U.S. patent application number 14/316904 was filed with the patent office on 2014-10-16 for method for adjusting spectrum width of narrow-band laser.
This patent application is currently assigned to USHIO DENKI. The applicant listed for this patent is Takahito KUMAZAKI, Masashi SHINBORI, Toru SUZUKI, Osamu WAKABAYASHI, Masaya YOSHINO. Invention is credited to Takahito KUMAZAKI, Masashi SHINBORI, Toru SUZUKI, Osamu WAKABAYASHI, Masaya YOSHINO.
Application Number | 20140307244 14/316904 |
Document ID | / |
Family ID | 39073299 |
Filed Date | 2014-10-16 |
United States Patent
Application |
20140307244 |
Kind Code |
A1 |
WAKABAYASHI; Osamu ; et
al. |
October 16, 2014 |
METHOD FOR ADJUSTING SPECTRUM WIDTH OF NARROW-BAND LASER
Abstract
An upper limit and a lower limit are preliminarily set for a
spectral line width common to a plurality of narrow-band laser
devices. When delivered or subjected to maintenance, the
narrow-band laser device is caused to laser oscillate to detect its
spectral line width before it is used as a light source for
semiconductor exposure. A spectral line width adjustment unit
provided in the narrow-band laser device is adjusted so that the
spectral line width assumes a value between the upper limit and the
lower limit. The present invention is able to suppress the
variation in spectral line width such as E95 bandwidth caused by
machine differences during the manufacture of the laser device, or
by replacement or maintenance of the laser device, whereby the
quality of integrated circuit patterns formed by the semiconductor
exposure tool can be stabilized.
Inventors: |
WAKABAYASHI; Osamu;
(Hiratsuka-shi, JP) ; KUMAZAKI; Takahito;
(Hiratsuka-shi, JP) ; SUZUKI; Toru; (Oyama-shi,
JP) ; SHINBORI; Masashi; (Yokohama-shi, JP) ;
YOSHINO; Masaya; (Oyama-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
WAKABAYASHI; Osamu
KUMAZAKI; Takahito
SUZUKI; Toru
SHINBORI; Masashi
YOSHINO; Masaya |
Hiratsuka-shi
Hiratsuka-shi
Oyama-shi
Yokohama-shi
Oyama-shi |
|
JP
JP
JP
JP
JP |
|
|
Assignee: |
USHIO DENKI
Tokyo
JP
KOMATSU LTD.
Tokyo
JP
|
Family ID: |
39073299 |
Appl. No.: |
14/316904 |
Filed: |
June 27, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11822126 |
Jul 2, 2007 |
8804780 |
|
|
14316904 |
|
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|
|
Current U.S.
Class: |
355/67 |
Current CPC
Class: |
H01S 3/139 20130101;
H01S 3/106 20130101; H01S 3/225 20130101; G03F 7/2006 20130101;
H01S 3/08036 20130101; H01S 3/137 20130101 |
Class at
Publication: |
355/67 |
International
Class: |
G03F 7/20 20060101
G03F007/20 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 4, 2006 |
JP |
2006-184425 |
Claims
1-8. (canceled)
9. A narrow-band laser device used as a light source for
semiconductor exposure, comprising: a laser chamber configured to
oscillate laser light; a line narrowing unit arranged on a rear
side of the laser chamber and configured to narrow a spectral line
width of the laser light output from the laser chamber; a spectral
detecting unit configured to detect the spectral line width; and a
spectral line width adjustment unit configured to adjust the
spectral line width; wherein the spectral line width adjustment
unit is arranged on a front side of the laser chamber and has a
cylindrical convex lens and a cylindrical concave lens which are
arranged on an optical path of the laser light.
10. The narrow-band laser device according to claim 9, wherein the
spectral line width adjustment unit adjusts the spectral line
width, before a semiconductor exposure, into a value between an
upper limit and a lower limit of a spectral line width, which are
allowed for the semiconductor exposure and which are common to a
plurality of narrow-band laser devices.
11. A spectral line width adjustment method of adjusting a spectral
line width of laser light emitted from a narrow-band laser device
used as a light source for semiconductor exposure, comprising:
oscillating the laser light with the narrow-band laser device;
detecting a spectral line width of the laser light oscillated with
the narrow-band laser device; and adjusting the spectral line width
with a spectral line width adjustment unit of the narrow-band laser
device; wherein the spectral line width adjustment unit is arranged
on a front side of the laser chamber and has a cylindrical convex
lens and a cylindrical concave lens which are arranged on an
optical path of the laser light.
12. The spectral line width adjustment method according to claim
11, wherein: the method is performed before a semiconductor
exposure, and further comprises the step of setting an upper limit
and a lower limit of a spectral line width, before said oscillating
of the laser light, which are allowed for the semiconductor
exposure and which are common to a plurality of narrow-band laser
devices; and said adjusting of the spectral line width adjusts the
spectral line width into a value between the upper limit and the
lower limit
Description
[0001] This application is a divisional of Ser. No. 11/822,126,
filed Jul. 2, 2007, which is hereby incorporated by reference in
its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field the Invention
[0003] The present invention relates to a method for adjusting a
spectral line width such as E95 bandwidth of a narrow-band laser
when using a narrow-band laser as a light source to expose a
semiconductor. The E95 bandwidth means a spectral line width of the
spectral area of laser light where 95% energy is concentrated. The
present invention particularly relates to a method for reducing the
deviation in spectral line width such as E95 bandwidth among a
plurality of narrow-band laser devices.
[0004] 2. Description of the Related Art
[0005] The recent trend of refining the configuration and
increasing the degree of integration of semiconductor integrated
circuits has increased the demand for improvement in resolution of
a semiconductor exposure tool (hereafter, referred to as the
"exposure tool"). For this purpose, the related art tries to
decrease the wavelength of light emitted by an exposure light
source. Recently, a gas laser device has replaced a traditional
mercury lamp as an exposure light source. Such a gas laser device
for exposure is for example a KrF excimer laser emitting vacuum
vacuum ultraviolet light with a wavelength of 248 nm or an ArF
excimer laser emitting vacuum vacuum ultraviolet light with a
wavelength of 193 nm.
[0006] Studies are being conducted for next-generation exposure
technologies, represented by an immersion exposure technique in
which space between a wafer and an exposure lens of an exposure
tool is filled with liquid to change the index of refraction to
thereby decrease the apparent wavelength of the exposure light
source. When the immersion exposure is performed by using an ArF
excimer laser as an exposure light source, the wafer is irradiated
with vacuum ultraviolet light with a wavelength of 134 nm in the
liquid. This technique is referred to as the ArF immersion exposure
(or ArF immersion lithography).
[0007] A next-next generation exposure light source which is viewed
with high degree of expectation is an F2 laser emitting vacuum
ultraviolet light with a wavelength of 157 nm. Further, the F2
laser is possibly used as an exposure light source to perform the
immersion technique as described above. It is believed that, in
this case, a wafer is irradiated with vacuum ultraviolet light with
a wavelength of 115 nm.
[0008] KrF and ArF excimer lasers have a free running line width as
wide as about 350 to 400 pm. The use of these projection lens will
cause occurrence of chromatic aberration, resulting in lose of
resolution. Therefore, it is necessary to narrow the spectral line
width of laser light emitted by the gas laser device until the
chromatic aberration is reduced to a negligible level. For this
reason, a line narrowing module having a line narrowing element
(e.g. etalon or grating) is provided in a laser resonator of the
gas laser device, so that the spectral line width is narrowed. A
laser whose spectral line width is narrowed is referred to as the
"narrow-band laser". In general, a laser spectral line width is
represented by a full width at half maximum. As shown in FIG.
22(a), the term "full width at half maximum (FWHM)" refers to a
spectral line width of a part of the laser light spectral where the
light intensity is a half of the peak value.
[0009] The image formation performance of an exposure tool can be
accurately evaluated by an optical simulation calculation method
using optical system data of the exposure tool and laser spectral
profile. It is known from the results of the optical simulation
calculation that the image formation performance of an exposure
tool is greatly affected not only by the full width at half maximum
of laser light spectral but also by components in the spectral
skirts. Therefore, a new definition called E95 bandwidth (also
referred to as spectral purity width) has been introduced to define
a spectral line width. As shown in FIG. 22(b), the E95 bandwidth is
an index indicating a spectral line width of a part of spectral
area of laser light where 95% of energy is concentrated. There is a
correlation between the E95 bandwidth and image formation
performance of an optical system of the exposure tool. The E95
bandwidth is thus required to be suppressed to 0.5 pm or less in
order to guarantee a high quality for integrated circuits
produced.
[0010] The E95 bandwidth and the spectral line width at full width
at half maximum can be varied for example by changing the wavefront
of laser light. One of techniques to change the laser light
wavefront is disclosed in the Patent Document 1 (Japanese Patent
Application Laid-Open No. 2000-312048) which relates to a device
for changing the curvature of a grating.
[0011] However, it has recently been made known that if the value
of the E95 bandwidth or the spectral line width at full width at
half maximum is either too large or too small in comparison with a
designed value for the optical system of the exposure tool, the
quality of the integrated circuit pattern is deteriorated. This is
described in the Patent Document 2 (U.S. Pat. No. 6,721,340) and
the Patent Document 3 (Japanese Patent Application Laid-Open No.
2001-267673).
[0012] When a plurality of laser devices are compared, those laser
devices do not necessarily have an equivalent spectral line width
such as E95 bandwidth even if they have the same configuration. It
is rather common that the spectral line width such as E95 bandwidth
differs among the plurality of laser devices. FIG. 23 is a
histogram showing the E95 bandwidths in a plurality of conventional
laser devices. As shown in FIG. 23, the maximum value of E95
bandwidth was 0.450 pm, the minimum value 0.210 pm, the mean value
0.340 pm, and the standard deviation was 0.061 pm. Five out of
twenty devices exhibited a variation in the E95 bandwidth exceeding
an allowable range of the E95 bandwidth for an optical system of an
exposure tool, for example a range of from 0.350 to 0.450 pm. The
result revealed that if these five laser devices having an E95
bandwidth exceeding the allowable range were used as an exposure
light source, the quality of integrated circuit patterns was
deteriorated to such an extent that it is impossible to produce a
semiconductor device.
[0013] It is believed that the spectral line width such as E95
bandwidth differs among laser devices due to machine differences
thereof The machine differences among laser devices include the
followings.
[0014] (1) Individual differences among optical elements (line
narrowing elements) such as: [0015] i) variation in diffractive
wavefront of gratings; [0016] ii) variation in transmission
wavefront of prisms; and [0017] iii) variation in position and
optical axis among optical elements in a line narrowing module;
[0018] (2) Machine differences in adjustment of laser optical axis
such as: [0019] i) variation in chamber discharge position and
optical axis when chambers are replaced; [0020] ii) variation in
position and optical axis among line narrowing modules; [0021] iii)
variation in optical axis among laser resonators;
[0022] (3) Machine differences of laser chambers such as: [0023] i)
variation in discharge position [0024] ii) variation in discharge
position and discharge state.
[0025] In a practical exposure process of semiconductor device
manufacture, laser devices or modules are replaced due to failure
or end of service life of the devices. Due to the machine
differences as described above, a replacing laser device will have
a different spectral line width such as E95 bandwidth from that of
a replaced laser device even if they are of a same type. Moreover,
the spectral line width such as E95 bandwidth will vary even in a
same laser device between before and after maintenance thereof This
means that the spectral line width such as E95 bandwidth is changed
as a result of replacement or maintenance of the laser device, and
if such change exceeds an allowable range of the spectral line
width such as E95 bandwidth for an optical system of the exposure
tool, the quality of integrated circuit patterns is deteriorated to
such an extent that it is impossible to manufacture a semiconductor
device.
[0026] The present invention has been made in view of the
circumstances described above. It is an object of the prevent
invention to suppress variation in spectral line width such as E95
bandwidth due to machine differences caused during manufacture of
laser devices and variation in spectral line width such as E95
bandwidth caused by replacement of maintenance of a laser device,
and thus to stabilize the quality of integrated circuit patterns
formed by a semiconductor exposure tool.
SUMMARY OF THE INVENTION
[0027] A first aspect of the invention provides a narrow-band laser
spectral line width adjustment method for adjusting the spectral
line width of laser light when a narrow-band laser is used as a
light source for semiconductor exposure, the method comprising the
steps of: setting an upper limit and a lower limit for a spectral
line width common to a plurality of narrow-band laser devices;
causing the narrow-band laser device to laser oscillate prior to
semiconductor exposure to detect a spectral line width; and
adjusting a spectral line width adjustment unit provided in the
narrow-band laser device to adjust the spectral line width to be a
value between the upper limit and the lower limit.
[0028] According to the first aspect of the invention, an upper
limit and a lower limit are preliminarily set for a spectral line
width common to a plurality of narrow-band laser devices. When
delivered or subjected to maintenance, the narrow-band laser device
is caused to laser oscillate to detect its spectral line width
before it is used as a light source for semiconductor exposure. A
spectral line width adjustment unit provided in the narrow-band
laser device is adjusted so that the spectral line width assumes a
value between the upper limit and the lower limit. This makes it
possible, even if the narrow-band laser device is replaced with
another one before semiconductor exposure, to minimize the
difference in spectral line width between the replaced narrow-band
laser device and the replacing narrow-band laser device. Further,
even if the narrow-band laser device is subjected to maintenance
before conducting semiconductor exposure, the difference in
spectral line width of the narrow-band laser device between before
and after the maintenance can be minimized.
[0029] In a second aspect of the invention according to the first
aspect, the spectral line width adjustment unit has a wavefront
adjuster which is arranged on an optical path inside a laser
resonator of the narrow-band laser device, and is designed to
adjust the curvature radius of an optical wavefront with a straight
line connecting the apex of the cylindrical shape of the optical
wavefront being set substantially perpendicular to the wavefront
dispersion surface of a wavelength selection element arranged
inside the laser resonator of the narrow-band laser device, and the
wavefront adjuster is adjusted so that the spectral line width
assumes a value between the upper limit and the lower limit.
[0030] In a third aspect of the invention according to the second
aspect, the spectral line width adjustment unit includes: a
cylindrical concave lens and cylindrical convex lens whose central
axes are arranged on the optical path inside the laser resonator of
the narrow-band laser device and whose mechanical axes are arranged
substantially perpendicular to the wavefront dispersion surface of
the wavelength selection element arranged inside the laser
resonator; and a lens distance variable mechanism for varying the
distance between the cylindrical concave lens and the cylindrical
convex lens along the optical path, and the lens distance variable
mechanism is adjusted so that the spectral line width assumes a
value between the upper limit and the lower limit.
[0031] In a fourth aspect of the invention according to the second
aspect, the spectral line width adjustment unit includes: a
cylindrical mirror whose central axis is arranged on the optical
path inside the laser resonator of the narrow-band laser device,
and whose mechanical axis is arranged substantially perpendicular
to the wavefront dispersion surface of the wavelength selection
element arranged inside the laser resonator; and a mirror curvature
variable mechanism for varying a curvature of the cylindrical
mirror, and the mirror curvature variable mechanism is adjusted so
that the spectral line width assumes a value between the upper
limit and the lower limit.
[0032] In a fifth aspect of the invention according to the second
aspect, the spectral line width adjustment unit includes: a grating
used as the wavelength selection element; and a grating curvature
variable mechanism for varying a curvature of the grating while
keeping a linear shape of a multiplicity of grooves of the grating,
and the grating curvature variable mechanism is adjusted so that
the spectral line width assumes a value between the upper limit and
the lower limit.
[0033] In a sixth aspect of the invention according to the first
aspect, the spectral line width adjustment unit includes: two or
more prisms arranged on an optical path inside a laser resonator of
the narrow-band laser device for expanding a beam in a direction
substantially perpendicular to the wavefront dispersion surface of
a wavelength selection element arranged inside the laser resonator;
and a prism angle variable mechanism for varying a rotation angle
of the two or more prisms to change a beam expansion factor, and
the prism angle variable mechanism is adjusted so that the spectral
line width assumes a value between the upper limit and the lower
limit.
[0034] The third to sixth aspects of the invention each relate to a
specific method of adjusting the spectral line width in the first
aspect of the invention.
[0035] In a seventh aspect of the invention according to the first
aspect, the narrow-band laser device includes an oscillation stage
laser for generating and outputting seed light, and one or more
amplification stage chambers or amplification stage lasers for
receiving and amplifying the laser light output from a previous
stage laser, and outputting the amplified laser light; and the
spectral line width adjustment unit includes a spectral line width
variable mechanism arranged on a laser optical path between the
oscillation stage laser and the amplification stage chamber or the
amplification stage laser, and the spectral line width variable
mechanism is adjusted so that the spectral line width assumes a
value between the upper limit and the lower limit.
[0036] The seventh aspect of the invention relates to a specific
method of adjusting the spectral line width when the narrow-band
laser device is a double-chamber system having an oscillation stage
and an amplification stage in the first aspect.
[0037] In an eighth aspect of the invention according to the first
aspect, the narrow-band laser device includes an oscillation stage
laser for generating and outputting seed light, and one or more
amplification stage chambers or amplification stage lasers for
receiving and amplifying the laser light output from a previous
stage laser, and outputting the amplified laser light; and the
spectral line width adjustment unit includes a spectral line width
variable mechanism arranged on a laser optical path inside a laser
resonator of the oscillation stage laser, and the spectral line
width variable mechanism is adjusted so that the spectral line
width assumes a value between the upper limit and the lower
limit.
[0038] The eighth aspect of the invention relates to a specific
method for adjusting the spectral line width when the narrow-band
laser device is a double-chamber system having an oscillation stage
and an amplification stage in the first aspect.
[0039] The present invention is able to minimize the deviation in
spectral line width such as E95 bandwidth among laser devices can
be minimized, and the deviation in spectral line width such as E95
bandwidth of a same laser device between before and after it is
subjected to maintenance. Therefore, the spectral line width of
laser light output by the laser device does not exceed the
allowable range of spectral line width such as E95 bandwidth for an
optical system of the exposure tool. This makes it possible to
stabilize the quality of integrated circuit patterns formed by the
semiconductor exposure tool and thus improves the yield of
semiconductor devices. Furthermore, the yield of laser production
and the yield in maintenance are improved, whereby the laser
production cost and the maintenance cost can be reduced
effectively.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] FIG. 1 is a diagram showing an example of a device
configuration for adjusting a spectral line width of a narrow-band
laser device;
[0041] FIGS. 2(a) and 2(b) are diagrams showing a configuration of
an E95 bandwidth adjustment unit and the positional relationship
among an output coupler, the E95 bandwidth adjustment unit, a laser
chamber, and a line narrowing module, according to a first
embodiment of the invention;
[0042] FIGS. 3(a) and 3(b) are diagrams showing a configuration of
an E95 bandwidth adjustment unit according to a second embodiment
of the invention;
[0043] FIG. 4 is a diagram showing the relationship between a
micrometer relative scale, an E95 bandwidth, and a laser output
relative value when the E95 bandwidth adjustment unit according to
the second embodiment is used;
[0044] FIG. 5 is a histogram of E95 bandwidths due to laser machine
differences when the E95 bandwidth adjustment unit according to the
second embodiment is employed;
[0045] FIG. 6 is a diagram showing a configuration of an E95
bandwidth adjustment unit according to a third embodiment and
positional relationship among the E95 bandwidth adjustment unit, a
laser chamber and a line narrowing module;
[0046] FIG. 7 is a diagram showing a state in which the E95
bandwidth adjustment unit is attached to the rear side of the laser
chamber;
[0047] FIGS. 8(a) and 8(b) are diagrams showing a configuration of
an E95 bandwidth adjustment unit according to a fourth embodiment
of the invention;
[0048] FIG. 9 is a diagram showing a state in which the E95
bandwidth adjustment unit according to the fourth embodiment is
provided in a line narrowing module;
[0049] FIGS. 10(a) and 10(b) are diagrams showing a configuration
of an E95 bandwidth adjustment unit according to a fifth embodiment
of the invention;
[0050] FIG. 11 is a diagram showing a state in which the E95
bandwidth adjustment unit according to the fifth embodiment is
provided in a line narrowing module;
[0051] FIG. 12 is a diagram showing a configuration of an E95
bandwidth adjustment unit according to a sixth embodiment of the
invention;
[0052] FIG. 13 is a diagram showing a relationship among a
micrometer relative scale, an E95 bandwidth, and a laser output
relative value when the E95 bandwidth adjustment unit according to
the sixth embodiment is employed;
[0053] FIG. 14 is a diagram showing a configuration of an E95
bandwidth adjustment unit according to a seventh embodiment of the
invention;
[0054] FIG. 15 is a diagram showing a state in which the E95
bandwidth adjustment unit is provided in a PO (amplification stage
laser) of a double-chamber system;
[0055] FIG. 16 is a diagram showing positional relationship among
an E95 bandwidth adjustment unit, a laser chamber, and a line
narrowing module according to an eighth embodiment of the
invention;
[0056] FIGS. 17(a) and 17(b) are diagrams showing a configuration
of the E95 bandwidth adjustment unit according to the eighth
embodiment;
[0057] FIG. 18 is a diagram showing a state in which the E95
bandwidth adjustment unit is provided between a PO and an MO
(oscillation stage laser) of a double-chamber system;
[0058] FIG. 19 is a diagram showing a state in which a cylindrical
lens is arranged between the MO and the PO;
[0059] FIG. 20 is a diagram showing a state in which a prism is
arranged between the MO and the PO;
[0060] FIG. 21 is a diagram showing a state in which a slit is
arranged between the MO and the PO;
[0061] FIGS. 22(a) and 22(b) are diagrams for explaining the FWHM
and the E95 bandwidth; and
[0062] FIG. 23 is a histogram of E95 bandwidths due to laser
machine differences according to conventional techniques.
DETAILED DESCRIPTION OF THE INVENTION
[0063] Preferred embodiments of the present invention will be
described with reference to the accompanying drawings. While the
spectral line width includes several types such as FWHM and E95,
the following description will be made taking the E95 bandwidth as
an example.
[0064] FIG. 1 shows an example of a device configuration for
adjusting the spectral line width of a narrow-band laser
device.
[0065] In a narrow-band laser device 1 as shown in FIG. 1, a slit
90r and a line narrowing module 30 are arranged on an optical path
on the rear side (the right side in the drawing) of a laser chamber
20, and a slit 90f and an E95 bandwidth adjustment unit 40 are
arranged on an optical path on the front side (on the left side in
the drawing) of the laser chamber 20. Further, a monitor module 60
and an output coupler 50 having an incidence surface coated with a
PR film and an emission surface coated with an AR film are arranged
on an optical path on the front side (the left side in the drawing)
of the E95 bandwidth adjustment unit 40. The line narrowing module
30 and the output coupler 50 together form a resonator.
[0066] A pair of discharge electrodes 21 and 22 are provided in the
inside of the laser chamber 20. The discharge electrodes 21 and 22
are arranged parallel to each other in the longitudinal direction
thereof, and such that the discharge surfaces thereof face each
other, being spaced from each other by a predetermined distance.
Further, windows 23 and 24 are provided in a laser light output
portion on the optical axis of laser light in the laser chamber 20.
The windows 23 and 24 are made of a material having transparency to
laser light such as CaF2. The windows 23 and 24 are arranged such
that the outer surfaces thereof are parallel to each other, and
arranged at a Brewster angle to reduce the reflection loss of laser
light.
[0067] Laser gas is sealed inside the laser chamber 20 as a laser
medium. The laser gas used in the case of F2 laser is gas mixture
composed of F2 gas and a buffer gas such as He or Ne. The laser gas
used in the case of KrF excimer laser is gas mixture composed of Kr
gas, F2 gas, and a buffer gas such as He or Ne. The laser gas used
in the case of ArF excimer laser is gas mixture composed of Ar gas,
F2 gas, and a buffer gas such as He or Ne. The supply and discharge
of the laser gas is controlled by a gas supply/discharge mechanism
(not shown).
[0068] High voltage is applied by a power supply circuit 70 to the
discharge electrodes 21 and 22 provided in the laser chamber 20.
Electric discharge occurs when the voltage between the discharge
electrodes 21 and 22 exceeds a predetermined voltage. The laser gas
in the laser chamber 20 is excited by the electric discharge to
shift to a high energy level and then to a low energy level,
resulting in emission of light.
[0069] There are provided in the line narrowing module 30 optical
elements such as prism beam expanders (hereafter, each referred to
as the "prism") 32 and 33 and a grating 31 serving as a wavelength
dispersive element. Although two prisms are provided in the example
shown in FIG. 1, the number of the prisms can be determined
arbitrarily. The grating 31 and the prisms 32 and 33 are usually
fixed to a casing of the line narrowing module 30 by means of a
fixing member. However, in some cases, they may be fixed rotatably.
In such a case, the prisms 32 and 33 and the grating 31 are fixed
to a rotation mechanism not shown in the drawing. The incident
angle of laser light to the grating 31 and the prisms 32 and 33 is
changed by driving the rotation mechanism. Further, the line
narrowing module 30 may be formed of optical elements such as a
total reflection mirror and an etalon serving as a wavelength
dispersive element.
[0070] The E95 bandwidth adjustment unit 40 is composed of optical
elements for adjusting the E95 bandwidth of laser light. The E95
bandwidth adjustment unit 40 can be configured in several manners,
which will be described later with reference to FIGS. 2(a) and 2(b)
to FIG. 21.
[0071] The monitor module 60 is provided with a beam splitter 61
and a monitor 62. The monitor 62 is comprised of a monitor for
detecting an E95 bandwidth or central wavelength and a monitor for
detecting laser light energy. The monitor for detecting an E95
bandwidth or central wavelength includes a spectrometer having, for
example, a diffuser panel, an etalon, a condenser lens, a line
sensor and so on. Laser light entering the monitor module 60 is
split by the beam splitter 61 so that part of the laser light
enters the monitor 62 while the rest is emitted to the outside.
[0072] A laser controller 80 calculates energy, wavelength, and
spectral line width of laser light based on a spectral detected by
the monitor 62 of the monitor module 60. Based on the calculation
results, the laser controller 80 outputs a command signal
indicating a charging voltage of the power supply circuit 70, and a
command signal for driving the rotation mechanism to which the
optical elements of the line narrowing module 30 are fixed.
[0073] There are provided, in the outside of the narrow-band laser
device 1, a high resolution spectrometer 4 for detecting the
spectral of laser light output by the narrow-band laser device 1, a
condenser lens 2 and an optical fiber 3 for guiding laser light
from the narrow-band laser device to the high resolution
spectrometer 4, and a personal computer 9 for retrieving the
detection result from the high resolution spectrometer 4 and
displaying the spectral of the laser light on a display device.
[0074] The laser light emitted by the narrow-band laser device 1 is
collected by the condenser lens 2. The light emitted by the
condenser lens 2 passes through the optical fiber 3 and enters the
high resolution spectrometer 4. In the high resolution spectrometer
4, the light passes through the condenser lens 5 and illuminates an
entrance slit 11. Light transmitted through the entrance slit is
reflected by a concave mirror 6a, diffracted by a grating 7, and
reflected by a concave mirror 6b. A diffraction image is thus
formed on a CCD line sensor 8. This diffraction image changes its
image forming position according to the diffraction angle at the
grating 7 that is changed depending on a wavelength. The CCD line
sensor 8 is thus enabled to detect the spectral of the light. The
spectral detected by the CCD line sensor 8 is converted into a
signal which is introduced into the personal computer 9. The
personal computer 9 has a display device 10 connected thereto, and
the spectral detected by the CCD line sensor 8 is displayed on this
display device 10. Although the description of the high resolution
spectrometer 4 has been made taking an example of a commonly used
Czerny-Turner spectrometer, any other high resolution spectrometer
may be used as long as it is capable of measuring E95 bandwidth
sufficiently.
[0075] Description will be made of procedures of a spectral line
width adjusting method.
[0076] In the first place, an upper limit .DELTA..lamda.HL and a
lower limit .DELTA..lamda.LL are set for the E95 bandwidth common
to narrow-band lasers used for semiconductor exposure. The upper
limit .DELTA..lamda.HL and the lower limit .DELTA..lamda.LL are set
within a range of E95 bandwidth allowed for the optical system of
the semiconductor exposure tool.
[0077] Before using the narrow-band laser device 1 as a light
source for the exposure tool, for example after the assembly of the
narrow-band laser device 1 or directly after maintenance of the
narrow-band laser device 1, the condenser lens 2, the optical fiber
3, the high resolution spectrometer 4, the personal computer 9, and
the display device 10 are arranged outside the narrow-band laser
device 1, as shown in FIG. 1. The narrow-band laser device 1 is
then laser oscillated. During the laser oscillation, a spectral of
the laser light is detected by the high resolution spectrometer 4,
and is displayed on the display device 10.
[0078] Looking at the display device 10, the operator adjusts the
E95 bandwidth adjustment unit 40 of the narrow-band laser device 1
such that the E95 bandwidth takes a value between the upper limit
.DELTA..lamda.HL and the lower limit .DELTA..lamda.LL. The E95
bandwidth varies in accordance with the adjustment of the E95
bandwidth adjustment unit 40. When the E95 bandwidth becomes a
value between the upper limit .DELTA..lamda.HL and the lower limit
.DELTA..lamda.LL, the E95 adjustment unit 40 is fixed to terminate
the adjustment of the E95 bandwidth.
[0079] Although, according to the embodiment shown in FIG. 1, the
high resolution spectrometer 4 provided outside the narrow-band
laser device 1 is used, a small-sized spectral detector may be
used, providing the same within the narrow-band laser device 1.
Further, the monitor 62 of the monitor module 60 provided in the
narrow-band laser device 1 may be used.
[0080] Description will be made of specific configuration of the
E95 bandwidth adjustment unit 40.
[0081] FIGS. 2(a) and 2(b) show configuration of the E95 bandwidth
adjustment unit and positional relationship among the output
coupler, the E95 bandwidth adjustment unit, the laser chamber, and
the line narrowing module, according to the first embodiment. FIG.
2(a) is a plan view and FIG. 2(b) is a side view. The first
embodiment is designed to adjust the optical wavefront by changing
the distance between two lenses. The optical wavefront has a
cylindrical shape. A straight line connecting the apex of the
cylindrical shape is set approximately perpendicular to the
wavefront dispersion surface of a wavelength selection element
(grating) in the laser resonator, and the curvature of the
cylindrical optical wavefront is varied, whereby the laser E95
bandwidth can be changed. The wavefront dispersion surface
corresponds to an x-z plane in FIGS. 2(a) and 2(b), where the
direction orthogonal to a multiplicity of grooves formed in the
diffraction surface of the grating 31 is defined as the x axis, the
direction parallel to the grooves formed in the diffraction surface
of the grating 31 is defined as the y axis, and the direction
orthogonal to the diffraction surface of the grating 31 is defined
as the z axis.
[0082] The E95 bandwidth adjustment unit 40 shown in FIGS. 2(a) and
2(b) has a cylindrical concave lens 41 and a cylindrical convex
lens 42 which face each other with a distance therebetween, the
distance being freely adjustable. The cylindrical concave lens 41
and the cylindrical convex lens 42 are arranged such that central
axes thereof are located on the optical path in the laser
resonator, and such that mechanical axes thereof are approximately
perpendicular to the wavefront dispersion surface of the grating
31. The central axes of the cylindrical concave lens 41 and
cylindrical convex lens 42 are defined by a straight line
connecting the centers of curvature radii of the cylindrical
surfaces. The mechanical axis of the cylindrical concave lens 41 is
defined by a straight line connecting the most recessed points in
the lens. The mechanical axis of the cylindrical convex lens 42 is
defined by a straight line connecting the most protruding point in
the lens. The cylindrical concave lens 41 is fixed to the upper
surface of a movable plate 43. The movable plate 43 is movable
along a linear guide 45 formed on a uniaxial stage 44. The uniaxial
stage 44 is arranged such that the direction in which the linear
guide 45 is extended is parallel to the optical axis.
[0083] A convex portion 43a is formed on one side face of the
movable plate 43 so as to protrude therefrom. The head of the
micrometer 46 abuts on the front side of the convex portion 43a,
while the head of a protrusion 47 abuts on the rear side of the
convex portion 43a. The micrometer 46 is extendable and retractable
in the direction in which the linear guide 45 is extended, and the
extension of the micrometer 46 applies a pressing force to the
convex portion 43a in the direction toward the protrusion 47. A
spring which is extendable and retractable in the direction in
which the linear guide 45 is extended is connected to the head of
the protrusion 47, so that the spring applies an urging force to
the convex portion 43a in the direction toward the micrometer 46.
Consequently, the movable plate 43 is moved along linear guide 45
by extension or retraction of the micrometer 46.
[0084] A fixing screw 48 is provided on the other side of the
movable plate 43. The fixing screw 48 is screwed in a through hole
formed in the movable plate 43 so that the tip end thereof abuts on
the linear guide 45. The movable plate 43 is fastened to the
uniaxial stage 43 by tightening the fixing screw 48. The movable
plate 43 is released by loosening the fixing screw 48. It should be
understood that the fixing screw 48 may be omitted as long as the
movable plate 43 can be sufficiently fixed to the uniaxial stage 43
by means of the micrometer 46 and the protrusion 47.
[0085] The E95 bandwidth adjustment unit 40, the laser chamber 20,
and the line narrowing module 30 are arranged in orientation as
shown in FIGS. 2(a) and 2(b). More specifically, the E95 bandwidth
adjustment unit 40, the laser chamber 20, and the line narrowing
module 30 are arranged such that the centers of the curvature radii
of the cylindrical surfaces of the cylindrical concave lens 41 and
cylindrical convex lens 42 provided in the line narrowing module 30
are located on the laser optical axis, and such that the mechanical
axes of the cylindrical concave lens 41 and cylindrical convex lens
42 are parallel to the multiplicity of grooves formed in the
diffraction surface of the grating 31.
[0086] FIGS. 3(a) and 3(b) show configuration of an E95 bandwidth
adjustment unit according to a second embodiment. FIG. 3(a) is a
plan view and FIG. 3(b) is a side view. In the second embodiment, a
planoconcave cylindrical lens 101 and a planoconvex cylindrical
lens 102 are provided respectively in place of the cylindrical
concave lens 41 and the cylindrical convex lens 42 shown in FIGS.
2(a) and 2(b). Configuration of the second embodiment is identical
with that of the first embodiment shown in FIGS. 2(a) and 2(b),
except for the planoconcave cylindrical lens 101 and the
planoconvex cylindrical lens 102. In the second embodiment, the
output coupler 50 shown in FIG. 1 is not required since the
planoconvex cylindrical lens 102 functions as an output coupler.
The incidence surface (the surface closer to the laser chamber) of
the planoconvex cylindrical lens 102 is coated with an
anti-reflection (AR) film, while the emission surface (the surface
further from the laser chamber) is coated with a partial-reflection
(PR) film. Similarly to the configuration shown in FIGS. 2(a) and
2(b), the centers of the curvature radii of the planoconcave
cylindrical lens 101 and planoconvex cylindrical lens 102 are
located on the laser optical axis, and the mechanical axes of the
planoconcave cylindrical lens 101 and planoconvex cylindrical lens
102 are parallel to a multiplicity of grooves formed on the
diffraction surface of the grating 31.
[0087] FIG. 4 shows relationship among a micrometer relative scale,
an E95 bandwidth, and a laser output relative value when the E95
bandwidth adjustment unit according to the second embodiment is
used. In FIG. 4, the relative scale of the micrometer 46 (the axis
of abscissa) of "1" corresponds to a state in which the
planoconcave cylindrical lens 101 and the planoconvex cylindrical
lens 102 are separated from each other by a predetermined distance.
As the relative scale of the micrometer 46 increases, the
planoconcave cylindrical lens 101 is separated further from the
planoconvex cylindrical lens 102.
[0088] As seen from FIG. 4, the E95 bandwidth monotonically
increases from 0.23 pm to 1.2 pm along with the increase of the
micrometer relative scale. On the other hand, as the micrometer
relative scale increases from 1 to 9, the laser output relative
value monotonically increases from 0.42 to 1.63. As the micrometer
relative scale increases from 9 to 11, the laser output
monotonically decreases from 1.63 to 1.2.
[0089] When the target value of E95 bandwidth is set to 0.4 pm, for
example, adjustment is made such that the relative scale of the
micrometer 46 becomes 4.2. The laser output relative value is 0.95
in this state. Once the E95 bandwidth attains the target value, the
fixing screw 48 is tightened to fix the movable plate 43.
[0090] FIG. 5 is a histogram showing the E95 bandwidth varied due
to laser machine differences when the E95 bandwidth adjustment unit
according to the second embodiment is used.
[0091] A plurality of narrow-band laser devices were prepared as
test samples. The lower limit .DELTA..lamda.LL of the E95 bandwidth
was set to 0.30 pm, while the upper limit .DELTA..lamda.HL is set
to 0.50 pm. The narrow-band laser devices were oscillated and the
E95 bandwidth adjustment unit was adjusted so that the E95
bandwidth assumed a value between the upper limit .DELTA..lamda.HL
and the lower limit .DELTA..lamda.LL. The maximum value of the E95
bandwidth was 0.440 pm, the minimum value 0.360 pm, the mean value
0.405 pm, and the standard deviation was 0.029 pm. These variations
due to the machine differences were effectively contained in the
allowable E95 bandwidth range of from 0.350 pm to 0.450 pm.
[0092] FIG. 6 shows configuration of an E95 bandwidth adjustment
unit according to a third embodiment and positional relationship
among the E95 bandwidth adjustment unit, a laser chamber, and a
line narrowing module. FIG. 6 is a plan view. The third embodiment
is designed to adjust the optical wavefront by changing the
curvature of a cylindrical mirror.
[0093] An E95 bandwidth adjustment unit 40 shown in FIG. 6 has a
cylindrical mirror 111 the curvature of which is adjustable. In the
third embodiment, a beam splitter 117 is arranged between the
cylindrical mirror 111 and a laser chamber 20. The beam splitter
117 functions as an output coupler. Two rods 112 are connected, at
one end thereof, to the opposite edges of the rear face of the
cylindrical mirror 111. One end of a spring 113 is connected to the
center of the rear face of the cylindrical mirror 111. The other
ends of the two rods 112 are connected to a plate 114 arranged
behind the cylindrical mirror 111, and the other end of the spring
113 is connected to the head of a micrometer 115 arranged behind
the cylindrical mirror 111. The micrometer 115 is fixed to the
plate 114. The micrometer 115 is provided with a fixing screw 116
for fixing the extension or retraction.
[0094] The cylindrical mirror 111 is arranged such that the center
of the curvature radius of its cylindrical surface is located on
the laser optical axis, and the mechanical axis of the cylindrical
surface is parallel to a multiplicity of grooves formed in a
diffraction surface of a grating 31 (i.e. substantially
perpendicular to a wavefront dispersion surface of the grating 31).
The definition of the mechanical axis of the cylindrical surface is
the same as the definition of the mechanical axis of the
cylindrical concave lens 41 described above.
[0095] When extended, the micrometer 115 pushes the center of the
cylindrical mirror 111 by way of the spring 113. When retracted,
the micrometer 115 pulls the center of the cylindrical mirror 111
by way of the spring 113. The curvature of the cylindrical surface
of the cylindrical mirror 111 is adjusted in this manner.
[0096] The description so far has been made regarding the
configuration in which the E95 bandwidth adjustment unit is
arranged on the front side of the laser chamber. However, as shown
in FIG. 7, the E95 bandwidth adjustment unit may be arranged on the
rear side of the laser chamber to adjust the E95 bandwidth.
Description will be made of this embodiment.
[0097] FIGS. 8(a) and 8(b) show a configuration of an E95 bandwidth
adjustment unit according to a fourth embodiment. FIGS. 8(a) and
8(b) show a same E95 bandwidth adjustment unit but different
patterns of wavefront adjustment. The configuration of the E95
bandwidth adjustment unit 40' shown in FIGS. 8(a) and 8(b)
coincides, in many aspects, with that of the E95 bandwidth
adjustment unit 40 shown in FIGS. 2(a) and 2(b). They are different
only in that a cylindrical concave lens 121 is not fixed to a
movable plate but a cylindrical convex lens 122 is fixed to the
movable plate.
[0098] The E95 bandwidth adjustment unit 40' shown in FIGS. 8(a)
and 8(b) has a cylindrical concave lens 121 and a cylindrical
convex lens 122 facing each other with a distance which is
adjustable. The cylindrical convex lens 122 is arranged on the rear
side of the laser chamber 20 such that the center of the curvature
radius of the cylindrical surface is located on the laser optical
axis, and the mechanical axis of the cylindrical surface is
parallel with a multiplicity of grooves formed on a diffraction
surface of a grating 31 (i.e. such that the mechanical axis is
substantially orthogonal to the wavefront dispersion surface). The
cylindrical concave lens 121 is arranged on the rear side of the
cylindrical convex lens 122 such that the center of the curvature
radius of the cylindrical surface is located on the laser optical
axis and the mechanical axis of the cylindrical surface is parallel
with the multiplicity of grooves formed on the diffraction surface
of the grating 31 (i.e., such that the mechanical axis is
substantially orthogonal to the wavefront dispersion surface). The
cylindrical convex lens 122 is fixed to the upper surface of a
movable plate 123. The movable plate 123 is movable along a linear
guide 125 formed on a uniaxial stage 124. The uniaxial stage 124 is
arranged such that the direction in which the linear guide 125
extends is parallel to the optical axis.
[0099] A convex portion 123a is formed on one side of movable plate
123 so as to protrude therefrom. The head of a micrometer 126 abuts
on the front face of the convex portion 123a, and the head of a
protrusion 127 abuts on the rear face of the convex portion 123a.
The micrometer 126 is extendable and retractable in the direction
in which the linear guide 125 extends, and extension of the
micrometer 126 applies a pressing force to the convex portion 123a
in the direction towards the protrusion 127. The head of the
protrusion 127 is connected to a spring which is extendable and
retractable in the direction in which the linear guide 125 extends.
This spring applies an urging force to the convex portion 123a in
the direction towards the micrometer 126. Accordingly, the movable
plate 123 is moved along the linear guide 125 by extension or
retraction of the micrometer 126.
[0100] A fixing screw 128 is provided on the other side of the
movable plate 123. The fixing screw 128 is screwed into a through
hole formed in the movable plate 123 and the tip end of the screw
abuts on the linear guide 125. The movable plate 123 is fixed to
the uniaxial stage 123 by tightening the fixing screw 128. The
movable plate 123 is released by loosening the fixing screw 128. It
should be understood that the fixing screw 128 may be omitted as
long as the movable plate 123 can be effectively fixed to the
uniaxial stage 123 by means of the micrometer 126 and the
protrusion 127.
[0101] As shown in FIG. 9, the E95 bandwidth adjustment unit 40'
shown in FIGS. 8(a) and 8(b) may be provided between a grating 31
and a prism 33 provided in the line narrowing module 30.
[0102] FIGS. 10(a) and 10(b) show configuration of an E95 bandwidth
adjustment unit according to a fifth embodiment. FIGS. 10(a) and
10(b) show a same E95 bandwidth adjustment unit but different
patterns of wavefront adjustment. The configuration of the E95
bandwidth adjustment unit 40' shown in FIGS. 10(a) and 10(b)
coincides, in many aspects, with that of the E95 bandwidth
adjustment unit 40 shown in FIG. 6. They are different only in that
no beam splitter is provided and the optical incident direction is
different from the reflection direction in the E95 bandwidth
adjustment unit 40'.
[0103] The E95 bandwidth adjustment unit 40' shown in FIGS. 10(a)
and 10(b) has a cylindrical mirror 131 the curvature of which is
adjustable. Two rods 132 are connected, at one ends thereof, to the
opposite edges of the rear face of the cylindrical mirror 131. One
end of a spring 133 is connected to the center of the rear face of
the cylindrical mirror 131. The other ends of the two rods 132 are
connected to a plate 134 arranged behind the cylindrical mirror
131, and the other end of the spring 133 is connected to the head
of a micrometer 135 arranged behind the cylindrical mirror 131. The
micrometer 135 is fixed to the plate 134. The micrometer 135 is
provided with a fixing screw 136 for fixing the extension or
retraction.
[0104] The cylindrical mirror 131 is arranged in such an
orientation that the incident direction of laser light is different
from the reflection direction. The cylindrical mirror 131 is
arranged such that the mechanical axis of the cylindrical surface
is parallel with a multiplicity of grooves formed in the
diffraction surface of a grating 31. The definition of the
mechanical axis of the cylindrical surface is the same as the
definition of the mechanical axis of the cylindrical concave lens
41 described above.
[0105] When extended, the micrometer 135 pushes the center of the
cylindrical mirror 131 by way of the spring 133, and when retracted
the micrometer 135 pulls the center of the cylindrical mirror 131
by way of the spring 133. The curvature of the cylindrical surface
of the cylindrical mirror 131 is adjusted in this manner.
[0106] As shown in FIG. 11, the E95 bandwidth adjustment unit 40'
shown in FIGS. 10(a) and 10(b) may be provided between a prism 32
and a prism 33 provided in the line narrowing module 30. In this
case, it is desirable to provide an operating portion of the
micrometer 135 outside the casing of the line narrowing module
30.
[0107] FIG. 12 shows configuration of an E95 bandwidth adjustment
unit according to a sixth embodiment. The sixth embodiment is
designed to adjust the optical wavefront by changing the curvature
of a grating provided in a line narrowing module. The configuration
of the micrometer or the like used in the third and fifth
embodiments is applied to the adjustment of the curvature of the
grating.
[0108] Two rods 142 are connected, at one ends thereof, to the
opposite edges of the rear face of the grating 31. One end of a
spring 143 is connected to the center of the rear face of the
grating 31. The other ends of the two rods 142 are connected to a
plate 144 arranged behind the grating 31, and the other end of the
spring 143 is connected to the head of a micrometer 145 arranged
behind the grating 31. The micrometer 145 is fixed to the plate
144. The micrometer 145 is provided with a fixing screw 146 for
fixing the extension or retraction.
[0109] When extended, the micrometer 145 pushes the center of the
grating 31 by way of the spring 143, and when retracted, the
micrometer 145 pulls the center of the grating 31 by way of the
spring 143. In this manner, the curvature of the diffraction
surface is adjusted while keeping the multiplicity of the grooves
of the grating 31 in linear shape.
[0110] FIG. 13 shows relationship among a micrometer relative
scale, an E95 bandwidth, and a laser output relative value when the
E95 bandwidth adjustment unit according to the sixth embodiment is
used. In FIG. 13, the relative scale of the micrometer 145 (the
axis of abscissa) of "1" corresponds to a state in which the
grating 31 has a predetermined curvature. As the relative scale of
the micrometer 146 increases, the center of the grating 31 is
pushed further out.
[0111] As seen from FIG. 13, as the micrometer relative scale
increases from one to six, the E95 bandwidth monotonically
decreases from 0.40 pm to 0.23 pm. As the micrometer relative scale
increases from six to eleven, the E95 bandwidth monotonically
increases from 0.23 pm to 0.5 pm. On the other hand, as the
micrometer relative scale increases from one to six, the laser
output relative value monotonically increases from 0.1 to 0.5, and
as the micrometer relative scale increases from six to eleven, the
laser output relative value monotonically decreases from 0.5 to
0.1.
[0112] When the target value of the E95 bandwidth is set to 0.4 pm,
for example, the adjustment is made such that the relative scale of
the micrometer 145 becomes one. The laser output relative value in
this state is 0.1. Once the E95 bandwidth attains the target value,
the fixing screw 146 is tightened to fix the micrometer 145.
[0113] It will be examined, on the basis of the result shown in
FIG. 4 and the result shown in FIG. 13, which is more advantageous
when the adjustment of the E95 bandwidth is made on the front side
of the laser chamber or when made on the rear side. The laser
output relative values in FIG. 4 and FIG. 13 are indicated on the
same scale so that the laser output values can be compared
relatively.
[0114] According to the configuration in which the E95 bandwidth
adjustment unit is arranged on the front side of the laser chamber,
as shown in FIG. 4, an advantageous characteristic is obtained that
the E95 bandwidth monotonically increases along with the increase
of the micrometer scale reading. Accordingly, it can be seen that
the E95 bandwidth can be enlarged simply by extending the
micrometer, whereas the E95 bandwidth can be narrowed simply by
retracting the micrometer.
[0115] On the other hand, when the E95 bandwidth adjustment unit is
arranged on the rear side of the laser chamber, as shown in FIG.
13, the E95 bandwidth monotonically increases along with the
increase of the scale reading of the micrometer. However, once the
scale reading of the micrometer has increased to some extent, the
E95 bandwidth thereafter monotonically decreases along with the
increase of the scale reading. Accordingly, it is impossible to
determine how to operate the micrometer for enlarging or narrowing
the E95 bandwidth, until the micrometer is actually operated to
observe how the E95 bandwidth varies.
[0116] As a result, it can be concluded that the adjustment can be
done easier when the E95 adjustment unit is arranged on the front
side than on the rear side of the laser chamber. Further, comparing
the laser output relative values of FIG. 4 and FIG. 13, it can be
seen that greater laser output can be obtained when the E95
adjustment unit is arranged on the front side than on the rear side
of the laser chamber. Thus, it can be concluded that it is more
advantageous to perform adjustment of the E95 bandwidth on the
front side of the laser chamber.
[0117] FIG. 14 shows configuration of an E95 bandwidth adjustment
unit according to a seventh embodiment. The seventh embodiment is
designed to adjust the expansion ratio of a beam entering a grating
31 by changing the rotation angle of a prism provided in a line
narrowing module. When the incident beam is expanded in a direction
perpendicular to the wavefront dispersion surface of the grating
31, the spread angle of the beam is reduced and hence the spectral
line width is narrowed.
[0118] A prism 32 is fixed to a rotary plate 151, and the rotary
plate 151 is rotatably supported by a rotary stage 152. A convex
portion 151a is formed on a side face of the rotary plate 151 so as
to protrude therefrom. The head of a micrometer 153 abuts on the
front face of the convex portion 151a, and the head of a protrusion
154 abuts on the rear face of the convex portion 151a. The
extension of the micrometer 153 gives a pressing force to the
convex portion 151a in the direction towards the protrusion 154. A
spring which is extendable and retractable is connected to the head
of the protrusion 154, so that the urging force is given to the
convex portion 151a by means of this spring in the direction
towards the micrometer 153. Accordingly, the rotary plate 151 is
rotated by extension and retraction of the micrometer 153.
[0119] A prism 33 is fixed to the rotary plate 156 in the same
manner as the prism 32 is fixed to the rotary plate 151. Therefore,
description thereof will be omitted.
[0120] In order to adjust the E95 bandwidth, the micrometer 153 is
adjusted to rotate the rotary plate 151 and the prism 32, and the
micrometer 158 is adjusted to rotate the rotary plate 156 and the
prism 33, while ensuring not to change the laser oscillation
wavelength. During this operation, the rotary plate 151 and the
prism 32 are rotated in the opposite direction to the direction in
which the rotary plate 156 and the prism 33 are rotated, while
matching the rotation angles thereof, whereby the beam expansion
ratio by the prisms 32 and 33 is changed. The E95 bandwidth becomes
greater as the expansion ratio increases, and the E95 bandwidth
becomes smaller as the expansion ratio decreases.
[0121] It should be understood that, as shown in FIG. 15, the
present invention is also applicable to adjustment of the E95
bandwidth in a narrow-band laser device having two laser chambers,
so-called double-chamber system. Description will be made of
configuration of an E95 bandwidth adjustment unit used in a
double-chamber system.
[0122] For example, a double-chamber system includes an MO
(oscillation stage laser) 200 for generating seed laser light and a
PO (amplification stage laser) 300 for amplifying laser light
output from the MO 200. In the MO 200, a line narrowing module 230
is arranged on the rear side of a laser chamber 220, and an output
coupler 250 is arranged on the front side. The line narrowing
module 230 is provided with a grating 231 and prisms 232 and 233.
In the PO 300, a rear mirror 331 is arranged on the rear side of a
laser chamber 320, and an output coupler 350 is arranged on the
front side. In this embodiment, a rear mirror 331 is coated with a
partial-reflection (PR) film having a reflectance of 80 to 90%, for
example.
[0123] The MO 200 according to this embodiment has the output
coupler 250, an E95 bandwidth adjustment unit, the laser chamber
220, and a line narrowing module 230. Laser light output by the MO
200 and having a narrow spectral line width is reflected by mirrors
501 and 502, and injected into the PO 300. In the PO 300, the seed
laser light is introduced into the rear mirror 331 from the rear
side thereof, and a part of the seed laser light is transmitted
through the rear mirror 331. The transmitted seed light is
amplified between the rear mirror 331, the laser chamber 320, and
the output coupler 350 of the laser amplification stage to cause
laser oscillation. Laser light output from the PO 300 is split by a
beam splitter 503. One part of the laser light is output to the
outside while the other part of the laser light is input to a
monitor module 560. In the monitor module 560, the laser light is
split by a beam splitter 561, an E95 bandwidth or a central
wavelength is detected by a wavelength monitor 562, and pulse
energy is detected by an energy monitor 563.
[0124] The configuration described above in relation to the first
to seventh embodiments may be provided on the front side or rear
side of the laser chamber 220 provided in the MO 200. FIG. 15 shows
an arrangement in which the configuration of the first to third
embodiments is applied to the double-chamber system.
[0125] FIG. 16 shows positional relationship among an E95 bandwidth
adjustment unit, a laser chamber, and a line narrowing module
according to an eighth embodiment. FIGS. 17(a) and 17(b) show
configuration of an E95 bandwidth adjustment unit according to the
eighth embodiment, as viewed in the direction indicated by A in
FIG. 16. The eighth embodiment is designed to adjust a width of a
slit.
[0126] The E95 bandwidth adjustment unit 240 has a slit formed by
two blades 401 and 402 which are movable in the dispersion
direction of a grating 231. The blades 401 and 402 are movably
attached to a linear guide rail (not shown). The blade 401 is given
an urging force in a direction toward the blade 402 by a plunger
screw 403 having a spring incorporated therein. The blade 402 is
given an urging force in a direction toward the blade 401 by a
plunger screw 404 having a spring incorporated therein. The head of
a triangular member 405 is inserted between the blade 401 and the
blade 402. The triangular member 405 is a planar member having a
thickness equivalent to that of the blades 401 and 402, and is
movable in the direction parallel to the discharge direction of the
laser chamber 220. The side faces of the triangular member 405 are
slidably in contact with the blades 401 and 402, while the bottom
face of the triangular member 405 is in contact with the head of a
micrometer 406.
[0127] When the micrometer 406 is extended as shown in FIG. 17(b),
the triangular member 405 advances between the blades 401 and 402.
This causes the blades 401 and 402 to move in the directions
separating from each other along the side faces of the triangular
member 405. When the micrometer 406 is retracted as shown FIG.
17(a), the triangular member 405 is retracted from between the
blades 401 and 402. This causes the blades 401 and 402 to move in
the directions approaching to each other along the side faces of
the triangular member 405. The slit width is varied in this
manner.
[0128] Since the grating 231 is an angular dispersive element, the
E95 bandwidth of the MO 200 can be adjusted by adjusting the region
in which the MO 200 laser oscillates with respect to the dispersion
direction. Although in the configuration shown in FIG. 16, the E95
bandwidth adjustment unit 240 according to the eighth embodiment is
arranged on the front side of the laser chamber 220, the E95
bandwidth adjustment unit 240 according to the eighth embodiment
may be arranged on the rear side of the laser chamber 220 or in the
interior of the line narrowing module 230.
[0129] In the double-chamber system, as shown in FIGS. 18(a) and
2(b), the E95 bandwidth adjustment unit may be arranged on an
optical path between the MO 200 and the PO 300.
[0130] FIG. 19 shows an arrangement in which cylindrical lenses are
arranged between the MO and the PO.
[0131] A planoconvex cylindrical lens 411 and a planoconcave
cylindrical lens 412 are arranged on an optical path between the MO
200 and the PO 300 so as to face each other. Either the planoconvex
cylindrical lens 411 or the planoconcave cylindrical lens 412 is
movable along the optical axis. A moving mechanism for moving the
lens may be the same as the one shown in FIGS. 2(a) and 2(b), for
example. Further, a cylindrical convex lens and a cylindrical
concave lens may be used in place of the planoconvex cylindrical
lens 411 and the planoconcave cylindrical lens 412.
[0132] The spread of a beam injected into the PO 300 in the
dispersion direction of a dispersive element (grating 231) mounted
in the MO 200 can be adjusted by adjusting the distance between the
planoconvex cylindrical lens 411 and the planoconcave cylindrical
lens 412. As a result, the E95 bandwidth of laser light amplified
and oscillated by the PO 300 can be varied. The E95 bandwidth
becomes smaller when the beam is spread wider in the dispersion
direction by adjusting the distance between the planoconvex
cylindrical lens 411 and the planoconcave cylindrical lens 412. In
contrast, the E95 bandwidth becomes greater when the beam spread is
reduced with respect to the dispersion direction of the grating 231
by adjusting the distance between the planoconvex cylindrical lens
411 and the planoconcave cylindrical lens 412.
[0133] FIG. 20 shows an arrangement in which prisms are arranged
between the MO and the PO.
[0134] Two prisms 421 and 422 are arranged on an optical path
between the MO 200 and the PO 300. The two prisms 421 and 422 are
rotatable. A rotation mechanism for rotating the prisms may be the
same as the mechanism shown in FIG. 14, for example.
[0135] The prisms 421 and 422 are rotated in opposite direction
while matching the rotation angles thereof Thus, the beam expansion
ratio is varied by the prisms 421 and 422. The adjustment of the
beam expansion ratio makes it possible to adjust the width of a
beam injected into the PO 300 in the dispersion direction of a
dispersive element (grating 231) mounted in the MO 200. As a
result, the E95 bandwidth of laser light amplified and oscillated
by the PO 300 can be varied. Specifically, the E95 bandwidth
becomes smaller when the beam expansion ratio is increased by
adjusting the rotation angle of the prisms 421 and 422. In
contrast, the E95 bandwidth becomes greater when the beam expansion
ratio is reduced with respect to the dispersion direction of the
grating 231 by adjusting the rotation angle of the prisms 421 and
422.
[0136] FIG. 21 shows an arrangement in which a slit is arranged
between the MO and the PO.
[0137] A slit 431 is arranged on an optical path between the MO 200
and the PO 300. The slit 431 may be the same one as shown in FIGS.
17(a) and 17(b), for example.
[0138] The E95 bandwidth of laser light amplified and oscillated by
the PO 300 can be varied by adjusting the width of the slit 431.
The E95 bandwidth becomes greater when the width of the slit 431 is
increased. In contrast, the E95 bandwidth becomes smaller when the
width of the slit 431 is reduced. Even if a beam injected into the
PO 300 is narrower than a discharge width, output laser light can
be spread out by causing the light to reciprocate through an
optical resonator of the PO 300 as long as the beam has a spread
angle.
[0139] It should be understood that the present invention is also
applicable to a narrow-band laser device having three or more laser
chambers. In this case as well, the E95 bandwidth adjustment unit
may be provided in the MO or between the stages. Further, although
the description above of the embodiments has been made taking the
MOPO system as an example of the double-chamber system, the present
invention is also applicable to an MOPA-type double-chamber system
in which no laser resonator is provided in the amplification stage
so that seed light is directly amplified.
[0140] According to the present invention, the deviation in
spectral line width such as E95 bandwidth among the laser devices
can be minimized. Further, also in a same laser device, the
deviation in spectral line width such as E95 bandwidth before and
after the maintenance of the device can be minimized. Therefore,
the spectral line width of laser light output from the laser device
will not exceed the allowable range of the spectral line width such
as E95 bandwidth for an optical system of the exposure tool. This
makes it possible to stabilize the quality of integrated circuit
patterns formed by the semiconductor exposure tool, and thus the
yield of semiconductor devices can be improved. Furthermore, the
yield of laser production and the yield in maintenance are
improved, whereby the laser production cost and the maintenance
cost can be reduced effectively.
* * * * *