JP6716086B2 - Light source device, inspection device, and method for controlling light source device - Google Patents

Description

The present invention relates to a light source device, an inspection device, and a method for controlling a light source device.

In the process of manufacturing a photomask master plate for semiconductor exposure, which is becoming finer, it is necessary to measure minute defects in the master plate. For a reticle on which a fine exposure pattern is drawn, it is necessary to measure whether the actual pattern is drawn correctly or whether there are any defects on the pattern.

For such a purpose, a semiconductor defect inspection apparatus is used which irradiates an object to be measured with light of continuous or high repetitive pulse output, and catches and compares the intensity change due to the scattering or the like. Although there are various types of semiconductor defect inspection systems, generally, the shorter the wavelength of the light source, the higher the resolution. For this reason, in recent years, a light source in the deep ultraviolet region by wavelength conversion of laser light using a nonlinear optical crystal has been mainly used. Due to the principle of the device that captures intensity changes, the light source output must always be stable for a long time, and stabilization control is performed by some method.

Patent Document 1 discloses a light source device for generating deep ultraviolet light of 193 nm using a CLBO (CsLiB ₆ O ₁₀ ) crystal or a BBO (β-BaB ₂ O ₄ ) crystal. In Patent Document 1, an output light monitoring device that monitors the power of the output light, an output light adjusting device that operates the power of the fundamental wave so that the power of the output light is constant, and a fundamental wave monitor that monitors the power of the fundamental wave. And a device.

JP, 2006-30594, A

Yushi Kaneda, et al. ,"Continuous-wave, single-frequency 229 nm laser source for laser cooling of cadmium atoms," Opt. Lett. 41, 705-708 (2016)

The BBO crystal and the CLBO crystal have a problem that the wavelength conversion crystal itself is damaged when used for a long time and the conversion efficiency is lowered. Therefore, in Patent Document 1, the BBO crystal is shifted when the power of the fundamental wave reaches a predetermined value during the feedback control so that the power of the output light becomes constant.

In Patent Document 1, when the power of the fundamental wave reaches a predetermined value, it is determined that the wavelength conversion crystal has deteriorated, and the light receiving position of incident light with respect to the BBO crystal is changed. By doing so, the wavelength-converted light can be generated at a location where the BBO crystal is not deteriorated. Therefore, it is possible to prevent a decrease in conversion efficiency.

However, according to Non-Patent Document 1, the conversion efficiency is greatly reduced immediately after the incident light is incident on the wavelength conversion crystal. Therefore, when the method of Patent Document 1 is used, the output of the wavelength-converted light may not be stabilized immediately after shifting the BBO crystal.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a light source device and an inspection device capable of stabilizing the output of wavelength-converted light with a simple configuration. ..

A light source device according to an aspect of the present embodiment is a laser light source that generates a fundamental wave, a laser power source that drives the laser light source, and the fundamental wave or a harmonic thereof as incident light to generate wavelength-converted light. Based on one nonlinear optical crystal, a detector that detects the wavelength-converted light, a drive mechanism that changes the incident position of the incident light with respect to the nonlinear optical crystal, and the wavelength conversion based on a detection signal from the detector. A control unit that feedback-controls the output power of the laser power source so that the output of light is constant, and the control unit changes the incident position when the output power exceeds a threshold value. The drive mechanism is controlled so that the incidence position does not change even if the output power exceeds the threshold value for a predetermined period after the incidence position changes. The output of wavelength-converted light can be stabilized with a simple configuration.

In the above light source device, it is preferable that the nonlinear optical crystal is a BBO crystal.

In the above light source device, it is preferable that the laser light source operates with continuous output.

In the above-mentioned light source device, it is preferable that the laser power source supplies to the laser light source an output power exceeding a rated maximum output of the laser light source during the predetermined period. Thereby, a laser light source having a low rated maximum output can be used.

An inspection apparatus according to the present embodiment includes the above-mentioned light source device and an image pickup device for picking up an image of an inspection target illuminated by the wavelength-converted light from the light source device. As a result, stable illumination is possible, and stable inspection is possible.

In the above inspection apparatus, when the inspection target is not inspected, the incident position of the incident light is changed by the drive mechanism so that the incident light is incident on the nonlinear optical crystal. Good.

A method of controlling a light source device according to the present embodiment, a laser light source for generating a fundamental wave, a laser power source for driving the laser light source, and the fundamental wave or its harmonics as incident light to generate wavelength-converted light. A method for controlling a light source device, comprising: at least one nonlinear optical crystal; a detector that detects the wavelength-converted light; and a drive mechanism that changes an incident position of the incident light with respect to the nonlinear optical crystal. Based on the detection signal from the detector, the step of feedback controlling the output power of the laser power supply so that the output of the wavelength-converted light becomes constant, and when the output power exceeds a threshold, the incident position Controlling the drive mechanism to change, and controlling the drive mechanism so that the incident position does not change even if the output power exceeds the threshold value for a predetermined period after the incident position changes. , Are provided. The output of wavelength-converted light can be stabilized with a simple configuration.

In the above control method, it is preferable that the nonlinear optical crystal is a BBO crystal.

In the above control method, it is preferable that the laser light source operates at continuous output.

In the above control method, the laser power supply may supply the laser light source with output power exceeding the rated maximum output of the laser light source during the predetermined period.

According to the present invention, it is possible to provide a light source device, an inspection device, and a control method of a light source device that can stabilize the output of wavelength-converted light with a simple configuration.

It is a figure which shows the structure of the light source device concerning this Embodiment. It is a graph which shows the output change of wavelength conversion light when the output of the incident light which injects into a nonlinear optical crystal is made constant. 6 is a graph showing a change in output of incident light immediately after a shift timing. It is a graph which shows the output of incident light at the time of carrying out feedback control so that the output of wavelength conversion light may be fixed. It is a figure which shows the structure of the inspection apparatus using a light source device.

The light source device according to the present embodiment generates wavelength-converted light using, for example, a wavelength conversion element (nonlinear optical crystal). In the present embodiment, a light source device used as an illumination light source of a semiconductor inspection device such as a photomask will be described, but the application of the light source device is not limited to the inspection device.

The light source device 100 according to the present embodiment will be described with reference to FIG. FIG. 1 is a diagram showing a configuration of the light source device 100. The light source device 100 includes a laser light source 11, a laser power source 12, a motor driver 13, a control PC 14, a motor 15, a stage 16, a lens 17, an external resonator 20, a mirror 31, and a mirror 32. The beam sampler 33 and the detector 34 are provided.

The laser light source 11 generates a laser beam L1 that is a fundamental wave. The laser light L1 generated by the laser light source 11 becomes incident light that enters the wavelength conversion crystal 26 described later. Specifically, the laser light source 11 generates a continuous output blue laser light having a wavelength of 488 nm. The laser light L1 having a wavelength of 488 nm is in the vertical single mode.

The laser power supply 12 outputs electric power for driving the laser light source 11. That is, the laser power source 12 supplies electric power to the laser light source 11, so that the laser light source 11 generates the laser light L1. As will be described later, a control PC (personal computer) 14 controls the output power of the laser power supply 12.

The laser light L1 from the laser light source 11 is incident on the external resonator 20 via the lens 17. The external resonator 20 is a ring-type external resonator having four optical mirrors 21-24. The optical mirrors 21 to 24 are high reflection mirrors. The optical mirror 21 and the optical mirror 22 are plane mirrors. The optical mirror 23 and the optical mirror 24 are concave mirrors. The external resonator 20 further includes a nonlinear optical crystal 26 and an actuator 25. A nonlinear optical crystal 26 is arranged inside the external resonator 20.

The fundamental-wave laser beam L1 is guided into the external resonator 20 from the back surface of the optical mirror 21, which is a partial reflection mirror. The laser light L1 introduced into the external resonator 20 is repeatedly reflected by the optical mirror 22, the optical mirror 23, the optical mirror 24, and the optical mirror 21 in order. As a result, the laser light L1 resonates, so that the intensity of the laser light L1 can be increased. Further, an actuator 25 for adjusting the external resonator length is attached to the optical mirror 22. The control PC 14 appropriately controls the actuator 25 to maintain resonance. As a result, in the external resonator 20, the laser light L1 is enhanced to 50 times or more the incident power.

Further, a nonlinear optical crystal 26 is arranged between the optical mirror 23 and the optical mirror 24. As the non-linear optical crystal 26, for example, a BBO crystal, an LBO (LiB ₃ O ₅ ) crystal, a CLBO crystal, or the like can be used. The nonlinear optical crystal 26 wavelength-converts the laser light L1 and generates wavelength-converted light L2. Here, a BBO crystal is used as the nonlinear optical crystal 26. The nonlinear optical crystal 26 generates the second harmonic of the laser light L1 as the wavelength converted light L2. Therefore, the wavelength converted light L2 becomes an ultraviolet laser light having a wavelength of 244 nm. By properly maintaining the angle and temperature of the nonlinear optical crystal 26, the phase matching condition for the second harmonic generation is satisfied. Thereby, the wavelength-converted light L2 having a wavelength of 244 nm can be generated with a conversion efficiency of several tens of percent.

Then, the wavelength-converted light L2 generated by the nonlinear optical crystal 26 is extracted from the optical mirror 24. The optical mirror 24 is provided with a film having high reflection at a wavelength of 488 nm and antireflection for a wavelength of 244 nm. As the optical mirror 24, a dichroic mirror that reflects the laser light L1 and transmits the wavelength-converted light L2 may be used.

The wavelength converted light L2 extracted from the external resonator 20 is reflected by the mirrors 31 and 32 and enters the beam sampler 33. The beam sampler 33 transmits a part of the wavelength converted light L2 and reflects a part thereof. The wavelength-converted light L2 that has passed through the beam sampler 33 becomes output light L3 used in the inspection of the photomask. For example, the output light 13 that has passed through the beam sampler 33 is used as illumination light for the inspection device, as described later. The wavelength converted light L2 reflected by the beam sampler 33 becomes detection light L4 incident on the detector 34. It should be noted that the beam sampler 33 only needs to extract the detection light L4 in an amount of light that can be detected by the detector 34.

The detector 34 is a photodiode, a photomultiplier, or the like. The detector 34 outputs a detection signal corresponding to the detection light L4 to the control PC 14. The detector 34 generates a detection signal based on the detection light amount of the detection light L4 and outputs it to the control PC 14. The control PC 14 controls the output power of the laser power supply 12 based on the detection signal.

Specifically, the output power of the laser power supply 12 is adjusted so that the amount of light detected by the detector 34 becomes constant. The control PC 14 serves as a control unit that performs feedback control so that the output of the wavelength converted light L2 becomes constant. When the signal strength of the detection signal from the detector 34 decreases, the control PC 14 increases the output power of the laser power supply 12. As a result, the output of the laser light L1 is increased, so that the output of the wavelength converted light L2 is kept constant. On the other hand, when the signal strength of the detection signal from the detector 34 increases, the control PC 14 decreases the output power of the laser power supply 12. As a result, the output of the laser light L1 becomes low, so that the output of the wavelength-converted light L2 is kept constant. In this way, the control PC 14 performs feedback control so that the light intensity of the wavelength converted light L2 from the nonlinear optical crystal 26 becomes constant.

The nonlinear optical crystal 26 is placed on the stage 16. The stage 16 is a drive stage to which the motor 15 is attached. The motor 15 is a stepping motor or a servo motor, and is connected to the motor driver 13. The motor driver 13 operates the motor 15 according to a control signal from the control PC 14. That is, the stage 16, the motor 15, and the motor driver 13 serve as a drive mechanism for changing the incident position of the laser light on the nonlinear optical crystal 26. Specifically, the motor 15 moves the stage 16 in the direction orthogonal to the optical axis. As a result, the incident position of the laser light on the nonlinear optical crystal 26 shifts.

By doing so, the incident position of the incident light on the nonlinear optical crystal 26 can be changed. That is, when the motor 15 moves the stage 16, the nonlinear optical crystal 26 fixed on the stage 16 moves. Therefore, the laser light L1 comes into different positions of the nonlinear optical crystal 26.

The control PC 14 controls the motor driver 13 based on the detection signal. The control PC 14 controls the incident position of the laser light L1 on the nonlinear optical crystal 26. The control of the incident position of the laser light L1 by the control PC 14 will be described later.

Here, the output fluctuation of the wavelength-converted light L2 when the output of the incident light entering the nonlinear optical crystal 26 is constant will be described with reference to FIG. FIG. 2 is a graph showing the time change of the output of the wavelength-converted light L2 when the output of the incident light (that is, the laser light L1) entering the nonlinear optical crystal 26 is constant. The output of the incident light corresponds to the output power that the laser power supply 12 supplies to the laser light source 11. That is, FIG. 2 shows changes in the output of the wavelength-converted light L2 when the laser power supply 12 supplies the laser light source 11 with a constant output power. In FIG. 2, the output (W) of the incident light (laser light L1) is shown in the upper part, and the output (W) of the wavelength conversion light L2 is shown in the lower part. In addition, in FIG. 2, the output of the incident light is constant at 1 W.

Here, at timings T11 and T13, the motor 15 shifts the incident position of the incident light on the nonlinear optical crystal 26. Then, in FIG. 2, the fixed periods immediately after changing the incident position of the incident light are shown as periods A1 and A2. Further, the periods from the period A1 and the period A2 until the incident position of the incident light is changed are shown as periods B1 and B2. That is, the period B1 is a period from the end (T12) of the period A1 to the timing (T13) of changing the incident position next.

At the shift timings T11 and T13 immediately after changing the incident position of the incident light, the conversion efficiency sharply decreases, and the output of the wavelength converted light L2 becomes the lowest. Specifically, immediately after the shift, the output of the wavelength converted light L2 is about 0.2 W. Then, in the periods A1 and A2 after changing the incident position, the output of the wavelength-converted light gradually increases with time. At the end (T12, T14) of the period A1 and the period A2, the output of the wavelength converted light L2 reaches 0.3 W and is saturated.

Then, in the periods B1 and B2 after the periods A1 and A2, the output of the wavelength-converted light gradually decreases. That is, in the periods B1 and B2, the non-linear optical crystal 26 deteriorates due to the irradiation of the laser light L1, and thus the conversion efficiency gradually decreases. For example, after 200 hours, the conversion efficiency is reduced by 10% to 0.27W.

In this way, the conversion efficiency is significantly reduced at the shift timings T11 and T13 when the incident position of the incident light is shifted. For example, the wavelength conversion efficiency is reduced by about 30%. FIG. 3 shows an output change of the wavelength converted light L2 from the shift timing. In FIG. 3, the horizontal axis represents time (hr) and the vertical axis represents the output (a.u.) of the wavelength-converted light L2. As shown in FIG. 3, at the shift timing (0:00), the output of the wavelength converted light L2 is the lowest. Then, the output of the wavelength-converted light L2 gradually increases, and after about 2 hours have passed, the output is almost returned to the original output. Further, the output of the wavelength-converted light L2 becomes maximum about 6 hours after the shift timing (6:00).

In the control method described in Patent Document 1, feedback control is performed so that the output light has a constant power. Then, when the power of the incident light reaches a predetermined value during the feedback control, the incident position is shifted. However, as described above, the conversion efficiency is significantly reduced at the shift timing. Therefore, in order to make the power of the output light constant, it is necessary to greatly increase the output of the incident light immediately after the shift timing. Immediately after the shift timing, it becomes necessary to further change the incident position of the incident light. Therefore, according to the control method of Patent Document 1, the incident position of the incident light cannot be stabilized, and it is difficult to stabilize the output.

Therefore, in the present embodiment, the control PC 14 stabilizes the output by the control described below. The control method according to the present embodiment will be described with reference to FIG. FIG. 4 is a graph showing the time change of the output of the incident light (laser light L1) when the output of the wavelength converted light L2 is controlled to be constant.

The control PC 14 performs feedback control so that the output of the wavelength converted light L2 becomes constant. That is, the control PC 14 controls the output power of the laser power supply 12 so that the detection signal from the detector 34 becomes a constant value. Here, the output power output from the laser power source 12 to the laser light source 11 corresponds to the output of the incident light. Further, in the present embodiment, the threshold TH is set for the output of incident light. Then, the control PC 14 compares the output power of the laser power supply 12 (output of incident light) with the threshold value TH. When the output of the incident light reaches the threshold value TH, the control PC 14 controls the motor driver 13 to shift the incident position of the incident light with respect to the nonlinear optical crystal 26. That is, when the output of the incident light exceeds the threshold value TH, the motor 15 drives the stage 16 to move the nonlinear optical crystal 26.

In FIG. 4, timings T1 and T3 are shift timings for shifting the nonlinear optical crystal 26. At timings T1 and T3, the conversion efficiency is significantly reduced. In order to keep the output of the wavelength-converted light L2 constant, the output of the incident light is maximized at the timings T1 and T3. Then, in the periods C1 and C2 immediately after shifting the nonlinear optical crystal 26, the conversion efficiency gradually increases. For example, the conversion efficiency recovers from the timing T2. Similarly, the conversion efficiency recovers from the timing T4. Therefore, the incident light output gradually decreases in the periods C1 and C2. The period C1 is a period from the shift timing T1 to the timing T2, and the period C2 is a period from the timing T3 to the timing T4.

In at least a part of the periods C1 and C2, the output of the incident light exceeds the threshold TH. Therefore, in the present embodiment, the nonlinear optical crystal 26 does not move during the constant period C1 and the period C2 immediately after the shift timing even if the output of the incident light exceeds the threshold value TH. That is, the control PC 14 controls so that the incident position does not change even if the output power supplied from the laser power supply 12 exceeds the threshold TH in the predetermined period C1 and the period C2 after the incident position has changed. That is, in the period C1 and the period C2, the control PC 14 controls so that the motor 15 stops. By doing so, the position of the stage 16 can be fixed. Therefore, even if the conversion efficiency is temporarily reduced immediately after the shift of the nonlinear optical crystal 26, the incident position of the laser light L1 on the nonlinear optical crystal 26 becomes constant. Therefore, the wavelength-converted light L2 can be stably generated. The times of the period C1 and the period C2 may be set in advance. For example, the period C1 and the period C2 can be set to a time of about 2 hours to 6 hours.

On the other hand, after the end of the period C1 and the period C2, that is, when the output of the incident light exceeds the threshold value TH in the period D1 and the period D2, the control PC 14 controls the motor driver 13 to shift the incident position. Let That is, in the period D1 after the period C1 and the period D2 after the period C2, the control PC 14 compares the output of the incident light with the threshold value TH, and shifts the nonlinear optical crystal 26 according to the comparison result. For example, in FIG. 4, the output of the incident light exceeds the threshold value TH immediately before the timings T3 and T5. Therefore, immediately before the timings T3 and T5, the control PC 14 controls the motor driver 13 so as to change the incident position.

By doing so, when the nonlinear optical crystal 26 deteriorates to some extent by the irradiation of the laser beam L1, the incident position moves to another position of the nonlinear optical crystal 26. The non-linear optical crystal 26 can be irradiated with the laser light L1 at an unused portion. Therefore, it is possible to stably generate the wavelength-converted light L2 with high conversion efficiency. Since it is possible to prevent the conversion efficiency of the nonlinear optical crystal 26 from remarkably lowering, the amount of output power supplied from the laser power source 12 to the laser light source 11 can be reduced. Therefore, the wavelength converted light L2 can be stably generated.

In the periods C1 and C2, the output power supplied from the laser power source 12 to the laser light source 11 temporarily increases. However, the period C1 and the period C2 are about 1 to 6 hours as described above. On the other hand, the period D1 and the period D2 are 100 to 200 hours. The period C1 and the period C2 are sufficiently shorter than the period D1 and the period D2. Therefore, for a short time, there is no problem even if the laser light source 11 oscillates the laser at the rated maximum output or more.

For example, in FIG. 4, when the laser light source 11 whose rated maximum output is 1 W is used, the rated maximum output is exceeded in the period C1 and a part of the period C2. For example, at timings T1 and T3, the incident light output is 1.16W. However, the time exceeding the rated maximum output is about 2 hours at maximum, which is only about 1% of the total operating time (about 200 hours). Therefore, an increase in the load on the laser light source 11 has almost no effect on the life of the device.

A case will be considered in which the laser light source 11 is always operated at a rated maximum output of 1 W or less. In the case of using the nonlinear optical crystal 26 having the characteristics shown in FIGS. 2 and 4, in order to stabilize the output, it is necessary to stabilize the output at the timing with the lowest conversion efficiency, that is, the output immediately after the shift timing. Will end up. That is, when operated at a rated maximum output of 1 W or less, only 0.2 W of output light can be obtained.

On the other hand, when the laser light source 11 is operated so as to exceed the rated maximum output of 1 W in the periods C1 and C2 as in the present embodiment, 0.27 W of output light can be stably obtained. By operating beyond the rated maximum output in the range of 10 to 20% for a short time, the wavelength-converted light L2 having a higher output can be stably obtained.

Specifically, in FIG. 4, a value that exceeds the rated maximum output (1 W) by 16% (1.16 W) is the maximum output of incident light throughout the entire operation period. In this way, the laser power supply 12 temporarily supplies the laser light source 11 with output power exceeding the rated maximum output of the laser light source 11. Therefore, even when the relatively small laser light source 11 is used, the wavelength-converted light L2 having a high output can be obtained. Further, since the time exceeding the rated maximum output is sufficiently shorter than the total operation time as described above, the influence on the laser light source 11 is small.

Note that it is preferable to set an appropriate value in advance for the value of the threshold value TH for shifting the incident position. Specifically, it is preferable to set the threshold value TH such that the conversion efficiency is shifted at the timing when the conversion efficiency is reduced to about 90% of the maximum conversion efficiency. That is, it is preferable to use, as the threshold value TH, a value increased by 5% to 10% from the timing (for example, T2) at which the incident light output becomes the lowest.

Further, for the periods C1 and C2 in which the nonlinear optical crystal 26 is not shifted even if the incident light output exceeds the threshold value TH, an appropriate time can be set according to the incident light output or the like. Further, the lengths of the periods C1 and C2 may be set according to the material of the nonlinear optical crystal 26. The period during which the nonlinear optical crystal 26 is not shifted even if the incident light output exceeds the threshold value is preferably, for example, less than 6 hours.

In the above description, the non-linear optical crystal 26 is a BBO crystal, but the non-linear optical crystal 26 is not limited to the BBO crystal and may be an LBO crystal or a CLBO crystal. Although the nonlinear optical crystal 26 converted the light having the wavelength of 488 nm into the second harmonic of the wavelength 244, the wavelength is not limited to the above example. Further, the laser light source 11 is not limited to the continuous wave laser, and may be a pulse laser.

In the light source device 100 described above, the nonlinear optical crystal 26 is arranged inside the external resonator 20, but the arrangement of the nonlinear optical crystal 26 is not limited to this. It suffices that the non-linear optical crystal 26 is arranged in the optical path on which the fundamental laser light L1 or its harmonics enter. That is, the light source device 100 may be provided with at least one nonlinear optical crystal 26 that generates wavelength-converted light by using the fundamental wave or its harmonic as incident light. For example, two or more nonlinear optical crystals 26 may be provided. Further, it may be a pulsed laser that does not use a resonator. Alternatively, a pulsed or continuous wave laser with an internal conversion method may be used.

Next, the configuration of the inspection device using the light source device 100 according to the present embodiment will be described with reference to FIG. FIG. 5 is a diagram showing the overall configuration of the inspection device 300. The inspection apparatus 300 shown in FIG. 5 is an inspection apparatus for a mask used in an exposure process of semiconductor manufacturing. The photomask to be inspected is mainly used for lithography in which DUV light of 193 nm is used as an exposure wavelength. Of course, the inspection target is not limited to the photomask.

As shown in FIG. 5, the inspection device 300 includes a light source device 100, lenses 302a to 302d, homogenizing optical systems 303a and 303b, a λ/2 wavelength plate 304, a polarization beam splitter 305, a λ/4 wavelength plate 306, an objective lens. 307, an imaging lens 311, a two-dimensional photodetector 312, a half mirror 313a, mirrors 313b to 313c, a condenser lens 314, and a 3λ/4 wavelength plate 315.

The light source device 100 generates illumination light L111 that is a P wave. The illumination light L111 corresponds to the output light L3 in FIG. The illumination light L111 is split into two illumination lights by the half mirror 313a. Here, the illumination light L111 transmitted through the half mirror 313a becomes the reflected illumination laser light L301, and the illumination light L111 reflected by the half mirror 313a becomes the transmitted illumination laser light L306.

The laser light L301 for reflective illumination is condensed by the lens 302a and enters the homogenizing optical system 303a. For the homogenizing optical system 303a, for example, a so-called rod-type integrator is suitable.

From the homogenizing optical system 303a, laser light L301 for reflected illumination whose intensity distribution is spatially homogenized is emitted. The laser light L301 for reflective illumination passes through the lens 302b and the λ/2 wavelength plate 304, and thereby the polarization direction is rotated by 90 degrees and becomes an S wave. Then, the reflected illumination laser light L301 that has become an S wave enters the polarization beam splitter 305 and is reflected downward in FIG. 5 like the reflected illumination laser light L302. The reflected illumination laser light L302 passes through the λ/4 wavelength plate 306 and becomes circularly polarized reflected illumination laser light L303. The reflected illumination laser beam L303 passes through the objective lens 307 and illuminates the observation region 310 in the pattern surface 309 of the mask 308. The above is an illumination system called reflection illumination. The reflected light that is reflected by the pattern surface 309 of the mask 308 and travels upward is the laser light L304.

On the other hand, the laser light L306 for transmitted illumination supplied from the light source device 100 is reflected by the mirror 313b. The laser light L306 for transmitted illumination reflected by the mirror 313b is condensed by the lens 302c and enters the homogenizing optical system 303b. By passing through the homogenizing optical system 303b, the laser light L307 for transmitted illumination having a spatially uniform intensity distribution is emitted. The transmitted illumination laser light L307 passes through the lens 302d, is reflected by the mirror 313c, passes through the 3/4 wavelength plate 315, and becomes the circularly polarized transmitted illumination laser light L308. Then, the laser light L308 for transmitted illumination passes through the condenser lens 314 and illuminates the observation region 310 in the pattern surface 309 of the mask 308. The above is an illumination system called transmitted illumination. The transmitted light that passes through the mask 308 and travels upward becomes the laser light L304.

The laser beam L304 reflected by the mask 308 or the laser beam L304 transmitted by the mask 308 passes through the objective lens 307, then passes through the λ/4 wavelength plate 306, and returns to linearly polarized light. The laser light L304 traveling upward is a P wave whose polarization direction is orthogonal to that of the laser light L302 for transmissive illumination traveling downward, and is transmitted through the polarization beam splitter 305. As a result, it travels like the laser beam L305, passes through the imaging lens 311, and strikes the two-dimensional photodetector 312. Therefore, the two-dimensional photodetector 312 images the mask 308 illuminated by the wavelength-converted light. The observation area 310 is magnified and projected on the two-dimensional photodetector 312, and the pattern is inspected. An image pickup device such as a CCD sensor, a CMOS sensor, or a TDI sensor can be used as the two-dimensional photodetector 312.

As described above, the light source device 100 can stably generate the illumination light L111 that is the wavelength conversion light L2. Therefore, the defect can be detected with high accuracy.

Here, when the inspection device 300 is not inspected, the light source device 100 shifts the nonlinear optical crystal 26 and irradiates the nonlinear optical crystal 26 with laser light. As a result, it is possible to prevent the inspection from being performed immediately after the shift timing during the period in which the conversion efficiency temporarily decreases. That is, when the mask 308 is not inspected, the nonlinear optical crystal 26 is shifted to irradiate the nonlinear optical crystal 26 with the laser light L1. Specifically, after the nonlinear optical crystal 26 is shifted, the nonlinear optical crystal 26 is irradiated with the laser light L1 for about 2 to 6 hours. By doing so, the temporary decrease in conversion efficiency immediately after the shift timing is recovered. Then, after the irradiation is finished, the inspection is restarted.

During non-inspection, feedback control may not be performed so that the output of the wavelength converted light L2 becomes constant. Therefore, the nonlinear optical crystal 26 can be irradiated with the laser light L1 within a range in which the output of the laser light source 11 does not exceed the maximum rated power. By doing so, it is possible to recover the conversion efficiency temporarily dropped immediately after the shift timing when the inspection is not performed. Even if the laser light source 11 operates so as not to exceed the maximum rated power, the output of the wavelength converted light L2 at the time of inspection can be stabilized. In other words, it is possible to operate the laser light source 11 so as not to exceed the maximum rated power throughout the inspection and non-inspection. During non-inspection, idling is performed so that the output power of the laser power source 12 is lower than that during inspection.

For example, when the inspection is not performed for a certain period, the operator operates the input device of the control PC 14 to specify the non-inspection mode. Then, the control PC 14 shifts the nonlinear optical crystal 26 and irradiates the nonlinear optical crystal 26 with the laser light L1 within the rated maximum output of the laser light source 11. By doing so, it is possible to recover a temporary decrease in conversion efficiency during non-inspection. After irradiating the nonlinear optical crystal 26 with the laser light L1 for a certain period of time, the control PC 14 may control the laser light source 11 not to operate.

Alternatively, the laser light L1 may be previously irradiated to one or a plurality of locations of the nonlinear optical crystal 26 to such an extent that the temporary reduction in conversion efficiency can be recovered. Specifically, before the light source device 100 is installed in the inspection device 300, the nonlinear optical crystal 26 is irradiated with the laser light L1 for about 1 to 6 hours, and the irradiation position is stored in the control PC 14. Then, the light source device 100 is installed in the inspection device 300. During the inspection, the stage 16 is moved accurately so that the irradiation position stored in the control PC 14 is irradiated with the laser light L1. By doing so, the conversion efficiency immediately after the shift can be suppressed.

According to the present embodiment, in the light source device 100 in which the wavelength of the laser light is shortened by using the nonlinear optical crystal 26, it is possible to realize the light output control with low cost and high reliability. In the semiconductor inspection light source device 100, if the amount of irradiation light on the object to be measured fluctuates even a little, the measured data will vary and accurate inspection results cannot be obtained. Also, output stability over a long period of time is required. Therefore, the light source device 100 according to the present embodiment can stabilize the amount of laser light. Therefore, by illuminating the inspection target with the wavelength-converted light L2 from the light source device 100, a stable inspection can be performed.

Although the embodiments of the present invention have been described above, the present invention includes appropriate modifications without impairing the objects and advantages thereof, and is not limited by the above embodiments.

11 laser light source 12 laser power supply 13 motor driver 14 control PC
15 Motor 16 Stage 20 External Resonator 21 Optical Mirror 22 Optical Mirror 23 Optical Mirror 24 Optical Mirror 25 Actuator 26 Nonlinear Optical Crystal 31 Mirror 32 Mirror 33 Beam Sampler 34 Detector 100 Light Source Device

Claims (10)

A laser light source that generates a fundamental wave,
A laser power source for driving the laser light source,
At least one nonlinear optical crystal that generates wavelength-converted light using the fundamental wave or a harmonic thereof as incident light;
A detector for detecting the wavelength-converted light,
A drive mechanism that changes the incident position of the incident light with respect to the nonlinear optical crystal;
Based on a detection signal from the detector, a control unit that feedback-controls the output power of the laser power source so that the output of the wavelength-converted light becomes constant, and
The control unit controls the drive mechanism to change the incident position when the output power exceeds a threshold value after a predetermined period has elapsed after the incident position has changed,
Wherein the predetermined period after the incident position is changed, while performing the feedback control, so that the incidence position as the output power exceeds the threshold value does not change, and controlling said drive mechanism,
The light source device , wherein the predetermined period is a period set within a range of 1 hour to 6 hours . The light source device according to claim 1, wherein the nonlinear optical crystal is a BBO crystal. The light source device according to claim 1, wherein the laser light source operates with continuous output. The light source device according to claim 1, wherein the laser power source supplies the laser light source with output power that exceeds a rated maximum output of the laser light source during the predetermined period. A light source device according to any one of claims 1 to 4,
An image pickup device for picking up an image of an inspection target illuminated with the wavelength-converted light from the light source device. In the non-test when not inspect the inspection object, said by the drive mechanism by changing the incident position of the incident light, the inspection apparatus according to claim 5 to be incident the incident light before Symbol nonlinear optical crystal. A laser light source that generates a fundamental wave,
A laser power source for driving the laser light source,
At least one nonlinear optical crystal that generates wavelength-converted light using the fundamental wave or a harmonic thereof as incident light;
A detector for detecting the wavelength-converted light,
A driving method for changing an incident position of the incident light with respect to the nonlinear optical crystal, and a method for controlling a light source device,
Based on a detection signal from the detector, a step of feedback controlling the output power of the laser power source so that the output of the wavelength-converted light becomes constant,
A step of controlling the drive mechanism so as to change the incident position when the output power exceeds a threshold value after a predetermined period has elapsed from the change of the incident position,
Wherein the predetermined period after the incident position is changed, while performing the feedback control, so that the incidence position as the output power exceeds the threshold value does not change, and a process of controlling the drive mechanism,
The method for controlling a light source device, wherein the predetermined period is a period set in a range of 1 hour to 6 hours . The method for controlling a light source device according to claim 7, wherein the nonlinear optical crystal is a BBO crystal. The method for controlling a light source device according to claim 7, wherein the laser light source operates with continuous output. The light source device control method according to claim 7, wherein the laser power source supplies, to the laser light source, output power that exceeds a rated maximum output of the laser light source during the predetermined period.

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