JP2009026932A - Narrow band laser equipment for exposur - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide narrow band laser equipment for exposure that can make most of seed light from a narrow band oscillating stage laser into the implantation light of an amplifying stage laser. <P>SOLUTION: Injection synchronous type discharging excitation laser equipment is composed of the narrow-band oscillating stage laser (MO) 10 and the amplifying stage laser (PO) 20 at which a resonator is arranged, wherein a unidirectional beam diffusion device 5 is prepared between the narrow-band oscillating stage laser (MO) 10 and the amplifying stage laser (PO) 20. The unidirectional beam diffusion device 5 linearly condenses seed light, or forms a light condensing point of a virtual image at a position short of the OC of the amplifying stage laser (PO) to inject an MO laser beam diffused in one direction from the light condensing point into a resonator of the amplifying stage laser (PO) as the seed light. This enables most of the seed light from the narrow-band oscillating stage laser (MO) 10 used as implantation light into the amplifying stage laser (PO), thus enhancing the injection efficiency of the seed light. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an injection-locked discharge-pumped laser apparatus for an exposure apparatus composed of a narrow-band oscillation stage laser and an amplification stage laser. The present invention relates to a narrow band laser device for exposure with high injection efficiency.

In recent years, excimer lasers have been used as light sources for semiconductor exposure apparatuses. In particular, in a technology node of 60 nm or less, an ArF laser light source having a high output (40 W or more) and an ultra-narrow band (0.2 pm or less) is employed.
The requirements for an ArF laser light source as a light source for an exposure apparatus are shown below.
1. Along with ensuring high dose stability and increasing throughput, an output of 40 W or more is required.
2. In order to increase the resolution of the projection lens, the NA of the projection lens is being increased. As the NA increases, chromatic aberration occurs, and a very narrow band (0.2 pm or less) is required.
3. There is a demand for extending the life of laser light sources.
In order to satisfy the requirements of the light source, a double chamber type (two-stage type) ArF laser has been put into practical use. The form of the double chamber type laser device is roughly divided into a MOPA (Master Oscillator Power Amplifier) system in which no resonator mirror is provided on the amplifier side and a MOPO (Master Oscillator Power Oscillator) system in which a resonator mirror is provided.
However, in order to increase the output such as 90 W, the load on the optical elements (particularly the chamber window and OC) of the amplifier (PA) or the amplification stage laser (PO) becomes large, and the lifetime of these optical elements becomes a problem. Accordingly, there is a demand for extending the life of laser light sources.

Patent Document 1 discloses a MOPA laser device.
The one described in Patent Document 1 is equipped with an oscillation stage laser (MO) equipped with a narrowband module for narrowing the band, outputs a laser beam having a very narrow spectrum width, and this seed light is amplified by an amplifier (PA). By injecting into the discharge region of the chamber and amplifying the power, an ultra-narrow band and high output are realized.
Patent Document 2 proposes a MOPO laser device that injects seed light from an oscillation stage laser (MO) into a low coherence resonator of an amplification stage laser (PO).
By adopting the MOPO method with low spatial coherence, a higher amplification efficiency and a longer pulse width are realized while maintaining the beam quality equivalent to that of the MOPA compared to the MOPA method.
US Patent Application Publication No. 2002/0154668 International Publication No. 2004/095661 Pamphlet

FIG. 14 shows a configuration example of the above-described MOPO laser device.
In the figure, a laser beam emitted from an oscillation stage laser (MO) 10 functions as a seed laser beam, and an amplification stage laser (PO) 20 has a function of amplifying the seed laser beam. The oscillation stage laser (MO) 10 and the amplification stage laser (PO) 20 have laser chambers 11 and 21, respectively, and a pair of electrodes 1a and 2a facing each other and spaced apart by a predetermined distance are installed inside.
The chamber members 11 and 21 of the oscillation stage laser 10 and the amplification stage laser 20 are provided with window members 12a, 12b, 22a, and 22b made of a material that is transmissive to the laser oscillation light, respectively.
The oscillation stage laser (MO) 10 has a narrow band module (LNM) 3 composed of an enlarging prism 3a and a grating (diffraction grating) 3b in order to narrow the spectral line width. The optical element and the output coupling mirror (OC) 14 constitute a laser resonator.

The grating (diffraction grating) 3b arranged in the LNM 3 is arranged such that the dispersion direction (prism beam expansion direction) is perpendicular to the discharge direction of the electrode 1a.
The laser chamber 11 is filled with buffer gas, Ar gas, and F ₂ gas, and is discharged by applying a voltage between the electrodes 1a from a power source (not shown), and excited by this discharge to form an ArF excimer.
When the ArF excimer is separated into Ar gas and F, light having a wavelength of 193 nm is emitted. The wavelength of 193 nm light is selected by the LNM 3 to narrow the spectrum from about 400 pm to 0.2 pm and output from the OC 14 of the oscillation stage laser (MO) 10. For example, a predetermined spread angle [the spread angle in the discharge direction of the electrode 1a (V direction: paper surface direction in FIG. 12A)] from the OC 14 is about 2 mrad, and the spread angle in the direction perpendicular to the discharge direction (H direction) is About 1 mrad, the beam size is 12 mm in the V direction and 1 mm in the H direction.

Here, when this beam is reflected by the high reflection mirrors 4a and 4b and injected from the side position of the rear mirror 25 of the resonator of the amplification stage laser (PO) 20, it is as follows.
When the distance from the OC 14 of the oscillation stage laser (MO) 10 to the rear mirror 25 of the amplification stage laser (PO) 20 is 1 m, the beam at the injection position on the side of the rear mirror 25 has a beam divergence angle of the oscillation stage laser ( MO) is the same as when output from the OC 14, but the beam profile is 14 (= 12 + 2) mm in the V direction and 2 (= 1 + 1) mm in the H direction.
FIG. 14B shows a top view of the amplification stage laser (PO) 20.
As can be seen from this figure, a part of the beam of the oscillation stage laser (MO) 10 is reflected by the high reflection portion formed on the rear mirror 25 and is not injected into the resonator of the amplification stage laser (PO) 20. Furthermore, a part of the beam of the oscillation stage laser (MO) 10 away from the rear mirror 25 is out of the discharge region, is not amplified, and is not used as injection light.

On the other hand, the central part of the beam of the oscillation stage laser (MO) 10 passes through the side part of the rear mirror 25 and passes through the discharge part. In synchronization with this, a voltage is applied to the electrode 2a of the amplification stage laser (PO) 20 to discharge it, and the injected beam is amplified.
The amplified beam reaches the OC 24 of the amplification stage laser (PO) 20, and a part thereof is transmitted and output as output light. A part of the light is reflected and again passes through the discharge part and is amplified. Then, it reaches the high reflection portion of the rear mirror 25, is highly reflected, passes through the discharge portion again, and is amplified. Part of this beam passes through the OC 24 and is output as output light. The reflected light from the OC 24 is again transmitted through the discharge section and amplified, and this resonance is repeated.

As described above, in the case of side injection that is injected into the side of the rear mirror 25, the width of the effective injection beam in the H direction is smaller than about 1 mm, and when a beam with a beam width of 2 mm is injected, about half of the oscillation occurs. The beam of the stage laser (MO) 10 was not used as seed light.
Here, the problem of the side injection method is shown. However, the present invention is not limited to this. For example, the distance between the oscillation stage laser (MO) 10 and the amplification stage laser (PO) 20 is 2 m, and the oscillation stage laser (MO) ) Assuming that the beam size at 10 OC14 is 12 mm in the V direction, 1 mm in the H direction, the beam divergence angle is 2 mrad in the V direction, and 1 mrad in the H direction, the MO beam at the position of the rear mirror 25 of the amplification stage laser (PO) 20 The size is 16 in the V direction (= 12 + 2 × 2) mm and 3 in the H direction (= 1 + 2 × 1) 3 mm.
When the rear mirror 25 of the optical resonator of the amplification stage laser (PO) 20 is a partial reflection mirror and injection is performed from the rear surface of the rear mirror, if the effective injection area is 12 mm in the V direction and 2 mm in the H direction, the injection efficiency is 50% (= [12 × 2 / (16 × 3)] × 100).
The present invention has been made to solve the above-described problems, and an object of the present invention is to make most of the seed light from the narrow-band oscillation stage laser as the injection light of the amplification stage laser. It is another object of the present invention to provide a narrow band laser device for exposure in which seed light is not reflected by a high reflection portion formed on a rear mirror of an amplification stage laser (PO).

In order to solve the above problems, in the present invention, the MO laser light emitted from the oscillation stage laser (MO) is condensed linearly at a position before the OC (output coupling mirror) of the amplification stage laser (PO). (Or, a virtual image condensing point is formed at a position in front of the OC), and the MO laser beam diverging in one direction from the condensing point condensing linearly or the condensing point of the virtual image is used as a seed light for amplification. Injection into a resonator of a stage laser (PO).
That is, in the present invention, the above-mentioned problem is solved as follows.
(1) In an injection-locked laser device comprising a narrow-band oscillation stage laser (MO) and an amplification stage laser (PO) provided with a resonator, an amplification stage laser emits MO laser light emitted from the oscillation stage laser (MO). (PO) Optical means for condensing linearly at a position before the OC (or forming a virtual image condensing point at a position before the OC) and a condensing point or virtual image condensed linearly There is provided injection means for injecting the MO laser light diverging in one direction from the condensing point as seed light into the resonator of the amplification stage laser (PO).
(2) As an optical means of (1), an optical means provided with a cylindrical concave lens or a cylindrical convex high reflection mirror is used. (3) As an optical means of (1), a cylindrical convex lens or a cylindrical concave high reflection mirror is provided. Once the light is condensed into a line shape, optical means for diverging in one direction is used.
(4) As the optical means of (1), an optical element combined with a cylindrical concave / convex lens or a cylindrical concave / convex surface high reflection mirror is used, and once condensed in a line shape, the light is diffused in one direction.
(5) In (1) above, the direction in which the MO laser beam is diverged in one direction is set to be substantially perpendicular to the discharge direction of the amplification stage laser (PO) and the oscillation stage laser (MO).

In the present invention, the MO laser light is linearly condensed at a position before the OC (output coupling mirror) of the amplification stage laser (PO), or a condensing point of a virtual image is formed at a position before the OC, Since the MO laser beam diverging in one direction from the condensing point or the virtual image condensing point is injected into the resonator of the amplification stage laser (PO) as a seed light, the following An effect can be obtained.
(1) A part of the MO beam is not reflected by the high-reflection mirror of the rear mirror, and most of the injected MO beam can be used as injection light, and can be amplified in the discharge region. Further, since the injection is from the OC side, when the OC reflectance is 20% to 30%, the injection efficiency is 80% to 70%, and the injection efficiency is high.
(2) Since a mirror of a normal PO resonator can be adopted, the alignment of the resonator is easy and the manufacturing cost can be reduced.
(3) Since a beam that spreads in one direction is injected as seed light, the entire discharge region can be filled with seed light, so that generation of ASE (Amplified Spontaneous Emission) can be suppressed. Further, since the amplified light beam spreads every time it resonates with the amplification stage laser (PO), the load per unit area on the optical elements of the laser window and the PO resonator can be reduced. For this reason, the lifetime of the optical elements of the window and the PO resonator is extended.

FIG. 1 shows the configuration of a MOPO-type narrow-band laser device for exposure according to a first embodiment of the present invention. FIG. 1 (a) is a side view and FIG. 1 (b) is a top view of an amplification stage laser (PO). It is. The present embodiment shows a case where an amplification stage laser (PO) using a Fabry-Perot resonator is provided, the MO laser light is condensed into a linear shape, and then diverged and injected into the amplification stage laser (PO).
As shown in FIG. 1A, an oscillation stage laser (MO) 10 includes a narrow-band module (hereinafter referred to as LNM) equipped with a prism beam expander 3a and a diffraction grating 3b in order to narrow the spectral line width. 3), a laser chamber 11 equipped with an MO power source (not shown), and an output coupling mirror (OC: Output Coupler, hereinafter referred to as OC) 14.
The dispersion direction of the grating 3b arranged in the LNM 3 (the beam expanding direction of the prism 3a) is arranged in a direction perpendicular to the discharge direction of the electrode 1a. The laser chamber 11 is filled with buffer gas, Ar gas, and F ₂ gas, and is discharged by applying a voltage between the electrodes 1a from an MO power source (not shown), and excited by this discharge to form an ArF excimer. .
It emits light with a wavelength of 193 nm when the ArF excimer is separated into Ar gas and F. The wavelength of 193 nm light is selected by the LNM 3 to narrow the spectrum from about 400 pm to 0.2 pm and output from the OC 14 of the oscillation stage laser (MO) 10.

A beam output from the oscillation stage laser (MO) 10 passes through a unidirectional beam divergence device 5 including a cylindrical concave lens 5b and a cylindrical convex lens 5a. With this device, the beam converges in one direction (perpendicular to the discharge).
As shown in FIGS. 1A and 1B, this beam is highly reflected in the order of the high-reflection mirrors 4a, 4b, and 4c, and reaches the high-reflection mirror 7 having a knife edge. Condensed linearly. The high reflection mirror 7 is a mirror (hereinafter referred to as a knife edge mirror 7) having one side formed in a knife edge shape so that the output laser beam is not scattered. In FIG. Is formed in the shape of a knife edge, and is condensed in a line shape in the vicinity of this side.
The seed light reflected by the knife edge mirror 7 spreads in one direction at a predetermined divergence angle and reaches the OC 24 of the amplification stage laser (PO) 20. The seed light transmitted through the OC 24 of the amplification stage laser (PO) 20 passes through the discharge space of the PO chamber 21 through the window 22b, reaches the rear mirror 25 through the window 22a, and is highly reflected.

  Then, in synchronization with passing through the discharge space again through the window 22a, discharge is started between the electrodes 2a of the PO chamber 21 by the high-voltage power source, and the seed light diverging in one direction is amplified. . Then, part of the light is reflected by the OC 24 through the window 22b, and is again transmitted through the discharge portion and amplified. Then, the light reaches the rear mirror 25, is highly reflected, passes through the discharge portion again, and is amplified. Then, the light passes through the OC 24 and is output as output light, and the reflected light transmits and amplifies the discharge again to repeat this resonance.

As described above, in this embodiment, the MO laser beam is arranged in a line near the end of the knife edge mirror 7 by the one-way beam divergence device 5 by arranging the knife edge mirror 7 at a position before the OC 24. Then, the MO laser light diverging in one direction from the condensing point that is linearly condensed is injected as seed light into the resonator of the amplification stage laser (PO) 20 from the OC 24, and the following advantages are obtained.
(1) As shown in FIG. 14, a part of the MO laser beam is not reflected by the high reflection mirror of the rear mirror. For this reason, most of the injected MO beam is used as injection light and is amplified in the discharge region.
(2) Since the injection is from the OC 24, when the OC reflectance is 20% to 30%, the injection efficiency is 80% to 70%, and the injection efficiency is high.
(3) Since a mirror of a normal PO resonator can be adopted, the alignment of the resonator is easy and the manufacturing cost can be reduced.
That is, there is no need to designate an area of HR (high reflection) coat and an area of PR (partial reflection) coat on the front mirror (OC), or designate an AR (antireflection) coat area and HR coat area as the rear mirror. The front mirror can be a normal mirror with a PR coat on the entire surface, and the rear mirror can be an HR coat on the entire surface.

(4) Since a beam that spreads in one direction is injected as seed light, the entire discharge region can be filled with seed light, so that generation of ASE (Amplified Spontaneous Emission) can be suppressed. That is, since the discharge region is filled with seed light, light other than seed light is not amplified and undesired output is not generated.
(5) Since a beam that spreads in one direction is injected as seed light, the beam of light amplified every time it resonates with the amplification stage laser (PO) 20 spreads in the discharge direction. For this reason, since the load per unit area with respect to the optical element of a laser window and PO resonator can be reduced, the lifetime of the optical element of a window and PO resonator becomes long.

FIG. 2 is an enlarged view of the optical path when seed light having a divergence angle is injected into the amplification stage laser (PO) as in this embodiment, and is a top view of the amplification stage laser (PO). is there.
The seed light output from the oscillation stage laser (MO) 10 is condensed into a line shape on the surface of the knife edge mirror 7 by the high reflection mirror 4b and the high reflection mirror 4c.
The condensed light is reflected by the knife edge mirror 7, and the seed light is transmitted obliquely at a predetermined divergence angle and angle through the OC 24 and injected into the discharge region via the window 22b. Then, it passes through the discharge region, reaches the rear mirror 25 through the window 22a, is turned back, and is again passed through the discharge region of the laser chamber 21 through the window 22a, so that a pulsed voltage is applied to the electrode 2a. The discharge electrode is discharged and the seed light is amplified.
Then, the light passes through the window 22b and reaches the OC 24, a part of the light passes through the OC 24 and is amplified as laser light, and a part of the light is returned to the laser chamber 21 again as feedback light and discharged through the window 22b. By passing through the area, the signal is amplified and reaches the rear mirror 25 again through the window 22a. Then, it is folded, passed through the discharge region via the window 22a, and amplified again. This light reaches the OC 24 through the window 22b, and repeats the above-described processes to amplify and oscillate.

Here, as shown in FIG. 2, numerical values of various parameters are defined as follows.
LL: distance from the linear focusing point of the MO laser beam to the OC 24 of the amplification stage laser (PO) L: distance from the resonator length of the amplification stage laser (PO) RL: distance to the gain region (discharge region) of the rear mirror 25 GL: Effective gain length (discharge area length)
HL: Effective gain width (discharge area width)
Y: Distance from the central axis of the amplification stage laser (PO) to the linear focusing point

FIG. 3 shows an optical path diagram when the optical path of the amplification stage laser (PO) 20 of the laser apparatus of FIG. 2 is developed in series.
Since an optical resonator is a system in which light reciprocates in the resonator, it can be expressed in the same way as arranging a resonator mirror and a laser chamber in series.
When discharge is performed in synchronization with the central axis of the amplification stage laser (PO) 20 and the second passage through the discharge area of the amplification stage laser (PO) 20, the discharge region for suppressing the generation of ASE is formed with seed light. When the conditions for satisfying all are calculated, it is as follows.
Here, the divergence angle θ of the beam from the linear condensing point of the seed light is set, and the central optical axis of the amplification stage laser (PO) 20 (the axis parallel to the longitudinal axis of the electrode 2a and passing through the center of the discharge region). The angle between the optical path passing through the second discharge region of the amplification stage laser (PO) and the optical path with the smallest angle is α, and the central optical axis of the amplification stage laser (PO) 20 and seed light injection The angle formed by the optical axis (the seed optical center optical axis) is β, and the angle of the optical path that passes through the central optical axis of the amplification stage laser (PO) 20 and the second discharge region of the amplification stage laser (PO). Let γ be the angle formed with the maximum optical path.

θ = γ−α (1)
Here, if α and γ are small, the following equations (2) and (3) hold.
α = (Y−HL / 2) / (LL + L + RL + GL) (2)
γ = (Y + HL / 2) / (LL + L + RL) (3)
From the above formulas (1), (2) and (3),
The beam divergence angle θ of the seed light is expressed by the following equation (4).
θ = γ−α = (Y + HL / 2) / (LL + L + RL) − (Y−HL / 2) / (LL + L + RL + GL) (4)
An angle β formed by the central optical axis of the amplification stage laser (PO) 20 and the seed light injection optical axis (seed light central optical axis) is expressed by the following equation (5).
β = (Y−HL / 2) / (LL + L + RL + GL / 2) (5)

If seed light is injected so as to satisfy such a condition, that is, the divergence angle θ is larger than the above angle and β is substantially the above angle, the generation of ASE is suppressed, the injection efficiency is high, and the amplification is performed. Can oscillate.
Here, the position of the linear condensing point is the position where light is actually condensed by the one-way beam diverging device. However, if the beam is diverging immediately after exiting the beam diverging device, the virtual position of the beam diverging device is assumed. What is necessary is just to calculate from the position of a typical condensing point.
For example, in the case of functioning as a concave lens, the position of the focal point of the concave lens may be calculated as the position of the condensing point virtually.

FIG. 4 shows the configuration of a MOPO-type narrow-band laser device for exposure according to the second embodiment of the present invention. FIG. 4 (a) is a side view and FIG. It is. The present embodiment shows a case where an amplification stage laser (PO) using a Fabry-Perot resonator is provided and the MO laser light is diverged without being linearly condensed and injected into the amplification stage laser (PO). When the beam is diverged immediately after it exits the beam diverging device, there is a virtual condensing point of the beam diverging device, and this condensing point is referred to as a virtual image condensing point here.
The configuration and function of the oscillation stage laser (MO) 10 are the same as those shown in FIG. 1. The oscillation stage laser (MO) 10 has a prism beam expander 3a and a diffraction grating (grading) in order to narrow the spectral line width. ) 3L mounted LNM3, laser chamber 11 and OC14. As described above, the dispersion direction of the grating 3b arranged in the LNM 3 (the beam expansion direction of the prism) is arranged in a direction perpendicular to the discharge direction of the electrodes. And as mentioned above, it discharges by applying a voltage between electrodes 1a, is excited by this discharge, an ArF excimer is formed, and light with a wavelength of 193 nm is emitted. The wavelength of the 193 nm light is selected by the LNM 3 to be narrowed and output from the OC 14 of the oscillation stage laser (MO) 10.

The beam output from the oscillation stage laser (MO) 10 passes through a unidirectional beam divergence device 5 ′ composed of a cylindrical concave lens 5b and a cylindrical convex lens 5a. This device diverges the beam in one direction (perpendicular to the discharge). Here, in the present embodiment, the beam is diverged immediately after exiting from the one-way beam diverging device 5 ′, and the beam is not condensed. However, there is a virtual image condensing point, which is a virtual condensing point, and this position is as shown in FIG. 4 (a), between the one-way beam divergence device 5 and the OC 14 of the oscillation stage laser (MO) 10. It is in.
The divergent beam is highly reflected in the order of the high reflection mirrors 4a, 4b, and 4c, and reaches the high reflection mirror 7 on which the knife edge is formed.
The seed light reflected by the knife edge mirror 7 spreads in one direction at a predetermined divergence angle and reaches the OC 24 of the amplification stage laser (PO) 20. As described above, the OC 24 passes through the discharge space in the chamber 21, and a discharge is generated and amplified between the electrodes 2 a in synchronization therewith. Further, it reaches the rear mirror 25 and is highly reflected, and a discharge is generated and amplified in synchronization with passing through the discharge space again.
Then, the light reaches the OC 24, part of the light is reflected, is again transmitted through the discharge space, is amplified, and the light transmitted through the OC 24 is output as output light. Similarly, light transmitted through the OC is output as output light, and the reflected light transmits and amplifies the discharge again to repeat this resonance.

As described above, in the present embodiment, the MO laser light is disposed on the front side of the OC 24 with the knife edge mirror 7, and the MO laser light diverged by the one-way beam diverging device 5 ′ is applied to the knife edge mirror 7. The MO laser beam reflected near the end and diverging in one direction is injected from the OC 24 into the resonator of the amplification stage laser (PO) 20 as seed light, which is shown in the first embodiment (1). Advantages similar to those of (5) can be obtained.
The injection efficiency is somewhat worse than that in the first embodiment. That is, it is necessary to use a wide area of the knife edge mirror for injection, and it is difficult to inject all seed light into the PO resonator without kicking the output laser beam.

FIG. 5 shows the configuration of a MOPO-type narrow-band laser device for exposure according to a third embodiment of the present invention. FIG. 5 (a) is a side view and FIG. 5 (b) is a top view of an amplification stage laser (PO). It is. In this embodiment, there is an amplification stage laser (PO) by a ring resonator using a high reflection mirror, and the MO laser beam is condensed and then diverges and injected into the amplification stage laser (PO). Show.
The configuration and function of the oscillation stage laser (MO) 10 are the same as those shown in FIG. 1. The oscillation stage laser (MO) 10 has a prism beam expander 3a and a diffraction grating (grading) in order to narrow the spectral line width. ) 3L mounted LNM3, laser chamber 11 and OC14. As described above, the dispersion direction of the grating 3b arranged in the LNM 3 (the beam expansion direction of the prism) is arranged in a direction perpendicular to the discharge direction of the electrodes.
And as mentioned above, it discharges by applying a voltage between electrodes 1a, is excited by this discharge, an ArF excimer is formed, and light with a wavelength of 193 nm is emitted. The wavelength of the 193 nm light is selected by the LNM 3 to be narrowed and output from the OC 14 of the oscillation stage laser (MO) 10.

As shown in FIGS. 5A and 5B, the beam output from the oscillation stage laser (MO) 10 passes through the unidirectional beam divergence device 5.
With this device, the beam converges in one direction (perpendicular to the discharge). This convergent beam is reflected by the high reflection mirror 4a and is once condensed into a linear shape. After condensing, the seed light is reflected by the high reflection mirror 4b while diverging in one direction.
Then, the light is further reflected by the high reflection mirror 4 c and seed light is injected into the resonator from the OC 24 of the ring resonator of the amplification stage laser (PO) 20. The seed light transmitted through the OC 24 is reflected by the high reflection mirror 6a while the beam diverges in one direction, is incident on the discharge space of the laser chamber 21 in an inclined manner, and a voltage is applied to the discharge electrode 2a in synchronization with the seed light. Discharge.
The seed light transmitted through the discharge space is amplified, is transmitted through the chamber 21, is folded back by the two high reflection mirrors 6b and 6c, and is again guided to the discharged discharge space and is amplified. Part of the amplified light passes through the OC 24 and is output as a laser, and the reflected light of the OC 24 is fed back into the ring resonator and resonates.
And it outputs as a laser pulse from OC24. When the reflectance of the OC24 is 20% to 30%, the injection efficiency is 80% to 70%, and a high injection efficiency can be obtained.

As described above, in this embodiment, at least two high reflection mirrors are provided in one set of ring resonators, and laser light is returned to the laser chamber by two high reflection mirrors. The same function can be achieved even if the total reflection prism with a slightly smaller angle (several mrad) is returned by Fresnel reflection.
In this embodiment, the following merits are obtained.
(1) Since the injection is from the OC 24, the injection efficiency is high.
(2) Since a beam that spreads in one direction is injected as seed light, the entire discharge region can be filled with seed light, so that generation of ASE (Amplified Spontaneous Emission) can be suppressed. That is, since the discharge region is filled with seed light, light other than seed light is not amplified and undesired output is not generated.
(3) Since a beam that spreads in one direction is injected as seed light, the beam of light amplified every time it resonates with the amplification stage laser (PO) 20 spreads in the discharge direction. For this reason, since the load per unit area with respect to the optical element of a laser window and PO resonator can be reduced, the lifetime of the optical element of a window and PO resonator becomes long.
In this embodiment, the MO beam is condensed on the line between the high reflection mirrors 4a and 4b. However, the present invention is not limited to this. Thus, the unidirectional beam divergence device may diverge in one direction from the beginning.

FIG. 6 shows the configuration of a MOPO-type narrow-band laser device for exposure according to a fourth embodiment of the present invention. FIG. 6 (a) is a side view and FIG. 6 (b) is a top view of an amplification stage laser (PO). It is. The present embodiment has an amplification stage laser (PO) by a ring resonator using a total reflection right angle prism, condenses the MO laser light and then diverges and injects it into the amplification stage laser (PO). Indicates.
The configuration and function of the oscillation stage laser (MO) 10 are the same as those shown in FIG. 1. The oscillation stage laser (MO) 10 has a prism beam expander 3a and a diffraction grating (grading) in order to narrow the spectral line width. ) 3L mounted LNM3, laser chamber 11 and OC14. As described above, the dispersion direction of the grating 3b arranged in the LNM 3 (the beam expansion direction of the prism) is arranged in a direction perpendicular to the discharge direction of the electrodes.
And as mentioned above, it discharges by applying a voltage between electrodes 1a, is excited by this discharge, an ArF excimer is formed, and light with a wavelength of 193 nm is emitted. The wavelength of the 193 nm light is selected by the LNM 3 to be narrowed and output from the OC 14 of the oscillation stage laser (MO) 10.

As shown in FIGS. 6A and 6B, the beam output from the oscillation stage laser (MO) 10 passes through the unidirectional beam divergence device 5. This apparatus 5 converges the beam in one direction (perpendicular to the discharge).
This convergent beam is reflected by the high reflection mirror 4a and is once condensed into a linear shape. After condensing, the seed light is injected into the resonator from the OC 24 of the ring resonator of the amplification stage laser (PO) 20 while the beam diverges in one direction. The OC 24 is AR (antireflection) coated on the incident side and PR (partial reflection) coated on the resonator side.
The seed light transmitted through the OC 24 is reflected by the total high-reflection right-angle prism 8a while the beam diverges in one direction, passes through the window 22a of the laser chamber 21 through a region parallel to the discharge space, and passes through the window 22b. It is incident and reflected on the total reflection right-angle prism 8b.
Then, a voltage is applied between the electrodes 2a to be discharged in synchronism with the passage of seed light between the discharge electrodes of the laser chamber 21 through the window 22b.

The seed light transmitted through the discharge space is amplified and transmitted through the chamber 21, and a part of the light is reflected from the OC 24 and output as a laser. The transmitted light from the OC 24 is fed back into the ring resonator and resonates. And it outputs as a laser pulse from OC24.
When the reflectance of the OC24 is 70% to 80%, the injection efficiency is 80% to 70%, and a high injection efficiency can be obtained.
Also in this embodiment, the advantages (1) to (3) of the third embodiment can be obtained.
In this embodiment, the MO beam is condensed on the line between the high reflection mirrors 4a and 4b. However, the present invention is not limited to this. Thus, the unidirectional beam divergence device may diverge in one direction from the beginning.

Next, a configuration example of the one-way beam divergence device will be described.
FIG. 7 shows an example of the configuration of a unidirectional beam diverging apparatus for diverging a beam in one direction. FIG. 7A is a side view of the unidirectional beam diverging apparatus, and FIG. 7B is a top view.
In this embodiment, a configuration example in the case where the unidirectional beam divergence device is constituted by a cylindrical plano-convex lens and a cylindrical plano-concave lens is shown.
As shown in FIG. 7, the cylindrical plano-convex lens 5 a is fixed to the base 51. On the other hand, the cylindrical plano-concave lens 5b is fixed on a uniaxial stage movable in the optical axis direction. That is, a movable plate 52 is movably mounted on the linear guide 53, and the cylindrical plano-concave lens 5 b is installed and fixed on the movable plate 52. It is fixed by a fixing screw 56 of the moving plate 52 of the single axis stage. The position of the cylindrical plano-concave lens 5b in the optical axis direction can be fixed and adjusted to a desired position in the moving direction of the moving plate by a fixing screw 56 of the moving plate 52 of the uniaxial stage.
Further, a micrometer 54 is attached to a table to which the linear guide 53 is attached, and these movers are engaged with the protrusions 52 a of the moving plate 52.
The cylindrical plano-concave lens 5b can be moved in the direction of the arrow in FIG.

In the figure, the wavefront of the laser beam input from the convex surface of the cylindrical plano-convex lens 5a as a plane wave is refracted by this lens and converted into a cylindrical spherical wave. Then, the light enters from the plane of the cylindrical plano-concave lens 5b, and the light is refracted at the concave surface portion to be converted into cylindrical spherical waves having different curvature radii. Then, the laser beam is condensed into a linear shape, and again becomes a cylindrical spherical wave, and the beam diverges in one direction.
The advantages of the embodiment shown in FIG. 7 are as follows.
(1) The angle at which the beam is diverged can be adjusted by changing the distance between the cylindrical lenses.
(2) By changing the distance between the cylindrical lenses, the position of the linear condensing point of the beam can be adjusted.
(3) It is difficult to manufacture a long focal lens with a cylindrical lens. A long distance (1 m or more) can be easily configured as a composite focal length by combining cylindrical concave and convex lenses that are easy to manufacture as in this embodiment.

In FIG. 7, as an example of diverging the beam in one direction, a method of combining cylindrical concave / convex lenses is shown, but the following method may be used without being limited thereto.
(1) Cylindrical concave lens unit (2) Cylindrical convex lens unit (3) Cylindrical concave mirror unit (4) Cylindrical convex mirror unit It is possible to combine a plurality of the above lenses and mirrors.

Hereinafter, other examples of combinations of the optical elements of the one-way beam divergence device will be described.
FIG. 8 shows a configuration example using one cylindrical concave lens, cylindrical convex lens, cylindrical convex mirror, and cylindrical concave mirror.
FIG. 8A shows an example in which one cylindrical concave lens 5b is used. In this case, as shown in the figure, light diverges and a linear condensing point of a virtual image is formed on the light incident side of the lens 5b.
FIG. 8B shows an example in which one cylindrical concave mirror 5c is used. In this case, the light is condensed as shown in the figure, and a linear condensing point is formed on the light emitting side of the mirror 5c.
FIG. 8C shows an example in which one cylindrical convex lens 5a is used. In this case, the light is condensed as shown in the figure, and a linear condensing point is formed on the light emitting side of the lens 5a.
FIG. 8D shows an example in which one cylindrical convex mirror 5d is used. In this case, the light diverges as shown in the figure, and a virtual image linear condensing point is formed on the back side of the mirror 5d.

FIG. 9 shows an example in which cylindrical concave and convex lenses are combined. By combining the cylindrical concave lens 5b and the cylindrical convex lens 5a as shown in FIGS. 9 (a) and 9 (b), and setting the focal length, interval, etc. of both lenses 5a and 5b, the lens as shown in FIG. A linear condensing point can be formed on the light emitting side of 5a, or a virtual condensing point of a virtual image can be formed on the light incident side of the lens 5b as shown in FIG.
FIG. 10 shows an example in which a cylindrical lens and a cylindrical mirror are combined.
FIG. 10A shows an example in which a cylindrical concave lens 5b and a cylindrical concave mirror 5c are combined. As shown in FIG. 10, light is condensed and a linear condensing point is formed on the light exit side of the cylindrical concave mirror 5c. Is done.
FIG. 10B is an example in which a cylindrical convex lens 5a and a cylindrical convex mirror 5d are combined. As shown in FIG. 10, light diverges and a linear condensing point of a virtual image is formed on the back side of the cylindrical convex mirror 5d. Is done.
FIG. 11 shows an example in which two mirrors are combined.
FIG. 11A shows an example in which a cylindrical convex mirror 5d and a cylindrical concave mirror 5c are combined. As shown in FIG. 11, light is condensed and a linear condensing point is formed on the light emitting side of the cylindrical concave mirror 5c. It is formed.
FIG. 11B shows an example in which a cylindrical concave mirror 5c and a cylindrical convex mirror 5d are combined. As shown in FIG. 11B, light diverges, and a linear condensing point of a virtual image is formed on the back side of the cylindrical convex mirror 5d. It is formed.

FIG. 12 shows the configuration of a MOPO-type narrow band laser device for exposure according to a fifth embodiment of the present invention, FIG. 12 (a) is a side view, and FIG. 12 (b) is a top view of an amplification stage laser (PO). It is. This example shows a configuration when applied to a high-power, high-repetition ArF laser.
The laser apparatus of the present embodiment includes an oscillation stage laser (MO) 10 that outputs laser light having a narrow spectral line width, a beam expander 9 that expands the output MO laser light at least in the discharge gap direction, and one direction. A one-way beam diverging device 5 for condensing and diverging the beam, a high reflection (HR) mirror 4a for injecting an MO beam from the OC 24 side of the amplification stage laser (PO) 20, and a knife edge high reflection mirror 7; And an amplification stage laser (PO) 20 for amplifying the MO laser beam.
The oscillation stage laser (MO) 10 includes an LNM 3 on which a prism beam expander 3a and a diffraction grating (3b) 3b are mounted to narrow a spectral line width, a laser chamber 11 on which a 12 kHz power source 16 is mounted, and an OC 14. Is done.
As described above, the dispersion direction of the grating 3b arranged in the LNM 3 (the beam expansion direction of the prism) is arranged in a direction perpendicular to the discharge direction of the electrodes.

The laser chamber 11 is filled with buffer gas, Ar gas, and F ₂ gas. By narrowing the electrode width and the electrode gap, the discharge width is narrowed, and the gas flow rate between the electrodes is increased, resulting in 12 kHz. A stable discharge is formed by applying a voltage from the power source to the electrodes.
An ArF excimer is formed by being excited by the discharge, and emits light having a wavelength of 193 nm when the ArF excimer is separated into Ar gas and F.
The wavelength of 193 nm light is selected by the LNM 3 to narrow the spectrum from about 400 pm to 0.1 pm and output from the OC 14 of the oscillation stage laser (MO) 10.
The oscillation stage laser (MO) 10 oscillates at a repetition frequency of 12 kHz, and the time width of the laser emission pulse is about 30 ns.
The output light of the oscillation stage laser (MO) 10 is incident on the beam expander 9 so as to have a beam width equivalent to the electrode gap of the amplification stage laser (PO) 20 and is output after being expanded.
Then, the light is incident on the one-way beam divergence device 5 that diverges the beam in one direction, and is converted into a beam that converges in one direction (perpendicular to the discharge) when transmitted therethrough.

This beam passes through the high reflection mirror 4a and the knife edge high reflection mirror 7, and is condensed linearly. Then, the beam diverges in one direction. This laser beam is the OC 24 of the amplification stage laser (PO) 20 and the laser. It is injected into a stable resonator composed of the chamber 21 and the rear mirror 25.
In the laser chamber 21 of the amplification stage laser (PO) 20, two pairs of electrodes 2a-1 and 2a-2 are arranged in series, and a 6 kHz power source 26 is connected to each electrode pair.
When the injection light coming from the oscillation stage laser (MO) 10 is injected into the optical resonator at 12 kHz, the 6 kHz power source is alternately operated in synchronization with each other, and the respective electrode pairs 2a-1, 2a-2 are alternately operated. The light thus discharged is amplified and oscillated in the optical resonator, and the light amplified from the OC 24 is laser-emitted at 12 KHz and output.
The output light detects pulse energy by a power monitor (not shown), and the result is sent to an energy controller (not shown). Based on the detection result, the energy controller sends a control signal to each 6 kHz power source 26 of the amplification stage laser (PO) 20 and to the 12 kHz power source 16 of the oscillation stage laser (MO) 10 via a synchronous controller (not shown).

The advantages of this embodiment are as follows.
(1) Since the optical resonator of the amplification stage laser (PO) 20 is composed only of a simple OC (having the same reflectivity over the entire surface) and a rear mirror, it is a high repetition, high pulse energy, high output ArF laser beam. On the other hand, it has a long life,
(2) Since the beam of the oscillation stage laser (MO) 10 is condensed in one direction and then diverged and injected from the OC 24 side, the injection efficiency is high. When the OC reflectance is 20% to 30%, the injection efficiency is 70% to 80%.
(3) Since the beam is diverged and injected in the direction perpendicular to the discharge direction, the discharge region is filled with the injection beam, so that generation of ASE (free run component) is suppressed.
(4) Since the beam of the oscillation stage laser (MO) 10 is condensed in one direction, the beam is diverged and injected from the OC24 side of the amplification stage laser (PO) 20, so that the amplification stage laser (PO) Even when the two electrode pairs 2a-1 and 2a-2 of 20 are alternately discharged with respect to the seed light, the change in beam quality is small (amplification stage laser (PO) electrode pair 2a-1 and electrode pair, The difference in optical quality when 2a-2 is discharged is reduced).
(5) Since a beam that spreads in one direction is injected as seed light, the amplified light beam spreads in the discharge direction every time it resonates with the amplification stage laser (PO) 20, so that laser window and PO resonance Since the load per unit area on the optical element of the resonator can be reduced, the lifetime of the optical element of the window and the PO resonator is extended.

FIG. 13 shows an optical path diagram when the optical path of the amplification stage laser (PO) having the divided electrodes of FIG. 12 is developed in series.
The difference from the case of FIG. 3 is that the gain region GL is divided, and instead of the GL, the OC side electrode 2a-2 is changed from the rear end position of the rear side electrode 2a-1 in the gain region of the two divided electrodes. By setting the length to the OC side end position of GL ′ as GL ′, it is possible to calculate the seed light injection angle and the beam divergence angle for filling the discharge region for suppressing the generation of ASE with the seed light. it can.
Here, the divergence angle θ of the beam from the linear condensing point of the seed light is set as described above, and the central optical axis of the amplification stage laser (PO) 20 (the center of the discharge region is parallel to the longitudinal axis of the electrode 2a). ) And the optical axis passing through the second discharge region of the amplification stage laser (PO) and the angle formed by the optical path with the smallest angle is α, and the central optical axis of the amplification stage laser (PO) 20; Of the optical paths passing through the central optical axis of the amplification stage laser (PO) 20 and the second discharge region of the amplification stage laser (PO), the angle formed by the seed light injection optical axis (center optical axis) is β. An angle formed by the optical path having the maximum angle is represented by γ.

θ = γ−α (1)
Here, if α and γ are small, the following equations (2) and (3) hold.
α = (Y−HL / 2) / (LL + L + RL + GL ′) (2) ′
γ = (Y + HL / 2) / (LL + L + RL) (3)
From the above formulas (1), (2) and (3),
The beam divergence angle θ of the seed light is expressed by the following equation (4).
θ = γ−α = (Y + HL / 2) / (LL + L + RL) − (Y−HL / 2) / (LL + L + RL + GL ′) (4) ′
An angle β formed by the center optical axis of the amplification stage laser (PO) 20 and the seed light injection optical axis (center optical axis) is expressed by the following equation (5) ′.
β = (Y−HL / 2) / (LL + L + RL + GL ′ / 2) (5) ′

If seed light satisfying such conditions is injected, generation of ASE is suppressed, injection efficiency is high, and amplification oscillation is possible.
Here, the position of the linear condensing point is the position where light is actually condensed by the one-way beam diverging device. However, when the beam is diverging immediately after exiting the beam diverging device, the beam diverging as described above. What is necessary is just to calculate from the position of the virtual condensing point of an apparatus. For example, in the case of functioning as a concave lens, the position of the focal point of the concave lens may be calculated as the position of the condensing point virtually.

It is a figure which shows the structure of the narrow band laser apparatus for MOPO system exposure of 1st Example of this invention. It is the figure which expanded and showed the amplification stage laser (PO) optical path of the 1st Example. FIG. 3 is an optical path diagram when an optical path of an amplification stage laser (PO) of the laser apparatus of FIG. 2 is developed in series. It is a figure which shows the structure of the narrow-band laser apparatus for exposure of the MOPO system of 2nd Example of this invention. It is a figure which shows the structure of the narrow-band laser apparatus for exposure of the MOPO system of the 3rd Example of this invention. It is a figure which shows the structure of the narrow-band laser apparatus for exposure of the MOPO system of the 4th Example of this invention. It is a figure which shows the structural example of a one-way beam divergence apparatus. It is a figure which shows the example of a combination (1) of the optical element of a one-way beam divergence apparatus. It is a figure which shows the example (2) of a combination of the optical element of a one-way beam divergence apparatus. It is a figure which shows the example (3) of a combination of the optical element of a one-way beam divergence apparatus. It is a figure which shows the example of a combination (4) of the optical element of a one-way beam divergence apparatus. It is a figure which shows the structure of the narrow-band laser apparatus for exposure of the MOPO system of the 5th Example of this invention. FIG. 13 is an optical path diagram when the optical path of the amplification stage laser (PO) of the laser apparatus of FIG. 12 is developed in series. It is a figure which shows the structural example of the laser apparatus of a MOPO system.

Explanation of symbols

1a, 2a Discharge electrode 3 LMN
4a to 4c High reflection mirror 5,5 'One-way beam divergence device 5a Convex cylindrical lens 5b Concave cylindrical lens 6a to 6c High reflection mirror 7 Knife edge mirror 8a, 8b Total reflection right angle prism 9 Beam expander 10 Oscillation stage laser (MO )
11, 21 Chamber 12a, 12b Window member 22a, 22b Window member 13, 23 Slit 14 OC (Output coupling mirror)
20 Amplification stage laser (PO)
24 OC (output coupling mirror)
25 Rear mirror

Claims (5)

An injection-locked laser device comprising a narrow-band oscillation stage laser (MO) and an amplification stage laser (PO) provided with a resonator,
The MO laser beam radiated from the oscillation stage laser (MO) is condensed linearly at a position before the output coupling mirror (OC) of the amplification stage laser (PO), or the output of the output coupling mirror (OC) Optical means for forming a condensing point of a virtual image at a position in front,
Injecting means for injecting into the resonator of the amplification stage laser (PO) using the MO laser light diverging in one direction from the condensing point or the virtual image condensing point as a seed light. A narrow-band laser device for exposure. A narrow band laser device for exposure, wherein an optical means comprising a cylindrical concave lens or a cylindrical convex high reflection mirror is used as the optical means according to claim 1.   2. An exposure narrowband laser apparatus comprising: a cylindrical convex lens or a cylindrical concave high reflection mirror as optical means according to claim 1; and optical means for once diverging in a line and then diverging in one direction. The optical means according to claim 1, comprising an optical element having a combination of a cylindrical concave / convex lens or a cylindrical concave / convex surface high reflection mirror, and once condensing in a line shape, an optical means for diverging in one direction was used. A narrow-band laser device for exposure. The exposure direction according to claim 1, wherein the direction in which the MO laser beam is diverged in one direction is substantially perpendicular to the discharge direction of the amplification stage laser (PO) and the oscillation stage laser (MO). Narrow band laser device.

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