of the reticle R is located herein on the
X-coordinate axis and that identical chip patterns are formed in
the X-direction in the circuit pattern region PA on both sides
astride the central point Cr. As is apparent from the state of FIG.
22, the orthogonal length of the circuit pattern region PA is
larger than the diameter of the circular vision field IFo, and an
entire image (corresponding to a two-chips portion) of the circuit
pattern region PA is subjected to scanning exposure in a one-shot
region on the wafer W.
[0292] When the reticle R is located at the approach run start
position on the left-hand side with respect to the illumination
region 415A' as shown in FIG. 22(A), an image by the small opening
portion 415C of the fixed blind 415 is irradiated as three opening
images 415C1, 415C2 and 415C3 at three locations on the transparent
portion outside the light shield band SBR on the right-hand side of
the reticle R. In the case of this embodiment, if it is intended to
detect only a variation in the transmittance of the illumination
optical system or the projection optical system PL, only one
opening image, e.g., opening image 415C2, would be enough. In this
embodiment, however, such three opening images are disposed in a
row in the Y-direction on the left-hand side of the illumination
region 415A' in order to allow a quantitative detection of some
irregularity of variations in transmittance in the vision field
IFo.
[0293] Therefore, the detector 432A as shown in FIGS. 20 and 21 is
provided therein with photoelectric elements for individually
receiving the monitoring light by each of the opening images 415C1,
415C2 and 415C3, and a difference of transmittance in the
Y-direction within the vision field IFo can be determined by
comparing signal levels from the photoelectric elements with each
other.
[0294] While the reticle R is located at the approach run position
on the left-hand side in the manner as described above, the
monitoring light LBm by the light opening images 415C1, 415C2 and
415C3 is received by the detector 432A through the transparent
portion of the reticle R and the projection optical system PL. The
resulting detection signal Sa is then compared with a signal from
the photoelectric detector 409 of FIG. 1, so that a variation in
transmittance of the whole system including the illumination
optical system and the projection optical system PL, ranging from
the beam splitter 408 to the main condenser lens system 419 in FIG.
20 can be detected.
[0295] As the reticle R starts moving to the right-hand side in the
X-direction from the approach run position of FIG. 22(A), the
movable blades 416A and 416B in FIG. 21 also move in the
X-direction in synchronism therewith to block the small opening
portion 415C of the fixed blind 415. Therefore, as the reticle R
starts an approach run to arrive at a scanning exposure state, the
ultraviolet pulse illumination light is irradiated into the
exposing illumination region 415A' only, as shown in FIG. 22(B). In
FIG. 22(B), upper and lower edges Ec and Ed of the illumination
region 415A' are located on the light shield bands SBU and SBD
defining the upper and lower sections of the circuit pattern region
PA of the reticle R, respectively, upon irradiating the circuit
pattern region PA of the reticle R with the pulse illumination
light within the illumination region 415A'.
[0296] When the scanning exposure has been conducted in the manner
as described above and then the reticle R has arrived at the
right-hand side of the illumination region 415A' as shown in FIG.
22(C), the pulse illumination light within the illumination region
415A' is blocked by the action of the movable blades 416A and 416B,
and the pulse illumination light from the small opening portion
415B of the fixed blind 415 is irradiated outside the light shield
band SBL on the left-hand side of the reticle R as the monitoring
light RBm. This allows three opening images 415B1, 415B2 and 415B3
by the small opening portion 415B of the fixed blind 415 are
projected into the transparent portion on the left-hand side of the
reticle R.
[0297] Then, the monitoring light by each of the three opening
images 415B1, 415B2 and 415B3 is detected in a photoelectric mode
individually by a photoelectric element inside the detector 432B
through the reticle R and the projection optical system PL. The
resulting photoelectric signal Sb is then compared with a signal
from the photoelectric detector 409 of FIG. 20, so that a variation
in transmittance of the whole system including the illumination
optical system and the projection optical system PL ranging from
the beam splitter 408 to the main condenser lens system 419 in FIG.
20 is detected, thereby determining a difference of the
transmittance within the vision field IFo, as needed.
[0298] As described above, the present invention in this embodiment
enables a detection of the variation in transmittance of the whole
system with both of the illumination optical system and the
projection optical system PL added thereto, while the reticle R is
located at the approach run position for scanning exposure, as
shown in FIGS. 22(A) and 22(C). Therefore, a variation in
transmittance can be detected one after another immediately before
the start of scanning exposure of each shot region, upon
sequentially exposing plural shot regions on the wafer W in order
in a step-and-scan system. Moreover, a transmittance that could
vary during a period of time of exposing one sheet of wafer W can
be detected at a nearly real time.
[0299] Now, a description will be made of characteristics in a
variation of transmittance by both of the illumination optical
system and the projection optical system PL, with reference to FIG.
23. In FIG. 23, the X-axis represents an elapse of time t while the
Y-axis represents a transmittance .epsilon. (%). Further, the
exposure apparatus is suspended for a long period of time (for
example, for 1 or 2 days) prior to time T0 and stayed in such a
state that no pulse illumination light passes at all through both
of the illumination optical system and the projection optical
system PL. Further, the characteristics as shown in FIG. 23 are
given by measuring the energy of the pulse light at the leaving
portion of the excimer laser light source 401 and the energy of the
pulse light measured at the image plane of the projection optical
system PL by means of an identical detector and then by plotting
the ratios of the energies calculated from the experimental
results.
[0300] As the exposure apparatus has been started and the
ultraviolet pulse light having a constant frequency has been
started being irradiated at time T0, the transmittance is reduced
from .epsilon.0 to .epsilon.1 for a very short period of time until
time T1, immediately after the irradiation of the ultraviolet pulse
illumination light at time T0. As the irradiation continued
thereafter, the transmittance was allowed to be increased gradually
from .epsilon.1. As the time elapses to time T2, the irradiation
was suspended. At this time the transmittance rose up to
.epsilon.2. After time T2, the transmittance reduced gradually in a
nearly linear way, and the transmittance reaches .epsilon.3
(<.epsilon.2) after an elapse of time to time T3 (after one or
two hours after time T2).
[0301] As the irradiation of the pulse illumination light restarted
at time T3, then the transmittance starts increasing from
.epsilon.3 and then reaches .epsilon.4 at which the transmittance
is in a saturated state. Then, no variation in transmittance can be
recognized any longer even if the irradiation of the pulse
illumination light was continued. As the irradiation was stopped at
time T4, it is then found that the transmittance is reduced
gradually in a linear way.
[0302] In the characteristics as shown in FIG. 23, it is considered
that the tendency of a variation in the initial stage during time
T0 to T1 is caused by the physical properties of the lens element
(quartz or fluorite) itself due to the irradiation of the pulse
illumination light and, however, that the tendency of a variation
during the period of time from time T1 to T2 or T3 to T4 is caused
due to the fact that impurities such as water molecules,
hydrocarbon molecules or otherwise adsorbed on the surface of the
lens element or the reflecting mirror have been washed out upon
irradiation of the ultraviolet pulse illumination light. In
addition, it is considered that the variation in transmittance
during the period of time from time T2 to T3 and time T4 et seq. is
caused due to the fact that molecules of impurities floating in a
space surrounding the various optical elements are attached again
thereto gradually, even if the air inside the optical systems has
been replenished with nitrogen gases.
[0303] Therefore, it is difficult to predict the variation in
transmittance as shown in FIG. 23 indirectly on the basis of a
history of irradiation of the pulse illumination light and the
like, so that this embodiment adopts a type of directly detecting a
variation in intensity of the pulse illumination light passing
actually through both of the illumination light path and the
projection light path. Although the transmittance has reached
.epsilon.3 that is in a nearly saturated state during the period of
time from time T3 to time T4, it is further considered that an
ascent degree of transmittance resulting from the UV cleaning
action by the pulse illumination light passing through the
illumination optical system and the projection optical system PL is
kept in a state of balance with a descent degree of transmittance
resulting from re-adsorption of molecules of impurities to the
surfaces of various optical elements.
[0304] Then, a modification of the structure of a bottom end
portion of the projection optical system PL of FIG. 21 will be
described with reference to FIG. 24. FIG. 24 shows a section of the
bottom portion of the barrel of the projection optical system PL as
shown in FIGS. 20 and 21. Inside the barrel, in addition to the
lens element G2, there are shown a lens element GL2 and a lens
element GL4 located in the position closest thereto. The
light-transmitting optical element (a parallel flat plate made of
quartz) GL3, having the size that covers an imaging light flux
having a predetermined number of openings, including the main light
rays LEa and LEb travelling toward points Ea' and Eb' at which the
edges Ea and Eb on both ends of the illumination region 415A' are
projected, is tightly disposed on the bottom surface of the lens
element GL2.
[0305] On the other hand, the monitoring light LBm is incident to a
plate-shaped optical block GL5a mounted on the right-hand side of
the light-transmitting optical element GL3 under the bottom surface
of the lens element GL2, after passage through the lens elements
GL4 and GL2. The incident light LBm is reflected in a horizontal
way by the full reflection portion GMa formed at the tip end of the
optical block GL5a and then received by the detector 432A. On both
of the bottom surface section of the full reflection portion GMa at
the tip of the optical block GL5a and the optical block GL5a is
each formed a light shielding film or plate for preventing the
monitoring light LBm from reaching the wafer W.
[0306] Likewise, the monitoring light RBm is incident to a
plate-shaped optical block GL5b mounted on the left-hand side of
the light-transmitting optical element GL3 under the bottom surface
of the lens element GL2, after passage through the lens elements
GL4 and GL2. The incident light RBm is reflected in a horizontal
way by the full reflection portion GMb formed at the tip end of the
optical block GL5b, and the reflected light is then received by the
detector 432B. On both of the bottom surface sections of the full
reflection portion GMb at the tip of the optical block GL5b and the
optical block GL5b is each formed a light shielding film or plate
for preventing the monitoring light RBm from reaching the wafer
W.
[0307] The optical blocks GL5a and GL5b in this modification as
shown in FIG. 24 are set to be completely identical in function to
the light-transmitting optical element GL3 as shown in FIG. 21.
When it is difficult to make the reflecting portions GMa and GMb
integral with the light-transmitting optical element GL3, they can
be disposed separately from the light-transmitting optical element
GL3. When they are disposed separately from the light-transmitting
optical element GL3, the light-transmitting optical element GL3 of
FIG. 24 can be processed and adjusted individually as a correction
plate for correcting an optical aberration (including a coma
aberration, astigmatism or a certain kind of distortion) contained
in a partial image of the circuit pattern of the reticle R to be
projected onto the wafer W.
[0308] FIG. 25 is a circuit block diagram showing an example of a
detailed configuration of the inside of the exposure control unit
430 as shown in FIG. 20. The exposure control unit 430 has a
control processor (an operation processing circuit) 457 composed
centrally with some peripheral circuits. In FIG. 25, the
photoelectric signal from the photoelectric detector 409 as shown
in FIG. 20 is input into a sample/hold (S/H) circuit 450, and a
peak value in accordance with an energy amount per one pulse light
is held therein. The signal according to the energy amount is then
converted into a digital value by an analog-digital converter (ADC)
451, and plural pulse portions specified in advance in a memory
circuit 452 are saved one after another.
[0309] On the other hand, either one of the photoelectric signals
Sa and Sb output from the respective detectors 432A and 432B is
selected by a shift circuit 433, and the selected signal is input
into a sample/hold (S/H) circuit 453, a peak value in accordance
with the energy amount per one pulse light is held therein. The
signal according to the energy amount is then converted into a
digital value by an analog-digital converter (ADC) 454, and plural
pulse portions specified in advance in a memory circuit 455 are
saved one after another. The shift operation of the shift circuit
433 can be controlled on the basis of an instruction from the
control processor 457 so as to select a signal from the detector
432A, on the one hand, when the reticle R is located in the
position as shown in FIG. 21 or 22(A) and to select a signal from
the detector 432B, on the other, when the reticle R is located in
the position as shown in FIG. 22(C).
[0310] The control processor 457 reads a plurality of digital data
saved in the memory circuit 452 and computes an average value of
the plural digital data into a value Is of the intensity of an
original laser incident to the illumination optical system of the
exposure apparatus from the excimer laser light source 401.
Likewise, the control processor 457 reads a plurality of digital
data saved in the memory circuit 455 and computes an average value
of the plural digital data into a value Iw of the intensity of the
exposing illumination light at the position at which the
illumination light passes through the projection optical system
PL.
[0311] Then, the control processor 457 gives a ratio (Iw/Is) of the
computed intensity value Iw to the computed intensity value Is, and
the data value of the ratios is then saved as transmittance data in
a history memory relating to a variation in transmittance, disposed
in the control processor. Furthermore, the control processor 457
calculates a difference between a group of data of the
transmittance so far saved in the past in the history memory and
data saved at this time, and makes a decision as to whether the
difference is so large (for instance, resulting in an error by 1%
or more as a control precision) that correction is required in
terms of controlling the exposure amount.
[0312] In the case where, as a result of the such decision, it is
required to alter or correct the exposing conditions previously set
so as to provide a target exposure amount saved in the memory
circuit 459, the control processor 457 outputs an instruction for
correcting the intensity (energy) of the pulse light to the
variable light extinction device 406 as shown in FIG. 20. If the
adjustable scope would be minute, an instruction is given to the
excimer laser light source 401 as shown in FIG. 20, in order to
correct the oscillating intensity itself (adjust a high voltage
between discharging electrodes) of the pulse light.
[0313] In addition, the control processor 457 is associated with
the main control system 427 through an interface bus IB, and the
main control system 427 sends to the control processor 457, for
example, information on the reticle R which has finished its
movement for the scanning exposure and now reached the approach run
position. The control processor 457 then executes each of
operations including, for example, selecting the detector 432A or
432B, in response to the such information, taking a signal from the
detector selected, and correcting the exposing condition, etc., at
a real time during a series of the scanning exposure operations for
each of the plural shot regions on the wafer W.
[0314] In the system for controlling the exposure amount as
described above, the intensity of the ultraviolet pulse
illumination light reaching from the excimer laser light source 401
to the reticle R has been selected among the various exposing
conditions and corrected on the basis of the data of transmittance
saved one after another in the history memory in the control
processor 457. It is to be noted herein, however, that the
correction of the exposing conditions can also be executed by
minutely adjusting an absolute value of each velocity Vr and Vw,
while a ratio of the transferring velocity Vr of the reticle R to
the transferring velocity Vw of the wafer W at the time of the
scanning exposure is kept at a constant value. In this case,
however, a minute adjustment of the width Da in the scanning
direction of the illumination region 415A' by the slit-shaped or
rectangle-shaped opening portion 415A of the fixed blind 415 would
be required due to the fact that the excimer laser light source 401
is used as a pulse light.
[0315] On the contrary, it is also possible to execute the control
of the exposure amount by effecting a minute adjustment of the
width Da in the scanning direction of the illumination region
415A', without changing the ratio of the scanning velocities Vr and
Vw and the absolute values thereof. In this case, however, there is
a close relationship among the width Da of the illumination region
415A', the scanning velocities Vr and Vw, and the oscillating
frequency f of the excimer laser light source 401, so that it is
required to establish the relationship of f.times.Da=n.times.Vr
(the condition where the number of pulses to be oscillated during
the period of time when the reticle R moves in the distance
corresponding to the width Da at the scanning velocity Vr should be
set to be always an integer n), for example, on conditions that the
number n of pulses is set by a number of an appropriate pulse light
(for example, an integer from 30 to 50, inclusive), when it is
defined by the scanning velocity Vr on the reticle R side.
Therefore, in the case where the width Da is to be adjusted in a
minute mode without changing the scanning velocity Vr of the
reticle R, at least one of the integer n and the oscillating
frequency f should be altered.
[0316] In addition, in the case where a plurality of the small
opening portions 415B1-415B3 and 415C1-415C3, inclusive, are
projected along the lengthwise direction (the Y-direction) of the
illumination region 415A', as shown in FIGS. 22(A), (B) and (C),
and the transmitting energy for each small opening image is
detected by the photoelectric element individually disposed in the
detectors 432A and 432B, an irregularity of transmittance (an
irregularity of illuminance) in the Y-direction can be presumed.
Therefore, a transmittance distribution changing element may be
disposed in the vicinity of the position that is nearly conjugated
with the reticle R in the illumination optical system or in the
vicinity of the position of the pupil epo in accordance with the
irregularity of transmittance obtained, thereby allowing a
compensation for the irregularity of illuminance particularly in
the Y-direction.
[0317] In the embodiment as shown in FIG. 25, transmittance data
including both of the illumination optical system and the
projection optical system PL is computed on the basis of a ratio of
the intensity value of the illumination light detected by each of
the detectors 432A and 432B to the intensity value of the original
laser light energy, and the exposing conditions at the time of
controlling the exposure amount are corrected in accordance with a
variation in the transmittance data. The exposure amount, however,
can also be controlled at a necessary degree of precision simply
based on each of output signals from the detectors 432A and 432B,
without using the photoelectric detector 409. Therefore, a device
construction and operations necessary for this configuration will
be described hereinafter as a second embodiment of the present
invention, with reference to FIG. 26.
[0318] FIG. 26 shows a relationship of the position of the tip end
portion of the projection optical system PL with the position of
the wafer stage 424. In this embodiment, an illuminance detector
470 is disposed on the wafer stage 424 as a third photoelectric
detector. The exposure amount can be controlled by calibrating
results of detection by the detectors 432A and 432B on the basis of
the measured values which are obtained by measuring the intensity
or illuminance of the exposing energy leaving from the projection
optical system PL from time to time by means of the illuminance
detector 470 disposed on the wafer stage 424.
[0319] In FIG. 26, the wafer W is placed on the wafer stage 424
through a wafer holder WH, and the illuminance detector 470 is
mounted on the wafer stage 424 so as to allow the projection
optical system to be on a level with the top surface of the wafer W
(within the scope of approximately .+-.0.6 mm). Further, the
illuminance detector 470 is provided on its surface with a first
pinhole group 470a and a second pinhole group 470b, the first
pinhole group 470a comprising a plurality of pinholes, each having
a diameter of approximately 1 mm, arranged at a constant interval
in the Y-direction intersecting at a right angle with the direction
of the scanning exposure (in the direction perpendicular to the
paper surface of FIG. 26), and the second pinhole group 470b
disposed apart on the image plane side by a distance corresponding
to the width Da in the scanning exposure direction of the
illumination region 415A' by the fixed blind 415. The second
pinhole group 470b also comprises a plurality of pinholes arranged
at a constant distance in the Y-direction intersecting at a right
angle to the direction of the scanning exposure.
[0320] When the wafer stage 424 is aligned in a precise manner, as
shown in FIG. 26, on the basis of length measuring beams BMx to be
projected onto a reflecting mirror 424X on the wafer stage 424 from
a laser interferometer disposed in a stage drive control unit 425
(as shown in FIG. 20), these pinhole groups 470a and 470b are
disposed so as to correspond to the position within the image plane
of the main light rays LEa and LEb passing through the edges Ea'
and Eb' in the scanning direction (X-direction) of the illumination
region 415A' by the fixed blind 415, respectively.
[0321] Moreover, on the back side of each of the pinhole groups
470a and 470b of the illuminance detector 470, there are disposed
plural photoelectric elements 472 each for detecting the exposing
energy from the projection optical system PL passed through each
pinhole in a photoelectric mode individually. Each of the
photoelectric signal Sc from a group of the photoelectric elements
is output to the exposure control unit 430 as shown in FIGS. 20 and
25.
[0322] In the configuration as shown in FIG. 26, when the movable
blades 416A and 416B are full open in a state in which the
illuminance detector 470 is aligned in the manner as shown in FIG.
7, the illumination region 415A' having a uniform distribution of
illuminance is projected onto the illuminance detector 470, if no
reticle R is located on the illumination light path. And, the
illuminance value at each position of the plural pinholes, included
in the first pinhole group 470a and the second pinhole group 470b,
can be detected individually.
[0323] The calibration of the detectors 432A and 432B by means of
the illuminance detector 470 can be effected in a manner, for
example, as shown in FIG. 27. FIG. 27(A) shows a state in which the
reticle R is located in the approach run position on the left-hand
side, like FIG. 22(A). First, in this state, the wafer stage 424 is
aligned in the manner as shown in FIG. 26. Then, the movable blades
416A and 416B are set in the state as shown in FIG. 2, and images
415C1 to 415C3, inclusive, of the small opening portion 415C of the
fixed blind 415 are projected onto the transparent portion outside
the right-hand light shield band SBR of the reticle R in the manner
as shown in FIG. 27(A). Thereafter, the light transmitted (the
monitoring light LBm) is detected in a photoelectric mode by means
of the detector 432A of FIG. 26, and a level of the resulting
signal Sa is saved therein.
[0324] Then, the reticle R is allowed to move from the state of
FIG. 27(A) toward the right-hand side by a distance .DELTA.Hx, and
the movable blades 416A and 416B are opened to a small extent,
followed by restricting a slight portion of the width on the edge
Ea side of the illumination region 415A' having the width Da to a
slim slit-shaped illumination region 415AL and projecting it onto
the reticle R. At this time, the illumination region 415AL is
incident to the projection optical system PL after transmission
through the transparent portion outside the right-hand light shield
band SBR of the reticle R, and the light passed therethrough is
irradiated onto the first pinhole group 470a on the wafer stage
424. Therefore, the illuminance value of each light passed through
each pinhole of the first pinhole group 470a and received
individually by means of the photoelectric elements 472 represents
an irregularity of illuminance in the Y-direction of the
slit-shaped illumination region 415AL.
[0325] The exposure control unit 430 averages the values of
illuminance in the slit-shaped illumination region 415AL on the
basis of the signal Sc detected, and saves the resulting average
value as an average illuminance Value. The average illuminance
value reflects the exposure amount provided actually on the wafer W
at a high degree of fidelity. Therefore, in the case where the
average illuminance value has an error by k % with respect to the
set value in order to obtain a target exposure amount, it can be
the that the level of the signal Sa from the detector 432A, saved
in connection with FIG. 27(A), has also an error by approximately k
%.
[0326] Thus, the exposure control unit 430 makes a correction of k
% for the signal Sa from the detector 432A, which will be output
thereafter, and determines exposing conditions for obtaining an
appropriate exposure amount on the basis of the corrected signal
Sa'. Usually, the exposure apparatus of this type is so adapted as
to subject the plural sheets of wafers in a lot unit to exposure
processing. Therefore, it is considered that, although there is the
occasion that a variation in transmittance tends to become larger
upon processing the wafer at the top of the wafers in a lot unit,
no variation in transmittance to such a large extent will occur
thereafter and that the transmittance for the other wafers would
occur within a relatively small scope as the characteristics as
shown in FIG. 23 (after time T2 et seq.).
[0327] Therefore, in this embodiment, the exposure amount can be
controlled in a nearly accurate way without utilizing the
photoelectric detector 409 as shown in FIG. 20, if, whenever the
exposure processing for one sheet of a wafer has been finished, the
wafer stage 424 is aligned in the manner as shown in FIG. 26, the
illuminance value within an image projection region in the vision
field IFo of the projection optical system PL, that is, on the
image side of the illumination region 415A', is detected by the
illuminance detector 470 on the stage, and the detection signals Sa
and Sb from the respective detectors 432A and 432B disposed at the
bottom end portion of the projection optical system PL are
calibrated on the basis of the result of detection and then
used.
[0328] As shown in FIGS. 26 and 28, the second embodiment of the
present invention is configured such that illuminance within an
actual image projection region (the illumination region 415A') at
the time of the scanning exposure, in which the wafer is exposed to
light, is detected and the signals from the detectors 432A and 432B
are calibrated. Therefore, the second embodiment can reflect a
variation in transmittance within the actual image projection
region in an accurate way, so that it can present the advantage in
that the exposure amount can be controlled with a high degree of
precision. Moreover, in this embodiment of the present invention,
irregularities of illuminance within the image projection region
can be measured by means of the illuminance detector 470 on the
stage, and such irregularities of illuminance can be corrected as
needed.
[0329] Each example of the first embodiment of the present
invention has been described above. It should be noted herein,
however, that the method for measuring the transmittance of both of
the illumination optical system and the projection optical system
PL is not restricted to those examples and embodiments. For
instance, in the examples as shown in FIGS. 26 and 27 above, the
average illuminance value of the illuminance detected by the
illuminance detector 470 (or an individual illuminance value for
each pinhole) is compared with the intensity of the signal from the
photoelectric detector 409 of FIG. 1, immediately before the start
of the exposure processing one sheet of a wafer, a transmittance is
determined for the image projection region (a region within the
opening portion 415A of the fixed blind 415) at that point of time,
and a value of each detection signal of the detectors 432A and 432B
disposed at the bottom end portion of the projection optical system
PL can be evaluated by using the resulting transmittance as a
standard. Then, the value of each detection signal can be used for
the control of the exposure amount.
[0330] Generally, the projection exposure apparatus of this type
adopts, in many cases, a configuration such that several % of the
pulse illumination light leaving from the fly-eye lens system
disposed in the illumination optical system is reflected at the
beam splitter (or passed therethrough), the intensity of the
reflected light is detected with a photoelectric element (an
integrator sensor), and the resulting photoelectric signal is
integrated at every pulse illumination light to detect the exposure
amount provided on the wafer. In this case, the integrator sensor
can be used in place of the photoelectric detector 409 as shown in
FIG. 1.
[0331] Moreover, the photoelectric detectors 432A and 432B for
measuring transmittance are not required to be fixedly disposed at
the bottom end portion of the projection optical system PL, as
shown in FIGS. 20, 21 and 24, and they may be each of a movable
type. In this case, for example, as shown in FIG. 28, the apparatus
may be configured such that the illuminance of the pulse
illumination light can be measured at an optional position within
the vision field of the present invention, by providing movable
arms 482A and 482B so as to be inserted in and detached from the
vision field on the image plane side of the projection optical
system PL (a space interposed between the bottom surface of the
light-transmitting optical element GL3 and the wafer W) by means of
drive mechanisms 480A and 480B disposed on the outer wall of the
barrel of the projection optical system PL and mounting the
photoelectric detectors 484A and 484B each having a light receipt
surface extending in the Y-direction intersecting at a right angle
to the scanning direction (the X-direction) on the respective end
portions of the movable arms.
[0332] When the photoelectric detector 484A (or 484B) is disposed
so as to be inserted in or detached from the projection light path
on the image plane side of the projection optical system PL as
shown in FIG. 28, the measurement of the transmittance to be
determined by both of the illumination optical system and the
projection optical system PL may be conducted preferably by
projecting the exposing pulse illumination light onto a portion (or
an entirety) of the illumination region 415A' through the
transparent portion located outside the light shield band of the
reticle R as shown in FIG. 27(B), and receiving the pulse
illumination light passed through the projection optical system PL
by means of the photoelectric detector 484A (or 484B). With this
configuration, the results of measurement with higher precision can
be expected to be gained because the transmittance produced at a
light path corresponding to the inside of the illumination region
415A' within the vision field for use in the actual projection
exposure can be measured in a direct way.
[0333] Even in the case of the example as shown in FIG. 28, each of
the photoelectric signals Sa and Sb from the detectors 432A and
432B can be calibrated on the basis of the level of the
photoelectric signal from the photoelectric detector 484A (or 484B)
in substantially the same manner as in the example as shown in FIG.
26. In the case of the example as shown in FIG. 28, however, unlike
the construction as shown in FIG. 26, the photoelectric detector
484A (or 484B) can be inserted into the vision field, even if the
wafer W is located right under the projection optical system PL, so
that at an appropriate point of time during the operation of
exposure to wafers, the reticle R can be disposed as shown in FIG.
27(A), the slit-shaped illumination region 415AL as shown in FIG.
27(A) can be projected by means of the movable blades 416A and 416B
as shown in FIG. 27(A), and the light passed therethrough can be
received by the photoelectric detector 484A (or 484B),
respectively.
[0334] At that time, the pulse illumination light in the
illumination region 415AL to be projected onto the reticle R is
shielded to a full extent by means of the photoelectric detector
484A (or the movable arm 482B) so as to fail to reach the wafer W
after passage through the projection optical system PL.
[0335] Further, each of the above examples is configured such that
a variation in transmittance of the entire system including the
illumination optical system and the projection optical system PL
can be detected by photoelectrically detecting a portion of the
exposing energy leaving to the side closest to the image plane side
of the projection optical system PL. In the case of the optical
configuration in which a predetermined space is formed in the pupil
plane EP of the projection optical system PL, however, the
photoelectric detector is disposed so as to be inserted into or
detached from the space of the pupil plane EP, and the illumination
region 415AL is projected onto the transparent portion of the
reticle R in a state in which the reticle R is disposed in a state
as shown in FIG. 27(B), so that the light quality for monitoring a
variation in transmittance and calibrating the variation at the
time of controlling the exposure amount may be measured.
[0336] Then, a description will be made of the projection exposure
apparatus according to the present invention suitable for use in
practicing a third embodiment of the present invention, with
reference to the accompanying drawings. In this embodiment, the
present invention is applied to a scanning type projection exposure
apparatus of a step-and-scan type, which uses a projection optical
system of a reflection-refraction type as a projection optical
system.
[0337] FIG. 29 shows a brief configuration of the projection
exposure apparatus of this embodiment. In FIG. 29, illumination
light IL composed of pulse laser light emitting from an excimer
laser light source 502 with its emission state controlled by an
exposure control unit 501 is deviated by an eccentric mirror 503
and reaches a first illumination system 504. As the excimer laser
light source 502 in this embodiment, there may be used a
broad-banded laser light source of a KrF excimer laser (wavelength
of 193 nm) with a half value width of an oscillating spectrum
modified to 100 pm or greater. Further, as a light source for
exposure, there may be used a broad-banded laser light source of an
ArF excimer laser (wavelength of 193 nm), a metallic vapor laser
light source, a higher harmonics generating device of a YAG laser
or a bright line lamps such as mercury lamps, etc., or
otherwise.
[0338] The first illumination system 504 may include a beam
expander, a light quantity changing mechanism, an illumination
shift mechanism for shifting a light quantity of the illumination
light when a coherence factor (a so-called .sigma. value) of the
illumination optical system is altered, a fly-eye lens, and the
like. A secondary light source is formed on the emitting plane of
the first illumination system 504 with the illumination light IL
distributed in a plane-like manner, and a shift revolver 505 is
disposed on the plane on which the secondary light source is
formed, which is for use with an illumination-type opening stop for
shifting the illumination conditions to various other conditions.
The shift revolver 505 is provided on the side surface thereof
with, for example, a circular opening stop of a usual type, an
opening stop for a so-called shaping illumination composed of
plural openings deviated from the light axis, a ring-shaped opening
stop, and an opening stop for a small a value composed of a small
circular opening, and the like. The desired illumination-type
opening stop (a .sigma. stop) can be disposed on the emitting plane
of the first illumination system 504 by rotating the shift revolver
505 through a shift unit 506. Further, when the illumination-type
opening stop is shifted, an illumination shift mechanism in the
first illumination system 504 is shifted in synchronism with the
shift device so as to make the light quantity reach largest.
[0339] The operation of the shift device 506 is controlled by the
exposure control unit 501, and the operation of the exposure
control unit 501 is controlled by the main control unit 507 for
controlling the operation of the apparatus as a whole in a
comprehensive manner.
[0340] The illumination light IL passed through the
illumination-type opening stop set by the shift revolver 505 is
incident to the beam splitter 508 having a large transmittance and
a small reflectance, and the illumination light reflected by the
beam splitter 508 is received by the integrator sensor 509 composed
of a photoelectric detector such as a photodiode or otherwise. The
detection signal obtained by photoelectrically converting the
illumination light by the integrator sensor 509 is supplied to the
exposure control unit 501. The relationship of the detection signal
with the exposure amount on the wafer is measured and saved in
advance, and the exposure control unit 501 monitors the accumulated
exposure amount on the wafer from the detection signal. The
detection signal can be utilized for standardizing the output
signal of various sensor systems for use with the illumination
light for exposing.
[0341] The illumination light IL passed through the beam splitter
508 illuminates an illumination vision field stop (a reticle blind
system) 511 through a second illumination system 510. The
illumination vision field stop 511 has substantially the same
configuration as the reticle blind mechanism 23 of FIG. 1 has.
[0342] The operation of the movable blind in the illumination
vision field stop 511 is controlled by a drive device 512, and a
stage control unit 513 is driven in synchronism with the movable
blind in the scanning direction through the drive device 512, upon
scanning the wafer in synchronism with the reticle by the stage
control unit 513 in a manner as will be described hereinafter. The
illumination light IL passed through the illumination vision field
stop 511 illuminates a rectangular illumination region 515 at a
uniform illuminance distribution on a pattern surface (a bottom
surface) of the reticle R through a third illumination system 514.
The surface of the illumination vision field stop 511 on which the
fixed blind is disposed is conjugated with the pattern surface of
the reticle R, and the shape of the illumination region 515 is
defined by an opening of the fixed blind.
[0343] A description will be made of the configuration of the
embodiment as shown in FIG. 29 by referring to the plane
perpendicular to the paper plane of FIG. 29 on the plane parallel
to the pattern plane of the reticle R as the X-axis, the plane
parallel to the paper plane of FIG. 29 as the Y-axis, and the plane
perpendicular to the pattern plane of the reticle R as the Z-axis.
In this configuration, the illumination region 515 on the reticle R
is a rectangular region elongated in the X-direction, and the
reticle R is scanned in +Y-axial direction or -Y-axial direction
with respect to the illumination region 515 at the time of the
scanning exposure. In other words, the scanning direction is set to
be the Y-direction.
[0344] A pattern in the illumination region 515 on the reticle R is
reduced at a projection magnification .beta. (.beta. being, for
example, 1/4, 1/5, etc.) through the projection optical system PL
which is telecentric on both sides (or one side on the wafer side),
and an image is projected onto an exposure region 516 of the
surface of the wafer W with photoresist coated thereon.
[0345] The reticle R is held on the reticle stage 517, and loaded
through an air bearing on a guide extending in the Y-direction on a
reticle support table 518. Further, the reticle stage 517 has
substantially the same configuration as the reticle stage as shown
in FIGS. 1 and 20. In the drawing, reference numeral 519 denotes a
laser interferometer and reference symbol 519m denotes a moving
mirror.
[0346] On the other hand, the wafer W is held on a sample table 521
through a wafer holder 520, and the sample table 521 is mounted on
a wafer stage 522. The wafer stage 522 is mounted on a guide on a
base 523 through an air bearing. The wafer stage 22 has the same
configuration as the wafer stage as shown in FIGS. 1 and 20. In the
drawing, reference symbol 524m denotes a moving mirror, and
reference numeral 524 denotes a laser interferometer. The stage
control unit 513 controls the operation of a linear motor or
otherwise for driving the wafer stage 522 in accordance with the
measured value fed by the laser interferometer 524.
[0347] A command for starting the exposure is sent to the stage
control unit 513 from the main control unit 507 at the time of the
scanning and exposing, and the stage control unit 513 scans the
wafer W at a velocity Vw in the Y-direction through the wafer stage
522, in synchronism with scanning the reticle R at a velocity Vr in
the Y-direction through the reticle stage 517. The scanning
velocity Vw of the wafer W is set to .beta..times.Vr by using a
projection magnification .beta. from the reticle R to the wafer
W.
[0348] Further, the projection optical system PL is held on an
upper plate of a squared C-shaped column 525 disposed on the base
523. Moreover, a multipoint autofocus sensor 526 of an oblique
incident type (hereinafter referred to as an "AF sensor") is
disposed on a side surface portion in the X-direction of the
projection optical system PL, which can project a slit image or the
like in an oblique direction onto plural measurement points located
on the surface of the wafer W and output plural focus signals
corresponding to the Z-directional positions (hereinafter referred
to each as a "focus point") at the plural measurement points. The
plural focus signals from the multipoint AF sensor 526 are fed to a
focus-tilt control unit 527 which in turn gives the focus position
and an oblique angle on the surface of the wafer W on the basis of
the plural focus signals and then supplies the resulting data to
the stage control unit 513.
[0349] The stage control unit 513 drives a Z-stage mechanism and a
tilt mechanism in the wafer stage 522 in a servo system so as to
allow the supplied focus position and oblique angle to agree with a
focus position and an oblique angle of an imaging plane of the
projection optical system PL which have been determined in advance.
This allows the surface of the wafer W within the exposure region
516 to be restricted so as to agree with the imaging plane of the
projection optical system PL in an autofocus system and an
auto-levelling system even during the scanning exposure.
[0350] Further, an alignment sensor 528 of an off-axis type is
fixed to the +Y-directional side surface of the projection optical
system PL, and the position of an aligning wafer mark disposed in
each shot region of the wafer W is detected by means of the
alignment sensor 528 upon carrying out the alignment, the wafer
mark being provided in each shot region of the wafer W. The
detection signal is then fed to an alignment signal processing unit
529 to which a measured value from a laser interferometer 524 is
also supplied. The alignment signal processing unit 529 computes
coordinates in a stage coordinates system (X, Y) of the wafer mark
of a detection object from the detection signals and the measured
values of the laser interferometer 524, and the resulting
coordinates are then supplied to the main control unit 507. The
stage coordinates system (X, Y) is intended herein to mean a
coordinates system to be defined on the basis of the X-coordinate
and the Y-coordinate of the sample table 521 to be measured by
means of the laser interferometer 524. Further, the main control
unit 507 is arranged so as to determine the sequence coordinates in
the stage coordinates system (X, Y) of each shot region on the
wafer W from the supplied coordinates of the wafer mark and to
supply the resulting sequence coordinates to the stage control unit
513. Then, the stage control unit 513 controls the position of the
wafer stage 522 on the basis of the supplied sequence coordinates
upon the scanning exposure to each shot region.
[0351] On the sample table 521 is fixed a reference mark member FM,
and the reference mark member FM is provided on its surface with,
for example, a variety of reference marks that act each as a
reference for the position of an alignment sensor, as well as a
reference reflecting plane that becomes a reference for reflectance
of the wafer W. Moreover, on the top end portion of the projection
optical system PL is mounted a reflecting light detection system
530 for detecting a light flux, or otherwise, to be reflected from
the wafer W side through the projection optical system PL, and a
detection signal of the reflecting light detection system 530 is
then fed to a self measurement unit 531 under control of the main
control unit 507 as will be described hereinafter, the self
measurement unit 531 being arranged so as to monitor a reflectance
(a reflecting ratio) of the wafer W and a variation in
transmittance of the projection optical system PL, and to measure
irregularities of illuminance and a space image, etc.
[0352] Then, a description will be made of the configuration of the
projection optical system PL in FIG. 29 in more detail with
reference to FIG. 30.
[0353] FIG. 30 is a sectional view showing the projection optical
system PL. In FIG. 30, the projection optical system PL may be
divided into four sections in terms of its mechanism. The four
sections may include a first object section 541, a light axis
return section 543, a light axis deflection section 546 and a
second object section 552. Further, a concave mirror 545 is
disposed in the light axis turn section 543.
[0354] In the case where broad-banded laser light is used as
illumination light IL as in this embodiment, such laser light can
present the advantages in that an electric power can increase a
light quantity even if a power source would be the same, so that a
throughput can be increased, and that adverse influences or
otherwise due to interference to be caused by a decrease in
coherency can be reduced. It should be noted herein, however, that
in the case where illumination light in an ultraviolet area such as
KrF excimer laser light or ArF excimer laser light is used as in
this embodiment, a glass material to be used as a refractive lens
in the projection optical system PL should be restricted to quartz,
fluorite or otherwise, so that it is difficult to design the
projection optical system PL by a refraction optical system only.
Therefore, in this embodiment, a reflection optical system or a
refraction optical system, such as a concave mirror, which does not
cause any chromatic aberration, is used together in order to
achieve broad-banded achromatism. It should be noted herein that
generally the reflection optical system is a 1-to-1 (equally
magnified) optical system, however, when a reduced projection such
as a 1/4-fold or 1/5-fold projection is effected as in this
embodiment, a unique modification for the construction is required
in a manner will be described hereinafter.
[0355] In this configuration, the first object section 541 is
disposed right under the reticle R, and the first object section
541 has lenses L1, L2, L3 and L4 disposed fixedly in this order
from the reticle R side in a barrel 542 through a lens frame. Under
the barrel 542, a barrel 544 of the light axis turn section 543 is
disposed through a barrel 547 of the light axis deflection section
546, and lenses L11, L12-L20, inclusive, and L21, and the concave
mirror 545 are fixed in the barrel 544 in this order from the
reticle R side through a lens frame. The first object section 541
and the light axis turn section 543 are disposed coaxially each
other, and the light axis will hereinafter be referred to as light
axis AX1. The light axis AX1 extends in the direction perpendicular
to the pattern plane of the reticle R.
[0356] In this configuration, a small-sized mirror 548 having a
reflecting plane extending in +Y-axial direction obliquely at about
45.degree. with respect to the light axis AX1 is disposed in the
position deflected in the +Y-axial direction from the light axis
AX1 within the barrel 547 of the light axis deflection section 546
interposed between the barrel 542 and the barrel 544. The barrel
547 in turn is provided therein with lenses L31 and L32, a
correction optical system 549 and a beam splitter 550 in this order
in the +Y-axial direction from the small-sized mirror 548. A light
axis AX2 of the light axis deflection section 546 extends in the
direction intersecting at a right angle to the light axis AX1, and
the reflecting plane of the beam splitter 550 is disposed inclining
at approximately 45.degree. with respect to the light axis AX2 so
as to intersect with the reflecting plane of the small-sized mirror
548. The beam splitter 550 is a beam splitter arranged so as to
have a transmittance of 5% and a reflectance of approximately 95%,
and a way of using the light flux passed through the beam splitter
550 will be described hereinafter. The correction optical system
549 is disposed so as to move in a direction along the light axis
AX2 in a minute mode and comprises a lens group, or otherwise, that
can minutely adjust an inclining angle with respect to the flat
plane perpendicular to the light axis AX2. The position and the
including angle of the correction optical system 549 can be
controlled by an imaging characteristic correction unit 551. The
operation of the imaging characteristic correction unit 551 is
controlled by means of the main control unit 507 as shown in FIG.
29. Further, the position at which the correction optical system
549 is disposed is the position nearly conjugated with the pattern
plane of the reticle R, and the correction optical system 549 can
correct mainly an error in magnification, distortion, a focal
position, an astigmatism, a coma aberration, a curvature in an
image plane, and a spherical aberration. Moreover, the barrel 553
of the second object section 552 is disposed in a direction in
which the light axis AX2 is bent by means of the beam splitter 550,
so as to come into contact with the barrel 547, and the second
object section 552 is provided with lenses L41, L42, L43-L52,
inclusive, in the barrel 553 thereof in this order from the side of
the beam splitter 550 by the aid of a lens frame. Moreover, the
bottom surface of the second object section 552 is disposed so as
to face the surface of the wafer W. A light axis AX3 of the second
object section 552 is disposed extending in a direction parallel to
the light axis AX1 of the first object section 541 and the light
axis turn section 543 yet perpendicular to the light axis AX2 of
the light axis deflection section 546.
[0357] In this case, the rectangular illumination region 515 on the
reticle R by the illumination light IL is set at the position at
which it is deflected in -Y-axial direction from the light axis
AX1, and the illumination light passed through the illumination
region 515 (hereinafter referred to as an "imaging light flux") is
incident to the light axis turn section 543 through the lenses L1,
L2, L3 and L4 in the first object section 541 and then through the
inside of the barrel 547 of the light axis deflection section 546.
The imaging light flux incident to the light axis turn section 543
is then incident to the concave mirror 545 through the lenses L11,
L12-L20, inclusive, and L21, and then reflected by means of the
concave mirror 545. The reflected and condensed imaging light flux
passes through the lenses L21, L20-L12, inclusive, and L11, again
yet in the order opposite to the previous passage, and then, is
deflected in the +Y-axial direction by the small-sized mirror 548
in the barrel 547 of the light axis deflection section 546.
[0358] The imaging light flux reflected at the small-sized mirror
548 in the light axis deflection section 546 is then incident to
the beam splitter 550 through the lenses L31 and L32 and the
correction optical system 549. Upon this, an image (an intermediate
image) of a pattern in the illumination region 515 on the reticle
R, which has an approximately equal magnification, is formed in the
vicinity of the beam splitter 550 inside the barrel 547. A combined
system in combination of the first object section 541 with the
light axis turn section 543 is called herein "an
equal-magnification optical system". The imaging light flux
deflected in the -Z-axial direction with the beam splitter 550
advances toward the second object section 552 where the imaging
light flux in turn forms a reduced image of the pattern within the
illumination region 515 on the reticle R in the exposure region 516
on the wafer W through the lenses L41, L42-L51, inclusive, and L50.
In this sense, the second object section 552 will sometimes be
referred to as "a reduced projection system".
[0359] As described above, in this embodiment, the imaging light
flux passed through the illumination region 515 on the reticle R
nearly in the -Z-axial direction is turned nearly in the +Z-axial
direction by the first object section 541 and the light axis turn
section 543 within the projection optical system PL. Then, the
imaging light flux forms an intermediate image having a
magnification nearly equal to the pattern within the illumination
region 515 during the steps in which it is returned approximately
to the +Y-axial direction and then to the -Z-axial direction in
order by means of the light axis deflection section 546, thereafter
forming a reduced image of the illumination region 515 in the
exposure region 516 on the wafer W through the second object
section 552. In this configuration, the projection optical system
PL in this embodiment can have all the lenses L2-L4, L11-L21, L32
and L33, and L41-L52 disposed with the axis symmetrical to one
another and be made of quartz but three or four lenses being made
of fluorite. This simple construction alone can perform an
achromatism with a high degree of precision in the scope of
approximately 100 pm that in turn is a band width of the
broad-banded illumination light IL.
[0360] The projection optical system PL in this embodiment can be
divided into three systems in an optical mode, which include the
equal-magnification optical system composed of the first object
section 541 and the light axis turn section 543, the light axis
deflection section 546, and the reduced projection system composed
of the second object section 552, as described above. As to the
mechanical structure of the projection optical system, the
small-sized mirror 548 is interposed between the lens L4 of the
first object section 541 and the lens L11 of the light axis turn
section 543. In this construction, if the lens L4, the small-sized
mirror 548 and the lens L11 would be incorporated in the identical
barrel, it is required that the small-sized mirror 548 and the beam
splitter 550 within the light axis deflection section 546 have to
be incorporated in different barrels for adjustment purposes. If
the small-sized mirror 548 and the beam splitter 550 would be
incorporated into different barrels, however, there is the risk
that the right angle of intersection of the reflecting planes of
the two members with each other is caused to fluctuate. If the
right angle of intersection of those two reflecting planes would
fluctuate, it may cause deterioration in imaging performance. In
this embodiment, accordingly, the equal-magnification projection
system is divided into the first object section 541 and the light
axis turn section 543 with the interposition of the barrel 547 of
the light axis deflection section 546, and the small-sized mirror
548 and the beam splitter 550 are fixed in the barrel 547.
[0361] Upon the assembly of the projection optical system PL, each
of the first object section 541, the light axis turn section 543,
the light axis deflection section 546 and the second object section
552 is assembled together and adjusted in advance separately.
Thereafter, the barrel 544 of the light axis turn section 543 is
inserted into a through-hole formed in an upper plate of the column
525, and a lower portion of the barrel 553 of the second object
section 552 is likewise inserted into a through-hole formed
therein. A washer is inserted into a gap between a flange 544a of
the barrel 544 thereof and the upper plate of the column 525 as
well as a flange 553a of the barrel 553 and the upper plate
thereof, and the flanges 544a and 553a are temporarily fastened on
the upper plate of the column 525 with a screw. Then, the barrel
547 is mounted on the top ends of the barrels 544 and 553, and then
washer is inserted into a gap between a flange 547a of the barrel
547 and a flange 553b on the top end of the barrel 553, and
thereafter, the flange 547a is temporarily fastened on the flange
553b with a screw.
[0362] Next, laser beams for use with adjustment purposes are
irradiated into the barrel 544 from above of the lens L11 in the
barrel 544, thereby monitoring the position (the position on the
plane corresponding to the surface of the wafer W) from which the
laser beams leave the lens L52 disposed at the bottommost position
of the barrel 553 and pass therethrough and adjusting the monitored
position so as to agree with the target position, for example, by
adjusting the thickness of the washer to be disposed at the bottom
portion of the flanges 544a, 553a and 547a or transferring the
barrels 542, 553 and 547 in a transverse direction, or otherwise.
And, in a state in which the position of the laser beams agrees
with the target position, the flanges 544a, 553a and 547a are
fastened each with a screw, thereby fixing the light axis turn
section 543, the second object section 552 and the light axis
deflection section 546, respectively. Finally, the barrel 542 of
the first object section 541 is transferred in the -Y-axial
direction above the end portion of the barrel 547, and the barrel
542 is disposed on the barrel 547 by inserting a washer between a
flange (not shown) of the barrel 542 and a corresponding flange
(not shown) of the barrel 547. Once again, for instance, laser
beams for adjustment use are irradiated from above the lens L1 of
the barrel 542 to adjust the light axis, thereafter fastening the
barrel 542 on the barrel 547 with a screw and finishing the
assembly of the projection optical system PL with the projection
exposure apparatus.
[0363] Moreover, in this embodiment, the position of a gravity 554
of the entire system of the projection optical system PL is set
inside the projection optical system PL, yet outside the light path
of the imaging light flux, with stability of imaging
characteristics against vibration and a balance of the projection
optical system PL taken into account. In other words, in FIG. 30,
the gravity 554 of the projection optical system PL is set at the
position (inside the upper plate of the column 525) in the vicinity
of an intermediate position between the light axis turn section 543
and the second object section 552 and lower slightly from the
flange 544a of the barrel 544 and the flange 553a of the barrel
553. By setting the gravity 554 of the projection optical system PL
further in the vicinity of the flanges 544a and 553a in the manner
as described above, the projection optical system PL can withstand
vibration to a higher extent and provide a highly rigid
structure.
[0364] As described above, in this embodiment, an intermediate
image plane conjugated with the pattern plane of the reticle R
exists inside the light axis deflection section 546 of the
projection optical system PL and in the vicinity of the beam
splitter 550, and the correction optical system 549 is disposed in
the vicinity of the intermediate image plane. The imaging
characteristics, such as a projection magnification of a reduced
image of the reticle R to be projected on the wafer W, a distortion
and so on, can be corrected by minutely moving, for example, a lens
group acting as the correction optical system 549 in the direction
parallel to the light axis AX2 or by adjusting an inclining angle
of the lens group with respect to the plane perpendicular to the
light axis AX2 or by other means. In the contrast, a conventional
system has such an imaging characteristic correction mechanism
disposed approximately right under the reticle R. In this
embodiment, however, no such imaging characteristic correction
mechanism is disposed right under the reticle R and no limitation
is imposed from a mechanical point of view, so that the system
according to the present invention can present the advantage in
that the reticle support table 518 of FIG. 29 can be designed so as
to have a higher degree of rigidity. Moreover, by providing a
minutely movable optical system equivalent to the correction
optical system 549 on the light axis turn section 543 or the second
object section 552, a correction of an aberration (astigmatism,
coma aberration, etc.) of an projection image as well as a
correction of a curvature of an image plane can also be performed.
In addition, a combination of these configuration can further make
it possible to correct an error in a higher-order
magnification.
[0365] Then, the operation of the reflecting light detection system
530 and the self measurement unit 531 in FIG. 29 will be described
with reference to FIGS. 30 and 36.
[0366] First, as shown in FIG. 30, the illumination light IL passed
through the illumination region 515 on the reticle R is irradiated
on the wafer W side through the equal-magnification optical system
composed of the first object section 541 and the light axis turn
section 543, the light axis deflection section 546, and the second
object section 552 (the reduced projection system). In this
construction, if the reference mark member FM is set in place of
the wafer W, the light reflected from the reference mark member FM
is incident to the beam splitter 550 inside the light axis
deflection section 546 through the second object section 552, as
shown in FIG. 30. As the beam splitter 550 has a transmittance of
5%, then the reflected light passed through the beam splitter 550
is detected by means of the reflecting light detection system 530
as shown in FIG. 29. In FIG. 30, however, the reflecting light
detection system 530 is omitted.
[0367] FIG. 36 shows a sectional view along the flat plane
perpendicular to the X-axis passing through the light axis AX3 in
such a state that the reflecting light detection system 530 of FIG.
29 is superimposed on the light axis deflection section 546 of FIG.
30. In FIG. 36, the reflecting light detection system 530 comprises
a first reflecting light detection system 530a and a second
reflecting light detection system 530b. Further, the reference mark
member FM is set in an effective exposure field of the second
object section 552 of the projection optical system PL, and a
reference pattern such as, for example, a slit, pinhole or
otherwise, is formed by means of a light-passing opening in a film
(a metallic film, etc.) having a high rate of reflectance on the
reference mark member FM. By driving the wafer stage 522 of FIG.
29, a desired reference pattern formed on the reference mark member
FM can be transferred to a position in the vicinity of a
predetermined in the effective exposure field.
[0368] After the desired reference pattern has been set in the
vicinity of the predetermined position, the illumination light IL
passed through the reticle R as shown in FIG. 30 is irradiated onto
the reference mark member FM through the projection optical system
PL, and reflected light CL and BL are caused to emit toward the
second object section 552 from a region on the reference mark
member FM nearly symmetrical to each other with respect to the
light axis AX3.
[0369] Then, the reflected light CL is incident to the beam
splitter 550 in the light axis deflection section 546 through the
lenses L52 to L41, inclusive, in the second object section 552, and
the reflected light CL passed through the position C1 on the beam
splitter 550 is then incident to the first reflecting light
detection system 530a after passage through the opening of the
barrel 547. In the first reflecting light detection system 530a,
the reflected light CL is incident to a half mirror 603A through an
eccentric mirror 601A and a first relay lens 602A, and the light
flux reflected at the half mirror 603A is incident to the light
recipient plane of a pupil position photoelectric detector 604A
composed of a photodiode or otherwise. The detection signal of the
pupil position photoelectric detector 604A is supplied to the self
measurement unit 531.
[0370] The pupil position photoelectric detector 604A to be used
herein can function as a sensor for measuring a variation (a
variation in an attenuation factor of light passing through the
projection optical system) in transmittance of the projection
optical system PL by irradiation of illumination light having an
ultraviolet wavelength range.
[0371] In this embodiment, an intermediate image of a reference
pattern is formed in the vicinity of the beam splitter 550 by means
of the reflected light CL, and a Fourier transform pattern of the
intermediate image by the first relay lens 602A is formed on the
light receipt plane of the pupil position photoelectric detector
604A. In other words, the light receipt plane of the pupil position
photoelectric detector 604A comprises a Fourier transform plane (a
pupil plane) with respect to the surface of the reference mark
member FM. At this time, by transferring the reticle R of FIG. 30
relatively to the reference mark FM, the relationship of the
position of the pattern on the reticle R with the position of the
reference pattern on the reference mark FM can be detected by means
of the self measurement unit 531 based on a variation in the
detected signal from the pupil position photoelectric detector
604A.
[0372] On the other hand, the light flux passed through the half
mirror 603A forms an image of the reference mark on a image pickup
plane of an image pick-up element 606A composed of a
two-dimensional CCD and so on through a second relay lens 605A.
More specifically, the image pick-up plane of the image pickup
element 606A is disposed so as to be conjugated with the surface of
the reference mark member FM, and an image pickup signal of the
image pickup element 606A is supplied to the self measurement unit
531. Then, the self measurement unit 531 detects the relationship
of the position of the pattern on the reticle R with the position
of the reference pattern on the basis of the image pick-up signal,
in such a state that the reticle R and the reference mark member FM
are stayed static. Moreover, the first relay lens 602A and the
eccentric mirror 601A are both configured so as to be transferred
to an optional measurement position in a region (an illumination
field) corresponding to the effective exposure field of the second
object section 552. Therefore, the detection signal of the pupil
position photoelectric detector 604A and the image pick-up signal
of the image pickup element 606A at such an optional measurement
position can be incorporated.
[0373] The image pickup element 606A can function as a sensor for
detecting a variation in imaging characteristic (for example,
projection magnification, focal position, and at least one of five
aberrations of Seidel) of the projection optical system on the
basis of the projection optical system PL., which can be varied
upon irradiation of the illumination light having an ultraviolet
wavelength region.
[0374] In addition, in contrast to the first reflecting light
detection system 530a, the second reflecting light detection system
530b is disposed above the position C2 of the beam splitter 550 of
the light axis deflection section 546. The second reflecting light
detection system 530b comprising an eccentric mirror 601B, a first
relay lens 602B, a half mirror 603B, a pupil position photoelectric
detector 604B, a second relay lens 605B and an image pickup element
606B. The second reflecting light detection system 530b is further
configured so as to receive reflected light BL on the reference
mark member FM, which is reflected in a manner nearly symmetrical
to the reflected light CL. In an actual case, the first relay lens
602B and the eccentric mirror 601B of the second reflecting light
detection system 530b is disposed so as to move individually from
the first reflecting light detection system 530a, and the
measurement can be effected at two optional positions in the
illumination field corresponding to the effective exposure field of
the second object section 552.
[0375] Upon effecting an actual measurement, if the reticle R would
be of a type of passing light thoroughly, only the reflected light
around a reference pattern (an opening pattern) of the reference
mark member FM can be detected in the reflecting light detection
systems 530a and 530b through the second object section 552 and the
beam splitter 550, respectively, so that a distribution of the
light quantity on the reference pattern can be measured.
[0376] Moreover, in the case where a predetermined pattern is
formed on the reticle R, the light quantity returning to the
reflecting light detection systems 530a and 530b can be determined
by superimposing a projection image of the pattern on the reference
mark member FM over the reference pattern. Therefore, by receiving
the reflected light passed through the beam splitter 550 by means
of the reflecting light detection systems 530a and 530b, the
relationship of the position of the pattern on the reticle R with
the position of the pattern on the reference mark member FM can be
investigated.
[0377] The self measurement unit 531 can perform various operations
by processing the detection signals and the image pick-up signals
from the reflecting light detection systems 530a and 530b, the
operations including, for instance, aligning the reticle R with the
reference mark member FM, checking imaging characteristics of the
projection optical system PL on the reference mark member FM,
monitoring a reflectance of the wafer W on the basis of the
reflection amount on the reference mark member FM, detecting an
irregularity of illuminance within the exposure region 516 on the
wafer W, and so on.
[0378] In contrast thereto, conventional techniques include a
measurement of imaging characteristics or other operations in a
system where an irradiation system or a light receipt system is
disposed, for example, inside of the sample table 521, as shown in
FIG. 29, so that the structure inside the sample table 521 and on
the projection optical system thereof are made complicated. In this
embodiment, however, the corresponding structure can be simplified,
thereby leading to making the sample table 521 light in weight,
enabling a prevention of generating heat due to irradiation of the
illumination light, and so on. In addition, although a detection
system for detecting reflectance of a wafer by receiving the light
reflected from the wafer on the reticle R is used for conventional
systems, this embodiment can simplify mechanisms on the reticle
R.
[0379] As the detected signals from the reflecting light detection
systems 530a and 530b are input to the main control unit 507 during
scanning exposure, the main control unit 507 can detect illuminance
of the illumination light IL on the wafer W. Moreover, the main
control unit 507 outputs an instruction signal to exposure control
unit 501 on the basis of the illuminance detected, and adjusts the
intensity of the illumination light IL emitting from the excimer
laser light source 502. This allows a correction of a variation in
illuminance on the wafer W, which may occur attendant upon a
variation in transmittance of the projection optical system PL by
the irradiation of the illumination light IL.
[0380] It is to be noted herein that, in place of adjustment of the
intensity of the illumination light IL emitting from the excimer
laser light source 502, it can also be arranged, for instance, to
vary a latitudinal width of the fixed blind of the irradiation
vision field stop system 511, i.e., a width in the scanning
direction of the exposure region 516 of the projection optical
system PL, or to vary a frequency of pulse oscillation of the
excimer laser light source 502 or a velocity at which to scan the
wafer W during the scanning exposure. In summary, it can be
sufficient to adjust at least one of the intensity of the
illumination light IL, the width in the scanning direction of the
exposure region 516, the frequency for pulse oscillation, and the
scanning velocity of the wafer W. In addition, by varying a shape
of the fixed blind of the illumination vision field stop system
511, the main control unit 507 can correct irregularities of
illuminance on the wafer W, which may occur due to a variation in
transmittance of the projection optical system PL by irradiation of
the illumination light IL, on the basis of the detection signals
detected by the reflecting light detection systems 530a and
530b.
[0381] Moreover, the main control unit 507 can detect a variation
in imaging characteristic which may be caused by a variation in
transmittance of the projection optical system PL, on the basis of
the detection signals detected by the reflecting light detection
systems 530a and 530b. Furthermore, the main control unit 507 can
correct the imaging characteristic of the projection optical system
PL by controlling the imaging characteristic correction unit 551 on
the basis of the detected imaging characteristic. The imaging
characteristic referred to herein is intended to mean at least one
of an error in magnification, distortion, a focal position,
astigmatism, a coma aberration, a curvature in an image plane, and
a spherical aberration. Further, it can adjust a deviation of the
focal position and inclination of an image plane by transferring
the wafer W by means of the focus-tilt control unit 527.
[0382] In addition, in conventional cases, the detection light for
measuring an imaging characteristic or the like is different from
the exposing illumination light, so that there is the risk that the
imaging characteristics, etc. to be measured by the detection light
differ from the imaging characteristics to be measured under the
exposing illumination light due to disagreement of a number of
openings for the detection light (eventually a .sigma. value which
is a coherence factor) with a number (a .sigma. value) of openings
for the exposing illumination light. Moreover, conventional systems
have the problems, for example, that may arise with a lack of the
number of openings for the light receipt system for measuring such
imaging characteristics and so on. On the other hand, in the
embodiments of the present invention, the exposing illumination
light IL is used, as it is, as a detecting light, so that the first
and second reflecting light detection systems 530a and 530b can be
disposed with a margin so that the number of openings can be
increased to a sufficient number, thereby allowing measurement for
imaging characteristics and so on with high precision.
[0383] Then, a description will be made of the relationship between
the positions of the illumination region 515 on the reticle R and
the exposure region 516 on the wafer W as shown in FIG. 30, with
reference to FIG. 31.
[0384] FIG. 31(a) shows the illumination region 515 on the reticle
R as shown in FIG. 30. In FIG. 31(a), it is shown that an
illumination region 515 in a rectangular form elongated in the
X-direction is disposed at a position deviated slightly in the
-Y-direction with respect to the light axis AX1 in a circular
effective illumination vision field 541a of the first object
section 541 of the projection optical system PL as shown in FIG.
30. The direction parallel to the short side of the illumination
region 515 (a Y-direction) is the scanning direction in which the
reticle R is being scanned. As shown in FIG. 30, in the
equal-magnification optical system composed of the first object
section 541 and the light axis turn section 543, the imaging light
flux passed through the illumination region 515 of the reticle R is
led up to the small-sized mirror 548 after having been turned by
the concave mirror 545, so that it is required to deflect the
illumination region 515 with respect to the light axis AX1.
[0385] On the other hand, FIG. 31(b) shows the exposure region 516
on the wafer W (a region being conjugated with the illumination
region 515), as shown in FIG. 30. As shown in FIG. 31(b), the
exposure region 516 in a rectangular form elongated in the
X-direction at a position deviated slightly in the +Y-direction
with respect to the light axis AX3 in a circular effective exposure
field 552a of the second object section 552 of the projection
optical system PL as shown in FIG. 30.
[0386] Further, FIG. 31(c) shows the illumination region 515 in a
rectangular form at a position deviated slightly in the
-Y-direction with respect to the light axis AX1 in the circular
effective irradiation vision field 541a in the same shape as in
FIG. 31(a). Further, FIG. 31(d) shows an effective exposure field
552aA of a second object section that is modified from the second
object section 552 of FIG. 30, in which an exposure region 516A (a
region being conjugated with the illumination region 515 as shown
in FIG. 31(c)) in a rectangular form elongated in the X-direction
with a light axis AX3A of the effective exposure field 552aA
centered round the region. More specifically, the exposure region
516A on the wafer W can be set to be in a region with the light
axis-of the effective exposure field 552aA centered round the
region by altering the construction of the second object section
552 (the reduced projection system) in the final stage of the
projection optical system PL, as shown in FIG. 31(d). FIGS. 31(b)
and 31(d) can be selected by easiness of designing for removal of
an aberration of the projection optical system PL. FIG. 31(b) has
the advantage over FIG. 31(d) in that the designing can be made
easier, while FIG. 31(d) has the advantage over FIG. 31(b) in that
a lens dimension of the second object section (the reduced
projection system) can be made slightly smaller.
[0387] Then, a detailed description will be made of the
configuration of the alignment sensor 528 of an off-axis type in
FIG. 29 with reference to FIG. 32.
[0388] FIG. 32 shows a figure of the projection optical system PL
as shown in FIG. 30. As shown in FIG. 32, the projection optical
system PL is divided into the first object section 541, the light
axis deflection section 546, the light axis turn section 543 and
the second object section 552, which are required to be designed so
as not to be distorted due to outside disturbances such as
vibration, heat, and so on. At this end, a high degree of rigidity
is required for the column 525 with the flanges 544a and 553a
mounted thereon, particularly for a portion 525a of the column 525
interposed between the light axis turn section 543 and the second
object section 552. In order to ensure such a high degree of
rigidity, the alignment sensor 528 for detecting the position of a
wafer mark WM as an alignment mark on the wafer W is required to be
disposed on the side surface portion of the second object section
552 and on the side opposite to the portion 525a that requires such
high rigidity, i.e., on the side surface portion in the
+Y-direction of the wafer stage 522. Further, a portion 525b in the
column 525, which is located facing the +Y-directional side surface
portion of the second object section 552 and the +X-directional and
-X-directional side surface portions thereof becomes thinner by a
half or less with respect to the portion 525a having higher
rigidity, so that the alignment sensor 528 is disposed on the
bottom portion of the thinner portion 525b. This disposition allows
the first object section 541, the light axis deflection section
546, the light axis turn section 543 and the second object section
552 to be supported as an integral projection optical system PL,
even when the reticle R and the wafer W are scanned in the
direction indicated by arrow by scanning at the time of the
scanning exposure, thereby achieving a high degree of rigidity for
the projection optical system PL as a whole.
[0389] In the alignment sensor 528 of an off-axis type as shown in
FIG. 32, a broad-band (white) alignment light AL emitting from a
halogen lamp or the like, although not shown, and having a weak
photosensitivity to a photoresist on the wafer W, is led to the
inside of a barrel 561 of the alignment sensor 528 through an
optical guide 562. Inside the barrel 561, the alignment light AL
passes through a condenser lens 563 and then through a half mirror
564, and illuminates an observation vision field in a predetermined
scope containing the wafer mark WM on the wafer W through a first
object lens 565 and a prism-type eccentric mirror 566. The
reflecting light from the wafer mark WM is reflected by means of
the half mirror 564 through the eccentric mirror 566 and the first
object lens 565, thereby allowing a second object lens 567 to form
an image of the wafer mark WM on an indicator plate 568.
[0390] The light flux passed through the indicator plate 568 then
passes through a first relay lens 569, an eccentric mirror 570 and
a second relay lens 571 and again forms images of the wafer mark WM
and an indicator mark on an image pickup element 572 composed of a
two-dimensional CCD. The wafer mark WM so formed is a mark in the
form of, for example, a concave and convex Y-axial lattice arranged
at a predetermined pitch in the Y-direction, and the image pick-up
signals of the image pickup element 572 are supplied to an
alignment signal processing system 529 as shown in FIG. 29. The
alignment signal processing system 529 computes an amount of
deviation of the position of the wafer mark WM in the Y-direction
with respect to the indicator mark on the indicator plate 568, on
the basis of the image pick-up signals, and computes the
Y-coordinate in the stage coordinates system (X, Y) of the wafer
mark WM by adding a Y-coordinate measured by the laser
interferometer 524 of FIG. 29 to the amount of deviation of the
position, followed by supplying the Y-coordinate to the main
control unit 507. An X-axial wafer mark in a form in which the
wafer mark WM is rotated at 90.degree. is also provided in the
corresponding shot region on the wafer W, and the X-coordinate in
the stage coordinates system (X, Y) of the X-axial wafer mark can
be detected by means of the alignment sensor 528. The alignment of
the wafer W can be performed by detecting the coordinates of the
wafer mark provided in the predetermined shot region on the wafer W
by means of the alignment sensor 528 in the manner as described
above.
[0391] Further, in order to allow a measurement by the alignment
sensor 528 with high precision, it is preferred to make a distance
(a baseline amount) between the detection center (a center of the
projection image of the indicator mark on the wafer W) of the
alignment sensor 528 and the exposure center (a center of the
exposure region 516) of the projection optical system PL as small
as possible. At this end, the alignment sensor 528 is disposed to a
position as close as possible to the second object section 552 of
the projection optical system PL.
[0392] In addition to the alignment sensor 528 of an off-axis type,
the multipoint AF sensor 526 of FIG. 29 for detecting the focus
position and the inclination angle of the surface of the wafer W
should also be disposed at a position approaching to the closest
position to the second object section 552. Therefore, in this
embodiment, in order to prevent a mechanical interference between
the alignment sensor 528 and the AF sensor 526, the AF sensor 526
is disposed on the X-directional side surface portion of the second
object section 552 in a manner of intersecting with the alignment
sensor 528 at a right angle.
[0393] FIG. 33 shows the state in which the AF sensor 526 is
disposed. FIG. 33 shows the AF sensor 526 of FIG. 32 in section in
which the sectional plane passes through the light axis AX3 of the
second object section 552 and extends along the flat plane (an XZ
flat plane) perpendicular to the Y-axis. An upper half of FIG. 33
indicates a left-hand side view of the reticle R and the first
object section 541 as shown in FIG. 32, for brevity of explanation.
In FIG. 33, the AF sensor 526 is divided into two systems, one
being an illumination optical system 526a and a condensing optical
system 526b. The illumination optical system 526a and the
condensing optical system 526b are disposed on the side surface
portions in the -X-direction and the +X-direction of the second
object section 552, respectively, and on the bottom portion of the
thinner portion 525b of the column 525 of FIG. 32 thinner than the
portion 525a having a higher rigidity.
[0394] First, in the illumination optical system 526a in this
configuration, illumination light from a halogen lamp or otherwise,
although not shown, which is low in photosensitivity and nearly
white in color, is led to the side surface portion of the second
object section 552 through an optical guide 581, and then the
illumination light illuminates a multi-slit plate 584 through a
mirror 582 and a condenser lens 583, the multi-slit plate 584
having a plurality of slit-shaped openings arranged in a given
sequence. The illumination light passed through each of the
slit-shaped openings of the multi-slit plate 584 projects a
plurality of slit images (only one slit image 588 being indicated
as a representative in FIG. 33) that are conjugated images of the
plural slit-shaped openings onto the wafer W in a direction oblique
to the light axis AX3 through a lens 585, a vibration mirror 586
and a lens 587. The region onto which these slit images are
projected is a look-ahead region located in the rectangular
exposure region 516 on the wafer W as shown in FIG. 29 and on this
side in the scanning direction with respect to the exposure region
516.
[0395] The reflected light from the plural slit images on the wafer
W are incident to the condensing optical system 526b. In the
condensing optical system 526b, the reflected light passes through
the lens 589, the mirror 590 and the lens 591 and again forms
plural slit images (588, etc.) on a multi-slit plate 592 with
slit-shaped openings corresponding to the multi-slit plate 584
formed therein. Further, on the back surface of the multi-slit
plate 592, there is disposed a photoelectric detector 593 on which
photoelectric conversion elements such as, for example,
photodiodes, etc., for individually receiving the reflected light
passed through each of the slit-shaped openings of the multi-slit
plate 592, and a photoelectric conversion signal (hereinafter
referred to as "a focus signal") from each of the photoelectric
conversion elements of the photoelectric detector 593 is supplied
to the focus-tilt control unit 527.
[0396] In this case, when the slit image formed again on the
multi-slit plate 592 is vibrated in the latitudinal direction on
the corresponding slit-shaped opening, due to the vibration of the
vibration mirror 586, and the focus position (the position in the
Z-direction) on the surface of the wafer W fluctuates, the center
of vibration of the slit image and the center of the slit-shaped
opening corresponding thereto are caused to slide in a transverse
direction. Therefore, a signal corresponding to the amount of a
fluctuation of the focus position at the projection position of
each slit image (588, etc.) on the wafer W can be obtained by
shaping the focus signal that is a photoelectric conversion signal
of the reflected light passed through each of the slit-shaped
openings in synchronization with the drive signal of the vibration
mirror 586 in the focus-tilt control unit 527. Moreover, the AF
sensor 526 is calibrated in advance so as for the synchronization
shaping signals of the focus signals to become zero, when the
surface of the wafer W agrees with the imaging surface of the
projection optical system PL. Therefore, the focus-tilt control
unit 527 can give an average value and an inclination angle of the
focus positions in the exposure region 516 on the wafer W and a
look-ahead region corresponding thereto from the synchronization
shaping signals. The information on the average value and the
inclination angle is supplied to the stage control unit 513 through
the main control unit 507 at a nearly real time, and the stage
control unit 513 performs auto-focusing and auto-leveling so as to
bring the exposure region 516 on the wafer W into agreement with
the imaging plane of the projection optical system PL during the
scanning exposure in the manner as described above.
[0397] Then, in FIG. 29, the laser interferometers and the moving
mirrors disposed actually in a two-dimensional way are represented
herein each as a laser interferometer 524 and a moving mirror 524m,
respectively. Therefore, an example of a specific disposition of
the laser interferometers and the moving mirrors on the wafer side
in this embodiment will be described with reference to FIGS. 34 and
35.
[0398] FIG. 34 is a plan view showing the sample table 521 of FIG.
29 with the wafer W loaded thereon. In FIG. 34, an outer shape of
the second object section 552 of the projection optical system PL
as shown in FIG. 30 and the observation vision field 528a of the
alignment sensor 528 of FIG. 32 as well as the outer shapes of the
first object section 541 and the light axis turn section 543 and
the reticle R are illustrated in an accurate position relationship.
Further, FIG. 34 shows the state in which the light axis AX3 of the
second object section 552 is located on the reference mark member
FM on the sample table 521.
[0399] In this embodiment, as shown in FIG. 30, the column 525
between the first object section 541 and the light axis turn
section 543 of the projection optical system PL, and the second
object section 552 is of a secure structure in order to increase
rigidity, so that it is difficult to locate the laser
interferometer between them. Further, there is no space wide enough
to effect air conditioning by means of downflowing along the light
axis of the laser interferometer, even if the laser interferometer
could be interposed between them, so that the system has to be
configured such that the structure of the laser interferometer
becomes likely to undergo influences from fluctuation of air.
[0400] In order to avoid influences from fluctuation of air, in
this embodiment, as shown in FIG. 34, the laser interferometers are
disposed on the side opposite to the light axis turn section 543
with respect to the second object section 552 of the projection
optical system PL, i.e., in the +Y-direction and -X-direction with
respect to the second object section 552. In FIG. 34, a moving
mirror 524mY having a reflecting plane perpendicular to the Y-axis
is fixed to the side surface portion in the +Y-direction of the
sample table 521, and a moving mirror 524mX having a reflecting
plane (perpendicular to the X-axis) intersecting at a right angle
with the reflecting plane of the moving mirror 524mY is fixed to
the side surface portion in the -X-direction of the sample table
521. Moreover, the X-axis laser interferometer 524Y is disposed so
as to face the Y-axis moving mirror 524mY, and tri-axial laser
beams are irradiated from the laser interferometer 524 onto the
moving mirror 524mY in a direction parallel to the Y-axis. FIG. 34
shows the biaxial laser beams LBY1 and LBY2, among the tri-axial
laser beams, arranged at a predetermined interval in the
X-direction, the biaxial laser beams LBY1 and LBY2 being disposed
so as to pass through the light axis AX3 of the second object
section 552 and the center of the observation vision field 528a of
the alignment sensor 528 and then through the positions symmetrical
to the straight line parallel to the Y-axis.
[0401] Further, FIG. 35(a) is a side view of the sample table 521
of FIG. 34, when looked in the +X-direction. As shown in FIG.
35(a), the third-axial laser beams LBY3 are irradiated at a
predetermined Z-directional interval with respect to the bi-axial
laser beams LBY1 and LBY2 on the moving mirror 524mY in a direction
parallel to the Y-axis from the laser interferometer 524Y. As shown
in FIG. 35(b), the laser beams LBY3 passes through an intermediate
position in the X-direction between the biaxial laser beams LBY1
and LBY2. Then, at the laser interferometer 524Y, the Y-coordinates
Y1, Y2 and Y3 of the tri-axial laser beams LBY1, LBY2 and LBY3,
respectively, are always detected at a resolution of approximately
0.001 .mu.m and output to the stage control unit 513. The stage
control unit 513 gives, for example, an average value of the
Y-coordinates Y1 and Y2 and a difference between the such two
Y-coordinates as the Y-coordinate of the sample table 521 and the
yawing angle, respectively. Upon measuring the yawing angle, a
correction for a curvature of the moving mirror 524mY is also
effected.
[0402] Moreover, in FIG. 34, the X-axial laser interferometer 524X
is disposed so as to face the X-axially moving mirror 524mX, and
tri-axial laser beams are irradiated onto the moving mirror 524mX
in a direction parallel to the X-axis from the laser interferometer
524X. FIG. 34 shows bi-axial laser beams LBX1 and LBX2 arranged at
a predetermined Y-directional interval, out of the tri-axial laser
beams, and those laser beams LBX1 and LBX2 pass along the light
axis AX3 of the second object section 552 through a light path
parallel to the X-axis and on the center of the observation vision
field 528a of the alignment sensor 528 through a light path
parallel to the X-axis, respectively.
[0403] In addition, like FIGS. 35(a) and 35(b), the tri-axial laser
beams are irradiated at a predetermined interval in the Z-direction
with respect to the bi-axial laser beams LBX1 and LBX2 onto the
moving mirror 524mX in a direction parallel to the X-axis from the
laser interferometer 524X. Then, the laser interferometer 524X
always detects the X-coordinates X1 and X2 corresponding to the
bi-axial laser beams LBX1 and LBX2 and the X-coordinate X3
corresponding to the remaining mono-axial laser beams at a
resolution of approximately 0.001 .mu.m and outputs those
coordinates to the stage control unit 513. Further, the stage
control unit 513 sets the X-coordinate X1 corresponding to the
light axis AX3 as the X-coordinate of the sample table 521 upon
exposure to the wafer W, on the one hand, and the X-coordinate X2
corresponding to the center of the observation vision field 528a as
the X-coordinate of the sample table 521 upon alignment, on the
other. This allows a so-called Abbe's error resulting from a
deviation of the position between the position of a measuring
object and the measuring axis to become substantially zero each
upon exposure and upon alignment, so that the position can be
detected with high precision. In addition, like the Y-axial moving
mirror 524mY, a correction of a curvature of the moving mirror
524mX can also be performed on the basis of the two X-coordinates
X1 and X2.
[0404] As a result, in this embodiment, as shown in FIG. 34, the
laser interferometers 524Y and 524X are disposed in the
+Y-direction and -X-direction, respectively, with respect to the
sample table 521 and the projection optical system PL composed of
the light axis turn section 543, the second object section 552 and
so on is also disposed along the -Y-direction with respect to the
sample table 521. This configuration allows a space on the side in
+X-direction (in the direction symmetrical to the laser
interferometer 524X) with respect to the sample table 521 to be
utilized. Therefore, in this embodiment, a wafer conveyance system
containing a wafer loader WL for loading wafers on or unloading
them from the sample table 521, or the like, is disposed on the
side in the +X-direction with respect to the sample table 521.
[0405] This configuration allows air conditioning as downflowing
onto the light path of laser beams from the laser interferometers
524X and 524Y. More specifically, air or the like having a uniform
distribution of temperature and velocity, are blown from above, for
example, the laser beams LBY1, LBY2, LBX1, and LBX2, onto a floor
surface on which the projection exposure apparatus is disposed, and
then is recovered at the floor surface, thereby performing air
conditioning by downflowing. This air conditioning provides the
advantages that influences from fluctuation of air in the light
path of laser beams upon the laser interferometers 524X and 524Y
can be reduced, and precision for measuring, for example, the
position of the sample table 521 and the yawing angle thereof can
be improved.
[0406] Turning again to FIG. 35(a), the sample table 521 may be
made of ceramics, and the moving mirror 524mY (the moving mirror
534mX, too) may be made of ceramics equal to the material for the
sample table 521. The moving mirror 524mY is fixed to the side
surface of the sample table 521 through a fixing screw, although
not shown. On the other hand, the wafer W is held on the sample
table 521 through the wafer holder 520, so that the position of the
wafer W is deviated in the Z-direction with respect to the
positions of the light axes of the laser beams LBY1 and LBY2 from
the respective laser interferometer 524Y. If problems such as
pitching or otherwise would occur in the sample table 521 due to
this deviation, the positional deviation is caused to due to the
so-called Abbe's error by an amount .DELTA.Y between the
Y-coordinate measured by the laser interferometer 524Y and the
actual Y-coordinate of the sample table 521 (more precisely, the
wafer W). Therefore, in this embodiment, an inclination angle
.DELTA..theta. around the X-axis of the sample table 521 is
computed from a difference between an average value (Y1+Y2)/2 of
the Y-coordinates Y1 and Y2 to be measured by the laser beams LBY1
and LBY2 and the Y-coordinate Y3 to be measured by the laser beams
LBY3 passing through the position deviated in the Z-direction with
respect to the laser beams LBY1 and LBY2, respectively. Then, the
Abbe's error resulting from the difference between the height of
the wafer W and the height of the laser beams LBY1 and LBY2 is
corrected by correcting the average value of the Y-coordinates to
be measured by the laser beams LBY1 and LBY2 on the basis of the
inclination angle .DELTA..theta..
[0407] Likewise, for the X-axial laser interferometer 524X, the
Abbe's error contained in the measured values by the laser beams
LBX1 and LBX2 is corrected by using the measured value of the
third-axial laser beams.
[0408] By adopting the way of mounting the moving mirrors 524mY and
524mX on the side surfaces of the sample table 521, the space above
the moving mirrors 524mY and 524mX can be effectively utilized, for
instance, for locating an end portion of the wafer holder 520
therein, and so on. As a consequence, the entire size of the sample
table 521 can be reduced and the entire weight thereof can be made
lighter, so that performance for controlling the apparatus can be
improved at the time of the scanning and aligning the wafer W.
[0409] Moreover, in usual cases, complicated processing for ceramic
material requires a long time so that costs for manufacturing
become very expensive. Therefore, in this embodiment, although the
moving mirrors 524mY and 524mX as well as the sample table 521,
each requiring a high precision on the plane, are made of the same
ceramic material and each is manufactured separately, followed by
uniting those parts together. This can simplify the shape of the
individual part and consequently reduces costs for manufacturing
those parts as a whole. Further, in the case where a management of
temperature is rendered difficult, a material having a small
expansion coefficient, such as ZERODURE, etc., yet lower in
rigidity, may also be used as substitute for ceramics.
[0410] Although the alignment sensor 528 of an off-axis type as
used in the modes of the embodiments as described above is of an
image pickup type (FIA type), alignment sensors of other types may
also be adopted, which type includes a laser step alignment (LSA)
type for relatively scanning slit-shaped laser beams and a wafer
mark arranged in dot line or a two-light flux interference type
(LIA type) adapted so as to detect the position on basis of a phase
of interference light composed of a pair of diffraction light
generating in the identical direction from the wafer mark by
irradiating two coherent light fluxes onto the wafer mark in the
form of a diffraction grating. Further, in the modes of the
embodiments as described above, imaging characteristics are
corrected by driving the optical system in the projection optical
system PL, however, instead of the such correction, the imaging
characteristics can be corrected by using a variable mechanism for
pressure of gases present among the given lenses within the
projection optical system PL or a variable temperature
mechanism.
[0411] Further, in the modes of the embodiments as described above,
the illumination region 515 on the reticle R is fomed of a
rectangular shape, however, it is not restricted to such a
rectangular shape, and it may be of an arc-shaped shape or any
appropriate shape. As in the modes of the embodiments as described
above, however, in the case where the illumination region 515 is of
a rectangular shape that is nearly in contact with the effective
illumination vision field, the pattern region of the reticle R has
to be of a rectangle shape, too, so that this configuration can
provide the advantage that the length of scanning the reticle R can
be shortened.
[0412] Moreover, in the modes of the embodiments as described
above, the scanning type projection exposure apparatus is used. It
should be noted, however, that a projection exposure apparatus of a
type (a so-called stepper) for exposing the reticle and the wafer
in a state they are stayed still. Furthermore, the projection
optical system PL is not restricted to a reflection-refraction type
and may include an optical system of a refraction type or of a
reflection type.
[0413] As described above, it should be understood that the present
invention is not restricted to the modes of the embodiments as
illustrated above and encompasses any modifications and variations
not departing from the scope and spirit of the present
invention.
* * * * *