JP2008129035A - Light source device for mask inspection, and mask inspection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-performance and compact light source device for mask inspection, and to provide a mask inspection device using the light source device. <P>SOLUTION: The mask inspection device 1 in one embodiment of this invention is equipped with a light source 100 for mask inspection that has a laser light source, converts the wavelength of laser light outputted from the laser light source to output laser light at a wavelength of ≤400 nm and to output second harmonic waves of laser light at a wavelength of ≤400 nm. The second harmonic waves of laser light at a wavelength of ≤400 nm is used as illumination light for inspection. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a mask inspection light source device and a mask inspection apparatus used when detecting defects in a photomask (hereinafter simply referred to as a mask) used in a semiconductor manufacturing process.

  In general, a mask defect inspection method includes a mask pattern and design data comparison inspection method (generally referred to as a die-to-database comparison method) and a pattern comparison inspection method for two masks (generally a die-to-die comparison). Two methods are widely known. In any of these inspection methods, a mask pattern image is detected with a microscope. In that case, when using an optical microscope, it is necessary to illuminate the mask pattern with light. The light source (that is, mask inspection light source) is roughly classified into a case of using a lamp and a case of using a laser. In a mask inspection apparatus using a laser, a continuous laser that generates continuous laser light is generally used.

  In recent years, with the progress of semiconductors, that is, miniaturization, the defect size required to be detected has been reduced year by year. Therefore, in order to increase the defect detection sensitivity, it is necessary to shorten the wavelength of the inspection light source. Therefore, an argon laser having a wavelength of 364 nm has been used as a light source in a mask inspection apparatus that has been commercialized. Recently, a mask inspection apparatus using a continuous laser beam having a wavelength of 257 nm (this is a second harmonic wave having a wavelength of 514 nm, which is the maximum output line of an argon laser) is commercially available. However, further shortening of the wavelength of the inspection light source is desired from the viewpoint of detection sensitivity. A conventional mask inspection apparatus using such a continuous laser beam having a wavelength of 257 nm is disclosed in Non-Patent Document 1 or Non-Patent Document 2, for example.

  Since the pattern on the mask becomes finer as the semiconductor becomes finer, the light source of the mask inspection apparatus is also required to have a shorter wavelength in order to improve the defect detection sensitivity. As a next generation mask inspection light source, a light source having a wavelength of 200 nm or less is required. Therefore, for example, there is a mask inspection apparatus that generates 198.5 nm ultraviolet laser light, which is the sum frequency of the second harmonic of an argon laser with a wavelength of 488 nm and a fiber laser with a wavelength of 1064 nm, and uses this as a mask inspection light source. Has been developed. Such a mask inspection apparatus is disclosed in Patent Document 1 or Non-Patent Document 3, for example.

  On the other hand, in the mask inspection apparatus, a laser apparatus is used not only for the mask inspection light source as described above but also for an autofocus mechanism for focusing the objective lens on the observation part of the mask. Since the autofocus laser needs to follow the focus position at a high speed, a continuous oscillation type is preferable, or a high repetition type laser of several tens of kHz or more is required. Therefore, a blue semiconductor laser having a wavelength of 405 to 408 nm and a wavelength conversion solid-state laser having a wavelength of 473 nm are often used.

  Here, the wavelength of the autofocus laser of the mask inspection apparatus will be described. Generally, a patterned film formed on the pattern formation surface of a photomask has a thickness of about 100 to 300 nm. For this reason, at the time of defect inspection of the mask, it is necessary to focus on the pattern surface with an accuracy of about 100 nm or less. Therefore, the shorter the wavelength of the autofocus laser, the better. However, the autofocus laser needs to be irradiated onto the mask together with the illumination light of the mask inspection light source. For this reason, using a dichroic mirror, each light is coaxially irradiated and irradiated on the mask.

  The dichroic mirror has wavelength dependency in reflectance and transmittance. From the characteristics of this dichroic mirror, the wavelength of the autofocus laser needs to be at least about 100 nm away from the wavelength of the mask inspection light source. Therefore, conventionally, for example, when the wavelength of the inspection light source is 257 nm, the wavelength of the autofocus laser is longer than about 350 nm. In consideration of the compactness of the apparatus, the above-described semiconductor laser having a wavelength of 405 nm was optimal. Note that the use of a light source having a wavelength of 405 nm for autofocusing is disclosed in Patent Document 2, for example.

  As a continuous laser having a wavelength of 405 nm or less, a compact commercially available semiconductor laser (for example, manufactured by Nichia) can be obtained up to a wavelength of about 370 nm. However, in the semiconductor laser, when the wavelength is less than 0.4 μm, the laser output is greatly reduced. For example, a semiconductor laser having a wavelength of 385 nm is only commercially available with a maximum output of up to about 10 mW.

  On the other hand, as a wavelength conversion solid-state laser that continuously oscillates at a wavelength of 0.4 μm or less, the fourth harmonic of a YAG laser having a wavelength of 266 nm is representative. This YAG laser is commercially available with an output of several hundred mW. However, since the YAG laser is large and costs about 20 million yen, there are many problems in using it as an autofocus laser.

  In addition, in a mask inspection apparatus, a low-magnification observation optical system may be provided in order to observe not only a minute observation part but also a rather wide part. This is sometimes called a low magnification review. In this case, a laser or a lamp is necessary as illumination light. A conventional general mask inspection apparatus needs a laser apparatus for autofocusing and low magnification review. When an inspection light source is included, at least two laser apparatuses are necessary.

Furthermore, a solid-state laser with a wavelength conversion type wavelength of 193 nm using a laser with a wavelength of about 1547 nm has been developed, and there is a proposal to use it as a light source for a mask inspection apparatus. FIG. 7 shows a configuration of a conventional wavelength conversion type wavelength 193 nm solid-state laser. Since this conventional wavelength conversion type wavelength 193 nm solid-state laser uses a wavelength conversion method as shown in FIG. 7, the generation of laser light having a wavelength of 193 nm has a wavelength of 221 nm which is the seventh harmonic of the fundamental wave. And the sum frequency of the fundamental wave. For example, Patent Documents 3 and 4 disclose a mask inspection apparatus using such a conventional solid-state laser having a wavelength conversion type wavelength of 193 nm.
JP 2006-73970 A U.S. Pat. No. 6,661,580 JP-A-2005-010402 JP-A-2005-351919 Proceedings of SPIE Vol. 446, pp. 265-278, 2004. Toshiba Review, Vol. 58, No. 7, pp. 58-61, 2003 Proceedings of SPIE Vol. 5592, pp. 43, 2005.

  The inspection light source that generates ultraviolet light having a wavelength of 198.5 nm, which is a next-generation mask inspection light source, has the following problems. The inspection light source described in Patent Literature 1 or Non-Patent Literature 3 uses a large water-cooled argon laser. Therefore, not only the apparatus becomes huge, but also power consumption of several tens of kW is required, and there is a problem that the running cost is high due to replacement of the laser tube of the argon laser. Furthermore, since a laser device is also required for auto focus and low magnification review, it has been difficult to make the device configuration compact.

  Further, in the solid-state lasers described in Patent Documents 3 and 4 shown in FIG. 7, a laser beam having a wavelength of 387 nm is generated at an intermediate stage, but this is used for generating a wavelength of 221 nm. . In other words, if a part of the laser beam with a wavelength of 387 nm is separated and used for another application such as an autofocus light source, the power of the laser beam with a wavelength of 221 nm is reduced. The power of light will also decrease. Further, in these conventional techniques, since the sum frequency generation is used, it is difficult to improve the laser performance.

  The present invention has been made in view of the above problems, and provides a mask inspection light source device having a high performance and a compact configuration, and a mask inspection inspection using the mask inspection light source device.

  A mask inspection light source device according to a first aspect of the present invention includes a laser light source, outputs laser light having a wavelength of 400 nm or less using laser light output from the laser light source, and laser having a wavelength of 400 nm or less. It outputs the second harmonic of light. As a result, a mask inspection light source device having a high performance and a compact configuration can be provided. In addition, since the second harmonic of the laser beam having a wavelength of 400 nm or less has a wavelength of 200 nm or less, it is excellent in sensitivity as a mask inspection light source.

  In the mask inspection light source device according to the second aspect of the present invention, in the mask inspection light source device, the laser light having a wavelength of 400 nm or less is a fourth harmonic of light emitted from an erbium-doped fiber laser. is there.

  The mask inspection light source device according to a third aspect of the present invention is the above mask inspection light source device, wherein the laser light having a wavelength of 400 nm or less is a second harmonic of a titanium sapphire laser.

  A mask inspection apparatus according to a fourth aspect of the present invention includes the mask inspection light source device according to any one of the above, and an inspection illumination light that inspects a mask for a second harmonic of the laser light having a wavelength of 400 nm or less. It was used as. As a result, a mask inspection light source device having a high performance and a compact configuration can be provided. Further, since the second harmonic of the laser beam having a wavelength of 400 nm or less has a wavelength of 200 nm or less, the sensitivity can be improved.

  A mask inspection apparatus according to a fifth aspect of the present invention uses the laser beam having a wavelength of 400 nm or less as the autofocus laser beam in the mask inspection apparatus described above. When laser light having a wavelength of 200 nm or less, which is a mask inspection light source, is generated, laser light having a wavelength of 400 nm or less remaining without being converted into laser light having a wavelength of 200 nm or less can be used as a light source for autofocus. Therefore, a new laser light source device is not required, and the device configuration can be made compact without losing the power of the laser light having a wavelength of 200 nm or less for inspection.

  A mask inspection apparatus according to a sixth aspect of the present invention uses the laser beam having a wavelength of 400 nm or less as an observation laser beam for observing a mask in the mask inspection apparatus described above. When laser light having a wavelength of 200 nm or less, which is a mask inspection light source, is generated, laser light having a wavelength of 400 nm or less that remains without being converted into laser light having a wavelength of 200 nm or less can be used as the observation laser light. Therefore, a new laser light source device is not required, and the device configuration can be made compact without losing the power of the laser light having a wavelength of 200 nm or less for inspection.

  According to the present invention, it is possible to provide a mask inspection light source device having a high performance and a compact configuration, and a mask inspection device using the mask inspection light source device.

  Embodiments of the present invention will be described below with reference to the drawings. The following description shows preferred embodiments of the present invention, and the scope of the present invention is not limited to the following embodiments. In the following description, the same reference numerals denote the same contents.

  A mask inspection apparatus according to an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing a configuration of a mask inspection apparatus 1 according to the present embodiment. As shown in FIG. 1, the mask inspection apparatus 1 according to the present embodiment is roughly composed of a mask inspection light source 100 and a mask inspection apparatus main body 200. The mask inspection light source 100 is an ultraviolet light source that emits ultraviolet light. From the mask inspection light source 100, for example, a laser beam L08 with a wavelength of 193.4 nm and a laser beam L04c with a wavelength of 386.8 nm are extracted and supplied into the mask inspection apparatus 200.

  FIG. 2 shows the configuration of the mask inspection light source 100. As shown in FIG. 2, in the mask inspection light source 100, the fundamental laser 101 generates laser light L01 having a wavelength of 1547.2 nm. As the fundamental laser 101, a fiber amplifier using a semiconductor laser as seed light is suitable.

  In particular, as the fundamental laser 101, an erbium-doped fiber laser is preferably used in order to generate laser light having a wavelength of 400 nm or less. For example, if the wavelength of the mask inspection light source is 193 nm, it is necessary to use laser light having a wavelength of about 387 nm. The length four times the wavelength of about 387 nm is about 1547 nm. As is widely known, an erbium-doped fiber laser can generate laser light having a wavelength of 1.55 microns with an average output of 1 W or more. As a method of using the erbium-doped fiber laser, it is preferable to use a semiconductor laser having a wavelength of 1.55 microns for the oscillator and amplify the laser beam therefrom. In particular, the semiconductor laser is preferably a DFB type having a narrow wavelength width.

  A laser beam L01 having a wavelength of 1547.2 nm is incident on a wavelength conversion crystal (or called a non-linear optical crystal) 102a and includes a second harmonic wave having a wavelength of 773.6 nm and an unconverted residual fundamental wave. L01b is emitted. The laser beam L01b is incident on the dichroic mirror 103a, the laser beam L02a having a wavelength of 773.6 nm is reflected, and the laser beam L01c having a wavelength of 1547.2 nm which is a residual fundamental wave is transmitted. For example, an LBO crystal is preferably used for the wavelength conversion crystal 102a.

  The laser beam L02a having a wavelength of 773.6 nm is bent by the mirror 104a and then enters the wavelength conversion crystal 102b. Thus, the laser beam L02b including the wavelength 386.8 nm which is the second harmonic (that is, the fourth harmonic of the fundamental wave) and the unconverted portion is emitted. The laser beam L02b is incident on the dichroic mirror 103b, the laser beam L04a having a wavelength of 386.8 nm is reflected, and the laser beam L02c having a wavelength of 773.6 nm in the unconverted portion is transmitted. The wavelength conversion crystal 102b is preferably an LBO crystal, for example.

  The laser beam L04a having a wavelength of 386.8 nm is incident on the wavelength conversion crystal 102c after being bent by the mirror 104b. Thereby, the laser beam L04b including the wavelength 193.4m that is the second harmonic (that is, the eighth harmonic of the fundamental wave) and the unconverted portion is emitted. The laser beam L04b is incident on the dichroic mirror 103c, the laser beam L08 with a wavelength of 193.4 nm is reflected, and the laser beam L04c with a wavelength of 386.8 nm in the unconverted portion is transmitted. The laser beam L04c is output to the mask inspection apparatus 200. The laser beam L08 having a wavelength of 193.4 nm is reflected by the mirror 104c and proceeds toward the mask inspection apparatus 200 main body. The wavelength conversion crystal 102c may be anything that can generate a wavelength of 193.4 nm by a second harmonic of a wavelength of 386.8 nm, such as an SBBO crystal or a KBBF crystal. Specifically, IP04 manufactured by DEEP HOTONICS can be used. Thereby, wavelength conversion can be performed efficiently.

  The mask inspection light source 100 used in the mask inspection apparatus 1 according to the present embodiment uses an infrared laser whose fundamental wave has a wavelength of about 1.55 microns and converts the wavelength only three times. An ultraviolet laser beam having a wavelength of 193.4 nm can be generated. Therefore, the apparatus is simplified and compact as compared with the conventional wavelength conversion type 193 nm solid-state laser shown in FIG. Moreover, since sum frequency generation is not used, for example, the wavelength width can be narrowed. Therefore, performance can be improved.

  Next, the mask inspection apparatus main body 200 of the present invention will be described with reference to FIG. In the mask inspection apparatus 200, a laser beam L08 having a wavelength of 193.4 nm and a laser beam L04c having a wavelength of 386.8 nm extracted from the mask inspection light source 100 are supplied. The laser beam L08 enters the half mirror 201 and branches in two directions. Here, reflection illumination is performed by one of the laser beams L08 branched in two directions, and transmission illumination is performed by the other. First. The transmitted illumination will be described. The laser beam L11 emitted from the half mirror 201 is collected by the lens 202a and enters the uniformizing optical system 203a. As the uniformizing optical system 203a, for example, a so-called rod integrator is suitable. Alternatively, a bundle fiber can be used as the uniformizing optical system 203a. The laser light L11 propagates while repeating total reflection in the uniformizing optical system 203.

  A laser beam L12 having a spatially uniform intensity distribution is emitted from the homogenizing optical system 203a. This passes through the lens 202b, enters the polarization beam splitter 204a, and is reflected downward like a laser beam L13. The laser beam L13 passes through the dichroic mirror 205 and then becomes circularly polarized light through the λ / 4 wavelength plate 206a. The circularly polarized laser beam L13 illuminates the observation region 210a on the mask 208 through the objective lens 207a. The above is an illumination system called reflected illumination.

  The laser light L14 reflected from the mask 208 and traveling upward passes through the objective lens 207a and then passes through the λ / 4 wavelength plate 206a again to return to linearly polarized light. Here, the laser beam L14 traveling upward and the laser beam L13 traveling downward are orthogonal in polarization direction. Therefore, the laser beam L14 traveling upward passes through the polarization beam splitter 204a. As a result, it proceeds like the laser beam L15, passes through the imaging lens 211a, and strikes the two-dimensional photodetector 212a. As a result, the observation region 210a is enlarged and projected onto the two-dimensional photodetector 212a, and pattern inspection is performed. Thus, using the λ / 4 wavelength plate 206, the polarization directions of the laser light L13 incident on the mask and the laser light L14 reflected by the mask are orthogonalized. Thereby, the utilization efficiency of light can be improved.

  On the other hand, the laser beam L21 traveling downward through the half mirror 201 is reflected by the mirror 203a, passes through the lens 202c, and enters the uniformizing optical system 203b. The laser beam L21 travels through the homogenizing optical system 203b, so that a laser beam L23 having a spatially uniform intensity distribution is emitted. The homogenizing optical system 203b has the same configuration as the homogenizing optical system 203a. The laser beam L23 emitted from the homogenizing optical system 203b is reflected by the mirror 213b, passes through the condenser lens 214, and irradiates the observation region 210a on the mask 208. The above is an illumination system called transmitted illumination. Then, the transmitted light that has passed through the observation region 210a on the mask 208 is detected by the two-dimensional photodetector 212a, similarly to the transmitted illumination. That is, the light passes through the objective lens 207a, the λ / 4 wavelength plate 206a, the dichroic mirror 205, the polarization beam splitter 204a, and the imaging lens 211a and enters the two-dimensional photodetector 212a. Note that the observation area 210a by reflected illumination and the observation area 210a by transmitted illumination are at the same position. That is, the illumination position of the condenser lens 214 in the transmitted illumination and the illumination position of the objective lens 207a in the reflected illumination coincide with each other.

  By the way, in the mask inspection apparatus 1, by finely adjusting the interval between the observation area 210a of the mask 208 and the objective lens 207a, the image of the observation area 210a is projected sharply by the two-dimensional photodetector 212a. It is necessary to adjust. Therefore, the mask inspection apparatus 200 includes an autofocus mechanism as described below.

  In the autofocus mechanism of the mask inspection apparatus 1 of the present invention, the laser beam L04c having a wavelength of 386.8 nm extracted from the mask inspection light source 100 is used. That is, as indicated by a dotted line in FIG. 3, the laser beam L04c is used while being thin, hits the dichroic mirror 205, reflects downward like the laser beam L31, passes through the objective lens 207a, and passes through the mask 208. It hits the observation area 210a. The reflected laser light L14 hits the position sensor 216 because it is reflected by the triangular mirror 215 when reflected by the dichroic mirror 205 again. This position sensor 216 is also called a Japanese character sensor, and two light quantity sensors are connected to each other so that the center position of the laser beam hitting the sensor can be detected. This will be described below with reference to FIG.

  FIG. 4 is a diagram showing only an autofocus mechanism portion in the mask inspection apparatus 1 of the present invention. The autofocus laser beam L04c is initially indicated by a dotted line as in FIG. That is, it enters the mask 208 like the laser beam L31. Then, when the pattern surface of the mask 208 is the focal point position of the objective lens 207a, it proceeds like a laser beam L32. That is, the laser beam L32 reflected by the mask 208 enters the center of the position sensor 216. Here, when the mask 208 moves downward as indicated by an arrow (that is, when the distance between the mask 208 and the objective lens 207a is increased), the reflected light of the laser light L31 from the pattern surface of the mask 208 is as shown in FIG. The laser beam L32 ′ indicated by the middle one-dot chain line travels a different path from the laser beam L32. As a result, when the laser beam L32 ′ is reflected by the triangular mirror 215, the position sensor 216 shifts to the right in FIG. 4 like the laser beam L33 ′. The position sensor 216 is, for example, a two-divided photodiode, and outputs a difference between the two divided areas. Therefore, this shift amount is detected by the position sensor 216, and it is determined that the focus position of the mask 208 has shifted. Then, the autofocus mechanism works to correct the distance between the mask 208 and the objective lens 207a.

  As described above, the autofocus mechanism used in the mask inspection apparatus 1 of the present embodiment needs to use a thin laser beam, and is required to have a beam characteristic that is difficult to spread even if it is thin. Since the spread angle of the laser beam is proportional to the wavelength, it is preferable that the laser beam be as short as possible in order to make it difficult to spread a narrow beam. Therefore, in the present embodiment, an ultraviolet laser beam having a wavelength of 386.8 nm is used as the autofocus laser, and as a result, a conventional semiconductor laser having a wavelength of 405 nm or a solid-state laser having a wavelength of 473 nm is conventionally used. Since the wavelength is shortened compared to the case where it is used, the accuracy of autofocus is increased.

  On the other hand, as shown in FIG. 5, the transmittance characteristic of the dichroic mirror 205 is high at the wavelength of 193.4 nm of the inspection light source, but is highly reflective at the wavelength of 386.8 nm. Generally, in order to achieve high transmittance and high reflectance for two laser beams having different wavelengths incident on a dichroic mirror, the difference between the two wavelengths needs to be separated by at least 100 nm. . In the present invention, the difference between the two wavelengths is 193.4 nm, which is sufficiently separated, so that the dichroic mirror 205 can achieve very high separation efficiency. In other words, 386.8 nm, which is the wavelength of the autofocus laser of the present invention, is compatible with the two characteristics of higher autofocus accuracy and better separation characteristics at the dichroic mirror than before.

  Incidentally, in the mask inspection apparatus 1 of the present invention, as shown in FIG. 3, there are cases where the laser light L04c having a wavelength of 386.8 nm is used as illumination light for low-magnification review in addition to autofocus. This low magnification review illumination light will be described below. In the present embodiment, part of the laser light L04c is used as illumination light for low-magnification review.

  When providing a low-magnification review function, the dichroic mirror 205 in the mask inspection apparatus 200 is replaced with one having a characteristic of transmitting 30 to 50% of the P wave of the laser light L04c. However, with respect to the S wave, the characteristic of reflecting almost 100% is preferable. As a result, a part of the laser beam L04c supplied as the P wave passes through the dichroic mirror 205, is enlarged by the beam expander 217, passes through the λ / 2 wavelength plate 218, and becomes an S wave. The laser beam L04c that has become the S wave strikes the polarizing beam splitter 204b, reflects downward, and passes through the λ / 4 wavelength plate 206b. The λ / 4 wavelength plate 206b makes the S wave circularly polarized. The laser beam L04c that has passed through the λ / 4 wavelength plate 206b passes through the objective lens 207b and is irradiated onto the observation region 210b on the mask 208b. Reflected light from there passes through the objective lens 207b again, passes through the λ / 4 wavelength plate 206b, and then enters the polarization beam splitter 204b. Here, since the laser beam L04, which was a P wave, reciprocally passes through the λ / 4 wavelength plate 206b twice, it becomes an S wave. Therefore, the reflected light from the mask 208 is transmitted through the polarization beam splitter 204b. The reflected light that has passed through the polarizing beam splitter 204b passes through the imaging lens 211b and strikes the two-dimensional photodetector 212b. The enlargement ratio determined from the ratio of the focal lengths of the objective lens 207b and the imaging lens 211b is lower than the enlargement ratio of the inspection optical system determined from the ratio of the focal lengths of the objective lens 207a and the imaging lens 211a. It is used as a low magnification review. That is, it has a function of observing the observation area 210b at a low magnification.

  As described above, the mask inspection apparatus 1 of the present invention also has a low magnification review function. As described above, it is not necessary to provide a new light source or laser device, and a low magnification review function can be realized. Furthermore, the low magnification review is observed using 387 nm light which is unnecessary. For this reason, it is not necessary to divide and use the inspection laser light as the low magnification review light source, and thus the power of the inspection laser light L14 is not impaired.

  As described above, since laser light having a wavelength of 386.8 nm is used for low magnification review, the objective lens 207b and the imaging lens 211b are made of expensive DUV quartz or calcium fluoride as a glass material. There is no need to use normal quartz.

  Next, another configuration example of the mask inspection light source suitable for the mask inspection apparatus of the present invention will be described with reference to FIG. FIG. 6 is a configuration diagram of the mask inspection light source 300. A titanium sapphire laser is used as the fundamental laser 301 shown in FIG. It is known that a titanium sapphire laser can oscillate at a wavelength of 700 to 900 nm and an average output of 1 W or more. In order to generate laser light having a wavelength of 400 nm or less, the second harmonic of a titanium sapphire laser is used. As an operation mode of the titanium sapphire laser, in the present invention, a mode-locked high-speed pulse repetition operation with a high peak power is preferable because wavelength conversion is performed.

  In the present embodiment, laser light having a wavelength of 773.6 nm is extracted from the fundamental wave laser 301. Laser light L41a having a wavelength of 773.6 nm is incident on the wavelength conversion crystal 302a. As a result, the laser beam L41b including the wavelength 386.8 nm which is the second harmonic and the unconverted portion is emitted. The laser beam L41b is incident on the dichroic mirror 303a, the laser beam L42a having a wavelength of 386.8 nm is reflected, and the laser beam L41c having a wavelength of 773.6 nm in the unconverted portion is transmitted. The wavelength conversion crystal 302a is preferably an LBO crystal.

  The laser beam L42a having a wavelength of 386.8 nm is bent by the mirror 304a and then enters the wavelength conversion crystal 302b. As a result, the laser light L42b including the wavelength 193.4m that is the second harmonic (that is, the fourth harmonic of the fundamental wave) and the unconverted portion is emitted. The laser beam L42b is incident on the dichroic mirror 303b, the laser beam L43 having a wavelength of 193.4 nm is reflected, and the laser beam L42c having a wavelength of 386.8 nm in the unconverted portion is transmitted. The laser beam L43 having a wavelength of 193.4 nm is reflected by the mirror 304b and proceeds toward the mask inspection apparatus main body 200. In this embodiment, any wavelength conversion crystal 302b may be used as long as it can generate a wavelength of 193.4 nm by a second harmonic of a wavelength of 386.8 nm, such as an SBBO crystal or a KBBF crystal.

  As described above, the mask inspection apparatus according to the present invention is intended for a mask inspection apparatus equipped with a next-generation short-wavelength light source having a wavelength of 200 nm or less. It can be used not only for defect inspection, but also for mask quality control in semiconductor manufacturing plants. Furthermore, since the above mask inspection light source can be used at a repetition frequency of several MHz or more, it becomes a pseudo CW laser beam and is suitable for mask inspection. Thus, according to the present embodiment, it is possible to generate ultraviolet light having a wavelength of 193.4 nm without using sum frequency generation. Furthermore, the sensitivity can be improved by using 193.4 nm laser light as the inspection illumination light. Therefore, the inspection can be performed accurately. Moreover, since an argon laser is not required and the number of wavelength conversion crystals that generate the second harmonic can be reduced to 3 or less, the apparatus configuration can be made compact. Furthermore, loss of laser power can be reduced as the number of wavelength conversion crystals decreases. Therefore, the output power can be increased and the performance can be improved.

In addition, according to the present invention, a laser beam having a wavelength of 400 nm or less can be supplied as an autofocus laser beam without reducing the power of the laser beam for a mask inspection light source having a wavelength of 200 nm or less. There is no need to prepare.
In addition, since autofocus can be performed with laser light having a wavelength shorter than the wavelength 405 to 473 nm of the conventional autofocus light source, the resolution is increased and the spot of the autofocus light on the mask can be reduced. As a result, autofocus can be performed with high accuracy.

It is a figure which shows the structure of the mask inspection apparatus which concerns on embodiment. It is a figure which shows the structure of the mask test | inspection light source which concerns on embodiment. It is a figure which shows the structure of the mask inspection apparatus main body which concerns on embodiment. It is a figure for demonstrating the auto-focus mechanism which concerns on embodiment. It is a figure which shows the characteristic of the dichroic mirror used for the mask inspection apparatus which concerns on embodiment. It is a figure which shows the other structural example of the mask inspection light source which concerns on embodiment. It is a figure which shows the structure of the conventional wavelength conversion type | mold 193 nm solid state laser apparatus.

Explanation of symbols

1 Mask inspection device 100 Mask inspection light source
102a-c Wavelength conversion crystal 103a-c Dichroic mirror 104a-c Mirror 200 Mask inspection device 201 Half mirror 202a-d Lens 203a, b Uniform optical system 204a, b Polarization beam splitter 205 Dichroic mirror 206a, b λ / 4 wavelength plate 207a, b Objective lens 208 Mask 210a, b Observation area 212a, b Two-dimensional photodetector 213a, b Mirror 214 Condenser lens 215 Triangular mirror 216 Position sensor 217 Beam expander 218 λ / 2 wavelength plate 300 Mask inspection light source 301 Titanium sapphire laser 302a, b Wavelength conversion crystal 303a, b Dichroic mirror 304a, b Mirror L01a, c Laser light with a wavelength of 1547.2 nm L02a, c, L41a Wavelength 773. nm laser light L04a, c, L31 to 33, L32 ', L33', L42a, L43 wavelength 386.8nm laser light L08, L11-14, L21-24, L42c wavelength 193.4nm laser light L02b, L41b wavelength Laser light including 1547.2 nm and wavelength 773.6 nm nm L02b, L41b Laser light including wavelength 773.6 nm and wavelength 386.8 nm L04b, L42b Laser light including wavelength 386.8 nm and wavelength 193.4 nm

Claims (6)

Equipped with a laser light source,
A mask inspection light source device that outputs a laser beam having a wavelength of 400 nm or less using the laser light source and outputs a second harmonic of the laser beam having a wavelength of 400 nm or less.   2. The mask inspection light source device according to claim 1, wherein the laser light having a wavelength of 400 nm or less is a fourth harmonic of light emitted from an erbium-doped fiber laser.   The mask inspection light source device according to claim 1, wherein the laser light having a wavelength of 400 nm or less is a second harmonic of a titanium sapphire laser. A mask inspection light source device according to any one of claims 1 to 3,
A mask inspection apparatus that uses second harmonics of laser light having a wavelength of 400 nm or less as inspection illumination light for inspecting a mask.   The mask inspection apparatus according to claim 4, wherein the laser beam having a wavelength of 400 nm or less is used as an autofocus laser beam.   The mask inspection apparatus according to claim 4, wherein the laser light having a wavelength of 400 nm or less is used as an observation laser light for observing the mask.

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