U.S. patent application number 09/781993 was filed with the patent office on 2001-09-06 for exposure apparatus.
This patent application is currently assigned to Nikon Corporation. Invention is credited to Hagiwara, Shigeru, Hamatani, Masato.
Application Number | 20010019400 09/781993 |
Document ID | / |
Family ID | 13573853 |
Filed Date | 2001-09-06 |
United States Patent
Application |
20010019400 |
Kind Code |
A1 |
Hagiwara, Shigeru ; et
al. |
September 6, 2001 |
Exposure apparatus
Abstract
In the exposure apparatus of the present invention, a sealed
chamber defined by a first lens and a second lens in an input lens
system on a plane of incidence of a fly-eye lens in an illumination
optical system is provided. In a gas exchanging step, the impurity
gas in the sealed chamber is first exhausted through an
electromagnetic valve provided with a check valve and a gas exhaust
pipe, using a gas exhaust pump and then, a high-purity nitrogen gas
is supplied from a gas bomb through a gas supply pipe and an
electromagnetic valve provided with a check valve to the sealed
chamber. Using a pressure sensor provided in the sealed chamber,
the gas exchanging step is repeated while maintaining an amount of
change in pressure in the sealed chamber within a predetermined
allowable range, to thereby reduce the concentration of impurities
in the gas in the sealed chamber to a target value.
Inventors: |
Hagiwara, Shigeru; (Tokyo,
JP) ; Hamatani, Masato; (Saitama-ken, JP) |
Correspondence
Address: |
ARMSTRONG,WESTERMAN, HATTORI,
MCLELAND & NAUGHTON, LLP
1725 K STREET, NW, SUITE 1000
WASHINGTON
DC
20006
US
|
Assignee: |
Nikon Corporation
Tokyo
JP
|
Family ID: |
13573853 |
Appl. No.: |
09/781993 |
Filed: |
February 14, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09781993 |
Feb 14, 2001 |
|
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09047478 |
Mar 25, 1998 |
|
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6222610 |
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Current U.S.
Class: |
355/30 ; 355/53;
355/55; 355/67; 355/77 |
Current CPC
Class: |
G03F 7/70858 20130101;
G03F 7/70933 20130101; G03F 7/70883 20130101; G03F 7/70891
20130101 |
Class at
Publication: |
355/30 ; 355/53;
355/55; 355/67; 355/77 |
International
Class: |
G03B 027/52 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 27, 1997 |
JP |
75355/1997 |
Claims
What is claimed is:
1. An exposure apparatus for illuminating a pattern on a mask with
exposure light passing through an illumination optical system, to
thereby transfer said pattern on the mask to a substrate,
comprising: a sealed chamber provided in an optical path of said
exposure light in said illumination optical system, said sealed
chamber containing a gas and shielded from a gas surrounding said
sealed chamber in said illumination optical system; and a gas
exchanging device adapted to exchange the gas in said sealed
chamber with a predetermined gas.
2. The exposure apparatus according to claim 1, wherein said gas
exchanging device comprises: a gas exhausting system adapted to
exhaust the gas in said sealed chamber; a gas supplying system
adapted to supply the predetermined gas to said sealed chamber; a
pressure sensor provided in said sealed chamber to detect a
pressure in said sealed chamber; and a control system adapted to
control an operation of each of said gas exhausting system and said
gas supplying system, based on said pressure in the sealed chamber
detected by said pressure sensor, to thereby exchange the gas in
said sealed chamber with the predetermined gas.
3. The exposure apparatus according to claim 2, wherein when the
gas in said sealed chamber is exchanged with the predetermined gas,
said control system enables said gas exhausting system to exhaust
the gas in said sealed chamber and said gas supplying system to
supply the predetermined gas to said sealed chamber, while
maintaining an amount of change in said pressure in the sealed
chamber detected by said pressure sensor within a predetermined
allowable range.
4. The exposure apparatus according to claim 1, wherein said
illumination optical system comprises: a light source adapted to
emit exposure light; a shaping optical system adapted to shape said
exposure light passing therethrough; and an optical integrator
adapted to enable said exposure light to have a uniform illuminance
distribution after passing through said shaping optical system, and
said sealed chamber is defined by two optical members constituting
said shaping optical system.
5. The exposure apparatus according to claim 1, wherein an inert
gas is contained in said sealed chamber.
6. The exposure apparatus according to claim 1, wherein said sealed
chamber is provided at a position at which said exposure light
exhibits high illuminance.
7. The exposure apparatus according to claim 1, wherein said
illumination optical system includes an input lens system and said
sealed chamber is provided in said input lens system.
8. The exposure apparatus according to claim 1, further comprising
a device adapted to maintain a temperature of the gas in said
sealed chamber at a predetermined level.
9. The exposure apparatus according to claim 1, wherein the gas in
said sealed chamber is exchanged periodically during idling of said
exposure apparatus.
10. The exposure apparatus according to claim 1, wherein the gas in
said sealed chamber is exchanged during assembly and adjustment of
said exposure apparatus.
11. A method for conducting an exchange of gases in a sealed
chamber provided in an exposure apparatus, comprising a gas
exchanging step including: a first sub-step of exhausting a gas in
said sealed chamber from a gas exhaust side thereof, while said
sealed chamber is closed on a gas supply side thereof; and a second
sub-step of supplying an inert gas to said sealed chamber from the
gas supply side thereof, while said sealed chamber is closed on the
gas exhaust side thereof, wherein each of said first sub-step and
said second sub-step is conducted in a substantially stationary
state with respect to a pressure of the gas in said sealed
chamber.
12. The method according to claim 11, wherein said exchange of
gases in said sealed chamber is conducted periodically during
idling of said exposure apparatus.
13. The method according to claim 11, wherein said exchange of
gases in said sealed chamber is conducted during assembly and
adjustment of said exposure apparatus.
14. The method according to claim 11, wherein in said first
sub-step, a part of the gas in said sealed chamber is exhausted
from the gas exhaust side of said sealed chamber and said gas
exchanging step is conducted at least twice, and said method
further comprises a step of measuring a total gas exchange time by
counting the number of times said gas exchanging step is
conducted.
15. The method according to claim 14, wherein said exchange of
gases is conducted periodically during idling of said exposure
apparatus and said method further comprises the steps of: measuring
an idling time of said exposure apparatus; and comparing said
idling time with said total gas exchange time, and when said total
gas exchange time exceeds said idling time, a time for conducting
said gas exchanging step at one time is reduced.
16. An exposure apparatus comprising: an illumination optical
system adapted to emit exposure light, said exposure light being
adapted to illuminate a mask pattern to thereby transfer said mask
pattern to a substrate; a sealed chamber provided in said
illumination optical system; and a gas exchanging device adapted to
exhaust a gas in said sealed chamber and supply an inert gas to
said sealed chamber.
17. The exposure apparatus according to claim 16, wherein said
illumination optical system includes an input lens system, said
input lens system having at least one pair of lenses, and said
sealed chamber is defined by said at least one pair of lenses.
18. The exposure apparatus according to claim 17, wherein said gas
exchanging device comprises: a gas exhausting system adapted to
exhaust an impurity gas in said sealed chamber; a gas supplying
system adapted to supply an inert gas to said sealed chamber; and a
control system adapted to control said gas exhausting system and
said gas supplying system so that a change in pressure in said
sealed chamber is within a predetermined range.
19. The exposure apparatus according to claim 18, wherein said gas
exhausting system includes: a gas exhaust pipe adapted to exhaust
said impurity gas from said sealed chamber; an electromagnetic
valve provided in said gas exhaust pipe to open and close said gas
exhaust pipe, said electromagnetic valve being provided with a
check valve; and a gas exhaust pump connected to a gas exhaust side
of said electromagnetic valve in the gas exhaust pipe, wherein said
gas supplying system includes: a gas supply pipe adapted to supply
said inert gas to said sealed chamber; an electromagnetic valve
provided in said gas supply pipe to open and close said gas supply
pipe, said electromagnetic valve being provided with a check valve;
and a gas bomb connected to a gas supply side of said
electromagnetic valve in the gas supply pipe, and wherein said
control system is adapted to control said electromagnetic valve in
the gas exhaust pipe and said electromagnetic valve in the gas
supply pipe.
20. A projection exposure apparatus for transferring a pattern on a
mask to a photosensitive substrate, comprising: a light source
adapted to emit exposure light having a wavelength range in which a
photosensitive substrate is sensitive to said exposure light; an
illumination optical system provided between said light source and
said mask; a projection optical system provided between said mask
and said photosensitive substrate; a sealed chamber containing a
gas and provided in an optical path of said exposure light between
said light source and said photosensitive substrate; and a gas
circulating device connected to said sealed chamber, said gas
circulating device being adapted to exhaust the gas contained in
said sealed chamber to an outside thereof, to thereby compensate
for variations in intensity of said exposure light on said
photosensitive substrate.
21. The apparatus according to claim 20, wherein said sealed
chamber is defined by at least two optical members provided in said
illumination optical system.
22. The apparatus according to claim 20, wherein said gas
circulating device is adapted to supply nitrogen or helium to said
sealed chamber.
23. A projection exposure apparatus for transferring a pattern on a
mask to a photosensitive substrate, comprising: a light source
adapted to emit exposure light having a wavelength range in which a
photosensitive substrate is sensitive to said exposure light; a
sealed chamber provided in an optical path of said exposure light
between said light source and said photosensitive substrate; and a
gas circulating device having a sensor and connected to said sealed
chamber, said sensor being adapted to detect and output information
corresponding to a pressure in said sealed chamber, and said gas
circulating device being adapted to supply an inert gas to said
sealed chamber in accordance with the information outputted from
said sensor.
24. A method for transferring a pattern on a mask to a
photosensitive substrate, comprising the steps of: illuminating
said mask with exposure light, to thereby transfer said pattern on
the mask to a photosensitive substrate; and exchanging an inert gas
contained in a sealed chamber with another gas, said sealed chamber
being provided in an optical path of said exposure light, to
thereby compensate for variations in light transmittance and light
reflectance of an optical member provided in said optical path of
the exposure light.
25. An exposure apparatus for transferring a pattern on a mask to a
photosensitive substrate, comprising: an optical system adapted to
allow exposure light to enter, said exposure light being adapted to
be irradiated to a photosensitive substrate; and a device adapted
to supply a gas capable of suppressing attenuation of said exposure
light to said optical system, according to a change in light
transmittance of said optical system which occurs due to entrance
of said exposure light.
26. A method for making an apparatus for transferring a pattern on
a mask to a photosensitive substrate, comprising the steps of:
providing an optical system between a light source and a
photosensitive substrate, said light source being adapted to emit
exposure light, said exposure light being adapted to enter said
optical system and irradiate said photosensitive substrate; and
providing a device adapted to supply a gas capable of suppressing
attenuation of said exposure light to said optical system,
according to a change in light transmittance of said optical
system.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to an exposure apparatus which
is used for transferring a pattern on a mask to a substrate, such
as a wafer, in a photolithography process for producing
semiconductors, liquid crystal displays, thin-film magnetic heads,
etc.
[0002] As exposure apparatuses used for producing, for example,
semiconductors, there can be mentioned a projection exposure
apparatus, such as a stepper, in which a reticle as a mask is
illuminated with exposure light passing through an illumination
optical system, to thereby transfer a pattern on the reticle
through a projection optical system to a photoresist-coated wafer
(or a glass plate), and an exposure apparatus of a proximity type
or a contact type in which the pattern on the reticle is directly
transferred to the wafer, using the above-mentioned exposure light.
In these exposure apparatuses, ultraviolet light, such as an i-line
from a super-high pressure mercury-vapor lamp (wavelength: 365 nm),
has conventionally been used as exposure light.
[0003] In conventional exposure apparatuses, a series of lenses in
the illumination optical system are divided into blocks and fixedly
provided in lens barrels. In the illumination optical system,
chambers defined by adjacent lenses are sealed by providing sealing
materials between lenses and lens barrels. These sealing materials
also serve as adhesives for fixing the lenses to the lens barrels.
As such sealing materials, silicon-containing materials are
generally used. In other words, in the sealed chambers in the
illumination optical system, silicon-containing materials which
serve not only as sealing materials, but also as adhesives are
used. It is known that the sealing materials (or adhesives)
containing silicon generate an organosilicon gas.
[0004] In conventional exposure apparatuses in which ultraviolet
light is used as exposure light, ozone is produced from oxygen
molecules in an atmosphere, in the presence of ultraviolet light.
When an organosilicon gas is generated from the sealing materials
(or adhesives) containing silicon, the ozone produced from oxygen
in the presence of ultraviolet light oxidizes the organosilicon gas
and consequently, deposition of haze substance, such as silicon
dioxide (SiO.sub.2), on the surfaces of lenses is likely to occur.
This leads to a lowering of illuminance of exposure light and a
non-uniform distribution with respect to illuminance of exposure
light. Because low molecular weight siloxane contained in the
sealing materials (or adhesives) is a cause of the generation of
organosilicon gas, in order to prevent deposition of SiO.sub.2 on
the surfaces of lenses in an illumination optical system, recently,
materials having a low content of low molecular weight siloxane
have been used as the sealing materials (or adhesives).
[0005] Thus, in illumination optical systems in conventional
exposure apparatuses, sealing materials (or adhesives) which are
unlikely to generate an organosilicon gas, such as materials having
a low content of low molecular weight siloxane, are used. However,
such sealing materials exhibit poor operability due to a prolonged
solidification time. Further, even when the content of low
molecular weight siloxane in the sealing material is low,
liberation of silicon cannot be completely suppressed, so that an
organosilicon gas is generated in a small amount with a consequence
that a small amount of SiO.sub.2 is likely to be deposited on the
surface of lens.
[0006] As another example of sealing materials which are unlikely
to generate an organosilicon gas, there can be mentioned
non-evaporative two-liquid type adhesives. However, such two-liquid
type adhesives also have poor operability.
[0007] Recently, there has been an increasing tendency to use, as
exposure light, excimer laser beams having a short wavelength, such
as a KrF excimer laserbeam (wavelength: 248 nm) and an ArF excimer
laser beam (wavelength: 193 nm). On the other hand, it is known
that when light having a short wavelength, such as excimer laser
beams, is irradiated to adhesives containing silicon, silicon is
liberated in a large amount. Therefore, it is considered that when
excimer laser beams are used as exposure light, deposition of haze
substance on the surfaces of lenses occurs in a wide range in the
illumination optical system, so that countermeasures for deposition
of haze substance have been strongly desired.
BRIEF SUMMARY OF THE INVENTION
[0008] In view of the above situation, the present invention has
been made. It is a primary object of the present invention to
provide an exposure apparatus in which deposition of haze substance
on optical members, such as lenses, in an illumination optical
system can be suppressed, to thereby prevent a lowering of light
transmittance and light reflectance of the lenses.
[0009] According to the present invention, there is provided an
exposure apparatus for illuminating a pattern on a mask with
exposure light passing through an illumination optical system, to
thereby transfer the pattern on the mask to a substrate,
comprising:
[0010] a sealed chamber provided in an optical path of the exposure
light in the illumination optical system,
[0011] the sealed chamber containing a gas and shielded from a gas
surrounding the sealed chamber in the illumination optical system;
and
[0012] a gas exchanging device adapted to exchange the gas in the
sealed chamber with a predetermined gas.
[0013] In the above-mentioned exposure apparatus, when an inert gas
is contained in the sealed chamber, generation of ozone due to
ultraviolet light which is used as exposure light can be avoided,
so that even when an impurity gas, such as an organosilicon gas, is
generated from sealing materials which are used in optical members
(such as lenses) in contact with the gas in the sealed chamber,
deposition of haze substance, such as SiO.sub.2, on the surfaces of
optical members can be prevented. Further, when the gas in the
sealed chamber is periodically exchanged with the predetermined
gas, the impurity gas generated from the sealing materials can be
removed. Due to the above two effects, occurrence of haze on the
surfaces of optical members (leading to a lowering of light
transmittance and light reflectance of the optical members) can be
suppressed. As the inert gas contained in the sealed chamber, a
high-purity nitrogen gas and a rare gas, such as helium, may be
used.
[0014] In the above-mentioned exposure apparatus, it is preferred
that the gas exchanging device comprise:
[0015] a gas exhausting system adapted to exhaust the gas in the
sealed chamber;
[0016] a gas supplying system adapted to supply the predetermined
gas to the sealed chamber;
[0017] a pressure sensor provided in the sealed chamber to detect a
pressure in the sealed chamber; and
[0018] a control system adapted to control an operation of each of
the gas exhausting system and the gas supplying system, based on
the pressure in the sealed chamber detected by the pressure sensor,
to thereby exchange the gas in the sealed chamber with the
predetermined gas.
[0019] In the exposure apparatus having the gas exchanging device
arranged as mentioned above, it is possible to exchange an impurity
gas in the sealed chamber with an inert gas by repeating a gas
exchanging operation in which a step of exhausting the impurity gas
from the sealed chamber through the gas exhausting system and a
step of supplying the inert gas through the gas supplying system to
the sealed chamber are successively conducted.
[0020] In the present invention, it is more preferred that when the
gas in the sealed chamber is exchanged with the predetermined gas,
the control system enable the gas exhausting system to exhaust the
gas in the sealed chamber and the gas supplying system to supply
the predetermined gas to the sealed chamber, while maintaining an
amount of change in the pressure in the sealed chamber detected by
the pressure sensor within a predetermined allowable range. For
example, an impurity gas in the sealed chamber may be exchanged
with an inert gas by exhausting the impurity gas in an extremely
small amount from the sealed chamber through the gas exhausting
system and subsequently, supplying the inert gas in an amount equal
to the amount of exhausted impurity gas through the gas supplying
system to the sealed chamber so that a radical change in pressure
in the sealed chamber can be suppressed. By this arrangement,
stresses acting on lenses in contact with the gas in the sealed
chamber become low, so that deterioration in performance of the
illumination optical system can be avoided.
[0021] When the gas in the sealed chamber is exchanged with the
predetermined gas with high frequency during assembly of the
exposure apparatus, while suppressing a radical change in pressure
in the sealed chamber, solidification of sealing materials (or
adhesives) used in the lenses in contact with the gas in the sealed
chamber is promoted, so that the time required for assembling the
exposure apparatus can be reduced. In this case, because the gas
exchange is conducted in a substantially stationary state with
respect to the pressure in the sealed chamber, stresses acting on
support members for supporting the lenses in contact with the gas
in the sealed chamber are low and hence, damage to the lenses and
deformation of the support members can be prevented. After
operation of the exposure apparatus is started, it is preferred to
exchange the gas in the sealed chamber periodically during idling
of the exposure apparatus.
[0022] Further, in the present invention, it is preferred that the
illumination optical system in the exposure apparatus comprise a
light source adapted to emit exposure light, a shaping optical
system adapted to shape the exposure light passing therethrough and
an optical integrator adapted to enable the exposure light to have
a uniform illuminance distribution after passing through the
shaping optical system, and the sealed chamber be defined by two
optical members constituting the shaping optical system. Because
exposure light exhibits considerably high illuminance on a plane of
incidence of the optical integrator, deposition of haze substance
on the surfaces of lenses in the shaping optical system is likely
to occur. However, by providing a sealed chamber defined by lenses
in the shaping optical system and exchanging an impurity gas in the
sealed chamber with a predetermined gas, the above-mentioned
deposition of haze substance on the surfaces of lenses in the
shaping optical system can be avoided.
[0023] Further, according to the present invention, there is
provided a method for conducting an exchange of gases in a sealed
chamber provided in an exposure apparatus, comprising a gas
exchanging step including:
[0024] a first sub-step of exhausting a gas in the sealed chamber
from a gas exhaust side thereof, while the sealed chamber is closed
on a gas supply side thereof; and
[0025] a second sub-step of supplying an inert gas to the sealed
chamber from the gas supply side thereof, while the sealed chamber
is closed on the gas exhaust side thereof,
[0026] wherein each of the first sub-step and the second sub-step
is conducted in a substantially stationary state with respect to a
pressure of the gas in the sealed chamber.
[0027] Still further, according to the present invention, there is
provided an exposure apparatus comprising:
[0028] an illumination optical system adapted to emit exposure
light, the exposure light being adapted to illuminate a mask
pattern to thereby transfer the mask pattern to a substrate;
[0029] a sealed chamber provided in the illumination optical
system; and
[0030] a gas exchanging device adapted to exhaust a gas in the
sealed chamber and supply an inert gas to the sealed chamber.
[0031] Still further, according to the present invention, there is
provided a projection exposure apparatus for transferring a pattern
on a mask to a photosensitive substrate, comprising:
[0032] a light source adapted to emit exposure light having a
wavelength range in which a photosensitive substrate is sensitive
to the exposure light;
[0033] an illumination optical system provided between the light
source and the mask;
[0034] a projection optical system provided between the mask and
the photosensitive substrate;
[0035] a sealed chamber containing a gas and provided in an optical
path of the exposure light between the light source and the
photosensitive substrate; and
[0036] a gas circulating device connected to the sealed
chamber,
[0037] the gas circulating device being adapted to exhaust the gas
contained in the sealed chamber to an outside thereof, to thereby
compensate for variations in intensity of the exposure light on the
photosensitive substrate.
[0038] Still further, according to the present invention, there is
provided a projection exposure apparatus for transferring a pattern
on a mask to a photosensitive substrate, comprising:
[0039] a light source adapted to emit exposure light having a
wavelength range in which a photosensitive substrate is sensitive
to the exposure light;
[0040] a sealed chamber provided in an optical path of the exposure
light between the light source and the photosensitive substrate;
and
[0041] a gas circulating device having a sensor and connected to
the sealed chamber,
[0042] the sensor being adapted to detect and output information
corresponding to a pressure in the sealed chamber, and
[0043] the gas circulating device being adapted to supply an inert
gas to the sealed chamber in accordance with the information
outputted from the sensor.
[0044] Still further, according to the present invention, there is
provided a method for transferring a pattern on a mask to a
photosensitive substrate, comprising the steps of:
[0045] illuminating the mask with exposure light, to thereby
transfer the pattern on the mask to a photosensitive substrate;
and
[0046] exchanging an inert gas contained in a sealed chamber with
another gas,
[0047] the sealed chamber being provided in an optical path of the
exposure light,
[0048] to thereby compensate for variations in light transmittance
and light reflectance of an optical member provided in the optical
path of the exposure light.
[0049] Still further, according to the present invention, there is
provided an exposure apparatus for transferring a pattern on a mask
to a photosensitive substrate, comprising:
[0050] an optical system adapted to allow exposure light to
enter,
[0051] said exposure light being adapted to be irradiated to a
photosensitive substrate; and
[0052] a device adapted to supply a gas capable of suppressing
attenuation of said exposure light to said optical system,
according to a change in light transmittance of said optical system
which occurs due to entrance of said exposure light.
[0053] Still further, according to the present invention, there is
provided a method for making an apparatus for transferring a
pattern on a mask to a photosensitive substrate, comprising the
steps of:
[0054] providing an optical system between a light source and a
photosensitive substrate,
[0055] said light source being adapted to emit exposure light,
[0056] said exposure light being adapted to enter said optical
system and irradiate said photosensitive substrate; and
[0057] providing a device adapted to supply a gas capable of
suppressing attenuation of said exposure light to said optical
system, according to a change in light transmittance of said
optical system.
[0058] The foregoing and other objects, features and advantages of
the present invention will be apparent from the following detailed
description and appended claims taken in connection with the
accompanying drawings.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0059] FIG. 1 is a perspective view of a partially cut-away
exposure apparatus according to one embodiment of the present
invention.
[0060] FIG. 2 is a cross-sectional view of a construction including
an input lens system ILS and a gas exchange mechanism in the
exposure apparatus of FIG. 1.
[0061] FIG. 3 is a graph showing one example of a change in
pressure in the first sealed chamber 33A shown in FIG. 2 where a
gas exchanging step is repeatedly conducted.
[0062] FIG. 4 is a graph showing a relationship between the number
of times the gas exchanging step is conducted and the concentration
of impurity gas, with respect to the first sealed chamber 33A in
FIG. 2 where the gas exchanging step is repeatedly conducted.
DETAILED DESCRIPTION OF THE INVENTION
[0063] Hereinbelow, an exposure apparatus according to an
embodiment of the present invention is explained, with reference to
the drawings.
[0064] FIG. 1 shows a projection exposure apparatus as an exposure
apparatus according to an embodiment of the present invention. In
FIG. 1, illumination light IL1 from exposure light source 1
comprising a super-high pressure mercury-vapor lamp is collected by
an elliptic mirror 2 and reflected by a mirror 3 and a mirror 4
toward a shutter 5. The shutter 5 is rotated by a drive motor 6,
thereby opening and closing a passage for the illumination light
IL1. When the shutter 5 is in an open state, the illumination light
IL1 passes through the shutter 5, and illumination light exclusive
of an i-line is removed by an interference filter 7. The i-line
which has passed through the interference filter 7 constitutes
exposure light IL and is reflected by a mirror 8 disposed so as to
bend an optical path of the exposure light IL. The exposure light
IL then passes through an input lens system ILS comprising a first
lens 9A, a second lens 9B and a third lens 9C, and enters a fly-eye
lens 10 in the form of a substantially parallel beam. Incidentally,
as the exposure light IL, an h-line (wavelength: 405 nm) or a
g-line (wavelength: 436 nm) may be used, instead of the i-line. An
excimer laser beam, such as a KrF excimer laser beam and an ArF
excimer laser beam, an F.sub.2 laser beam (wavelength: 157 nm) or a
harmonic component of a YAG laser beam, may also be used as the
exposure light IL.
[0065] An aperture stop plate 11 for an illumination system is
rotatably provided on a plane of exit of the fly-eye lens 10. The
aperture stop plate 11 includes a normal circular aperture stop
13A, an aperture stop 13B for a modified light source, which
comprises a plurality of small eccentric apertures, an annular stop
13C and the like. These aperture stops are formed around a rotation
shaft of the aperture stop plate 11. A desired aperture stop for an
illumination system can be disposed on the plane of exit of the
fly-eye lens 10 by rotating the aperture stop plate 11 using a
drive motor 12. A part of the exposure light IL which has passed
through the desired aperture stop on the plane of exit of the
fly-eye lens 10 is reflected by a beam splitter 14 and enters an
integrator sensor 16 comprising a photoelectric conversion device
through a collective lens 15. Illuminance of the exposure light IL
on a wafer W can be indirectly monitored, based on a detection
signal supplied from the integrator sensor 16.
[0066] On the other hand, the exposure light IL which has passed
through the beam splitter 14 passes through a first relay lens 17A,
a projection type reticle blind (variable field stop) 18, a second
relay lens 17B, a mirror 19 disposed so as to bend the optical path
of the exposure light IL and a condenser lens 20, and illuminates a
reticle R. Thus, an illumination optical system is constituted by
the exposure light source 1, the condenser lens 20 and the elements
2 to 19 provided between the exposure light source 1 and the
condenser lens 20. Using the exposure light IL passing through this
illumination optical system, an image of a pattern 21 on the
reticle R is projected through a projection optical system PL to
the photoresist-coated wafer W.
[0067] In FIG. 1, a Z-axis is taken in a direction parallel to an
optical axis AX of the projection optical system PL and a
coordinate system defined by an X-axis and a Y-axis which is
perpendicular to the X-axis is contained in a plane perpendicular
to the Z-axis. The reticle R is held on a reticle stage 28 which is
adapted to perform alignment of the reticle R in an X direction, a
Y direction and a rotation direction. The wafer W is held on a
wafer holder 22 by suction. The wafer holder 22 is fixedly provided
on a wafer stage 23. The wafer stage 23 is adapted to adjust the
position of the wafer W along the Z-axis and a tilt angle of the
wafer W so that the surface of the wafer W coincides with an image
plane of the projection optical system PL. The wafer stage 23 is
also adapted to perform stepping of the wafer W in the X direction
and the Y direction and alignment of the wafer W. After exposure of
one shot area on the wafer W is finished, stepping of the wafer
stage 23 is conducted to thereby move another shot area on the
wafer W which is subsequently subjected to exposure to an exposure
field of the projection optical system PL, and exposure is
conducted. Exposure is repeatedly conducted in a manner such as
mentioned above by a so-called step-and-repeat exposure method, to
thereby conduct exposure of a plurality of shot areas on the wafer
W.
[0068] In the projection exposure apparatus in this embodiment of
the present invention, ultraviolet light is used as the exposure
light IL. Therefore, ozone is produced, in the presence of the
exposure light IL, from oxygen within ambient air. The ozone thus
produced oxidizes an organosilicon gas generated from sealing
materials (or adhesives) used in optical members, such as lenses
and mirrors, and deposition of haze substance, such as silicon
dioxide (SiO.sub.2), on the surfaces of optical members is likely
to occur. In the present invention, in order to prevent such
deposition of haze substance, a sealed chamber is provided in the
optical path of the exposure light IL in the illumination optical
system and a gas in the sealed chamber is exchanged with a
predetermined gas. In the illumination optical system, the
illuminance of the exposure light IL is especially high in the
optical path from the exposure light source 1 to the fly-eye lens
10 as an optical integrator. In this embodiment, the sealed chamber
is defined by adjacent lenses constituting the input lens system
ILS which is provided on the plane of incidence of the fly-eye lens
10.
[0069] FIG. 2 shows a construction including the input lens system
ILS and a gas exchange mechanism for the input lens system ILS. In
FIG. 2, the first lens 9A, the second lens 9B and the third lens 9C
are successively provided along the optical path of the exposure
light IL. The first lens 9A is fixed to a ring-shaped first lens
barrel 31A with a sealing material 45A being provided therebetween.
A second lens barrel 31B is disposed on a ring-shaped spacer 32A
above the first lens barrel 31A. The second lens 9B is fixed to the
second lens barrel 31B with a sealing material 45B being provided
therebetween. A third lens barrel 31C is disposed on a spacer 32B
above the second lens barrel 31B. The third lens 9C is fixed to the
third lens barrel 31C with a sealing material 45C being provided
therebetween. Each of the sealing materials 45A to 45C contains
silicon and also serves as an adhesive. In this embodiment, two
sealed chambers, namely, a first sealed chamber 33A and a second
sealed chamber 33B are provided in the input lens system ILS. The
first sealed chamber 33A is defined by the lenses 9A and 9B, the
lens barrels 31A and 31B and the spacer 32A and shielded from a gas
surrounding the first sealed chamber 33A. The second sealed chamber
33B is defined by the lenses 9B and 9C, the lens barrels 31B and
31C and the spacer 32B and shielded from a gas surrounding the
second sealed chamber 33B. The lens barrels 31A to 31C and the
spacers 32A and 32B are firmly fixed so as not to allow the lenses
9A to 9C to be displaced due to a change in atmospheric pressure.
Further, in order to maintain the temperature of a gas in each of
the sealed chambers 33A and 33B at a predetermined level, pipes 32C
and 32D, each of which allows a fluid having a temperature
controlled to a predetermined level to pass therethrough, are
disposed on respective outer surfaces of the spacers 32A and
32B.
[0070] A gas bomb 34 in which a high-purity nitrogen gas as an
inert gas is sealably contained under high pressure is provided
outside a chamber accommodating the projection exposure apparatus.
The high-purity nitrogen gas in the gas bomb 34 is supplied through
an electromagnetic valve 35, a chemical filter 36 and an HEPA
filter (high efficiency particulate air-filter) 37 to a gas supply
pipe 38. The opening and closing of the electromagnetic valve 35 is
controlled by a pressure control system 40 comprising a computer. A
first pipe 38a branched from the gas supply pipe 38 is connected to
the first sealed chamber 33A through an electromagnetic valve 39A
provided with a check valve. A second pipe 38b branched from the
gas supply pipe 38 is connected to the second sealed chamber 33B
through an electromagnetic valve 39B provided with a check valve.
The opening and closing of each of the electromagnetic valves 39A
and 39B is also controlled by the pressure control system 40.
[0071] Further, the first sealed chamber 33A is connected to a gas
exhaust pipe 41 through a first pipe 41a for gas exhaustion and an
electromagnetic valve 42A provided with a check valve. The second
sealed chamber 33B is connected to the gas exhaust pipe 41 through
a second pipe 41b for gas exhaustion and an electromagnetic valve
42B provided with a check valve. The gas exhaust pipe 41 opens to
the atmosphere outside the chamber accommodating the projection
exposure apparatus through a gas exhaust pump 43 and a filter
device (not shown). The opening and closing of each of the
electromagnetic valves 42A and 42B and the operation of the gas
exhaust pump 43 are controlled by the pressure control system 40.
Pressure sensors 44A and 44B are provided in the sealed chambers
33A and 33B, respectively, so as to detect pressures in the sealed
chambers 33A and 33B. Detection signals are supplied from the
pressure sensors 44A and 44B to the pressure control system 40.
Thus, the pressure control system 40 monitors respective pressures
of gasses in the sealed chambers 33A and 33B, based on the
detection signals from the pressure sensors 44A and 44B.
[0072] Basically, the gas exchange mechanism shown in FIG. 2 is
operated as follows. Initially, while the electromagnetic valves
39A and 39B on a gas supply side are closed, the pressure control
system 40 opens the electromagnetic valves 42A and 42B on a gas
exhaust side, and actuates the gas exhaust pump 43 so that a part
of the gas in the first sealed chamber 33A, that is, remaining
oxygen and an impurity gas, such as an organosilicon gas generated
from the sealing materials 45A and 45B, and a part of the gas in
the second sealed chamber 33B, that is, remaining oxygen and an
impurity gas, such as an organosilicon gas generated from the
sealing materials 45B and 45C, are exhausted. Subsequently, the
pressure control system 40 closes the electromagnetic valves 42A
and 42B on the gas exhaust side and opens the electromagnetic
valves 39A and 39B on the gas supply side, and also opens the
electromagnetic valve 35, to thereby supply the high-purity
nitrogen gas from the gas bomb 34 through the gas supply pipe 38 to
each of the sealed chambers 33A and 33B. The pressure control
system 40 ensures that the gas exchange is conducted in a
substantially stationary state so that no radical changes occur
with respect to the pressures of gases in the sealed chambers 33A
and 33B, which pressures are detected by the pressure sensors 44A
and 44B, respectively. Thus, the respective amounts of oxygen and
the impurity gas (such as an organosilicon gas generated from the
sealing materials) in each of the sealed chambers 33A and 33B
decrease, so that the respective concentrations of oxygen and
impurities in the gas in each of the sealed chambers 33A and 33B
become low and hence, a process of deposition of haze substance on
each of the lenses 9A to 9C is interrupted, to thereby prevent
occurrence of haze on the surfaces of these lenses.
[0073] In this embodiment, the electromagnetic valves 39A, 39B, 42A
and 42B, each provided with a check valve, are employed. Therefore,
the gasses in the sealed chambers 33A and 33B flow in a single
direction from the gas bomb 34 toward the gas exhaust pump 43
without occurrence of a reverse gas flow. Therefore, the impurity
gas in each of the sealed chambers 33A and 33B can be efficiently
exchanged with the high-purity nitrogen gas.
[0074] Next, referring to FIGS. 1 to 4, explanation is made on one
example of an operation for conducting an exchange of gases in the
first sealed chamber 33A in a substantially stationary state using
the gas exchange mechanism shown in FIG. 2. This operation is
mainly conducted during idling of the projection exposure apparatus
between exposure operations.
[0075] When the pressure P of the gas in the first sealed chamber
33A at a time point t.sub.0 when an exchange of gases is started is
indicated as an initial value P.sub.0, this initial value P.sub.0
is substantially equal to the pressure of a gas surrounding
the-illumination optical system (1 atm in this embodiment). At the
time point t.sub.0, the electromagnetic valve 42A on the gas
exhaust side is opened while the electromagnetic valve 39A on the
gas supply side is closed, and the gas exhaust pump 43 is actuated
so as to exhaust the gas in the first sealed chamber 33A until the
pressure P of the gas in the first sealed chamber 33A, which is
detected by the pressure sensor 44A, decreases by an amount
.DELTA.p which is within a predetermined allowable range. The time
period between the time point t.sub.0 and the time point when the
pressure P decreases by the allowable amount .DELTA.p is indicated
as .DELTA.t.sub.1.
[0076] FIG. 3 is a graph showing one example of a change in
pressure in the first sealed chamber 33A shown in FIG. 2 where the
exchange of gases is conducted. In the graph of FIG. 3, the change
in the pressure P in the first sealed chamber 33A is indicated by a
solid curved line 51. In FIG. 3, the abscissa indicates the time t
and the ordinate indicates the pressure P. In FIG. 3, the pressure
P decreases by the allowable amount .DELTA.p from the initial value
P.sub.0 at a time point t.sub.1. Therefore, in FIG. 3, the
above-mentioned time period .DELTA.t.sub.1 is indicated as the time
period between the time point t.sub.0 and the time point
t.sub.1.
[0077] Subsequently, the electromagnetic valve 42A on the gas
exhaust side is closed and the electromagnetic valve 39A on the gas
supply side is opened. The electromagnetic valve 35 is also opened,
to thereby supply the high-purity nitrogen gas from the gas bomb 34
to the first sealed chamber 33A. In this instance, using the
pressure sensor 44A, the high-purity nitrogen gas is supplied until
the pressure P in the first sealed chamber 33A is recovered to the
initial value P.sub.0. As indicated by the solid curved line 51 in
FIG. 3, the pressure P is recovered to the initial value P.sub.0 at
a time point t.sub.2. The time period between the time point
t.sub.1 and the time point t.sub.2 is indicated as .DELTA.t.sub.2.
Thereafter, the above-mentioned operation (hereinafter, frequently
referred to simply as "gas exchanging step") comprising a step of
exhausting the gas in the first sealed chamber 33A until the
pressure P of the gas in the first sealed chamber 33A decreases by
the allowable amount .DELTA.p from the initial value P.sub.0 (first
sub-step) and a step of supplying the high-purity nitrogen gas to
the first sealed chamber 33A until the pressure P is recovered to
the initial value P.sub.0 (second sub-step) is repeated. When the
gas exchanging step is repeated, the solid curved line 51 which
indicates the change in the pressure P exhibits a sine
waveform.
[0078] FIG. 4 is a graph showing a relationship between the number
n of times the gas exchanging step is conducted and the
concentration C of impurity gas, with respect to the first sealed
chamber 33A in FIG. 2 where the gas exchanging step is repeatedly
conducted. The graph of FIG. 4 is obtained in a manner as mentioned
below. When the amount of gas in the first sealed chamber 33A which
is exchanged at each gas exchanging step (hereinafter, frequently
referred to simply as "gas exchange amount") is indicated as
.DELTA.q, the value of .DELTA.q is determined in accordance with
the above-mentioned allowable amount .DELTA.p. Further, when the
internal volume of the first sealed chamber 33A is indicated as Q
and the concentration of impurity gas (such as an organosilicon
gas) in the gas in the first sealed chamber 33A after the gas
exchanging step is conducted at i time(s) (i=1, 2, . . . ) is
indicated as C.sub.i, because gases become mixed at a sufficiently
high rate, the concentration C.sub.i+1 of impurity gas after the
gas exchanging step is conducted (i+1) times is determined in
accordance with the following formula (1).
C.sub.i+1=C.sub.i(1-.DELTA.q/Q) (1)
[0079] From this formula (1), the concentration C.sub.i of impurity
gas is indicated by the following formula (2), using the
concentration C.sub.1 of impurity gas after the gas exchanging step
is conducted at one time.
C.sub.i=C.sub.1(1.DELTA.q/Q).sup.i-1 (2)
[0080] When a target value of the concentration C of impurity gas
is indicated as C.sub.L, the following formula (3) is obtained from
the formula (2), with respect to the number N of times the gas
exchanging step needs to be conducted for achieving the target
value C.sub.L.
C.sub.N=C.sub.i(1-.DELTA.q/Q).sup.N-1.ltoreq.C.sub.L (3)
[0081] Accordingly, with respect to the number n (n=1, 2, . . . ,
N) of times the gas exchanging step is conducted, the concentration
C of impurity gas in the gas in the first sealed chamber 33A
changes as indicated by a solid curved line 52 in the graph of FIG.
4. On the other hand, the formula (3) can be reformulated as
follows.
(1-.DELTA.q/Q).sup.N-1.ltoreq.C.sub.L/C.sub.1 (4A)
(N-1)log(1-.DELTA.q/Q).ltoreq.log(C.sub.L/C.sub.1) (4B)
[0082] With respect to the formula (4B), log (1-.DELTA.q/Q)<0
and log (C.sub.L/C.sub.1)<0. Therefore, the formula (4B) can be
reformulated as follows.
(N-1).ltoreq.log(C.sub.L/C.sub.1)/log(1-.DELTA.q/Q) (4C)
N.ltoreq.1+log(C.sub.L/C.sub.1)/log(1-.DELTA.q/Q) (4D)
[0083] Therefore, when the internal volume Q of the first sealed
chamber 33A, an appropriate gas exchange amount .DELTA.q (or the
allowable amount .DELTA.p of change in pressure of the gas in the
first sealed chamber 33A), the concentration C.sub.1 of
impurity-gas-after the gas exchanging step is conducted at one time
and the target value C.sub.L of the concentration C of impurity gas
are determined, the minimum value N.sub.min of the number N of
times the gas exchanging step needs to be conducted for suppressing
the concentration C of impurity gas to the target value C.sub.L or
less can be determined, in accordance with the formula (4D). In
this embodiment, the number of times the gas exchanging step is
conducted is N.sub.min which is the minimum value of the integer N
satisfying the formula (4D). Thus, the concentration C of impurity
gas can be suppressed to the target value C.sub.L or less by
conducting the gas exchanging step at N.sub.min time(s).
[0084] With respect to the gas exchange amount .DELTA.q (or the
allowable amount .DELTA.p of change in pressure of the gas in the
first sealed chamber 33A), when the gas exchange amount .DELTA.q is
too large, stresses acting on the lenses, such as the first lens 9A
in FIG. 2, become high, so that problems arise, such as
displacement, a change in aberration, damage and breakage of
lenses. Even when damage or breakage of lenses is avoided, a
substantial amount of stress is likely to have an adverse effect on
the aberration of lenses which has already been corrected.
Therefore, in this embodiment of the present invention, the gas
exchange amount .DELTA.q (or the allowable amount .DELTA.p of
change in pressure of the gas in the first sealed chamber 33A) is
suppressed to a level such that the pressure in the first sealed
chamber 33A changes in a substantially stationary state. For
example, the allowable amount .DELTA.p is determined as being an
amount several times the amount which is capable of being detected
by the pressure sensor 44A in the first sealed chamber 33A in FIG.
2, and the gas exchange amount .DELTA.q is determined from the thus
determined amount .DELTA.p. By this arrangement, an undesirable
increase in stress acting on lenses during the exchange of gases in
the first sealed chamber 33A can be prevented and the
above-mentioned problems accompanying the exchange of gases, such
as a change in aberration of lenses, can be suppressed within a
sufficiently narrow allowable range.
[0085] When the minimum value N.sub.min of the number N of times
the gas exchanging step is conducted, which is determined in
accordance with the formula (4D), becomes large so that a total gas
exchange time [i.e., the time period during which the gas
exchanging step is conducted at N.sub.min time(s)] exceeds an
idling time of the projection exposure apparatus, a time for
conducting the gas exchanging step at one time may be reduced by
reducing the time period t.sub.1 and the time period t.sub.2 in
FIG. 3. With respect to the second sealed chamber 33B in FIG. 2,
the impurity gas in the second sealed chamber 33B is exchanged with
the inert gas in substantially the same manner as in the first
sealed chamber 33A, while suppressing a change in aberration of
lenses and the like.
[0086] Preferably, the above-mentioned gas exchanging step is
conducted periodically during idling of the projection exposure
apparatus, because an organosilicon gas is gradually generated from
the sealing materials 45A to 45C in FIG. 2. By this arrangement,
gradual deposition of haze substance on the surfaces of lenses can
be prevented.
[0087] Although the gas exchanging step is conducted during idling
of the projection exposure apparatus in the above-mentioned
embodiment, in the present invention, the gas exchanging step may
be conducted during assembly and adjustment of the projection
exposure apparatus in a manner as mentioned below. That is,
immediately after the lenses 9A to 9C are fixed to the lens barrels
31A to 31C with the sealing materials 45A to 45C being provided
therebetween, the gas in each of the sealed chambers 33A and 33B
may be exchanged with a high-purity nitrogen gas through the gas
exchange mechanism in FIG. 2, while maintaining an amount of change
in pressure in each of the sealed chambers 33A and 33B at .DELTA.p
or less. In this instance, because the amount of change in pressure
during the gas exchanging step is as small as .DELTA.p or less, it
is unnecessary to wait until the sealing materials 45A to 45C are
completely solidified. Further, because the organosilicon gas
generated from the sealing materials 45A to 45C during
solidification thereof is efficiently exhausted through the gas
exhaust pump 43, the solidification time can be reduced and the
time for assembly can also be reduced. Further, there is no
phenomenon such that organosilicon substance adheres to and remains
on the surfaces of the lenses 9A to 9C and the inner walls of the
lens barrels 31A and 31C. Thus, deposition of haze substance on the
lenses 9A to 9C can be completely prevented.
[0088] In the above-mentioned embodiment, when moisture remains in
the gas supply pipe 38 in FIG. 2, such moisture enters the sealed
chambers 33A and 33B, in accordance with the flow of gas supplied
to the sealed chambers 33A and 33B. In this case, not only does a
lowering of efficiency in exhausting impurities occur, but also the
moisture react with coating materials on lenses in an early stage
and the resultant reaction product is likely to be deposited on the
surfaces of lenses, thereby contaminating the lenses. Therefore, it
is preferred to provide the gas supply pipe 38 with another exhaust
port and preliminarily clean the gas supply pipe 38 by flowing an
inert gas, such as a nitrogen gas (N.sub.2) and helium (He), from
this exhaust port through the gas supply pipe 38.
[0089] In the above-mentioned embodiment, the gas exchange
mechanism is provided in the input lens system ILS in FIG. 1.
However, in the present invention, the gas exchange mechanism may
also be applied to, for example, the interference filter 7, the
fly-eye lens 10, the beam splitter 14, the relay lenses 17A and 17B
in the illumination optical system, in order to prevent deposition
of haze substance on these optical members. Further, when two
fly-eye lenses 10 are provided so as to improve uniformity of
illuminance distribution of exposure light and a relay lens system
is provided between these two fly-eye lenses, the gas exchange
mechanism may be provided in this relay lens system.
[0090] Further, as the inert gas used in the gas exchange
mechanism, a high-purity nitrogen gas is employed in the
above-mentioned embodiment. However, in the present invention, a
chemically stable gas, for example, a rare gas, such as helium or
hydrogen, may also be used as the inert gas. In an exposure
apparatus in which a KrF excimer laser is used, dried air which is
chemically clean may be used as the inert gas. The above-mentioned
dried air is obtained by passing air through a chemical filter and
adjusting the humidity of the filtered air to, for example, about
5% or less. With respect to the gas bomb 34 connected through the
gas supply pipe 38 to the electromagnetic valves 39A and 39B on the
gas supply side and the gas exhaust pump 43 connected through the
gas exhaust pipe 41 to the electromagnetic valves 42A and 42B on
the gas exhaust side in FIG. 2, the gas bomb 34 and the gas exhaust
pump 43 may be temporarily connected only when the gas exchanging
step is conducted in each of the sealed chambers 33A and 33B. That
is, the sealed chambers 33A and 33B may be arranged so as to have a
construction which is capable of being connected to the gas bomb 34
and the gas exhaust pump 43 for conducting the gas exchanging
step.
[0091] Incidentally, when the pressure on the gas supply side is
set to a level such that no reverse gas flow occurs, as each of the
electromagnetic valves 39A, 39B, 42A and 42B, a simple
electromagnetic valve may be used, instead of the electromagnetic
valve provided with the check valve.
[0092] Generally, in the projection exposure apparatus, in order to
correct variations in image-forming characteristics, such as the
magnification and distortion of the projection optical system,
which are caused by a change in atmospheric pressure, and
variations in these image-forming characteristics which are caused
by irradiation of exposure light (so-called irradiation-dependent
variations), sealed chambers are provided in the projection optical
system at several sites where the above-mentioned variations in
image-forming characteristics can be effectively corrected and
pressures in these sealed chambers are actively changed.
Alternatively, the above-mentioned variations in image-forming
characteristics are corrected directly by controlling the positions
of lenses in the projection optical system (so-called lens
control). Especially, when the pressures in sealed chambers are
controlled, bellows are generally used.
[0093] Therefore, in the above-mentioned embodiment of the present
invention, a sealed chamber having a pressure which is capable of
being controlled may be provided in the projection optical system
PL so that the sealed chamber contains the gas in a space between
lenses which are useful for effectively conducting correction of
aberration in the projection optical system PL. In this case, the
pressure in the sealed chamber may be controlled utilizing a
pressure of the high-purity nitrogen gas, in stead of using
bellows. By this arrangement, not only can variations in
image-forming characteristics be corrected, but also deposition of
haze substance on the surfaces of lenses in contact with the gas in
the sealed chamber in the projection optical system PL can be
prevented.
[0094] When the sealed chamber is provided in an optical path
between the reticle and the wafer, the pressure of the inert gas
contained in the sealed chamber may not be controlled, and as
disclosed in, for example, U.S. Pat. No. 5,117,255, optical
characteristics (such as a focus position, a magnification,
aberrations and telecentricity) and image-forming characteristics
(such as image contrast) with respect to an image of the pattern on
the reticle may be adjusted by moving at least one optical member
in the projection optical system PL. In this case, an inert gas is
selectively supplied to the sealed chamber so as to compensate for
variations in light transmittance of the illumination optical
system and/or the projection optical system PL, i.e., variations in
light intensity of exposure light on the wafer. With respect to the
optical integrator provided in the illumination optical system, the
optical integrator is not limited to the fly-eye lens. A rod
integrator may also be used as the optical integrator. The fly-eye
lens and the rod integrator may be used in combination, as
disclosed in U.S. Pat. No. 4,918,583.
[0095] The present invention can be applied to not only a one-shot
exposure type projection exposure apparatus, but also a scanning
exposure type projection exposure apparatus, such as a
step-and-scan type. The present invention can also be applied to an
exposure apparatus of a proximity type or a contact type in which
the projection optical system is not used. Thus, the present
invention is not limited to the above-mentioned embodiment. Various
modifications are possible without departing from the scope of the
present invention as defined in the appended claims.
[0096] In the exposure apparatus of the present invention, a sealed
chamber is provided in an optical path of exposure light in the
illumination optical system. The gas in the sealed chamber is
exchangeable. Therefore, for example, when the gas in the sealed
chamber which is likely to generate haze substance is periodically
exchanged with another gas, deposition of substance which lowers
light transmittance and light reflectance of optical members, such
as lenses, in the illumination optical system is unlikely to occur.
Therefore, a lowering of illuminance of exposure light on the mask
and a non-uniform distribution with respect to illuminance of
exposure light can be suppressed.
[0097] Further, in the exposure apparatus of the present invention
in which a pressure sensor is provided in the sealed chamber, the
pressure in the sealed chamber can be maintained at a desired
level.
[0098] In this instance, it is preferred that when the gas is in
the sealed chamber is exchanged with a predetermined gas, the gas
in the sealed chamber be exhausted through the gas exhausting
system and the predetermined gas be supplied to the sealed chamber
through the gas supplying system, while maintaining an amount of
change in the pressure in the sealed chamber detected by the
pressure sensor within a predetermined allowable range, from the
viewpoint of suppressing a radical change in pressure in the sealed
chamber. When a radical change in pressure in the sealed chamber is
suppressed, stresses acting on optical members (such as lenses) in
contact with the gas in the sealed chamber become low, so that an
adverse effect on aberration of the optical members can be
avoided.
[0099] Further, the present invention is especially advantageous
when the illumination optical system comprises a light source
adapted to emit exposure light, a shaping optical system adapted to
shape the exposure light passing therethrough and an optical
integrator adapted to enable the exposure light to have a uniform
illuminance distribution after passing through the shaping optical
system, and the sealed chamber is defined by two optical members
constituting the shaping optical system, because it is possible to
exchange the gas in a region where the illuminance of exposure
light is high and therefore deposition of haze substance is likely
to occur, and prevent occurrence of haze in that region.
[0100] The entire disclosure of Japanese Patent Application No. Hei
9-75355 filed on Mar. 27, 1997 is incorporated herein by reference
in its entirety.
* * * * *