Wafer defect determination device, wafer defect determination system, and wafer defect determination method

Abstract

To provide a wafer defect determination device, a wafer defect determination system, and a wafer defect determination method, capable of determining a wafer defect without deteriorating the wafer state.SOLUTION: A wafer defect determination device 10 includes a control unit 12 for determining a defect occurring in an active layer 56 located on a surface side of an SOI wafer 50. The control unit 12 acquires a surface image obtained by photographing the surface of the active layer 56 and crystal orientation information for specifying the crystal orientation of the active layer 56 appearing in the surface image, determines whether the direction in which a linear defect appearing in the surface image extends substantially coincides with the crystal orientation of the active layer 56 based on the crystal orientation information, and determines the linear defect as a flaw penetrating the active layer 56 when the direction in which the linear defect extends substantially coincides with the crystal orientation of the active layer 56.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a wafer defect determination device, a defect determination system, and a wafer defect determination method. [Background technology]

[0002] Patent Document 1 describes an inspection method in which, when an invisible crack exists in a wafer, the crack is made to grow to form a fissure, thereby making it possible to identify wafers that have defects. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-99543 Summary of the Invention [Problem to be solved by the invention]

[0004] Growing cracks to make wafer defects identifiable can worsen the condition of the wafer, making repairable wafers unrepairable. It is therefore necessary to determine wafer defects without worsening the condition of the wafer.

[0005] Therefore, an object of the present disclosure is to propose a wafer defect discrimination device and defect discrimination system, as well as a wafer defect discrimination method, that can discriminate wafer defects without worsening the state of the wafer. [Means for solving the problem]

[0006] One embodiment of the present disclosure that solves the above problem is as follows. [1] A defect discrimination device including a control unit that discriminates defects occurring in an active layer located on the front surface side of an SOI wafer, The control unit acquiring a surface image obtained by photographing the surface of the active layer and crystal orientation information that identifies the crystal orientation of the active layer captured in the surface image; determining, based on the crystal orientation information, whether the direction in which the linear defect shown in the surface image extends substantially coincides with the crystal orientation of the active layer; If the direction in which the linear defect extends substantially coincides with the crystal orientation of the active layer, the linear defect is determined to be a flaw penetrating the active layer. Defect detection device. [2] The control unit Labeling defects shown in the surface image to generate labeled portions; If a ratio of the area of ​​the labeling portion to the area surrounded by a rectangular frame circumscribing the labeling portion is equal to or greater than a first determination threshold, or if a value obtained by dividing the area of ​​the labeling portion by the length of the periphery of the labeling portion is equal to or greater than a second determination threshold, the defect corresponding to the labeling portion is determined to be a stain; If a ratio of an area of ​​the labeling portion to an area surrounded by a rectangular frame circumscribing the labeling portion is less than the first determination threshold, or if a value obtained by dividing the area of ​​the labeling portion by the perimeter of the labeling portion is less than the second determination threshold, the defect corresponding to the labeling portion is detected as the linear defect. The defect detection device according to [1] above. [3] The control unit is configured to determine, among the plurality of pixels of the surface image, pixels whose brightness is equal to or greater than a brightness threshold as SG scratches, and detect pixels whose brightness is less than the brightness threshold as defects different from the SG scratches. [4] A defect detection device according to any one of [1] to [3] above; an imaging device for generating the surface image; a transfer device that transfers the SOI wafer and controls the orientation of the SOI wafer with respect to the imaging device to move the SOI wafer; A defect detection system comprising: the imaging device includes a line sensor that generates a linear image extending along an array direction using a plurality of imaging elements that are arranged along the array direction; The conveying device is outputting the crystal orientation information according to the control result of the orientation of the SOI wafer; Moving the SOI wafer in a direction intersecting the arrangement direction; The imaging device generates the surface image by combining the linear images captured by the line sensor at each position where the SOI wafer moves. [5] The imaging device is outputting, as a first surface image, the surface image obtained when the orientation of the SOI wafer is controlled so that a reference direction of the SOI wafer coincides with a first direction; outputting, as a second surface image, the surface image obtained when the orientation of the SOI wafer is controlled so that the reference direction of the SOI wafer coincides with a second direction; the control unit determines that a scratch penetrating the active layer has occurred in the SOI wafer when the extending direction of the linear defect detected in at least one of the first surface image and the second surface image substantially coincides with the crystal orientation of the active layer. The defect detection system described in [4] above. [6] The defect discrimination system according to [5] above, wherein the transfer device controls the orientation of the SOI wafer so that the first direction and the second direction are orthogonal to each other. [7] The defect detection system according to any one of [4] to [6] above, wherein the transport device controls the orientation of the SOI wafer so that the crystal orientation of the active layer is perpendicular to the arrangement direction. [8] A defect discrimination method executed by a defect discrimination device that discriminates defects occurring in an active layer located on the front surface side of an SOI wafer, comprising: acquiring a surface image of the surface of the active layer and crystal orientation information that identifies the crystal orientation of the active layer captured in the surface image; determining whether the direction in which the linear defect shown in the surface image extends substantially coincides with the crystal orientation of the active layer based on the crystal orientation information; If the direction in which the linear defect extends substantially coincides with the crystal orientation of the active layer, the linear defect is determined to be a flaw penetrating the active layer. A defect determination method comprising: [Effects of the Invention]

[0007] According to the wafer defect discrimination device, defect discrimination system, and wafer defect discrimination method of the present disclosure, defects in a wafer are discriminated without deteriorating the state of the wafer. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a block diagram showing an example of the configuration of a defect detection system according to an embodiment; [Figure 2] FIG. 1 is a cross-sectional view showing an example of the configuration of an SOI wafer. [Figure 3] FIG. 1 is a diagram schematically showing stresses acting during grinding of an SOI wafer. [Figure 4] FIG. 2 is a side view showing an example of the configuration of an imaging device and a transport device. [Figure 5] FIG. 10 is a diagram illustrating an example of the brightness distribution of an image of an SOI wafer. [Figure 6A] This is an example image showing contamination on an SOI wafer. [Figure 6B] This is an example image of a scratch-related defect on an SOI wafer. [Figure 7A] This is an example image of a surface scratch on an SOI wafer. [Figure 7B] This is an example image of a claw track on an SOI wafer. [Figure 8] 1 is a flowchart illustrating an example of a procedure for a defect determination method according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] (Configuration example of wafer defect discrimination system 100) A wafer defect discrimination system 100 (see FIG. 1) according to an embodiment of the present disclosure will be described below with reference to the drawings.

[0010] 1, a wafer defect detection system 100 includes a defect detection apparatus 10, an imaging apparatus 20, and a transport apparatus 30. The imaging apparatus 20 or the transport apparatus 30 may be included in the defect detection apparatus 10.

[0011] The object for which the defect discrimination system 100 discriminates defects is an SOI (Silicon On Insulator) wafer 50, as exemplified in FIG. 2. The SOI wafer 50 is a wafer in which a supporting wafer 52, a box layer 54, and an active layer 56 are stacked. The active layer 56 is located on the surface of the SOI wafer 50. The box layer 54 is located between the supporting wafer 52 and the active layer 56. The active layer 56 is located on the surface side of the SOI wafer 50. In other words, the box layer 54 and the active layer 56 are stacked on the surface of the supporting wafer 52. The defect discrimination system 100 discriminates defects occurring in the active layer 56 located on the surface of the SOI wafer 50.

[0012] The supporting wafer 52 and the active layer 56 are assumed to be single crystal silicon (Si), and the box layer 54 is assumed to be a silicon oxide film (SiO2).

[0013] The method for manufacturing the SOI wafer 50 includes the steps of forming a silicon oxide film that will become the box layer 54 on a silicon wafer that will become the support wafer 52, attaching the silicon wafer onto the box layer 54, and grinding the attached silicon wafer to form the active layer 56.

[0014] During the manufacturing of the SOI wafer 50, various defects occur in the active layer 56 of the SOI wafer 50. Defects that occur in the active layer 56 include SG (Surface Grind) scratches. SG scratches are streaky marks that appear on the surface of the active layer 56 along the direction of movement of the grinding tool when the active layer 56 is formed by grinding, i.e., on the surface of the active layer 56 where the active layer 56 is ground. Defects that occur in the active layer 56 include dirt. The dirt can be caused by the adhesion of substances other than silicon to the surface of the active layer 56. The dirt can be caused by the oxidation of the surface of the active layer 56. Defects that occur in the active layer 56 include scratches. The scratches can be caused by the surface of the active layer 56 being ground in a linear or curved shape.

[0015] Defects occurring in the active layer 56 include claw tracks. In this disclosure, a claw track is defined as a crack penetrating the active layer 56 from the surface to the interface with the box layer 54. In other words, a claw track is a scratch penetrating the active layer 56, i.e., a through scratch 58 (see FIG. 3 ). A claw track is defined as a defect occurring only in the active layer 56, and not in the supporting wafer 52.

[0016] 3, suppose that an SOI wafer 50 is attracted to a chuck 64 of a grinding machine and is ground by a grinding tool 62. At this time, suppose that a foreign object 66 is sandwiched between the support wafer 52 of the SOI wafer 50 and the chuck 64.

[0017] When a foreign object 66 is sandwiched between the support wafer 52 and the chuck 64, the SOI wafer 50 is pressed against the chuck 64 by the grinding tool 62, causing stress to be generated in the portion of the support wafer 52 that is in contact with the foreign object 66. The stress propagates to the active layer 56 via the support wafer 52 and the box layer 54. Because the Young's modulus of the silicon oxide film of the box layer 54 is greater than the Young's modulus of silicon in the active layer 56, the active layer 56 is significantly distorted at the interface between the box layer 54 and the active layer 56. Because the active layer 56 is significantly distorted at the interface with the box layer 54, a crack occurs in the active layer 56 from the interface with the box layer 54 toward the surface of the active layer 56, resulting in a scratch that penetrates the active layer 56, i.e., a through scratch 58.

[0018] The active layer 56, which is a silicon crystal, has a crystal orientation. The crystal orientation is the direction in which the crystal is easily cleaved. For example, if the crystal plane of the active layer 56 is <100> When expressed as: <110> Therefore, the crystal orientation of the active layer 56 is <110> The direction connecting the notch and the center of the SOI wafer 50 is <110> When the direction coincides with the direction of the notch, the crystal orientation of the active layer 56 coincides with the direction connecting the notch and the center of the SOI wafer 50. Also, when the direction perpendicular to the direction connecting the notch and the center of the SOI wafer 50 coincides with the direction of the notch, the crystal orientation of the active layer 56 coincides with the direction connecting the notch and the center of the SOI wafer 50. <110> When the direction coincides with the direction of the notch, the crystal orientation of the active layer 56 coincides with the direction perpendicular to the direction connecting the notch and the center of the SOI wafer 50.

[0019] Cleavage of a crystal is the progression of a crack that occurs in the crystal. Therefore, when a crack occurs in the active layer 56, the crack tends to occur along the crystal orientation of the active layer 56. For example, when the crystal plane is <100> In the active layer 56 expressed as follows, cracks tend to start at the position where the stress from the foreign substance 66 propagates to the active layer 56 and propagate in a cross direction that coincides with the crystal orientation.

[0020] <Configuration example of imaging device 20 and transport device 30> 4, in the defect discrimination system 100, the transfer device 30 transfers the SOI wafer 50 to the imaging device 20. The imaging device 20 photographs the surface of the SOI wafer 50 transferred by the transfer device 30.

[0021] The imaging device 20 includes a light source 22 and a line sensor 24. The line sensor 24 generates an image captured by a plurality of imaging elements arranged in one direction as a linear image along the arrangement direction of the plurality of imaging elements. In the example of Fig. 4, the plurality of imaging elements of the line sensor 24 are arranged along the depth direction of the paper. Hereinafter, the arrangement direction of the plurality of imaging elements of the line sensor 24 will also be simply referred to as the arrangement direction.

[0022] The light source 22 may be configured to emit illumination light substantially uniformly into the imaging range of the line sensor 24. The light source 22 may include a lamp such as a halogen lamp, or may include a light-emitting device such as an LED (Light Emitting Diode) or an LD (Laser Diode). The light source may be configured to be able to change the illuminance of the illumination light. The light source may be configured to be able to change the input power. The light source may be configured to be able to change the wavelength or spectrum of the illumination light. The light source may be configured to include a plurality of light-emitting devices.

[0023] The imaging device 20 emits irradiation light from a light source 22 toward the surface of the SOI wafer 50, and detects the light reflected from the surface of the SOI wafer 50 with a line sensor 24, thereby generating a linear image of the surface of the SOI wafer 50.

[0024] During imaging by the imaging device 20, the SOI wafer 50 is moved in a direction intersecting the arrangement direction by a transport device 30 (described later) or the like. The direction in which the SOI wafer 50 moves during imaging is also referred to as the movement direction. The movement direction may be a direction substantially perpendicular to the arrangement direction. The imaging device 20 generates a linear image of the surface of the SOI wafer 50 at each position to which the SOI wafer 50 moves, and generates an image of the entire surface of the SOI wafer 50 by combining the images at each position. The imaging device 20 may also generate an image of only a partial range of the surface of the SOI wafer 50.

[0025] The transport device 30 may transport the SOI wafer 50 to a position where it can be photographed by the imaging device 20. The transport device 30 may move the SOI wafer 50 along the movement direction while the imaging device 20 is photographing the SOI wafer 50. The transport device 30 may transport the SOI wafer 50 from the imaging device 20 after the imaging device 20 has photographed it. The transport device 30 may include a stage that holds the SOI wafer 50 while the imaging device 20 is photographing it. The transport device 30 may move the SOI wafer 50 by moving the stage. In order to transport the SOI wafer 50 to the stage, the transport device 30 may include an arm that is moved by a driving device such as a motor, or a hand or suction unit that holds the SOI wafer 50.

[0026] In the present disclosure, an XY coordinate system is set on a plane that holds the SOI wafer 50 on the stage of the transfer device 30. The XY coordinate system is set so that the arrangement direction coincides with the Y-axis direction. The transfer device 30 moves the SOI wafer 50 in a direction perpendicular to the arrangement direction, i.e., in the X-axis direction, while the imaging device 20 is capturing an image. In other words, the movement direction coincides with the X-axis direction.

[0027] 4, it is known that a claw track occurring in the normal direction of the plane containing the irradiated light and the reflected light, i.e., in the depth direction of the paper, is more likely to be detected by line sensor 24 than a claw track occurring along the plane containing the irradiated light and the reflected light, i.e., in the left-right direction of the paper. In other words, it is known that a claw track occurring in the arrangement direction, i.e., in the depth direction of the paper, is more likely to be detected by line sensor 24 than a claw track occurring in a direction perpendicular to the arrangement direction, i.e., in the left-right direction of the paper.

[0028] Therefore, the transfer device 30 may be configured to be able to rotate the SOI wafer 50 in the XY plane so that the orientation of the SOI wafer 50 can be changed with respect to the arrangement direction. By being able to rotate the SOI wafer 50, the transfer device 30 can control the orientation of the SOI wafer 50, i.e., the crystal orientation of the active layer 56.

[0029] When the crystal orientation of the active layer 56 of the SOI wafer 50 is specified by a notch, the transfer device 30 can control the position of the notch to thereby control the crystal orientation of the active layer 56. The crystal orientation of the active layer 56 is not limited to being specified by a notch, and may be specified by other features such as an orientation flat.

[0030] The transfer device 30 may control the orientation of the SOI wafer 50, for example, so that the crystal orientation of the active layer 56 of the SOI wafer 50 is perpendicular to the arrangement direction or so that the crystal orientation of the active layer 56 coincides with the arrangement direction. The transfer device 30 may control the orientation of the SOI wafer 50 so that the angle between the crystal orientation of the active layer 56 and the arrangement direction is any angle, such as 45 degrees or 60 degrees.

[0031] The stage of the transport device 30 may be included in the imaging device 20. The entire transport device 30 may be included in the imaging device 20. In other words, the transport device 30 may be configured integrally with the imaging device 20.

[0032] The configuration of the imaging device 20 is not limited to the configuration including the line sensor 24 as described above, but may be replaced with a configuration including various other cameras.

[0033] <Configuration example of defect detection device 10> The defect detection device 10 includes a control unit 12 , a communication unit 14 , and a display unit 16 .

[0034] The control unit 12 controls each component of the defect detection apparatus 10. The control unit 12 acquires an image of the surface of the SOI wafer 50 from the imaging device 20 via the communication unit 14. The control unit 12 may acquire various other information or data via the communication unit 14. The control unit 12 may output information for controlling the transport device 30 via the communication unit 14. The control unit 12 detects defects in the active layer 56 of the SOI wafer 50 based on the image of the surface of the SOI wafer 50. The control unit 12 displays the defect detection results on the display unit 16.

[0035] The control unit 12 may include at least one processor. The processor may execute programs that implement various functions of the control unit 12. The processor may be implemented as a single integrated circuit. An integrated circuit is also called an IC (Integrated Circuit). The processor may be implemented as multiple integrated circuits and discrete circuits that are connected to each other in a communicative manner. The processor may also be implemented based on various other known technologies.

[0036] The control unit 12 may further include a memory unit. The memory unit stores, for example, an image of the SOI wafer 50 or a defect determination result based on the image of the SOI wafer 50. The memory unit may include an electromagnetic storage medium such as a magnetic disk, or may include a memory such as a semiconductor memory or a magnetic memory. The memory unit may include a non-transitory computer-readable medium. The memory unit stores various information and programs executed by the control unit 12. The memory unit may function as a work memory for the control unit 12. At least a part of the memory unit may be configured as a separate entity from the control unit 12.

[0037] The communication unit 14 acquires an image of the surface of the SOI wafer 50 from the imaging device 20 and outputs it to the control unit 12. The communication unit 14 may acquire information for controlling the transport device 30 from the control unit 12 and output it to the transport device 30.

[0038] The communication unit 14 may include a communication device that transmits and receives information or data to and from other devices, such as the imaging device 20 or the transport device 30. The communication device may be communicatively connected to the other devices via a network. The communication device may be communicatively connected to the other devices via a wired or wireless connection. The communication device may include a communication module that connects to the network or the other devices. The communication module may include a communication interface such as a LAN (Local Area Network). The communication module may include a communication interface for contactless communication, such as infrared communication or NFC (Near Field communication). The communication module may realize communication using various communication methods, such as 4G or 5G. The communication method implemented by the communication device is not limited to the above examples and may include various other methods.

[0039] The display unit 16 may include a display device that outputs visual information such as images, characters, or graphics. The display device may include, for example, an LCD (Liquid Crystal Display), an organic EL (Electro-Luminescence) display, an inorganic EL display, or a PDP (Plasma Display Panel). The display device is not limited to these displays and may include displays of various other types. The display device may include a light-emitting device such as an LED or an LD. The display device may include various other devices.

[0040] The defect detection apparatus 10 may include an input device that accepts input of information, data, etc. from a user. The input device may include, for example, a touch panel or a touch sensor, or a pointing device such as a mouse. The input device may include physical keys. The input device may include an audio input device such as a microphone.

[0041] The defect detection device 10 may include, in addition to the display unit 16, an audio output device such as a speaker as a device for outputting information.

[0042] (Example of operation of defect determination system 100) The defect discrimination system 100 detects defects occurring in the active layer 56 and discriminates the type of the defects based on the surface image of the SOI wafer 50. The surface image is an image obtained by photographing the surface of the SOI wafer 50, i.e., the surface of the active layer 56. The defects include claw tracks, surface scratches, dirt, etc.

[0043] As described above, the claw track defect is a scratch that penetrates the active layer 56 and cannot be repaired in a later process. Therefore, the occurrence of the claw track reduces the manufacturing yield of the SOI wafer 50.

[0044] Furthermore, the claw tracks cause malfunctions when devices such as integrated circuits are fabricated in the active layer 56. Therefore, the occurrence and overlooking of claw tracks reduces the quality of the SOI wafer 50.

[0045] For the above reasons, there is a demand for improved accuracy in detecting claw tracks that occur in the active layer 56 of the SOI wafer 50. However, it is known that when claw tracks occur in the active layer 56, the claw tracks are difficult to visually detect. In the defect discrimination system 100 according to the present disclosure, the imaging device 20 can photograph the active layer 56 so that the claw tracks, which are difficult to visually detect, can be detected based on the surface image. Furthermore, the defect discrimination device 10 can improve the accuracy in discriminating claw tracks from various defects that appear in the surface image.

[0046] Next, an operation example of improving the detection accuracy of the croatrack generated in the active layer 56 by the defect discrimination system 100 will be described.

[0047] <Discrimination of SG streaks> As described above, the active layer 56 of the SOI wafer 50 is formed by grinding. Therefore, SG streaks are generated on the surface of the active layer 56. In the surface image illustrated in FIG. 5, the SG streaks appear as stripe-like patterns extending in a diagonal direction from the upper left to the lower right.

[0048] In the surface image illustrated in FIG. 5, defects different from the SG streaks appear within the broken-line frame represented as (2). The defects different from the SG streaks appear darker than the SG streaks. Therefore, the luminance of the pixels in which the defects different from the SG streaks appear is lower than the luminance of the pixels in which the SG streaks appear.

[0049] The control unit 12 of the defect discrimination device 10 calculates the average value of the luminance of the pixels in each row arranged in the left-right direction in the surface image illustrated in FIG. 5. The magnitude of the average value of the luminance of the pixels in each row is displayed as a graph on the left side of the surface image. The average value of the luminance of the pixels in the row surrounded by the broken-line frame represented as (2) is smaller than the average value of the luminance of the pixels in the rows surrounded by the broken-line frames represented as (1) and (3).

[0050] The control unit 12 can discriminate whether the pattern appearing in the surface image is an SG streak or a defect different from the SG streak by setting an appropriate threshold value for the average value of the luminance of the pixels. The threshold value set for the average value of the luminance of the pixels is also referred to as a luminance threshold value. The control unit 12 may determine that an SG streak appears when the luminance of the pixel is greater than or equal to the luminance threshold value, and may determine that a defect different from the SG streak appears when the luminance of the pixel is less than the luminance threshold value. The control unit 12 may set the luminance threshold value to a value between the value of the luminance of the pixels in which the SG streaks appear and the value of the luminance of the pixels in which the defects different from the SG streaks appear.

[0051] The control unit 12 may distinguish between SG scratches and defects other than SG scratches by image processing.The control unit 12 may distinguish between SG scratches and defects other than SG scratches by using a model for image processing.

[0052] <Distinguishing between stains and line defects> Defects different from SG streaks include stains and linear defects. The stains and linear defects shown in the surface image may be distinguished by, for example, the operation described below.

[0053] The surface images exemplified in FIGS. 6A and 6B show defects different from SG scratches. The control unit 12 performs labeling of pixels showing defects different from SG scratches. In the surface images exemplified in FIGS. 6A and 6B, the labeled portions are images showing the shapes of the labeled defects, and are displayed superimposed on the surface image as labeled portions 71 and 73. The control unit 12 calculates the areas of the labeled portions 71 and 73. The control unit 12 may calculate the number of labeled pixels as the areas of the labeled portions 71 and 73.

[0054] 6A and 6B, the control unit 12 sets rectangular frames 72 and 74 that circumscribe the labeling portions 71 and 73. The rectangular frames 72 and 74 may be displayed superimposed on the surface image. The control unit 12 calculates the area of ​​the region surrounded by the rectangular frames 72 and 74. The control unit 12 may calculate the number of pixels surrounded by the rectangular frames 72 and 74 as the area of ​​the region surrounded by the rectangular frames 72 and 74.

[0055] The control unit 12 may calculate a labeling area ratio. The labeling area ratio is the ratio of the area of ​​the labeling portions 71 and 73 to the area of ​​the rectangular frames 72 and 74. The labeling area ratio of the defect corresponding to dirt is larger than the labeling area ratio of the linear defect. The labeling area ratio of the labeling portion 71 in FIG. 6A is larger than the labeling area ratio of the labeling portion 73 in FIG. 6B. Therefore, the control unit 12 may determine that the labeling portion 71 in FIG. 6A is dirt and the labeling portion 73 in FIG. 6B is a linear defect.

[0056] The control unit 12 can determine whether a labeled defect is a stain or a linear defect by setting an appropriate threshold for the labeling area ratio. The threshold set for the labeling area ratio is also referred to as an area ratio threshold or a first determination threshold. The control unit 12 may determine the labeled defect as a stain when the labeling area ratio is equal to or greater than the area ratio threshold or the first determination threshold, and may determine the labeled defect as a linear defect when the labeling area ratio is less than the area ratio threshold or the first determination threshold. The control unit 12 may set the area ratio threshold or the first determination threshold to a value between the labeling area ratio of a defect corresponding to a stain and the labeling area ratio of a linear defect.

[0057] The control unit 12 may calculate the outer periphery lengths of the labeled portions 71 and 73. The control unit 12 may calculate a value obtained by dividing the area of ​​the labeled portions 71 and 73 by the outer periphery lengths. The value obtained by dividing the area of ​​the portion labeled as a defect corresponding to a stain by the outer periphery lengths is greater than the value obtained by dividing the area of ​​the portion labeled as a linear defect by the outer periphery lengths. The value obtained by dividing the area of ​​the labeled portion 71 in FIG. 6A by the outer periphery lengths is greater than the value obtained by dividing the area of ​​the labeled portion 73 in FIG. 6B by the outer periphery lengths. Therefore, the control unit 12 may determine that the labeled portion 71 in FIG. 6A is a stain and the labeled portion 73 in FIG. 6B is a linear defect.

[0058] The control unit 12 can determine whether the labeled defect is a stain or a linear defect by setting an appropriate threshold for the value obtained by dividing the area of ​​the labeled portion by the periphery. The threshold set for the value obtained by dividing the area of ​​the labeled portion by the periphery is also referred to as a second determination threshold. The control unit 12 may determine the labeled defect as a stain if the value obtained by dividing the area of ​​the labeled portion by the periphery is equal to or greater than the second determination threshold, and may determine the labeled defect as a linear defect if the value obtained by dividing the area of ​​the labeled portion by the periphery is smaller than the second determination threshold. The control unit 12 may set the second determination threshold to a value between the value obtained by dividing the area of ​​the portion labeled as a defect corresponding to a stain by the periphery and the value obtained by dividing the area of ​​the portion labeled as a linear defect by the periphery.

[0059] <Distinguishing between claw tracks and surface scratches> Linear defects include claw tracks and surface scratches. The surface image shown in Fig. 7A shows a linear defect that is surface scratch 75. The surface image shown in Fig. 7B shows a linear defect that is claw track 76. The control unit 12 may distinguish between surface scratch 75 and claw track 76 based on the direction in which the linear defect extends.

[0060] The following conditions are prerequisites for distinguishing between surface scratches 75 and claw tracks 76 based on the direction in which the linear defects extend. The notch direction in the surface images exemplified in FIGS. 7A and 7B is downward. The notch direction is the direction from the center of the SOI wafer 50 toward the notch. The XY coordinate system is set so that the notch direction coincides with the Y-axis direction and the direction perpendicular to the notch direction coincides with the X-axis direction. The crystal plane of the active layer 56 of the SOI wafer 50 is <100> In this case, the crystal orientation of the active layer 56 coincides with the notch direction and the direction perpendicular to the notch direction, that is, the X-axis direction and the Y-axis direction.

[0061] The control unit 12 may acquire crystal orientation information as a prerequisite for the crystal orientation. The crystal orientation information is information about the crystal orientation of the active layer 56 of the SOI wafer 50. The crystal orientation information may be generated according to the result of the transfer device 30 controlling the orientation of the SOI wafer 50. In other words, the transfer device 30 may output the crystal orientation information according to the result of controlling the orientation of the SOI wafer 50.

[0062] Under the above preconditions, the control unit 12 can determine whether the linear defect is a surface scratch 75 or a claw track 76 based on the direction in which the linear defect extends.

[0063] The control unit 12 detects the direction in which the linear defect extends. In Figures 7A and 7B, the longitudinal direction of the dashed frame surrounding the linear defect corresponds to the direction in which the linear defect extends.

[0064] Next, the control unit 12 calculates the angular difference between the direction in which the linear defect extends and the crystal orientation of the active layer 56. According to the above-mentioned preconditions, the crystal orientation of the active layer 56 is in two directions: the X-axis direction and the Y-axis direction. In the surface image illustrated in FIG. 7A, the linear defect corresponding to the surface scratch 75 extends in a direction close to the Y-axis direction. The angular difference between the linear defect in the surface image illustrated in FIG. 7A and the Y-axis direction is 31 degrees. In the surface image illustrated in FIG. 7B, the linear defect corresponding to the claw track 76 extends substantially along the X-axis direction. The angular difference between the linear defect in the surface image illustrated in FIG. 7B and the X-axis direction is less than 1 degree.

[0065] Considering the mechanism of claw track formation described above, claw tracks are likely to occur along the crystal orientation. Therefore, a linear defect extending along the crystal orientation is likely to be a claw track. The control unit 12 may determine that a linear defect is a claw track when the direction in which the linear defect extends substantially coincides with the crystal orientation. The control unit 12 may determine that a linear defect is a surface scratch when the direction in which the linear defect extends does not substantially coincide with the crystal orientation.

[0066] For example, the control unit 12 may determine that the direction in which the linear defect extends substantially coincides with the crystal orientation when the angular difference between the direction in which the linear defect extends and the crystal orientation of the active layer 56 is less than an angle threshold. In other words, in the present disclosure, the fact that the direction in which the linear defect extends substantially coincides with the crystal orientation corresponds to the fact that the angular difference between the direction in which the linear defect extends and the crystal orientation of the active layer 56 is less than the angle threshold. The angle threshold may be set to, for example, 10 degrees. The angle threshold is not limited to 10 degrees and may be set to another value as appropriate.

[0067] <Orientation of the SOI wafer 50 when capturing a surface image> As described above, claw tracks occurring in a direction perpendicular to the arrangement direction are less likely to be captured by the line sensor 24 than claw tracks occurring in the arrangement direction. To make it less likely that claw tracks will be overlooked, the defect discrimination system 100 may acquire multiple surface images of one SOI wafer 50 by using the imaging device 20 to capture images of the SOI wafer 50 while changing its orientation.

[0068] The imaging device 20 may output, as a first surface image, a surface image captured when the orientation of the SOI wafer 50 is controlled so that the reference direction of the SOI wafer 50 coincides with the first direction. The imaging device 20 may also output, as a second surface image, a surface image captured when the orientation of the SOI wafer 50 is controlled so that the reference direction of the SOI wafer 50 coincides with the second direction. Here, the reference direction is a direction set as a reference for the orientation of the SOI wafer 50. The reference direction may be set to coincide with the notch direction. The reference direction is not limited to the notch direction, and may be set in various other directions.

[0069] The first direction and the second direction are different directions. The first direction and the second direction may be directions perpendicular to each other. The first direction may coincide with the arrangement direction of the multiple imaging elements of the line sensor 24. When the first direction coincides with the arrangement direction, the second direction may coincide with the movement direction. When the first direction coincides with the movement direction, the second direction may coincide with the arrangement direction. The first direction and the second direction are not limited to these examples and may be set as appropriate.

[0070] The control unit 12 may detect that a claw track has occurred in the active layer 56 of the SOI wafer 50 when the direction in which the linear defect detected in at least one of the first surface image or the second surface image extends approximately coincides with the crystal orientation of the active layer 56.

[0071] Even if a claw track extends in the arrangement direction when the reference direction of the SOI wafer 50 coincides with the first direction, the same claw track extends in a direction perpendicular to the arrangement direction by rotating the SOI wafer 50 so that the reference direction of the SOI wafer 50 coincides with the second direction. Even if the control unit 12 cannot detect a claw track from the first surface image, it may be able to detect the claw track from the second surface image. As a result, the accuracy of claw track detection is improved.

[0072] <Output of defect detection results> The control unit 12 may display the defect detection results obtained by the above-described procedure on the display unit 16. The control unit 12 may also output the defect detection results to another output device.

[0073] The control unit 12 may output, as a defect detection result, at least whether a claw track has been detected in the active layer 56 of the SOI wafer 50. When outputting whether a claw track has been detected, the control unit 12 may determine whether the direction in which a linear defect shown in the surface image extends substantially coincides with the crystal orientation of the active layer 56. In this case, the control unit 12 does not need to distinguish between SG streaks and dirt.

[0074] The control unit 12 may output, as a defect detection result, information identifying the SOI wafer 50 in which a claw track has been detected. The control unit 12 may output, as a defect detection result, a result of identifying the type of defect. The control unit 12 may output, as a defect detection result, an image of the defect.

[0075] <Example of defect detection procedure> The control unit 12 of the defect detection apparatus 10 may execute a defect detection method including the steps of the flowchart illustrated in Fig. 8. The defect detection method may be realized as a defect detection program executed by a processor constituting the control unit 12. The defect detection program may be stored in a non-transitory computer-readable medium.

[0076] The control unit 12 acquires a surface image of the SOI wafer 50 from the imaging device 20 (step S1). The control unit 12 acquires, together with the surface image, information about the crystal orientation of the active layer 56 of the SOI wafer 50 shown in the surface image, i.e., crystal orientation information. The crystal orientation information may be included in the surface image.

[0077] The control unit 12 determines whether the brightness of each part of the surface image is equal to or greater than the brightness threshold (step S2). The control unit 12 may execute the procedures from step S2 onward for a part of the surface image that is recognized to contain some kind of pattern.

[0078] When the control unit 12 determines that the brightness of each portion of the surface image is equal to or greater than the brightness threshold value (step S2: YES), it determines (step S3) that the pattern shown in the surface image is an SG scratch that has occurred on the surface of the SOI wafer 50. After executing the procedure of step S3, the control unit 12 proceeds to the procedure of step S10.

[0079] If the control unit 12 determines that the brightness of a certain portion of the surface image is not greater than or equal to the brightness threshold (step S2: NO), that is, if it determines that the brightness is less than the brightness threshold, it considers that portion to be defective and determines the type of defect in the procedure of steps S4 to S9.

[0080] The control unit 12 performs labeling on portions of the surface image whose brightness is less than a brightness threshold, and calculates the area of ​​the labeled portion. The control unit 12 sets a rectangular frame circumscribing the labeled portion, and calculates the area of ​​the frame. The control unit 12 calculates the ratio of the area of ​​the labeled portion to the area of ​​the frame, i.e., the labeling area ratio. The control unit 12 determines whether the labeling area ratio is equal to or greater than an area ratio threshold (step S4).

[0081] If the labeling area ratio is equal to or greater than the area ratio threshold (step S4: YES), the control unit 12 determines that the defect corresponding to the labeled portion is a stain (step S5). If there are no other portions for which the type of defect must be determined, the control unit 12 executes the procedure of step S5 and then proceeds to the procedure of step S10. If there are other portions for which the type of defect must be determined, the control unit 12 returns to the procedure of step S4 and determines the type of defect for the other portions.

[0082] If the labeling area ratio is not equal to or greater than the area ratio threshold (step S4: NO), i.e., if the labeling area ratio is less than the area ratio threshold, the control unit 12 may consider the defect corresponding to the labeled portion to be a linear defect. The control unit 12 calculates the angle difference between the direction in which the linear defect extends and the crystal orientation, and determines whether the angle difference is less than the angle threshold (step S6). Specifically, the control unit 12 may approximate the linear defect with a straight line and calculate the angle difference between the approximated line and the crystal orientation. If the angle difference is not less than the angle threshold (step S6: NO), i.e., if the angle difference is equal to or greater than the angle threshold, the control unit 12 proceeds to step S9.

[0083] If the angle difference is less than the angle threshold value (step S6: YES), the control unit 12 determines whether a linear defect has occurred on the same radius in another SOI wafer 50 within the lot of the SOI wafer 50 (step S7). In this case, the control unit 12 makes the determination by referring to the determination results of the defect type in the other SOI wafer 50. If no linear defect has occurred on the same radius within the lot (step S7: NO), the control unit 12 proceeds to the procedure of step S9.

[0084] If a linear defect occurs on the same radius within the lot (step S7: YES), the control unit 12 determines that the linear defect is a claw track (step S8). If the determination result of the procedure of step S6 or S7 is NO, the control unit 12 determines that the linear defect is a surface scratch (step S9). If there are no other parts for which the type of defect must be determined, the control unit 12 performs the procedure of step S8 or S9 and then proceeds to the procedure of step S10. If there are other parts for which the type of defect must be determined, the control unit 12 returns to the procedure of step S4 and determines the type of defect for the other parts.

[0085] The control unit 12 outputs the defect detection result (step S10). After executing the procedure of step S10, the control unit 12 ends the execution of the procedure of the flowchart in FIG.

[0086] The control unit 12 does not have to execute steps S2 to S5 of the procedure in the flowchart of Fig. 8. When the control unit 12 judges YES in both steps S6 and S7 in the procedure in the flowchart of Fig. 8, the control unit 12 judges that the defect is a claw track. When the control unit 12 judges YES in at least one of steps S6 and S7, the control unit 12 may also judge that the defect is a claw track.

[0087] (summary) As described above, the defect discrimination system 100, the defect discrimination device 10, and the defect discrimination method according to this embodiment can detect claw tracks that are difficult to see with the naked eye from the surface image of the SOI wafer 50.

[0088] A comparative example involves applying ultrasonic vibrations to develop claw tracks so that they become visible. However, applying vibrations to an SOI wafer 50 that does not have claw tracks can cause defects such as surface scratches that would otherwise be repairable in a subsequent process to progress to an unrepairable level. For example, if the surface scratch is a crack that occurs in a shallow portion of the surface of the active layer 56 of the SOI wafer 50, within the thickness that will be polished in a subsequent process, it can be repaired when polishing is performed in the subsequent process. However, as the surface scratch progresses in the depth direction, the crack may extend to a depth that is unrepairable in a subsequent process. For this reason, it is difficult to apply the comparative example to wafers that will become products.

[0089] On the other hand, the method according to the present disclosure makes it possible to detect claw tracks that cannot be repaired in later processes with high accuracy without developing defects such as surface scratches that can be repaired in later processes, thereby determining wafer defects without worsening the wafer condition.

[0090] Furthermore, according to embodiments of the present disclosure, it is possible to improve the yield when manufacturing SOI wafers or when manufacturing devices from SOI wafers. Improving the yield increases the manufacturing efficiency of semiconductor products, enabling the production of more high-quality products, and contributes to the promotion of technological innovation and the sustainable development of the industry. Improving the yield also reduces the waste of materials consumed in the semiconductor product manufacturing process, contributing to the efficient use of resources. Furthermore, improving the yield reduces the waste of energy consumed in the semiconductor product manufacturing process, thereby contributing to the reduction of greenhouse gas emissions.

[0091] In other words, the defect detection system 100, defect detection device 10, and defect detection method disclosed herein contribute to "Goal 9: Industry, innovation and infrastructure," "Goal 12: Ensure sustainable consumption and production," or "Goal 13: Climate change action" in the Sustainable Development Goals (SDGs).

[0092] Although embodiments of the present disclosure have been described based on the drawings and examples, it should be noted that those skilled in the art could make various modifications or alterations based on the present disclosure. Therefore, it should be noted that these modifications and alterations are within the scope of the present disclosure. For example, functions included in each component or step can be rearranged so as not to cause logical inconsistencies, and multiple components or steps can be combined or divided into one. Although the embodiments of the present disclosure have been described mainly in terms of an apparatus, the embodiments of the present disclosure can also be realized as a method including steps executed by each component of the apparatus. The embodiments of the present disclosure can also be realized as a method, a program executed by a processor included in the apparatus, or a storage medium on which a program is recorded. It should be understood that these are also encompassed within the scope of the present disclosure.

[0093] The graphs included in this disclosure are schematic and do not necessarily correspond to the actual scale. [Industrial Applicability]

[0094] According to embodiments of the present disclosure, defects on a wafer are determined without deteriorating the condition of the wafer. [Explanation of symbols]

[0095] 100 Defect Detection System 10 defect discrimination device (12: control unit, 14: input unit, 16: output unit) 20 imaging device (22: light source, 24: line sensor) 30 Conveyor device 50 SOI wafer (52: supporting wafer, 54: box layer, 56: active layer, 58: claw track) 62 Grinding Tools 64 Chuck 66 Foreign matter 71, 73 Labeling part 72, 74 slots 75 Surface scratches 76 Claw Track

Claims

1. A defect discrimination device including a control unit that discriminates defects occurring in an active layer located on a front surface side of an SOI wafer, The control unit acquiring a surface image obtained by photographing the surface of the active layer and crystal orientation information that identifies the crystal orientation of the active layer captured in the surface image; determining, based on the crystal orientation information, whether the direction in which the linear defect shown in the surface image extends substantially coincides with the crystal orientation of the active layer; If the direction in which the linear defect extends substantially coincides with the crystal orientation of the active layer, the linear defect is determined to be a flaw penetrating the active layer. Defect detection device.

2. The control unit Labeling defects shown in the surface image to generate labeled portions; If a ratio of the area of ​​the labeling portion to the area surrounded by a rectangular frame circumscribing the labeling portion is equal to or greater than a first determination threshold, or if a value obtained by dividing the area of ​​the labeling portion by the length of the periphery of the labeling portion is equal to or greater than a second determination threshold, the defect corresponding to the labeling portion is determined to be a stain; If a ratio of an area of ​​the labeling portion to an area surrounded by a rectangular frame circumscribing the labeling portion is less than the first determination threshold, or if a value obtained by dividing the area of ​​the labeling portion by the periphery of the labeling portion is less than the second determination threshold, the defect corresponding to the labeling portion is detected as the linear defect. The defect detection device according to claim 1 .

3. 2. The defect discrimination device according to claim 1, wherein the control unit discriminates pixels of the surface image whose brightness is equal to or greater than a brightness threshold as SG scratches, and detects pixels whose brightness is less than the brightness threshold as defects different from the SG scratches.

4. The defect detection device according to any one of claims 1 to 3, an imaging device for generating the surface image; a transfer device that transfers the SOI wafer and controls the orientation of the SOI wafer with respect to the imaging device to move the SOI wafer; A defect detection system comprising: the imaging device includes a line sensor that generates a linear image extending along an array direction using a plurality of imaging elements that are arranged along the array direction; The conveying device is outputting the crystal orientation information according to the control result of the orientation of the SOI wafer; Moving the SOI wafer in a direction intersecting the arrangement direction; The imaging device generates the surface image by combining the linear images captured by the line sensor at each position where the SOI wafer moves.

5. The imaging device is outputting, as a first surface image, the surface image obtained when the orientation of the SOI wafer is controlled so that a reference direction of the SOI wafer coincides with a first direction; outputting, as a second surface image, the surface image obtained when the orientation of the SOI wafer is controlled so that the reference direction of the SOI wafer coincides with a second direction; the control unit determines that a scratch penetrating the active layer has occurred in the SOI wafer when the extending direction of the linear defect detected in at least one of the first surface image and the second surface image substantially coincides with the crystal orientation of the active layer. The defect detection system according to claim 4 .

6. 6. The defect determination system according to claim 5, wherein the transfer device controls the orientation of the SOI wafer so that the first direction and the second direction are perpendicular to each other.

7. 5. The defect detection system according to claim 4, wherein the transfer device controls the orientation of the SOI wafer so that the crystal orientation of the active layer is perpendicular to the arrangement direction.

8. A defect discrimination method executed by a defect discrimination device that discriminates defects occurring in an active layer located on a front surface side of an SOI wafer, comprising: acquiring a surface image of the surface of the active layer and crystal orientation information that identifies the crystal orientation of the active layer captured in the surface image; determining whether the direction in which the linear defect shown in the surface image extends substantially coincides with the crystal orientation of the active layer based on the crystal orientation information; If the direction in which the linear defect extends substantially coincides with the crystal orientation of the active layer, the linear defect is determined to be a flaw penetrating the active layer. A defect determination method comprising:

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