JP2011233918A - High output gas laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high output gas laser oscillator/amplifier including a resonator whose laser output does not reduce even in occurrence of a change in laser center wavelength by reducing a peak energy density of irradiation so as not to cause surface damage and distortion on a mirror in the resonator.SOLUTION: A gas laser device comprises a resonator including a rear-side mirror 1 and an output-side mirror 2, a laser chamber 3 filled with a laser gas disposed in the resonator, and excitation means 4 and 5 for exciting the laser gas in the laser chamber 3. Beam expansion optical systems 61 and 61' for increasing a diameter or a width of a laser beam on a mirror side are provided for at least one place between the laser chamber 3 and the rear-side mirror 1 and between the laser chamber 3 and the output-side mirror 2.

Description

  The present invention relates to a high-power gas laser device, and more particularly to a high-power gas laser oscillator and a high-power gas laser amplifier provided with a resonator.

As semiconductor integrated circuits are miniaturized and highly integrated, improvement in resolving power is demanded in semiconductor exposure apparatuses. For this reason, the wavelength of light emitted from the exposure light source is being shortened, and a gas laser device is used as the exposure light source instead of the conventional mercury lamp. As the current gas laser apparatus for exposure, a KrF excimer laser apparatus that emits ultraviolet light with a wavelength of 248 nm and an ArF excimer laser apparatus that emits ultraviolet light with a wavelength of 193 nm are used. As the next-generation exposure technology, we are trying to apply ArF excimer laser exposure to immersion technology that shortens the apparent wavelength of the exposure light source by filling the space between the exposure lens and the wafer with liquid and changing the refractive index. . In an ArF excimer laser immersion with a liquid refractive index of approximately 1.44, the wavelength is 134 nm. As a next-generation light source for exposure, a fluorine molecule (F ₂ ) laser device that emits ultraviolet light having a wavelength of 157 nm is prominent, and F ₂ laser immersion exposure may be adopted. It is said that the wavelength of 115 nm is obtained in the F ₂ laser immersion where the refractive index of the liquid is approximately 1.36.

By the way, a projection optical system is adopted as an optical system of many semiconductor exposure apparatuses. In the projection optical system, correction of chromatic aberration is performed by combining optical elements such as lenses having different refractive indexes. At present, there are no optical materials other than synthetic quartz and CaF ₂ suitable for use as the lens material of the projection optical system in the wavelength range of 248 nm to 115 nm of the laser wavelength which is an exposure light source. Since a lens having a high light transmittance at each wavelength is used, a KrF excimer laser projection lens is an all-refractive type monochromatic lens composed only of synthetic quartz, and an ArF excimer laser projection lens is a synthetic lens. An all-refractive type partial achromatic lens made of quartz and CaF ₂ is employed.

  However, since the spontaneous amplitudes of KrF excimer laser and ArF excimer laser are as wide as about 350 to 400 pm, when these projection lenses are used, chromatic aberration is generated and the resolving power is lowered. Therefore, it is necessary to narrow the spectral line width of the laser light emitted from the gas laser device before chromatic aberration can be ignored. For this reason, the laser device is provided with a narrow-band module having a narrow-band element (such as an etalon or a grating) in the laser resonator, so that the spectral line width is narrowed.

  Now, in immersion exposure, the transmittance of the lens decreases due to an increase in NA (numerical aperture), and therefore, in order to obtain a constant exposure amount, it is necessary to increase the output of a laser device as a light source. In order to increase the throughput of the exposure apparatus, it is necessary to increase the output of the laser apparatus. As a method for obtaining a high output after narrowing the spectral line width, there is a two-stage laser system. The two-stage laser system amplifies an oscillation stage laser (OSC laser) for outputting a narrow-band laser beam and a narrow-band laser beam (referred to as seed light). An amplification stage laser (AMP laser) for this purpose. FIG. 1 shows an outline of a basic configuration of an exposure two-stage laser apparatus (details will be described later).

  Two types of two-stage laser systems are known, the MOPO method and the MOPA method, depending on the amplification means. MOPO is an abbreviation for Master Oscillator and Power Oscillator and is also called injection lock system. This is a case where a resonator is disposed in the amplification chamber. MOPA is an abbreviation for Master Oscillator and Power Amplifier, and is a case where a resonator is not arranged in the amplification chamber. FIG. 1 shows the MOPO method. The amplification stage laser 60 includes a Fabry-Perot resonator composed of an input side mirror (rear side mirror) 1 and an output side mirror (front side mirror) 2, and a chamber 3 filled with a laser gas is disposed therebetween. Yes. Furthermore, it comprises discharge electrodes 4, 5, etc. that excite the laser gas in the chamber 3 to form a gain region. The oscillation stage laser 50 is typically a laser composed of a rear-side mirror and a front mirror 52 which are also used as optical elements in a narrow-band module 51 composed of, for example, a magnifying prism and a grating (diffraction grating). The resonator includes a chamber 53 filled with laser gas, and includes discharge electrodes 54 and 55 that excite the laser gas in the chamber 53 to form a gain region. In addition, the discharge area is opposed to the near side and the far side in the drawing.

In the oscillation stage laser 50, the laser beam has an average energy density of several mJ / cm ² , but in the amplification stage laser 60, the laser energy is amplified, so that the laser beam has an average energy density of several tens of mJ / cm ^2. . Further, the energy density is not uniform in the laser beam, and generally the central part is high and the base of the beam is distributed low. For this reason, the peak energy density is several times the average energy density.

  The peak energy density is high not only in the amplification stage laser of the two-stage laser system but also in a laser resonator of a high-power gas laser apparatus such as a carbon dioxide laser apparatus.

  In general, a laser resonator includes a front mirror that emits laser light and a rear mirror that has a high reflectivity. The output mirror has a PR film (partial reflection mirror coating) having a reflectance of several tens of percent on one side and an AR film (antireflection coating) on the other side. The rear mirror is provided with an HR film (high reflectance (total reflection) mirror coating). The rear-side mirror in the case of the amplification stage laser has a PR film having a high reflectivity of about 90%. Since only a part of the laser beam that has reached the output side mirror is output, the laser energy inside the resonator is several times higher than the energy output to the outside.

  For this reason, the energy density of the laser beam inside the resonator becomes very high, so that the mirror surface is irradiated by irradiating the output (side) mirror and the rear (side) mirror constituting the resonator with high-density photons. There was a problem of being damaged. In addition, since a beam with a high energy density is transmitted, absorption of light on the surface and inside of the beam increases and heat is generated. There is a problem that distortion is generated inside the optical element due to the thermal stress.

  By the way, the present applicants proposed in PCT / JP2004 / 005490 a high-power two-stage laser apparatus suitable for a semiconductor exposure apparatus with low spatial coherence. This two-stage laser device is a two-stage laser device for exposure comprising an oscillation stage laser and an amplification stage laser, the amplification stage laser comprising a Fabry-Perot etalon type resonator comprising an input side mirror and an output side mirror, The resonator constitutes a stable resonator, or the optical axis of the laser beam oscillated by the oscillation stage laser and input to the amplification stage laser makes an angle with the optical axis of the resonator of the amplification stage laser. The reflection surfaces of the rear-side mirror and output-side mirror of the resonator of the amplification stage laser are flat, and the normals of the rear-side mirror and output-side mirror are oscillated and amplified by the oscillation stage laser. The angle of the laser beam input to the stage laser is set at an angle with respect to the optical axis of the laser beam, and the laser beam oscillated by the oscillation stage laser has a greater distance between both mirrors. It was to be inputted from the stomach side in the resonator.

The high-power gas laser apparatus such as a carbon dioxide gas laser apparatus is not limited to the above-described KrF excimer laser apparatus, ArF excimer laser apparatus, and fluorine molecule (F ₂ ) laser apparatus for semiconductor exposure apparatuses. In a laser oscillator, and in a laser amplifier in a two-stage laser apparatus, the energy density of laser light inside the resonator becomes very high, so the durability of the rear side mirror and output side mirror constituting the resonator is poor. Become. In order to solve this problem, as proposed in PCT / JP2004 / 005490, it is possible to periodically move the used portion of these mirrors in a direction substantially perpendicular to the optical axis direction of the resonator. However, it requires moving parts and means for controlling its movement.

  The present invention has been made in view of such a situation, and an object of the present invention is to provide an output side mirror and a rear side mirror that constitute a resonator in a high output gas laser oscillator and a high output gas laser amplifier having a resonator. The peak energy density to be irradiated is reduced so that surface damage and distortion do not occur, and at this time, even if the center wavelength of the laser is changed, the laser output is not reduced.

The high-power gas laser device of the present invention includes a resonator composed of a rear-side mirror and an output-side mirror, a laser chamber disposed in the resonator and filled with laser gas, and excitation means for exciting the laser gas in the laser chamber. In a gas laser device comprising:
A beam expansion optical system that increases the diameter or width of the laser beam on the mirror side is interposed between at least one of the laser chamber and the rear side mirror and between the laser chamber and the output side mirror. It is what.

  In this case, a laser oscillator may be configured, or a laser amplifier may be configured. For example, it can be used for an amplification stage laser of a two-stage laser apparatus.

  In the above, the beam expanding optical system can be constituted by a beam expander prism system constituted by one or a plurality of triangular prisms.

  In this case, the rear mirror or output mirror is beamed by applying a high-reflectance mirror coating or a partial reflection mirror coating to the outermost plane of the triangular prism constituting the beam expander prism system opposite to the laser chamber. It can be constructed integrally with the expander prism system.

Another high-power gas laser device according to the present invention includes a resonator including a rear-side mirror and an output-side mirror, a laser chamber disposed in the resonator and encapsulating a laser gas, and exciting the laser gas in the laser chamber. In a gas laser device comprising electrodes arranged to face each other,
Even if the center wavelength of the laser changes between the output-side electrode end and the output-side mirror and between the rear-side electrode end and the rear-side mirror, the amount of change in laser output energy can be ignored. It can be made as small as possible, and a beam expansion optical system for expanding the diameter or width of the laser beam on the mirror surface is interposed.

  In this case, for example, it can be used for an amplification stage laser of a two-stage laser apparatus.

  And the beam expansion optical system is arranged between both the output side electrode end and the output side mirror, and between the rear side electrode end and the rear side mirror, the configuration of each beam expansion optical system is the same, It is desirable that the two electrodes arranged opposite to each other are arranged so that left and right and up and down are symmetrical within a cross section including the center line in the optical axis direction.

  Further, even if the beam expanding optical system is composed of a wedge substrate type beam expanding optical system composed of one or a plurality of wedge substrates, a beam expander prism system composed of one or a plurality of triangular prisms. It may consist of

  In the case of a wedge substrate type beam expanding optical system, at least one of the wedge substrates constituting the beam expanding optical system may be arranged as a window member of the laser chamber.

  Further, all of the wedge substrates constituting the beam expanding optical system may be arranged inside the laser chamber, and the wedge substrate on the middle output side mirror side or rear side mirror side may be arranged as a window member of the laser chamber. .

  In addition, the light incident on the wedge substrate or the triangular prism constituting the beam expansion optical system is reflected by the output side mirror or the rear side mirror, and the light path before returning to the wedge substrate or the triangular prism. It may be configured to be controllable so as to overlap the laser optical axis.

  Also, the output is made so that the optical path of the light incident on the beam expanding optical system and reflected and returned by the output side mirror or the rear side mirror overlaps the laser optical axis of the light before entering the beam expanding optical system. You may comprise so that the tilt angle of a side mirror or a rear side mirror is controllable.

  The above-described high-power gas laser device of the present invention is particularly suitable for application to an apparatus that oscillates or amplifies ultraviolet rays.

  According to the high-power gas laser device of the present invention, the beam expanding optical system for expanding the diameter or width of the laser beam on the mirror side is provided between the laser chamber and the rear side mirror and at least one between the laser chamber and the output side mirror. The amount of change in laser output energy can be ignored even if the center wavelength of the laser changes between the output side electrode end and the output side mirror, or between the rear side electrode end and the rear side mirror. The energy of the laser beam per unit area incident on the resonator optical element of the laser oscillator or laser amplifier can be reduced to a small extent and the beam expanding optical system for expanding the diameter or width of the laser beam on the mirror surface is interposed. (Energy density) is reduced to prevent surface damage of the optical element, thereby improving durability. It is possible to realize a long life. Further, it is possible to reduce the laser energy density incident on the optical element constituting the resonator mirror so that the optical element is not distorted. At this time, even if the center wavelength of the laser changes, the laser output can be prevented from decreasing.

It is a figure which shows the outline of the basic composition of the exposure 2 stage laser apparatus to which this invention is applied. It is a whole block diagram of one structural example of the exposure 2 stage laser apparatus provided with the basic composition like FIG. It is a figure which shows the outline | summary of one example of the amplification stage laser of the structure of FIG. 1, FIG. 2, and the principle of this invention. It is a figure which shows the principal part of one Example of the amplification stage laser by this invention used for the exposure 2 stage laser apparatus of arrangement | positioning like FIG. It is a figure which shows the principal part of the amplification stage laser of another Example by this invention. It is a figure which shows the principal part of the amplification stage laser of another Example by this invention. It is a figure which shows the principal part of the modification of the amplification stage laser of FIG. It is a figure which shows the principal part of the modification of the amplification stage laser of FIG. It is a figure for demonstrating the numerical example of the triangular prism used for the beam expander prism type | system | group used also as the front side mirror used for the Example of FIG.5 and FIG.8. It is a figure which shows the principal part of the modification of the Example of FIG. It is a principle figure of the deterioration of the shape of a spectrum and the output fluctuation when light interference occurs on the surface in the resonator of the amplification stage laser. It is a figure which shows the wavelength dependence of the output at the time of using a beam expander prism system. It is a figure which shows a mode that a beam optical path shifts | deviates with a wavelength in a triangular prism. It is a figure for demonstrating the method of preventing the wavelength dependence of an output by arrange | positioning a triangular prism on both sides of a resonator by inverting one side up and down with respect to the other. It is a figure for demonstrating the effect | action of the beam expansion optical system using a wedge board | substrate. It is a figure which shows the relationship between the incident angle of a laser beam path, the apex angle, and a deflection angle in the beam expansion optical system using a wedge board | substrate. It is a figure which shows the vertex angle dependence of the deflection angle of a wedge board | substrate. It is a figure which shows the vertex angle dependence of the expansion ratio of a wedge board | substrate. It is a figure which shows the incident angle dependence of the magnification of a wedge board | substrate and a triangular prism. It is a figure which shows the incident angle dependence of the deflection angle of a wedge board | substrate and a triangular prism. It is a figure for demonstrating the method to control so that a beam optical path may not shift | deviate by changing the beam incident angle to a beam expansion optical system according to it, if a wavelength changes. It is a figure which shows the principal part of the amplification stage laser of the Example which prevents the wavelength dependence of an output occurring. It is a figure which shows the wavelength dependence of an output when the triangular prism type beam expansion optical system is arrange | positioned only at the output side, and when the triangular prism type beam expansion optical system which is 180 degrees rotationally symmetrical is arrange | positioned also at the rear side. It is a figure which shows the principal part of the amplification stage laser of another Example which makes the wavelength dependence of an output not generate | occur | produce. It is a figure which shows the principal part of the amplification stage laser of the Example similar to FIG. 24 comprised using two wedge substrates in each beam expansion optical system. It is a figure for demonstrating the principle which makes the laser optical axis after the beam expansion optical system emission using two wedge substrates parallel to the laser optical axis before incidence. It is a figure which shows the wavelength dependence of the output of the wedge board | substrate type beam expansion optical system which uses a wedge board | substrate, and the triangular prism type beam expansion optical system which uses a triangular prism. It is a figure which shows the wavelength dependence of an output when the wedge board | substrate type | formula beam-expansion optical system which is mutually 180 degree rotation symmetrical is arrange | positioned on the output side and the rear side. It is a figure which shows the principal part of the amplification stage laser of the Example which uses one wedge board | substrate in a wedge board | substrate type beam expansion optical system also as a window member. It is a figure which shows the principal part of the amplification stage laser of the Example which puts all the wedge board | substrate type beam expansion optical systems in a chamber, and also uses the other wedge board | substrate as a window member. It is a figure which shows the principal part of the amplification stage laser of the Example of the system which controls the incident angle of a beam expansion optical system, and prevents an angle shift itself with a wavelength. It is a figure which shows the principal part of the amplification stage laser of the Example of the system which controls the tilt of the mirror which comprises a resonator, and prevents an angle shift itself with a wavelength. It is a control flowchart which shows the main routine of control in the system of FIG. 31, FIG. It is a flowchart which shows an example of the subroutine in the case of controlling the incident angle of the optical element of a beam expansion optical system by measuring a laser output. It is a flowchart which shows an example of the subroutine in the case of controlling the tilt angle of the mirror which comprises a resonator by measuring a laser output. It is a flowchart which shows an example of the subroutine in the case of controlling the incident angle of the optical element of a beam expansion optical system by measuring a spectrum. It is a flowchart which shows an example of the subroutine in the case of controlling the tilt angle of the mirror which comprises a resonator by measuring a spectrum.

  The high power gas laser apparatus of the present invention will be described below by taking an amplification stage laser of a two stage laser apparatus for exposure as an example. However, it is clear from the principle that the high-power gas laser device of the present invention can be applied to an excimer laser device, a carbon dioxide gas laser device and the like that do not include an amplification stage laser.

  FIG. 1 shows an outline of the basic configuration of an exposure two-stage laser apparatus to which the present invention is applied. This exposure two-stage laser device is a MOPO (Master Oscillator, Power Oscillator) system, which inputs and amplifies an oscillation stage laser (MO) 50 and seed light oscillated by the oscillation stage laser 50. It comprises an amplification stage laser (PO: Power Oscillator) 60 that outputs laser light. The amplification stage laser 60 is provided with a Fabry-Perot etalon type resonator composed of an input side mirror (rear side mirror) 1 and an output side mirror (front side mirror) 2, and a chamber 3 filled with a laser gas therebetween. Has been placed. Furthermore, it includes discharge electrodes 4 and 5 that excite laser gas in the chamber 3 to form a gain region, window members 17 installed at both ends of the chamber 3 along the optical axis extension, and the like.

  The oscillation stage laser 50 is typically composed of a rear-side mirror and a front mirror 52 that serve as optical elements in a narrow-band module 51 composed of, for example, a magnifying prism and a grating (diffraction grating). A laser resonator is provided with a chamber 53 filled with a laser gas, discharge electrodes 54 and 55 that excite the laser gas in the chamber 53 to form a gain region, and window members 57 installed at both ends of the chamber 53 along the optical axis extension. And so on.

  Further, although not essential between the oscillation stage laser 50 and the amplification stage laser 60, the beam cross-sectional area of the seed light input (incident) from the oscillation stage laser 50 to the amplification stage laser 60 can be reduced, or oscillation can be performed. A conversion optical system 70 (FIG. 2) for converting the divergence angle of the seed light from the stage laser 50 is arranged.

  Here, in this high-power laser system, the resonator composed of the input-side mirror 1 and the output-side mirror 2 of the amplification stage laser 60 is constituted by a stable resonator, or is oscillated by the oscillation stage laser 50 and is amplified. The optical axis of the laser light (seeded light) input to the laser beam and the optical axis of the resonator composed of the rear-side mirror 1 and the front-side mirror 2 of the amplification stage laser 60 are set at an angle, or The reflection surfaces of the rear-side mirror 1 and the output-side mirror 2 of the resonator of the amplification stage laser 60 are flat, and the normal lines of the rear-side mirror 1 and the output-side mirror 2 are oscillated by the oscillation stage laser 50 and input to the amplification stage laser 60. The laser light (seed light) oscillated by the oscillation stage laser 50 is set so as to form an angle with respect to the optical axis of the laser light (seed light) to be generated and mutually angled. Between 1 and 2 Distance by which to be input into the resonator from longer side, it is to achieve low coherence of the oscillation stage laser equivalent spatial coherence (PCT / JP2004 / 005490).

Next, one configuration example of the exposure two-stage laser apparatus having the above basic configuration will be described with reference to the overall configuration diagram of FIG.

When this MOPO system is a fluorine molecule (F ₂ ) laser device, the chambers 53 and 3 of the oscillation stage laser 50 and the amplification stage laser 60 are respectively composed of fluorine (F ₂ ) gas, helium (He) and neon (Ne). A laser gas comprising a buffer gas comprising, for example, is filled. When this MOPO system is a KrF excimer laser device, the chambers 53 and 3 in both the oscillation stage laser 50 and the amplification stage laser 60 are krypton (Kr) gas, fluorine (F ₂ ) gas, helium (He) or neon ( When the MOPO system is an ArF excimer laser device, both the oscillation stage laser 50 and the amplification stage laser 60 have respective chambers 53 and 3 with argon (Ar) gas, A laser gas comprising a fluorine (F ₂ ) gas and a buffer gas made of helium (He), neon (Ne), or the like is filled. In both the oscillation stage laser 50 and the amplification stage laser 60, the laser chambers 53 and 3 each have a discharge portion including a pair of discharge electrodes 54, 55, 4 and 5, respectively. These discharge parts are composed of a pair of cathode electrodes 55 and 5, and anode electrodes 54 and 4 that are installed vertically in the direction parallel to the paper surface. When a high voltage pulse is applied to the pair of electrodes 54, 55, 4 and 5 from the power sources 56 and 16, respectively, a discharge is generated between these electrodes.

Both the oscillation stage laser 50 and the amplification stage laser 60 are transparent to laser oscillation light such as CaF _{2 at the} upper ends of the pair of electrodes 54, 55, 4 and 5 installed in the chambers 53 and 3. Window members 57 and 17 made of a certain material are respectively installed. Here, the exposed surfaces of the window members 57 and 17 on the opposite side to the inside of the chambers 53 and 3 are arranged in parallel to each other and at a Brewster angle in order to reduce reflection loss with respect to the laser light. Further, the window members 57 and 17 are installed so that the P-polarized component of the laser light is in the horizontal direction.

Further, a cross flow fan (not shown in FIG. 2) is installed in the chambers 53 and 3 to circulate the laser gas in the chambers 53 and 3 and send the laser gas to the discharge part. The oscillation stage laser 50, the amplification stage laser 60 together, F ₂ gas into the chamber 53,3, F ₂ gas supply system for supplying a buffer gas, the buffer gas supply system, and to exhaust the laser gas in the chamber 53,3 A gas exhaust system is provided in the apparatus. In FIG. 2, these are collectively shown as a gas supply / exhaust control valve 58 and a gas supply / exhaust control valve 18. In the case of a KrF laser device and an ArF laser device, a Kr gas supply system and an Ar gas supply system are also provided. The gas pressures in the chambers 53 and 3 are monitored by pressure sensors P 1 and P 2, respectively, and the gas pressure information is sent to the utility controller 81. The utility controller 81 controls the gas supply / distribution control valves 58 and 18 to control the gas composition and the gas pressure in the oscillation stage chamber 53 and the amplification stage chamber 3, respectively.

  Laser power varies with gas temperature. For this purpose, gas temperature control is performed. The gas temperature is monitored by temperature sensors T 1 and T 2 installed in the respective chambers 53 and 3, and these temperature signals are sent to the utility controller 81. The utility controller 81 controls the cooling water flow rate using the cooling water flow rate control valves 59 and 19, respectively. As a result, the exhaust heat amounts of the heat exchangers 34 and 44 in the chambers 53 and 3 are controlled, respectively, and the temperature is controlled.

The oscillation stage laser 50 has a narrow band module (LNM) 51 composed of a magnifying prism and a grating (diffraction grating). The optical element in the narrow band module 51 and the front mirror 52 serve as a laser resonator. It is composed. Alternatively, although not shown, a narrowband module using an etalon and a total reflection mirror may be used instead of the magnifying prism and the grating.

  Part of the laser light emitted from the oscillation stage laser 50 and the amplification stage laser 60 is branched by a beam splitter (not shown) and guided to the monitor modules 35 and 45, respectively. The monitor modules 35 and 45 monitor laser light characteristics such as the output, line width, and center wavelength of the oscillation stage laser 50 and the amplification stage laser 60, respectively. In FIG. 2, the monitor modules 35 and 45 are installed in both the oscillation stage laser 50 and the amplification stage laser 60, but only one of them may be installed.

  The signal of the center wavelength from the monitor modules 35 and 45 is sent to the wavelength controller 82. Then, the wavelength controller 82 drives the optical element in the narrowband module 51 by the driver 83 to select the wavelength, and controls the wavelength so that the center wavelength of the oscillation stage laser 50 becomes a desired wavelength. The wavelength control described above is performed based on the wavelength information from the monitor module 45 through which a part of the laser light emitted from the amplification stage laser 60 is guided, so that the wavelength of the laser light emitted from the oscillation stage laser 50 is predetermined. It is also possible to issue a command from the wavelength controller 82 to the driver 83 so that the wavelength becomes the same wavelength.

  Laser output signals from the monitor modules 35 and 45 are sent to the energy controller 84. Then, the applied voltage is controlled via the synchronous controller 85, and the energy of the oscillation stage laser 50 and the amplification stage laser 60 is controlled to a desired value. The output signal of the monitor module 45 may be sent to the energy controller 84 as shown in (1) of the figure. However, instead of (1), an output monitor (not shown) is provided on the exposure apparatus 100 side, and the output there is output. You may send to the energy controller 84 like (2).

Laser light (seed light) from the oscillation stage laser 50 passes through the monitor module 35, then passes through a beam steering unit 86 including a reflection mirror and the like, passes through a conversion optical system 70, and is guided to the amplification stage laser 60. Injected. The conversion optical system 70 has the above-described mechanism for controlling the divergence angle of the oscillation stage laser 50 to a predetermined value so that the oscillation stage laser light (seed light) is injected into the amplification stage laser 60 at a predetermined divergence angle. is doing. In this MOPO system, the amplifying stage laser 60 includes the input side mirror (rear side mirror) 1 and the output side mirror (front side mirror) 2 as described above so that it can be amplified even with a small input. Is adopted. The laser light that has passed through the input side mirror 1 is reflected as shown by the arrow in FIG. 2 and effectively passes through the discharge part, and the power of the laser light increases. Then, a laser is emitted from the output side mirror 2.

  Each of the pair of discharge electrodes 54, 55, 4 and 5 of the oscillation stage laser 50 and the amplification stage laser 60 has a power source 56 constituted by a charger 31 / switch 32 / MPC (magnetic pulse compression circuit) 33, and A high voltage pulse is applied from the power source 16 constituted by the charger 41 / switch 42 / MPC (magnetic pulse compression circuit) 43, and discharge occurs between the electrodes 54, 55, 4 and 5. By this discharge, the laser gas filled in the laser chambers 53 and 3 is excited.

  The capacitors are charged by the chargers 31 and 41 in the respective power sources 56 and 16. When the switches 32 and 42 are turned on, the energy charged in the capacitor is transferred to the magnetic pulse compression circuits 33 and 43 as voltage pulses, and is pulse-compressed and applied to the pair of electrodes 54, 55, 4 and 5 described above. Is done. Although not shown, the power supplies 56 and 16 may further include a step-up transformer to boost the voltage pulse.

The switches 32 and 42 are turned on and off by an operation command (trigger signal) from the synchronous controller 85.

The synchronous controller 85 is connected to the charger 31 / switch 32 / MPC (magnetic pulse) so that the amplification stage laser 60 generates a discharge at the timing when the laser light emitted from the oscillation stage laser 50 is injected into the amplification stage laser 60. A trigger signal is sent to a power source 56 constituted by a compression circuit) 33 and a power source 16 constituted by a charger 41 / switch 42 / MPC (magnetic pulse compression circuit) 43. When the discharge timing of the oscillation stage laser 50 and the amplification stage laser 60 is shifted, the laser light emitted from the oscillation stage laser 50 is not efficiently amplified. The synchronous controller 85 obtains information on the discharge start of the oscillation stage laser 50 and the amplification stage laser 60 from the discharge detectors 36 and 46 and laser output information from the energy controller 84, respectively, and supplies it to the power source 56 of the oscillation stage laser 50. The delay time between the trigger signal to be transmitted and the trigger signal to be transmitted to the power supply 16 of the amplification stage laser 60 is set.

  The utility controller 81, the energy controller 84, and the wavelength controller 82 are connected to the main controller 80. The main controller 80 is connected to the exposure apparatus 100. The main controller 80 distributes the control assignment to each of the controllers 81, 84, and 82 in accordance with a command from the exposure apparatus 100, and each controller 81, 84, and 82 performs control that is shared by the command.

  The laser light emitted from the oscillation stage laser 50 is aligned by the beam steering unit 86 composed of two mirrors so as to pass through the discharge region of the amplification stage laser 60. The two mirrors constituting the beam steering unit 86 are driven by a driver 87 and controlled in angle to control the traveling direction of laser light emitted from the oscillation stage laser 50.

  Specific control of the beam steering unit 86 is as follows. For example, it is assumed that the traveling direction of the laser light emitted from the oscillation stage laser 50 is not aligned so as to pass through the discharge region of the amplification stage laser 60. In this case, a part or all of the laser light emitted from the oscillation stage laser 50 is shielded by, for example, the discharge electrodes 4 and 5 of the amplification stage laser 60 or reflected in an undesired direction, so that the amplification stage laser 60 No laser light is emitted from the laser beam, or the laser power becomes smaller than a desired value. Therefore, while monitoring the output of the laser light emitted from the amplification stage laser 60 with the monitor module 45, the beam steering unit 86 is controlled so that this output becomes maximum. That is, in FIG. 2, the result monitored by the monitor module 45 is sent to the wavelength controller 82. The wavelength controller 82 instructs the driver 87 to maximize the output based on the output result of the laser beam received from the monitor module 45, drives the beam steering unit 86, and emits it from the oscillation stage laser 50. The traveling direction of the laser beam to be controlled is controlled.

  For example, in the two-stage laser apparatus for exposure having such a configuration, the energy of the amplification stage laser 60 in which the energy of the laser beam inside the resonator composed of the rear-side mirror 1 and the front-side mirror 2 becomes very high according to the present invention. The beam expansion optical system is interposed between the chamber 3 and the rear side mirror 1 and between the chamber 3 and the front side mirror 2, respectively, and enters the rear side mirror 1 and the front side mirror 2 from the chamber 3 side. The diameter of the laser beam to be enlarged is increased, and as a result, the energy of the laser beam per unit area incident on the mirrors 1 and 2 is reduced, thereby improving the durability of the rear side mirror 1 and the front side mirror 2. It is the principle of the present invention to improve. Of course, as described above, in a high-power gas laser device such as an excimer laser device or a carbon dioxide gas laser device that does not include an amplification stage laser, the rear side mirror and the front side of the oscillation stage laser are configured in the same manner. The durability of the mirror can be improved on the same principle.

  FIG. 3 shows an outline of an example of the amplification stage laser 60 having such a configuration. FIG. 3 is a top view showing only the configuration of the amplification stage laser 60 of the exposure two-stage laser apparatus arranged as shown in FIG. 1, and a pair of discharge electrodes 4 and 5 are arranged in a direction perpendicular to the paper surface. The discharge region 22 occurs perpendicular to the paper surface, and therefore the laser gain region is substantially equal to the discharge region 22. Hereinafter, the laser gain region is also denoted by reference numeral 22. Beam expanding optical systems 61 and 61 ′ are disposed between the window members 17 and 17 provided at both ends of the laser chamber 3 and the rear-side mirror 1 and the front-side mirror 2, respectively. The width of at least a one-dimensional direction of the laser beam that has passed through is widened, and laser light (seed light) is incident on the rear-side mirror 1 positioned on the opposite side across the front-side mirror 2 and the laser gain region 22.

  As a result of such an arrangement, if the intensity of the output laser light from the amplification stage laser 60 is the same before and after insertion of the beam expansion optical systems 61 and 61 ′, the diameter of the laser beam after insertion is increased by the enlargement ratio. When the magnification is A, the energy density of the laser light applied to the mirrors 1 and 2 of the resonator is about 1 / A, and the energy density load on the mirrors 1 and 2 is reduced. Therefore, durability of the rear side mirror 1 and the front side mirror 2 is improved.

  Here, the beam expanding optical systems 61 and 61 ′ can be configured by a lens system in which two lens systems having different focal lengths are arranged at a confocal point, or a magnifying prism as in the following example.

  The window members 17 and 17 provided at both ends of the laser chamber 3 are attached perpendicular to the laser beam in FIG. 3, but the attachment angle is not particularly limited, and the window members 17 and 17 in the embodiment of FIG. As such, it may be attached at a Brewster angle or other angles.

  FIG. 4 is a view showing a main part of one embodiment of an amplification stage laser 60 used in the exposure two-stage laser apparatus arranged as shown in FIG. 1, and (a) is a top view showing a pair of discharges. The electrodes 4 and 5 are arranged in a direction perpendicular to the paper surface, and the discharge region 22 is generated perpendicular to the paper surface. FIG. 4B is a view when the front mirror 2 is viewed from the position of the rear mirror 1 by observing the A-A ′ cross section of FIG.

  In this embodiment, the optical axis of the seed light 23 oscillated by the oscillation stage laser 50 and the optical axis of the resonator composed of the rear side mirror 1 and the front side mirror 2 of the amplification stage laser 60 are set at an angle. This is one example of a case in which the seed light 23 is injected into the amplification stage laser 60 from a direction perpendicular to the discharge direction between the pair of discharge electrodes 4 and 5. In this embodiment, the seed light 23 is incident from a direction perpendicular to the direction. However, the injection of the seed light 23 is not limited to this perpendicular direction, and any direction (angle) may be injected with respect to the optical axis of the amplification stage laser 60.

  In this embodiment, a high reflectance (total reflection) mirror coating 8 is applied on the optical axis side from the position where the seed light 23 on the chamber 3 side of the rear side mirror 1 is incident, and on the chamber 3 side of the front side mirror 2. Has a partially reflecting mirror coating 10 and an anti-reflection coating 9 on the opposite side. The partial reflection mirror coating 10 of the front side mirror 2 may be provided not on the chamber side but on the laser light output side. In the following embodiment, the high reflectance (total reflection) mirror coating 8, the antireflection coating 9, and the partial reflection mirror coating 10 are omitted, but are the same as this embodiment.

The front mirror 2 may be formed of a transparent substrate on which the partial reflection mirror coating 10 and the antireflection coating 9 are not applied. For example, in the case where the oscillation stage laser oscillates naturally, when the wavelength of the laser beam is 193 nm of the ArF excimer laser beam, the surface reflectance of the transparent substrate (meteorite (CaF ₂ )) is about 4%, When reflection on the front and back of the substrate surface is used, an output side mirror (front side mirror) 2 for a wavelength of 193 nm having a reflectance of about 8% can be realized without coating. However, when the oscillation stage laser is a narrow-band laser, the light interferes with the front and back reflections of the substrate surface of the front mirror 2, and the spectrum of the amplified laser light is split. In such a case, it cannot be used as a laser for an exposure apparatus. This principle will be described later (FIG. 11).

  The partial reflection mirror coating 10 and the antireflection coating 9 of the front side mirror 2 as described above have a destruction threshold value. When laser light exceeding this is irradiated to the partial reflection mirror coating 10 and the antireflection coating 9, these are reflected. The coating will be destroyed. Even if the front-side mirror 2 is configured without being coated as described above, if the energy density of the laser beam is high, the surface of the transparent substrate and the inside thereof are destroyed. This embodiment is an embodiment for reducing the irradiation energy density to the front side mirror 2, and is composed of one or more triangular prisms 62, 63 between the laser chamber 3 and the front side mirror 2. Is incident obliquely from the side of the laser chamber 3 and exits at a substantially right angle from the opposite side, and the beam diameter is expanded in a one-dimensional direction, and the beam whose beam diameter is expanded is another triangular prism. A beam expanding optical system (beam expander prism system) 61 ′ that is obliquely incident on the slope of 63, exits at a substantially right angle from the opposite surface, and is further expanded in the one-dimensional direction and then exits is configured. Has been. Therefore, the energy density of the laser light applied to the front side mirror 2 is reduced as compared with the case where the beam expanding optical system (beam expander prism system) 61 ′ is not installed, and the life of the front side mirror 2 is further increased. In addition, high power laser oscillation is possible.

  FIG. 4B is a view when the front side mirror 2 side is seen from the position of the rear side mirror 1 in FIG. 4A, and the discharge electrodes 4 and 5, the discharge region 22, the front side mirror 2, and The cross-sectional relationship of the output laser beam emitted from the front mirror 2 is shown. When the beam expanding optical system (beam expander prism system) 61 ′ is not set in the resonator, the size is surrounded by a broken line a, and the size of the beam section is equal to or less than the section of the discharge region 22. However, when the beam expansion optical system (beam expander prism system) 61 ′ is provided, the output laser light is enlarged by the enlargement ratio.

  When the resistance of the antireflection coating and the partial reflection coating to the ultraviolet laser beam is compared, the antireflection coating has a higher durability because the number of coating layers is smaller. Therefore, in order to prevent a decrease in laser output from the amplification stage laser 60, an antireflection coating may be applied to the laser light transmitting surfaces of the triangular prisms 62 and 63 constituting the beam expander prism system 61 '. Further, such coating may be omitted as long as the output reduction of the amplification stage laser 60 does not cause a problem.

  When the oscillation stage laser 50 is a narrow-band laser, the surfaces of the prisms 62 and 63 are set at angles so as not to cause multiple interference between the front-side mirror 2 and the reflection surface of the rear-side mirror 1. It is desirable to do so. The reason for this will be described later (FIG. 11).

  In FIG. 4, since the beam expander prism system 61 ′ is installed so as to expand in the direction perpendicular to the discharge direction (plane direction of FIG. 4 (a)), the cross section of the output laser beam is shown in FIG. ) Is expanded horizontally. In this case, it is possible to expand the beam in only one direction in which the laser beam is narrow so that the laser beam has a shape close to a square. Therefore, the large front-side mirror 2 is not required, and the cost merit increases. . Further, by arranging the window member 17 at a Brewster angle so that the P-polarized component and the P-polarized component on the inclined surface of the magnifying prism coincide with the window member 17, the efficiency of the prism amplification stage laser is also increased. Become. In principle, it is also possible to enlarge the cross section of the output laser beam only in the vertical direction or in both the vertical and horizontal directions. In addition, by using a spherical lens or a cylindrical lens instead of the triangular prism or in combination with the triangular prism, the cross section of the output laser light can be freely enlarged vertically and horizontally.

  FIG. 5 shows a top view of another embodiment of the amplification stage laser 60 used in the exposure two-stage laser apparatus arranged as shown in FIG. In this embodiment, the function of the front side mirror 2 in the embodiment of FIG. 4 is constituted by the outermost triangular prism of the beam expander prism system 61 ′, two in FIG. 4 and FIG. This is an example in which the partial reflection mirror coating 10 is directly applied to the surface and combined, and the front mirror 2 is omitted. With such a configuration, it is possible to omit the front side mirror, which is a component of the resonator, and it is possible to reduce the cost of the laser device.

  Also in this example, when the resistance of the antireflection coating and the partial reflection coating to the ultraviolet laser beam is compared, the antireflection coating has a higher durability because the number of coating layers is smaller. Therefore, in order to prevent the laser output from the amplification stage laser 60 from being lowered, the laser beam transmitting surface other than the surface on which the partial reflecting mirror coating 10 of the triangular prisms 62 and 63 constituting the beam expander prism system 61 ′ is reflected is reflected. A protective coating may be applied. Further, such coating may be omitted as long as the output reduction of the amplification stage laser 60 does not cause a problem.

  When the oscillation stage laser 50 is a narrow-band laser, each of the surfaces other than the surface to which the partial reflection mirror coating 10 of the prisms 62 and 63 is applied is the reflection surface of the rear side mirror 1 and the partial reflection mirror coating 10. It is desirable to install at an angle that does not cause multiple interference with the applied surface. The reason for this will be described later (FIG. 11).

FIG. 6 shows a top view of still another embodiment of the amplification stage laser 60 used in the exposure two-stage laser apparatus arranged as shown in FIG. In this embodiment, the beam expander prism system 61 having the same configuration as that of the beam expander prism system 61 ′ is used as the laser chamber 3 in order to further reduce the irradiation energy density to the rear side mirror 1 in the embodiment of FIG. The energy density of the laser light disposed between the rear side mirrors 1 and irradiated to the rear side mirror 1 is reduced as compared with the case where the beam expander prism system 61 is not installed. This is intended to extend the life and enable high-power laser oscillation.

  Also in this case, when the resistance of the antireflection coating and the partial reflection coating to the ultraviolet laser beam is compared, the antireflection coating has a higher durability because the number of coating layers is smaller. Therefore, in order to prevent a decrease in laser output from the amplification stage laser 60, an antireflection coating may be applied to the laser light transmitting surfaces of the triangular prisms 62 and 63 constituting the beam expander prism systems 61 and 61 '. Further, such coating may be omitted as long as the output reduction of the amplification stage laser 60 does not cause a problem. When the oscillation stage laser 50 is a narrow-band laser, the surfaces of the prisms 62 and 63 are set at angles so as not to cause multiple interference between the reflection surfaces of the front-side mirror 2 and the rear-side mirror 1. It is desirable to do so. The reason for this will be described later (FIG. 11).

  FIG. 7 shows a modification of the amplification stage laser 60 of FIG. In this embodiment, since the function of the rear side mirror 1 is constituted by the outermost triangular prism of the beam expander prism system 61, two in FIG. 6, the seed light 23 on the surface of the triangular prism 63 on the incident light 23 incident side is provided. This is an example in which the high-reflectance (total reflection) mirror coating 8 is directly applied to the optical axis side from the position where the light enters, and the rear-side mirror 1 is omitted. With such a configuration, it is possible to omit the rear-side mirror, which is a component part of the resonator, and it is possible to reduce the cost of the laser device.

  Also in this case, when the resistance of the antireflection coating and the partial reflection coating to the ultraviolet laser beam is compared, the antireflection coating has a higher durability because the number of coating layers is smaller. Therefore, in order to prevent a decrease in laser output from the amplification stage laser 60, an antireflection coating may be applied to the laser light transmitting surfaces of the triangular prisms 62 and 63 constituting the beam expander prism systems 61 and 61 '. Further, such coating may be omitted as long as the output reduction of the amplification stage laser 60 does not cause a problem. When the oscillation stage laser 50 is a narrow-band laser, the surfaces of the prisms 62 and 63 are set at angles so as not to cause multiple interference between the reflection surfaces of the front-side mirror 2 and the rear-side mirror 1. It is desirable to do so. The reason for this will be described later (FIG. 11).

  FIG. 8 shows a modification of the amplification stage laser 60 of FIG. In this embodiment, the function of the front side mirror 2 is also composed of the outermost triangular prism of the beam expander prism system 61 ', as shown in FIG. This is an example in which the partial reflection mirror coating 10 is directly applied to the side surface and the front side mirror 2 is omitted. With such a configuration, it is possible to omit the rear-side mirror and the front-side mirror, which are components of the resonator, and it is possible to reduce the number of mounted optical components and the cost of the laser device.

FIG. 9 shows numerical examples of the triangular prisms 62 and 63 used in the beam expander prism system 61 ′ also used as the front-side mirror used in the embodiments of FIGS. Each triangular prism 62, 63, 63 ′ is made of meteorite (CaF ₂ ) and is applied to ArF excimer laser light having a wavelength of 193.4 nm. The refractive index of CaF ₂ at this wavelength is 1.50196. For example, FIG. 9A shows a case where the beam expander prism system 61 ′ is composed of one triangular prism 62. The beam expander prism system is obtained by directly applying the partial reflection mirror coating 10 to the exit side surface of the triangular prism 62. In order to deflect the laser beam that is transmitted through the partially reflecting mirror coating 10 and to be parallel to the laser beam that is incident on the triangular prism 62, the same configuration is provided on the output side of the triangular prism 62. The triangular prism 63 ′ is arranged so that the apex angle faces the opposite side. Here, assuming that the apex angles of the triangular prisms 62 and 63 ′ are α1 and α2, respectively, α1 = 38.1 ° and α2 = 40.0 °, and the incident angle θ of the inclined surface of the triangular prism 62 is 67.9 °. Thus, the light emission angle of the partial reflection surface 10 of the triangular prism 62 becomes 0 °, and the function as the front side mirror 2 of the amplification stage laser 60 is achieved. The beam expansion ratio here is 2.09 times. The angle of incidence on the inclined surface of the triangular prism 63 ′ is 66.0 °, and the triangular prism 62 and the triangular prism 63 ′ are arranged so that the apex angle faces the opposite side. The magnification of the triangular prism 63 ′ is 1.95 times. The total is 4.07 times. The merit of this method is that the front mirror is constituted by one prism (triangular prism 62), so that the number of transmitting surfaces becomes one, and the loss in the resonator of the amplification stage laser 60 can be reduced. It is possible to prevent light interference between individual prisms. Furthermore, the other prism 63 ′ can correct the beam emission direction in the same direction and can expand the beam, thereby preventing damage to the optical element after the amplification stage laser 60. It is possible to do.

  FIG. 9B shows a case where a beam expander prism system 61 ′ is composed of two slightly different triangular prisms 62 and 63, and the triangular prism 62 and the triangular prism 63 are arranged so that the apex angle faces the opposite side, The partial reflection mirror coating 10 is directly applied to the exit side surface of the outermost triangular prism 63 to constitute a beam expander prism system 61 ′. Here, if the apex angles of the triangular prisms 62 and 63 are α1 and α2, respectively, α1 = 40.0 ° and α2 = 38.1 °, and the incident angle of the inclined surface of the triangular prism 62 is 66.0 °. Thus, the light emission angle of the partial reflection surface 10 of the triangular prism 62 is 3.79 °. The beam expansion ratio here is 1.95 times. The incident angle of the triangular prism 63 on the inclined surface is 67.9 °, and when the triangular prism 62 and the triangular prism 63 are arranged so that the apex angle faces the opposite side, the emission angle of the partially reflective coating surface 10 of this prism Becomes 0 ° and functions as an output side mirror. The magnification of the triangular prism 63 is 2.09 times. The total is 4.07 times. The merit of this embodiment is that the enlargement ratio can be increased by about 4 times, so that the energy density is 1/4 or less of the conventional case, so that the durability of the partial reflection coating is the embodiment of FIG. It extends compared to In this embodiment, the design is such that the vertical surfaces of the triangular prisms 62 and 63 do not coincide with the optical axis. This is because when the oscillation stage laser 50 is a narrow-band laser, the light interferes with the two vertical surfaces, and the spectrum of the amplified laser light is split. In this embodiment, the triangular prisms 62 and 63 having slightly different apex angles are used to prevent light interference. Further, the oscillation efficiency of the amplification stage laser 60 can be increased by applying an antireflection coating to the inclined surface and exit surface of the triangular prism 62 and the inclined surface of the triangular prism 63. As long as the output reduction of the amplification stage laser 60 does not cause a problem, the antireflection coating may not be provided on a part or all of the surfaces.

  In FIG. 9B, a resonator of the amplification stage laser 60 with higher efficiency can be configured by using a prism whose incident angle is close to the Brewster angle. The apex angles of the triangular prisms 62 and 63 are α1 = 29.00 ° and α2 = 31.63 °, respectively, and the incident angle of the inclined surface of the triangular prism 62 is 56.30 ° of the Pryster angle. The light emission angle from the partial reflection surface 10 is −0.122 °. The beam expansion ratio here is 1.49 times. When the incident angle of the triangular prism 63 on the inclined surface is 51.94 ° and the triangular prism 62 and the triangular prism 63 are arranged so that the apex angles face opposite sides, the emission angle of the partially reflective coating surface 10 of this prism Becomes 0 ° and functions as an output side mirror. The magnification of the triangular prism 63 is 1.38 times. The total is 2.06 times. In this embodiment, the design is made so that the vertical surfaces of the triangular prisms 62 and 63 do not coincide with the optical axis. This is because when the oscillation stage laser 50 is a narrow-band laser, the light interferes with the two vertical surfaces, and the spectrum of the amplified laser light is split. In this embodiment, the triangular prisms 62 and 63 having slightly different apex angles are used to prevent light interference. Further, the merit of this embodiment is that the incident angle of the inclined surfaces of the triangular prisms 62 and 63 is substantially the Brewster angle, so that there is almost no reflection loss without coating, and the oscillation efficiency of the amplification stage laser 60 is high. Can be maintained.

  FIG. 10 shows a top view of the resonator of the amplification stage laser 60 when the seed light 23 is injected from the back surface of the input side mirror 1. In this embodiment, the pair of discharge electrodes 4 and 5 are arranged in a direction perpendicular to the paper surface, and the discharge region 22 is generated perpendicular to the paper surface. A difference from the embodiment of FIG. 5 is that the surface of the input side mirror 1 is provided with a partially reflecting mirror coating 101 having a high reflectance of, for example, a reflectance of about 90%. The seed light 23 is input from the back surface of the input side mirror 1, is transmitted 10% by the partially reflecting mirror coating 101, is transmitted through the rear side window member 17 arranged at the Brewster angle, and is formed by the discharge electrodes 4 and 5. Light passes through the discharge region 22 and is optically amplified. Then, the light passes through the front window member 17, passes through the triangular prism 62, expands the beam, enters from the inclined surface of the triangular prism 63, and partially passes through the partially reflecting mirror coating 10 applied to the vertical surface. , And output as laser output light, the remaining light is reflected, passes through the triangular prisms 63 and 62 again, and enters the front window member 17. The light transmitted through the front side window member 17 is amplified by transmitting through the laser discharge region 22. The light transmitted through the rear side window member 17 is again reflected by 90% by the partial reflection mirror coating 101 of the input side mirror 1 and returned to the laser chamber 3 again. In this way, by injecting the seed light 23 into the resonator of the amplification stage laser 60, the MOPO operation becomes possible. In this embodiment, an example in which the beam expanding optical system is installed as the front-side beam expanding optical system 61 ′ has been described. However, the present invention is not limited to this, and as in the embodiment of FIG. A magnifying optical system 61 may be arranged. Thereby, durability of the partial reflection mirror coating 101 of the input side mirror 1 can be improved.

FIG. 11 shows a principle diagram of spectrum shape deterioration and output fluctuation when light interference occurs on the surface in the resonator of the amplification stage laser 60. FIG. 11A shows an example of the amplification stage laser 60 in the case where the output side mirror 2 is a parallel plane substrate of CaF ₂ not coated as the output side mirror 2 with respect to the embodiment of FIG. . In this case, the reflectivity of the output side mirror 2 shows wavelength dependence due to light interference. FIG. 11B shows the wavelength dependence of the reflectance of the output side mirror 2 with a thin line. As an example, the reflectivity of a CaF ₂ parallel plane substrate of thickness d varies periodically between 0 and about 18% with respect to wavelength. This periodic free spectral range (FSR) can be calculated from the thickness d of the substrate, the refractive index n of the substrate, and the wavelength λ. That is, FSR = λ ² / (2nd). Here, if the wavelength λ = 193 nm, the substrate thickness d = 14 mm, and the refractive index n of CaF ₂ = 1.50196, the free spectral range is 0.89 pm. A broken line and a thick solid line in FIG. 11B indicate a spectrum profile in the case of applying the partial reflection mirror coating 10 to the surface of the output side mirror 2 and a spectrum profile in the case of an uncoated parallel plane substrate, respectively. When the output-side mirror 2 is an uncoated parallel substrate (thick solid line), the spectrum profile is split. The cause of this will be described below.

  When the reflectance of the output side mirror 2 becomes 0, the amplification stage laser 60 has a function of simply amplifying the seed light 23, and outputs a one-pass MOPA. In this case, since the function is merely an amplification, the laser output decreases. On the other hand, as the reflectance of the output-side mirror 2 increases, the MOPO operation in which the seed light 23 is optically resonated and output from the amplification stage laser 60 is performed, and the output of the amplification stage laser 60 increases. In this way, since the MOPA operation and the MOPO operation occur depending on the wavelength, the spectrum shape changes greatly, and the laser output also fluctuates greatly. In this example, the case where light interference occurs on both surfaces of the output mirror 2 is shown. For example, when the vertical surfaces of the triangular prisms 62 and 63 coincide with the optical axis of the optical resonator of the amplification stage laser 60, similar light is used. Therefore, it is necessary to remove the optical axis from the optical resonator.

  By the way, as described above, the beam expander prism system 61, 61 ′, which is composed of one or more triangular prisms 62, 63, is obliquely incident on one inclined surface and is emitted at a substantially right angle from the other surface, is provided in the laser chamber 3. The energy density applied to the mirrors 1 and 2 is reduced below the damage threshold by disposing the laser beam between the output mirror 2 and the output side mirror 2 and between the laser chamber 3 and the rear side mirror 1 to enlarge the diameter of the laser beam. In this case, since the refractive index of the prism changes depending on the wavelength, the angle at which the light traveling from the laser chamber 3 side enters the partial reflection mirror coating 10 of the output side mirror 2 is the wavelength in the case of FIG. Will be different. Therefore, even if the incident angle is vertical at a certain wavelength, if the incident angle is changed to another wavelength, the incident angle on the partial reflection mirror coating 10 is not vertical, so that the light reflected by the partial reflection mirror coating 10 is incident light. It returns to the laser chamber 3 along an axis different from the axis. When the reflected light is transmitted through the prisms 62 and 63, the axial deviation is further increased, and the rate of returning to the discharge region 22 is reduced, resulting in a problem that the laser output is reduced. FIG. 12 shows the wavelength dependence of the output when the beam expander prism system (beam expanding optical system) 61 'is used. It can be seen that the output is halved when the center wavelength is changed by 100 pm. It was also found that the vertical planes of the triangular prisms 62 and 63 had a problem that the irradiation energy density was high and the surface was damaged because the magnification rate of the beam size was small.

  Hereinafter, the principle and embodiment of the configuration for reducing the wavelength dependency of the output by another beam expanding optical system of the present invention will be described. Also, an embodiment will be described in which the irradiation energy density on the surface of the triangular prism is reduced in order to reduce the risk of damage to the vertical surface of the triangular prism.

As described above, the gas laser device includes an electrode and a power source for exciting a laser medium (laser gas), several kinds of gases serving as a laser medium, and a resonator for amplifying light. In general, mirrors serving as resonators are disposed at both ends of a laser chamber in which electrodes are disposed. A gas serving as a laser medium (in the case of an ArF excimer laser, F ₂ gas, Ar gas, Ne or He gas as a dilution gas) is enclosed in a chamber, and a high voltage is provided between discharge electrodes mounted facing each other. An electric field is applied and discharged there. The gas is excited by the discharge, and a laser medium (ArF ^* excimer molecule in the case of ArF excimer laser) is generated. Since the discharge electrode has an elongated shape, the gain region has a shape elongated in the longitudinal direction of the electrode. In general, the width is several mm, the height is several to several tens of mm, and the length is several hundred mm. The light spontaneously emitted from the laser medium oscillates by amplifying by reciprocating this elongated gain region several to several dozen times. In order to reciprocate the light, mirrors that are resonators are arranged at both ends. By this mirror, light reciprocates on the same axis and is output as a laser. In order to amplify the laser light, the same axis along which the light reciprocates is called a laser optical axis and is on the longitudinal axis of the electrode that generates the gain distribution.

In an optical element, the refractive index changes depending on the wavelength of light passing through the element. For example, in an ArF excimer laser or F ₂ laser, CaF ₂ is used as an optical element, and the refractive index n (λ) of CaF ₂ is
n (λ) = 1.7865829 -1.949727 × 10 ^-3 λ + 2.4708935 × 10 ^-6 λ ²
It is known that

Thus, when the wavelength of the laser beam changes, the refractive index of the optical element changes accordingly. FIG. 13 shows how the beam optical path is shifted depending on the wavelength in the triangular prism Pr. The laser beam path b in the center of FIG. Now, a case is assumed where light enters the triangular prism Pr from the laser optical axis and then returns after being reflected by the mirror Mi. In this figure, lambda is designed beam expander optical system for the wavelength of the ₀ for the wavelength of lambda _0, the beam path of the reflected light returns to the optical path and the same laser beam axis of the incident light Come. When such design, lambda ₀ from short-wavelength light (λ ₀ -dλ) is incident from the optical path b of the prism Pr, the refractive index of the prism Pr is _{n (λ 0 -dλ)> n} (λ 0) Therefore, it returns to the optical path a in the figure. Since the gain region (longitudinal direction of the electrode) of the laser medium is on the laser optical axis b, if the reflected light deviates from the laser optical axis b, the light is not amplified but attenuated and the output decreases. Become. Therefore, the light of the wavelength λ ₀ -dλ returning on the optical path a is attenuated. Similarly, when light (λ ₀ + dλ) having a wavelength longer than λ ₀ enters the prism Pr from the optical path b, the refractive index of the prism Pr becomes n (λ ₀ + dλ) <n (λ ₀ ). It returns to the optical path of c. Also in this case, the wavelength λ ₀ + dλ is attenuated because it is off the laser optical axis b.

  The amount of deviation of the emission angle depends on the size of the apex angle of the prism Pr. When the vertex angle is small, the angle deviation amount is small, and when the vertex angle is large, the angle deviation amount is also large.

  As described above, the laser light is normally amplified by stimulated emission within the laser medium after reciprocating within the resonator several to dozens of times. Therefore, in order to take out as laser light, it must not deviate from a gain region with a laser medium on the way. Since the laser gain region has a width corresponding to the electrode width, it is sufficient that the laser optical path does not deviate from the width. However, when a large angular deviation occurs as shown in FIG. 13, the number of times the light reciprocates inside the resonator increases. At the same time, it deviates from the gain region. This is the wavelength dependence of the output when using the beam expander prism systems 61 and 61 ′ composed of the triangular prisms 62 and 63 that are obliquely incident on one of the inclined surfaces and exit from the other surface at a substantially right angle. It is a cause that occurs.

  In order to prevent the wavelength dependency of the output from occurring, the above-described angular deviation may be corrected. Then, as shown in FIG. 14, what correct | amends the angle shift should just be arrange | positioned on the opposite side of a resonator. As a method therefor, there is a method in which the configuration of the triangular prism Pr and the mirror Mi arranged on the output side is left and right upside down and arranged on the rear side when the mirror Mi in FIG. Since the same configuration and shape, the same material, and the same incident angle, the magnitude of the angle deviation is the same. And since it is reversed, the direction of angular deviation is reversed. As a result, the optical path of the light reflected and returned from the rear side is parallel to the laser optical axis b. Although the position where the beam passes through the gain region is slightly deviated, the angle deviation is corrected, so that it is difficult for light to deviate from the gain region as compared to before the correction.

  As another method, when the wedge substrate is used as an element of the beam expanding optical system, an angular deviation due to light passing through the beam expanding optical system can be reduced. FIG. 15 shows a state of the beam expanding optical system when the wedge substrate We is used. This corresponds to a case where the apex angle of the triangular prism Pr is made small and incident obliquely on both slopes. The wedge angle α is several to several tens of degrees. Therefore, the amount of angular deviation of the light reflected and returned is small. When the wedge angle is 0 °, the angular deviation is 0 ° and returns to the incident optical axis. However, if the wedge angle is small, it is difficult to obtain a required beam expansion rate, and therefore it is necessary to increase the beam incident angle as compared with the triangular prism.

FIG. 16 shows the relationship between the incident angle, apex angle, and deflection angle of the laser beam path in the beam expanding optical system. As shown in the figure, when the laser light is incident on the wedge substrate We from the laser optical axis at an incident angle θ ₁ , the angles θ ₂ and θ as illustrated depend on the value of the refractive index n (λ) of the wedge substrate We. ₃ and refracted at θ ₄ and emitted from the wedge substrate We. The direction of the beam emitted from the wedge substrate We is shifted by an angle β ° from the laser optical axis before entering the wedge substrate We.

Now, the apex angle (wedge angle) of the wedge substrate We is α, the refractive index of the optical element is n (λ), and the refractive index of the atmospheric gas on which the wedge substrate We is placed is n ′ (in the case of air, n ′ = 1, in the case of nitrogen gas generally used as a purge gas, n ′ = 1.00032178), and assuming that the center wavelength of the laser is λ ₀ ,
n′sin θ ₁ = n (λ ₀ ) sin θ ₂ (1)
n (λ ₀ ) sin θ ₃ = n′sin θ ₄ (2)
θ ₃ = θ ₂ −α (3)
β = θ ₁ −θ ₂ + θ ₃ −θ ₄ (4)
It can be expressed by the relational expression The expressions (1) and (2) here are based on Snell's law.

Now, in the case of the wavelength λ _0, the angle formed by the laser optical axis incident on the beam expanding optical system and the mirror Mi is 90−β °.

At this time, the beam expansion rate M (A is used in the above, but M is used here) is:
M = (cos θ ₂ · cos θ ₄ ) / (cos θ ₁ · cos θ ₃ ) (5)
It can be expressed by the following formula.

If the laser wavelength is λ ₀ , the laser light reflected by the mirror Mi is returned to the laser optical axis before entering the beam expanding optical system. However, when the laser wavelength is changed to λ, as described above, since the refractive index of the wedge substrate We has wavelength dependence, the emission angle changes. If the direction of the beam emitted from the wedge substrate We is an angle β ′ ° with respect to the laser optical axis before entering the wedge substrate We, the angle of incidence on the mirror Mi is not perpendicular and becomes β′−β °. . For this reason, the light reflected by the mirror Mi deviates from the laser optical axis and is emitted at an angle γ ° with respect to the optical axis incident on the wedge substrate We as shown in the figure. At this time, if the angles when reflected by the mirror Mi and re-enter the beam expanding optical system are θ _{1 ′} , θ _{2 ′} , θ _{3 ′} , and θ _{4 ′} as shown in the figure,
n′sin θ _{4 ′} = n (λ) sin θ _{3 ′} (6)
n (λ) sin θ _{2 ′} = n _′ sin θ _{1 ′} (7)
θ _{4 ′} = θ ₄ + β′−β (8)
θ _{2 ′} = θ _{3 ′} + α (9)
γ = θ _{1 ′} −θ ₁ (10)
It can be expressed by the relational expression Using the above relational expression to calculate the apex angle α dependency of the deflection angle γ, the result shown in FIG. 17 is obtained. Here, when the laser light reflected by the mirror Mi is arranged so as to return to the incident optical axis under the conditions of the center wavelength λ ₀ = 193.368 nm, the incident angle θ ₁ = 52.35 °, and the apex angle α °, the wavelength It is calculated what the declination γ becomes when λ is changed to λ = 193 nm and λ = 193.7 nm. In addition, the right-angle prism shown in the figure has shown the case of the triangular prism Pr of FIG.

As a result, it can be seen that when the wavelength is shifted, the deviation angle γ decreases as the apex angle α decreases. When the apex angle α = 0 °, the deflection angle γ is 0 °. When the incident angle is 52.35 °, the value of the apex angle to become the right-angle prism Pr is α = θ ₂ , so α = 31.82 °. The deflection angle γ at this time is about 0.035 °, but the deflection angle can be reduced to 0.01 ° or less by making the apex angle 5 ° or less.

FIG. 18 shows the result of calculating the enlargement ratio in the model under the same conditions. As the apex angle is reduced, the declination angle is reduced, but as shown in FIG. For this reason, in order to obtain the same enlargement ratio, it is necessary to increase the incident angle when the apex angle is decreased. In addition, it can be seen that the dependency of the magnification rate on the apex angle is less affected by the laser wavelength (in FIG. 18, the curves of three wavelengths λ ₀ = 193.368 nm, λ = 193 nm, and λ = 193.7 nm overlap). Yes.)

FIG. 19 shows the dependency of the magnification M on the incident angle θ ₁ . In the figure, a right-angle prism (each apex angle was calculated as α = θ ₂ so that it becomes a right-angle prism for each incident angle) and apex angle α = 4. The case of 45 ° is shown. In the case of the same incident angle θ ₁ = 52.35 ° as described above, the magnification factor M is 1.37 times in the right-angle prism. In order to make this magnification the same when the apex angle is reduced, for example, when the apex angle is set to 4.45 °, the incident angle may be set to 67.1 °. Here, the apex angle is calculated as 4.45 °. However, when the apex angle is further smaller than 4.45 °, the required incident angle is 67.1 ° or more, and the apex angle is 4.4 °. In the case where the angle may be larger than 45 °, the incident angle can be 67.1 ° or less.

Here, although the incident angle is increased, the declination angle is somewhat increased by increasing the incident angle. FIG. 20 shows the dependence of the deflection angle γ on the incident angle θ ₁ . Similarly to FIG. 19, the case of a right-angle prism and the case of an apex angle of 4.45 ° are shown. The wavelengths are shown for λ = 193.0 nm and λ = 193.7 nm, respectively. The declination angle increases as the incident angle increases, but when the apex angle is small, the effect is small and hardly changes. Therefore, even if the incident angle is increased, the declination reduction effect by reducing the apex angle is greater. As shown in FIG. 20, when the enlargement magnification is 1.37, the deflection angle in the case of the right-angle prism is 0.036 °, whereas in the case of the apex angle of 4.45 °, the deviation angle is as small as 0.01 °. Here, as a representative of the wedge substrate We, the case where the apex angle (wedge angle) is 4.45 ° is shown, but even if the apex angle is different, the effect is the same as long as it is smaller than the apex angle of the right-angle prism. At the same magnification, the declination can be reduced, that is, the wavelength dependence of the output can be reduced.

As another method, there is a method of controlling the beam optical path so as not to be shifted by changing the beam incident angle to the beam expanding optical system when the wavelength changes. FIG. 21 shows the method. FIG. 21A shows the control when the wavelength is changed to the long wavelength by dλ, and FIG. 21B is the control when the wavelength is changed to the short wavelength by dλ. In the triangular prism beam expansion optical system (FIG. 13) designed for the wavelength λ ₀ , it is assumed that the wavelength is changed to λ ₀ + dλ. In this case, the angle is shifted along the optical path represented by the solid line in FIG. The angle deviation in the prism Pr at that time is defined as θ. If the incident angle is changed by θ so that the angle change θ is eliminated, the angle changes on the optical path represented by the dotted line. In order to change the incident angle, the position of the prism Pr is rotated. The center of rotation at this time is the incident point of the beam. The same applies to the case where the wavelength is changed to a short wavelength of λ ₀ -dλ (FIG. 21B). This time, if the prism Pr is rotated by θ in the opposite direction, the angle deviation is corrected and the laser optical axis is corrected. You can return it to b.

  Further, when the wavelength changes, there is a method of controlling the tilt (angle) of the output side mirror Mi or the rear side mirror Mi so that the beam optical path is not shifted. The principle is the same as in the case of FIG. 21, and since the traveling direction of the light reaching the mirror Mi is not perpendicular to the mirror Mi due to the change of the center wavelength, the tilt angle of the mirror Mi is adjusted so that this is perpendicular. Thus, the reflected light from the mirror Mi can be returned to the laser optical axis.

  Next, an embodiment using a method for preventing the wavelength dependence of output as described above from occurring will be described below.

  FIGS. 22A and 22B are top views of embodiments corresponding to FIGS. 6 and 7 and using the method of FIG. In this embodiment, triangular prism type beam expanding optical systems are arranged on the rear side and the output side beam expanding optical systems (BEX) 61 and 61 ′ at both ends of the chamber 3. As described above, in order to make the wavelength dependence of the output small enough to be ignored, the arrangement of the triangular prisms 62 and 63 of the rear side beam expanding optical system 61 is changed to the triangular prism 62 of the output side beam expanding optical system 61 ′. The arrangement of 63 sets is reversed up and down and left and right. With such an arrangement, even if the wavelength changes, the angle deviation from the laser optical axis of the beam that has changed after passing through the output side beam expanding optical system 61 ′ is transmitted through the rear side beam expanding optical system 61. It can be eliminated (offset). As a result, the wavelength dependence of the output is relaxed. The other components shown in FIGS. 22A and 22B are apparent from the above description, and will not be described.

  FIG. 23 shows the output wavelength when the triangular prism type beam expanding optical system 61 ′ is disposed only on the output side and when the triangular prism type beam expanding optical system 61 that is 180 ° rotationally symmetric is also disposed on the rear side. Indicates dependency. Thus, for example, when the ± 100 pm wavelength changes, the output is reduced by half in the one-side beam expanding optical system arrangement, but the output can be reduced by several percent in the two-side beam expanding optical system arrangement. If the output is reduced to this extent, it is possible to control the output to a constant level by increasing the voltage applied to the discharge electrodes 4 and 5 and the gas pressure in the chamber 3.

In FIG. 22B, the partial reflection mirror coating 10 is formed on the vertical surface of the second (outside) triangular prism 63 of the output side beam expanding optical system 61 ′ to replace the output side mirror. . Further, a partial reflection mirror coating 10 having a reflectivity of about 90% is formed on the vertical surface of the second (outer) triangular prism 63 of the rear side beam expanding optical system 61 to replace the rear side mirror. I have to. Enlarging the beam expanding optical systems 61 and 61 ′ so that the peak energy per unit area (irradiation peak fluence; mJ / cm ² ) of the laser light applied to the partial reflection mirror coating 10 does not exceed the damage threshold and the distortion threshold. The rate is set. In this case, the expansion ratio of the beam expansion optical system is the same for the beam expansion optical systems 61 and 61 ′ on the output side and the rear side, so that either one is set to the expansion ratio with the higher irradiation fluence. Here, the partial reflection mirror coating 10 and the antireflection coating 9 to be used are manufactured by forming thin films such as MgF ₂ , GdF ₃ , LaF ₃ , Al ₂ O ₃ , and AlF ₃ into a multilayer or a single layer. Examples of the film forming method include a resistance heating vapor deposition method, an electron beam method (EB), and an ion beam sputtering method (IBS).

  This method is also effective for systems other than the triangular prism type beam expanding optical systems 61 and 61 ', and can also be used for a wedge substrate type beam expanding optical system.

  Next, FIG. 24 shows an embodiment corresponding to FIG. 4 and FIG. 6, which is an embodiment (a) using the method using the wedge substrate of FIG. 16 and an embodiment combining FIG. 16 and FIG. The top view of b) is shown.

  By using the wedge substrate 92, the wavelength dependence of the output can be reduced. FIG. 24A shows a case where a beam expanding optical system 91 ′ composed of one wedge substrate 92 is arranged between the laser chamber 3 and the front side mirror 2, and FIG. This is a case of a double-sided beam expanding optical system arrangement in which a beam expanding optical system 91 composed of one wedge substrate 92 is also arranged between the rear side mirror 1 and the rear side mirror 1. In the case of FIG. 24B, the arrangement of the wedge substrate 92 of the rear side beam expansion optical system 91 is vertically and horizontally reversed with respect to the arrangement of the wedge substrate 92 of the output side beam expansion optical system 91 '. Even if the beam expanding optical system 91 ′ using a wedge substrate is disposed on one side (FIG. (A)), the wavelength dependence of the output can be reduced, but the beam expanding optical systems 91 and 91 ′ using a wedge substrate on both sides are provided. By arranging it, it is possible to further reduce the wavelength dependence of the output. In this configuration, since there is one wedge substrate, the structure is simple, and there is an advantage that the increase in the resonator length due to the insertion of the beam expanding optical systems 91 and 91 ′ can be reduced (the laser output increases as the resonator length increases). Is known to decrease.) However, as shown in FIGS. 24A and 24B, the laser beam output from the output side mirror 2 is tilted by the declination β ° in FIG. 16 from the laser beam axis in the laser chamber 3. For this reason, in order to correct this declination, there is a demerit that an optical system for correction is required after the output side mirror 2.

FIGS. 25A and 25B are examples corresponding to FIGS. 24A and 24B configured by using two wedge substrates 92 and 93 in each beam expanding optical system 91 and 91 ′. It is. The two wedge substrates 92 and 93 in the respective beam expanding optical systems 91 and 91 ′ are the same, and the second wedge substrate 93 is turned upside down with respect to the first wedge substrate 92. It is arranged in a letter “C” shape so that the beam incident angles are the same. By arranging in this way, the laser optical axis after emission of the beam expansion optical systems 91 and 91 ′ is made parallel to the laser optical axis before incidence of the beam expansion optical systems 91 and 91 ′ (deflection angle β = 0 °). Can do. This principle will be described with reference to FIG. FIG. 26 shows a laser beam path when the laser beam is incident on the two wedge substrates 92 and 93. As shown in the figure, the angle of the beam optical path on the second wedge substrate 93 is θ ₅ , θ ₆ , θ ₇ , θ _8, and the beam deflection angle of the emitted light from the first wedge substrate 92 is β _{1 If} the beam deflection angle of the emitted light from the second wedge substrate 93 is β ₂ ,
β ₁ = θ ₁ −θ ₂ + θ ₃ −θ ₄ (11)
β ₂ = θ ₁ −θ ₅ + θ ₆ −θ ₇ + θ ₈ (12)
It becomes. Now, if the second wedge substrate 93 has the same shape as the first wedge substrate 92 and is turned upside down to have the same incident angle (θ ₅ = θ ₁ ),
θ ₅ = θ ₁ (13)
θ ₆ = θ ₂ (14)
θ ₇ = θ ₃ (15)
θ ₈ = θ ₄ (16)
α ₁ = α ₂ (17)
Holds. Substituting these equations (13) to (17) into equation (12),
β ₂ = 0 (18)
It becomes. That is, under the above-described conditions, the deviation angle is set to 0, and the optical axis of the emitted laser light can be made parallel to the laser optical axis in the chamber 3.

  Another advantage of using two wedge substrates 92 and 93 in the beam expanding optical systems 91 and 91 ′ is that the magnification obtained with one sheet can be doubled. In addition, since the chromatic dispersion directions are two and opposite directions, the arrangement is designed to weaken the influence of dispersion. However, as the number increases, the resonator length may increase and the output may decrease. Therefore, it is necessary to make the beam expanding optical systems 91 and 91 'small.

  With the beam expansion systems 91 and 91 ′ as shown in FIGS. 24 and 25, the peak fluence irradiated to the antireflection coating 9 and the partial reflection mirror coating 10 of the output side mirror 2 can be reduced below the damage threshold. Since the wavelength dispersion is small, the wavelength dependence of the output can be ignored.

  FIG. 27 is a diagram showing the wavelength dependence of the outputs of a wedge-substrate beam expanding optical system using a wedge substrate and a triangular prism beam expanding optical system using a triangular prism. In both cases, the magnification ratio of the beam expansion optical system is 1.87 times. In the case of the triangular prism type, the incident angle is 52.35 ° and the apex angle is 31.82 °. In the case of the wedge substrate type, the incident angle is 67.1 ° and the wedge angle is 4.45 °. The wedge substrate type has a larger incident angle in order to increase the magnification. FIG. 27 shows that the wavelength dependency of the output is smaller in the wedge substrate type even when the magnification is the same. In this case, for example, when the ± 100 pm wavelength is changed, the output is halved when the beam expanding optical system is arranged on one side, but when the beam expanding optical system is arranged on both sides, the output is several percent. It can be seen that reduction is sufficient.

  FIG. 25B shows an example in which the wedge substrate type beam expanding optical system 91 is arranged upside down and horizontally with respect to the front side beam expanding optical system 91 'on the rear side. In this system, the wavelength dependency of the output can be further reduced by combining the double-sided beam expanding optical system and the wedge substrate type. In this method, even when the peak fluence irradiated to the high-reflection partial reflection mirror coating 10 of the rear side mirror 1 is equal to or greater than the damage threshold, the irradiation peak fluence can be reduced by the enlargement ratio. It is valid. FIG. 28 shows the wavelength dependence of output in this arrangement. As can be seen from FIG. 28, the wavelength dependence disappears in the range of 193 nm to 193.7 nm. It can be seen that this method is effective when the wavelength is greatly changed.

The incident angles of the wedge substrates 92 and 93 are the Brewster angle at which the P-polarized reflectance is 0 (in the case of ArF laser wavelength 193.368 nm, 56.34 °, and in the case of F ₂ laser wavelength 157.63 nm). Often greater than 57.32 °). In this case, it is necessary to attach an antireflection film on the surface so that the P-polarized reflectance can be ignored at the incident angle. For example, when a beam expansion optical system with a beam expansion ratio of 2.0 times is designed, the incident angle is 68.7 ° and the wedge angle is 4.4 °. Further, the incident angle on the back surface of the wedge substrate is 60.0 °. Since the P-polarized reflectance at an incident angle of 60.0 ° is 0.2%, it is not necessary to attach an antireflection film to this surface, but since the first surface is 68.7 °, it is necessary to attach an antireflection film. There is.

  In designing the beam expanding optical system, it is necessary to prevent the beam expanding optical system itself from being damaged. In the case of the triangular prism type beam expanding optical systems 61 and 61 'described above, the beam irradiation area on the vertical surface of the triangular prism is smaller than that of the inclined surface, and the irradiation peak fluence is increased. In particular, since the irradiation peak fluence of the vertical surface of the first prism 62 having a low magnification is high, the triangular prism type may be damaged when the laser output energy is high. However, in the case of this wedge substrate type, compared with the triangular prism type, the portion corresponding to the vertical plane receives light on the slope of the wedge substrate, so the irradiation area is large and the irradiation fluence can be reduced. is there. In designing the beam expansion optical system, it is necessary to design the surface of the triangular prism or the wedge substrate of each beam expansion optical system to be equal to or less than the damage threshold together with the expansion ratio.

  Next, an embodiment in which one wedge substrate 92 in the wedge substrate type beam expanding optical systems 91 and 91 ′ is also used as a window member at the end of the chamber 3 will be described. FIGS. 29A and 29B are embodiments corresponding to FIGS. 25A and 25B, and FIG. 29A shows a case where the beam expansion optical system 91 ′ is disposed only on the output side. (B) is a case where the beam expansion optical system 91 is also arranged on the rear side. Both show examples in which one wedge substrate 92 of the wedge substrate type beam expanding optical systems 91 and 91 ′ is used as a window member to form a chamber window / wedge substrate 94. In this method, one or two elements that have been used for the window member 17 of the substantial chamber 3 can be reduced, so that one or two light losses in the optical element can be eliminated. The cost for one or two sheets can be reduced. Further, since the resonator length can be shortened by one or two elements, there is an advantage that the output is increased.

FIGS. 30A and 30B are embodiments corresponding to FIGS. 29A and 29B. FIG. 30A shows a case where the beam expansion optical system 91 ′ is disposed only on the output side. (B) is a case where the beam expansion optical system 91 is also arranged on the rear side. In this embodiment, the wedge substrate type beam expanding optical systems 91 and 91 ′ are all placed in the chamber 3, and the other wedge substrate 93 is used as the chamber window / wedge substrate 94. By doing in this way, it can be made a simple structure in appearance. In addition, CaF ₂ that can be used as a material for the wedge-substrate-type beam expanding optical systems 91 and 91 ′ has F atoms on its surface desorbed by laser irradiation. For this reason, it is known that exposure to F ₂ gas atmosphere compensates for missing F atoms and makes it difficult to damage (Non-patent Document 1). For this reason, there is an advantage that the damage threshold of the beam expanding optical systems 91 and 91 ′ themselves can be improved by placing the beam expanding optical systems 91 and 91 ′ inside the chamber 3.

  In addition to the above, as a configuration for reducing the wavelength dependence of the output and expanding the diameter of the laser beam, a negative power and a positive power cylindrical lens or a rotationally symmetric lens are arranged so as to be in focus with each other (telephoto system). There is a method of expanding the beam diameter. The beam diameter or width is expanded by a negative power lens, and the beam is returned to parallel light by a positive power lens placed after the negative power lens. In this arrangement, the wavelength is not angularly dispersed, so there is no wavelength dependency of the output. However, when the lens is arranged perpendicular to the laser optical axis, the irradiation fluence at the lens is high, and the lens itself may be damaged. In order to reduce the irradiation fluence, the concave mirror may be disposed in place of the negative power lens, but in this case, there is a disadvantage that the aberration increases.

  Next, an embodiment will be described in which the optical path is prevented from shifting by controlling the beam incident angle to the beam expanding optical system in accordance with the wavelength change of FIG.

  FIG. 31 shows an example of a method of controlling the incident angle of the beam expanding optical system so that the angle shift itself does not occur depending on the wavelength. In FIG. 31, the triangular prism type beam expanding optical system 61 'is used. However, the present invention is applicable and effective in the case of using a wedge substrate type beam expanding optical system. In order to enable this control, a mechanism capable of rotating the optical elements 62 and 63 constituting the beam expanding optical system 61 ′ is provided (in FIG. 31, rotary stages 111 and 112 for supporting the triangular prisms 62 and 63 are provided. ). When the main controller 105 senses a change in wavelength, it sends a signal to the rotary stage controller 106 to rotate the triangular prisms 62 and 63 by an angle corresponding to the wavelength change to control the incident angle. The monitor module 107 is arranged on the output side of the output side mirror 2, and the energy or spectrum of the output laser light is measured by the energy sensor or spectrometer 108 therein, and the maximum transmission wavelength of the output light becomes the target wavelength λ. Thus, feedback control is performed to finely adjust the incident angle.

  In this way, even if the wavelength is changed, by adjusting the optical axis, the laser beam can always pass on the laser optical axis having a gain region, thereby preventing a decrease in output.

  FIG. 32 shows an example of a system in which the tilt (angle) of the mirror constituting the resonator is controlled so that the angle shift itself does not occur due to the wavelength. In FIG. 32, the triangular prism type beam expanding optical system 61 'is used. However, the present invention is also applicable and effective when using a wedge substrate type beam expanding optical system. In order to enable this control, the output side mirror 2 is provided with a tilt control mechanism 110. When the main controller 105 senses a change in wavelength, it sends a signal to the output-side mirror controller 109 to control the amount of tilt corresponding to the wavelength change via the tilt control mechanism 110. The monitor module 107 is arranged on the output side of the output side mirror 2, and the energy or spectrum of the output laser light is measured by the energy sensor or spectrometer 108 therein, and the maximum transmission wavelength of the output light becomes the target wavelength λ. Thus, feedback control is performed to finely adjust the tilt amount.

  In this way, even if the wavelength is changed, by adjusting the optical axis, the laser beam can always pass on the laser optical axis having a gain region, thereby preventing a decrease in output.

  In FIG. 32, the method of controlling the tilt angle of the output side mirror 2 is adopted, but the same effect can be obtained by controlling the tilt angle of the rear side mirror 1.

  Hereinafter, the control in the system of FIGS. 31 and 32 will be described. FIG. 33 shows a main routine of the control flowchart. In step ST1, when the laser apparatus receives a command for setting the center wavelength to λ from the exposure apparatus 100 (FIG. 2), a subroutine ST2 for setting the center wavelength of the seed light of the oscillation stage laser 50 to λ is executed. Although not shown, as a method of changing the wavelength, there is a method of changing the incident angle of the magnifying prism, the incident angle of the grating (diffraction grating), or the tilt angle of the front mirror 52 in the narrowband module 51. Thereafter, a subroutine ST3 for adjusting the maximum transmission wavelength of the amplification stage laser 60 to λ is performed.

  34 to 37 show examples of these subroutines ST3. Hereinafter, it demonstrates in order.

  FIG. 34 shows a subroutine for controlling the incident angle of the optical elements (triangular prisms 62 and 63) of the beam expanding optical system 61 '. First, in step ST11, the main controller 105 calculates the rotation angle θ corresponding to the wavelength λ. The value of θ can be obtained from the equation of wavelength dependency of the refractive index in the material of the optical elements 62 and 63 and the Snell equation. Then, the value of the angle θ is commanded to the rotary stages 111 and 112 of the beam expanding optical system. Next, in step ST12, the rotary stages 111 and 112 are θ-controlled according to the command value. Next, the angle θ is finely adjusted so that the laser output is maximized. First, in step ST13, the parameter N is set to zero. Next, in step ST14, the monitor module 107 measures the laser output and sets the value of the parameter E as the measured value E1. Here, the parameter E means an energy value before fine adjustment. Next, in step ST15, the rotary stages 111 and 112 are rotated by a small amount k · dθ. An optimal value is set in advance as the value of the coefficient k. When the value of k is negative, it rotates in the reverse direction. Next, in step ST16, the monitor module 107 measures the laser output again, and sets the value of the parameter E ′ as the measured value E2. Here, the parameter E ′ means the energy value after fine adjustment. Next, in step ST17, it is determined whether E '> E. When E ′> E, the laser output is increased by fine adjustment. Therefore, in step ST18, the value of the parameter E is set to E ′, the process returns to step ST15, and the rotary stages 111 and 112 are again set to a very small amount k. -A routine for rotating dθ is performed. If it is determined in step ST17 that E '<E, it means that the energy has decreased, and thus it has already been at the position of the output peak or the control direction has been reversed. Here, the parameter N is determined in step ST19. The value of N indicates the number of times E ′ <E. When N = 0, that is, when the energy decreases after adjustment for the first time. In this case, since the position must be returned to the original state, the sign of k is inverted (k = k × (−1)) in order to reverse the rotation direction in step ST20. Then, the value of the parameter N is set to 1, and the value of the parameter E is set to E ′. Then, returning to step ST15, a routine for rotating the rotary stages 111 and 112 by a small amount k · dθ again is performed. When N = 1, it means that there is a history of reversing the adjustment direction before. If it was at the position of the output peak in the stage before fine adjustment originally, the output decreased by fine adjustment once. Therefore, the adjustment direction is reversed and the adjustment is made toward the peak. This means that the output has decreased for the second time due to passing through. Or, since the output of the first fine adjustment was reversed and the output decreased, the adjustment direction was reversed, the adjustment was made toward the peak, and the output decreased by the second time due to passing the peak. Means when. In either case, since the peak is at a position that exceeds the adjustment by one adjustment, the adjustment direction is finally reversed (k = k × (−1)) in step ST21, and the rotation stage is determined in step ST22. 111 and 112 are rotated by k · dθ. An energy peak is at this position.

  FIG. 35 shows a subroutine for controlling the tilt angle of the mirror constituting the resonator. First, in step ST31, the main controller 105 calculates a tilt amount x corresponding to the wavelength λ. The value of x is determined by the vertical direction of the mirror (in this case, the output side mirror 2) and the progress of the laser light to the mirror from the wavelength dependence equation and the Snell equation of the material of the optical elements 62 and 63. An angle difference α in the direction is calculated, and a tilt amount x corresponding to the angle α is calculated. Then, the output side mirror tilt adjusting mechanism 110 is commanded to the value of the tilt amount x. Next, in step ST32, the tilt amount of the output side mirror 2 is controlled in accordance with this command value. Next, the tilt amount x is finely adjusted so that the laser output is maximized. First, in step ST33, the parameter N is set to zero. Next, in step ST34, the monitor module 107 measures the laser output and sets the value of the parameter E as the measured value E1. Here, the parameter E means an energy value before fine adjustment. In step ST35, the tilt control mechanism 110 is rotated by a small amount k · dx. An optimal value is set in advance as the value of the coefficient k. When the value of k is negative, it rotates in the reverse direction. Next, in step ST36, the monitor module 107 measures the laser output again, and sets the value of the parameter E ′ as the measured value E2. Here, the parameter E ′ means the energy value after fine adjustment. Next, in step ST37, it is determined whether E '> E. When E ′> E, the laser output is increased by fine adjustment. Therefore, in step ST38, the value of parameter E is set to E ′, and the process returns to step ST35 to again adjust the tilt adjustment mechanism 110 by a small amount k ·. A routine for rotating dx is performed. If it is determined in step ST37 that E '<E, it means that the energy has decreased, and thus it has already been at the position of the output peak or the control direction has been reversed. Here, the parameter N is determined in step ST39. The value of N indicates the number of times E ′ <E. When N = 0, that is, when the energy decreases after adjustment for the first time. In this case, since the position must be returned to the original state, the sign of k is inverted (k = k × (−1)) in order to reverse the rotation direction in step ST40. Then, the value of the parameter N is set to 1, and the value of the parameter E is set to E ′. Then, returning to step ST35, a routine for rotating the tilt adjustment mechanism 110 by a small amount k · dx is performed. When N = 1, it means that there is a history of reversing the adjustment direction before. If it was at the position of the output peak in the stage before fine adjustment originally, the output decreased by fine adjustment once. Therefore, the adjustment direction is reversed and the adjustment is made toward the peak. This means that the output has decreased for the second time due to passing through. Or, since the output of the first fine adjustment was reversed and the output decreased, the adjustment direction was reversed, the adjustment was made toward the peak, and the output decreased by the second time due to passing the peak. Means when. In any case, since the peak is at a position that exceeds the adjustment by one adjustment, the adjustment direction is finally reversed (k = k × (−1)) in step ST41, and the tilt adjustment is performed in step ST42. The mechanism 110 is rotated by k · dx. An energy peak is at this position.

  Although the case where the tilt angle of the output side mirror 2 is controlled has been described above, the same effect can be obtained by controlling the tilt angle of the rear side mirror 1.

  FIG. 36 is a subroutine for controlling the incident angle of the optical elements (triangular prisms 62 and 63) of the beam expanding optical system 61 'by measuring the spectrum. First, in step ST51, the main controller 105 calculates the rotation angle θ corresponding to the wavelength λ. The value of θ can be obtained from the equation of wavelength dependency of the refractive index in the material of the optical elements 62 and 63 and the Snell equation. Then, the value of the angle θ is commanded to the rotary stages 111 and 112 of the beam expanding optical system. Next, in step ST52, the rotary stages 111 and 112 are θ-controlled according to the command value. Next, the monitor module 107 measures the spectrum so that the maximum transmission wavelength becomes λ, and enters a fine adjustment routine. In step ST53, in order to perform spectrum measurement, the injection light (seed light) of the oscillation stage laser 50 is blocked. As a blocking method, a shutter may be provided on the optical path and closed. Thereafter, laser oscillation is performed by the amplification stage laser 60 alone. The spectrum waveform of the output light at this time is measured by the monitor module 107 on the emission side of the optical path of the amplification stage laser 60 in step ST54. The measured center wavelength is λ1. Next, in step ST55, the difference dλ = λ1−λ from the target wavelength λ is calculated. Next, in step ST56, it is determined whether dλ is within an allowable value. As the allowable value, an optimum value is determined in advance. If it is within the allowable value, the injection light of the oscillation stage laser 50 is introduced in step ST57, and the subroutine ends. If dλ is over the allowable value in step ST56, fine adjustment is performed. Therefore, in step ST58, the rotary stages 111 and 112 are rotated by k · dθ. An optimal value is set in advance as the value of the coefficient k. When the value of k is negative, it rotates in the reverse direction. Next, in step ST59, the spectrum is measured again. The center wavelength at this time is λ2. In step ST60, the difference dλ ′ = λ2−λ from the target wavelength λ is calculated. dλ ′ is the difference from the target after fine adjustment, and dλ is the difference from the target before fine adjustment. Next, in step ST61, it is determined whether dλ ′ <dλ. In the case of dλ ′> dλ, the control indicates that the difference from the target is opened by the control, so the control direction is reverse. Therefore, in step ST62, the adjustment direction is reversed (k = k × (−1)), the value of dλ is set to dλ ′, and the routine returns to step ST58 to rotate the rotary stages 111 and 112 again by k · dθ. Do. In step ST61, if dλ ′ <dλ, it indicates that the control has approached the target. In step ST63, it is determined whether dλ ′ is within an allowable value. Here, if it is within the allowable value, the injection light of the oscillation stage laser 50 is introduced in step ST57, and the subroutine ends. If it is not within the allowable value in step ST63, it means that the adjustment is insufficient. In step ST64, the value of dλ is set to dλ ′, and the process returns to step ST58 to rotate the rotary stages 111 and 112 again by k · dθ. The routine to be executed is performed.

  FIG. 37 shows a subroutine for controlling the tilt angle of the mirror constituting the resonator by measuring the spectrum. First, in step ST71, the main controller 105 calculates a tilt amount x corresponding to the wavelength λ. The value of x is determined by the vertical direction of the mirror (in this case, the output side mirror 2) and the progress of the laser light to the mirror from the wavelength dependence equation and the Snell equation of the material of the optical elements 62 and 63. An angle difference α in the direction is calculated, and a tilt amount x corresponding to the angle α is calculated. Then, the output side mirror tilt adjustment mechanism 110 is commanded to the value of the tilt amount x. Next, in step ST72, the tilt amount of the output side mirror 2 is controlled in accordance with this command value. Next, the monitor module 107 measures the spectrum so that the maximum transmission wavelength becomes λ, and enters a fine adjustment routine. In step ST73, the injection light (seed light) of the oscillation stage laser 50 is blocked in order to perform spectrum measurement. As a blocking method, a shutter may be provided on the optical path and closed. Thereafter, laser oscillation is performed by the amplification stage laser 60 alone. The spectrum waveform of the output light at this time is measured by the monitor module 107 on the emission side of the optical path of the amplification stage laser 60 in step ST74. The measured center wavelength is λ1. Next, in step ST75, a difference dλ = λ1−λ from the target wavelength λ is calculated. Next, in step ST76, it is determined whether dλ is within an allowable value. As the allowable value, an optimum value is determined in advance. If it is within the allowable value, the injection light of the oscillation stage laser 50 is introduced in step ST77, and the subroutine ends. If dλ is over the allowable value in step ST76, fine adjustment is performed. Therefore, in step ST78, the tilt control mechanism 110 is rotated by a small amount k · dx. The coefficient k is set to an optimum value in advance. When the value of k is negative, it rotates in the reverse direction. Next, in step ST79, the spectrum is measured again. The center wavelength at this time is λ2. In step ST80, a difference dλ ′ = λ2−λ from the target wavelength λ is calculated. dλ ′ is the difference from the target after fine adjustment, and dλ is the difference from the target before fine adjustment. Next, in step ST81, it is determined whether dλ ′ <dλ. In the case of dλ ′> dλ, the control indicates that the difference from the target is opened by the control, so the control direction is reverse. Therefore, in step ST82, the adjustment direction is reversed (k = k × (−1)), the value of dλ is set to dλ ′, and the routine returns to step ST78 to rotate the adjustment mechanism 110 by k · dx. . If dλ ′ <dλ in step ST81, it indicates that the target has been approached by the control. In step ST83, it is determined whether dλ ′ is within an allowable value. Here, if it is within the allowable value, the injection light of the oscillation stage laser 50 is introduced in step ST77, and the subroutine ends. If it is not within the allowable value in step ST83, it means that the adjustment is not sufficient. Therefore, in step ST84, the value of dλ is set to dλ ′, and the process returns to step ST78 to rotate the tilt control mechanism 110 by k · dx again. Do the routine.

  Although the case where the tilt angle of the output side mirror 2 is controlled has been described above, the same effect can be obtained by controlling the tilt angle of the rear side mirror 1.

The high power gas laser apparatus of the present invention has been described by taking the amplification stage laser of the two-stage laser apparatus for exposure as an example. However, the amplification stage laser of other multi-stage gas laser apparatuses or an oscillation stage laser without using the amplification stage laser. By applying the principle of the present invention to a gas laser device consisting of only a laser beam, a beam expanding optical system for increasing the diameter or width of the mirror side beam is interposed between at least one mirror constituting the resonator and the laser gas chamber. By doing so, the laser energy density incident on the optical element constituting the resonator mirror is reduced to prevent surface damage of the optical element, thereby improving the durability and extending the life. Can be realized. Further, it is possible to reduce the laser energy density incident on the optical element constituting the resonator mirror so that the optical element is not distorted. At this time, even if the center wavelength of the laser changes, the laser output can be prevented from decreasing.

  As mentioned above, although the high output gas laser apparatus of this invention has been demonstrated based on the principle and description of an Example, this invention is not limited to these Examples, A various deformation | transformation is possible.

P1, P2 ... Pressure sensors T1, T2 ... Temperature sensor Pr ... Triangular prism Mi ... Mirror We ... Wedge substrate 1 ... Input side mirror (rear side mirror)
2 ... Output side mirror (front side mirror)
3 ... Laser chamber 4, 5 ... Discharge electrode 4, 54 ... Anode electrode 5, 55 ... Cathode electrode 8 ... High reflectivity (total reflection) mirror coating 9 ... Antireflection coating 10 ... Partial reflection mirror coating 16, 56 ... Power supply 17 57 ... Window member 18 ... Gas supply / exhaust control valve 19, 59 ... Cooling water flow rate control valve 22 ... Discharge area (laser gain area)
23 ... seed light 31 ... charger 32 ... switch 33 ... MPC (magnetic pulse compression circuit)
34, 44 ... heat exchangers 35, 45 ... monitor modules 36, 46 ... discharge detector 41 ... charger 42 ... switch 43 ... MPC (magnetic pulse compression circuit)
DESCRIPTION OF SYMBOLS 50 ... Oscillation stage laser 51 ... Narrow-band module 52 ... Front mirror 53 ... Laser chamber 54, 55 ... Discharge electrode 58 ... Gas supply / exhaust control valve 60 ... Amplification stage laser 61, 61 '... Beam expansion optical system (beam expander) Prism system)
62, 63, 63 '... Triangular prism 70 ... Conversion optical system 80 ... Main controller 81 ... Utility controller 82 ... Wavelength controller 83 ... Driver 84 ... Energy controller 85 ... Synchronous controller 86 ... Beam steering unit 87 ... Drivers 91, 91' ... Beam expansion optical system (wedge substrate type beam expansion optical system)
92, 93 ... wedge substrate 94 ... chamber window / wedge substrate 100 ... exposure apparatus 101 ... partial reflection mirror coating 105 ... main controller 106 ... rotary stage controller 107 ... monitor module 108 ... energy sensor or spectrometer 109 ... output side mirror controller 110: tilt control mechanism 111, 112 ... rotary stage

Claims (16)

In a gas laser apparatus comprising: a resonator comprising a rear side mirror and an output side mirror; a laser chamber disposed in the resonator and filled with a laser gas; and an excitation means for exciting the laser gas in the laser chamber.
A beam expansion optical system that increases the diameter or width of the laser beam on the mirror side is interposed between at least one of the laser chamber and the rear side mirror and between the laser chamber and the output side mirror. A high-power gas laser device.   2. The high-power gas laser device according to claim 1, wherein the laser oscillator constitutes a laser oscillator.   2. The high-power gas laser device according to claim 1, wherein a laser amplifier is configured.   4. The high-power gas laser device according to claim 3, wherein the high-power gas laser device is used in an amplification stage laser of a two-stage laser device.   5. The high-power gas laser device according to claim 1, wherein the beam expanding optical system is a beam expander prism system including one or a plurality of triangular prisms.   By applying a high-reflectance mirror coating or a partial reflection mirror coating to the outermost plane of the triangular prism constituting the beam expander prism system on the side opposite to the laser chamber, the rear side mirror or the output side mirror is 6. The high-power gas laser device according to claim 5, wherein the high-power gas laser device is formed integrally with a beam expander prism system. A resonator composed of a rear side mirror and an output side mirror, a laser chamber disposed in the resonator and filled with a laser gas, and electrodes disposed to face each other to excite the laser gas in the laser chamber In the gas laser device provided,
Even if the center wavelength of the laser changes between the output-side electrode end and the output-side mirror and between the rear-side electrode end and the rear-side mirror, the amount of change in laser output energy can be ignored. A high-power gas laser apparatus characterized in that it can be made as small as possible, and a beam expanding optical system for expanding the diameter or width of the laser beam on the mirror surface is interposed.   8. The high-power gas laser device according to claim 7, wherein the high-power gas laser device is used in an amplification stage laser of a two-stage laser device.   The beam expanding optical system is disposed between both the output side electrode end and the output side mirror and between the rear side electrode end and the rear side mirror, and the configuration of each beam expanding optical system is the same. 9. The high output according to claim 7 or 8, wherein the electrodes are arranged so that left and right and up and down are symmetrical within a cross section including a center line in the optical axis direction of the electrodes arranged opposite to each other. Gas laser device.   10. The high-power gas laser device according to claim 7, wherein the beam expanding optical system is a wedge substrate type beam expanding optical system including one or a plurality of wedge substrates. 11.   The high-power gas laser device according to any one of claims 7 to 9, wherein the beam expanding optical system includes a beam expander prism system including one or a plurality of triangular prisms.   11. The high-power gas laser device according to claim 10, wherein at least one of the wedge substrates constituting the beam expanding optical system is arranged as a window member of the laser chamber.   All of the wedge substrates constituting the beam expanding optical system are arranged inside the laser chamber, and the wedge substrate on the output side mirror side or the rear side mirror side is arranged as a window member of the laser chamber. 13. The high-power gas laser device according to claim 10 or 12,   The light path of the light that is reflected by the output side mirror or the rear side mirror and returns to the wedge substrate or the triangular prism is incident on the wedge substrate or the triangular prism constituting the beam expanding optical system. 12. The high-power gas laser device according to claim 10, wherein the high-power gas laser device is configured to be controllable so as to overlap with a laser optical axis of light before entering.   The optical path of the light incident on the beam expanding optical system and reflected and returned by the output side mirror or the rear side mirror overlaps the laser optical axis of the light before entering the beam expanding optical system. 12. The high-power gas laser device according to claim 10, wherein a tilt angle of the output-side mirror or the rear-side mirror is controllable.   The high-power gas laser device according to any one of claims 1 to 15, wherein the high-power gas laser device oscillates or amplifies ultraviolet rays.

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