JP2011059324A - Wavelength conversion device, laser device, and wavelength conversion method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wavelength conversion device, a laser device and a wavelength conversion method that can perform wavelength conversion by a wavelength conversion optical element having deliquescent property with high conversion efficiency in a long-term stable manner with a simple configuration. <P>SOLUTION: The wavelength conversion device has a heater 52 that heats the wavelength conversion optical element having deliquescent property, a temperature sensor 53 that detects temperature of the wavelength conversion optical element, a temperature controlling section 82 that controls driving of the heater 52 based on the temperature detected by the temperature sensor 53 and adjusts the temperature of the wavelength conversion optical element so as to be maintained within a predetermined temperature range, and a shift mechanism that shifts a position at which a light is received at the wavelength conversion optical element with a predetermined degree, and, when the position at which the light is received at the wavelength conversion optical element is shifted, the temperature controlling section 82 controls the driving of the heater 52 so that the temperature of the wavelength conversion optical element becomes an optimum temperature where output intensity of a laser light whose wavelength is converted within the predetermined temperature range becomes a maximum. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a wavelength conversion device, a laser device, and a wavelength conversion method for wavelength-converting an input fundamental wave laser beam and outputting it as a harmonic laser beam using a wavelength conversion optical element having deliquescence.

  A laser apparatus that includes the wavelength conversion apparatus as described above and outputs ultraviolet light includes, for example, an exposure apparatus that forms a fine structure in a semiconductor device, various optical inspection apparatuses that observe the fine structure, and a laser used for ophthalmic treatment. It is used as a light source for therapeutic devices, for example, laser light in the infrared wavelength region generated by a semiconductor laser and amplified by an optical amplifier is sequentially wavelength-converted in a wavelength conversion device having a plurality of wavelength conversion elements, and finally In particular, a configuration is known in which ultraviolet light having the same wavelength λ = 193 nm as the oscillation wavelength of an ArF excimer laser is output (see, for example, Patent Document 1).

  There are various configurations of wavelength conversion devices, specifically, types and combinations of wavelength conversion optical elements used in the wavelength conversion device, but nonlinear optical crystals mainly used as wavelength conversion optical elements have angle dependency. In order to perform wavelength conversion with high efficiency, it is necessary to precisely adjust the incident angle of the laser light incident on the wavelength conversion optical element to achieve phase matching (see, for example, Patent Document 2). . In this angle phase matching, laser light is incident at an angle (phase matching angle) at which the conversion efficiency is highest within a predetermined allowable angle with respect to the optical axis of the wavelength conversion optical element, so that desired phase matching conditions are obtained. Can be satisfied.

Further, when using a nonlinear optical crystal having deliquescence such as CsLiB ₆ O ₁₀ (CLBO) crystal as a wavelength conversion optical element, it is necessary to prevent moisture absorption contained in the atmosphere, for example, nitrogen gas or the like It is required to maintain a temperature rise state heated to about 150 ° C. in a case filled with an inert gas (see, for example, Patent Document 3). Therefore, in such a wavelength conversion device using the wavelength conversion optical element, a heater for heating the wavelength conversion optical element used in a temperature rising state, a temperature sensor for detecting the element temperature, and the like are provided, and are always within a predetermined temperature range. It is configured to be held in a heated state.

JP 2000-200747 A JP 2002-90787 A JP 2001-51311 A

  The wavelength conversion optical element as described above has a lifetime according to the wavelength and power of the input laser beam. If the wavelength conversion optical element is used at the same light receiving position for a long time, the crystal is damaged and wavelength conversion is performed. Efficiency may be reduced. Therefore, in order to stably obtain high-quality ultraviolet light output, the light receiving position of the laser beam in the wavelength conversion optical element is shifted every predetermined time that becomes the use limit, and light is periodically passed through the crystal. It is necessary to change the route.

  Here, the phase matching condition is specific to the refractive index of the wavelength conversion optical element. If there is almost no change in the refractive index for each light receiving position in the wavelength conversion optical element, the phase matching condition is determined at each light receiving position. The phase matching condition does not change. However, when a wavelength conversion optical element having deliquescence such as the above-mentioned CLBO crystal is used, if a temperature distribution is generated in the crystal heated by the heater, the wavelength conversion optics is caused by the temperature dependence of the refractive index. The phase matching condition collapses for each light receiving position of the element (the phase matching angle changes), and an actuator for angle adjustment is required to restore the phase matching condition for each light receiving position. However, even if an angle adjustment actuator is used, if the wavelength conversion optical element is held in a substantially sealed case considering deliquescent properties, the angle adjustment mechanism itself and its control become complicated. There is.

  The present invention has been made in view of such a problem, and has a wavelength that can stably perform wavelength conversion by a wavelength conversion optical element having deliquescent properties for a long period of time with a high conversion efficiency with a simple configuration. An object is to provide a conversion device, a laser device, and a wavelength conversion method.

  According to the first aspect illustrating the present invention, the wavelength conversion optical element having deliquescence is used in a temperature-raised state heated within a predetermined temperature range, and the input fundamental wave laser light is wavelength-converted to generate a harmonic. A wavelength conversion device that outputs laser light, a heater that heats the wavelength conversion optical element, a temperature detection unit that detects the temperature of the wavelength conversion optical element, and a heater control based on the temperature detected by the temperature detection unit And a temperature control unit that adjusts the temperature of the wavelength conversion optical element to be maintained within a predetermined temperature range, and a shift mechanism that shifts the light receiving position of the wavelength conversion optical element by a predetermined amount. When the light receiving position is shifted, the temperature control unit drives the heater so that the temperature of the wavelength conversion optical element becomes the optimum temperature at which the output intensity of the laser light whose wavelength is converted within the predetermined temperature range becomes maximum. Wavelength conversion apparatus characterized by being configured to control is provided. The predetermined temperature range is preferably set in a temperature range in which the wavelength conversion optical element does not reach deliquescence. In addition, a holder for holding the wavelength conversion optical element, a heater, and a temperature detection unit are accommodated in a case filled with an inert gas to form an element unit, and an input laser beam is introduced into the case. A configuration in which an entrance and an exit for deriving wavelength-converted laser light are formed as an opening is also a preferable aspect.

  According to the second aspect illustrating the present invention, the fundamental wave laser beam emitted from the laser beam generator is provided with the laser beam generator that emits the fundamental wave laser beam and the wavelength converter configured as described above. A laser device is provided that is configured to be converted into a harmonic laser beam and output by a conversion device. A configuration that further includes an optical amplifier that optically amplifies the fundamental laser beam generated from the laser beam generator and outputs the amplified laser beam to the wavelength converter is also a preferable aspect.

  According to the third aspect exemplifying the present invention, a wavelength conversion optical element having deliquescent properties is used in a heated state heated within a predetermined temperature range, and the input fundamental wave laser light is wavelength-converted to generate a harmonic. A wavelength conversion method for outputting as laser light, the step of shifting the light receiving position of the wavelength conversion element, and the laser light wavelength converted by the wavelength conversion optical element within a predetermined temperature range each time the light receiving position is shifted. The step of calculating the optimum temperature of the wavelength conversion optical element that maximizes the output intensity, and the step of controlling the driving of the heater so that the wavelength conversion optical element is maintained at the optimum temperature, A wavelength conversion method is provided.

  According to the present invention, with a simple configuration, wavelength conversion by a wavelength conversion optical element having deliquescence can always be stably performed with high efficiency. Therefore, it is possible to provide a wavelength conversion device, a laser device, and a wavelength conversion method that can be used stably over a long period of time while suppressing a change in output intensity of laser light with time.

It is a schematic block diagram of the laser apparatus which concerns on 1st Embodiment shown as an example of application of this invention. It is a schematic block diagram of the laser head in the said laser apparatus. It is a schematic block diagram of the wavelength conversion part in the said laser apparatus. It is a front sectional view of a crystal unit in the laser device. It is a general | schematic block diagram of the control unit in the said laser apparatus. It is a flowchart which shows the wavelength conversion method in the said laser apparatus. It is a graph which shows the fluctuation | variation of the output intensity with respect to the crystal temperature of the wavelength conversion optical element which has the deliquescence property in the said laser apparatus. It is a schematic block diagram of the laser apparatus concerning 2nd Embodiment. It is a general | schematic block diagram of the control unit of 2nd Embodiment. It is a schematic block diagram of the laser apparatus concerning 3rd Embodiment. It is a general | schematic block diagram of the control unit of 3rd Embodiment.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. As a representative example of a laser apparatus provided with a wavelength conversion apparatus to which the present invention is applied, a schematic configuration of the laser apparatus 1 according to the first embodiment used as a light source apparatus of an exposure apparatus that transfers a reticle pattern to a substrate is illustrated. 1 and a schematic configuration of the laser head 2 in the laser device 1 are shown in FIG. 2. First, the laser device 1 will be outlined with reference to these drawings.

  For convenience in application to a laser system that uses this device as a light source device, the laser device 1 has a small box-shaped laser head 2 that has an output function of outputting ultraviolet light and that is easily incorporated into the laser system. The laser head 2 is provided with a control rack 3 which is provided separately from the laser head 2 and has a control function. The laser head 2 and the control rack 3 are connected to various electric cables and light for pumping light transmission. It is configured to be interconnected by an interface 4 such as a fiber, a purge gas supply gas tube, and a cooling water pipe.

  The laser head 2 includes a laser beam generator 10 that emits fundamental laser light in the infrared to visible region, and a wavelength converter 20 that converts the wavelength of the fundamental laser beam emitted from the laser beam generator 10 into ultraviolet light. It is comprised so that ultraviolet light may be output from the output end.

  The laser light generation unit 10 includes a laser light source 11 that generates laser light (seed light) Ls that serves as seed light, and optical amplifiers 12 and 13 that amplify the seed light Ls generated by the laser light source 11. The As the laser light source 11 and the optical amplifiers 12 and 13, those having an appropriate oscillation wavelength and amplification factor are used according to the application and function of the laser system using the laser device 1. As such a laser light source 11, a distributed feedback semiconductor laser (DFB semiconductor laser) that generates laser light having a single wavelength with a wavelength λ = 1.547 [μm] is used, and a semiconductor laser is used as the first-stage optical amplifier 12. As the pumping erbium (Er) -doped fiber optical amplifier (EDFA) and the second stage optical amplifier 13, a configuration using a Raman laser pumped EDFA is exemplified.

  The wavelength conversion unit 20 converts the wavelength of the laser light (fundamental laser light amplified by the optical amplifiers 12 and 13) Lr emitted from the laser light generation unit 10 into ultraviolet light having a predetermined wavelength. In the laser apparatus 1, the fundamental wave laser light having the wavelength λ = 1.547 [μm] emitted from the laser light generation unit 10 is sequentially wavelength-converted by a plurality of wavelength conversion optical elements, and finally the fundamental wave 8 is obtained. Ultraviolet light having a wavelength λ = 193 [nm], which is the same wavelength as that of the ArF excimer laser, is output as a harmonic (eighth harmonic).

As described above, there are various known forms of the configuration (type and combination of wavelength conversion optical elements) of the wavelength conversion unit that converts the wavelength of the fundamental laser beam in the infrared region (or visible region) into ultraviolet light. The present invention can be applied to any form of wavelength conversion unit as long as it includes a wavelength conversion optical element having deliquescence that is used in a heated state heated to a predetermined temperature by a heater. In the present embodiment, as an example of the wavelength conversion unit, the laser beam generation unit 10 divides the fundamental laser beam emitted from one laser light source 11 into three and amplifies it by two stages of optical amplifiers 12 and 13. Then, the three amplified fundamental laser beams Lr (Lr ₁ , Lr ₂ , Lr ₃ ) are made incident on the wavelength converter 20, and the fundamental wave, the second harmonic (λ = 774 [nm]), and the fifth harmonic FIG. 3 shows a configuration example in which (λ = 309 [nm]) is generated and 7th harmonic (λ = 221 [nm]) and 8th harmonic (λ = 193 [nm]) are generated by generating these sum frequencies. The configuration of the wavelength conversion unit using CLBO (CsLiB ₆ O ₁₀ ) crystal having deliquescence for the wavelength conversion optical element for generating the seventh harmonic wave and the wavelength conversion optical element for generating the eighth harmonic wave is shown. explain.

First, the first fundamental wave laser light Lr ₁ incident as P-polarized light is incident condensing the optical wavelength conversion element 21 by the lens 31, the frequency by second harmonic generation (SHG) is a fundamental wave (omega) A double wave of twice (2ω) and half the wavelength λ is generated. The double wave of the P-polarized light generated by the wavelength conversion optical element 21 and the fundamental wave of the P-polarized light transmitted through the wavelength conversion optical element 21 are condensed and incident on the wavelength conversion optical element 22 by the lens 32 to generate a sum frequency ( (ω + 2ω) generates a harmonic whose frequency is three times the fundamental wave (3ω). In these wavelength conversion optical elements 21 and 22, for example, a PPLN crystal is used as the wavelength conversion optical element 21 for generating the second harmonic wave, and an LBO crystal is used as the wavelength conversion optical element 22 for generating the third harmonic wave. In addition, as the wavelength conversion optical element 21, a PPKTP crystal, a PPSLT crystal, an LBO crystal, or the like can be used.

  The third harmonic wave of the S-polarized light generated by the wavelength conversion optical element 22 and the fundamental wave and the second harmonic wave of the P-polarized light transmitted through the wavelength conversion optical element 22 are transmitted through the two-wavelength wavelength plate 41 and only the second harmonic wave is transmitted. Convert to S-polarized light. As the two-wavelength wave plate 41, for example, a wave plate made of a uniaxial crystal flat plate cut in parallel with the optical axis of the crystal is used. The wavelength plate 41 rotates the polarization with respect to light of one wavelength (second harmonic), and the thickness of the wavelength plate (crystal) so that the polarization does not rotate with respect to light of the other wavelength. The light of one wavelength is cut by an integral multiple of λ / 2, and the light of the other wavelength is cut by an integral multiple of λ.

  The second and third harmonics, both of which are S-polarized light, are condensed and incident on the wavelength conversion optical element 23 by the lens 33, and a fifth harmonic (5ω) is generated by sum frequency generation (2ω + 3ω). From the wavelength conversion optical element 23, the fifth harmonic of the P-polarized light generated by the wavelength conversion optical element 23, the second and third harmonics of the S-polarized light transmitted through the wavelength conversion optical element 23, and the basics of the P-polarization A wave is emitted. For example, an LBO crystal is used as the wavelength conversion optical element 23 for generating the fifth harmonic wave, but a BBO crystal or a CBO crystal can also be used. Here, the fifth harmonic wave emitted from the wavelength conversion optical element 23 has an elliptical cross section for walk-off. Accordingly, the elliptical cross-sectional shape is shaped into a circle by the two cylindrical lenses 34v and 34h, and is incident on the dichroic mirror 44.

  On the other hand, the second fundamental laser beam Lr2 incident as P-polarized light is condensed and incident on the wavelength conversion optical element 24 by the lens 35, and a second harmonic is generated by the second harmonic generation. From the wavelength conversion optical element 24, a double wave and a fundamental wave of the P-polarized light generated by the wavelength conversion optical element 24 are emitted and incident on the dichroic mirror 45 through the lenses 36 and 37. As the wavelength conversion optical element 24, a PPLN crystal can be used, and a PPKTP crystal, a PPSLT crystal, an LBO crystal, or the like may be used.

The third fundamental laser beam Lr ₃ incident as S-polarized light is incident on the dichroic mirror 45 via the lens 38. The dichroic mirror 45 is configured to transmit light in the fundamental wavelength band and reflect light in the second wavelength band. The dichroic mirror 45 is incident on the dichroic mirror 45 and is converted into a wavelength converter. The P-polarized second harmonic generated by the optical element 24 is synthesized on the same axis.

  The combined fundamental wave of S-polarized light and second harmonic wave of P-polarized light are incident on the dichroic mirror 44. The dichroic mirror 44 is configured to transmit light of the fundamental wave and the second harmonic waveband and reflect light of the fifth harmonic waveband, and the S-polarized fundamental wave incident on the dichroic mirror 44. And the 2nd harmonic of P-polarized light and the 5th harmonic of P-polarized light generated by the wavelength converting optical element 23 are combined on the same axis.

  The fundamental wave of S-polarized light, the second harmonic of P-polarized light, and the fifth harmonic of P-polarized light thus combined on the same axis are made incident on the wavelength conversion optical element 25. Here, lenses (34v, 34h, 36, 37, 38) are provided in the optical paths of the fundamental wave, the second harmonic wave, and the fifth harmonic wave, respectively, and the light of each wavelength synthesized on the same axis is wavelength-converted. The light is focused and incident on the optical element 25. In the wavelength conversion optical element 25, sum frequency generation (2ω + 5ω) is performed by the 2nd harmonic of P-polarized light and the 5th harmonic of P-polarized light, and a 7th harmonic (7ω) is generated. From the wavelength conversion optical element 25, the light of each wavelength transmitted through the wavelength conversion optical element 23 is emitted together with the seventh harmonic wave of the S-polarized light generated by the wavelength conversion optical element 25. A CLBO crystal is used as the wavelength conversion optical element 25 that generates the seventh harmonic wave.

  These lights enter the wavelength conversion optical element 26, where the S-polarized fundamental wave and the S-polarized 7th harmonic are combined by sum frequency generation (ω + 7ω) to generate the P-polarized 8th harmonic (8ω). Is done. A CLBO crystal is used as the wavelength conversion optical element 26 that generates the eighth harmonic wave. The wavelength conversion optical element 26 emits light of other wavelength components such as a fundamental wave and a second harmonic wave transmitted through the wavelength conversion optical element 26 in addition to the eighth harmonic wave generated by the wavelength conversion optical element 26. However, when only the 8th harmonic wave is output from the wavelength conversion unit 20 (laser device 1), these may be separated by using a dichroic mirror, a polarization beam splitter, and a prism.

  Further, in the wavelength conversion unit 20, a part of the eighth harmonic wave emitted from the wavelength conversion optical element 26 is reflected by the beam splitter 46, and the output intensity of the ultraviolet laser light (193 [nm]) from the laser device 1 is increased. Guided to a photodetector 47 for monitoring. The photodetector 47 detects the output intensity of the received eighth harmonic wave and outputs the detection signal to the control rack 3.

  In the wavelength conversion unit 20 configured as described above, the wavelength conversion optical element 25 for generating the seventh harmonic wave and the wavelength conversion optical element 26 for generating the eighth harmonic wave are both CLBO crystals and have deliquescence. is doing. Therefore, for these wavelength conversion optical elements 25 and 26, in a case filled with an inert gas such as nitrogen gas, a predetermined temperature range preset by a heater (for example, a temperature range of 150 ± 10 ° C. is illustrated) It is necessary to maintain the heated temperature. In addition, these wavelength conversion optical elements 25 and 26 are easily damaged by long-time use (especially CLBO crystals are easily damaged) and may reduce wavelength conversion efficiency. Therefore, it is necessary to periodically change (shift) the light receiving position of the laser light in the wavelength conversion optical elements 25 and 26 to change the light passage path in these crystals. For this reason, the wavelength conversion unit 20 stably maintains the temperature rising state within such a predetermined temperature range and periodically increases the temperature conversion optical elements 25 and 26 in order to change the light receiving position of the laser light. In addition, a crystal unit 50 that is movably held is formed.

  Now, the configuration of the crystal unit 50 will be described with additional reference to FIG. In the following description regarding FIG. 4, the top, bottom, left, and right directions of the paper surface are referred to as the top, bottom, left, and right directions as they are, and the direction perpendicular to the paper surface is referred to as the front and back direction. The light travels in the front-rear direction, and the optical axis is set to extend in the front-rear direction. Therefore, FIG. 4 shows a cross-sectional view when the crystal unit 50 is cut in a plane orthogonal to the optical axis.

  The crystal unit 50 includes a crystal holder 51 that holds the wavelength conversion optical elements 25 and 26 (hereinafter collectively referred to as a wavelength conversion optical element 27), and a biaxial direction (vertical and vertical) of the crystal holder 51 that is orthogonal to the optical axis. And a rectangular box-shaped unit case 70 that accommodates them, and the wavelength conversion optical element 27 has an incident angle on the optical axis of the wavelength conversion unit 20. It is arranged in a state of being positioned so as to have a phase matching angle (incident angle satisfying phase matching conditions).

  The crystal holder 51 is formed in a substantially rectangular parallelepiped shape using a metal material, and the wavelength converting optical element 27 is embedded in a state where the entire outer periphery excluding the incident surface and the emitting surface of the laser light in the wavelength converting optical element 27 is embedded. Wearing. The crystal holder 51 is provided with a heater 52 for heating the wavelength conversion optical element 27 and a temperature sensor 53 for detecting the temperature of the wavelength conversion optical element 27, and a control unit described later provided in the control rack 3. 80, the wavelength conversion optical element 27 is held within the predetermined temperature range of about 150 ° C. set in advance.

  The shift mechanism 60 includes a horizontal base 61 and a first stage provided on the base 61 so as to be movable in the X direction on a rail (not shown) provided in the horizontal direction (X direction). 62, a vertical frame 63 provided so as to extend from the first stage 62 in the vertical direction (Z direction), a second stage 64 provided movably in the Z direction along the vertical frame 63, and a second stage 64 A two-stage support frame 65 that is fixed to the stage 64 and is L-shaped in front view.

  A first electric motor M1 is provided in the first stage 62, and the first stage 62 is moved in the X direction along the rail by rotating it based on a drive signal input from the control unit 80. Can be moved. Further, a second electric motor M2 is provided in the second stage 64, and the second stage 64 is moved along the vertical frame by rotating the second electric motor M2 based on a drive signal input from the control unit 80. Can be moved in the direction. For this reason, the crystal holder 51 attached to the shift mechanism 60 via the support frame 65 can be arbitrarily combined in the two axial directions (vertical and horizontal directions) perpendicular to the optical axis by combining the rotational operations of the electric motors M1 and M2. It is possible to move to the position.

  The shift mechanism 60 is provided with a position detector 66 (see FIG. 5) that detects the coordinates of the crystal holder 51 (wavelength conversion optical element 27) and outputs a signal representing the coordinate values to the control unit 80. Yes. The position detector 66 includes an X-axis encoder and a Z-axis encoder that detect the positions of the crystal holder 51 (wavelength conversion optical element 27) in the X-axis and Z-axis directions, respectively.

  The unit case 70 has an entrance 71 for introducing laser light (coaxially synthesized fundamental wave, second harmonic wave, and fifth harmonic wave) into the crystal unit 50 on the front side thereof (see FIG. 3). An exit port 72 (see FIG. 3) for deriving the ultraviolet laser light Lv wavelength-converted by the wavelength conversion optical element 27 is provided on the rear surface side.

At the top of the unit case 70, a heater 52 for heating the wavelength conversion optical element 27, a temperature sensor 53 for detecting the crystal temperature, an electrical connector 73 for inputting / outputting control signals to the electric motors M1, M2, etc. are provided. A gas connector 74 is provided for blocking contact with the atmosphere and always maintaining the wavelength conversion optical element 27 in a dry state. The laser head 2 is provided with an electric cable 75 having a connector detachable from the electric connector 73 and a gas tube 76 having a connector detachable from the gas connector 74, and the electric cable 75 and the gas tube passing through the interface 4 are provided. The control signal and the N ₂ gas are supplied from the control rack 3 side through 76.

In the control rack 3, the operation of each part constituting the laser device 1 is comprehensively controlled to control the emission of the ultraviolet laser light Lv by the laser head 2, and the crystal unit 50 connected by the gas connector 74. In addition, a gas supply unit 90 that supplies N ₂ gas to each unit of the laser device 1, an excitation light source unit (not shown) that excites the optical amplifiers 12 and 13, and the like are provided (see FIG. 1).

  In such a configuration, the wavelength conversion optical element 27 is installed on the optical axis of the wavelength conversion unit 20 so that the incident angle becomes the phase matching angle as described above. Occurs, due to the temperature dependence of the refractive index, the phase matching condition that has been maintained up to that point is changed (shifting the phase matching angle) as the light receiving position of the laser beam is changed (shifted). There is a problem that the wavelength conversion efficiency of the laser light in the wavelength conversion optical element 27 is lowered. At this time, an actuator for adjusting the angle is required in the configuration in which the angle phase matching is performed by adjusting the angle of the wavelength conversion optical element 27 (the angle formed by the laser optical axis and the crystal optical axis) each time the light receiving position is shifted. As a result, the overall size of the laser device is increased, and when the angle adjusting actuator is provided in the case considering deliquescent properties, the angle converting mechanism itself and its control are complicated.

  Therefore, in the control unit 80 of the laser apparatus 1, when the light receiving position of the wavelength conversion optical element 27 is shifted, even when the phase matching condition is lost due to the change in the refractive index due to the temperature distribution in the wavelength conversion optical element 27. Rather than performing angle phase matching using an angle adjusting actuator, the temperature of the wavelength conversion optical element 27 is within a temperature range that does not deviate from a predetermined temperature range set from the viewpoint of preventing deterioration due to deliquescent. It has a temperature control function for setting the optimum temperature to match the phase matching condition that maximizes the wavelength conversion efficiency.

  A block diagram showing a schematic configuration of the control unit 80 is shown in FIG. The control unit 80 includes, for example, a so-called microcomputer including a CPU (Central Processing Unit), a ROM (Read On Memory), a RAM (Random Access Memory), and the like. The drive control unit 81 that controls the drive of the electric motors M1 and M2 of the stages 62 and 64 to shift the light receiving position of the laser beam in the wavelength conversion optical element 27, and the wavelength conversion optical element 27 satisfies the phase matching condition. And a temperature control unit 82 for controlling the driving of the heater 52 so as to achieve a predetermined optimum temperature.

  In the drive control unit 81, a recommended shift time of each light receiving position in the wavelength conversion optical element 27 is set in advance in a memory in the control unit, and the use time used for wavelength conversion at the currently used light receiving position is a laser. As the apparatus 1 is operated, it is sequentially accumulated and stored. When the usage time of the light receiving position is about to reach the recommended shift time, the drive control unit 81 drives and controls the stages 62 and 64 of the shift mechanism 60 to move the crystal holder 51 by a preset shift amount. To shift the light receiving position of the laser beam. The drive control unit 81 detects the position of the wavelength conversion optical element 27 (light receiving position of the laser beam) based on the detection signal from the position detection unit (linear encoder) 66 in each stage 62 and 64.

  The temperature controller 82 drives the heater to drive the temperature of the wavelength conversion optical element 27 (the temperature detected by the temperature sensor 53) each time the laser light receiving position of the wavelength conversion optical element 27 is shifted over time. The output intensity of the laser beam is monitored by the photodetector 47 while changing within a predetermined temperature range, the detection temperature (optimum temperature) at which the output value of the photodetector 47 is maximum is found, and the wavelength conversion optical element 27 is The energization to the heater 52 is controlled (feedback control) so that the optimum temperature is maintained.

  As described above, the temperature control unit 82 satisfies the phase matching condition with the refractive index change caused by the temperature distribution of the wavelength conversion optical element 27 every time the light receiving position of the laser light in the wavelength conversion optical element 27 is changed. Even if it disappears, in order to restore the phase matching condition at the light receiving position, temperature control of the wavelength conversion optical element 27 is performed so that the output intensity of the laser light is always maximized regardless of the light receiving position.

  The wavelength conversion device included in the laser device 1 means a device including the wavelength conversion unit 20 and the control unit 80.

  Next, the wavelength conversion apparatus configured as described above and the wavelength conversion method in the laser apparatus 1 including the wavelength conversion apparatus will be described with additional reference to the flowchart shown in FIG.

  In step S101, the drive control unit 81 of the control unit 80 sets the actual use time used for wavelength conversion for the light receiving position currently in use in the wavelength conversion optical element 27 to a predetermined recommended shift time (for example, 10 hours). When reaching, the stages 62 and 64 of the shift mechanism 60 are driven to move the wavelength conversion optical element 27 by a predetermined shift amount, and the light receiving position of the laser beam in the wavelength conversion optical element 27 is changed. Here, as the predetermined shift amount, for example, 100 [μm] which is the same value as the beam diameter is exemplified.

  In step S102, the temperature control unit 82 drives and controls the heater 52 via an SSR (solid state relay) or the like, and changes the temperature detected by the temperature conversion optical element 27 by the temperature sensor 53 within a predetermined temperature range. In addition, the output intensity of the laser beam corresponding to each detection temperature is monitored by the photodetector 47, and the relationship between the crystal temperature of the wavelength conversion optical element 27 at the light receiving position and the output intensity of the laser beam is acquired. As exemplified above, the predetermined temperature range is a temperature range in which moisture adsorbed on the crystal surface can be released from the viewpoint of preventing deterioration due to deliquescence (for example, ± 10 ° C. with respect to a set temperature of 150 ° C. 140 [deg.] C. to 160 [deg.] C.), whereby the phase matching can be adjusted in a low dehumidification environment in which the wavelength conversion optical element 27 can be stably held.

  In step S103, the temperature control unit 82 obtains an optimum temperature at which the output intensity of the laser beam detected by the photodetector 47 is maximized (maximum) within the predetermined temperature range. Here, the relationship between the crystal temperature (relative value) of the wavelength conversion optical element 27 and the output intensity (relative value) of the laser light obtained in the previous step S102 is shown in FIG. 7, and in this step S103, The optimum temperature when the output intensity of the laser beam appears as a peak (maximum) can be obtained. Depending on the temperature distribution generated in the wavelength conversion optical element 27, the optimum temperature may be obtained as the same temperature at adjacent light receiving positions or as a different temperature.

  In step S104, the temperature control unit 82 adjusts the crystal temperature of the wavelength conversion optical element 27 to the optimum temperature obtained in step S103 (the output intensity of the laser beam is maximized). Specifically, the temperature control unit 82 calculates a temperature deviation (temperature deviation = optimum temperature−detected temperature) based on the optimum temperature obtained in step S103 and the detected temperature (actual temperature) from the temperature sensor 53. Then, a drive signal corresponding to the temperature deviation is output, and feedback control is performed by switching on / off the energization of the heater 52 so that the wavelength conversion optical element 27 becomes the optimum temperature (maintained at the optimum temperature). I do. Thereby, the wavelength conversion optical element 27 is maintained at the optimum temperature at which the output intensity of the laser beam is maximized.

  In step S105, the drive control unit 81 obtains the remaining usable time by subtracting the actual use time of the light receiving position in the currently used wavelength conversion optical element 27 from the recommended shift time. When the usage time reaches the recommended shift time (usable time), the stages 62 and 64 of the shift mechanism 60 are driven to shift the light receiving position of the wavelength conversion optical element 27 to the next light receiving position. The phase matching by temperature control described in S102 to S104 is executed again.

  On the other hand, in step S106, when the use of all the light receiving positions in the wavelength conversion optical element 27 is completed with the expiration of the actual use time (when the shift of the light reception positions a predetermined number of times is completed), the wavelength conversion optical element Replace 27 with a new one.

  As described above, according to the wavelength conversion device and the laser device 1 configured as described above, when the light receiving position of the laser light is sequentially shifted for each set time in the wavelength conversion optical element 27 having deliquescence, the wavelength conversion is performed. By controlling the temperature of the optical element 27 so as to maintain the optimum output intensity at the light receiving position, the phase matching condition is always satisfied while preventing the adsorption of moisture to the crystal surface having deliquescence. It is possible to stably supply the high output ultraviolet light. In addition, in this configuration, a temperature control heater and a temperature sensor provided from the viewpoint of preventing deterioration due to deliquescence, etc. are used for phase matching adjustment, so that an expensive actuator for angle tuning and complicated control are required. The phase matching can be adjusted with a simple configuration that does not, and the entire apparatus can be miniaturized as the cost decreases.

  Next, a laser device including the wavelength conversion device according to the second embodiment will be described. A schematic configuration diagram of the laser device 101 of the second embodiment is shown in FIG. 8, and a schematic block diagram of a control unit 180 in the laser device 101 is shown in FIG. In this embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted. The description will focus on differences from the first embodiment.

  The laser device 101 has an output function for outputting ultraviolet light and a small box-shaped laser head 2 that is easily incorporated into a laser system, and a housing that is provided separately from the laser head 2 and that has a control function for the laser head 2. It is composed of a body-shaped control rack 103, and the laser head 2 and the control rack 103 are interconnected by an interface 4.

The control rack 103 includes a control unit 180 that controls the operation of each part constituting the laser device 101 to control the emission of the ultraviolet laser light Lv by the laser head 2, and a crystal unit 50 that is connected by a gas connector 74. In addition, a gas supply unit 90 that supplies N ₂ gas to each unit of the laser apparatus 101 is provided.

  The control unit 180 controls the drive of the shift mechanism 60 (the electric motors M1 and M2 of the stages 62 and 64) to shift the light receiving position of the laser beam in the wavelength conversion optical element 27, and the wavelength conversion optics. A data storage unit 183 that stores the optimum temperature for each light receiving position of the laser beam in the element 27, and a temperature control that controls the driving of the heater 52 so that the wavelength conversion optical element 27 has a predetermined optimum temperature that satisfies the phase matching condition. Part 182.

  The data storage unit 183 is obtained by measuring in advance the optimum temperature (detection temperature of the temperature sensor 53 when the output intensity of the laser beam is maximized) for each position where the wavelength conversion optical element 27 receives the laser beam. Based on the measurement result, mapping data generated by mapping the optimum temperature corresponding to each light receiving position is stored.

  The temperature control unit 182 reads the mapping data in the data storage unit 183 each time the laser light receiving position of the wavelength conversion optical element 27 is shifted over a predetermined time, and the wavelength conversion optical element 27 stores the mapping data in advance. The energization to the heater 52 is controlled so that the optimum temperature corresponding to the set light receiving position is obtained. The temperature control unit 182 recognizes the coordinate value of the current light receiving position in the wavelength conversion optical element 27 based on the detection information from the position detection unit 66, and reads the optimum temperature corresponding to the coordinate value from the mapping data. Thus, the value of the optimum temperature at the light receiving position is acquired.

  The wavelength conversion device included in the laser device 101 means a device including the wavelength conversion unit 20 and the control unit 180.

  According to the wavelength conversion device and the laser device 101 according to the second embodiment as described above, the heater and the temperature sensor for temperature control provided from the viewpoint of preventing deterioration due to deliquescence and the like are used for adjusting the phase matching. With a simple configuration, it becomes possible to stably supply high-power ultraviolet light that always satisfies the phase matching condition while preventing moisture adsorption to the crystal surface having deliquescence. Further, since the temperature of the wavelength conversion optical element 27 is adjusted based on the mapping data generated in advance, the wavelength conversion optical element 27 is adjusted to the optimum temperature at the next light reception position after the light reception position is shifted. The time required to do so is shortened, and the operating rate of the laser apparatus 101 can be improved.

  Next, a laser device including the wavelength conversion device according to the third embodiment will be described. A schematic configuration diagram of a laser device 201 according to the third embodiment is shown in FIG. 10, and a schematic block diagram of a control unit 280 in the laser device 201 is shown in FIG. In this embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted. The description will focus on differences from the first embodiment.

  The laser apparatus 201 includes a small box-shaped laser head 2 that has an output function for outputting ultraviolet light and that is easily incorporated into a laser system, and a housing that is provided separately from the laser head 2 and that has a control function for the laser head 2. The laser head 2 and the control rack 203 are connected to each other by an interface 4.

The control rack 203 includes a control unit 280 that controls the operation of each unit constituting the laser device 201 to control the emission of the ultraviolet laser light Lv by the laser head 2, and the crystal unit 50 connected by the gas connector 74. In addition, a gas supply unit 90 that supplies N ₂ gas to each unit of the laser device 201 is provided.

  The control unit 280 controls the drive of the shift mechanism 60 (the electric motors M1 and M2 of the stages 62 and 64) to shift the light receiving position of the laser beam in the wavelength conversion optical element 27, and a predetermined temperature range. A data storage unit 283 for storing the relationship between the crystal temperature of the wavelength conversion optical element 27 and the output intensity of the laser beam, and wavelength conversion based on the relationship between the crystal temperature and the output intensity stored in the data storage unit 283. A temperature control unit 282 that controls the driving of the heater 52 so that the optical element 27 has a predetermined optimum temperature that satisfies the phase matching condition is provided.

  The data storage unit 283 stores the crystal temperature (detected temperature by the temperature sensor 53) of the wavelength conversion optical element 27 and the laser light at each light receiving position in the wavelength conversion optical element 27 based on the experimental results measured in advance. A data table (table corresponding to FIG. 7) indicating the relationship with the output intensity is stored.

  When the temperature control unit 282 detects that the output intensity of the laser beam is reduced by the photodetector 47 when the light receiving position of the laser beam in the wavelength conversion optical element 27 is shifted over a predetermined time. , Calculate the decrease in output intensity (maximum output intensity-current output intensity), and read the temperature correction value that compensates for the decrease in output intensity from the data table. The temperature is raised or lowered, and energization to the heater is controlled so that the wavelength conversion optical element 27 reaches the optimum temperature. Here, regarding the temperature control direction (in the temperature increasing or decreasing direction) of the wavelength conversion optical element 27 at this time, the temperature gradient is known in advance by the temperature change before and after the shift of the light receiving position. The temperature may be changed in the direction by the temperature correction value. In addition, the temperature of the wavelength conversion optical element 27 is changed in advance in the direction of either the temperature raising side or the temperature falling side by a minute temperature, and the temperature is increased in the direction in which the output intensity of the laser light detected by the photodetector 47 increases. It may be changed. The temperature control unit 282 recognizes the coordinate value of the current light receiving position in the wavelength conversion optical element 27 based on the detection information from the position detection unit 66, and outputs the crystal temperature and output corresponding to the coordinate value from the data table. By reading the intensity relationship, a temperature correction value for compensating for the decrease in output intensity is calculated.

  The wavelength conversion device included in the laser device 201 means a device including the wavelength conversion unit 20 and the control unit 280.

  According to the wavelength conversion device and the laser device 201 according to the third embodiment as described above, the heater and the temperature sensor for temperature control provided from the viewpoint of preventing deterioration due to deliquescence and the like are used for adjusting the phase matching. With a simple configuration, it becomes possible to stably supply high-power ultraviolet light that always satisfies the phase matching condition while preventing moisture adsorption to the crystal surface having deliquescence. Further, since the driving of the heater is controlled based on the temperature correction value corresponding to the decrease in output intensity, the wavelength conversion optical element 27 is set to the optimum temperature at the next light receiving position after the light receiving position is shifted. The time required for adjustment is shortened, and the operating rate of the laser apparatus 201 can be improved.

  As described above, according to the above-described first to third embodiments, the temperature control heater and the temperature sensor provided from the viewpoint of preventing deterioration due to the tide are used for adjusting the phase matching. The wavelength conversion by the wavelength conversion optical element 27 having the property can be performed stably with high efficiency at all times. Accordingly, it is possible to provide a wavelength conversion device that can be used stably over a long period of time while suppressing a change in the output intensity of the laser light, and a laser device 1 including the wavelength conversion device.

  Although the preferred embodiment of the present invention has been described so far, the present invention is not limited to this embodiment. For example, in the above-described embodiment, the wavelength conversion optical element 27 (25, 26) made of the CLBO crystal for generating the 7th harmonic and the 8th harmonic has been described as the wavelength conversion optical element having deliquescence. However, the present invention is not limited to this, and as an optical crystal having deliquescence other than CLBO crystal, wavelength conversion optical element 22 made of LBO crystal for generating third harmonic wave and wavelength conversion made of LBO crystal for generating fifth harmonic wave The present invention may be applied to the optical element 23, other BBO crystals, CBO crystals, and the like. Further, as the optical crystal that generates the 7th harmonic wave and the 8th harmonic wave, an optical crystal other than the CLBO crystal may be used.

  In the above embodiment, the wavelength conversion optical elements 25 and 26 (the portion indicated by the reference numeral 50 surrounded by a two-dot chain line in FIG. 3) are exemplified as one unit, but the embodiment is limited to this. Instead, the crystal units are configured with each of the wavelength conversion optical elements 25 and 26 as one unit, or the crystal unit is configured with the entire wavelength conversion unit 20 including the wavelength conversion optical elements 25 and 26 as one unit. May be. In the above-described embodiment, the temperature measurement of the wavelength conversion optical elements 25 and 26 is performed each time the light receiving position of the laser beam is shifted. However, the temperature measurement may be performed every multiple shifts.

  Further, in the above-described embodiment, the laser light generation unit 10 amplifies the laser light (seed light) Ls generated by the laser light source 11 by the two-stage optical amplifiers 12 and 13 connected in series, and the amplified laser. Although the configuration in which the light Lr is incident on the wavelength conversion unit 20 has been exemplified, the optical amplifier has one or three or more stages according to the output and amplification factor of the laser light source 11, or the wavelength conversion unit 20 is not provided with an optical amplifier. Depending on the configuration of the wavelength conversion unit 20, the laser light emitted from the laser light source 11 may be divided into a plurality of pieces and amplified by a plurality of optical amplifiers provided in parallel. It may be composed of a row of optical amplifiers. In addition, although description is omitted for simplification of description, an optical modulator such as an EOM that cuts out an optical pulse between the laser light source 11 and the optical amplifier 12, or between the optical amplifier 12 and the wavelength conversion unit 20, or a single color A narrow band filter or the like for enhancing light is provided as appropriate.

Further, the wavelength of the ultraviolet light Lv from the light source device 1 is not limited to 193 nm, and may be the same wavelength band as that of a KrF excimer laser, an F ₂ laser, or the like. Further, the application example of the light source device according to the present invention is not limited to the exposure apparatus, and can be used in various other apparatuses such as various optical inspection apparatuses and laser treatment apparatuses.

1, 101, 201 Laser device 10 Laser light generation unit 20 Wavelength conversion unit 27 Wavelength conversion optical element 47 Photo detector 50 Crystal unit 51 Crystal holder 52 Heater 53 Temperature sensor 60 Shift mechanism 70 Unit cases 80, 180, 280 Control unit 82 , 182 and 282 Temperature control unit 183 and 283 Data storage unit

Claims (9)

A wavelength conversion device that uses a wavelength conversion optical element having deliquescence in a temperature-raised state heated within a predetermined temperature range, converts the wavelength of the input fundamental wave laser beam and outputs it as a harmonic laser beam,
A heater for heating the wavelength conversion optical element;
A temperature detector for detecting the temperature of the wavelength conversion optical element;
A temperature control unit that controls driving of the heater based on a temperature detected by the temperature detection unit and adjusts the temperature of the wavelength conversion optical element to be maintained within the predetermined temperature range;
A shift mechanism for shifting the light receiving position of the wavelength conversion optical element by a predetermined amount,
When the light receiving position of the wavelength conversion optical element is shifted, the temperature control unit optimizes the temperature at which the output intensity of the laser light whose wavelength is converted within the predetermined temperature range is the maximum temperature of the wavelength conversion optical element. The wavelength converter is configured to control the driving of the heater so that   The wavelength conversion device according to claim 1, wherein the predetermined temperature range is set in a temperature range in which the wavelength conversion optical element does not reach deliquescent. A light detection unit for detecting the output intensity of the laser light wavelength-converted by the wavelength conversion optical element;
Each time the light receiving position of the wavelength conversion optical element is shifted, the temperature control unit monitors the output intensity detected by the light detection unit while changing the temperature of the wavelength conversion optical element within the predetermined temperature range. The drive of the heater is controlled by using the temperature detected by the temperature detection unit when the output intensity from the wavelength conversion optical system is maximized as the optimum temperature. 2. The wavelength converter according to 2. A light detection unit for detecting the output intensity of the laser light wavelength-converted by the wavelength conversion optical element;
A light receiving position in the wavelength conversion optical system based on a result measured in advance as the optimum temperature as the detection temperature of the temperature detection unit when the output intensity from the wavelength conversion optical device becomes maximum within the predetermined temperature range. Mapping data generated by mapping the optimum temperature for each
When the light receiving position of the wavelength converting optical element is shifted, the temperature control unit reads the optimum temperature at the light receiving position from the mapping data and detects the wavelength converting optical element detected by the temperature detecting unit. The wavelength converter according to claim 1, wherein the driving of the heater is controlled so that the temperature becomes the optimum temperature at the light receiving position. A light detection unit for detecting the output intensity of the laser light wavelength-converted by the wavelength conversion optical element;
A data table storing a relationship between the temperature of the wavelength conversion optical element detected by the temperature control unit and the output intensity of the harmonic laser beam detected by the light detection unit within the predetermined temperature range. In addition, when the light receiving position is shifted when the output intensity at the current light receiving position is maximum, the temperature control unit is configured to read from the data table based on the amount of decrease in the output intensity of the laser light before and after the shift. A temperature correction amount for compensating the amount of decrease is obtained, and the heater is driven so that the temperature of the wavelength conversion optical element detected by the temperature detection unit becomes the optimum temperature changed by the temperature correction amount. The wavelength conversion device according to claim 1, wherein the wavelength conversion device is configured to be controlled. The holder for holding the wavelength conversion optical element, the heater, and the temperature detection unit are housed in a case filled with an inert gas to form an element unit,
6. The case according to claim 1, wherein an incident port for introducing an input laser beam and an exit port for deriving a wavelength-converted laser beam are formed in the case. The wavelength converter described. A laser beam generator for emitting a fundamental laser beam;
Comprising the wavelength conversion device according to any one of claims 1 to 6,
2. A laser apparatus comprising: a fundamental laser beam emitted from the laser beam generation unit that is converted into a harmonic laser beam by the wavelength converter and output.   The laser apparatus according to claim 7, further comprising an optical amplifier that optically amplifies the fundamental laser beam generated from the laser beam generator and outputs the amplified laser beam to the wavelength converter. A wavelength conversion method for converting a wavelength of an input fundamental wave laser beam and outputting it as a harmonic laser beam by using a wavelength conversion optical element having deliquescence in a heated state heated within a predetermined temperature range,
Shifting the light receiving position of the wavelength conversion element;
Calculating the optimum temperature of the wavelength conversion optical element that maximizes the output intensity of the laser light wavelength-converted by the wavelength conversion optical element within the predetermined temperature range each time the light receiving position is shifted; and
And a step of controlling driving of the heater so that the wavelength conversion optical element is maintained at the optimum temperature.

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