JP4800145B2 - Driver laser for extreme ultraviolet light source device - Google Patents

Description

  The present invention relates to a driver laser that irradiates light to a target in an LPP (laser produced plasma) EUV (extreme ultra violet) light source device that generates extreme ultraviolet light used to expose a semiconductor wafer or the like.

  In recent years, along with miniaturization of semiconductor processes, miniaturization of photolithography has been rapidly progressing, and in the next generation, fine processing of 100 nm to 70 nm, and further fine processing of 50 nm or less have been required. Yes. For this reason, for example, an exposure apparatus that combines an EUV light source that generates extreme ultraviolet light with a wavelength of about 13 nm and a reduced projection reflection optical system (catadioptric system) is expected to meet fine processing of 50 nm or less.

  In such an EUV light source device, a short pulse laser is generally used as a driving light source (driver). This is because the short pulse laser is suitable for obtaining high CE (conversion efficiency: conversion efficiency from irradiation laser light to EUV light) in the LPP type EUV light source device.

FIG. 12 is a schematic diagram showing a configuration of an oscillation amplification type laser used as a driver.
Oscillation amplification type laser 10 shown in FIG. 12 includes a configured oscillator 11 by the short pulse CO ₂ laser, an amplifier 12 for amplifying the laser light short pulse CO ₂ laser is generated. Here, when the amplifier 12 does not have an optical resonator, the laser system having such a configuration is called a MOPA (Master Oscillator Power Amplifier) system. The amplifier 12 includes carbon dioxide (CO ₂ ), nitrogen (N ₂ ), helium (He), and, if necessary, CO containing hydrogen (H ₂ ), carbon monoxide (CO), xenon (Xe), and the like. _{2 It} has the discharge device which excites laser gas by discharge.
Unlike the amplifier 12 shown in FIG. 12, when a resonator is provided in the amplification stage, laser oscillation can be performed by the amplification stage alone. A laser system having such a configuration is called a MOPO (Master Oscillator Power Oscillator) system.

The laser beam having the energy A emitted from the oscillator 11 is amplified to the laser beam having the desired energy B by the amplifier 12. The laser light having this energy B is condensed through a laser light propagation system or by a lens, and irradiated to an EUV light emitting target material selected from tin (Sn), xenon (Xe), and the like.
Here, in FIG. 12, only one stage of amplifier is provided in order to amplify the laser energy A to the laser energy B. However, when the desired laser energy B cannot be obtained, a multi-stage amplifier is used. May be.

Next, a configuration example of a short pulse CO ₂ laser that is an oscillator will be described. Patent Document 1 discloses a configuration of a short pulse RF (Radio Frequency excitation) -CO ₂ laser (FIG. 5 of Patent Document 1). In this RF-CO ₂ laser, high repetition operation of laser pulses is possible up to about 100 kHz. In practical use, it is necessary to obtain 100 W class EUV emission. However, when the CE by the CO ₂ laser is estimated to be 0.5% and the propagation loss is estimated to be 70%, the output required for the CO ₂ laser is about 60 kW. Become. In order to achieve an output of 60 kW in a short pulse laser, a repetition frequency of about 50 kHz to 100 kHz is required in consideration of durability of an optical element or the like. Note that the pulse width of the laser light emitted from the oscillator is desirably 100 ns or less.

The reason is as follows. The output of the CO ₂ laser is E _total , the pulse oscillation repetition frequency is f _i (i = 1, 2, 3,...), And the optical energy of one pulse is E _pj (j = 1, 2, 3,...). Then, there is a relationship of E _total = f ₁ × E _p1 = f ₂ × E _p2 . Here, when _Ep is large, the damage given to the optical element through which the laser light is transmitted increases, so that the optical element is rapidly deteriorated. Therefore, _{E p} is smaller is desirable. Therefore, to reduce the _{E p} in order to obtain the desired _{E total,} may be increased repetition frequency f.

In order to realize such a high repetition frequency, it is appropriate to use an RF (Radio Frequency excitation) -CO ₂ laser. The reason is, as the pulsed CO ₂ lasers, but this addition also has TEA (Transverse Excitation Atmospheric) -CO ₂ laser, the state of the art, 2 kHz about repetitive operation is because the limit.

  Referring to FIG. 5 of Patent Document 1, this laser apparatus includes a multipass waveguide laser oscillator 400 and a multipass waveguide laser amplifier 400a. The resonator of the oscillator 400 is constituted by total reflection mirrors 408 and 406. Between these mirrors, a Q switch, an RF discharge unit, and a thin film polarizer (TFP) are provided. When the Q switch is off, the laser light reciprocates between the mirror 408 and the mirror 406, and the light intensity increases due to stimulated emission at that time. When the Q switch is turned on when the light intensity is sufficiently increased, a short pulse with a peak is reflected by the TFP 404 and is shown in the lower part of FIG. 5 via the mirror 409 and the λ / 2 wave plate. It is introduced into a multipass waveguide laser amplifier 400a. The introduced light is amplified by an amplifier, and the laser light is emitted to the outside. A laser having such a configuration is called a Q-switched cavity-dumped laser.

  By the way, it is known that self-excited oscillation or parasitic oscillation (hereinafter simply referred to as “self-excited oscillation”) can occur in the amplifier when the gain of the amplifier of the oscillation amplification type laser is high. Such self-excited oscillation can occur not only in amplifiers having resonators in the MOPO system, but also in amplifiers having no resonators in the MOPA system. When the self-oscillation light generated in the amplifier returns to the direction of the oscillator and enters the oscillator, the optical elements (eg, Pockels cell, wave plate, polarizing element, etc.) in the oscillator are destroyed, or laser resonance in the oscillator The laser oscillation may become unstable due to the disturbance.

It is known that the destruction of the oscillator due to the self-oscillation light as described above can be prevented to some extent by arranging a spatial filter between the oscillator and the amplifier (for example, see Non-Patent Document 1 below).
Non-Patent Document 1 describes that the oscillation stage CO ₂ laser itself should not cause an air breakdown in the spatial filter. For example, it is described that when a laser intensity incident on a spatial filter from an oscillation stage laser is 1 mJ, a lens and a pinhole are arranged so that air breakdown does not occur at 1 mJ. In addition, it is described that the self-oscillation light having a high directivity slightly stronger than 1 mJ from the amplification stage to the oscillation stage causes air breakdown by being arranged in this way. It is described that the self-oscillation light is absorbed by the plasma generated by the air breakdown and does not reach the oscillation stage or is considerably attenuated to reach the oscillation stage. Further, since components such as an optical element of the oscillation stage CO ₂ laser are resistant to 1 mJ (oscillation stage output), the intensity of the self-excited oscillation light reaching the oscillation stage is 1 mJ ( It is described that the oscillation stage is not destroyed if the output is less than (oscillation stage output).
US Pat. No. 6,697,408 (FIG. 5) Tochitsky et al., “Efficient shortening of self-chirped picosecond pulses in a high-power CO2 amplifier”, Optics Letter (Optics Letters), 2001, Vol. 26, No. 11, p. 813-815

  As described above, Non-Patent Document 1 describes that the destruction of the oscillation stage due to the self-excited oscillation light can be prevented to some extent by arranging the spatial filter between the oscillation stage and the amplification stage. However, if the intensity of the self-excited oscillation light after being attenuated by the plasma generated by the air breakdown is stronger than the tolerance of the oscillation stage optical element or the like, the oscillation stage optical element or the like is destroyed. In particular, when the amplification stage includes a plurality of amplifiers and self-excited oscillation occurs in the subsequent-stage amplifier, the self-excited oscillation light is amplified by an amplifier positioned in front of the amplifier in which the self-excited oscillation has occurred and oscillated. There is a high possibility that the steps will be destroyed.

  Further, the laser light emitted from the oscillation amplification type laser may be reflected by the EUV light emission target material, debris, etc., and may enter the oscillation amplification type laser. In this case, the reflected light reflected by the EUV light emission target material or the like may be amplified by the amplification stage, and the oscillation stage may be destroyed.

  On the other hand, in order to efficiently amplify the laser beam in the amplification stage and efficiently focus the laser beam on the target material, the laser beam incident on the amplification stage from the oscillation stage does not include a higher-order mode. It is desirable that the beam profile be a single mode and that the beam profile be close to a circle.

  Therefore, in view of the above points, an object of the present invention is to provide a driver laser for an extreme ultraviolet light source device that can prevent destruction of an oscillator and can efficiently amplify laser light. To do.

  In order to solve the above problems, a driver laser for an extreme ultraviolet light source apparatus according to one aspect of the present invention irradiates a target material with laser light output from a laser light source, thereby converting the target material into plasma and generating extreme ultraviolet light. A driver laser system used in an extreme ultraviolet light source device for generating an oscillator that oscillates and outputs laser light, and at least one that inputs laser light output from the oscillator and amplifies and outputs the laser light An amplifier, an oscillator and driving means for driving the at least one amplifier, and at least one spatial filter that inputs laser light output from the oscillator or at least one amplifier, and spatially filters and outputs the laser light. To detect the occurrence of breakdown in at least one spatial filter At least one breakdown detection means, at least one breakdown detecting means when detecting the occurrence of a breakdown, and control means for causing the drive means to stop the drive of the at least one amplifier.

  According to the present invention, it is possible to stop the driving of the amplifier when breakdown occurs. Thereby, destruction of the oscillator can be prevented. Further, it is possible to efficiently amplify laser light in a single mode that does not include a higher-order mode.

Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. The same constituent elements are denoted by the same reference numerals, and the description thereof is omitted.
FIG. 1 is a schematic diagram showing an outline of an LPP type EUV light source apparatus to which a driver laser for an extreme ultraviolet light source according to the present invention (hereinafter also simply referred to as “driver laser”) is applied. As shown in FIG. 1, the LPP type EUV light source device includes a driver laser 1, an EUV light generation chamber 2, a target material supply unit 3, and an optical system 4.

The driver laser 1 is an oscillation amplification type laser device that generates a driving laser beam used to excite a target material. The configuration of the driver laser 1 will be described in detail later.
The EUV light generation chamber 2 is a vacuum chamber in which EUV light is generated. The EUV light generation chamber 2 is provided with a window 21 for transmitting the laser light 6 generated from the driver laser 1 into the EUV light generation chamber 2. In addition, a target injection nozzle 31, a target collection cylinder 32, and a condenser mirror 8 are disposed inside the EUV light generation chamber 2.

  The target material supply unit 3 supplies a target material used for generating EUV light into the EUV light generation chamber 2 via a target injection nozzle 31 that is a part of the target material supply unit 3. Among the supplied target materials, those which are no longer necessary without being irradiated with the laser light are recovered by the target recovery cylinder 32. As the target substance, various known materials (eg, tin (Sn), xenon (Xe), etc.) can be used. The state of the target material may be any of solid, liquid, and gas, and is supplied to the space in the EUV light generation chamber 2 in any known manner such as a continuous flow (target jet) or a droplet (droplet). May be. For example, when a liquid xenon (Xe) target is used as the target material, the target material supply unit 3 includes a gas cylinder for supplying high-purity xenon gas, a mass flow controller, a cooling device for liquefying xenon gas, and a target injection nozzle. Composed of etc. When generating droplets, a vibration device such as a piezo element is added to the configuration including them.

The optical system 4 includes, for example, a condensing lens, and condenses the laser light 6 emitted from the driver laser 1 so as to form a focal point on the trajectory of the target material. As a result, the target material 5 is excited and turned into plasma, and EUV light 7 is generated.
The condensing mirror 8 is a concave mirror in which, for example, a Mo / Si film that reflects 13.5 nm light with high reflectivity is formed on the surface thereof, and condenses and transmits the generated EUV light 7 by reflecting it. Guide to the optical system. Further, the EUV light is guided to an exposure apparatus or the like via a transmission optical system. In FIG. 1, the condensing mirror 8 condenses EUV light in the front direction of the paper.

Next, the driver laser according to the first embodiment of the present invention will be described.
FIG. 2 is a schematic diagram showing a driver laser according to the present embodiment. As shown in FIG. 2, the driver laser 1 includes an oscillator 41 that oscillates laser light by resonance, a spatial filter 42 that spatially filters laser light emitted from the oscillator 41, and a laser that is filtered by the spatial filter 42. An amplifier 43 for amplifying light, a breakdown sensor 44 for detecting an air breakdown in the spatial filter 42, a drive unit 46 for driving the oscillator 41 and the amplifier 43, and a control unit 45 for controlling the drive unit 46. It has.

  FIG. 3 is a schematic diagram showing the oscillator 41. As shown in FIG. 3, the oscillator 41 includes a laser medium 100, a rear mirror 101 and a high reflection (HR) mirror 102, a polarization beam splitter 104, a Pockels cell (PC) 105, and a λ / A four-wave plate 106 and a reflection mirror 107 are included.

The laser medium 100 is filled in a discharge tube (or chamber) (not shown), and the drive unit 46 (FIG. 2) is disposed on an electrode pair (not shown) disposed in the discharge tube (or chamber). The laser medium 100 is excited by discharging at a predetermined timing. The laser medium 100 includes carbon dioxide (CO ₂ ), nitrogen (N ₂ ), helium (He), and, if necessary, hydrogen (H ₂ ), carbon monoxide (CO), xenon (Xe), and the like. CO ₂ laser gas containing
The laser light passes through the laser medium 100 while reciprocating between the rear mirror 101 and the HR mirror 102, and thereby is excited by CW (continuous oscillation) or pulse.

The polarization beam splitter 104 emits p-polarized light in the same direction as the traveling direction of incident light, and emits s-polarized light in a direction substantially perpendicular to the incident light, thereby separating incident light into p-polarized light and s-polarized light. .
The λ / 4 wavelength plate 106 rotates the polarization plane of light passing therethrough by λ / 4 (90 °).

  A Pockels cell (Q switch) is an optical element that utilizes an EO effect (electro optic effect) in which the refractive index and anisotropy of a crystal change when an electric field is applied to the crystal. By controlling the electric field applied to the Pockels cell, the plane of polarization of light passing through it can be rotated by a desired angle. In this embodiment, by controlling the switching of the Pockels cell 105, the laser beam is extracted upward in the figure. For this purpose, a reflection mirror 107 is provided for changing the direction of the extracted laser beam. Yes. Such a configuration is called a Q-switched cavity-dumped laser.

  By activating and deactivating the Pockels cell 105 at a predetermined timing, the laser light emitted outside the resonator constituted by the rear mirror 101 and the HR mirror 102 is cut out to a desired pulse width. Thereby, the laser beam can be shortened.

  FIG. 4 is a schematic diagram showing the spatial filter 42 and the breakdown sensor 44. As shown in FIG. 4, the spatial filter 42 includes a condenser lens 111, a pinhole plate 112, and a collimator lens 113. The breakdown sensor 44 includes a sound sensor 121 and an optical sensor 122.

  A pinhole 112 a is formed in the pinhole plate 112, and the laser light output from the oscillator 41 is condensed on the pinhole 112 a by the condenser lens 111. The laser beam focused on the pinhole 112a is then diffused, collimated by the collimating lens 113, and enters the amplifier 43.

When air breakdown occurs in the spatial filter 42 and the air is turned into plasma, sound and / or light is generated, and the sound sensor 121 and / or the optical sensor 122 detects such sound and / or light, An air breakdown detection signal notifying that the air breakdown has been detected is output to the control unit 45. Instead of the spatial filter in the _{air, N 2, He, Ar,} CO 2, or, SF _6, or may be arranged in these mixed gas.

  The intensity of the output laser beam of the oscillator 41 and the focused spot diameter in the pinhole 112a are determined (designed) so that breakdown does not occur due to the laser beam incident on the spatial filter 42 from the oscillator 41. Therefore, breakdown occurs in the spatial filter 42 when self-excited oscillation occurs in the amplifier 43 or when reflected light from the EUV light emission target material or debris is amplified by the amplifier 43.

FIG. 5 is a schematic diagram showing the amplifier 43. As shown in FIG. 5, the amplifier 43 includes windows 131 and 132, discharge tubes 141 to 148, and mirrors 151 to 158. The discharge tubes 141 to 148 are filled with a laser medium, and the drive unit 46 (FIG. 2) applies predetermined electrodes to electrode pairs (the electrode pairs will be described later) disposed in the discharge tubes 141 to 148, respectively. The laser medium is excited by discharging at a timing. Note that the windows 131 and 132 may contain ZnSe or the like. The laser medium may be carbon dioxide (CO ₂ ), nitrogen (N ₂ ), helium (He), and, if necessary, hydrogen (H ₂ ), carbon monoxide (CO), xenon (Xe), etc. The CO ₂ laser gas may be included.

  The laser light incident in the X-axis direction from the spatial filter 42 passes through the window 131 and enters the discharge tube 141 and is amplified. The laser light amplified in the discharge tube 141 is reflected by the mirror 151 in the Y-axis direction, and enters the discharge tube 142 to be amplified. The laser light amplified in the discharge tube 142 is reflected in the reverse direction of the X axis by the mirror 152 and is incident on the discharge tube 143 to be amplified. The laser light amplified in the discharge tube 143 is reflected by the mirror 153 in the reverse direction of the Y axis, and enters the discharge tube 144 to be amplified.

  The laser light amplified in the discharge tube 144 is reflected by the mirror 154 in the Z-axis direction, further reflected by the mirror 155 in the Y-axis direction, and incident on the discharge tube 145 and amplified. The laser light amplified in the discharge tube 145 is reflected in the X-axis direction by the mirror 156 and incident on the discharge tube 146 to be amplified. The laser beam amplified in the discharge tube 146 is reflected by the mirror 157 in the reverse direction of the Y axis, and enters the discharge tube 147 to be amplified. The laser light amplified in the discharge tube 147 is reflected by the mirror 158 in the direction opposite to the X axis, and enters the discharge tube 148 to be amplified. The laser light amplified in the discharge tube 148 passes through the window 132 and enters the EUV light generation chamber (FIG. 1).

  6A is a schematic diagram showing an example of the arrangement of electrodes in the discharge tube of the amplifier 43, and FIG. 6B is a schematic diagram of the gain region of the amplifier 43 as viewed from the laser optical axis side. In FIG. 6A, the window and the mirror are not shown.

  As shown in FIG. 6 (a), an electrode 141a is disposed at the top of the discharge tube 141, an electrode 141b is disposed at the bottom of the discharge tube 141, and the electrode 142a is disposed on the front side of the discharge tube 142 in the drawing. Electrodes 142b are arranged on the back side of the paper surface of 142, respectively. Thus, by rotating the arrangement direction of the electrode pair of each discharge tube by 90 degrees about the laser optical axis as shown in FIG. 6B, the gain region 43a can be enlarged to the inner wall of the discharge tube. Can do.

FIG. 6C is a schematic diagram showing another example of the arrangement of electrodes in the discharge tube of the amplifier 43. In FIG. 6C, the window and the mirror are not shown.
As shown in FIG. 6C, the discharge tube 141 has electrodes 141a and 141b arranged in a spiral shape. As described above, by arranging the electrode pairs in a spiral shape on the discharge tube, the gain region 43a can be enlarged to the inner wall of the discharge tube as in FIG. 6B.

  Thus, when the amplifier 43 does not have an optical resonator, the laser system having such a configuration is called a MOPA (Master Oscillator Power Amplifier) system. The amplifier 43 may further include an optical resonator. A laser system having such a configuration is called a MOPO (Master Oscillator Power Oscillator) system.

  Referring again to FIG. 1, the laser light emitted from the driver laser 1 is condensed on the trajectory of the target material by the optical system 4. As a result, the target material 5 is excited and turned into plasma, and EUV light 7 is generated.

Next, a case where self-excited oscillation occurs in the amplifier 43 of the driver laser 1 will be described.
FIG. 7 is a schematic diagram illustrating a state in which self-oscillation light generated in the amplifier 43 is incident on the spatial filter 42.

As shown by a solid line in FIG. 7, self-excited oscillation light having strong directivity is condensed on the pinhole of the pinhole plate 112 by the collimator lens 113. In addition, when the spatial filter 42 is arrange | positioned in the air, it is known that the laser beam intensity | strength which an air breakdown generate | occur | produces is 2.5-3 J / cm < ² > (refer nonpatent literature 1). . Therefore, when the focused spot diameter is 10 ⁻² cm, air breakdown occurs in the vicinity of the pinhole of the pinhole plate 112 when the intensity of the self-excited oscillation light is about 0.2 mJ or more, and the plasma 114 is generated.

  When the air breakdown occurs, sound and / or light diffuses from the vicinity of the pinhole of the pinhole plate 112. And the sound sensor 121 and / or the optical sensor 122 detects such a sound and / or light, and outputs an air breakdown detection signal to the control part 45 (FIG. 2). When the control unit 45 receives the air breakdown detection signal from the sound sensor 121 and / or the optical sensor 122, the control unit 45 causes the driving unit 46 (FIG. 2) to stop discharging in the electrode pair (FIG. 6) in the amplifier 43. Control. At this time, the control unit 45 may control the drive unit 46 so as to stop the discharge in the electrode pair in the oscillator 41.

When the plasma 114 is generated by the air breakdown, the self-oscillation light generated before stopping the discharge in the electrode pair in the amplifier 43 and reaching the pinhole of the pinhole plate 112 is absorbed and / or diffused by the plasma 114. Therefore, the intensity and / or the total amount of the self-oscillation light incident on the oscillator 41 becomes very small.
Further, as indicated by a dotted line in FIG. 7, the self-oscillation light having a weak directivity is not condensed on the pinhole of the pinhole plate 112 but is blocked by the pinhole plate 112, and thus does not enter the oscillator 41.

  As described above, according to the present embodiment, when the air breakdown occurs in the spatial filter 42, the self-excited oscillation generated in the amplifier 43 can be stopped. Further, the self-excited oscillation light having low directivity is shielded by the pinhole plate 112. Thereby, destruction of the optical element of the oscillator 41 can be prevented.

  Even when the laser beam (reflected light) reflected by the target material or debris in the EUV light generation chamber 2 (FIG. 1) is amplified by the amplifier 43 and incident on the spatial filter 42, an air breakdown occurs. Similarly to the above, the discharge at the electrode pair (FIG. 6) in the amplifier 43 can be stopped. Thereby, amplification of reflected light can be stopped, and destruction of the optical element of the oscillator 41 can be prevented.

  In addition, according to the present embodiment, by using the spatial filter 42, it is possible to efficiently amplify the laser light and efficiently focus the laser light on the target material. FIG. 8 is a schematic diagram showing a spatial distribution of laser light passing through the spatial filter 42, and FIG. 9 is a schematic diagram showing a beam profile of the laser light.

  As shown in FIG. 8, even if the spatial distribution B1 of the laser light emitted from the oscillator 41 is in order, if the dust D1 exists on the optical path of the laser light, the space of the laser light after passing through the dust D1. The distribution B2 is disturbed. FIG. 9A shows a beam profile of the laser light at this time. Referring to FIG. 8 again, the laser light passes through the pinhole 112a of the pinhole plate 112 and is filtered, so that the spatial distribution B3 of the laser light is adjusted again. FIG. 9B is a diagram showing the beam profile of the laser light at this time. When laser light having a beam profile as shown in FIG. 9B enters the amplifier 43, the amplifier 43 efficiently amplifies the laser light and efficiently concentrates the laser light on the target material. It becomes possible to do.

  Even when the laser light emitted from the oscillator 41 includes a high-order transverse mode, if the laser light passes through the spatial filter 42, the high-order transverse mode is filtered, so that the amplifier 43 amplifies the laser light. It is possible to efficiently focus the laser beam on the target material.

  In the present embodiment, the case where the spatial filter 42 (FIG. 4) is realized by using the condensing lens 111, the pinhole plate 112, and the collimating lens 113 has been described, but as shown in FIG. It is also possible to realize a spatial filter using a concave mirror 114 instead of the condenser lens 111. Furthermore, as shown in FIG. 10B, a spatial filter can be realized by using a concave mirror 115 instead of the collimating lens 113.

Next, a driver laser according to a second embodiment of the present invention will be described.
FIG. 11 is a schematic diagram showing a driver laser according to the present embodiment. As shown in FIG. 11, the driver laser 9 emits laser light emitted from the amplifier 43 in addition to the oscillator 41, the spatial filter 42, the amplifier 43, the breakdown sensor 44, the control unit 45, and the driving unit 46. A second spatial filter 47 for filtering, a second amplifier 48 for amplifying the laser light filtered by the spatial filter 47, and a second breakdown sensor 49 for detecting an air breakdown in the spatial filter 47 In addition. The spatial filter 47, the amplifier 48, and the breakdown sensor 49 can be configured similarly to the spatial filter 42, the amplifier 43, and the breakdown sensor 44.

  When an air breakdown occurs in the spatial filter 42, the breakdown sensor 44 outputs a first air breakdown detection signal notifying that the air breakdown has been detected to the control unit 45. When an air breakdown occurs in the spatial filter 47, the breakdown sensor 49 outputs a second air breakdown detection signal notifying that the air breakdown has been detected to the control unit 45. When the control unit 45 receives the first and / or second air breakdown detection signal, the control unit 45 controls the driving unit 46 to stop the discharge in the electrode pair in the amplifier 43 and / or the amplifier 48. At this time, the control unit 45 may control the drive unit 46 so as to stop the discharge in the electrode pair in the oscillator 41. Further, when the control unit 45 receives the first air breakdown detection signal, the driving unit 46 may be controlled so as to stop the discharge at the electrode pair in the amplifier 43. Further, when the control unit 45 receives the second air breakdown detection signal, the driving unit 46 may be controlled so as to stop the discharge at the electrode pair in the amplifier 48.

  According to the present embodiment, when an air breakdown occurs in the spatial filter 42 and / or the spatial filter 47, the driving of the amplifier 43 and / or the amplifier 48 can be stopped. Thereby, destruction of the optical element of the oscillator 41 can be prevented.

  In this embodiment, the spatial filter 42 is disposed between the oscillator 41 and the amplifier 43, and the spatial filter 47 is disposed between the amplifier 43 and the amplifier 48. However, the spatial filter 42 is provided as necessary. Only one of the spatial filters 47 may be arranged. For example, if the amplifiers 43 and 48 are unlikely to self-oscillate but the laser beam is highly likely to be reflected by the target material or the like, only the spatial filter 47 may be disposed. Further, when there is a high possibility that the amplifier 43 self-oscillates, the spatial filter 42 may be disposed.

  Here, the case where the number of amplifier stages is one and two has been described, but the present invention can also be applied to the case where the number of amplifier stages is three or more.

  The present invention can be used in a driver laser that irradiates light onto a target of an LPP type EUV light source that generates extreme ultraviolet light for exposing a semiconductor wafer or the like.

It is a schematic diagram which shows the outline | summary of the LPP type EUV light source device to which the driver laser for extreme ultraviolet light sources which concerns on this invention is applied. It is a mimetic diagram showing a driver laser concerning a 1st embodiment of the present invention. FIG. 3 is a schematic diagram showing the oscillator shown in FIG. 2. It is a schematic diagram which shows the spatial filter and breakdown sensor which are shown in FIG. FIG. 3 is a schematic diagram showing the amplifier shown in FIG. 2. FIG. 3 is a schematic diagram showing the amplifier shown in FIG. 2. It is a schematic diagram which shows the spatial filter and breakdown sensor which are shown in FIG. It is a schematic diagram which shows the spatial distribution of the laser beam which passes the spatial filter shown in FIG. It is a figure which shows the beam profile of the laser beam which passes the spatial filter shown in FIG. It is a schematic diagram which shows the other example of the spatial filter shown in FIG. It is a schematic diagram which shows the driver laser which concerns on the 2nd Embodiment of this invention. It is the schematic which shows the structure of an oscillation amplification type laser.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Driver laser, 2 ... EUV light generation chamber, 3 ... Target material supply part, 4 ... Optical system, 5 ... Target material, 6 ... Laser light, 7 ... EUV light, 8 ... Condensing mirror, 10 ... Oscillation amplification type Laser, 11, 41 ... Oscillator, 12, 43, 48 ... Amplifier, 21 ... Window, 31 ... Target injection nozzle, 32 ... Target recovery cylinder, 42, 47 ... Spatial filter, 44, 49 ... Breakdown sensor, 45 ... Control 46, drive unit, 100 ... laser medium, 101 ... rear mirror, 102 ... front mirror, 104 ... polarization beam splitter, 105 ... Pockels cell, 106 ... λ / 4 wavelength plate, 111 ... condensing lens, 112 ... pinhole Plate, 112a ... Pinhole, 113 ... Collimate lens, 114, 115 ... Concave mirror, 121 ... Sound sensor, 122 ... Optical sensor, 131 132 ... window, 141 to 148 ... discharge tube, 141a, 141b, 142a, 142b ... electrode, 151-158 ... mirror

Claims (5)

A driver laser used in an extreme ultraviolet light source device that generates extreme ultraviolet light by irradiating a target material with laser light output from a laser light source to turn the target material into plasma,
An oscillator that oscillates and outputs laser light;
At least one amplifier for inputting the laser beam output from the oscillator, amplifying the laser beam and outputting the amplified laser beam;
Driving means for driving the oscillator and the at least one amplifier;
At least one spatial filter that inputs laser light output from the oscillator or the at least one amplifier, and spatially filters the laser light to output the laser light;
At least one breakdown detection means for detecting occurrence of breakdown in the at least one spatial filter;
Control means for causing the drive means to stop driving the at least one amplifier when the at least one breakdown detection means detects the occurrence of a breakdown;
A driver laser for an extreme ultraviolet light source device. The spatial filter is
A pinhole plate with pinholes formed thereon;
Condensing means for condensing the laser light output from the oscillator or the at least one amplifier in the pinhole;
Collimating means for collimating the laser light that has passed through the pinhole;
The driver laser for an extreme ultraviolet light source device according to claim 1, comprising:   3. The driver laser for an extreme ultraviolet light source device according to claim 1, wherein the breakdown detection means includes a sound sensor and / or an optical sensor. 4. The driver laser for an extreme ultraviolet light source device according to claim 1, wherein the oscillator and / or the amplifier includes CO ₂ as a laser medium.   The driver laser for an extreme ultraviolet light source device according to any one of claims 1 to 4, which is a MOPA (Master Oscillator Power Amplifier) or a MOPO (Master Oscillator Power Oscillator).