EUV mask blanks inspection equipment

Abstract

To provide an EUV mask blanks inspection device capable of effectively detecting defects in a multilayer film with irradiation other than EUV. [Solution] The EUV mask blank inspection device 11 includes a support 15 that supports an EUV mask blank 14 having a multilayer film that reflects EUV light, an optical system 22 that guides linearly polarized light beam 16a that is incident perpendicularly on the multilayer film to the EUV mask blank 14, a light receiving element that separates and receives linearly polarized light beam 16b that is reflected perpendicularly from the multilayer film, and a displacement mechanism 21 that displaces light beam 16a relative to the EUV mask blank 14.

Description

[Technical Field]

[0001] The present invention relates to an EUV (extreme ultraviolet) mask blank inspection apparatus that detects defects in EUV mask blanks. [Background technology]

[0002] In EUV mask blanks, the reflector is established based on a multilayer film. The multilayer film is optimized for a wavelength of 13.5 nm. In the multilayer film, high refractive index layers and low refractive index layers with an optical path difference of 1 / 4 wavelength are repeatedly stacked. Layers of molybdenum (Mo) and silicon (Si) are used for the repeated stacking. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2024-127783 [Non-patent literature]

[0004] [Non-Patent Document 1] Tsuneo Terasawa, “Actinic Mask Blank Inspection and Signal Analysis for Detecting Phase Defects Down to 1.5nm in Height”, Japanese Journal of Applied Physics, 48(6), 2009 Summary of the Invention [Problem to be solved by the invention]

[0005] Patent Document 1 discloses an EUV mask blank inspection system that detects defects in multilayer films. In an EUV mask blank inspection system, EUV light is irradiated onto an EUV mask blank. Phase defects and foreign matter adhesion are detected based on the scattering of the EUV light. As mentioned above, the multilayer film of an EUV mask blank is optimized for EUV with a wavelength of 13.5 nm, ensuring sufficient reflected light for defect detection. However, there are many constraints, such as the need for a light source such as an LPP (laser-produced plasma) to generate EUV light, and the optical system that guides the EUV light must be composed only of reflecting mirrors.

[0006] An object of the present invention is to provide an EUV mask blanks inspection apparatus that can effectively detect defects in a multilayer film using radiation other than EUV. [Means for solving the problem]

[0007] According to one aspect of the present invention, there is provided an EUV mask blanks inspection device including: a support for supporting an EUV mask blank having a multilayer film that reflects EUV light; an optical system for guiding a linearly polarized light beam that is incident perpendicularly on the multilayer film to the EUV mask blank; a light receiving element for separating and receiving the linearly polarized light from the light beam that is reflected perpendicularly from the multilayer film; and a displacement mechanism for displacing the light beam relative to the EUV mask blank. [Effects of the Invention]

[0008] As described above, according to the disclosed embodiment, an EUV mask blank inspection apparatus is provided that can effectively detect defects in a multilayer film using irradiation other than EUV. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic diagram illustrating the configuration of an EUV mask blanks inspection apparatus according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram illustrating the configuration of an optical path unit. [Figure 3]1 is a graph showing the amount of light transmitted through and reflected from a multilayer film according to the number of layers in the multilayer film. [Figure 4] FIG. 10 is a schematic diagram illustrating the configuration of an optical path unit according to another specific example. [Figure 5] FIG. 10 is a schematic diagram illustrating the configuration of an EUV mask blanks inspection apparatus according to a second embodiment of the present invention. [Figure 6] FIG. 10 is a schematic diagram illustrating the configuration of an optical path unit used in an EUV mask blanks inspection apparatus according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0011] FIG. 1 shows a schematic configuration of an EUV mask blank inspection apparatus 11 according to a first embodiment of the present invention. The EUV mask blank inspection apparatus 11 includes a chamber body 13 defining a clean room 12, a support 15 housed in the clean room 12 and supporting an EUV mask blank 14, an inspection head 17 housed in the clean room 12 and irradiating a light beam 16a perpendicularly onto the surface of the EUV mask blank 14 and receiving a light beam 16b perpendicularly reflected from the EUV mask blank 14, and a light source group 18 supplying the light beam to the inspection head 17. The clean room 12 may be filled with air or an inert gas. Atmospheric pressure or a vacuum may be established within the clean room 12. The EUV mask blank 14 is formed in a rectangular shape, for example, 150 mm x 150 mm. The EUV mask blank 14 has a plate thickness of 6 mm.

[0012] The EUV mask blank inspection apparatus 11 includes a displacement mechanism 21 that displaces the light beam 16a relative to the EUV mask blank 14. Here, the inspection head 17 is fixed immovably within the clean room 12. The displacement mechanism 21 is connected to the support 15. The displacement mechanism 21 drives the support 15 according to an xy coordinate system set in a horizontal plane. The EUV mask blank 14 on the support 15 is displaced in the horizontal direction in nanometer units.

[0013] The inspection head 17 includes a frame 23 that connects and supports multiple optical path units 22. Each optical path unit 22 individually guides the separated light beams 16a, 16b. The inspection head 17 functions as an optical system that guides the multiple light beams 16a, 16b in parallel. The inspection head 17 forms light spots in a predetermined positional relationship on the surface of the EUV mask blank 14. The light spots may be arranged, for example, at equal intervals on a straight line. The light spots may also be arranged in a matrix (array).

[0014] As shown in FIG. 2, each optical path unit 22 includes an individual optical system 26 that guides a light beam 16a from one light source 18a in the light source group 18 to a multilayer film 24 on the EUV mask blank 14, and a light-receiving element (photodiode) 27 that separates and receives linearly polarized light from the light beam 16b reflected from the multilayer film 24. In the EUV mask blank 14, the multilayer film 24 forms a reflecting mirror. The multilayer film 24 is formed on the surface of a quartz substrate 28. The multilayer film 24 is optimized for a wavelength of 13.5 nm. For optimization, the angle of incidence of light is set to, for example, 6°. The multilayer film is formed by repeatedly stacking high-refractive index layers and low-refractive index layers with an optical path difference of ¼ wavelength. A stacked film 29 of molybdenum (Mo) 29a and silicon (Si) 29b is used for the repeated stacking. The light-receiving element 27 generates an electrical signal according to the intensity of the irradiated light.

[0015] The individual optical system 26 includes a first half-wave plate 32 that adjusts the angle of the linearly polarized light, a polarizing beam splitter 33 that transmits p-polarized light and reflects s-polarized light, a Faraday rotator 34 that rotates the polarization plane by 45°, a second half-wave plate 35 that adjusts the angle of the linearly polarized light, and an objective lens 36 that adjusts the focus. Linearly polarized light is supplied to the first half-wave plate 32 from a single light source 18a. The light source 18a generates near-infrared light with a wavelength of, for example, 980 nm. The light source 18a may be, for example, a semiconductor laser element, a light-emitting diode, or another semiconductor light-emitting element. Semiconductor light-emitting elements generate near-infrared light effectively even in the atmosphere at room temperature. The light is introduced from the light source 18a into the optical path unit 22 via a PANDA fiber 37. The PANDA fiber 37 maintains the linear polarization of the light. The light beam 16a passes through a first half-wave plate 32, a polarizing beam splitter 33, a Faraday rotator 34, a second half-wave plate 35, and an objective lens 36, and is incident perpendicularly (at an incident angle of 0°) on the multilayer film 24. The linear polarization of the light beam 16a is maintained. In this example, the light source 18a is installed outside the chamber body 13. The optical path may be split by a coupler 38. The light source 18a may be isolated from the vacuum in the clean room 12. However, the light source 18a may also be located inside the clean room 12.

[0016] The objective lens 36 receives the light ray 16b that is reflected perpendicularly from the multilayer film 24. The polarizing beam splitter 33 separates the linearly polarized light from the reflected light. The light ray having the maintained linear polarization from the light ray 16a that is irradiated onto the EUV mask blank 14 is reflected by the polarizing beam splitter 33. The light ray reflected by the polarizing beam splitter 33 reaches the light receiving element 27. The light ray having the polarization that is rotated from the linear polarization of the light ray 16a that is irradiated onto the EUV mask blank 14 is transmitted through the polarizing beam splitter 33.

[0017] A control unit 39 is connected to the displacement mechanism 21 and the inspection head 17, controlling their operation. The control unit 39 supplies a control signal to the displacement mechanism 21. The control signal defines the position of the support 15 according to the x-, y-, and z-coordinate axes in three-dimensional space. The EUV mask blank 14 is positioned relative to the light beam 16a. The control unit 39 receives an electrical signal from the light receiving element 27 for each position. The control unit 39 scans the light beam 16a evenly over the surface of the EUV mask blank 14 according to a determined path. The control unit 39 calculates the intensity distribution of the light beam 16b on the surface of the EUV mask blank 14.

[0018] Next, the operation of the EUV mask blanks inspection apparatus 11 will be described. The EUV mask blanks 14 are set on the support 15. The control unit 39 supplies a control signal to the light source 18a. In response to the supplied control signal, the light source 18a emits near-infrared light. Linear polarization is established in the light beam. The linearly polarized light beam passes through the PANDA fiber 37, the first half-wave plate 32, the polarizing beam splitter 33, the Faraday rotator 34, the second half-wave plate 35, and the objective lens 36. The light beam 16a, while maintaining its linear polarization, is irradiated onto the multilayer film 24 of the EUV mask blanks 14. The linearly polarized light beam 16a is incident perpendicularly on the multilayer film 24.

[0019] The light ray 16b reflected perpendicularly from the multilayer film 24 passes through the objective lens 36, the second half-wave plate 35, and the Faraday rotator 34. The light ray 16b is reflected at the boundary surface of the polarizing beam splitter 33. Linearly polarized light is separated from the light ray 16b. The separated linearly polarized light is received by the light receiving element 27. The light receiving element 27 outputs an electrical signal according to the intensity of the light ray. The electrical signal is passed to the control unit 39.

[0020] The control unit 39 causes the EUV mask blank 14 to be displaced along a determined path in a horizontal plane. A control signal is supplied from the control unit 39 to the displacement mechanism 21 to displace the EUV mask blank 14. Since multiple light beams 16a are irradiated in parallel, the amount of displacement of the EUV mask blank 14 decreases. The light beams 16a scan the entire area of ​​the EUV mask blank 14. The control unit 39 generates an intensity distribution of the light beams over the entire area of ​​the EUV mask blank 14. The control unit 39 may generate an image that visually displays the intensity distribution.

[0021] If, for example, a phase defect or foreign matter adheres to the multilayer film 24 of the EUV mask blank 14, the polarization of the reflected light ray 16b is eliminated. The amount of linearly polarized light decreases. The light receiving element 27 receives the change in polarization. Phase defects and foreign matter on the EUV mask blank 14 are detected according to the change in polarization. Because the light ray is displaced relative to the EUV mask blank 14, defects are detected across the entire EUV mask blank 14. Because the light ray 16b is reflected perpendicularly from the multilayer film 24, the reflected light from each layered film overlaps and is intensified. The change in polarization accurately reflects the defect. Defects can be detected well even if the amount of reflected light decreases.

[0022] The inventors calculated the amount of transmitted and reflected light through the multilayer film 24 based on a simulation model. In the simulation model, the multilayer film was formed using a 3 nm molybdenum layer and a 4 nm silicon layer. The multilayer film was repeatedly stacked. As shown in Figure 3, the amount of reflected light decreased down to wavelengths of approximately 1000 nm for multilayer films with a total of 40 layers, 60 layers, and 80 layers. In all cases, it was confirmed that light rays with short wavelengths do not pass through the multilayer film 24. Light rays with wavelengths that pass through the multilayer film 24 are likely to pass through the lens. Lenses can be used in optical systems. The configuration of the individual optical system 26 is simplified. In the objective lens 36, light rays 16a and 16b enter and exit the multilayer film 24 perpendicularly, establishing a high-density optical path through the multilayer film 24.

[0023] In this embodiment, a semiconductor light-emitting element is used to generate the light beam, so that light emission is achieved in the atmosphere. A vacuum environment is avoided. A light source that is significantly cheaper than a plasma light source is used. The semiconductor light-emitting element may be, for example, a semiconductor laser or a light-emitting diode.

[0024] The light receiving element 27 detects the linearly polarized light. When the linearly polarized light is eliminated by the reflected light beam 16b, the intensity of the linearly polarized light changes. Defects on the EUV mask blank 14 are detected according to the change in intensity.

[0025] In this embodiment, the inspection head 17 guides multiple light beams 16a in parallel. A light receiving element 27 that receives a light beam 16b is installed for each individual optical system 26. Defects are detected at multiple locations simultaneously on the EUV mask blank 14. The operating time required for defect detection is shortened.

[0026] As shown in FIG. 4 , the optical path unit 22 may be replaced with an optical path unit 42 according to another specific example. The optical path unit 42 includes an individual optical system 43 that guides a light beam 16 a from one light source 18 a belonging to the light source group 18 to the multilayer film 24 of the EUV mask blank 14, a first light receiving element (photodiode) 44 that separates and receives linearly polarized light from the light beam 16 b reflected from the multilayer film 24, and a second light receiving element (photodiode) 45 that separates and receives linearly polarized light from the light beam 16 b reflected from the multilayer film 24. The first light receiving element 44 receives a light beam having a polarization rotated from the linearly polarized light of the light beam 16 a irradiated onto the EUV mask blank 14. The first light receiving element 44 detects the intensity of the light beam having a polarization plane rotated due to the influence of a defect in the multilayer film 24. The first light receiving element 44 outputs an electrical signal corresponding to the intensity of the detected light beam. The second light receiving element 45 receives a light beam having linear polarization that is maintained from the light beam 16a irradiated onto the EUV mask blank 14. The second light receiving element 45 detects the intensity of the polarization that is maintained regardless of defects in the multilayer film 24. The second light receiving element 44 outputs an electrical signal according to the intensity of the detected light beam.

[0027] The individual optical system 43 includes a first half-wave plate 46 that adjusts the angle of the linearly polarized light, a first polarizing beam splitter 47 that transmits p-polarized light and reflects s-polarized light, a Faraday rotator 48 that rotates the polarization plane by 45°, a second half-wave plate 49 that adjusts the angle of the linearly polarized light, a second polarizing beam splitter 51 that transmits p-polarized light and reflects s-polarized light, and an objective lens 52 that adjusts the focus. A linearly polarized light beam is supplied to the first half-wave plate 46 from one light source 18a. The light source 18a generates near-infrared light with a wavelength of, for example, 980 nm. The light source 18a may be, for example, a semiconductor laser element, a light-emitting diode, or another semiconductor light-emitting element. The light beam is introduced from the light source 18a into the optical path unit 42 via a PANDA fiber 37. The PANDA fiber 37 maintains the linear polarization of the light beam. Light ray 16a passes through first half-wave plate 46, first polarizing beam splitter 47, Faraday rotator 48, second half-wave plate 49, second polarizing beam splitter 51, and objective lens 52, and is incident perpendicularly (at an incident angle of 0°) on multilayer film 24. The linear polarization of light ray 16a is maintained.

[0028] The objective lens 52 receives the light ray 16b reflected perpendicularly from the multilayer film 24. The second polarizing beam splitter 51 separates the linearly polarized light from the reflected light. The light ray having a polarization rotated from the linear polarization of the light ray 16a irradiating the EUV mask blank 14 is reflected by the second polarizing beam splitter 51. The light ray reflected by the second polarizing beam splitter 51 reaches the first light receiving element 44. The light ray having the linear polarization that is maintained from the light ray 16a irradiating the EUV mask blank 14 is transmitted through the second polarizing beam splitter 51. The first polarizing beam splitter 47 separates the linearly polarized light from the reflected light. The light ray having the linear polarization that is maintained from the light ray 16a irradiating the EUV mask blank 14 is reflected by the first polarizing beam splitter 47. The light ray reflected by the first polarizing beam splitter 47 reaches the second light receiving element 45. The light beam 16 a irradiating the EUV mask blank 14 has a polarized light beam rotated from the linearly polarized light beam, and passes through the first polarizing beam splitter 47 .

[0029] In this embodiment, the first light receiving element 44 detects the plane of polarization that rotates from linearly polarized light. When the linearly polarized light is eliminated in the reflected light ray 16b, the intensity of the light other than linearly polarized light changes. Defects on the EUV mask blank 14 are detected according to the change in intensity.

[0030] FIG. 5 shows a schematic configuration of an EUV mask blanks inspection apparatus 61 according to a second embodiment of the present invention. In addition to the configuration of the first embodiment, the EUV mask blanks inspection apparatus 61 further includes an inspection head 63 housed in the clean room 12, which irradiates a light beam 62a perpendicularly onto the back surface of the EUV mask blanks 14 and receives a light beam 62b perpendicularly reflected from the EUV mask blanks 14, and a light source group 64 which supplies the light beam to the inspection head 63. The light beam 62a passes through the quartz substrate 28 of the EUV mask blanks 14 and reaches the multilayer film 24 from the back side. The inspection head 63 is configured in the same manner as the inspection head 17 described above. The light source group 64 includes light sources 18a connected to individual optical path units 22, as described above. The optical path unit 22 may be replaced with the optical path unit 42.

[0031] FIG. 6 shows a schematic configuration of an optical path unit 65 used in an EUV mask blank inspection apparatus according to a third embodiment of the present invention. The individual optical systems 66 of the optical path unit 65 include a first half-wave plate 46, a first polarizing beam splitter 47, a Faraday rotator 48, a second half-wave plate 49, and a second polarizing beam splitter 51; a scan mirror 67 that receives the light beam transmitted through the second polarizing beam splitter 51 and oscillates around a horizontal axis; and fθ lenses 68a and 68b that receive the light beam from the scan mirror 67 and direct it vertically to the objective lens 52. A galvanometer mirror, for example, is used as the scan mirror 67. The galvanometer mirror scans the light beam 16a along the x-coordinate axis. The displacement of the support 15 is reduced in response to the scanning of the light beam 16a. [Explanation of symbols]

[0032] 11 EUV mask blanks inspection equipment 14 EUV mask blanks 15 Support 16a Ray of light 16b Ray of light 21 Displacement mechanism 23 frames 24 Multilayer film (for EUV mask blanks) 26 Optical system (individual optical system) 27 Photodetector 36 Objective Lens 43 Optical system (individual optical system) 44 First light receiving element 45 Second light receiving element 61 EUV mask blanks inspection equipment 66 Optical system (individual optical system)

Claims

1. a support for supporting an EUV mask blank having a multilayer film that reflects EUV; an optical system that guides linearly polarized light that is incident perpendicularly to the multilayer film onto the EUV mask blank; a light receiving element that separates the linearly polarized light from the light beam that is perpendicularly reflected from the multilayer film and receives the separated light; a displacement mechanism that displaces the light beam relatively to the EUV mask blank; Equipped with The light is near-infrared and has a wavelength that is transmitted through the multilayer film. EUV mask blanks inspection equipment.

2. a semiconductor light-emitting element that generates the light beam; The EUV mask blanks inspection apparatus according to claim 1 .

3. The optical system includes an objective lens having an optical axis perpendicular to the surface of the EUV mask blank. The EUV mask blanks inspection apparatus according to claim 2 .

4. The light receiving element detects the linearly polarized light. The EUV mask blanks inspection apparatus according to claim 1 .

5. The light receiving element detects polarized light that is rotated from the linearly polarized light. The EUV mask blanks inspection apparatus according to claim 4 .

6. A frame is provided on one of the support members, which holds a plurality of the optical systems that guide a plurality of the light beams in parallel and a plurality of the light receiving elements that receive the light beams for each of the optical systems. The EUV mask blanks inspection apparatus according to claim 1 .

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