JP2012252289A - Laser device, exposure apparatus, and inspection apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser device capable of efficiently using a wavelength conversion optical element without requiring a considerable man-hour to create a light resistance intensity map or the like.SOLUTION: A laser device LS comprises a laser light output part 1 for outputting fundamental wave laser light La, and a wavelength conversion part 3 for converting a wavelength of the fundamental wave laser light to output conversion light Lv. The wavelength conversion part 3 includes a damage detection device 60(70) for detecting occurence of damage in a beam propagation region of a wavelength conversion optical element by detecting state change of light emitted from the wavelength conversion optical element to output a detection signal.

Description

  The present invention relates to a laser device configured to include a laser light output unit that outputs laser light, and a wavelength conversion unit that converts the wavelength of laser light output from the laser light output unit and outputs the laser light.

  As the laser apparatus as described above, an all-solid-state laser apparatus that is suitably used for an exposure apparatus, various inspection apparatuses, phototherapy apparatuses, and the like is known. Such a laser apparatus includes a laser beam output unit that outputs a fundamental wave laser beam having a predetermined wavelength, and a wavelength conversion unit that converts the wavelength of the fundamental wave laser beam output from the laser beam output unit. The wavelength conversion unit is provided with a wavelength conversion optical element, for example, configured to sequentially convert the wavelength of the fundamental laser beam in the infrared region by a plurality of wavelength conversion optical elements and output the laser beam in the ultraviolet region. (See Patent Document 1 and Patent Document 2).

  FIG. 9 shows a schematic configuration of the laser apparatus described in Patent Document 1. This laser device includes a laser beam output unit 901 that outputs a fundamental laser beam having a wavelength of about 1.5 μm, and an ultraviolet laser beam having a wavelength of 200 nm or less by converting the wavelength of the fundamental laser beam output from the laser beam output unit 901. And a wavelength conversion unit 903 for outputting. The laser light output unit 901 is provided with a laser light source 911 that generates seed light of the fundamental laser light and a fiber optical amplifier 921 that amplifies the seed light generated by the laser light source 911. The wavelength conversion unit 903 is provided with wavelength conversion optical elements 931 to 936, optical elements 941 to 945 such as a polarization beam splitter and a mirror, lenses 951 to 958, and the like.

  The fundamental laser beam having a wavelength of about 1.5 μm generated by the laser light source 911 and amplified by the fiber optical amplifier 921 is output from the laser beam output unit 901 and enters the polarization beam splitter 941 of the wavelength conversion unit 903. Of the fundamental laser light that has entered the polarization beam splitter 941, the p-polarized component light is transmitted through the polarization beam splitter 941 and condensed and incident on the wavelength conversion optical element 931 via the lens 951. On the other hand, of the fundamental laser light incident on the polarization beam splitter 941, the light of the s-polarized component is reflected by the polarization beam splitter 941 and condensed and incident on the wavelength conversion optical element 934 via the mirrors 942 and 943 and the lens 956. .

The wavelength conversion optical element 931 generates the second harmonic of the p-polarized fundamental wave (fundamental laser beam), and the wavelength is ½ of the fundamental wave and the frequency is twice the fundamental wave (second wave). Harmonics). As the wavelength converting optical element 931, for example, a PPLN (Periodically Poled LiNbO ₃ ) crystal is used. The double wave of the p-polarized light generated by the wavelength conversion optical element 931 and the fundamental wave of the p-polarization transmitted through the wavelength conversion optical element 931 are condensed and incident on the wavelength conversion optical element 932 via the lens 952.

The wavelength conversion optical element 932 generates a sum frequency of the fundamental wave and the second harmonic, and generates a third harmonic (third harmonic). As the wavelength conversion optical element 932, for example, an LBO (LiB ₃ O ₅ ) crystal is used. The third wave of the s-polarized light generated by the wavelength conversion optical element 932 and the second wave of the p-polarized light transmitted through the wavelength conversion optical element 932 rotate the polarization plane only through the two-wavelength wave plate 945 and the lens 953 Then, the light is focused and incident on the wavelength conversion optical element 933.

The wavelength conversion optical element 933 generates a sum frequency of the second harmonic and the third harmonic, and generates a fifth harmonic (fifth harmonic). As the wavelength converting optical element 933, for example, a BBO (β-BaB ₂ O ₄ ) crystal is used. The p-polarized fifth harmonic wave generated by the wavelength conversion optical element 933 enters the dichroic mirror 944 via the lenses 954 and 955.

  In the wavelength conversion optical element 934, the second harmonic generation of the s-polarized fundamental wave (fundamental laser beam) is performed, and a second harmonic is generated. As the wavelength conversion optical element 934, for example, an LBO crystal is used. The double wave of the p-polarized light generated by the wavelength conversion optical element 934 and the fundamental wave of the s-polarized light transmitted through the wavelength conversion optical element 934 are incident on the dichroic mirror 944 via the lenses 957 and 958.

  The dichroic mirror 944 is configured to transmit light in the fifth harmonic waveband and reflect light in the fundamental and second harmonic wavebands. Therefore, the 5th harmonic wave of the p-polarized light generated by the wavelength conversion optical element 933 passes through the dichroic mirror 944 and is condensed and incident on the wavelength conversion optical element 935. Further, the p-polarized double wave generated by the wavelength conversion optical element 934 and the s-polarized fundamental wave transmitted through the wavelength conversion optical element 934 are reflected by the dichroic mirror 944 and superimposed coaxially with the fifth harmonic, thereby converting the wavelength. The light is focused and incident on the optical element 935.

The wavelength conversion optical element 935 generates a sum frequency of a fifth harmonic and a second harmonic, and generates a seventh harmonic (seventh harmonic). The 7th harmonic wave of the s-polarized light generated by the wavelength conversion optical element 935 and the fundamental wave of the s-polarized light transmitted through the wavelength conversion optical element 935 are incident on the wavelength conversion optical element 936 to generate sum frequency, and the wavelength is fundamental. An eighth harmonic wave (eighth harmonic wave) that is 1/8 of the wave and whose frequency is eight times that of the fundamental wave is generated. As the wavelength conversion optical elements 935 and 936, for example, CLBO (CsLiB ₆ O ₁₀ ) crystal is used. The eighth harmonic wave is laser light in the ultraviolet region having a wavelength of 200 nm or less, and the ultraviolet laser light generated in this way is output from the laser device.

JP 2006-308908 A JP 2004-86193 A

  Since the wavelength conversion efficiency of the wavelength conversion optical element is generally proportional to the power density of the incident light, the laser light incident on each wavelength conversion optical element is condensed and incident via the condenser lens. However, as the power of the fundamental laser beam incident on the wavelength conversion unit increases with the demand for higher output for the laser device, damage occurs in the beam propagation region of the wavelength conversion optical element through which the laser beam is transmitted, As a result, there has been a problem that the power of the output light is reduced.

  For example, in the wavelength conversion unit 903 described above, the wavelength conversion optical element 931 that converts a fundamental wave into a double wave is a quasi phase matching (QPM) type wavelength conversion optical element (hereinafter, QPM) such as a PPLN crystal. Called crystal). In such a QPM crystal, when the power density of incident light increases, optical damage in which the refractive index inside the crystal changes due to the photorefractive effect occurs.

  The wavelength conversion optical elements 932 to 936 use bulk crystals such as LBO, BBO, and CLBO. However, these crystals are incident due to impurities included in the crystal growth stage or imperfections in the crystal structure. As the power density of light increases, damage occurs at these defects. Damage based on defects can occur in QPM crystals as well.

  The occurrence of damage in the high power region as described above generally differs depending on the type of crystal, production lot, etc., but even within the same crystal, damage occurs due to relatively short laser beam incidence (durability). There are places where damage is difficult (high durability) even if laser light is incident for a long time.

  As a method for dealing with such a situation, it is conceivable to measure the durability of each wavelength conversion optical element in advance and shift each wavelength conversion optical element within the incident plane based on the measurement result. That is, for each wavelength conversion optical element, the laser light having a predetermined power is incident while changing the incident position of the laser light, and the time (durability) until damage occurs at each position is measured in advance. Then, according to the measured durability of each part, the wavelength conversion optical element is shifted every predetermined time (or the wavelength conversion optical element is moved at a predetermined speed), and the crystal plane is always new before damage occurs. The laser beam is configured to be incident on.

  However, if the wavelength conversion optical element is shifted at regular intervals, the period must be within the damage occurrence time at the position with the lowest durability, and the efficiency of the relatively expensive wavelength conversion optical element can be reduced. Cannot be used effectively. On the other hand, if the period (or moving speed) to be shifted is changed between a place with high durability and a place with low durability, it is necessary to measure and map the durability of each part comparatively finely, which requires a lot of man-hours. In addition, it is impossible to cope with a decrease in durability due to a change over time of the wavelength conversion optical element.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a laser device that can efficiently use a wavelength conversion optical element without requiring a large number of steps. It is another object of the present invention to provide an exposure apparatus and the like that can operate efficiently.

  In order to solve the above problems and achieve the object, a first aspect illustrating the present invention is a laser device. The laser device includes a laser light output unit that outputs laser light, and a wavelength conversion unit that converts the wavelength of the laser light output from the laser light output unit and outputs the laser light. The wavelength converter includes a wavelength conversion optical element that converts the wavelength of incident laser light and emits it, and a laser beam that passes through the wavelength conversion optical element by detecting a change in the state of light emitted from the wavelength conversion optical element. And damage detection means (for example, damage detection devices 60 and 70 in the embodiment) that detect that damage has occurred in the beam propagation region and output a detection signal.

  The damage detection means detects an increase state of the beam diameter when the beam diameter of the laser light emitted from the wavelength conversion optical element increases by a predetermined amount or more from the initial beam diameter when the wavelength conversion is started. Thus, the detection signal can be output. Alternatively, the damage detection means can be configured to detect the scattered light and output a detection signal when the scattered light is generated in the beam propagation region.

  When detecting an increase state of the beam diameter, the damage detection means passes the laser beam emitted from the wavelength conversion optical element in the initial state as it is, and the laser emitted from the wavelength conversion optical element in the increase state of the beam diameter. An aperture (for example, the aperture of the aperture 61 in the embodiment) set so that the outer peripheral portion of the light is applied, and a reflected light detector that detects the laser beam emitted from the wavelength conversion optical element and reflected by the aperture are configured. be able to. One form of detecting an increase in the beam diameter is when the wavelength conversion optical element is a quasi phase matching type wavelength conversion optical crystal.

  A second aspect illustrating the present invention is an exposure apparatus. This exposure apparatus is output from one of the laser apparatuses described above, a mask support section that holds a photomask on which a predetermined exposure pattern is formed, an exposure object support section that holds an exposure object, and a laser apparatus. An illumination optical system for irradiating a photomask held by a mask support with laser light, and a projection optical system for projecting light transmitted through the photomask onto an exposure target held by an exposure target support Is done.

  A third aspect illustrating the present invention is an inspection apparatus. This inspection apparatus irradiates the test object held by the test object support part with any one of the above laser apparatuses, the test object support part that holds the test object, and the laser beam output from the laser apparatus. An illumination optical system and a detector that detects light from the test object are provided.

  In the laser device according to the first aspect, damage is generated in the beam propagation region of the laser light transmitted through the wavelength conversion optical element by detecting a change in the state of the light emitted from the wavelength conversion optical element in the wavelength conversion unit. Damage detection means for detecting this and outputting a detection signal is provided. Therefore, the wavelength conversion optical element can be used without shifting until damage occurs in the beam propagation region of the wavelength conversion optical element. Further, when damage occurs, a detection signal is output from the damage detection means, so that the wavelength conversion optical element can be immediately shifted based on the detection signal. Accordingly, a laser apparatus that can use the wavelength conversion optical element to the maximum efficiency without requiring a great amount of man-hours for measuring and mapping the durability of each crystal part in advance for each wavelength conversion optical element is provided. can do.

  The exposure apparatus of the second aspect is configured to include a laser apparatus having the damage detection means as described above. Therefore, the laser device can be used without shifting the wavelength conversion optical element until damage occurs in the beam propagation region of the wavelength conversion optical element, and when the damage occurs, the detection signal output from the damage detection means is used. Based on this, the wavelength conversion optical element can be shifted. Therefore, in this exposure apparatus, each time the wavelength conversion optical element is replaced in the laser apparatus, it does not require a great deal of man-hours, and each wavelength conversion optical element can be used to the maximum efficiency. An exposure apparatus capable of efficient operation can be provided.

  The inspection apparatus according to the third aspect includes a laser device having the above-described damage detection means. Therefore, the laser device can be used without shifting the wavelength conversion optical element until damage occurs in the beam propagation region of the wavelength conversion optical element, and when the damage occurs, the detection signal output from the damage detection means is used. Based on this, the wavelength conversion optical element can be shifted. Therefore, in this inspection apparatus, each time the wavelength conversion optical element is replaced in the laser apparatus, it does not require a large number of man-hours, and each wavelength conversion optical element can be used to the maximum efficiency. An inspection apparatus capable of efficient operation can be provided.

It is a schematic block diagram which illustrates the whole structure of a laser apparatus. It is a schematic block diagram of the wavelength conversion optical system in the said laser apparatus. It is a schematic block diagram of the damage detection apparatus of a 1st structure form. It is explanatory drawing which represented typically the change of the beam profile before and after a damage generate | occur | produces with a wavelength conversion optical element. It is a schematic block diagram of the damage detection apparatus of a 2nd structure form. It is explanatory drawing which represented typically the generation | occurrence | production state of the scattered light before and after damage generate | occur | produces with a wavelength conversion optical element. It is a schematic block diagram of the exposure apparatus shown as a 1st application example of the system provided with the laser apparatus. It is a schematic block diagram of the test | inspection apparatus shown as the 2nd application example of the system provided with the laser apparatus. It is a schematic block diagram of the wavelength conversion optical system in the conventional laser apparatus.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 1 shows a schematic configuration of a laser apparatus LS to which the present invention is applied. The laser device LS includes a laser beam output unit 1 that outputs a fundamental wave laser beam, a wavelength conversion unit 3 that converts the fundamental wave laser beam output from the laser beam output unit 1 into a laser beam having a predetermined wavelength, and outputs the laser beam. A control unit 8 that controls the operation of the light output unit 1 and the wavelength conversion unit 3 is provided.

  The laser light output unit 1 and the wavelength conversion unit 3 can be appropriately set according to the use and function of a system configured using the laser device LS. In the present embodiment, as an example, a fundamental wave laser beam La having a wavelength of 1547 nm is output from the laser beam output unit 1 and wavelength-converted by the wavelength conversion unit 3 to output an ultraviolet laser beam Lv having a shortest wavelength of 193 nm. explain.

  In the present embodiment, the laser light output unit 1 includes a laser light generation unit 10 that outputs seed light that is seed light of the fundamental laser light, and an amplification unit that amplifies the seed light output from the laser light generation unit 10. 20 shows a configuration constituted by 20. The laser light generation unit 10 is provided with a laser light source 11 that generates seed light Ls having a wavelength of 1547 nm, and the amplification unit 20 amplifies the seed light Ls generated by the laser light source 11 to generate a fundamental wave laser having a predetermined intensity. A fiber optical amplifier 21 that outputs light La is provided.

  As the laser light source 11, a DFB (Distributed Feedback) semiconductor laser having an oscillation wavelength of 1.5 μm band can be suitably used. The DFB semiconductor laser can perform CW oscillation and pulse oscillation, and can control the pulse waveform at high speed by controlling the excitation current. Further, the DFB semiconductor laser can output seed light having a wavelength of 1547 nm which is narrowed by controlling the temperature. The laser beam generator 10 is provided with an external modulator such as an EOM (Electro Optic Modulator), and the output light of the CFB or pulse-oscillated DFB semiconductor laser is cut out by the external modulator so as to output pulsed light having a required waveform. You may comprise.

  The fiber optical amplifier 21 may be one that is doped with an appropriate medium according to the wavelength band to be amplified. An erbium-doped fiber optical amplifier (EDFA) having a core doped with erbium (Er) can be suitably used as a fiber optical amplifier that amplifies seed light having a wavelength of 1.5 μm. The fundamental laser beam La emitted from the fiber optical amplifier 21 is output from the laser beam output unit 1 and input to the wavelength conversion unit 3.

  The wavelength conversion unit 3 is provided with a wavelength conversion optical system 30 including a plurality of wavelength conversion optical elements and mirrors. A schematic configuration of the wavelength conversion optical system 30 is shown in FIG. In the figure, p-polarized light whose polarization plane is parallel to the paper surface is indicated by up and down arrows, and s-polarized light whose polarization surface is perpendicular to the paper surface is indicated by ◯ marks with dots. Further, the fundamental wave is represented by ω, and its n-order harmonic is represented by nω.

The wavelength conversion optical system 30 includes a first series I and a second fundamental wave laser in which the first fundamental laser light La ₁ is incident and propagated out of the fundamental laser light La output from the laser light output unit 1. The second series II in which the light La ₂ is incident and propagated, and the third series III in which the laser light propagated through the first and second series is coaxially superimposed and propagated are arranged in these three series. Wavelength conversion optical elements 31 to 36, optical elements 41 to 45 such as a polarizing beam splitter and a mirror, lenses 51 to 58, and the like.

In the first series I, the first fundamental laser beam La ₁ having a wavelength of 1547 nm and a frequency ω is sequentially converted into ω → 2ω → 3ω → 5ω by the wavelength conversion optical elements 31, 32, 33 provided in this series. Then, the generated fifth harmonic (5th harmonic) 5ω is incident on the third series III. In the second series II, the second fundamental wave laser beam La ₂ having a wavelength of 1547 nm and a frequency ω is wavelength-converted from ω → 2ω by the wavelength conversion optical element 34 provided in this series, and the generated second harmonic wave (first wave) (Second harmonic) 2ω and the fundamental wave ω transmitted without wavelength conversion are incident on the third series III.

  In the third series III, in the wavelength conversion optical element 35, the seventh harmonic (seventh harmonic) 7ω is generated by the sum frequency generation of the fifth harmonic 5ω generated in the first series and the second harmonic 2ω generated in the second series. In the wavelength conversion optical element 36, the eighth harmonic (eighth harmonic) 8ω is generated by the sum frequency generation of the seventh harmonic 7ω and the fundamental wave ω. Then, the ultraviolet laser beam Lv having a wavelength of 193 nm generated in this way is output from the wavelength conversion unit 3. Hereinafter, the configuration of the wavelength conversion unit 3 and the state of the laser beam in each unit will be described in detail.

A polarization beam splitter 41 is provided at the input unit of the wavelength conversion unit 3, and the fundamental laser beam La incident on the wavelength conversion unit 3 is converted into a first fundamental laser beam La ₁ and a second _one by the polarization beam splitter 41. And the fundamental laser beam La ₂ . That is, of the fundamental wave laser light La incident on the wavelength converting portion 3, p-polarized light component transmitted through the polarization beam splitter 41, is incident on the first sequence I is the first fundamental wave laser light La _1. Of the fundamental laser beam La incident on the wavelength converter 3, the s-polarized component is reflected by the polarization beam splitter 41 and becomes the _second fundamental laser beam La ₂ and enters the second series II.

The first fundamental laser beam La ₁ incident on the first series is condensed and incident on the wavelength conversion optical element 31 via the lens 51, and the second harmonic 2ω is generated by the second harmonic generation. The p-polarized double wave 2ω generated in the wavelength conversion optical element 31 and the p-polarized fundamental wave ω transmitted through the wavelength conversion optical element 31 are condensed and incident on the wavelength conversion optical element 32 through the lens 52, and the sum. The third generation wave 3ω of s-polarized light is generated by frequency generation.

The wavelength conversion optical element 31 for generating a second harmonic is a quasi phase matching type wavelength conversion crystal such as a PPLN (Periodically Poled LiNbO ₃ ) crystal, a PPLT (Periodically Poled LiTaO ₃ ) crystal, and a PPKTP (Periodically Poled KTiOPO ₄ ) crystal. (QPM crystal) is preferably used. The wavelength converting optical element 32 for generating the third harmonic is preferably an LBO (LiB ₃ O ₅ ) crystal. Note that an LBO crystal can also be used as the wavelength conversion optical element 31.

  The third wave 3ω of s-polarized light generated by the wavelength converting optical element 32 and the second wave 2ω of p-polarized light transmitted through the wavelength converting optical element 32 are transmitted through the two-wavelength wave plate 45 and only the second wave 2ω is s-polarized. Convert to As the two-wavelength wave plate 45, for example, a wave plate made of a uniaxial crystal flat plate cut in parallel to the optical axis of the crystal is used. This wave plate rotates the polarization plane with respect to light of one wavelength (second harmonic 2ω), and prevents the polarization plane from rotating with respect to light of the other wavelength (third harmonic 3ω). Is cut to be an integral multiple of λ / 2 for light of one wavelength and to an integral multiple of λ for light of the other wavelength.

The second harmonic wave 2ω and the third harmonic wave 3ω, both of which are s-polarized light, are focused and incident on the wavelength conversion optical element 33 via the lens 53, and the frequency is 5 times the fundamental wave and the wavelength is 1/5 due to sum frequency generation. A fifth harmonic 5ω of (309 nm) is generated. For example, a BBO (β-BaB ₂ O ₄ ) crystal is suitably used as the wavelength converting optical element 33 for generating the fifth harmonic wave. Note that a CLBO (CsLiB ₆ O ₁₀ ) crystal can also be used as the wavelength conversion optical element 33.

  The fifth harmonic wave 5ω of p-polarized light emitted from the BBO crystal has an elliptical beam cross section due to the walk-off. Therefore, the beam cross section is shaped into a circular shape by the cylindrical lenses 54 and 55, and the dichroic mirror 44 Make it incident.

The second fundamental laser beam La ₂ incident on the second series II is condensed and incident on the wavelength conversion optical element 34 via the mirrors 42 and 43 and the lens 56, and the second harmonic 2ω is generated by the second harmonic generation. generate. An LBO crystal is preferably used as the wavelength conversion optical element 34. In addition, the wavelength conversion optical element 34 can also use the QPM crystal similar to the wavelength conversion optical element 31 mentioned above. The p-polarized double wave 2ω generated by the wavelength conversion optical element 34 and the s-polarized fundamental wave ω transmitted through the wavelength conversion optical element 34 are incident on the dichroic mirror 44 through lenses 57 and 58.

  The dichroic mirror 44 is configured to have wavelength selectivity that transmits light in the wavelength band of the fifth harmonic wave and reflects light in the wavelength band of the fundamental wave and the second harmonic wave. Therefore, the fifth harmonic 5ω generated by the wavelength conversion optical element 33 passes through the dichroic mirror 44 and enters the third series III. On the other hand, the second harmonic wave 2ω generated by the wavelength conversion optical element 34 and the fundamental wave ω transmitted through the wavelength conversion optical element 34 are reflected by the dichroic mirror 44 and superimposed on the fifth harmonic wave 5ω and incident on the third series III. To do.

  In the third series III, a wavelength conversion optical element 35 and a wavelength conversion optical element 36 are disposed. The wavelength conversion optical element 35 generates a sum frequency of the fifth polarized wave 5ω of p-polarized light incident from the first series I and the second harmonic wave 2ω of p-polarized light incident from the second series II, and the frequency is the fundamental wave. A 7th harmonic wave 7ω having a wavelength 7 times and 1/7 (221 nm) is generated. A CLBO crystal is preferably used for the wavelength conversion optical element 35 for generating the seventh harmonic wave.

  The 7th harmonic wave 7ω of s-polarized light generated by the wavelength conversion optical element 35 and the fundamental wave ω of s-polarized light incident from the second series II and transmitted through the wavelength conversion optical element 35 are incident on the wavelength conversion optical element 36. The sum frequency generation generates an eighth harmonic wave 8ω having a frequency eight times that of the fundamental wave and a wavelength of 1/8 (193 nm). A CLBO crystal is preferably used as the wavelength conversion optical element 36 for generating the eighth harmonic wave.

  Then, an ultraviolet laser beam Lv (eighth harmonic wave 8ω) having a wavelength of 193 nm generated by the wavelength conversion optical element 36 is output from the wavelength conversion unit 3.

In the laser apparatus LS exemplified in the present embodiment, a fundamental laser beam La having a high power level is emitted from the laser beam output unit 1, and the wavelength conversion optical elements 31 to 36 of the wavelength conversion unit 3 collect the light through a lens. The power density of the incident laser beam (in the case of pulsed light, the value obtained by dividing the peak power by the condensing cross-sectional area) is an extremely high value on the order of MW / cm ² .

  In the wavelength conversion optical element used at such a power level, damage is likely to occur in the propagation region of the laser beam through which the laser beam having a high power density is transmitted. When the damage occurs, the beam profile changes, the wavelength conversion efficiency decreases, etc. As a result, the output of the ultraviolet laser beam Lv can be reduced. On the other hand, with respect to the individual wavelength conversion optical elements provided in the wavelength conversion unit, the method of measuring and mapping the durability of each part in advance, and shifting the wavelength conversion optical element based on the map, requires a large amount of man-hours. In addition, the wavelength conversion optical element cannot be efficiently used.

  Therefore, in the laser device LS, the wavelength conversion unit 3 is provided with a damage detection device that detects that damage has occurred in the beam propagation region of the wavelength conversion optical element and outputs a detection signal. The damage detection devices 60 and 70 are configured to detect that damage has occurred in the beam propagation region of the wavelength conversion optical element by detecting a change in the state of light emitted from the wavelength conversion optical element. The damage detection device 60 is a damage detection device according to a first configuration described in detail later, and the damage detection device 70 is a damage detection device according to a second configuration.

  The “state of light emitted from the wavelength conversion optical element” refers to, for example, the beam profile of laser light emitted from the wavelength conversion optical element, the generation state of scattered light emitted from the wavelength conversion optical element, and the like. That is, when the damage detection devices 60 and 70 are damaged in the beam propagation region of the wavelength conversion optical element, the damage detection devices 60 and 70 are configured to detect a change in the state of light caused by the occurrence of the damage and output a detection signal. The

  The signals of the damage detection devices 60 and 70 are input to the control unit 8, and the control unit 8 executes a predetermined corresponding operation when the detection signals are input from the damage detection devices 60 and 70. As the corresponding operation, for example, an alarm operation for displaying that the wavelength conversion optical element is damaged on the control panel of the laser apparatus, or the wavelength conversion optical element where the damage is generated is moved by a predetermined amount by a crystal shift mechanism (not shown). Examples include a crystal shift operation for shifting the laser light incident on the wavelength conversion optical element so as to pass through a new area that is not damaged.

  FIG. 3 shows a schematic configuration diagram of the damage detection device 60 of the first configuration form, and FIG. 5 shows a schematic configuration diagram of the damage detection device 70 of the second configuration mode. Hereinafter, the damage detection device of each configuration mode will be described in detail. explain.

(First configuration form)
The damage detection device 60 according to the first configuration form has an increased state of the beam diameter when the beam diameter of the laser light emitted from the wavelength conversion optical element increases by a predetermined amount or more from the initial beam diameter when the wavelength conversion is started. And a detection signal (beam diameter increase detection signal) is output. In FIG. 3, the damage detection device 60 is composed of an aperture 61 provided on the optical path of the laser beam emitted from the wavelength conversion optical element 31 and a reflected light detector 65 for detecting the laser beam reflected by the aperture 61. The case where it comprises is illustrated.

  In the laser device LS of the present embodiment, the wavelength conversion optical element 31 is preferably a QPM crystal such as PPLN or PPLT. As described above, in the QPM crystal, when the power density of incident light is increased, optical damage is likely to occur due to the photorefractive effect. When optical damage occurs, the refractive index of the beam propagation region changes inside the crystal, and the beam profile of the output light changes accordingly.

  When light damage occurs in the wavelength conversion optical element 31, not only the wavelength conversion efficiency in the wavelength conversion optical element 31 is lowered but also the wavelength conversion optical elements 32, 33, and 35 in the subsequent stages due to the change in the beam profile. , 36 changes the focused spot position and the spot diameter, which causes a significant decrease in the output of the ultraviolet laser beam Lv.

  FIG. 4 schematically shows changes in the beam profile before and after optical damage occurs in the wavelength conversion optical element 31, and (a) in the initial state where wavelength conversion is started (before optical damage occurs). The beam profile of incoming / outgoing light and (b) the beam profile of incoming / outgoing light after optical damage has occurred are shown. In the figure of (b), the beam profile of the emitted light in the initial state is indicated by a two-dot chain line. As shown in the figure, when light damage occurs in the wavelength conversion optical element 31, the beam profile of the emitted light changes in the direction in which the beam diameter increases.

  The aperture 61 of the damage detection device 60 passes through the laser light before optical damage occurs (without significant reflection, diffraction, etc.) as it passes, and when the beam diameter increases due to optical damage, The outer peripheral portion is set so as to be applied to the opening edge portion (reflection or scattering occurs).

  Specifically, the aperture diameter of the aperture 61 is set to about 1.8 to 2.2 times the initial beam diameter at the position where the aperture 61 is disposed. For example, when the aperture diameter is twice the initial beam diameter, the outer periphery of the laser beam is applied to the aperture edge when the beam diameter of the emitted light emitted from the wavelength conversion optical element 31 slightly increases. Thus, the laser beam is reflected (scattered) and detected by the reflected light detector 65 before the beam diameter increases to 1.1 times the initial state. The reflected light detector 65 only needs to be able to detect light having a wavelength of at least one of the fundamental wave and the second harmonic wave emitted from the wavelength conversion optical element 31, for example, for light in the infrared to visible region. A photodiode having detection sensitivity can be used.

  The fact that the reflected light is detected by the reflected light detector 65 means that the beam diameter of the laser light emitted from the wavelength conversion optical element 31 has increased from the initial state, that is, light in the beam propagation region of the wavelength conversion optical element 31. Means that damage has occurred.

  Thus, in the damage detection device 60, when optical damage occurs in the QPM crystal represented by the wavelength conversion optical element 31, the state is immediately detected and a detection signal is output. Therefore, the wavelength conversion optical element 31 can be used without shifting until damage occurs in the beam propagation region in use. When the damage occurs, a detection signal is output from the reflected light detector 65, so that the wavelength conversion optical element 31 can be shifted immediately based on the detection signal. Therefore, the wavelength conversion optical element can be utilized to the maximum efficiency without requiring a great amount of man-hours for measuring and mapping the durability of each part of the crystal in advance.

  In the above, when the beam diameter of the laser light emitted from the wavelength conversion optical element has increased by a predetermined amount or more from the initial beam diameter, the aperture 61 and the reflection from the aperture 61 as an example of means for detecting the increased state. The configuration using the reflected light detector 65 that detects light is exemplified. However, the present technology is not limited to such a configuration example, and any configuration that can detect an increase state of the beam diameter of the laser light emitted from the wavelength conversion optical element may be used. For example, a slit having a predetermined opening width may be used instead of the aperture 61 having a predetermined opening diameter, or a reflecting needle or a scattering member may be arranged at a position spaced by a predetermined dimension from the optical axis of the emitted light. Further, a mirror, an optical fiber, or the like may be arranged at a position spaced by a predetermined dimension from the optical axis of the emitted light and guided to the reflected light detector 65.

(Second configuration form)
The damage detection apparatus 70 of the second configuration form is configured to detect the scattered light and output a detection signal (scattered light detection signal) when the scattered light is generated in the beam propagation region of the wavelength conversion optical element. The FIG. 5 illustrates a configuration in which a scattered light detector 75 that detects scattered light generated in the beam propagation region of the wavelength conversion optical element 33 is disposed in the vicinity of the wavelength conversion optical element 33.

  In the laser apparatus LS of the present embodiment, bulk crystals are used for the wavelength conversion optical elements 32 to 36. In a bulk crystal, when the power density of incident light increases due to impurities contained in the crystal growth stage or imperfection of the crystal structure, damage occurs in these defective portions. The wavelength converting optical element 33 for generating the fifth harmonic wave uses a BBO crystal. It has been empirically confirmed that this BBO crystal is easily damaged at a high power level.

  FIG. 6 schematically shows the generation state of scattered light before and after damage occurs in the wavelength conversion optical element 33, and (a) an initial state where wavelength conversion is started (before damage occurs); (B) shows a state after damage has occurred. As shown in the figure, when damage occurs in the wavelength conversion optical element 33, the laser light transmitted through the vicinity of the damaged portion is scattered and the scattered light is emitted to the surroundings. The exit direction and intensity distribution of the scattered light vary depending on the magnitude of the damage that has occurred and the wavelength of the transmitted laser light, but are generally emitted in a wide solid angle range centering on the damaged part.

  The scattered light detector 75 is disposed close to the wavelength conversion optical element 33 so that the scattered light emitted from the damaged portion is detected when damage occurs in the beam propagation region of the wavelength conversion optical element 33. The FIG. 6 shows a configuration example in which the scattered light detector 75 is arranged close to the exit surface side of the wavelength conversion optical element 33. The reflected light detector 75 only needs to be able to detect scattered light emitted from the wavelength conversion optical element 33.

  Specifically, the laser light transmitted through the wavelength conversion optical element 33 in this configuration is mainly a second harmonic, a third harmonic, and a fifth harmonic, and can detect light of at least one of these wavelengths. A simple photodetector can be used. At this time, since the second harmonic and the third harmonic are in the visible region, a photodiode having detection sensitivity with respect to light in the visible region can be used. Thereby, the damage detection apparatus 70 can be comprised simply and at low cost.

  As described above, in the damage detection apparatus 70, when a damage based on a crystal structure defect occurs in a bulk crystal or a QPM crystal represented by the wavelength conversion optical element 33, the state is immediately detected and a detection signal is output. . Therefore, the wavelength conversion optical element can be used without shifting until damage occurs in the beam propagation region in use. Further, when damage occurs, a detection signal is output from the reflected light detector 75, so that the wavelength conversion optical element can be immediately shifted based on the detection signal. Therefore, the wavelength conversion optical element can be utilized to the maximum efficiency without requiring a great amount of man-hours for measuring and mapping the durability of each part of the crystal in advance.

  In the embodiment, the case where the damage detection apparatus 70 is applied to the damage detection of the wavelength conversion optical element 33 is exemplified, but as is apparent from the above description, the damage detection apparatus 70 of this configuration form is a bulk crystal. Regardless of whether it is a QPM crystal, it is also applicable to damage detection of other wavelength conversion optical elements 31, 32, 34 to 36.

In the embodiment described above, the fundamental laser beam La output from the laser beam output unit 1 is divided into two by the polarization beam splitter 41 and is incident on the first and second series of the wavelength conversion unit 3. Illustrated. However, the specific configurations of the laser light output unit 1 and the wavelength conversion unit 3 can be appropriately polarized according to the application and function of the laser device. For example, the first and second fundamental laser beams La ₁ and La ₂ are emitted from the laser beam output unit 1 and directly incident on the first and second series of the wavelength conversion unit 3, or the laser beam First, second, and third fundamental laser beams La ₁ , La ₂ , and La ₃ are emitted from the output unit 1. The fifth harmonic generated in the first series and the second harmonic generated in the second series. , And the third fundamental laser beam La ₃ may be superimposed and incident on the third series. Furthermore, although the fundamental wavelength laser beam with a wavelength of 1.5 μm is incident on the wavelength conversion unit 3 and the wavelength conversion optical system 30 converts the wavelength to a wavelength of 193 nm, the wavelength and wavelength of the incident / exit light to the wavelength conversion unit 3 are exemplified. Various known forms can be applied to the specific configuration and the like of the conversion optical system 30.

  The laser device LS as described above is small and light and easy to handle, optical processing devices such as exposure devices and stereolithography devices, inspection devices such as photomasks and wafers, observation devices such as microscopes and telescopes, The present invention can be suitably applied to a measuring device such as a length measuring device or a shape measuring device, and a system such as a phototherapy device.

  As a first application example of a system including a laser device LS, an exposure apparatus used in a photolithography process for manufacturing a semiconductor or a liquid crystal panel will be described with reference to FIG. The exposure apparatus 100 is in principle the same as photolithography, and a device pattern precisely drawn on a quartz glass photomask 113 is applied to an exposure object 115 such as a semiconductor wafer or glass substrate coated with a photoresist. Optically project and transfer.

  The exposure apparatus 100 includes the laser apparatus LS, the illumination optical system 102, the mask support table 103 that holds the photomask 113, the projection optical system 104, and the exposure object support table 105 that holds the exposure object 115. And a driving mechanism 106 that moves the exposure object support table 105 in a horizontal plane. The illumination optical system 102 includes a plurality of lens groups, and irradiates the photomask 113 held on the mask support unit 103 with the laser light output from the laser device LS. The projection optical system 104 is also composed of a plurality of lens groups, and projects the light transmitted through the photomask 113 onto the exposure object 115 on the exposure object support table.

  In the exposure apparatus 100 having such a configuration, the laser light output from the laser apparatus LS is input to the illumination optical system 102, and the laser light adjusted to a predetermined light flux is applied to the photomask 113 held on the mask support 103. Irradiated. The light that has passed through the photomask 113 has an image of a device pattern drawn on the photomask 113, and this light of the exposure object 115 held on the exposure object support table 105 via the projection optical system 104. A predetermined position is irradiated. As a result, the image of the device pattern on the photomask 113 is image-exposed at a predetermined magnification on the exposure object 115 such as a semiconductor wafer or a liquid crystal panel.

  According to such an exposure apparatus 100, every time the wavelength conversion optical element is replaced in the laser apparatus LS, it does not require a great number of man-hours, and each wavelength conversion optical element can be used to the maximum efficiency. Thus, an exposure apparatus capable of efficient operation can be provided.

  Next, as a second application example of the system including the laser device LS, FIG. 8 showing a schematic configuration of an inspection device used in an inspection process of a photomask, a liquid crystal panel, a wafer, or the like (test object). The description will be given with reference. An inspection apparatus 200 illustrated in FIG. 8 is suitably used for inspecting a fine device pattern drawn on a light-transmitting object 213 such as a photomask.

  The inspection apparatus 200 includes a laser device LS, an illumination optical system 202, a test object support table 203 that holds the test object 213, a projection optical system 204, and a TDI that detects light from the test object 213. (Time Delay and Integration) A sensor 215 and a drive mechanism 206 that moves the object support base 203 in a horizontal plane are configured. The illumination optical system 202 includes a plurality of lens groups, and adjusts the laser beam output from the laser device LS to a predetermined light flux and irradiates the test object 213 held by the test object support unit 203. The projection optical system 204 is also composed of a plurality of lens groups, and projects the light transmitted through the test object 213 onto the TDI sensor 215.

  In the inspection apparatus 200 having such a configuration, a laser beam output from the laser apparatus LS is input to the illumination optical system 202, and a laser beam adjusted to a predetermined light flux is held on the object support table 203. The test object 213 such as is irradiated. The light from the object 213 (transmitted light in this configuration example) has an image of a device pattern drawn on the object 213, and this light is transmitted to the TDI sensor 215 via the projection optical system 204. Projected and imaged. At this time, the horizontal movement speed of the test object support table 203 by the drive mechanism 206 and the transfer clock of the TDI sensor 215 are controlled in synchronization.

  Therefore, an image of the device pattern of the test object 213 is detected by the TDI sensor 215, and by comparing the detection image of the test object 213 detected in this way with a predetermined reference image set in advance, The defect of the fine pattern drawn on the test object is extracted.

  According to such an inspection apparatus 200, each time the wavelength conversion optical element is exchanged in the laser device LS, it does not require a large number of man-hours, and each wavelength conversion optical element can be used as efficiently as possible. Thus, it is possible to provide an inspection apparatus that enables efficient operation. In the case where the test object 213 does not have optical transparency like a wafer or the like, the reflected light from the test object is incident on the projection optical system 204 and guided to the TDI sensor 215 in the same manner. can do.

LS laser device La fundamental wave laser beam Lv ultraviolet laser beam 1 laser beam output unit 3 wavelength conversion unit 10 laser beam generation unit 20 amplification unit 30 wavelength conversion optical system 31 to 36 wavelength conversion optical element (31 pseudo phase matching type wavelength conversion Optical crystal)
60 Damage detection apparatus (damage detection means) of the first configuration form
61 Aperture (opening)
65 Reflected light detector 70 Damage detection device (damage detection means) of the second configuration form
75 Scattered light detector 100 Exposure apparatus 102 Illumination optical system 103 Mask support base 104 Projection optical system 105 Exposure object support table 113 Photomask 115 Exposure object 200 Inspection apparatus 202 Illumination optical system 203 Test object support stage 204 Projection optical system 213 Test object 215 TDI sensor (detector)

Claims (7)

A laser beam output unit that outputs a laser beam, and a wavelength conversion unit that wavelength-converts and outputs the laser beam output from the laser beam output unit,
In the wavelength converter,
A wavelength conversion optical element that converts the wavelength of the incident laser light and emits it;
Damage detection that detects the occurrence of damage in the beam propagation region of the laser light that passes through the wavelength conversion optical element and outputs a detection signal by detecting a change in the state of light emitted from the wavelength conversion optical element And a laser device. The damage detection means includes
When the beam diameter of the laser beam emitted from the wavelength conversion optical element is increased from the initial beam diameter when the wavelength conversion is started, the increase state of the beam diameter is detected and the detection signal is output. The laser device according to claim 1, wherein the laser device is configured. The damage detection means includes
The laser apparatus according to claim 1, wherein when the scattered light is generated in the beam propagation region, the scattered light is detected and the detection signal is output. The damage detection means includes
An opening set so that the laser light emitted from the wavelength conversion optical element in the initial state passes through as it is and the outer periphery of the laser light emitted from the wavelength conversion optical element is applied in the increased beam diameter state; ,
The laser apparatus according to claim 2, further comprising a reflected light detector that detects laser light emitted from the wavelength conversion optical element and reflected by the opening.   5. The laser device according to claim 2, wherein the wavelength conversion optical element is a quasi phase matching type wavelength conversion optical crystal. A laser device according to any one of claims 1 to 5;
A mask support for holding a photomask on which a predetermined exposure pattern is formed;
An exposure object support for holding the exposure object;
An illumination optical system for irradiating the photomask held by the mask support with the laser beam output from the laser device;
An exposure apparatus comprising: a projection optical system that projects light transmitted through the photomask onto an exposure target held by an exposure target support. A laser device according to any one of claims 1 to 5;
An object support for holding the object;
An illumination optical system for irradiating a test object held by the test object support unit with laser light output from the laser device;
An inspection apparatus comprising: a detector that detects light from the test object.

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