JP4065880B2 - Laser apparatus and sum frequency generation method - Google Patents

Description

  The present invention relates to a laser device or a sum frequency generation method, and, for example, to a light source used for inspection of a mask used for semiconductor manufacturing or a manufactured wafer and a method for generating the light.

  In recent years, the circuit line width required for a semiconductor element has been increasingly narrowed as LSI is highly integrated and has a large capacity. These semiconductor elements use an original pattern pattern (also called a photomask, mask, or reticle; hereinafter collectively referred to as a mask) on which a circuit pattern is formed to expose the pattern on the wafer by a so-called reduction projection exposure apparatus called a stepper. It is manufactured by transferring and forming a circuit. Therefore, a pattern drawing apparatus capable of drawing a fine circuit pattern is used for manufacturing a mask for transferring such a fine circuit pattern onto a wafer. A pattern circuit may be directly drawn on a wafer using such a pattern drawing apparatus. The electron beam drawing apparatus is also described in the literature (see, for example, Patent Document 1). Alternatively, development of a laser beam drawing apparatus for drawing using a laser beam in addition to an electron beam has been attempted and disclosed in the literature (for example, see Patent Document 2).

  Here, as represented by a 1 gigabit class DRAM (Random Access Memory), a pattern constituting a large scale integrated circuit (LSI) is going to be on the order of submicron to nanometer. One of the major causes of a decrease in yield in the manufacture of LSI is a defect of a mask used when an ultrafine pattern is exposed and transferred onto a semiconductor wafer by a photolithography technique. In particular, with the miniaturization of the pattern dimensions of LSIs formed on semiconductor wafers, the dimensions that must be detected as pattern defects have become extremely small. Therefore, an apparatus for inspecting such a defect has been developed. This apparatus includes an illumination optical system that illuminates a mask, a sensor that detects an image of the mask and outputs an image signal, and an inspection apparatus that inspects a mask pattern based on the output image signal. .

  As described above, the mask pattern of the mask is increasingly miniaturized and highly integrated as the performance of semiconductor devices increases. Along with this, inspection apparatuses are required to exhibit high resolution. In order to realize high resolution, it is necessary to shorten the wavelength of the illumination light, and therefore it is necessary to use a laser light source having an inspection wavelength in the deep ultraviolet region.

  In general, the deep UV laser that oscillates at the fundamental wave is almost a pulsed laser because the shorter wavelength laser transition has a shorter fluorescence lifetime. As a continuous output light source having the shortest wavelength, an argon ion laser is known, but it is practically only 350.7 nm. In order to obtain a continuous light source in the deep ultraviolet region necessary for inspection, it is necessary to perform wavelength conversion to the short wavelength side using a continuous wave long wavelength laser as a fundamental wave. That is, it is necessary to perform sum frequency generation using a plurality of lasers having a wavelength longer than a predetermined wavelength as a fundamental wave with continuous output. However, wavelength conversion is a non-linear process and requires a high electric field to increase conversion efficiency. On the other hand, since continuous oscillation essentially provides a low electric field, a special conversion technique is required for wavelength conversion. Here, in order to increase the electric field strength in the nonlinear medium, a resonator configuration in which the fundamental wave is confined in the nonlinear crystal must be employed. The resonator configuration for sum frequency generation includes an internal resonator method in which the laser amplification medium is installed in the resonator, and an external resonator method in which the fundamental wave source is independent of the sum frequency generation resonator. There is.

  As a method of generating deep ultraviolet light by an external resonator, there is a method in which ultraviolet light having a wavelength of 373 nm and infrared light having a wavelength of 780 nm are caused to interact in a nonlinear crystal BBO to generate light having a wavelength of 254 nm. There is an example in which the 373 nm light is locked to the resonator by the resonator length control, and for the 780 nm light, the oscillation frequency is tuned to the resonator length, and the coherent light of two wavelengths is resonated by one resonator ( For example, refer nonpatent literature 1). In addition, an example in which 2.3 mW output was obtained in 196.5 nm in the deep ultraviolet wavelength region by generating a sum frequency of ultraviolet light with a wavelength of 266 nm and infrared light with a wavelength of 780 nm was shown in 2001 in Seattle, USA at the International Conference Advanced It is reported in Solid-State Lasers (lecture number WA6). In this example, a 780 nm titanium sapphire laser is used as infrared light, a nonlinear crystal is placed in this resonator, and an external resonator of 266 nm ultraviolet light is assembled to this nonlinear crystal. In addition, a 1064 nm wavelength Nd: YAG laser was emphasized by an external resonator, and a double wave of an argon laser having a wavelength of 244 nm was injected into the nonlinear crystal CLBO inside the resonator from the outside of the resonator to obtain continuous light having a wavelength of 199 nm There is an example (for example, refer to Patent Document 3). In these examples, the fundamental waves are all controlled to single longitudinal mode oscillation.

Here, in the fundamental wave which is single longitudinal mode oscillation, the deep ultraviolet light generated with the sum frequency also becomes a single longitudinal mode (longitudinal single mode). The longitudinal single mode deep ultraviolet light has a narrow line width of the light source reflecting its oscillation line width. As a light source for illumination, the narrower line width is less affected by chromatic aberration of the optical system, while each optical component of the illumination system has a certain interference pattern (speckle) due to coherence. It may occur as interference noise (speckle noise). When interference noise occurs, the lighting effect may be significantly deteriorated. Therefore, it is desired to generate a sum frequency using a multimode having a wide spectrum width in the longitudinal mode (frequency domain). However, when the multimode is used, the oscillation mode is split into multiple frequencies, so the electric field strength of each mode decreases even with the same output. Since conversion efficiency is remarkably deteriorated as compared with conversion, deep ultraviolet light having an amount of light necessary for an optical device, particularly an inspection device, cannot be obtained, and a light source for generating a sum frequency has not been put to practical use. Here, as a conventional example of sum frequency generation using a multimode with a wide spectral width, sum frequency generation by two multimode lights of the same wavelength, which is a very special condition of the sum frequency (second harmonic generation) (For example, refer to Patent Document 4). In this example, in order to generate the sum frequency of the same wavelength, the second harmonic is generated by one external resonator.
Japanese Patent Laid-Open No. 2002-237445 US Pat. No. 5,386,221 JP 2004-55695 A US Pat. No. 5,696,780 “Laser cooling of silicon atoms”, Proceedings of the 22nd Annual Conference of the Laser Society of Japan (2002 Osaka) p137

  As described above, as the light source for illumination, the narrower line width has less adverse effect due to chromatic aberration of the optical system, while interference noise occurs in each optical component of the illumination system, and the illumination effect is improved. May be significantly worse. Although this interference noise can take measures against the measurement system to some extent, it has become a major limitation on the design of the measurement system and has become an obstacle to the establishment of the apparatus. On the other hand, except for a very special case as described in Patent Document 4, a sum frequency generation mechanism using a multimode with a wide spectrum width has not been put into practical use.

  An object of the present invention is to overcome the above-mentioned problems, to provide a sum frequency generation method using a multimode, and to provide a laser device that serves as a laser light source that generates such a sum frequency.

The sum frequency generation method of one embodiment of the present invention includes:
A first laser light generating step for generating a first laser light having a first wavelength by using a first laser light source ;
A second laser light source having a standing wave type resonator inside thereof is used to generate a second laser light having a second wavelength different from the first wavelength as a longitudinal multimode light. Laser light generation process;
The first laser light generated by the first laser light generation step is taken into the first external resonator to resonate, and the first laser light taken through the nonlinear crystal is passed through the first crystal A resonance process;
The second laser light generated by the second laser light generation step is configured to have a resonator length that is 2n times (where n is an integer) the resonator length in the second laser light source. A second resonance step in which the second laser light is taken in and resonated in an external resonator, and the taken-in second laser light passes through the nonlinear crystal;
It is provided with.

And the laser device of one aspect of the present invention using such a sum frequency generation method,
A first laser light source for generating a first laser light having a first wavelength;
A second laser light source for generating a second laser beam having a second wavelength different from the first wavelength as a longitudinal multimode light;
A first external resonator that takes in and resonates with the first laser light generated from the first laser light source;
A non-linear crystal provided in the first external oscillator;
A second external resonator arranged so that the second laser light generated from the second laser light source is taken in and resonated, and the taken-in second laser light passes through the nonlinear crystal; When,
With
The second laser light source has a standing wave type resonator inside,
The second external resonator is configured to have a resonator length 2n times (where n is an integer) the resonator length in the second laser light source .

  According to the present invention, since the first external resonator and the second external resonator are separately provided, the multimode light can be resonated by the second external resonator, and the electric field strength is increased. Can do. Therefore, the conversion efficiency of the multimode light when the sum frequency is generated can be increased, and a multimode sum frequency can be obtained even when laser beams having different frequencies are used.

Embodiment 1 FIG.
Hereinafter, it demonstrates using drawing.
FIG. 1 is a conceptual diagram showing the configuration of the laser apparatus in the first embodiment.
In FIG. 1, a laser device 100 includes a laser light source 200 that generates infrared light having a wavelength of 238 nm to 400 nm as a fundamental wave 1 that is laser light of a longitudinal single mode, and a multimode for a longitudinal mode (frequency domain). As a fundamental wave 2 that is laser light, a laser light source 300 that generates ultraviolet light having a wavelength of 750 nm to 1300 nm, an external resonator 400 that takes in the fundamental wave 1 generated from the laser light source 200 and resonates, and a laser light source 300 The external resonator 500 which takes in and resonates the fundamental wave 2 produced | generated from this, and the nonlinear crystal 600 provided in the external resonators 400 and 500 are provided. That is, in the first embodiment, the single-mode fundamental wave 1 and the multi-mode fundamental wave 2 are adopted for the longitudinal mode (frequency domain), and the external resonator 400 and the external resonator 500 that are independent electric field enhancement resonators, respectively. And configure.
The external resonator 400 includes an impedance matching mirror 412 and high reflection mirrors 414, 416, and 418, and constitutes a ring resonator. The external resonator 500 includes an impedance matching mirror 512 and high reflection mirrors 514, 516, and 518, constitutes a ring resonator, and further includes high reflection mirrors 522 and 524. Each mirror is a movable mirror.

FIG. 2 is a diagram showing the external resonator for the fundamental wave 1 and the external resonator for the fundamental wave 2 separately.
In FIG. 2, the external resonator for the fundamental wave 1 and the external resonator for the fundamental wave 2 are shown separately to facilitate understanding of the configuration of FIG. 1.

First, the fundamental wave 1 is generated from the laser light source 200 as a laser beam generation process of the fundamental wave 1.
On the other hand, the fundamental wave 2 is generated from the laser light source 300 as the laser beam generation process of the fundamental wave 2.

  Then, as a resonance process of the fundamental wave 1, the fundamental wave 1 is taken into the external resonator 400 to be resonated, and the nonlinear crystal 600 is passed through the incorporated fundamental wave 1. In the external resonator 400, the fundamental wave 1 output from the laser light source 200 is taken into the external resonator 400 from the impedance matching mirror 412, reflected by the high reflection mirrors 414, 416, 418, and further reflected by the impedance matching mirror 412. By doing so, a resonator is configured. Here, the nonlinear crystal 600 is disposed on the optical path between the high reflection mirror 416 and the high reflection mirror 418.

  Similarly, as the resonance process of the fundamental wave 2, the fundamental wave 2 is taken into the external resonator 500 to resonate, and the taken-in fundamental wave 2 passes through the nonlinear crystal 600. In the external resonator 500, the fundamental wave 2 oscillated from the laser oscillator 300 is taken into the external resonator 500 from the impedance matching mirror 512, reflected by the high reflection mirrors 514, 516 and 518, and further reflected by the impedance matching mirror 512. By doing so, a resonator is configured. Here, the nonlinear crystal 600 is disposed on the optical path between the impedance matching mirror 512 and the high reflection mirror 514. Further, in the external resonator 500, the fundamental wave 2 reflected by the high reflection mirror 516 is repeatedly reflected by the mirror pair of the pair of high reflection mirrors 522 and 524, and then the high reflection mirror that becomes the original optical path. The fundamental wave 2 is returned to 518.

  Then, as the sum frequency generation process, the fundamental wave 1 and the fundamental wave 2 which are resonated and have an increased electric field intensity are passed through the nonlinear crystal 600 to generate the sum frequency, and the sum frequency as an output is extracted outside. .

FIG. 3 is a diagram showing the relationship between the fundamental wave and the sum frequency.
As shown in FIG. 3A, when the sum frequency is generated using the fundamental wave between the longitudinal single mode lights, the output sum frequency is also the longitudinal single mode light. Conventionally, since the sum frequency was generated using the fundamental wave of the longitudinal single mode light, the line width of the output sum frequency was narrowed, and interference noise was a problem. FIG. 3B shows a case where sum frequency generation is performed using a fundamental wave of longitudinal single mode light and a fundamental wave of multimode. In such a case, the output sum frequency becomes multimode light, and the spectrum width can be widened. Similarly, as shown in FIG. 3C, when the sum frequency is generated using the multimode fundamental waves, the output sum frequency becomes multimode light, and the spectrum width can be widened. .
Here, when a light source by non-linear conversion such as sum frequency is used as the illumination light source for measurement, the fundamental wave which is single longitudinal mode oscillation reflects the oscillation line width, and the line width of the light source is It is narrowed. For example, the oscillation line width of a 1064 nm Nd: YAG laser is 1 MHz. The line width of the second harmonic of the argon laser having a wavelength of 244 nm is 14 MHz. The line width of the light source by these sum frequencies is from (142 + 12) 1/2 to 14 MHz. On the other hand, in the case of a laser light source of multimode oscillation, the oscillation line width varies greatly depending on the light source, but is usually as wide as 1 GHz to 30 GHz. Therefore, a laser light source that generates a multimode that has a wide spectral width and is easy to control is desired.

FIG. 4 is a diagram for explaining a case where sum frequency generation is performed by single-passing a multimode fundamental wave.
FIG. 4 shows a case where sum frequency generation is performed using a fundamental wave of longitudinal single mode light and a fundamental wave of multimode. For multimode light that is difficult to assemble as will be described later, sum frequency generation is performed with longitudinal single-mode light resonated by an external resonator using a single path that passes through a nonlinear crystal without assembling the resonator. The output light becomes a minute amount of light in accordance with the multimode light having a small electric field. This is insufficient as a laser device used as a light source. Therefore, it is necessary to improve the electric field strength for multimode light.

  In the first embodiment, as shown in FIG. 1, a sum frequency output of a necessary light amount can be obtained by improving the electric field strength of multimode light using an external resonator 500.

In the first embodiment, as one of the fundamental waves, neodymium, which is a single longitudinal mode laser, is used as a fundamental wave 1 that is a quadruple wave (wavelength 266 nm) of an active substance YAG laser (Nd: YAG). This is obtained by generating the second harmonic twice with a single longitudinal mode Nd: YAG laser as a fundamental wave. The line width of this light source is 10 kHz.
FIG. 5 is a conceptual diagram showing a configuration of a laser light source that generates a fourth harmonic of Nd: YAG (wavelength 266 nm).
In the laser light source 200 that generates the fundamental wave 1, first, an Nd: YAG laser having a wavelength of 1064 nm is oscillated from the laser light source 210 and is composed of an impedance matching mirror 221 and high reflection mirrors 222, 223, and 224. The resonator 220 is used to resonate and pass through the nonlinear crystal 225. Thereby, a double harmonic (532 nm) can be obtained. Further, the second harmonic (532 nm) is resonated using a ring resonator 230 including an impedance matching mirror 231 and high reflection mirrors 232, 233, and 234, and passes through the nonlinear crystal 235. Thereby, a 4th harmonic (266 nm) can be obtained.

  Next, a broadband (multimode) Nd: YAG laser (wavelength: 1064 nm) is used as another fundamental wave. This is the fundamental wave 2. An etalon was placed in the resonator in the laser light source 300 that oscillates the fundamental wave 2 to perform frequency control, and the oscillation line width was set to 10 GHz.

As shown in FIG. 1, an external resonator 400 having a wavelength of 266 nm is formed, and CLBO (CsLiB6O10) is formed as a nonlinear crystal 600 in a phase matching condition that satisfies the sum frequency generation condition at wavelengths 266 nm and 1064 nm. : Cesium lithium borate). Further, an external resonator 500 for a broadband Nd: YAG laser was configured so as to overlap with the optical path of this CLBO, and a double resonator configuration as shown in FIG. 1 was performed. The line width of the broadband light source was 10 GHz.
Here, for example, assuming that 1064 nm is ordinary light, 266 nm is ordinary light, and the sum frequency 213 nm is abnormal light, the energy conservation law is 1064 (o) +266 (o) = 213 as a sum frequency generation condition at a crystal temperature of 160 degrees. (E) is satisfied, and the phase matching condition, that is, the phase matching angle θ (azimuth angle and internal angle at the time of crystal incidence) as an angular momentum conservation law is 68.5 degrees.

FIG. 6 is a diagram illustrating an equation for wavelength conversion.
When the wavelength of the fundamental wave 1 is λ1, the wavelength of the fundamental wave 2 is λ2, and the wavelength of the sum frequency is λ3, the relationship shown in FIG. 6 is established between the wavelengths λ1, λ2, and λ3. Therefore, by generating the sum frequency of these two fundamental waves, it is possible to obtain a multimode Nd: YAG fifth harmonic wave (wavelength 213 nm) that becomes deep ultraviolet light.

Here, in order to form an external resonator for a broadband multimode fundamental wave, the resonator length (effective optical length) of the resonator in which the external resonator 500 is in the laser light source 300 of the fundamental wave 2 is used. ) Can be achieved by having a resonator length (effective optical length) that is an integral multiple of. That is, the two resonators of the external resonator 500 and the resonator in the laser light source 300 may have a resonator length having an equivalent frequency interval. However, if the resonator in the laser light source 300 that oscillates the multimode fundamental wave 2 is a standing wave type resonator and the optical length of the resonator is L, the wavelength conversion for the fundamental wave 2 is performed. The external resonator 500 is a ring resonator as shown in FIG . Therefore, it is possible to achieve the external resonator 500 as a ring resonator by configuring a resonator having an optical resonator length of at least an integral multiple of 2L (2nL).

  By the way, the ring resonator is usually configured with a resonator length of several tens of cm, for example, 22 cm. On the other hand, a laser having an output of 1 W or more used as a multimode laser often has an optical length of the resonator of 1 m or more. If this is the case, the resonator length of the external resonator 500 will be at least 2 m. However, it is difficult from the viewpoint of the mechanical stability of the optical system to increase the distance between the mirrors of the ring resonator in order to extend the resonator length. That is, it is generally difficult to stably realize such a resonator having a long optical length. Therefore, in this embodiment, as a resonator length adjusting means, a high reflection mirror pair is installed in the external resonator 500, and multiple reflections are generated by adjusting the installation angle, thereby adjusting the substantial resonator length. I was able to. Thereby, a small and robust external resonator having a long resonator length can be realized.

FIG. 7 is a diagram for explaining the operation of the high reflection mirror pair.
In the external resonator 500, the light beam of the fundamental wave 2 reflected by the high reflection mirror 516 is taken by the mirror pair of the pair of high reflection mirrors 522 and 524, and is repeatedly reflected on the other side to increase the optical path length. After that, the fundamental wave 2 is returned to the high reflection mirror 518 which is the original optical path. For example, as shown in FIG. 7A, the angle θ1 of the high-reflection mirror 524 and the angle θ2 of the high-reflection mirror 522 are changed from the state where the number of reflections is small, as shown in FIG. By adjusting so that it may be in many states, it can be set to the installation angle at which the fundamental wave 2 resonates.
For example, as an example of a highly reflective mirror pair, the substrate is made of synthetic quartz and the shape is formed on a disk. However, it may be rectangular. Further, the configuration is suitable as long as the reflecting surfaces face each other and can be adjusted from parallel installation to several degrees. Further, the reflectance is more preferably about 99.999% at the wavelength. Further, the surface accuracy is more preferably 1 / 50λ or less at the wavelength.

FIG. 8 is a conceptual diagram showing another configuration of the laser apparatus in the first embodiment.
In the laser apparatus 100 in FIG. 8, the position where the laser light source 200 is disposed is different from the configuration in FIG. Therefore, the positions where the impedance matching mirror 412 and the high reflection mirrors 414, 416, and 418 constituting the external resonator 400 are also different from the configuration of FIG. In FIG. 8, the position where the laser light source 200 is arranged is equivalent to the case where the position is rotated about 180 ° about the nonlinear crystal 600 as compared with the position shown in FIG. 1. Even in such a configuration, the sum frequency can be generated similarly.

  As described above, according to the configuration of the first embodiment, the sum frequency generation can be performed by using the longitudinal single mode fundamental wave and the multimode fundamental wave without taking a complicated configuration. As a result, it is possible to obtain high-power deep ultraviolet light with a controlled line width that does not cause interference noise.

Embodiment 2. FIG.
In the first embodiment, the external resonator is formed for the sum frequency for all the modes of the fundamental wave 2. However, in the second embodiment, the external resonance is performed for the sum frequency for some modes. A case of forming a vessel will be described.
First, in Embodiment 2, an example in which a multimode argon laser is used as the fundamental wave 2 will be described. In an argon laser having an output of 1 W or more, the optical length of the resonator is often 1 m or more. Even if the horizontal mode (spatial region) is a single mode, the vertical mode is a multi-mode unless the frequency is limited. Here, the longitudinal mode interval of the resonator having an optical length of 1 m is the speed of light / 2 × 1 m, which is about 150 MHz. When the gain width of the argon laser used is 15 GHz, there are about 100 longitudinal modes. In order to form an external resonator for the sum frequency for all of these modes, if this external resonator is formed of a ring resonator, the optical length of the resonator must be 2 m. In such a case, the resonator length adjusting means as described in the first embodiment is required.
However, considering the optical loss associated with the formation of the resonator, it may not always be necessary to emphasize all the modes with the resonator. The inventor has found that sufficient fundamental wave emphasis may be obtained by resonating a plurality of partial modes among the multimodes of the fundamental wave 2. For example, even when a resonator having a mode interval of 900 MHz was used, a result that sufficient fundamental wave enhancement was obtained was obtained. In this case, the ring resonator can be formed with a resonator length of about 33 cm, and a small resonator can be formed.

FIG. 9 is a conceptual diagram showing the configuration of the laser apparatus in the second embodiment.
9, the laser device 110 is the same as the configuration of FIG. 1 except that the pair of high reflection mirrors 522 and 524 is excluded from the configuration of FIG. 1. That is, the laser device 110 is generated from the laser light source 200 that generates the fundamental wave 1 that is the longitudinal single-mode laser light, the laser light source 300 that generates the fundamental wave 2 that is the multi-mode laser light, and the laser light source 200. The external resonator 400 that takes in and resonates the fundamental wave 1, the external resonator 500 that takes in and resonates the fundamental wave 2 generated from the laser light source 300, and the nonlinear crystal provided in the external oscillators 400 and 500. 600. That is, in the first embodiment, the single-mode fundamental wave 1 and the multi-mode fundamental wave 2 are adopted, and the external resonator 400 and the external resonator 500 that are independent electric field enhancement resonators are configured.
The external resonator 400 includes an impedance matching mirror 412 and high reflection mirrors 414, 416, and 418, and constitutes a ring resonator. The external resonator 500 includes an impedance matching mirror 512 and high reflection mirrors 514, 516, and 518, and forms a ring resonator.

FIG. 10 is a diagram for explaining the relationship between the mode interval and the resonator length.
FIG. 10A shows a spectrum of the fundamental wave 2 that is a multimode laser beam. Here, the mode interval can be represented by light velocity c / resonator length L. Therefore, by thinning out several of all longitudinal modes, in other words, by resonating every few, the mode interval is widened, and the resonator length L can be reduced accordingly. As shown in FIG. 10B, by resonating all longitudinal modes every six lines, the mode interval can be increased by a factor of 6, and the resonator length L can be reduced to 1/6. Therefore, the originally required resonator length 2 m can be about 33 cm.

  As a result of experiments, the inventor has found that the effect of the external resonator 500 for obtaining high-power deep ultraviolet light with controlled line width that does not cause interference noise using multi-mode light is at least 1 of all longitudinal modes. It has been found that it is preferable to emphasize a mode of / 10 or higher.

  For example, the line width of the light source obtained at the sum frequency of the longitudinal single mode fundamental waves is 10 kHz, and obtained at the sum frequency obtained by resonating all longitudinal modes using the multimode fundamental wave as in the first embodiment. If the line width of the light source is 10 GHz, the line width of the light source becomes 1 GHz or more by sufficiently resonating the number of all longitudinal modes as in the second embodiment, and the interference noise is sufficiently suppressed. Can do.

Embodiment 3 FIG.
FIG. 11 is a conceptual diagram showing the configuration of the inspection apparatus.
In FIG. 11, a configuration example of an inspection apparatus including an image input apparatus that inspects a mask defect at a level of 70 nm in an inspection apparatus having an illumination system on which the laser apparatus 100 serving as a light source according to the first or second embodiment is mounted. Indicates. The inspection apparatus includes a light source 100 that is a laser device configured according to the first embodiment or the second embodiment, and a high-power deep ultraviolet light with a controlled line width that does not cause interference noise emitted from the light source 100 as a half mirror. The substrate 630 is reflected on the substrate 630 side by 610, and the substrate 630 on which a reflection type inspection pattern such as a mask or a wafer to be measured is formed is illuminated via the objective lens 620. Light reflected from the substrate 630 passes through the half mirror 610 through the objective lens 620 and is received by the sensor 650 through the projection lens 640. Then, the processor 660 performs image processing to obtain an image of the pattern to be inspected. In other words, the above-described sum frequency output is irradiated and illuminated on the pattern to be inspected via the half mirror, the image is taken into the sensor, and the presence or absence of defects is inspected by signal processing by the processor.

  In order to inspect the mask defect at the 70 nm level, a laser having a wavelength of 200 to 257 nm is required. In the laser apparatus configured according to the first embodiment or the second embodiment serving as a light source, interference having a wavelength of 213 nm is required. Since high-power deep ultraviolet light with a controlled line width that does not cause noise can be irradiated, it is possible to inspect mask defects at the 70 nm level.

  As described above, according to the first embodiment or the second embodiment, it is possible to obtain a light source with high output and controlled oscillation line width that does not generate interference noise as measurement illumination. Furthermore, according to the third embodiment, it is possible to provide an illumination device or an inspection device equipped with a stable deep ultraviolet light source, thereby enabling high-speed and precise measurement. In addition, here, a reflection type inspection apparatus that acquires an image of a pattern to be inspected using reflected light is described, but this is a transmission type inspection apparatus that acquires an image of an inspected pattern using transmitted light. It goes without saying that it doesn't matter.

  The embodiments have been described above with reference to specific examples. However, the present invention is not limited to these specific examples.

  Furthermore, even if multi-mode fundamental waves having different wavelengths are used, if each uses an external resonator equipped with a reflecting mirror pair, sum frequency generation can be similarly performed without taking a complicated configuration. As a result, it is possible to obtain high-power deep ultraviolet light with a controlled line width that does not cause interference noise.

  Further, the description of the control method of the impedance matching mirror and the high reflection mirror is omitted, but the required control method can be appropriately selected and used. Similarly, what is required for the configuration of the optical system can be appropriately selected and used.

  In addition, all reflection mirrors or sample inspection apparatuses that include the elements of the present invention and whose design can be appropriately changed by those skilled in the art are included in the scope of the present invention.

1 is a conceptual diagram illustrating a configuration of a laser device in Embodiment 1. FIG. It is the figure which showed the external resonator for fundamental waves 1 and the external resonator for fundamental waves 2 separately. It is a figure which shows the relationship between a fundamental wave and a sum frequency. It is a figure for demonstrating the case where a multimode fundamental wave is single-passed and sum frequency generation is performed. It is a conceptual diagram which shows the structure of the laser oscillator which generates the 4th harmonic (wavelength 266nm) of Nd: YAG. It is a figure which shows the type | formula of wavelength conversion. It is a figure for demonstrating operation | movement of a highly reflective mirror pair. FIG. 6 is a conceptual diagram showing another configuration of the laser apparatus in the first embodiment. FIG. 5 is a conceptual diagram showing a configuration of a laser device in a second embodiment. It is a figure for demonstrating the relationship between a mode space | interval and resonator length. It is a conceptual diagram which shows the structure of an inspection apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Laser apparatus 200,300 Laser light source 400,500 External resonator 412,512 Impedance matching mirror 600 Nonlinear crystal 414,416,418,514,516,518,522,524 High reflection mirror

Claims (5)

A first laser light source for generating a first laser light having a first wavelength;
A second laser light source for generating a second laser beam having a second wavelength different from the first wavelength as a longitudinal multimode light;
A first external resonator that takes in and resonates with the first laser light generated from the first laser light source;
A non-linear crystal provided in the first external oscillator;
A second external resonator arranged so that the second laser light generated from the second laser light source is taken in and resonated, and the taken-in second laser light passes through the nonlinear crystal; When,
With
The second laser light source has a standing wave type resonator inside,
The laser device, wherein the second external resonator is configured to have a resonator length 2n times (where n is an integer) the resonator length in the second laser light source .   The laser device further takes in the second laser light taken into the second external resonator in a part of the optical path in the second external resonator, and repeatedly reflects the second laser light. 2. The laser device according to claim 1, further comprising a pair of mirrors for returning the second laser light on an optical path in the second external resonator. A first laser light generating step for generating a first laser light having a first wavelength by using a first laser light source ;
A second laser light source having a standing wave type resonator inside thereof is used to generate a second laser light having a second wavelength different from the first wavelength as a longitudinal multimode light. Laser light generation process;
The first laser light generated by the first laser light generation step is taken into the first external resonator to resonate, and the first laser light taken through the nonlinear crystal is passed through the first crystal A resonance process;
The second laser light generated by the second laser light generation step is configured to have a resonator length that is 2n times (where n is an integer) the resonator length in the second laser light source. A second resonance step in which the second laser light is taken in and resonated in an external resonator, and the taken-in second laser light passes through the nonlinear crystal;
A sum frequency generation method comprising: 4. The sum frequency generation method according to claim 3, wherein in the second resonance step, the resonator length is adjusted by repeatedly reflecting the second laser beam to each other using a pair of mirrors.   2. The laser device according to claim 1, wherein the second external resonator resonates in a plurality of partial modes among the multimodes of the second laser light.

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