JP2017187547A - EUV mask inspection apparatus and focus adjustment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an EUV mask inspection apparatus capable of properly adjusting focus positions and to provide a focus adjustment method thereof.SOLUTION: The EUV mask inspection apparatus includes: an EUV light source 130 which generates illumination light EUV 141 for illuminating an EUV mask 103; a magnification optical system 133 which includes a plurality of reflection mirrors that reflect regular reflection light S142 reflected at the EUV mask 103; a CCD camera 112 which captures an image of the EUV mask 103 by detecting the regular reflection light S142 via the magnification optical system 133; an AF laser device 120 which oscillates at wavelengths of 445 to 473 nm for generating AF light; an AF sensor 124 which detects laser light AF 145 reflected at the EUV mask; and a control part 132 which adjusts the focus position of the illumination light EUV 141 in the EUV mask 103 according to the result detected by the AF sensor 124.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an EUV mask inspection apparatus and a focus adjustment method.

  With regard to lithography technology that is responsible for semiconductor miniaturization, ArF exposure apparatuses using an ArF excimer laser with an exposure wavelength of 193 nm as an exposure light source are widely used. Further, as called ArF immersion lithography, an immersion technique for increasing the resolution by filling the space between the objective lens of the exposure apparatus and the wafer with water is also used for mass production. In order to realize further miniaturization, technological development for practical use of EUVL (Extremely UltraViolet Lithography) having an exposure wavelength of 13.5 nm has been widely performed.

  Unlike a photomask (hereinafter simply referred to as a mask) used in an ArF exposure apparatus, a mask (hereinafter referred to as an EUV mask) used in EUVL is a reflection type. As shown in FIG. 5, a multilayer film 52 for reflecting extreme ultraviolet rays (hereinafter referred to as EUV light) is formed on a substrate 51 made of low thermal expansion glass. It has a layered structure. The multilayer film 52 usually has a structure in which several tens of layers of molybdenum (Mo) and silicon (Si) are alternately stacked (often referred to as a Mo / Si multilayer film).

  With this configuration, EUV light having a wavelength of 13.5 nm can be reflected up to about 65%. An absorber 54 (for example, tantalum, boron, nitride (TaBN)) that absorbs EUV light is deposited on the multilayer film 52 to form a blank (unpatterned mask). However, a ruthenium (Ru) film is deposited as a protective film 53 on the uppermost surface of the multilayer film 52 before the absorber 54 is formed. Absorber 54 is formed on the entire mask to complete the blank. Next, the absorber 54 is formed into a pattern using a resist process. Thereby, the EUV mask 50 with a pattern is completed. Further, the pattern of the absorber 54 is covered with a pellicle 55.

  On the other hand, an inspection apparatus called an ABI (Actinic M blank inspection) apparatus using an EUV light source is used for defect inspection of EUV mask blanks. In the ABI apparatus, an optical system is configured to detect a defect by dark field illumination. The ABI device is described in Non-Patent Document 1, for example. According to this, a Schwarzschild optical system with a magnification of 26 times is used as the detection optical system. That is, an enlargement optical system that enlarges the inspection area by 26 times and projects it onto an image sensor such as a CCD (Charged Coupled Device) is used.

  When a defect is detected in the EUV mask blank, a review function for examining the shape and size of the defect may be provided in the ABI apparatus. When the review function is used, bright field illumination that illuminates the regular reflected light of the illumination light to reach the CCD is used. However, since the defects are small, the shape cannot be accurately determined with a Schwarzschild optical system of about 26 times. For this reason, an apparatus for observing defects at a high magnification of about 1200 times in total by enlarging the projected image several tens of times by using a concave mirror has been put into practical use. Such a review function is disclosed in Patent Document 1, for example.

  When the review function of the ABI apparatus is used, it is necessary to accurately focus in order to accurately observe the shape of a minute defect. In general, an automatic focus adjustment mechanism (Auto Focus: AF) for a mask is irradiated with an AF laser beam on the mask surface, and the reflected light is divided into two sensors or an AF sensor such as a CCD. There is a method of detecting a change in focus by guiding to the head. This is generally called an optical lever system. The meaning of this name is that the laser light reflected simply on the mask surface is not applied to the sensor as it is, but the portion of the mask surface where the laser light hits is enlarged and guided to the AF sensor. It is widely known that a subtle change in focus can be detected by enlarging.

  However, there are two types of AF optical systems based on the optical lever system. One is to provide an optical system for enlarging the mask surface exclusively for AF. For example, a convex surface may be used to enlarge and project the mask surface onto the AF sensor. The other is that a part of the magnifying optical system for inspection is used, and there is a feature that an optical system dedicated to AF is unnecessary.

  By the way, in a mask used in ArF lithography, KrF lithography or the like, the pattern surface is covered with a transparent thin film called a pellicle. The pellicle is provided in order to prevent minute dust and foreign matters (these are called particles) in the atmosphere from adhering to the pattern surface.

  The pellicle for the optical mask is made of a fluorine-based polymer material. Even if particles of a certain size or less adhere to the upper surface of the pellicle, there is no problem during exposure. That is, when the wafer is exposed, since the position of the particle and the position of the pattern surface (position in the optical axis direction) are different, the image of the particle projected on the wafer is blurred. Therefore, the particle image is not exposed. Thus, the pellicle is an extremely effective member for preventing particles from adhering to the pattern surface of the mask even when the particles are floating in the atmosphere.

However, EUV light having a wavelength of 13.5 nm does not pass through a pellicle made of a polymer material for an optical mask. Instead, very thin silicon (Si) films are known to transmit EUV light to some extent. Therefore, it has been studied to use a silicon thin film for the EUV mask pellicle 55 (hereinafter referred to as EUV pellicle). Specifically, it has been studied to realize a silicon thin film aiming at a thickness of 40 nm that transmits about 90% of EUV light. However, it is not easy to realize a full size having an area of 110 × 142 mm ² with a thickness of 40 nm. For this reason, if the thickness can be reduced to nearly 50 nm, the EUV pellicle 55 made of silicon can be used. The EUV pellicle 55 is described in Non-Patent Document 2.

Japanese Patent No. 5008012

Takashi Yamane, et al, “Actinic EUVL M blank inspection and phase defect characterization,” Proceedings of SPIE, Vol. 7379, 73790H (2009). Luigi Scaccabarozzi, et al., “Investigation of EUV pellicle feasibility,” SPIE Vol. 8679, 867904, 2013. Kenneth GoLDberg, Iacopo Mochi, “Defect Detection and Inspection Unmasked,” International Workshop on EUV Lithography 2010. Internet homepage (searched on March 22, 2016) http://refractiveindex.info/ Internet homepage (searched on March 22, 2016) http://www.nichia.co.jp/jp/about_nichia/index.html

  In a system that uses an inspection optical system as an AF optical system, the AF laser light needs to be highly transmitted through the inspection optical system. In the case of the ABI apparatus, each mirror of the inspection optical system is a multilayer mirror for EUV. The EUV multilayer mirror is designed to have a high reflectance with respect to a wavelength of 13.5 nm. Therefore, as shown in FIG. 6, it is preferable to use an ultraviolet laser having a wavelength of around 250 nm, which is highly reflected by the multilayer film, as the AF laser. FIG. 6 shows a calculation result by NTT Advanced Technology Co., Ltd., which manufactures a multilayer film mirror for EUV.

  On the other hand, FIG. 7 shows transmittance characteristics of a silicon thin film (thickness 50 nm) having a wavelength of 200 nm or more. The horizontal axis indicates the wavelength, and the vertical axis indicates the transmittance. FIG. 7 shows data calculated based on the data of the absorption rate with respect to the wavelength in the silicon thin film. As is apparent from FIG. 7, it can be seen that only light having a wavelength of 350 nm or more, that is, almost visible light is transmitted.

  Therefore, when the EUV mask 50 with the pattern on which the pellicle 55 is mounted is to be observed using the above-described review function of the ABI device, the AF laser beam is transmitted through the EUV pellicle in order to focus on the pattern surface. There is a need to. For this reason, it is necessary to use a laser device having a wavelength of 350 nm or more as the AF light source. In this case, as is clear from FIG. 8 shown in Non-Patent Document 3, when the wavelength is longer than ultraviolet, such as 488 nm, the distance that the laser light penetrates in the multilayer film increases.

  As a result, as shown in FIG. 9, since the reflected light travels in a multiplexed manner, the spot that hits the AF sensor extends in one direction. Therefore, there is a problem that the focus detection accuracy is lowered.

  Further, when the detection optical system is used for the optical lever AF optical system, as described above, when the wavelength becomes longer than 250 nm, the reflectance of the multilayer mirror decreases. For this reason, it becomes a problem that the AF laser requires a high output. Therefore, the wavelength of the AF laser light is preferably as short as possible.

  As a light source that is as short as possible at a wavelength of 350 nm or longer that can pass through the EUV pellicle 55, there is a GaN (gallium nitride) based semiconductor laser (laser diode, hereinafter referred to as LD) LD that operates at a wavelength of 405 nm. GaN (gallium nitride) based LDs are widely used.

  However, as a result of calculating the transmittance of the silicon thin film at a wavelength of 405 nm, it was found that the transmittance at the film thickness of 40 nm is only about 10% although it is approximately 40% at the film thickness of 40 nm (see FIG. 3). . In contrast, it has been found that at wavelengths of 445 nm, 445 nm, and 473 nm, a transmittance of 30% or more can be obtained at a film thickness of 40 to 50 nm (see FIG. 3). Note that the values of n and k of the complex refractive index N (= n−ik) necessary for calculating the transmittance are obtained from the information shown on the homepage of Non-Patent Document 4 below.

  Regarding the wavelength of the LD, for example, it is shown in the item of laser diode in the product information on the homepage of Non-Patent Document 5. According to this, strictly speaking, an LD having a wavelength of 445 nm has an oscillation spectrum extending in a wavelength range of 440 nm to 450 nm. Similarly, an LD having a wavelength of 457 nm has an oscillation spectrum extending in a wavelength range of 450 nm to 460 nm. Further, the LD having a wavelength of 473 nm has an oscillation spectrum extending in a wavelength range of 468 nm to 478 nm.

  An object of the present invention is to provide an EUV mask inspection apparatus and a focus adjustment method that can appropriately adjust the focus.

  An EUV mask inspection apparatus according to an aspect of this embodiment includes a plurality of EUV light sources that generate EUV light for illuminating an EUV (Extremely Ultraviolet) mask, and a plurality of reflecting mirrors that reflect the EUV light reflected by the EUV mask. An optical system having the optical system, an imaging device that detects the EUV light through the optical system and images the EUV mask, and a semiconductor laser that oscillates at a wavelength of 445 nm to 473 nm to generate AF (Auto Focus) light An apparatus, an AF sensor that detects the AF light reflected by the EUV mask, and a control unit that adjusts a focus position of the EUV light in the EUV mask according to a detection result of the AF sensor. It is provided. Thereby, the focus can be adjusted appropriately.

  In the above EUV mask inspection apparatus, it is preferable that an oscillation wavelength of the semiconductor laser apparatus is 445 nm. As a result, an EUV mask with an EUV pellicle formed of a 40 nm to 50 nm silicon film can be appropriately inspected.

  In the above EUV mask inspection apparatus, the AF sensor may detect the AF light through one or more reflecting mirrors included in the optical system. Thereby, the detection optical system of AF light can be simplified.

  In the above EUV mask inspection apparatus, the focus position may be adjusted by an optical lever method.

  In the EUV mask inspection apparatus, it is preferable that the EUV mask has a pellicle.

  In the above EUV mask inspection apparatus, pattern inspection of the EUV mask may be performed.

  The focus adjustment method according to the present embodiment includes an EUV light source that generates EUV light for illuminating an EUV mask, an optical system that includes a plurality of reflecting mirrors that reflect the EUV light reflected by the EUV mask, and the optical An EUV mask inspection apparatus comprising: an imaging device that detects the EUV light through a system and images the EUV mask; and a semiconductor laser device that oscillates at a wavelength of 445 nm to 473 nm to generate AF light. A focus adjustment method, the step of detecting AF light reflected by the EUV mask with an AF sensor; the step of adjusting the focus position of the EUV light in the EUV mask based on the detection result of the AF light; It is equipped with. Thereby, the focus can be adjusted appropriately.

  ADVANTAGE OF THE INVENTION According to this invention, the EUV mask inspection apparatus and focus adjustment method which can adjust a focus appropriately can be provided.

It is a figure which shows the review apparatus for EUV mask concerning Embodiment 1. FIG. It is explanatory drawing which showed a part of test | inspection apparatus. It is a calculation result which shows the transmittance | permeability of the silicon thin film with respect to the laser beam in wavelength 405nm, 445nm, 457nm, and 473nm. It is a figure which shows the inspection apparatus concerning Embodiment 2. FIG. It is sectional drawing which shows the general structure of an EUV mask. It is a calculation result which shows the reflectance characteristic of the multilayer film for EUV. It is a calculation result which shows the transmittance | permeability characteristic in a 50-nm-thick silicon film It is explanatory drawing which showed absorption of the light of various wavelengths in the multilayer film for EUV masks. It is explanatory drawing which showed the mode of reflection of the laser beam which injects into a multilayer film surface.

  Hereinafter, a specific configuration of the present embodiment will be described 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 indicate substantially the same contents.

Embodiment 1. FIG.
The inspection apparatus according to the present embodiment is an ABI apparatus that performs an actinic inspection on an EUV mask with a pellicle. Specifically, the ABI device is equipped with a review mechanism. Therefore, in this embodiment, the inspection apparatus 100 will be described as an EUV mask review apparatus. FIG. 1 is a diagram illustrating an EUV mask review apparatus according to a first embodiment. The inspection object is an EUV mask such as a patterned EUV mask or an unpatterned EUV mask (mask blank). For example, an EUV mask review apparatus performs pattern inspection on an EUV mask with a pellicle.

  The inspection apparatus 100 includes an EUV light source 130, a drop mirror 102, a control unit 132, a magnifying optical system 133, an AF laser device 120, a condensing lens 121, an AF sensor 124, and a CCD camera 112. The magnifying optical system 133 has four reflecting mirrors: a concave mirror 108, a convex mirror 109, a plane mirror 110, and a concave mirror 111. The concave mirror 108 and the convex mirror 109 constitute a Schwarzschild optical system 107.

  The EUV light source 130 generates illumination light EUV 141. The illumination light EUV 141 is, for example, EUV light having a wavelength of 13.5 nm that is the same as the exposure wavelength. Thereby, an actinic inspection can be performed. The illumination light EUV 141 proceeds while being narrowed down by a concave mirror (not shown). The illumination light EUV 141 is incident on the lower surface of the drop mirror 102. The dropping mirror 102 reflects the incident illumination light EUV 141 in the direction of the EUV mask 103.

  The EUV mask 103 has a substrate 104 and an EUV pellicle 106. The upper surface of the substrate 104 is a pattern surface 105. An EUV pellicle 106 is attached to the EUV mask 103. The pattern surface 105 is covered with an EUV pellicle 106. The illumination light EUV 141 is collected on the pattern surface 105.

  The illumination light EUV 141 illuminates a part of the pattern surface 105. The pattern surface 105 reflects a part of the illumination light EUV 141. That is, the illumination light EUV 141 is reflected according to the pattern on the pattern surface 105. The regular reflection light S142 traveling from the portion irradiated with the illumination light EUV141 enters the Schwarzschild optical system 107. The Schwarzschild optical system 107 includes a concave mirror 108 and a convex mirror 109. The regular reflection light S142 from the pattern surface 105 is reflected by the concave mirror 108 and enters the convex mirror 109.

  The convex mirror 109 reflects the regular reflection light S <b> 242 toward the plane mirror 110. Further, the regular reflection light S <b> 242 is reflected by the plane mirror 110 and the concave mirror 111 and enters the CCD camera 112. The CCD camera 112 has a plurality of light receiving pixels arranged in a two-dimensional array, and detects the incident regular reflection light S242. An image captured by the CCD camera 112 is input to the control unit 132. The control unit 132 inspects the EUV mask based on the captured image.

  Here, the magnifying optical system 133 will be described. The Schwarzschild optical system 107 has an enlargement factor of about 26 times. On the other hand, the concave mirror 111 also has an enlargement function. For this reason, a magnification of about 1200 times in total is obtained by two-stage expansion of the front stage (Schwarzschild optical system 107) and the rear stage (concave mirror 111). That is, the pattern surface 105 of the EUV mask 103 is magnified about 1200 times and projected onto the CCD camera 112. The concave mirror 108, the convex mirror 109, the plane mirror 110, and the concave mirror 111 constitute a magnifying optical system 133 for inspection. The CCD camera 112 detects the specularly reflected light S242 via the magnifying optical system 133. Therefore, the CCD camera 112 captures an enlarged image of the EUV mask 103.

  Next, the AF optical system will be described. In the focus adjustment in the inspection apparatus 100, the distance between the pattern surface 105 of the EUV mask 103 and the Schwarzschild optical system 107 is adjusted. For example, the EUV mask 103 is placed on a drive stage (not shown). Then, the controller 132 drive stage is driven in a direction perpendicular to the pattern surface 105. As an AF mechanism for that purpose, an optical lever system using a part of the inspection optical system (magnification optical system 133) is used as described below.

  The AF laser device 120 has, for example, a laser diode (LD) having a center wavelength of 445 nm. The AF laser device 120 emits blue laser light AF143. The laser beam AF143 travels while being narrowed down through the condenser lens 121. The laser beam AF143 is reflected by the mirror 122. The mirror 122 is arranged at a position where the illumination light EUV 141 is not incident.

  The laser beam AF143 reflected by the mirror 122 enters the drop mirror 102. The drop mirror 102 reflects the laser beam AF143 toward the EUV mask 103. The laser beam AF143 passes through the EUV pellicle 106 and enters the pattern surface 105. The laser beam AF143 is focused on the pattern surface 105 of the EUV mask 103.

  In FIG. 1, the optical axis of the laser beam AF143 is indicated by a one-dot chain line. The laser beam AF143 is obliquely incident on the pattern surface 105. The optical axis of the laser beam AF143 is deviated from the direction perpendicular to the pattern surface 105. Further, as shown in FIG. 1, the optical axes of the laser light AF143 and the illumination light EUV141 are shifted. Therefore, the incident angle at which the optical axis of the laser beam AF143 enters the drop mirror 102 and the incident angle at which the optical axis of the illumination light EUV 141 enters the drop mirror 102 are different.

  The laser beam AF144 reflected by the pattern surface 1005 enters the Schwarzschild optical system 107 in the same manner as the regular reflection light S242. Therefore, the laser beam AF 144 is reflected by the concave mirror 108 and the convex mirror 109. The optical axes of the laser beam AF143 and the illumination beam EUV141 are shifted. Therefore, the laser beam AF 144 passes through the side of the plane mirror 110 and enters the plane mirror 123. That is, the regular reflection light S242 is incident on the plane mirror 110, whereas the laser beam AF143 is not incident on the plane mirror 110.

  The laser beam AF145 reflected by the plane mirror 123 enters the AF sensor 124. The AF sensor 124 is a two-divided sensor such as a two-divided photodiode. The AF sensor 124 outputs a detection signal corresponding to the detection result to the control unit 132. The control unit 132 adjusts the focus position according to the detection signal. Specifically, the control unit 132 drives the stage on which the EUV mask 103 is placed in a direction perpendicular to the pattern surface 105. Accordingly, the position of the laser beam AF145 incident on the AF sensor 124 changes so as to follow the pattern surface 105 changing up and down. By always feeding back an AF adjustment signal from the AF sensor 124, it is possible to always focus.

  For example, the optical system is adjusted so that the laser beam AF145 is incident on the center of the AF sensor 124 when in the in-focus position. Thereby, when it exists in a focus position, the output from two photodiodes becomes equal. When deviating from the in-focus position, the output from one photodiode is higher than the output from the other photodiode. The focus can be adjusted by taking the ratio of the signals of the two photodiodes included in the AF sensor 124.

The outer NA (NAout) of the concave mirror 108 constituting the Schwarzschild optical system 107 is 0.27. That is, the concave mirror 108 can reflect a light beam having an incident angle of 15.7 ° (= sin ⁻¹ (NAout)) or less reflected from the EUV mask 103. In that case, the incident angle (θ shown in FIG. 2) when the laser beam AF143 enters the pattern surface 105 of the EUV mask 103 via the drop mirror 102 needs to be set to 15.7 ° or less. When the incident angle θ is as large as possible, the AF sensitivity in the optical lever system increases. Therefore, in the present embodiment, the maximum incident angle θ of the laser beam AF143 is about 15 degrees.

As a result, as shown in the graph of FIG. 3B, the transmittance of the silicon thin film with a thickness of 40 nm is about 50%. When the film thickness is 50 nm, the transmittance is about 56%. FIG. 3 shows the relationship between the thickness of the silicon film and the transmittance. FIGS. 3A to 3D show transmittance graphs when the wavelength of incident light (laser beam AF143) is 405 nm, 445 nm, 457 nm, and 473 nm, respectively. In FIG. 3, the horizontal axis represents the thickness (nm) of the silicon film, and the vertical axis represents the transmittance (%). The transmittance of the EUV pellicle 106 changes according to the wavelength of incident light and the thickness of the silicon film. FIG. 3 is a simulation result of a configuration in which Si ₃ N ₄ having a thickness of 4 nm is formed on both sides of the silicon film with an incident angle of incident light of 15 degrees.

  As shown in FIG. 3A, when the wavelength of the laser beam AF143 is 405 nm, the transmittance with respect to a silicon thin film having a thickness of 50 nm is only about 8%. For this reason, it becomes difficult to use a laser beam having a wavelength of 405 nm as the laser beam AF143. Further, as shown in FIGS. 3C and 3D, when the wavelength is 457 nm or 473 nm, the transmittance at the film thickness of 50 nm is increased, but the transmittance at the film thickness of 40 nm is the wavelength. Compared to 445 nm. Therefore, in this embodiment, a 445 nm LD is used for the AF laser device 120.

  Thus, the semiconductor laser device having an oscillation wavelength of 445 nm is used as the AF laser device 120. By doing so, light having a high transmittance with respect to the silicon thin film can be used as the laser light AF143. Since the amount of light detected by the AF sensor 124 can be increased, the focus position can be adjusted appropriately. In particular, it is suitable for focus adjustment in an inspection apparatus for the EUV mask 103 with the EUV pellicle 106 having a thickness of 40 nm to 50 nm. Since the inspection can be performed at an appropriate focus position, the EUV mask 103 can be inspected accurately.

  In the above description, a semiconductor laser device having an oscillation wavelength of 445 nm is used as the AF laser device 120. However, the AF laser device 120 is not limited to 445 nm. The oscillation wavelength of the AF laser device 120 may be 445 to 473 nm. By using such blue laser light, the laser light AF143 passes through the EUV pellicle 106 with a high transmittance with respect to a silicon film of 40 to 50 nm.

  Further, in the present embodiment, a part of the magnifying optical system 133 for guiding the specularly reflected light S242 reflected by the EUV mask 103 to the CCD camera 112 is used for detecting the laser light AF145. That is, the AF sensor 124 detects the laser light AF145 via one or more of the plurality of reflecting mirrors included in the magnifying optical system 133. Specifically, the laser beam AD 145 reflected by the concave mirror 108 and the convex mirror 109 is detected by the AF sensor 124. By doing so, the AF detection optical system can be simplified.

  According to the first embodiment, in the EUV mask review function, not only blanks but also the EUV mask 103 with a pattern on which the EUV pellicle 106 is mounted can be accurately focused. Therefore, the defect of the EUV mask 103 with a pattern or the pattern itself can be observed with high sensitivity. Furthermore, the pattern inspection of the EUV mask 103 with a pattern can be performed with high accuracy.

Embodiment 2. FIG.
The second embodiment will be described with reference to FIG. FIG. 4 is a diagram illustrating an inspection apparatus 200 according to the second embodiment. In the second embodiment, the inspection apparatus 200 is a pattern inspection apparatus that performs pattern inspection of the EUV mask 203. In the second embodiment, a part of the configuration of the AF optical system is different from the first embodiment. Specifically, the optical path from the EUV mask 203 to the AF sensor 224 is different from that in the first embodiment. Note that the description of the same configuration as that of Embodiment 1 will be omitted as appropriate.

  The EUV light source 230 generates illumination light EUV241. The illumination light EUV241 travels while being narrowed by a concave mirror (not shown). The illumination light EUV 241 is incident on the lower surface of the drop mirror 202. The illumination light EUV 241 is reflected by the drop mirror 202 and enters the EUV mask 203. An EUV pellicle 206 is attached to the EUV mask 203. The illumination light EUV 241 passes through the EUV pellicle 206 and illuminates a part of the pattern surface 105 of the substrate 204.

  When the illumination light EUV241 is irradiated onto the pattern surface 205, the illumination light EUV241 is reflected according to the pattern on the pattern surface 205. The specularly reflected light S242 reflected and reflected by the pattern surface 205 is reflected by the concave mirror 208, the concave mirror 209, the concave mirror 210, and the plane mirror 211, and enters the TDI camera 212. The concave mirror 208, the concave mirror 209, the concave mirror 210, and the plane mirror 211 constitute a magnifying optical system as in the first embodiment. The TDI camera 212 images the illuminated area of the pattern surface 205.

  As in the first embodiment, an LD with a wavelength of 445 nm is used as the AF laser device 220. The laser beam AF243 emitted from the AF laser device 220 enters the condenser lens 221. The laser light AF 243 that has passed through the condenser lens 221 proceeds while being narrowed down and enters the mirror 222. The laser beam AF243 reflected by the mirror 222 enters the drop mirror 202. The laser beam AF243 reflected by the drop mirror 202 is condensed on the pattern surface 205 of the EUV mask 203.

  The laser beam AF 244 reflected by the pattern surface 205 is reflected by the concave mirror 208, the concave mirror 209, and the concave mirror 210. The concave mirror 208, the concave mirror 209, and the concave mirror 210 constitute a magnifying optical system. The optical axes of the laser beam AF243 and the illumination beam EUV241 are shifted. Therefore, the laser beam AF242 reflected by the concave mirror 210 passes by the side of the plane mirror 211 and enters the plane mirror 223. That is, the regular reflection light S242 is reflected by the plane mirror 211, whereas the laser beam AF244 is not reflected by the plane mirror 211.

  The laser beam AF245 reflected by the plane mirror 223 enters the AF sensor 224. The AF sensor 224 is a two-divided sensor as in the first embodiment. The AF sensor 224 detects the AF 245 and outputs a detection signal corresponding to the detected light amount to the control unit 232.

  Thereby, the focus of the pattern surface 205 can be always adjusted. That is, as the AF mechanism of the inspection apparatus 200, an optical lever system that uses a part of the magnifying optical system 233 for inspection (three of four mirrors) is used.

  As described above, the AF laser beam AF244 enters the plane mirror 223 after passing through three of the four multilayer mirrors constituting the magnifying optical system 233. Then, the plane mirror 223 is used to separate the laser beam AF244 from the regular reflection light S242. On the other hand, in the inspection apparatus 100 of the first embodiment shown in FIG. 1, the laser beam AF 144 passes through the two multilayer mirrors of the concave mirror 108 and the convex mirror 109 constituting the Schwarzschild optical system. This embodiment is different from the present embodiment in that it is separated from the regular reflection light S142. However, in either case, the pattern surfaces 105 and 205 of the EUV masks 103 and 203 are imaged in the vicinity of the AF sensors 124 and 224 that receive the AF laser beams AF145 and AF245.

  In the first concave mirror 208 of the four multilayer mirrors constituting the projection optical system of the inspection apparatus 200, the outer NA is as high as 0.35. That is, the incident angle corresponding to NA = 0.35 is 20.5 °. Accordingly, the AF laser light AF243 is incident on the pattern surface 205 of the EUV mask 203 at about 18 degrees. As a result, as shown in FIG. 3, the transmittance of the silicon thin film having a thickness of 50 nm is about 45%. By using the laser beam AF241 having a wavelength of 445 nm, it is possible to obtain a transmittance that is 4 to 5 times higher than that at the wavelength of 405 nm. FIG. 3 is a simulation result when the incident angle is 15 degrees, but since the difference in transmittance between the incident angle of 18 degrees and the incident angle of 15 degrees is small, even if the incident angle is 18 degrees, The transmittance is substantially the same as in FIG.

  Of course, a blue semiconductor laser device having a wavelength of 457 nm or 473 nm may be used as the LD of the AF laser device 220. The AF laser device 120 may oscillate at a wavelength of 445 to 473 nm in order to generate AF light. By using a semiconductor laser device having an oscillation wavelength of 445 to 473 nm, the amount of light detected by the AF laser light AF245 is increased. Therefore, the focus position can be adjusted appropriately. Since the inspection can be performed at an appropriate focus position, the EUV mask 203 can be inspected accurately.

  According to the present embodiment, the defect of the EUV mask 103 with a pattern or the pattern itself can be observed with high sensitivity. As a result, the pattern inspection of the EUV mask 103 with a pattern can be performed with high accuracy. Thereby, it can test | inspect correctly.

  Furthermore, in the present embodiment, a part of the magnifying optical system 233 for guiding the regular reflection light S242 reflected by the EUV mask 203 to the TDI camera 212 is used for detection of the laser light AF245. In other words, the AF sensor 224 detects the laser beam AF245 via one or more reflecting mirrors among the plurality of reflecting mirrors included in the magnifying optical system 233. Specifically, the laser light AF 245 reflected by the concave mirror 208, the concave mirror 209, and the concave mirror 210 is detected by the AF sensor 224. By doing so, the AF detection optical system can be simplified.

  As mentioned above, although embodiment of this invention was described, this invention contains the appropriate deformation | transformation which does not impair the objective and advantage, Furthermore, it does not receive the limitation by said embodiment.

50 EUV mask 51 Substrate 52 Multilayer film 53 Protective film 54 Absorber 55 Pellicle 100 Inspection device 102 Drop mirror 103 EUV mask 104 Substrate 105 Pattern surface 106 EUV pellicle 107 Schwarzschild optical system 108 Concave mirror 109 Convex mirror 110 Plane mirror 111 Concave mirror 112 CCD AF laser device 121 Condensing lens 122 Mirror 123 Plane mirror 124 AF sensor 130 EUV light source 132 Control unit 133 Magnifying optical system 200 Inspection device 202 Drop mirror 203 EUV mask 204 Substrate 205 Pattern surface 206 EUV pellicle 208 Concave mirror 209 Concave mirror 211 Concave mirror 211 Plane mirror 220 AF laser device 221 Condensing lens 222 Mirror 223 Plane mirror 224 AF sensor 230 UV light source 232 control unit 233 magnifying optical system EUV141, EUV241 illumination light S142, S242 specular light AF143~AF145, AF243~AF245 laser beam

Claims (7)

An EUV light source that generates EUV light for illuminating an EUV (Extremely Ultraviolet) mask;
An optical system having a plurality of reflecting mirrors that reflect the EUV light reflected by the EUV mask;
An imaging device for detecting the EUV light via the optical system and imaging the EUV mask;
A semiconductor laser device that oscillates at a wavelength of 445 nm to 473 nm in order to generate AF (Auto Focus) light;
An AF sensor for detecting the AF light reflected by the EUV mask;
An EUV mask inspection apparatus comprising: a control unit that adjusts a focus position of the EUV light in the EUV mask according to a detection result of the AF sensor.   2. The EUV mask inspection apparatus according to claim 1, wherein an oscillation wavelength of the semiconductor laser device is 445 nm.   The EUV mask inspection apparatus according to claim 1, wherein the AF sensor detects the AF light through one or more reflecting mirrors included in the optical system.   The EUV mask inspection apparatus according to claim 1, wherein the focus position is adjusted by an optical lever method.   The EUV mask inspection apparatus according to claim 1, wherein the EUV mask has a pellicle.   The EUV mask inspection apparatus according to claim 1, wherein pattern inspection of the EUV mask is performed. An EUV light source for generating EUV light for illuminating the EUV mask;
An optical system having a plurality of reflecting mirrors that reflect the EUV light reflected by the EUV mask;
An imaging device for detecting the EUV light via the optical system and imaging the EUV mask;
A focus adjustment method for an EUV mask inspection apparatus comprising: a semiconductor laser device that oscillates at a wavelength of 445 nm to 473 nm in order to generate AF light,
Detecting AF light reflected by the EUV mask with an AF sensor;
Adjusting the focus position of the EUV light in the EUV mask based on the detection result of the AF light.