JP2011192849A - Laser device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve a low coherence and a high intensity of a laser beam. <P>SOLUTION: A laser device 1 converting a seed beam Lb output from a solid-state laser 10 into a laser beam L1 having a wavelength shorter than that of the seed beam Lb and then amplifying the laser beam L1 to be output includes a low coherence mechanism 20 which reduces the coherence of the seed beam Lb before converting the seed beam Lb into the short-wavelength laser beam L1. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a laser device, and more particularly to a laser device used for exposure in manufacturing a semiconductor device.

  Conventionally, a laser device that outputs laser light in the vacuum ultraviolet region, such as an ArF laser, has been used as a light source for exposure in semiconductor device manufacturing. In this exposure laser light source device, it is necessary to narrow the spectral line width to such an extent that the chromatic aberration of the projection lens can be ignored. Further, in order to suppress the occurrence of speckles during exposure, it is necessary to reduce the coherence of the laser light output from the laser device. Thus, for example, in Patent Document 1 shown below, the output laser light is reduced in coherence by arranging an optical delay element on the optical path. For example, in Patent Document 2 shown below, a laser beam is reduced in coherence by disposing a pulse width expansion device between an oscillator (master oscillator: MO) and an amplifier (preamplifier: PA).

JP 11-312631 A Japanese Unexamined Patent Publication No. Hei 4-2611083

  However, in a wavelength region with a relatively short wavelength, such as an ArF laser with a wavelength of 193 nm, it is difficult to realize a low coherence mechanism (such as OPS) with a transmittance of 70% or higher and a relatively high transmission efficiency. In particular, in order to satisfy the resolution required for the exposure apparatus when performing two-step exposure (double patterning), further reduction in coherence is required. However, in order to promote low coherence, it is necessary to increase the number of parts of the low coherence mechanism. However, when the number of parts increases, the transmission efficiency of the low coherence mechanism decreases. As a result, the light intensity of the laser beam input to the exposure apparatus is reduced, thereby causing a problem that the throughput of the exposure apparatus is reduced.

  Accordingly, the present invention has been made in view of the above-described problems, and an object thereof is to provide a laser apparatus that can realize low coherence and high intensity of laser light.

  In order to achieve this object, a laser device according to the present invention converts a laser beam output from a laser light source into a laser beam having a shorter wavelength than the laser beam, and then amplifies and outputs the laser beam. And a low-coherence unit for reducing the coherence of the laser light before converting the laser light into the short-wavelength laser light.

  According to the present invention, since the laser beam is reduced in coherence before the laser beam is converted into a short wavelength, the laser beam can be reduced in the long wavelength stage where the energy loss is relatively small. As a result, it is possible to realize a laser device that can output laser light with low coherence and high intensity.

FIG. 1 is a schematic diagram showing a schematic configuration of a laser apparatus according to Embodiment 1 of the present invention. FIG. 2 is a schematic diagram showing a schematic configuration of the master oscillator according to the first embodiment of the present invention. FIG. 3 is a schematic diagram showing a schematic configuration of the Ti: sapphire master oscillator according to the first embodiment of the present invention. FIG. 4 is a schematic diagram showing a schematic configuration of the Ti: sapphire power oscillator according to the first embodiment of the present invention. FIG. 5 is a schematic diagram showing a schematic configuration of the low coherence mechanism according to Embodiment 1 of the present invention. FIG. 6 is a schematic diagram showing a schematic configuration of the wavelength conversion mechanism according to the first embodiment of the present invention. FIG. 7 is a schematic diagram showing a schematic configuration of the wavelength conversion mechanism according to the first modification of the first embodiment of the present invention. FIG. 8 is a schematic diagram showing a schematic configuration of a low coherence mechanism according to the second modification of the first embodiment of the present invention. FIG. 9 is a schematic diagram showing a schematic configuration of a low coherence mechanism according to the third modification of the first embodiment of the present invention. FIG. 10 is a schematic diagram showing a schematic configuration when the low coherence mechanism shown in FIG. 9 is viewed from another angle. FIG. 11 is a schematic diagram showing a schematic configuration of a low coherence mechanism according to Modification 4 of Embodiment 1 of the present invention. FIG. 12 is a schematic diagram showing a schematic configuration when the low coherence mechanism shown in FIG. 11 is viewed from the optical axis. FIG. 13 is a schematic diagram showing a schematic configuration of a low coherence mechanism according to Modification 5 of Embodiment 1 of the present invention. FIG. 14 is a schematic diagram showing a schematic configuration of a Ti: sapphire power oscillator according to the sixth modification of the first embodiment of the present invention. FIG. 15 is a schematic diagram showing a schematic configuration of a Ti: sapphire power oscillator according to Modification 7 of Embodiment 1 of the present invention. FIG. 16 is a schematic diagram showing a schematic configuration of a Ti: sapphire power amplifier PA10 according to the eighth modification of the first embodiment of the present invention. FIG. 17 is a schematic diagram showing a schematic configuration of the master oscillator in the laser apparatus according to the ninth modification of the first embodiment of the present invention. FIG. 18 is a schematic diagram showing a schematic configuration of a laser apparatus according to Embodiment 2 of the present invention. FIG. 19 is a schematic diagram showing a schematic configuration when the optical system in the laser apparatus shown in FIG. 18 is viewed from another angle.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In the following description, each drawing only schematically shows the shape, size, and positional relationship to the extent that the contents of the present invention can be understood. Therefore, the present invention is illustrated in each drawing. It is not limited to only the shape, size, and positional relationship. Moreover, in each figure, a part of hatching in a cross section is abbreviate | omitted for clarification of a structure. Furthermore, the numerical values exemplified below are merely preferred examples of the present invention, and therefore the present invention is not limited to the illustrated numerical values.

(Embodiment 1)
First, a laser apparatus according to Embodiment 1 of the present invention will be described in detail with reference to the drawings. In the first embodiment, an ArF laser whose output laser light has a center wavelength of 193 nm is taken as an example of the laser device. However, the present invention is not limited to this, and various laser devices such as an excimer laser such as a KrF laser, a XeCl laser, or an XeF laser, or an EUV light source that is a light source of extreme ultraviolet light can be applied.

  For example, a laser beam having a relatively short wavelength such as a laser beam having a wavelength of about 193 nm has a larger energy loss due to an optical element such as a high reflection mirror or a partial reflection mirror than a laser beam having a relatively long wavelength. For this reason, when laser light having a short wavelength is repeatedly reflected using a high reflection mirror or a partial reflection mirror, energy loss due to scattering and absorption becomes very large. On the other hand, according to the first embodiment, the low coherence mechanism (low coherence unit) is provided before the wavelength conversion mechanism (wavelength conversion unit) that converts the wavelength to a short wavelength. For this reason, it is possible to reduce the coherence of the laser light at a long wavelength stage where the energy loss is relatively small. As a result, in the first embodiment, it is possible to realize a laser device 1 capable of outputting a laser beam with low coherence and high intensity while maintaining a spectral line width such that chromatic aberration can be ignored. It becomes. As a result, a laser apparatus that can improve the throughput of the exposure apparatus can be realized.

  FIG. 1 is a schematic diagram showing a schematic configuration of the laser apparatus according to the first embodiment. As shown in FIG. 1, the laser apparatus 1 includes a master oscillator MO1 that outputs a laser beam L1, and a power oscillator PO1 that amplifies the laser beam L1 output from the master oscillator MO1 and outputs the amplified laser beam L2. Prepare. The laser beam L1 output from the master oscillator MO1 is input to the power oscillator PO1 through an optical system including, for example, high reflection mirrors M1 and M2.

  The master oscillator MO1 includes, for example, a solid-state laser 10 made of a laser crystal such as a Ti: sapphire crystal, a low-coherence mechanism 20 that lowers the laser light Lc output from the solid-state laser 10, and a low-coherence laser light ( And a wavelength conversion mechanism 30 that converts Ld (hereinafter referred to as low coherence light) into short-wavelength laser light L1. That is, in the first embodiment, the laser light is reduced in coherence before being amplified and before being shortened by wavelength conversion. Thereby, the energy loss of the laser beam that occurs when the coherence is reduced can be reduced.

  On the other hand, the power oscillator PO1 includes a rear mirror 41 that functions as one resonator mirror of the resonator, a chamber 43 that includes an amplification region that amplifies laser light that reciprocates within the resonator, and one resonator mirror of the resonator. And an output coupler 46 that functions as an output end of the laser beam, and a slit 42 that maintains the directivity of the laser beam reciprocating in the resonator. The chamber 43 is provided with windows 44a and 44b for enhancing the hermeticity of the chamber 43 and for taking in laser light. The chamber 43 is provided with a pair of discharge electrodes 45a and 45b disposed so as to sandwich a region (amplification region) through which laser light passes, and is filled with argon fluoride (ArF) gas. . A high frequency voltage is applied to the discharge electrodes 45a and 45b from an RF power source (not shown). Thereby, an amplification region made of activated ArF gas is formed between the discharge electrodes 45a and 45b, and the laser light passing through the amplification region is amplified. The amplified laser light is output from the output coupler 46 as output laser light L2.

  Next, the master oscillator MO1 in FIG. 1 will be described in detail with reference to the drawings. FIG. 2 is a schematic diagram showing a schematic configuration of the master oscillator according to the first embodiment. As shown in FIG. 2, the solid state laser 10 of the master oscillator MO1 includes a Ti: sapphire master oscillator MO10, a Ti: sapphire power oscillator PO10, and a laser beam output from the Ti: sapphire master oscillator MO10. An optical system including high-reflection mirrors M11 and M12 guided to PO10, and a pumping laser PL that supplies laser light for amplification to Ti: sapphire master oscillator MO10 and Ti: sapphire power oscillator PO10. Laser light having a relatively long wavelength output from the solid-state laser 10 (for example, laser light in a wavelength band included in the vicinity of 386 to 774 nm) is reduced in coherence by the low coherence mechanism 20 and then relatively reduced in the wavelength conversion mechanism 30. It is converted into laser light having a short target wavelength (for example, a wavelength band of 193 nm), and then input to the power oscillator PO1 in FIG. 1 through an optical system including the high reflection mirrors M1 and M2. Details of Ti: sapphire master oscillator MO10 and Ti: sapphire power oscillator PO10, and details of low coherence mechanism 20 and wavelength conversion mechanism 30 will be described later.

  Next, the Ti: sapphire master oscillator MO10 in the solid-state laser 10 of FIG. 2 will be described in detail with reference to the drawings. FIG. 3 is a schematic diagram showing a schematic configuration of the Ti: sapphire master oscillator according to the first embodiment. As shown in FIG. 3, the Ti: sapphire master oscillator MO10 is a so-called Littman type laser. The Ti: sapphire master oscillator MO10 is diffracted by the high reflection mirror 11 and the output coupler 15 forming the resonator, the Ti: sapphire crystal 12 and the grating 13 disposed on the optical path in the resonator, and the grating 13. And a high reflection mirror 14 that reflects the laser beam back to the grating 13. The high reflection mirrors 11 and 14 form a resonator different from the high reflection mirror 11 and the output coupler 15. The output coupler 15 also functions as an optical output terminal that outputs the seed light Lb.

  In this configuration, the high reflection mirror 11 transmits light (hereinafter referred to as pump light) La1 from the pumping laser PL (see FIG. 2) and reflects the laser light from the Ti: sapphire crystal 12. Pump light La1 input through the high reflection mirror 11 is incident on the Ti: sapphire crystal 12. The light input / output end face of the Ti: sapphire crystal 12 is Brewster cut. Thereby, reflection of the laser beam at this end face is suppressed. The Ti: sapphire crystal 12 on which the pump light La1 is incident oscillates by a resonator composed of the high reflection mirror 11, the grating 13, the high reflection mirror 14, and the output coupler 15, thereby emitting pulsed laser light. The laser light emitted from the Ti: sapphire crystal 12 is diffracted by the grating 13. Here, the output coupler 15 is arranged, for example, in the emission direction of the 0th-order diffracted light with respect to the grating 13. Further, the high reflection mirror 14 is arranged with respect to the grating 13 in the emission direction of ± m-order diffracted light. Therefore, the wavelength of the seed light Lb output from the Ti: sapphire master oscillator MO10 can be selected by adjusting the angle of the high reflection mirror 14 with respect to the grating 13. As a result, the spectral line width of the laser light Lb output from the Ti: sapphire master oscillator MO10 can be set to a spectral line width such that chromatic aberration during exposure can be ignored.

  As described above, the seed light Lb output from the Ti: sapphire master oscillator MO10 is incident on the Ti: sapphire power oscillator PO10 via the optical system including the high reflection mirrors M11 and M12. Here, FIG. 4 shows a schematic configuration of the Ti: sapphire power oscillator according to the first embodiment. As shown in FIG. 4, the Ti: sapphire power oscillator PO10 is a so-called Fabry-Perot laser. The Ti: sapphire power oscillator PO10 is incident from a high reflection mirror 17 and an output coupler 19 forming a resonator, a Ti: sapphire crystal 18 disposed on an optical path in the resonator, and a Ti: sapphire master oscillator MO10. And a high reflection mirror 16 for guiding the pump light La2 from the seed light Lb and the pumping laser PL into the resonator.

  In this configuration, the high reflection mirror 16 reflects the seed light Lb from the Ti: sapphire master oscillator MO10 to the resonator side and transmits the pump light La2 from the pumping laser PL to the resonator side. The one high reflection mirror 17 forming the resonator transmits the seed light Lb and the pump light La2 via the high reflection mirror 16, and reflects the laser light from the Ti: sapphire crystal 18. The pump light La2 and the seed light Lb input through the high reflection mirror 17 are incident on the Ti: sapphire crystal 18. The light input / output end face of the Ti: sapphire crystal 18 is Brewster cut. Thereby, reflection of the laser beam at this end face is suppressed. The Ti: sapphire crystal 18 on which the pump light La2 and the seed light Lb are incident oscillates by a resonator composed of the high reflection mirror 17 and the output coupler 19, thereby emitting pumped-up pulsed laser light. The laser beam emitted from the Ti: sapphire crystal 18 is output as the laser beam Lc via the output coupler 19.

  The laser beam Lc output from the Ti: sapphire power oscillator PO10 is input to the low coherence mechanism 20 to reduce the coherence. FIG. 5 shows a schematic configuration of the low coherence mechanism according to the first embodiment. As shown in FIG. 5, the low coherence mechanism 20 includes a beam splitter 21a that reflects part of the laser light Lc and transmits part of the laser light Lc, and an optical image of the laser light Lc reflected by the beam splitter 21a again. And a plurality of concave high-reflection mirrors 21b to 21e that form an optical path for transfer image formation. Thus, by delaying a part of the incident laser beam Lc, the laser beam can be reduced in coherence. In the present description, the laser light that has been reduced in coherence by the low coherence mechanism 20 is referred to as low coherence light Ld.

Here, the wavelength of the seed light Lb output from the Ti: sapphire master oscillator MO10 is λ _{solid_mo} , the spectral line width is Δλ _{solid_mo,} and the high reflection mirror 17 and output coupler of the Ti: sapphire power oscillator PO10 in the solid-state laser 10 are used. When the optical path length of the resonator formed by L 19 is L _reso and the optical path length of the low coherence mechanism 20 is L _ops , the coherent length L _coh of the low coherence light Lc satisfies the relationship of the following formula 1.

  Further, as described above, the low coherence light Ld output from the low coherence mechanism 20 is input to the wavelength conversion mechanism 30 and converted into laser light of a desired wavelength band. FIG. 6 shows a schematic configuration of the wavelength conversion mechanism according to the first embodiment. As shown in FIG. 6, the wavelength conversion mechanism 30 includes a condenser lens 131, an SHG crystal 30a, a collimator lens 132, high reflection mirrors 133 and 134, a condenser lens 135, an SHG crystal 30b, and a collimator lens. 136 and a high reflection mirror 137.

  The low coherence light Ld from the low coherence mechanism 20 is first condensed on the SHG crystal 30 a by the condenser lens 131 in the wavelength conversion mechanism 30. The SHG crystal 30a is, for example, a BBO crystal, and emits, for example, pulsed laser light of second harmonic light (wavelength = 2ω) with respect to the incident low coherence light Ld (wavelength = ω). The laser light emitted from the SHG crystal 30 a is collimated by the collimator lens 132 and then enters the condenser lens 135 via the high reflection mirrors 133 and 134. The high reflection mirror 133 reflects laser light having a wavelength of 2ω and transmits laser light having a wavelength of ω. Therefore, only the laser beam having a wavelength of 2ω is guided to the condenser lens 135. As a result, the spectral line width of the laser light can be maintained at a spectral line width such that chromatic aberration during exposure can be ignored.

  The condensing lens 135 condenses the incident laser light on the SHG crystal 30b. The SHG crystal 30b is, for example, a KBBF crystal, and emits, for example, pulsed laser light of second harmonic light (double wavelength = 4ω) with respect to incident laser light (wavelength = 2ω). The KBBF crystal is suitable for wavelength conversion to laser light in the wavelength band of vacuum ultraviolet light of about 193 nm, and has an advantage that its lifetime is long. The laser light emitted from the SHG crystal 30 b is collimated by the collimator lens 136 and then enters the high reflection mirror 137. The high reflection mirror 137 transmits laser light having a wavelength of 2ω, reflects the laser light having a wavelength of 4ω, and outputs the laser light as laser light L1. As a result, the spectral line width of the laser light L1 can be maintained at a spectral line width such that chromatic aberration during exposure can be ignored. This laser beam L1 is the laser beam L1 output from the master oscillator MO1.

  As described above, the laser beam L1 output from the master oscillator MO1 is incident on the power oscillator PO1 through the high reflection mirrors M1 and M2 as described above, and is amplified for exposure in the power oscillator PO1. The output laser beam L2 is output to an exposure apparatus (not shown).

  As described above, in the first embodiment, the low coherence mechanism is provided before the wavelength conversion mechanism that converts the wavelength into a short wavelength. For this reason, it is possible to reduce the coherence of the laser light at a short wavelength stage where the energy loss is relatively small. As a result, in the first embodiment, it is possible to realize the laser device 1 capable of outputting laser light with low coherence and high intensity. In the first embodiment, an optical element (for example, the high reflection mirrors 133 and 137) that reflects only the laser beam having the target wavelength is provided at each stage. Therefore, the spectral line is such that chromatic aberration during exposure can be ignored. It is possible to generate the output laser beam L2 whose width is maintained.

・ Modification 1
Here, Modification 1 of Embodiment 1 will be described in detail with reference to the drawings. In the first embodiment described above, the low coherence mechanism 20 is arranged in the previous stage (input stage) of the wavelength conversion mechanism 30. That is, the laser device 1 has a configuration for reducing the coherence of the laser light before being shortened. However, this invention is not limited to this, For example, as shown in FIG. 7, you may provide the low coherence mechanism 20 in the wavelength conversion mechanism 30-1. FIG. 7 is a schematic diagram showing a schematic configuration of a wavelength conversion mechanism according to the first modification of the first embodiment.

  As shown in FIG. 7, in the wavelength conversion mechanism 30-1, the low coherence mechanism 20 is disposed on the optical path between the two SHG crystals 30a and 30b. In other words, the wavelength conversion mechanism 30-1 has a configuration for reducing the coherence of the laser light after the first stage in the two-stage wavelength reduction. Even with such a configuration, similarly to the above-described first embodiment, it is possible to reduce the coherence of the laser light at a short wavelength stage where energy loss is relatively small. As a result, in the first modification, it is possible to realize the laser device 1 that can output laser light with low coherence and high intensity. Not only this modification but also a plurality of wavelength conversion mechanisms, a low coherence mechanism may be provided between the plurality of wavelength conversion mechanisms.

  For example, when the wavelength of the seed light Lb from the Ti: sapphire master oscillator MO10 is about 773.6 nm, there is an optical element with a small energy loss even for the wavelength of the second harmonic light (= about 386.8 nm). . Therefore, as in the first modification, the configuration in which the laser light after the first-stage wavelength reduction is reduced in coherence is compared with the case where the coherence is reduced before the first-stage wavelength reduction. Thus, the wavelength conversion efficiency can be improved. Since other configurations are the same as those of the first embodiment, detailed description is omitted here.

・ Modification 2
Next, a modification of the low coherence mechanism 20 according to the first embodiment will be described in detail with reference to the drawings. FIG. 8 is a schematic diagram showing a schematic configuration of a low coherence mechanism according to the second modification of the first embodiment. As shown in FIG. 8, the low coherence mechanism 20-1 includes a partial reflection mirror 121 and a high reflection mirror 122 that are inclined by a predetermined angle θ with respect to incident light (laser light Lc). A partial reflection coat 121 a is formed on the light incident surface of the partial reflection mirror 121. A high reflection coating 122 a is formed on the reflection surface of the high reflection mirror 122. On the other hand, the partial reflection mirror 121 and the high reflection mirror 122 are arranged so that the surfaces on which the partial reflection coat 121a and the high reflection coat 122a are formed face each other. The partial reflection mirror 121 and the high reflection mirror 122 are disposed so as to be inclined with respect to the incident axis of the laser light Lc, and are disposed in parallel to each other so that a part of the laser light Lc is the partial reflection mirror 121. A repetitive optical path is formed that is repeatedly reflected while being emitted through the. That is, a part of the laser light Lc incident on the partial reflection coat 121 is transmitted through the partial reflection mirror 121 and the rest is reflected on the high reflection mirror 122. The laser light incident on the high reflection mirror 122 is incident on the partial reflection mirror 121 again, part of which is transmitted through the partial reflection mirror 121 and the rest is reflected on the high reflection mirror 122. By repeating this, a plurality of laser beams (repeatedly reflected laser beam beams) Ld1 transmitted through the partial reflection mirror 121 are output from the partial reflection mirror 121.

Here, if the gap between the partial reflection mirror 121 and the high reflection mirror 122 is d, the optical path length L _ops of the low coherence mechanism 20-1 is 2d. Therefore, the difference in optical path length between the laser beams in the repetitively reflected laser beam Ld1 is longer than the coherent length L _coh . For this reason, the plurality of laser beams in the repetitively reflected laser beam Ld1 do not interfere with each other. As a result, the laser light L1 obtained by wavelength conversion of the repetitively reflected laser beam Ld1 by the wavelength conversion mechanism 30 becomes low coherence light. As a result, the laser light L1 input to the power oscillator PO1 can be made low-coherence light.

・ Modification 3
Next, another modified example of the low coherence mechanism will be described in detail with reference to the drawings. FIG. 9 is a schematic diagram showing a schematic configuration of a low coherence mechanism according to the third modification of the first embodiment. FIG. 10 is a schematic diagram showing a schematic configuration when the low coherence mechanism shown in FIG. 9 is viewed from another angle. As shown in FIGS. 9 and 10, the low coherence mechanism 20-2 further includes a repetitively reflected laser beam Ld1 transmitted through the partial reflection mirror 121 in addition to the configuration of the low coherence mechanism 20-1 shown in FIG. A partial reflection mirror 221 and a high reflection mirror 222 are provided that form a repeated optical path for repeatedly reflecting the portion while emitting the light through the partial reflection mirror 221. However, the inclination of the partial reflection mirror 221 and the high reflection mirror 222 with respect to the optical axis of the laser light Lc is 90 ° with respect to the inclination of the partial reflection mirror 121 and the high reflection mirror 122 with respect to the optical axis of the laser light Lc, for example. It is rotating. In addition, a partial reflection coat 121 a is formed on the light incident surface of the partial reflection mirror 221. A high reflection coat 122 a is formed on the reflection surface of the high reflection mirror 222.

  Thus, by forming two repetitive optical paths having different directions inclined with respect to the optical axis of the laser light Lc, a repetitively reflected laser beam Ld2 having no two-dimensional interference can be generated. As a result, the laser light L1 obtained by wavelength conversion of the repetitively reflected laser beam Ld2 by the wavelength conversion mechanism 30 becomes low coherence light, so that the laser light L1 input to the power oscillator PO1 can be low coherence light.

Modification 4
Next, another modified example of the low coherence mechanism will be described in detail with reference to the drawings. FIG. 11 is a schematic diagram showing a schematic configuration of a low coherence mechanism according to the fourth modification of the first embodiment. FIG. 12 is a schematic diagram showing a schematic configuration when the low coherence mechanism shown in FIG. 11 is viewed from the optical axis. As shown in FIGS. 11 and 12, the low coherence mechanism 20-2 is formed in a transparent substrate 322 that is transparent to the laser beam Lc, and in the laser beam region RB in which at least the laser beam Lc is incident on the transparent substrate 322. And a random phase shifter 321 including a plurality of fine films 321a. Each fine film 321a can transmit the laser beam Lc and has a refractive index different from that of the vacuum. Further, the film thickness along the optical axis of each fine film 321a is random. For this reason, the phase of the laser beam Lc that has passed through the random phase shifter 321 is randomly shifted in that portion. For this reason, the laser light Lc transmitted through the random phase shifter 321 becomes low coherence light Ld having a spatially random phase shift.

・ Modification 5
Further, as shown in FIG. 13, by using the random phase shifter 323 in which the transparent substrate 322 of the random phase shifter 321 shown in FIGS. 11 and 12 is replaced with a reflective substrate 324 that reflects the laser light Lc, the above-described modification is performed. The transmission type low coherence mechanism 20-2 shown in Example 4 can be transformed into a reflection type low coherence mechanism 20-3. FIG. 13 is a schematic diagram illustrating a schematic configuration of a low coherence mechanism according to the fifth modification of the first embodiment.

Modification 6
Next, a modification of the Ti: sapphire power oscillator PO10 in the solid-state laser 10 according to the first embodiment will be described in detail with reference to the drawings. FIG. 14 is a schematic diagram showing a schematic configuration of a Ti: sapphire power oscillator according to the sixth modification of the first embodiment. As shown in FIG. 14, the Ti: sapphire power oscillator PO10-1 is a so-called ring type laser. The Ti: sapphire power oscillator PO10-1 is disposed on the optical path in the resonator, with high reflection mirrors 217 to 219 and an input / output coupler 216 forming a resonator having a ring-shaped (eight-shaped) optical path. Ti: sapphire crystal 18.

  In this configuration, the input / output coupler 216 transmits the seed light Lb from the Ti: sapphire master oscillator MO10 and reflects the laser light from the Ti: sapphire crystal 18. The high reflection mirror 218 transmits the pump light La2 from the pumping laser PL to the resonator side, and reflects the laser light from the Ti: sapphire crystal 18. The seed light Lb taken into the resonator travels on a ring-shaped (eight-shaped) optical path formed by the high reflection mirrors 217 to 219 and the input / output coupler 216, and then is output via the input / output coupler 216. . Thus, by using a ring-shaped laser for the Ti: sapphire power oscillator PO10-1, it is possible to amplify the laser light more efficiently than when, for example, a Fabry-Perot laser is used. Furthermore, since the input / output coupler 216 having a relatively low reflectance is used at the incident end of the seed light Lb, it is possible to suppress the lower light amount lower limit value of the seed light Lb.

・ Modification 7
Next, another modification of the Ti: sapphire power oscillator will be described in detail with reference to the drawings. FIG. 15 is a schematic diagram showing a schematic configuration of a Ti: sapphire power oscillator according to the seventh modification of the first embodiment. As shown in FIG. 15, the Ti: sapphire power oscillator PO10-2 is a so-called regenerative amplification type amplifier. The Ti: sapphire power oscillator PO10-2 includes highly reflective mirrors 315 and 319 forming a resonator, a Pockels cell 316, a Ti: sapphire crystal 18, a polarizer 317, and a Pockels arranged on an optical path in the resonator. A cell 318. The Pockels cells 316 and 318 function as λ / 4 plates, for example, during the period when a voltage is applied.

  In this configuration, for example, S-polarized seed light Lb is incident from the Ti: sapphire master oscillator MO10. The seed light Lb first enters a polarizer 317 inclined by 45 ° with respect to the optical path of the resonator. For example, the polarizer 317 reflects S-polarized light and transmits P-polarized light. Therefore, the S-polarized seed light Lb incident from the Ti: sapphire master oscillator MO10 is reflected by the polarizer 317 and is introduced into the resonator. At this time, a voltage is applied only to the Pockels cell 318. As a result, the seed light Lb that has passed through the Pockels cell 318 twice when reflected by the high reflection mirror 319 can be converted into P-polarized laser light. Note that a voltage is applied to the Pockels cell 318 only during a period in which the seed light Lb is introduced into the resonator. Subsequently, the voltage application to the Pockels cell 318 is stopped. Thereby, since the polarization state of the laser beam in the resonator does not change, the laser beam can be confined in the resonator. The confined laser beam reciprocates one or more times through the resonator. At this time, reproduction is amplified by passing through the Ti: sapphire crystal 18 a plurality of times. Thereafter, a voltage is applied to the Pockels cell 316. As a result, the laser light that has passed through the Pockels cell 316 twice when reflected by the high reflection mirror 315 is converted into S-polarized laser light. As a result, this laser beam is reflected by the polarizer 317 and output as the laser beam Lc.

・ Modification 8
Next, in the first embodiment, a case where a Ti: sapphire power amplifier PA10 is used instead of the Ti: sapphire power oscillator PO10 will be described in detail with reference to the drawings. FIG. 16 is a schematic diagram showing a schematic configuration of a Ti: sapphire power amplifier PA10 according to the eighth modification of the first embodiment. As shown in FIG. 16, the Ti: sapphire power amplifier PA <b> 10 includes a plurality of high reflection mirrors 413 to 419 and a Ti: sapphire crystal 18. The plurality of high reflection mirrors 413 to 419 form a multipath through which the seed light Lb input from the Ti: sapphire master oscillator MO10 passes through the Ti: sapphire crystal 18 a plurality of times (four times in this example). Further, the pump light La2 from the pumping laser PL is also incident on the Ti: sapphire crystal 18 through the high reflection mirror 413. That is, the high reflection mirror 413 transmits the pump light La2 and reflects the laser light from the Ti: sapphire crystal 18. Thus, when passing through the Ti: sapphire crystal 18 a plurality of times, the seed light Lb is multipass amplified and then output as the laser light Lc.

Modification 9
In the first embodiment, the case where the laser device 1 is an ArF laser is taken as an example. However, as described above, the laser device 1 is not limited to the ArF laser. Therefore, as a ninth modification of the first embodiment, a case where the laser device 1 is a KrF laser will be described as an example. FIG. 17 is a schematic diagram showing a schematic configuration of the master oscillator in the laser apparatus according to the ninth modification of the first embodiment. Note that the power oscillator PO10 described above can also be used in the ninth modification.

  As shown in FIG. 17, in the master oscillator MO2 according to the present modification 9, the wavelength conversion mechanism 30 is replaced with a wavelength conversion mechanism 30A in the same configuration as the master oscillator MO1 shown in FIG. In the ninth modification, the Ti: sapphire master oscillator MO10 of the solid-state laser 10 outputs seed light Lb having a wavelength of, for example, 745.3 nm. Other configurations are the same as those in the first embodiment, and therefore, a duplicate description is omitted here.

  The wavelength conversion mechanism 30A has the same configuration as that of the wavelength conversion mechanism 30, and the SHG crystal 30c in which the first stage SHG crystal 30a, which was a BBO crystal, is an LBO crystal, and the second stage SHG crystal 30b, which is a KBBF crystal. Are replaced by THG crystals 30d which are BBO crystals. The SHG crystal 30c outputs the second harmonic light (wavelength = 496.8 nm) of the low coherence light Ld (wavelength = 745.3 nm) incident from the low coherence mechanism 20. The THG crystal 30d uses the low-coherence light Ld as a fundamental wave, or uses the sum frequency of the low-coherence light Ld and the second harmonic light output from the SHG crystal 30c as a fundamental wave. (Wavelength = 248.4 nm) is output. This third harmonic light is guided to the power oscillator PO1 as laser light L1.

  As described above, the laser device 1 according to the first embodiment is not limited to the ArF laser but can be appropriately applied to a KrF laser and other lasers.

(Embodiment 2)
Next, a laser device according to Embodiment 2 of the present invention will be described in detail with reference to the drawings. FIG. 18 is a schematic diagram showing a schematic configuration of a laser apparatus according to Embodiment 2 of the present invention. FIG. 19 is a schematic diagram showing a schematic configuration when the optical system in the laser apparatus shown in FIG. 18 is viewed from another angle. In addition, about the structure similar to Embodiment 1 mentioned above, the overlapping description is abbreviate | omitted by attaching | subjecting the same code | symbol.

  As shown in FIG. 18, the laser device 2 has the same configuration as the laser device 1 shown in FIG. 1, except that the power oscillator PO1 is replaced with a power oscillator PO2 that is a ring type laser. The laser device 2 also includes a shutter M3 that prevents the laser light L2 output from the power oscillator PO2 from being guided to the exposure device.

  As shown in FIGS. 18 and 19, the power oscillator PO2 includes high reflection mirrors 46a, 46b, 41a and 41b that form a ring-shaped optical path, and an output coupler 46 formed of a partial reflection mirror, and an optical coupler on the optical path. And a disposed chamber 43. In FIG. 18 and FIG. 19, the slit 42 (see FIG. 1) is omitted, but the slit 42 may be disposed on the optical path.

  In the above configuration, as shown in FIG. 19, the laser light L1 output from the master oscillator MO1 is incident on the power oscillator PO2 via the optical system including the high reflection mirrors M1 and M2. The incident laser beam L1 is first reflected by the high reflection mirrors 46a and 46b, and then enters the chamber 43 through the window 44a. The laser light L1 incident in the chamber 43 is amplified when passing through the amplification region between the two discharge electrodes 45a and 45b to which a voltage is applied, and then is emitted from the chamber 43 through the window 44b. The emitted laser light L1 is reflected by the high reflection mirrors 41a and 41b, so that it enters the chamber 43 again through the window 44b, and is amplified when passing through the amplification region in the chamber 43. Light exits through 44a. The laser beam L1 that has passed through the amplification region in the chamber 43 in this manner is then partially output as the laser beam L2 via the output coupler 46. The remaining laser light L1 reflected by the output coupler 46 travels again on the optical path formed by the high reflection mirrors 46a, 46b, 41a and 41b and the output coupler 46.

  With the configuration as described above, in the second embodiment, the laser beam L1 can be subjected to multipath amplification in the power oscillator PO2, so that the laser beam L2 with higher intensity can be generated. In the second embodiment, it is possible to block the waveguide of the laser beam L2 to the exposure apparatus using the shutter M3 arranged at the output stage of the power oscillator PO2. The shutter M3 opens / blocks the optical path of the laser light L2, for example, under drive control by a control mechanism (not shown). Since other configurations and effects are the same as those in the first embodiment, detailed description thereof is omitted here.

  In addition, the above-described embodiment and its modifications are merely examples for carrying out the present invention, and the present invention is not limited to these, and various modifications according to specifications and the like are within the scope of the present invention. Furthermore, it is obvious from the above description that various other embodiments are possible within the scope of the present invention. For example, it is needless to say that the modification examples illustrated as appropriate for each embodiment can be applied to other embodiments.

DESCRIPTION OF SYMBOLS 1, 2 Laser apparatus 10 Solid state laser 12, 18 Ti: Sapphire crystal 13 Grating 15, 19, 46 Output coupler 20, 20-1, 20-2, 20-3 Low coherence mechanism 21a Beam splitter 21b-21e Concave high reflection mirror 30, 30-1, 30A Wavelength conversion mechanism 30a, 30b, 30c, 30d SHG crystal 41 Rear mirror 42 Slit 43 Chamber 44a, 44b Window 45a, 45b Discharge electrode 121, 221 Partial reflection mirror 121a Partial reflection coat 122a High reflection coat 131, 135 Condenser lens 132, 136 Collimate lens 216 Input / output coupler 316, 318 Pockels cell 317 Polarizer 321, 323 Random phase shifter 321a Fine film 322 Transparent substrate 324 Reflective substrate L1 L2, Lc Laser light La1, La2 Pump light Lb Seed light Ld Low coherence light Ld1, Ld2 Repetitively reflected laser beam M1, M2, M11, M12, 11, 14, 16, 17, 41a, 41b, 46a, 46b, 122 133, 134, 137, 217 to 219, 222, 315, 319, 413 to 419 High reflection mirror M3 shutter MO1, MO2 master oscillator MO10 Ti: sapphire master oscillator PA10 Ti: sapphire power amplifier PL pumping laser PO1, PO2 power oscillator PO10, PO10-1, PO10-2 Ti: Sapphire power oscillator RB Laser beam region

Claims (12)

A laser device having an amplification unit that amplifies and outputs the laser light after converting the laser light output from the laser light source into laser light having a shorter wavelength than the laser light,
A laser apparatus comprising: a low-coherence unit configured to reduce the coherence of the laser light before converting the laser light into the short-wavelength laser light. A wavelength conversion unit that converts the laser light into the short-wavelength laser light by performing a plurality of stages of shortening the wavelength,
2. The laser device according to claim 1, wherein the coherence reduction unit reduces the coherence of the laser light during the plurality of stages of wavelength reduction.   The low coherence unit includes one or more optical elements that form an optical path that shifts the phase of at least a part of the laser light with respect to the phase of the laser light. The laser apparatus described. The one or more optical elements are:
A beam splitter that transmits a part of the laser light and reflects a part thereof;
One or more mirrors forming the optical path for transferring and imaging an optical image of the part of the laser beam reflected by the beam splitter to the beam splitter;
Including
4. The laser device according to claim 3, wherein an optical axis of the laser light transmitted through the beam splitter and an optical axis of the laser light reflected by the beam splitter after passing through the optical path coincide with each other.   The one or more optical elements reflect at least a part of the laser light by repeatedly reflecting at least a part of the laser light while transmitting in the same direction as the transmission direction of the laser light. The laser apparatus according to claim 3, wherein the laser apparatus is shifted with respect to the phase. The one or more optical elements are:
A partially reflecting mirror that is arranged to be inclined with respect to the incident axis of the laser light and reflects a part of the laser light while transmitting a part thereof;
A high-reflection mirror disposed in parallel and opposite to the partial reflection mirror;
Including
The laser light is incident on the partial reflection mirror and then repeatedly reflected between the partial reflection mirror and the high reflection mirror while being partially transmitted in the same direction as the transmission direction of the laser light. The laser device according to claim 5.   By transmitting at least a part of the laser light transmitted through the partial reflection mirror while repeatedly transmitting in the same direction as the transmission direction of the transmitted laser light, the phase of at least a part of the transmitted laser light is transmitted. The laser device according to claim 6, further shifted with respect to the phase of the laser beam.   The laser device according to claim 3, wherein the one or more optical elements include a random phase shifter that randomly shifts a phase of a part of the laser light.   9. The laser device according to claim 8, wherein the random phase shifter has a structure in which a plurality of fine films having different refractive indexes with respect to vacuum and having different film thicknesses are two-dimensionally arranged.   The laser apparatus according to claim 9, wherein the plurality of fine films are provided on a transparent substrate that transmits the laser light.   The laser apparatus according to claim 9, wherein the plurality of fine films are provided on a reflective substrate that reflects the laser light.   The laser apparatus according to claim 1, wherein the laser apparatus is an ArF laser, a KrF laser, a XeCl laser, or a XeF laser.

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