Wafer inspection device

Abstract

Provided is a wafer inspection device capable of detecting various kinds of malfunctions by using one light beam. The wafer inspection device comprises: a support body that supports a wafer 14; an optical system 26 that irradiates an edge or a surface of a flat region of the wafer 14 with a linearly polarized light beam 16a incident on the surface of the wafer 14 in a direction perpendicular thereto; a first light-receiving element 27 that receives a component other than a linearly polarized light component from a light beam 16c reflected from the edge or the surface of the wafer 14 and outputs an electric signal according to the intensity; a second light-receiving element 28 that receives the linearly polarized light component from the light beam 16c reflected from the edge or the surface of the wafer 14 and outputs an electric signal according to the intensity; and a control unit that detects a defect in the edge or the surface of the wafer 14 on the basis of the electric signal from the first light-receiving element 27 and the electric signal from the second light-receiving element 28.

Description

Wafer inspection apparatus

[0001] The present invention relates to a wafer inspection apparatus that detects defects in a wafer based on irradiation with light rays.

[0002] Patent Document 1 discloses a wafer inspection apparatus that irradiates the surface of a wafer with a light ray and detects defects in the wafer based on the reflected light. The wafer inspection apparatus detects particles (minute foreign matter and defect particles), COP (crystal originated particles), residues (residues of chemical substances, fine particles, and impurities), scratches (minute scratches) with a size of about 0.1 [μm], as well as LLPD with a maximum size of about 16 [μm].[

[0003] Japanese Unexamined Patent Publication No. 2023-38254

[0004] In wafer inspection apparatuses, dark-field inspection and bright-field inspection are combined. In dark-field inspection, the surface of the wafer is irradiated with a light ray at a large incident angle when diffuse reflected light is generated. Diffuse reflected light is collected perpendicularly to the surface of the wafer. In bright-field inspection, the surface of the wafer is irradiated with a light ray from the vertical direction when forming an image. Reflected light is collected perpendicularly to the surface of the wafer. This makes the optical system more complex relative to the surface of the wafer.

[0005] An object of the present invention is to provide a wafer inspection apparatus capable of detecting various types of defects with a single light ray.

[0006] According to one aspect of the present invention, there is provided a wafer inspection apparatus comprising: a support body that supports a wafer; an optical system that irradiates the surface of a flat region or an edge portion of the wafer with a linearly polarized light ray incident in a direction perpendicular to the surface of the wafer; a first light-receiving element that receives components other than the linearly polarized light from the light ray reflected from the surface or the edge portion of the wafer and outputs an electric signal corresponding to the intensity; a second light-receiving element that receives the linearly polarized component from the light ray reflected from the surface or the edge portion of the wafer and outputs an electric signal corresponding to the intensity; and a control unit that detects defects on the surface or the edge portion of the wafer based on the electric signal from the first light-receiving element and the electric signal from the second light-receiving element.

[0007] As described above, according to the form of disclosure, a wafer inspection apparatus capable of detecting various types of defects with a single light beam is provided.

[0008] This is a schematic diagram illustrating the configuration of a wafer inspection apparatus according to the first embodiment of the present invention. This is a schematic diagram illustrating the configuration of an optical path unit. This is a schematic diagram illustrating the configuration of an optical path unit used in a wafer inspection apparatus according to the second embodiment of the present invention. This is a schematic diagram illustrating the configuration of an optical path unit used in a wafer inspection apparatus according to the third embodiment of the present invention. This is a schematic diagram illustrating the configuration of an optical path unit used in a wafer inspection apparatus according to the fourth embodiment of the present invention. This is a schematic diagram illustrating the configuration of an optical path unit used in a wafer inspection apparatus according to the fifth embodiment of the present invention. This is a schematic diagram illustrating the configuration of an optical path unit used in a wafer inspection apparatus according to the sixth embodiment of the present invention. This is a schematic diagram illustrating the configuration of a control unit used in a wafer inspection apparatus according to the seventh embodiment of the present invention. This is a schematic plan view illustrating the structure of a wafer. This is an enlarged partial cross-sectional view illustrating the structure of a wafer. This is a schematic diagram illustrating the configuration of an optical path unit used in a wafer inspection apparatus according to the eighth embodiment of the present invention.

[0009] One embodiment of the present invention will be described below with reference to the attached drawings.

[0010] Figure 1 schematically shows the configuration of a wafer inspection apparatus 11 according to the first embodiment of the present invention. The wafer inspection apparatus 11 comprises a chamber body 13 that partitions a clean room 12, a support body 15 housed in the clean room 12 and supporting a wafer 14, an inspection head 17 housed in the clean room 12 that irradiates a light ray 16a perpendicularly to the surface of the wafer 14 and receives a light ray 16b reflected perpendicularly from the wafer 14, and a group of light sources 18 that supply light rays to the inspection head 17. The clean room 12 may be filled with air or with an inert gas. Atmospheric pressure or a vacuum may be established in the clean room 12. The wafer is formed from, for example, silicon (Si). The wafer is formed into a disc having a diameter of, for example, 300 [mm].

[0011] The wafer inspection apparatus 11 includes a displacement mechanism 21 that displaces a light ray 16a relative to the wafer 14. Here, the inspection head 17 is fixed immovably within the cleanroom 12. The displacement mechanism 21 is connected to a support 15. The displacement mechanism 21 drives the support 15 according to an xy coordinate system set in the horizontal plane. The wafer 14 on the support 15 is displaced horizontally in nanometer units.

[0012] The inspection head 17 includes a frame 23 that connects and supports a plurality of optical path units 22. Each optical path unit 22 individually guides the separated individual light rays 16a and 16b. The inspection head 17 functions as an optical system that guides a plurality of light rays 16a and 16b in parallel. The inspection head 17 forms spots of light on the surface of the wafer 14 in predetermined positional relationships. The spots of light may be arranged, for example, at equal intervals along a straight line. The spots of light may also be arranged in a matrix (array).

[0013] As shown in Figure 2, each optical path unit 22 includes an individual optical system 26 that guides a light ray 16a from one light source 18a belonging to the light source group 18 to the surface of the wafer 14, a first photodetector (photodiode) 27 that separates and receives linearly polarized light from the light ray 16b reflected from the surface of the wafer 14, and a second photodetector (photodiode) 28 that separates and receives linearly polarized light from the light ray 16b reflected from the surface of the wafer 14. The first photodetector 27 receives light having a polarization rotated from the linearly polarized light ray 16a irradiated onto the wafer 14. The first photodetector 27 detects the intensity of light having a rotated polarization plane due to the effect of defects in the wafer 14. The first photodetector 27 outputs an electrical signal corresponding to the intensity of the detected light ray. The second photodetector 28 receives light having linearly polarized light maintained from the light ray 16a irradiated onto the wafer 14. The second photodetector 28 detects the polarization intensity that is maintained regardless of defects in the wafer 14. The second photodetector 28 outputs an electrical signal corresponding to the intensity of the detected light ray.

[0014] The individual optical system 26 includes a first half-wave plate 31 for adjusting the angle of linear polarization, a first polarization beam splitter 32 that transmits p-polarized light and reflects s-polarized light, a Faraday rotator 33 that rotates the polarization plane by 45°, a second half-wave plate 34 for adjusting the angle of linear polarization, a second polarization beam splitter 35 that transmits p-polarized light and reflects s-polarized light, and an objective lens 36 for adjusting the focus. Linearly polarized light rays are supplied to the first half-wave plate 31 from a single light source 18a. The light source 18a generates near-infrared light having a wavelength of, for example, 980 nm. For example, a semiconductor laser element, a light-emitting diode, or other semiconductor light-emitting element can be used as the light source 18a. The light rays are introduced from the light source 18a to the optical path unit 22 via a PANDA fiber 37. The PANDA fiber 37 maintains the linear polarization of the light rays. The light ray 16a passes through the first half-wave plate 31, the first polarizing beam splitter 32, the Faraday rotator 33, the second half-wave plate 34, the second polarizing beam splitter 35, and the objective lens 36, and is incident on the wafer 14 perpendicularly [incident angle 0°] to the surface of the wafer 14. The linear polarization of the light ray 16a is maintained. Here, the light source 18a is installed outside the chamber body 13. The optical path may be split by the coupler 38. The light source 18a can be isolated from the vacuum inside the cleanroom 12. However, the light source 18a may be placed inside the cleanroom 12.

[0015] The objective lens 36 receives the light ray 16b reflected perpendicularly from the surface of the wafer 14. The second polarizing beam splitter 35 separates the linearly polarized light from the reflected light. The light ray having a rotational polarization from the linearly polarized light ray 16a irradiated onto the wafer 14 is reflected by the second polarizing beam splitter 35. The light ray reflected by the second polarizing beam splitter 35 reaches the first photodetector 27. The light ray with linear polarization maintained from the light ray 16a irradiated onto the wafer 14 passes through the second polarizing beam splitter 35. The first polarizing beam splitter 32 separates the linearly polarized light from the reflected light. The light ray with linear polarization maintained from the light ray 16a irradiated onto the wafer 14 is reflected by the first polarizing beam splitter 32. The light ray reflected by the first polarizing beam splitter 32 reaches the second photodetector 28. Light rays having a polarization that has been rotated from the linear polarization of the light ray 16a irradiated onto the wafer 14 pass through the first polarization beam splitter 32.

[0016] A control unit 39 is connected to the displacement mechanism 21 and the inspection head 17 to control their operation. The control unit 39 supplies control signals to the displacement mechanism 21. The control signals define the position of the support 15 according to the x, y, and z coordinate axes in three-dimensional space. The wafer 14 is positioned relative to the light ray 16a. The control unit 39 receives electrical signals from the first photodetector 27 and the second photodetector 28 for each position. The control unit 39 scans the surface of the wafer 14 evenly with the light ray 16a according to a predetermined path. The control unit 39 calculates the distribution of the intensity of the light ray 16b on the surface of the wafer 14, consisting of linearly polarized components and non-linearly polarized components.

[0017] Next, the operation of the wafer inspection apparatus 11 will be described. The wafer 14 is set on the support 15. The control unit 39 supplies a control signal to the light source 18a. In response to the supply of the control signal, the light source 18a emits near-infrared light. Linear polarization is established in the light ray. The linearly polarized light ray passes through the PANDA fiber 37, the first half-wave plate 31, the first polarization beam splitter 32, the Faraday rotator 33, the second half-wave plate 34, the second polarization beam splitter 35, and the objective lens 36. The light ray 16a is irradiated onto the surface of the wafer 14 while maintaining linear polarization. The linearly polarized light ray 16a is incident perpendicularly to the surface of the wafer 14.

[0018] Light rays 16b reflected perpendicularly from the surface of the wafer 14 pass through the objective lens 36. Light rays 16b enter the second polarizing beam splitter 35. Linearly polarized light is separated from light rays 16b. Light rays with linear polarization maintained from light rays 16a pass through the second polarizing beam splitter 35. Light rays with polarization rotated from the linear polarization of light rays 16a irradiated onto the wafer 14 are reflected at the interface of the second polarizing beam splitter 35. Light rays other than linearly polarized light that have been separated are received by the first photodetector 27. The first photodetector 27 outputs an electrical signal according to the intensity of the light rays. The electrical signal is passed to the control unit 39.

[0019] Light rays that have passed through the second polarizing beam splitter 35 pass through the second half-wave plate 34 and the Faraday rotator 33. Light rays 16b are reflected at the interface of the first polarizing beam splitter 32. Linearly polarized light rays are separated from light rays 16b. The separated linearly polarized light rays are received by the second photodetector 28. The second photodetector 28 outputs an electrical signal according to the intensity of the light rays. The electrical signal is passed to the control unit 39.

[0020] The control unit 39 causes the wafer 14 to displace according to a predetermined path in the horizontal plane. A control signal is supplied from the control unit 39 to the displacement mechanism 21 when the wafer 14 is displaced. As multiple light rays 16a are irradiated in parallel, the amount of displacement of the wafer 14 decreases. The light rays 16a scan the entire surface of the wafer 14. The control unit 39 generates an intensity distribution of the light rays across the entire surface of the wafer 14. The control unit 39 may also generate an image that visually displays the intensity distribution.

[0021] If a defect smaller than the irradiated light spot exists on the surface of wafer 14, the polarization of the reflected light ray 16b is eliminated. The first photodetector 27 detects the change in polarization. Depending on the change in polarization, defects such as particles (tiny foreign matter or defect particles) of about 0.1 [μm] in size, COP (particulate defects), residues (residues of chemical substances, fine particles, or impurities), and scratches (fine scratches) are detected. If a defect larger than the irradiated light spot exists on the surface of wafer 14, the second photodetector 28 detects the change in reflectivity. Depending on the change in reflectivity, LLPDs up to about 16 [μm] in size are detected. LLPDs include particles, COP, residues, and scratches. Since the linearly polarized component and the non-linearly polarized component are separated from a single common light ray, various types of defects can be detected with a single light ray. Since the light ray is displaced relative to wafer 14, defects can be detected across the entire wafer 14.

[0022] In this embodiment, the individual optical system 26 includes an objective lens 36 having an optical axis perpendicular to the surface of the wafer 14. Light rays are shone perpendicularly from the objective lens 36 onto the surface of the wafer 14. Light rays reflected from the wafer 14 enter the objective lens 36 perpendicularly to the surface of the wafer 14. The optical path can be limited to only the objective lens 36. The structure of the optical system is simplified relative to the surface of the wafer 14. The optical system is reduced in size.

[0023] In this embodiment, the inspection head 17 includes a support 15 with a plurality of individual optical systems 26 that guide a plurality of light rays 16a in parallel, and a frame 23 that holds a first photodetector 27 and a second photodetector 28 that are combined for each individual optical system 26. Defects are detected simultaneously at multiple locations on the wafer 14 depending on the parallel light rays. The operating time required for defect detection is reduced. Because the optical systems are reduced in size, they are arranged at a high density on the surface of the wafer 14.

[0024] Figure 3 schematically shows the configuration of an optical path unit 41 used in a wafer inspection apparatus according to a second embodiment of the present invention. In the wafer inspection apparatus 11, the optical path unit 22 can be replaced with the optical path unit 41. The individual optical system 42 of the optical path unit 41 includes a first half-wave plate 31, a first polarizing beam splitter 32, a Faraday rotator 33, a second half-wave plate 34, and a second polarizing beam splitter 35, a scan mirror 43 that receives light rays transmitted through the second polarizing beam splitter 35 and oscillates around the horizontal axis, and fθ lenses 44a and 44b that receive light rays from the scan mirror 43 and guide the light rays vertically to the objective lens 36. For example, a galvanometer mirror is used for the scan mirror 43. The galvanometer mirror scans the light ray 16a along the x-coordinate axis. The displacement of the support 15 is reduced in accordance with the scanning of the light ray 16a.

[0025] Figure 4 schematically shows the configuration of an optical path unit 51 used in a wafer inspection apparatus according to a third embodiment of the present invention. In the wafer inspection apparatus 11, the optical path unit 22 can be replaced with the optical path unit 51. In addition to the configuration of the individual optical system 42, the individual optical system 52 of the optical path unit 51 includes a focusing mechanism (autofocus optical system) 53 that detects the focus of the objective lens 36 and drives the objective lens 36 in the direction of the optical axis of the objective lens 36 according to the detected focus. The focusing mechanism 53 detects the focus of the objective lens 36 based, for example, on the astigmatism method. Light rays reflected from the wafer 14 are guided from the cylindrical lens 54 to the four-segment photodetector 55. When the objective lens 36 is in focus on the surface of the wafer 14, a circular spot is formed on the four-segment photodetector 55. Light is irradiated evenly onto the four photodetectors. If the objective lens 36 is closer or further away from the position of focus, an elliptical spot is formed on the four-segment photodetector 55. The drive element 56 drives the objective lens 36 according to the output of the four-segment photodetector 55. For example, a piezo actuator is used as the drive element 56. A drive voltage is applied to the piezo actuator according to the output of the four-segment photodetector 55. In the optical path 58 established from the light source 57 to the objective lens 36, a polarizing beam splitter 59 that separates the detected light from the optical path 58, a quarter-wave plate 61 that converts the light ray between linearly polarized and circularly polarized light, and a beam splitter 62 that separates the light ray from the optical path 36a of the objective lens 36 are arranged. Here, the objective lens 36 is formed with a numerical aperture NA that has a depth of focus smaller than the height difference formed on the surface of the wafer 14.

[0026] The focusing mechanism 53 focuses the objective lens 36 on the surface of the wafer 14 in accordance with the drive of the objective lens 36. A large numerical aperture is required for the objective lens 36 to collect diffusely reflected light. A large numerical aperture reduces the depth of focus. Even if blurring occurs due to differences in height on the surface of the wafer 14, the focusing mechanism 53 corrects the blurring in accordance with the drive of the objective lens 36. A well-focused state is established while effectively collecting diffusely reflected light. Defects in the wafer 14 are detected well.

[0027] Figure 5 schematically shows the configuration of an optical path unit 65 used in a wafer inspection apparatus according to the fourth embodiment of the present invention. In the wafer inspection apparatus 11, the optical path unit 22 can be replaced with the optical path unit 65. In addition to the configuration of the optical path unit 51, the optical path unit 65 includes a third photodetector 67 that receives fluorescence separated from components other than linearly polarized light, and a fourth photodetector 68 that receives fluorescence separated from the linearly polarized component. The third photodetector 67 is combined with a dichroic mirror 69 placed between the second polarizing beam splitter 35 and the first photodetector 27. The dichroic mirror 69 separates the excitation light and fluorescence (long wavelength) from the light ray containing components other than linearly polarized light reflected by the second polarizing beam splitter 35. The fourth photodetector 68 is combined with a dichroic mirror 71 placed between the first polarizing beam splitter 32 and the second photodetector 28. The dichroic mirror 71 splits the light ray containing the linearly polarized component reflected by the first polarizing beam splitter 32 into excitation light and fluorescence (long wavelength). The third photodetector 67 and the fourth photodetector 68 output electrical signals corresponding to the fluorescence intensity. For fluorescence detection, the third photodetector 67 and the fourth photodetector 68 can be photodetectors (PDs), as well as PMTs (photomultiplier tubes) or APDs (avalanche photodiodes).

[0028] The silicon wafer 14 emits fluorescence in response to dislocation defects. Dislocation defects arise based on shifts or distortions in the atomic arrangement. The third photodetector 67 and the fourth photodetector 68 receive the fluorescence. Dislocation defects are detected in response to the detection of fluorescence. Dislocation defects are separated from defects such as particles (tiny foreign matter or defective particles), COP (particulate defects), residues (residues of chemical substances, fine particles, or impurities), and scratches (tiny scratches).

[0029] Figure 6 schematically shows the configuration of an optical path unit 73 used in a wafer inspection apparatus according to the fifth embodiment of the present invention. In the wafer inspection apparatus 11, the optical path unit 22 can be replaced with the optical path unit 73. In addition to the configuration of the optical path unit 51, the optical path unit 73 includes a third photodetector 74 that receives fluorescence separated from components other than linearly polarized light for each specific wavelength, and a fourth photodetector 75 that receives fluorescence separated from the linearly polarized component for each specific wavelength. The third photodetector 74 is combined with a dichroic mirror 76 placed between the second polarizing beam splitter 35 and the first photodetector 27, and a diffraction grating 77 that spectrally analyzes the fluorescence branched by the dichroic mirror 76. The dichroic mirror 76 branches the excitation light and fluorescence (long wavelength) from the light ray containing components other than linearly polarized light reflected by the second polarizing beam splitter 35. For example, a line sensor can be used for the third photodetector 74. The line sensor receives fluorescence for each spectrally analyzed wavelength. The third photodetector 74 outputs an electrical signal corresponding to the fluorescence intensity for each wavelength.

[0030] The fourth photodetector 75 combines a dichroic mirror 78 positioned between the first polarizing beam splitter 32 and the second photodetector 28, and a diffraction grating 79 that spectrally analyzes the fluorescence split by the dichroic mirror 78. The dichroic mirror 78 splits the light ray containing the linearly polarized component reflected by the first polarizing beam splitter 32 into excitation light and fluorescence (long wavelength). For example, a line sensor is used for the fourth photodetector 75. The line sensor receives fluorescence for each spectrally analyzed wavelength. The fourth photodetector 75 outputs an electrical signal corresponding to the fluorescence intensity for each wavelength.

[0031] The silicon wafer 14 emits fluorescence in response to dislocation defects. Dislocation defects arise from shifts or distortions in the atomic arrangement. The third photodetector 74 and the fourth photodetector 75 receive the fluorescence. Dislocation defects are detected in response to the fluorescence. Dislocation defects are separated from defects such as particles (tiny foreign matter or defective particles), COP (particulate defects), residues (residues of chemical substances, fine particles, or impurities), and scratches (tiny scratches). When the fluorescence is received, it is spectrally separated by diffraction gratings 77 and 79. The intensity of the fluorescence is detected for each wavelength. Dislocation defects are classified according to wavelengths D1, D2, D3, and D4.

[0032] Figure 7 schematically shows the configuration of an optical path unit 81 used in a wafer inspection apparatus according to the sixth embodiment of the present invention. In the wafer inspection apparatus 11, the optical path unit 22 can be replaced with the optical path unit 81. In addition to the configuration of the optical path unit 51, the optical path unit 81 includes a third photodetector 82 that receives fluorescence separated from components other than linearly polarized light for each specific wavelength, and a fourth photodetector 83 that receives fluorescence separated from the linearly polarized component for each specific wavelength. The third photodetector 82 is combined with a dichroic mirror 84 placed between the second polarizing beam splitter 35 and the first photodetector 27, and a diffraction grating 85 that spectrally separates the fluorescence branched by the dichroic mirror 84. The dichroic mirror 84 branches the excitation light and fluorescence (long wavelength) from the light ray containing components other than linearly polarized light reflected by the second polarizing beam splitter 35. A MEMS (Micro-Electrical Mechanisms) 86 that drives the diffraction grating 85 is connected to the diffraction grating 85. The MEMS 86 allows the third photodetector 82 to receive fluorescence at each spectrally separated wavelength. The third photodetector 82 outputs an electrical signal corresponding to the fluorescence intensity at each wavelength.

[0033] The fourth photodetector 83 combines a dichroic mirror 87 positioned between the first polarizing beam splitter 32 and the second photodetector 28, and a diffraction grating 88 that spectrally separates the fluorescence separated by the dichroic mirror 87. The dichroic mirror 87 separates the excitation light and fluorescence (long wavelength) from the linearly polarized light ray reflected by the first polarizing beam splitter 32. A MEMS (Micro-Electro-Mechanical Systems) 89 that drives the diffraction grating 88 is connected to the diffraction grating 88. The MEMS 89 causes the fourth photodetector 83 to receive fluorescence at each spectrally separated wavelength. The fourth photodetector 83 outputs an electrical signal corresponding to the fluorescence intensity at each wavelength.

[0034] The silicon wafer 14 emits fluorescence in response to dislocation defects. Dislocation defects arise based on shifts or distortions in the atomic arrangement. The third photodetector 82 and the fourth photodetector 83 receive the fluorescence. Dislocation defects are detected in response to the fluorescence. Dislocation defects are separated from defects such as particles (tiny foreign matter or defective particles), COP (particulate defects), residues (residues of chemical substances, fine particles, or impurities), and scratches (tiny scratches). When the fluorescence is received, it is spectrally separated by diffraction gratings 85 and 88. The intensity of the fluorescence is detected for each wavelength. Dislocation defects are classified according to wavelengths D1, D2, D3, and D4.

[0035] Figure 8 schematically shows a control unit 91 used in a wafer inspection apparatus 11 according to the seventh embodiment of the present invention. In the wafer inspection apparatus 11, the control unit 39 can be replaced with the control unit 91. The control unit 91 includes a microprocessor (MPU) 93 that compares the registered data of the wafer 92 with the measured data of the wafer 92. In generating the measured data, the MPU 93 receives electrical signals from the first photodetector 27 and the second photodetector 28. The light ray 16a scans the surface of the wafer 92 evenly according to a path determined by the operation of the displacement mechanism 21. The control unit 91 identifies the distribution of the intensity of the light ray 16b across the entire surface of the wafer 92. The intensity of linearly polarized light and the intensity of non-linearly polarized light are calculated for each coordinate point in the xy plane. As shown in Figure 9, for example, a circuit pattern 94 is formed on the surface of the wafer 92. The same electronic circuit is manufactured in each die 95.

[0036] The registered data is stored, for example, in the storage device 96. The registered data is formed in advance using the output signals of a good wafer 92 assumed by the first photodetector 27 and the second photodetector 28. The intensity of linearly polarized light and the intensity of non-linearly polarized light are calculated for each coordinate point in the xy plane. For example, CAD data of the wafer 92 is used for the calculation. If the measured data deviates from the registered data, the control unit 91 detects a defect in the circuit pattern 94.

[0037] In addition, as shown in Figure 10, control units 39 and 91 may create a distribution other than linearly polarized light across the entire surface of the wafer 97 based on the electrical signal of the first photodetector 27. For example, if an oxide film 102 is uniformly formed on the surface of the silicon substrate 101 in response to thermal oxidation, or a metal film or other thin film 103 is uniformly formed, or a photoresist 104 is uniformly coated, or if the STI (shallow trench isolation) 106 embedded in the active region 105 is planarized, then a distribution other than linearly polarized light will be uniformly detected across the entire surface of the wafer 97. If a defect exists, the polarization is eliminated in the reflected light ray 16b. The first photodetector 27 receives the change in polarization. Depending on the change in polarization, defects in the oxide film 102, the thin film 103, the photoresist 104, and the STI 106 are detected. Here, control units 39 and 91 may create a linearly polarized light distribution across the entire surface of the wafer 97 based on the electrical signal of the second photodetector 28 instead of the electrical signal of the first photodetector 27. Control units 39 and 91 may also create linearly polarized and non-linearly polarized light distributions across the entire surface of the wafer 97 based on the electrical signals of the first photodetector 27 and the second photodetector 28. Since the linearly polarized component and the non-linearly polarized component are separated from a single common ray, various types of defects can be detected with a single ray.

[0038] In the embodiments described above, the case in which a wafer is used as the object to be inspected was described. However, the present invention is not limited to this, and various other substrates, such as glass substrates used in semiconductor chip packages or flat panel displays, may also be used as the object to be inspected.

[0039] Figure 11 is a schematic diagram illustrating the configuration of an optical path unit 22 used in a wafer inspection apparatus according to the eighth embodiment of the present invention. In the embodiments described above, linearly polarized light rays were shone perpendicularly to the surface of a flat region of the wafer 14, and defects were detected by receiving the light rays reflected perpendicularly from the wafer 14. However, the eighth embodiment differs from the embodiments described above in that light rays are shone perpendicularly to the surface of the wafer 14 at the edge of the wafer 14, and defects at the edge of the wafer 14 are detected by receiving the light rays reflected from the edge of the wafer 14. The edge of the wafer 14 is the part where the thickness of the wafer 14 gradually decreases toward the center of the wafer 14 due to edge roll-off.

[0040] The wafer inspection apparatus according to the eighth embodiment comprises, for example, a chamber body 13, a support body 15, an inspection head 17, and a light source group 18, similar to the first embodiment described above (see Figure 1). The support body 15 is housed in a clean room 12 partitioned by the chamber body 13 and supports a wafer 14. The wafer inspection apparatus includes a displacement mechanism that displaces a light ray 16a relative to the wafer 14. The inspection head 17 is fixed immovably within the clean room 12. The displacement mechanism is connected to the support body 15. The displacement mechanism drives the support body 15 according to an xy coordinate system set in the horizontal plane. Furthermore, the displacement mechanism rotates the support body 15 in the horizontal plane including the xy coordinate system. The wafer 14 on the support body 15 is displaced in nanometer units in the horizontal and rotational directions. The wafer 14 on the support body 15 rotates circumferentially in the horizontal plane with the center of the wafer 14 as the center of rotation. The wafer 14 is rotated, and the irradiation position of the light ray 16a is displaced along the circumferential direction of the wafer 14 within the region of the edge of the wafer 14.

[0041] The inspection head 17 includes a frame 23 that connects and supports a plurality of optical path units 22. The optical path units 22 and the frame 23 have the same configuration as in the first embodiment described above. As shown in Figure 11, each optical path unit 22 includes an individual optical system 26 that guides a light ray 16a from one light source 18a belonging to the light source group 18 to the edge portion of the wafer 14, a first photodetector (photodiode) 27 that separates and receives linearly polarized light from the light ray 16c reflected from the edge portion of the wafer 14, and a second photodetector (photodiode) 28 that separates and receives linearly polarized light from the light ray 16c reflected from the edge portion of the wafer 14.

[0042] The edge of the wafer 14 has a slope called edge roll-off. As shown in Figure 11, at the edge of the wafer 14, specularly reflected light 16d is generated when the light ray 16a from the optical path unit 22 is specularly reflected, depending on the slope shape of the irradiation position. In the figure, L1 indicates the tangent to the light ray 16a at the irradiation position on the edge of the wafer 14.

[0043] The objective lens 36 does not receive specularly reflected light 16d reflected at the edge at an angle greater than or equal to the numerical aperture of the objective lens 36. Here, when a light ray 16a is incident on a perfectly smooth mirror surface or an optically ideal flat surface, only specularly reflected light 16d is generated. In contrast, when a light ray 16a is incident on a surface that is not a perfectly smooth mirror surface or an optically ideal flat surface, a backscattered component is generated in addition to the specularly reflected light 16d. Furthermore, the greater the surface roughness of the surface on which the light ray 16a is incident, the greater the intensity of the backscattered component, and the polarization state of the backscattered light changes from the polarization state of the incident light ray 16a. The edge of the wafer 14 has a steep slope, but the surface is not an optically ideal flat surface, so when a light ray 16a is incident on the edge of the wafer 14, backscattering occurs in addition to specularly reflected light 16d. Also, if there is a defect at the edge, the surface roughness changes due to the defect, and the intensity and phase information of the backscattering change, causing the polarization to rotate or disappear.

[0044] In the first embodiment, defect detection is performed using the light ray 16b vertically reflected from the wafer 14, whereas in the eighth embodiment, defect detection is performed using the light ray 16c reflected by backscattering from the edge portion of the wafer 14 instead of the light ray 16b.

[0045] The wafer inspection apparatus according to the eighth embodiment irradiates the edge portion of the wafer 14 supported by a support 15 with a linearly polarized light ray 16a incident in a direction perpendicular to the surface of the wafer 14 by an inspection head 17 of an optical system. The wafer inspection apparatus causes a first light-receiving element 27 to receive components other than linearly polarized light from the light ray 16c reflected from the edge portion of the wafer 14, outputs an electrical signal corresponding to the intensity, and causes a second light-receiving element 28 to receive the linearly polarized component from the light ray 16c reflected from the edge portion of the wafer 14, and outputs an electrical signal corresponding to the intensity. The wafer inspection apparatus causes a control unit 39 to detect defects at the edge portion of the wafer 14 based on the electrical signal from the first light-receiving element 27 and the electrical signal from the second light-receiving element 28. Accordingly, the wafer inspection apparatus can detect various types of defects at the edge portion of the wafer 14 with a single light ray.

[0046] In the above-described eighth embodiment, the case where the optical path unit 22 according to the first embodiment shown in FIG. 2 is applied to detect various types of defects at the edge portion of the wafer 14 has been described, but the present invention is not limited thereto. For example, the individual optical system 42 of the optical path unit 41 according to the second embodiment shown in FIG. 3, the individual optical system 52 of the optical path unit 51 according to the third embodiment shown in FIG. 4, the optical path unit 65 according to the fourth embodiment shown in FIG. 5, the optical path unit 73 according to the fifth embodiment shown in FIG. 6, the optical path unit 81 according to the sixth embodiment shown in FIG. 7, and the optical path unit according to the seventh embodiment shown in FIG. 8 may be applied to detect various types of defects at the edge portions of wafers 14, 92, and 97.

[0047] In this case, in the second to seventh embodiments, linearly polarized light rays 16a incident perpendicular to the surface of wafers 14, 92, and 97 are irradiated onto the edges of wafers 14, 92, and 97 by their respective optical systems, similar to the eighth embodiment. In each wafer inspection apparatus according to the second to seventh embodiments, the control units 39 and 31 can detect defects in the edges of wafers 14, 92, and 97 based on the electrical signals of the first light-receiving element 27 and the second light-receiving element 28, thereby achieving the same effects as in the eighth embodiment.

[0048] 11 Wafer inspection device 14 Wafer 15 Support 16a Light ray 16b Light ray 16c Light ray 21 Displacement mechanism 23 Frame 26 Optical system (individual optical system) 27 First photodetector 28 Second photodetector 36 Objective lens 39 Control unit 52 Optical system (individual optical system) 53 Focusing mechanism 91 Control unit 92 Wafer 97 Wafer

Claims

1. A wafer inspection apparatus comprising: a support for supporting a wafer; an optical system for irradiating the surface or edge of a flat region of the wafer with linearly polarized light rays incident perpendicular to the surface of the wafer; a first photodetector that receives components other than linearly polarized light from the light rays reflected from the surface or edge of the wafer and outputs an electrical signal corresponding to the intensity; a second photodetector that receives the linearly polarized light component from the light rays reflected from the surface or edge of the wafer and outputs an electrical signal corresponding to the intensity; and a control unit that detects defects on the surface or edge of the wafer based on the electrical signals of the first photodetector and the second photodetector.

2. The wafer inspection apparatus according to claim 1, wherein the optical system comprises an objective lens having an optical axis perpendicular to the surface of the wafer.

3. The wafer inspection apparatus according to claim 2, further comprising a focusing mechanism that detects the focus of the objective lens and drives the objective lens in the direction of the optical axis of the objective lens according to the detected focus.

4. The wafer inspection apparatus according to claim 1, wherein the optical system irradiates the surface of the wafer with the light ray, and the control unit detects defects on the surface of the wafer.

5. The wafer inspection apparatus according to claim 1, wherein the optical system irradiates the edge portion of the wafer with the light beam, and the control unit detects defects in the edge portion of the wafer.

6. A wafer inspection apparatus according to claim 1, further comprising: a first polarizing beam splitter that reflects light rays other than linearly polarized light from the light rays reflected from the surface or edge portion of the wafer; and a second polarizing beam splitter that reflects linearly polarized light rays from the light rays reflected from the surface or edge portion of the wafer, wherein the first photodetector receives the components other than linearly polarized light reflected by the first polarizing beam splitter, and the second photodetector receives the components of linear polarization reflected by the second polarizing beam splitter.

7. The wafer inspection apparatus according to claim 6, further comprising a Faraday rotator between the first polarizing beam splitter and the second polarizing beam splitter, wherein light rays transmitted through the first polarizing beam splitter pass through the Faraday rotator and are incident on the second polarizing beam splitter.

8. The wafer inspection apparatus according to claim 1, further comprising a third photodetector for receiving fluorescence separated from components other than linearly polarized light.

9. The wafer inspection apparatus according to claim 8, further comprising a fourth photodetector for receiving fluorescence separated from the linearly polarized light component.

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