JP2009156728A - Inspection light source apparatus and defect inspection apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-performance and compact inspection light source apparatus, and a defect inspection apparatus using it. <P>SOLUTION: The defect inspection apparatus 1 of the invention has a laser light source for generating a laser light with a 1 μm wavelength band, and an inspection light source 100 for outputting a fifth harmonic of the laser light with the 1 μm wavelength band, and outputting a fourth harmonic of the laser light with the 1 μm wavelength band. The fifth harmonic is used for an inspecting illumination light. The fourth harmonic is used for an auto-focusing laser light. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an inspection light source device and a defect inspection apparatus used when detecting defects such as 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, the inspection light source) is roughly classified into a case where a lamp is used and a case where a laser is used. In a defect 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. In order to increase the defect detection sensitivity, it is necessary to shorten the wavelength of the inspection light source. Therefore, a defect 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 in 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 defect 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.

  On the other hand, in the defect inspection apparatus, a laser apparatus is used not only for the 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 high speed, a continuous oscillation type laser 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 defect inspection apparatus will be described. In general, 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 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. Due to the characteristics of this dichroic mirror, the wavelength of the autofocus laser needs to be at least about 50 nm away from the wavelength of the 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 310 nm. In consideration of the compactness of the apparatus, the above-described semiconductor laser having a wavelength of 405 nm was optimal. For example, Patent Document 1 discloses that a light source having a wavelength of 405 nm is used for autofocus.

  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 a semiconductor laser, the laser output is greatly reduced when the wavelength is shorter than 400 nm. 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 type solid-state laser that continuously oscillates at a wavelength of 400 nm 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 has a large apparatus and is very expensive, there are many problems in using it as a laser dedicated to autofocus.

In addition, in a defect 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. In the conventional general defect inspection apparatus, another laser apparatus is necessary for autofocusing and low magnification review. When the inspection light source is included, at least two laser apparatuses are necessary.
U.S. Pat. No. 6,661,580 Proceedings of SPIE Vol. 446, pp. 265-278, 2004. Toshiba Review, Vol. 58, No. 7, pp. 58-61, 2003

  As described above, since the conventional defect inspection apparatus requires a laser device different from the inspection light source for autofocusing and low magnification review, it is difficult to make the apparatus configuration compact.

  The present invention has been made against the background of the above circumstances, and an object of the present invention is to provide an inspection light source device having a high performance and a compact configuration, and a defect inspection apparatus using the inspection light source device.

  The inspection light source device according to the first aspect of the present invention includes a laser light source that generates laser light having a wavelength of 1 μm band, outputs a fifth harmonic of the laser light, and a fourth harmonic of the laser light. It outputs waves. Thereby, the inspection light source device having a high performance and a compact configuration can be provided. Further, the fifth harmonic of the laser light having a wavelength of 1 μm band has a wavelength of about 200 nm, and is excellent in sensitivity as an inspection light source.

An inspection light source device according to a second aspect of the present invention is the above-described inspection light source device, wherein the laser light source is any one of an Nd: YAG laser, an Nd: YVO ₄ laser, an Nd: YLF laser, a fiber laser, and a glass laser. It is.

  A defect inspection apparatus according to a third aspect of the present invention includes the inspection light source device according to any one of the above, and uses the fifth harmonic of the laser light as inspection illumination light. As a result, a defect inspection apparatus having a high performance and a compact configuration can be provided. Further, the fifth harmonic of the laser light having a wavelength of 1 μm band has a wavelength of about 200 nm, and is excellent in sensitivity as an inspection light source.

  A defect inspection apparatus according to a fourth aspect of the present invention uses the fourth harmonic of the laser light as the autofocus laser light in the defect inspection apparatus. When the fifth harmonic of the 1 μm band wavelength laser light, which is the inspection light source, is generated, the remaining fourth harmonic of the 1 μm band laser light that is not converted is used as an autofocus light source. be able to. Therefore, a new laser light source device is not required, and the device configuration can be made compact.

  A defect inspection apparatus according to a fifth aspect of the present invention uses the fourth harmonic of the laser light as the observation laser light in the defect inspection apparatus. When the fifth harmonic of the 1 μm band wavelength laser light, which is the inspection light source, is generated, the fourth harmonic of the 1 μm wavelength laser light remaining without being converted is used as the observation laser light. Can do. Therefore, a new laser light source device is not required, and the device configuration can be made compact.

  According to the present invention, it is possible to provide an inspection light source device having a high performance and a compact configuration, and a defect inspection device using the 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 defect 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 defect inspection apparatus 1 according to the present embodiment. As shown in FIG. 1, the defect inspection apparatus 1 according to the present embodiment is roughly composed of an inspection light source 100 and a defect inspection apparatus main body 200. The inspection light source 100 is an ultraviolet light source that emits ultraviolet light. In the present embodiment, for example, laser light L08 with a wavelength of 213 nm and laser light L07 with a wavelength of 266 nm are extracted from the inspection light source 100 and supplied into the defect inspection apparatus main body 200.

FIG. 2 shows the configuration of the inspection light source 100. In the inspection light source 100 according to the present invention, the fundamental laser 101 generates laser light having a wavelength of 1 μm band. As shown in FIG. 2, in the present embodiment, the fundamental laser 101 generates laser light L01 having a wavelength of 1064 nm. As the fundamental laser 101, a solid-state laser using an Nd: YVO ₄ crystal is suitable. Note that the fundamental laser 101 is not limited to this, and a solid-state laser using an Nd: YAG crystal, a solid-state laser using an Nd: YLF crystal, a fiber laser, a glass laser, or the like can be used. Further, the wavelength of the laser light generated from the fundamental wave laser 101 is not limited to 1064 nm and can be changed as appropriate.

  A laser beam L01 having a wavelength of 1064 nm is incident on a wavelength conversion crystal (or called a non-linear optical crystal) 102a, and a laser beam L02 including a wavelength of 532 nm which is the second harmonic and an unconverted residual fundamental wave is emitted. The For the wavelength conversion crystal 102a, for example, an LBO crystal or the like can be used.

  The laser beam L02 including the second harmonic wave having a wavelength of 532 nm and the fundamental wave having a wavelength of 1064 nm is incident on the wavelength conversion crystal 102b. As a result, the laser beam L03 including the second harmonic (the fourth harmonic of the fundamental wave) having a wavelength of 266 nm and unconverted laser light is emitted. The wavelength conversion crystal 102b is preferably, for example, a CLBO crystal or a BBO crystal.

  The laser beam L03 is incident on the dichroic mirror 103a, the laser beam L05 having a wavelength of 266 nm and the laser beam L05 having a wavelength of 1064 nm which is a residual fundamental wave are reflected, and the laser beam L04 having a wavelength of 532 nm which is not converted is transmitted.

  The laser beam L05 having a wavelength of 266 nm including the residual fundamental wave is bent by the mirror 104a and enters the wavelength conversion crystal 102c. As a result, a laser beam L06 including a laser beam having a wavelength of 213 nm (the fifth harmonic of the fundamental wave), which is the sum frequency, and a laser beam having an unconverted wavelength of 266 nm is emitted. The wavelength conversion crystal 102c is preferably a BBO crystal or a CLBO crystal.

  The laser beam L06 is incident on the dichroic mirror 103b, the laser beam L08 having a wavelength of 213 nm is reflected, and the laser beam L07 having a wavelength of 266 nm in the unconverted portion is transmitted. The laser beam L08 having a wavelength of 213 nm is reflected by the mirror 104b and proceeds toward the defect inspection apparatus main body 200. The laser beam L07 having a wavelength of 266 nm is output to the defect inspection apparatus main body 200.

  The inspection light source 100 used in the defect inspection apparatus 1 according to the present embodiment uses an infrared laser whose fundamental wave has a wavelength of 1.06 μm, and converts the wavelength only three times, and the wavelength of 213 nm, which is inspection light. UV laser light can be generated. Further, unconverted 266 nm laser light remaining when generating the wavelength of 213 nm can be reused. For this reason, it is not necessary to provide a laser device different from the inspection light source for autofocusing or low magnification review unlike the conventional defect inspection device, and the device configuration can be simplified.

  Next, the configuration of the defect inspection apparatus main body 200 of the present invention will be described with reference to FIG. In the defect inspection apparatus main body 200, a laser beam L08 having a wavelength of 213 nm and a laser beam L07 having a wavelength of 266 nm extracted from the 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 beam L11 propagates while repeating total reflection in the uniformizing optical system 203a.

  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 can be enlarged and projected onto the two-dimensional photodetector 212a to obtain a pattern image. In this way, using the λ / 4 wavelength plate 206a, 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 213a, 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 defect 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 defect inspection apparatus 1 includes an autofocus mechanism as described below.

  In the autofocus mechanism of the defect inspection apparatus 1 of the present invention, the laser beam L07 having a wavelength of 266 nm extracted from the inspection light source 100 is used as AF light. That is, as shown by the dotted line in FIG. 1, the laser beam L07 is used while being thin, hits the dichroic mirror 205, is reflected downward like the laser beam L31, passes through the objective lens 207a, and is observed in the observation region 210a of the mask 208. It hits. The reflected laser beam L32 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. 3 is a diagram showing an autofocus mechanism in the defect inspection apparatus 1 of the present invention. The laser beam L07 for autofocus 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 is moved 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. 3 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 defect 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 266 nm is used as the autofocus laser. As a result, a semiconductor laser having a wavelength of 405 nm that has been conventionally used or a solid-state laser having a wavelength of 473 nm is used. Since the wavelength is shortened compared to the case, the accuracy of autofocus is increased.

  On the other hand, the transmittance characteristic of the dichroic mirror 205 has wavelength dependency. Due to the characteristics of this dichroic mirror, the wavelength of the autofocus laser needs to be at least about 50 nm away from the wavelength of the inspection light source. In the present embodiment, the wavelength of the inspection light source is 213 nm, and the wavelength of the autofocus laser light is 266 nm. For this reason, the laser beam with a wavelength of 213 nm shows a high transmittance, but the laser beam with a wavelength of 266 nm can be highly reflected, and the separation efficiency at the dichroic mirror 205 can be made extremely high. Therefore, according to the present invention, it is possible to achieve both of the two characteristics that the accuracy of autofocus is higher than the conventional one and the separation characteristic of the dichroic mirror is good.

  In the present embodiment, laser light having a wavelength of 266 nm is used for autofocusing, but the present invention is not limited to this. For example, it can be used as low-magnification review illumination light in addition to autofocus.

  Further, as shown in FIG. 4, it is also possible to use part of the laser beam L07 having a wavelength of 266 nm for autofocus and the rest as illumination light for low-magnification review. When the laser beam L07 having a wavelength of 266 nm is used for both autofocus and low magnification review, the dichroic mirror 205 in the defect inspection apparatus main body 200 is replaced with one having a characteristic of transmitting 30 to 50% of the P wave of the laser beam L07. . However, with respect to the S wave, the characteristic of reflecting almost 100% is preferable.

  As a result, a part of the laser beam L07 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 L07 that has become an 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 L07 that has passed through the λ / 4 wavelength plate 206b passes through the objective lens 207b and is applied to the observation region 210b on the mask 208.

  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.

  As described above, a low-magnification review function can be realized using a 266-nm laser beam that is unnecessary for inspection without providing a new light source or laser device. Since it is not necessary to branch the inspection laser beam L08 as a low magnification review light source, the power of the inspection laser beam L08 is not impaired. In addition, since laser light having a wavelength of 266 nm is used for low magnification review, it is not necessary to use expensive DUV quartz or calcium fluoride as a glass material for the objective lens 207b and the imaging lens 211b. Quartz can be used.

  As described above, the defect inspection apparatus according to the present invention can be used not only for defect inspection at the time of manufacturing a next-generation mask but also for mask quality control in a semiconductor manufacturing factory. Furthermore, since the inspection light source can be used at a repetition frequency of several MHz or more, it becomes pseudo CW laser light and is suitable for mask inspection. According to the present embodiment, a laser beam having a wavelength of 213 nm can be generated only by performing wavelength conversion three times. By using this as inspection illumination light, the sensitivity can be improved and the inspection can be performed accurately. When a fiber laser that oscillates at 1030 nm is used as a laser light source with a wavelength of 1 μm band, the wavelength of the inspection laser beam can be 206 nm and the wavelength of the autofocus laser beam can be 257.5 nm, further improving the sensitivity. Can be made.

  In addition, according to the present invention, laser light having a wavelength of 266 nm can be supplied as autofocus laser light without reducing the power of the inspection light source laser light at all, and there is no need to provide a laser device dedicated to autofocus. Further, 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 defect inspection apparatus which concerns on embodiment. It is a figure which shows the structure of the test | inspection light source 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 other structure of the defect inspection apparatus which concerns on embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Defect inspection apparatus 100 Inspection light source 102a-102c Wavelength conversion crystal 103a-103c Dichroic mirror 104a-104c Mirror 200 Defect inspection apparatus main body 201 Half mirror 202a-202d Lens 203a, 203b Uniform optical system 204a, 204b Polarization beam splitter 205 Dichroic mirror 206a, 206b λ / 4 wave plate 207a, 207b Objective lens 208 Mask 210a, 210b Observation area 211a, 211b Imaging lens 212aa, 212b Two-dimensional photodetector 213a, 213b Mirror 214 Condenser lens 215 Triangular mirror 216 Position sensor 217 Beam expander 218 λ / 2 wavelength plate L01 Laser light with a wavelength of 1064 nm L02 Wavelength of 1064 nm and wavelength of 532 nm Laser light L03 laser light including wavelength 1064 nm, wavelength 532 nm and wavelength 266 nm L04 laser light including wavelength 532 nm L05 laser light including wavelength 1064 nm and wavelength 266 nm L06 laser light including wavelength 1064 nm, wavelength 266 nm and wavelength 213 nm L07 laser having wavelength 266 nm Light L08 Laser light with a wavelength of 213 nm

Claims (5)

A laser light source for generating laser light having a wavelength of 1 μm band;
An inspection light source device that outputs a fifth harmonic of the laser light and outputs a fourth harmonic of the laser light. The inspection light source device according to claim 1, wherein the laser light source is any one of an Nd: YAG laser, an Nd: YVO ₄ laser, an Nd: YLF laser, a fiber laser, and a glass laser. The inspection light source device according to claim 1 or 2,
A defect inspection apparatus that uses the fifth harmonic of the laser light as inspection illumination light.   The defect inspection apparatus according to claim 3, wherein the fourth harmonic of the laser beam is used as an autofocus laser beam.   The defect inspection apparatus according to claim 3, wherein the fourth harmonic of the laser beam is used as an observation laser beam.

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