Mixed crystal detection system and method for polished wafer

Abstract

The embodiment of the invention provides a mixed crystal detection system and method for a polished wafer, and relates to the field of polished wafers. The polarized light transmission device is utilized to irradiate linearly polarized light onto a target polished section, so that the target polished section reflects elliptically polarized light to the image acquisition device, the image acquisition device acquires an image of the target polished section to obtain a target image, and the processor performs stray crystal detection operation on the target image to obtain candidate stray crystals. And target mixed crystals are screened out from the candidate mixed crystals according to the attribute information of the candidate linear mixed crystals, and a mixed crystal detection result of the target polished wafer is determined based on the parameter information of the target mixed crystals. In addition, through primary screening and secondary screening of mixed crystal detection, the accuracy of the detected mixed crystals can be ensured. In addition, the whole process is automatically realized, and the problems of low detection accuracy and relatively low efficiency existing in manual detection can be avoided.

Description

Technical Field

[0001] The present application relates to the field of polishing sheets, and more specifically, to a system and method for detecting impurities in polishing sheets. Background Art

[0002] At present, the mainstream method of producing 4H crystal silicon carbide substrates is to use the physical vapor transport (PVT) method. When the temperature field is improperly controlled or the seed crystal is poorly bonded, it is very easy to produce a different crystal structure from the 4H crystal, which is called a stray crystal defect (stray crystal for short). The presence of stray crystals will destroy the integrity of the 4H crystal, which will not only lead to a decrease in the electrical and mechanical properties of the substrate, but also affect the epitaxial growth, thereby reducing the reliability of the device. Therefore, it is very important to detect stray crystals during the production process of silicon carbide substrates.

[0003] Therefore, how to realize the detection of impurity crystals in polishing wafers is a technical problem that technical personnel in this field need to solve urgently. Summary of the invention

[0004] In view of this, the present application provides a system and method for detecting stray crystals in a polishing sheet to solve the problem of urgently needing to realize stray crystal detection in a polishing sheet.

[0005] In order to solve the above technical problems, this application adopts the following technical solutions:

[0006] A polishing sheet impurity crystal detection system, comprising:

[0007] Polarized light transmission device, image acquisition device and processor;

[0008] The polarized light transmission device is used to irradiate linear polarized light onto the target polishing sheet, so that the target polishing sheet reflects elliptically polarized light to the image acquisition device;

[0009] The image acquisition device is used to acquire the image of the target polishing sheet to obtain a target image;

[0010] The processor is used to perform a miscellaneous crystal detection operation on the target image to obtain candidate miscellaneous crystals, screen out target miscellaneous crystals from the candidate miscellaneous crystals using attribute information of the candidate miscellaneous crystals, and determine a miscellaneous crystal detection result of the target polishing sheet based on parameter information of the target miscellaneous crystals.

[0011] Optionally, the polarized light transmission device comprises:

[0012] A light source, an analyzer, a polarizer and a beam splitter prism; the light source, the polarizer and the beam splitter prism are arranged in sequence, the analyzer is arranged above the beam splitter prism, and the analyzer and the polarizer are arranged vertically;

[0013] The light output by the light source passes through the polarizer and the beam splitter prism in sequence to obtain linearly polarized light and irradiates the target polished sheet. The elliptically polarized light reflected by the target polished sheet passes through the beam splitter prism and the analyzer in sequence to be output to the image acquisition device.

[0014] Optionally, the target polishing sheet is disposed on a stage;

[0015] The stage fixes the target polishing sheet via an outer ring foot and an inner ring foot;

[0016] The loading platform is arranged on a guide rail so that the loading platform can move on the guide rail.

[0017] Optionally, the processor is further configured to:

[0018] Controlling the outer ring foot of the loading platform to rise;

[0019] Controlling the stage to move according to a preset step length and trajectory; wherein each time the stage moves, the image acquisition device acquires an image of the target polishing sheet to obtain a target image;

[0020] After the loading platform finishes moving along the trajectory, the inner ring foot of the loading platform is controlled to rise, and the outer ring foot of the loading platform is controlled to fall;

[0021] The stage is controlled to move so that the image acquisition device acquires the image of the target polishing sheet at the outer ring foot of the stage to obtain a target image.

[0022] Optionally, the stage controls the adsorption force between the stage and the target polishing wafer through an air pressure regulating device.

[0023] A method for detecting stray crystals of a polishing sheet is applied to a processor in the above-mentioned stray crystal detection system of the polishing sheet; the method for detecting stray crystals of the polishing sheet comprises:

[0024] Performing a miscellaneous crystal detection operation on the target image to obtain candidate miscellaneous crystals;

[0025] Screening out target impurity crystals from the candidate impurity crystals using the attribute information of the candidate impurity crystals;

[0026] Based on the parameter information of the target miscellaneous crystals, a miscellaneous crystal detection result of the target polishing wafer is determined.

[0027] Optionally, performing a miscellaneous crystal detection operation on the target image to obtain candidate miscellaneous crystals includes:

[0028] Based on the shooting order of the target images, performing a stitching operation on the target images to obtain a first image;

[0029] Performing image noise reduction processing on the first image to obtain a second image;

[0030] performing an image enhancement operation on the second image to obtain a third image;

[0031] A miscellaneous crystal detection operation is performed on the third image using a miscellaneous crystal detection model to determine candidate miscellaneous crystals in the target polishing wafer.

[0032] Optionally, performing a miscellaneous crystal detection operation on the third image using a miscellaneous crystal detection model to determine candidate miscellaneous crystals in the target polishing wafer includes:

[0033] Determining a grayscale abnormal area in the third image based on the grayscale value of each pixel in the third image;

[0034] A miscellaneous crystal detection model is used to perform a miscellaneous crystal detection operation on the grayscale abnormal region to obtain a detection result of whether the grayscale abnormal region is a miscellaneous crystal, so as to determine the candidate miscellaneous crystals in the target polishing wafer using the detection result.

[0035] Optionally, the attribute information includes area; and screening out target impurity crystals from the candidate impurity crystals using the attribute information of the candidate impurity crystals comprises:

[0036] Calculating the area of ​​the candidate impurity crystal;

[0037] Candidate impurity crystals with an area greater than an area threshold are screened out and used as target impurity crystals.

[0038] Optionally, determining the detection result of the target impurity crystals of the target polishing wafer based on the parameter information of the target impurity crystals includes:

[0039] Calculating the distance between any two vertices of the target impurity crystal in the third image;

[0040] The maximum distance is taken as the diameter of the target impurity crystal;

[0041] Counting the number of target impurity crystals in the target polishing wafer;

[0042] Determining the grade of the target polishing sheet based on the number and diameter of the target impurity crystals;

[0043] The grade of the target polishing sheet, the number, position and diameter of the target miscellaneous crystals are taken as miscellaneous crystal detection results.

[0044] The embodiment of the present application provides a system and method for detecting impurities of a polishing sheet, wherein the polarized light transmission device is used to irradiate linear polarized light onto a target polishing sheet, so that the target polishing sheet reflects elliptically polarized light to the image acquisition device, so that the image acquisition device acquires the imaging of the target polishing sheet to obtain a target image, the processor performs an impurity crystal detection operation on the target image to obtain candidate impurities, uses the attribute information of the candidate impurities to screen out target impurities from the candidate impurities, and determines the impurity crystal detection result of the target polishing sheet based on the parameter information of the target impurities, thereby realizing impurity crystal detection of the polishing sheet. In addition, the present invention realizes the primary screening and secondary screening of impurities by performing an impurity crystal detection operation on the target image to obtain candidate impurities and using the attribute information of the candidate impurities to screen out target impurities from the candidate impurities, thereby ensuring the accuracy of the impurities detected. In addition, the entire process of the present invention is automatically realized, which can avoid the problems of low detection accuracy and low efficiency due to lack of experience in manual detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the related technologies, the drawings required for use in the embodiments or the related technical descriptions are briefly introduced below. Obviously, the drawings described below are merely embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0046] Figure 1 A schematic structural diagram of a polishing wafer impurity detection system provided by an embodiment of the present invention;

[0047] Figure 2 A schematic structural diagram of another impurity crystal detection system for a polishing sheet provided by an embodiment of the present invention;

[0048] Figure 3 Another optical path transmission diagram for detecting impurities in a polishing sheet provided by an embodiment of the present invention;

[0049] Figure 4 A method flow chart of a method for detecting impurity crystals in a polishing sheet provided by an embodiment of the present invention;

[0050] Figure 5 A flow chart of a method for determining candidate impurity crystals provided by an embodiment of the present invention;

[0051] Figure 6 A schematic diagram of a miscellaneous crystal provided by an embodiment of the present invention;

[0052] Figure 7 A schematic diagram of impurity crystal detection provided by an embodiment of the present invention;

[0053] Figure 8 A schematic diagram of the structure of an electronic device provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0054] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0055] At present, the mainstream method of producing 4H crystal silicon carbide substrates is to use the Physical Vapor Transport (PVT) method. When the temperature field is improperly controlled or the seed crystal is poorly bonded, it is very easy to produce a different crystal structure from the 4H crystal, which is called a stray crystal defect (stray crystal for short). The presence of stray crystals will destroy the integrity of the 4H crystal, which will not only lead to a decrease in the electrical and mechanical properties of the substrate, but also affect the epitaxial growth, thereby reducing the reliability of the device. Therefore, it is very important to detect stray crystals during the production process of silicon carbide substrates.

[0056] When implementing the detection of impurity crystals in polished sheets, a manual detection method can be used. Specifically, the polished sheet is observed manually through reflection and transmission of a strong light, and the impurity crystals are determined based on the experience and subjective judgment of the detection personnel. Then, the impurity crystals of the polished sheet are observed through reflection under a microscope to detect the impurity crystal diameter. The entire process requires manual observation and sample movement, resulting in low detection efficiency. It is also easily limited by manual experience, resulting in low detection accuracy.

[0057] To this end, the embodiment of the present invention has developed a system for detecting impurities in polishing sheets, which can use the polarized light transmission device to irradiate linear polarized light onto the target polishing sheet, so that the target polishing sheet reflects elliptically polarized light to the image acquisition device, so that the image acquisition device acquires the imaging of the target polishing sheet to obtain the target image, and the processor performs an impurity crystal detection operation on the target image to obtain candidate impurities, and uses the attribute information of the candidate impurities to screen out the target impurities from the candidate impurities, and based on the parameter information of the target impurities, determines the impurity crystal detection result of the target polishing sheet, and realizes impurity crystal detection of the polishing sheet. In addition, the present invention realizes the primary screening and secondary screening of impurities by performing an impurity crystal detection operation on the target image to obtain candidate impurities and using the attribute information of the candidate impurities to screen out the target impurities from the candidate impurities, which can ensure the accuracy of the detected impurities. In addition, the entire process of the present invention is automatically realized, which can avoid the problems of low detection accuracy and low efficiency due to lack of experience in manual detection.

[0058] Based on the above content, an embodiment of the present invention provides a polishing sheet impurity crystal detection system, referring to Figure 1 , which may include:

[0059] Polarized light transmission device 101 , image acquisition device 102 and processor 103 .

[0060] The polarized light transmission device 101 is used to irradiate linearly polarized light onto a target polishing sheet, so that the target polishing sheet reflects elliptically polarized light to the image acquisition device 102 .

[0061] In actual scenarios, the target polishing sheet refers to the polishing sheet being tested, which may or may not have stray crystals. If stray crystals exist, the stray crystal detection system for the polishing sheet in the embodiment of the present invention can be used to detect the number, position, diameter and other information of the stray crystals.

[0062] When performing impurity crystal detection on a polishing sheet, it is necessary to collect an image of the target polishing sheet. In order to successfully collect the image, it is necessary to utilize polarized light reflected by the polishing sheet to realize image collection.

[0063] Therefore, in the embodiment of the present invention, the polarized light transmission device 101 is used to irradiate the target polishing sheet with linear polarized light. After the target polishing sheet receives the linear polarized light, it will perform a reflection operation. At this time, what is reflected is elliptically polarized light. The elliptically polarized light will be output to the image acquisition device 102, so that the image acquisition device 102 can perform an image acquisition operation on the target polishing sheet.

[0064] In actual scenarios, the image acquisition device 102 is a camera. In general scenarios, the camera can be an area array camera with a camera resolution of 4 μm and a 1X (camera magnification is one) lens for acquiring the image of the target polishing sheet to obtain a target image.

[0065] The obtained target image will be transmitted to the processor 103. In the embodiment of the present invention, the processor 103 can be a high-performance computer, server, etc., for realizing data processing functions.

[0066] The processor 103 performs a miscellaneous crystal detection operation on the target image to obtain candidate miscellaneous crystals, selects target miscellaneous crystals from the candidate miscellaneous crystals using the attribute information of the candidate miscellaneous crystals, and determines a miscellaneous crystal detection result of the target polishing wafer based on the parameter information of the target miscellaneous crystals.

[0067] More specifically, the processor 103 first performs a miscellaneous crystal detection operation on the target image to preliminarily obtain the miscellaneous crystals in the target polished sheet, which are called candidate miscellaneous crystals. In actual scenarios, the candidate miscellaneous crystals may be real miscellaneous crystals or other impurities, such as stains. Therefore, it is necessary to further judge the candidate miscellaneous crystals to determine whether they are real miscellaneous crystals.

[0068] When making a judgment, the attribute information of the candidate impurity crystals may be used, wherein the attribute information may be the area, that is, the area of ​​the candidate impurity crystals may be used for secondary screening.

[0069] Generally speaking, impurities are hexagonal in appearance. Some small stains may be coincidentally misjudged as impurities because of their similar shapes. However, after data collection and observation, it is difficult for large stains to present a hexagonal appearance. Therefore, by controlling the area, stains and impurities can be effectively identified, which can avoid the situation where some small stains are misjudged as impurities. In actual scenarios, when the area is greater than the area threshold, the candidate impurity is considered to be a real impurity. The area threshold can be set according to the actual situation, such as 50μm. 2 , 100μm 2 , 200μm 2 、300μm 2 , 400μm 2 wait.

[0070] After obtaining the real target impurity crystals by secondary screening of the candidate impurity crystals, the impurity crystal detection result of the target polished sheet can be determined based on the parameter information of the target impurity crystals, wherein the parameter information can be the quantity, diameter, number, polished sheet grade and other information of the target impurity crystals.

[0071] The detection result of the impurity crystals can be output in the form of pictures, charts, etc. For example, the actual impurity crystal picture can be output as a picture, and the number, diameter, number, polishing sheet grade and other information of the target impurity crystals can be output as a chart.

[0072] In this embodiment, the polarized light transmission device 101 can be used to irradiate linear polarized light onto the target polishing sheet, so that the target polishing sheet reflects elliptically polarized light to the image acquisition device 102, so that the image acquisition device 102 acquires the imaging of the target polishing sheet to obtain the target image, and the processor 103 performs a miscellaneous crystal detection operation on the target image to obtain candidate miscellaneous crystals, and uses the attribute information of the candidate miscellaneous crystals to screen out the target miscellaneous crystals from the candidate miscellaneous crystals, and determines the miscellaneous crystal detection result of the target polishing sheet based on the parameter information of the target miscellaneous crystals, thereby realizing the miscellaneous crystal detection of the polishing sheet. In addition, the present invention realizes the primary screening and secondary screening of miscellaneous crystals by performing a miscellaneous crystal detection operation on the target image to obtain candidate miscellaneous crystals and using the attribute information of the candidate miscellaneous crystals to screen out the target miscellaneous crystals from the candidate miscellaneous crystals, which can ensure the accuracy of the detected miscellaneous crystals. In addition, the entire process of the present invention is automatically realized, which can avoid the problems of low detection accuracy and low efficiency due to lack of experience in manual detection.

[0073] In another implementation of the present application, a specific structure of the polarized light transmission device 101 is provided. Figure 2, the polarized light transmission device 101 may include:

[0074] A light source, an analyzer, a polarizer and a beam splitter prism; the light source, the polarizer and the beam splitter prism are arranged in sequence, the analyzer is arranged above the beam splitter prism, and the analyzer and the polarizer are arranged vertically.

[0075] Specifically, the shaking of the machine may cause problems such as ghosting and missing of the pictures taken by the camera, so a marble load-bearing plate 1 is used to stabilize the test system and improve the reliability of the camera to collect images. The polishing sheet 8 is a silicon carbide polishing sheet, which is used as a test sample, that is, the target polishing sheet in the embodiment of the present invention. The camera can be an area array camera 2, which includes a 1X lens 3 for collecting polishing sheet images.

[0076] The analyzer 4, the light source 5, the beam splitter 6 and the polarizer 7 constitute a polarized light transmission device 101 for constructing a polarization detection channel. Among them, the light source 5 can adopt a coaxial light source, the function of the coaxial light source is to make the reflected light of the object to be measured perpendicular to the optical axis of the camera, and is often used as bright field illumination. In one implementation, the coaxial light source can be a power-adjustable coaxial white light source with a power range of 30-60W and an adjustable exposure time, as a light source for reflected polarization.

[0077] like Figure 2 As shown, the light source 5, the polarizer 7 and the beam splitter prism 6 are arranged horizontally in sequence, and the analyzer 4 is arranged above the beam splitter prism 6, specifically, it can be directly above. The analyzer 4 and the polarizer 7 are arranged vertically. Among them, the polarizer 7 is arranged on the left side of the beam splitter prism 6, and the analyzer 4 is arranged above the beam splitter prism 6, and the two are placed at 90 degrees, and the beam splitter prism 6 is between the analyzer 4 and the polarizer 7, and an orthogonal polarization detection channel is constructed.

[0078] Based on the above-mentioned structure, the light output by the light source passes through the polarizer and the beam splitter in turn to obtain linearly polarized light and irradiates the target polished sheet. The elliptically polarized light reflected by the target polished sheet passes through the beam splitter and the analyzer in turn to be output to the image acquisition device 102.

[0079] Specifically, the light path direction is as follows Figure 3 As shown. The light source 5 can emit light in different directions, but only light in a specific direction can pass through the polarizer 7. The polarizer 7 outputs linear polarized light, which is reflected by the beam splitter 6 and irradiated onto the polishing sheet 8. The polishing sheet 8 reflects elliptically polarized light, which passes through the beam splitter 6 and irradiates onto the analyzer 4. The analyzer 4 only allows light in a specific direction to be output, and the light in the specific direction will be output to the 1X lens 3, so that the camera uses light to collect images.

[0080] The polishing sheet 8, i.e., the target polishing sheet, is arranged on the stage 9. In one implementation, the stage 9 is an X / Y / Z axis movable stage, comprising 6 ceramic vacuum tubes for supporting the silicon carbide polishing sheet, and the step length is adjustable (2-50mm). Among them, 3 ceramic vacuum tubes of the 6 ceramic vacuum tubes can be used as outer ring feet, and the other 3 ceramic vacuum tubes can be used as inner ring feet. The stage 9 fixes the target polishing sheet through the outer ring feet and the inner ring feet. Among them, the 3 ceramic vacuum tubes as the outer ring feet can be arranged in a triangular structure, and similarly, the 3 ceramic vacuum tubes as the inner ring feet can also be arranged in a triangular structure. In the actual scene, the outer ring feet can be used to fix the polishing sheet 8 first, and then the camera can be used to capture other areas of the polishing sheet 8 except the outer ring feet, and then the inner ring feet of the stage are controlled to rise, and the outer ring feet of the stage are controlled to fall, and then the camera is used to capture the image of the polishing sheet in the outer ring foot area.

[0081] The stage 9 is set on the guide rail 11, and the motor 12 can drive the stage 9 to move on the guide rail 11 based on the control of the processor 103, such as a high-performance computer 14, so as to adjust the camera's acquisition area so that the camera can capture images at any position of the polishing sheet 8.

[0082] In one implementation, in order to stably set the polishing sheet 8 on the stage 9, an air pressure regulating device is provided on the stage 9, and the stage controls the adsorption force between the stage and the target polishing sheet through the air pressure regulating device to prevent the polishing sheet 8 from slipping off the stage 9. In a specific implementation, the air pressure regulating device may include a CDA (Compressed Dry Air) supply device 10 and a PV (pressure vacuum) supply device 13, which can control the pressure of the adsorbed polishing sheet and stabilize the polishing sheet. Among them, the CDA supply device 10 exhausts to provide positive pressure, and the PV supply device 13 inhales to provide negative pressure. The two work together to ensure the stability of the vacuum system.

[0083] On the basis of the above structure, the acquisition area of ​​the camera can be adjusted by controlling the stage 9 to move on the guide rail 11 , so that the camera can acquire images at any position of the polishing sheet 8 .

[0084] Specifically, when collecting images, the processor 103 is further used to:

[0085] 1) Control the outer ring feet of the loading platform to rise.

[0086] Before starting the impurity crystal detection, it is necessary to place the silicon carbide polishing wafer on the stage 9 with the silicon surface facing upward using a suction pen / manipulator.

[0087] Then the software is initialized, and the stage 9 returns to the origin. The user clicks the start test button on the processor 103, and the impurity crystal detection operation starts.

[0088] The processor 103 controls the three outer ring feet of the stage 9 to rise and utilizes the CDA supply device 10 and the PV supply device 13 to vacuum absorb the polishing sheet 8 .

[0089] 2) Control the stage to move according to a preset step length and trajectory.

[0090] Wherein, each time the stage 9 moves once, the image acquisition device 102 acquires an image of the target polishing sheet to obtain a target image.

[0091] Specifically, in an embodiment of the present invention, in order to accurately capture the image of the polishing sheet 8, the complete image of the polishing sheet 8 is not captured each time the image is captured, but only a partial image is captured, such as only capturing images of two pixel blocks or five pixel blocks of the polishing sheet 8. Subsequently, through a stitching operation, all the captured images are stitched together to obtain the overall image of the polishing sheet 8.

[0092] Therefore, the stage 9 needs to be continuously moved so that the area array camera 2 continuously collects partial images of the polishing sheet 8 to obtain a target image.

[0093] In actual scenarios, it is necessary to pre-set the step length of the stage 9, which is the preset step length mentioned above. In addition, the trajectory of the stage 9 can also be set. In the embodiment of the present invention, in order to completely collect images of various parts of the polishing sheet 8, an S-shaped moving trajectory can be used. That is, during the movement according to the S-shaped moving trajectory, the area array camera 2 performs image acquisition operations according to the preset step length.

[0094] In specific implementation, starting from the upper left of the polishing sheet, the stage moves in an S-shaped manner according to the set step length. Each time the stage moves the light source 5, an exposure is performed and the area array camera 2 takes a picture. This continues until the entire polishing sheet is photographed. At this time, the stage moves to the lower right of the polishing sheet. When exposing, the exposure time can be set. The longer the exposure time, the greater the amount of light entering. The most appropriate exposure time can be selected according to the clarity and noise of the captured image, and then the timed exposure can be set according to the moving speed of the stage 9. In the shooting procedure, the positions of the stage 9 and the polishing sheet 8 are fixed.

[0095] 3) After the loading platform finishes moving along the trajectory, the inner ring feet of the loading platform are controlled to rise, and the outer ring feet of the loading platform are controlled to fall.

[0096] Specifically, after the stage finishes moving along the trajectory, the area where the polishing sheet 8 is supported by the outer ring foot is interfered by the outer ring foot, and therefore, the image of the polishing sheet 8 at the outer ring foot is not collected at this time, but images of all areas except the outer ring foot area are collected.

[0097] Then, the inner ring foot of the stage 9 is controlled to rise, and the polishing sheet 8 is supported by the inner ring foot. Then, the outer ring foot of the stage 9 is controlled to fall, and the CDA supply device 10 and the PV supply device 13 are used to adsorb the polishing sheet 8 to collect the image of the polishing sheet 8 at the outer ring foot.

[0098] 4) Controlling the movement of the stage so that the image acquisition device 102 acquires the image of the target polishing sheet at the outer ring foot of the stage to obtain a target image.

[0099] In this embodiment, the stage 9 is controlled to move to photograph the three outer ring feet of the polishing sheet 8 to complete the data. Specifically, the x and y axes of the stage 9 can be moved so that the image acquisition range of the area array camera 2 is the area where the outer ring feet are located, and then the image of the target polishing sheet at the outer ring feet is acquired. Subsequently, the position of the stage 9 is adjusted in sequence to acquire the image of the target polishing sheet at the next set of outer ring feet, until the image of the target polishing sheet at each outer ring foot is acquired to obtain the target image. At this point, the image of each part of the polishing sheet 8 is acquired, and multiple target images are obtained.

[0100] In this embodiment, a complete polishing sheet image is composed of multiple high-resolution target images. The number of image shots depends on the set step size.

[0101] Subsequently, the processor 103 is used to perform a miscellaneous crystal detection operation on the target image to obtain candidate miscellaneous crystals, and the target miscellaneous crystals are screened out from the candidate miscellaneous crystals using the attribute information of the candidate miscellaneous crystals. Based on the parameter information of the target miscellaneous crystals, the miscellaneous crystal detection result of the target polishing wafer is determined.

[0102] In this embodiment, the polishing sheet is supported by alternating outer ring feet and inner ring feet, so that accurate images of each position of the polishing sheet can be completely acquired, and then it can be detected whether there are impurity crystals at each position.

[0103] Based on the embodiment of the above-mentioned polishing sheet miscellaneous crystal detection system, another embodiment of the present application provides a polishing sheet miscellaneous crystal detection method, which is applied to the processor in the above-mentioned polishing sheet miscellaneous crystal detection system. Figure 4 , the method for detecting impurity crystals of the polishing sheet comprises:

[0104] S11, performing a miscellaneous crystal detection operation on the target image to obtain candidate miscellaneous crystals.

[0105] In this embodiment, a developing device (whose structure is as shown in FIG. 1 ) including a camera, a lens, a stage, a polishing sheet, a beam splitter, a polarizer, an analyzer, etc. Figure 3 As shown in the figure, multiple target images are obtained, and the multiple target images are transmitted to the processor.

[0106] The processor first performs a miscellaneous crystal detection operation on the target image to preliminarily obtain the miscellaneous crystals in the target polished wafer, which are called candidate miscellaneous crystals.

[0107] S12: Screening out target miscellaneous crystals from the candidate miscellaneous crystals by using the attribute information of the candidate miscellaneous crystals.

[0108] In actual scenarios, the candidate impurity crystal may be a real impurity crystal, or may be other impurities, such as stains, etc. Therefore, it is necessary to further judge the candidate impurity crystal to determine whether it is a real impurity crystal.

[0109] When making a judgment, the attribute information of the candidate impurity crystals may be used, wherein the attribute information may be the area, that is, the area of ​​the candidate impurity crystals may be used for secondary screening.

[0110] Generally speaking, impurities are hexagonal in appearance. Some small stains may be coincidentally misjudged as impurities because of their similar shapes. However, after data collection and observation, it is difficult for large stains to present a hexagonal appearance. Therefore, by controlling the area, stains and impurities can be effectively identified, which can avoid the situation where some small stains are misjudged as impurities. In actual scenarios, when the area is greater than the area threshold, the candidate impurity is considered to be the real target impurity. The area threshold can be set according to the actual situation, such as 50μm. 2 , 100μm 2 , 200μm 2 、300μm 2 , 400μm 2 wait.

[0111] S13. Determine the detection result of the target impurity crystals of the target polishing wafer based on the parameter information of the target impurity crystals.

[0112] After obtaining the real target impurity crystals by secondary screening of the candidate impurity crystals, the impurity crystal detection result of the target polished sheet can be determined based on the parameter information of the target impurity crystals, wherein the parameter information can be the quantity, diameter, number, polished sheet grade and other information of the target impurity crystals.

[0113] The detection result of the impurity crystals can be output in the form of pictures, charts, etc. For example, the actual impurity crystal picture can be output as a picture, and the number, diameter, number, polishing sheet grade and other information of the target impurity crystals can be output as a chart.

[0114] In this embodiment, the polarized light transmission device 101 can be used to irradiate linear polarized light onto the target polishing sheet, so that the target polishing sheet reflects elliptically polarized light to the image acquisition device, so that the image acquisition device acquires the imaging of the target polishing sheet to obtain the target image, and the processor performs a miscellaneous crystal detection operation on the target image to obtain candidate miscellaneous crystals, and uses the attribute information of the candidate miscellaneous crystals to screen out the target miscellaneous crystals from the candidate miscellaneous crystals, and determines the miscellaneous crystal detection result of the target polishing sheet based on the parameter information of the target miscellaneous crystals, thereby realizing the miscellaneous crystal detection of the polishing sheet. In addition, the present invention realizes the primary screening and secondary screening of miscellaneous crystals by performing a miscellaneous crystal detection operation on the target image to obtain candidate miscellaneous crystals and using the attribute information of the candidate miscellaneous crystals to screen out the target miscellaneous crystals from the candidate miscellaneous crystals, which can ensure the accuracy of the detected miscellaneous crystals. In addition, the entire process of the present invention is automatically realized, which can avoid the problems of low detection accuracy and low efficiency due to lack of experience in manual detection.

[0115] In another implementation of the present application, refer to Figure 5 , performing a miscellaneous crystal detection operation on the target image to obtain candidate miscellaneous crystals may include:

[0116] S21. Based on the shooting order of the target images, perform a stitching operation on the target images to obtain a first image.

[0117] Specifically, when capturing images of the polishing sheet, the target image captured each time is only an image of a partial area of ​​the polishing sheet, and since the polishing sheet moves according to a fixed preset step size and trajectory, the shooting order of the captured target images corresponds to the positions of the polishing sheet. The target images can be spliced ​​according to the shooting order of the target images to obtain a completed image of the polishing sheet, which is referred to as the first image in this embodiment.

[0118] S22: Perform image noise reduction processing on the first image to obtain a second image.

[0119] Specifically, in order to avoid the influence of noise interference on the detection of impurity crystals during the image acquisition process, the first image is subjected to image noise reduction processing in the embodiment of the present invention. When performing image noise reduction, a mean filter algorithm can be used to traverse the entire polishing sheet area to perform noise reduction processing on the image.

[0120] The mean filter algorithm can be expressed by the following formula:

[0121]

[0122] Where x is the horizontal coordinate of the pixel, y is the vertical coordinate of the pixel, J(x, y) is the grayscale value after filtering corresponding to the pixel frame, I(x+i, y+j) is the grayscale value before filtering corresponding to the pixel frame, i, j are loop variables, and m, n are the number of rows and columns of the filter window. After traversing the entire image starting from the first valid pixel, denoising is completed and the second image is obtained. The larger the value of (m, n), the larger the pixel frame processed at one time, but details will be lost. The smaller the value of (m, n), the richer the details, but the amount of calculation becomes larger. Therefore, the value of (m, n) can be selected according to actual needs.

[0123] S23. Perform an image enhancement operation on the second image to obtain a third image.

[0124] Specifically, in order to better reflect the gray value difference of different regions and better identify the impurity crystals, the embodiment of the present invention may perform an image enhancement operation on the second image.

[0125] Image enhancement is to perform sharpening enhancement processing on the second image, and the sharpening enhancement processing method can use the Sobel operator.

[0126] The principle of the sobel operator is:

[0127] Template in the horizontal direction through the Sobel algorithm Template with vertical orientation Perform convolution operation on each pixel in the second image to detect the grayscale change at the edge of the image and obtain the horizontal gradient value G x (i, j) and the vertical gradient value G y (i, j), where i, j represent the pixel coordinates in the second image, and then calculate the gradient magnitude Finally, it is added to the grayscale value of the corresponding pixel in the second image to achieve sharpening and obtain the third image.

[0128] S24: Perform a miscellaneous crystal detection operation on the third image using a miscellaneous crystal detection model to determine candidate miscellaneous crystals in the target polishing wafer.

[0129] In this embodiment, the impurity crystal detection model can be an AI (Artificial Intelligence) model. The impurity crystal sample data of different morphologies in the database are improved, and the AI ​​model is morphologically trained in advance through a large amount of impurity crystal sample data of different morphologies, so that the AI ​​model can compare the detected image with the impurity crystal sample data in the database. When the similarity is higher than the similarity threshold (such as 70%), the AI ​​model marks the corresponding target on the polishing sheet as "impurity crystal defect to be confirmed". At this time, the target is the candidate impurity crystal in the embodiment of the present invention.

[0130] In one implementation, when identifying candidate impurity crystals, the grayscale abnormal region in the third image may be determined based on the grayscale value of each pixel in the third image.

[0131] Specifically, in order to improve the processing efficiency of the AI ​​model, feature extraction can be performed before the third image is input into the AI ​​model. Based on the grayscale value of each pixel in the third image, the grayscale value abnormality is screened out, such as an area greater than the grayscale threshold. This area is called a grayscale abnormal area. Generally, the grayscale value of the edge of the impurity crystal is different from the grayscale value of other areas. Therefore, the edge of the impurity crystal can be determined through the grayscale abnormal area.

[0132] Then, a miscellaneous crystal detection model is used to perform a miscellaneous crystal detection operation on the grayscale abnormal region to obtain a detection result of whether the grayscale abnormal region is a miscellaneous crystal, so as to determine the candidate miscellaneous crystals in the target polishing wafer using the detection result.

[0133] Specifically, the impure crystal detection model is used to perform impure crystal detection operations on the grayscale abnormal area, such as edge contour recognition, geometric feature recognition, texture feature recognition, etc. The specific recognized features can be size, shape, rectangularity and other features. These features are used to compare with the features of the impure crystal sample data in the database, and the similarity is calculated. If the similarity is lower than the similarity threshold, the grayscale abnormal area is not impure crystal. If the similarity is higher than the similarity threshold, the grayscale abnormal area is impure crystal, that is, the detection result of whether the grayscale abnormal area is impure crystal is obtained. If the detection result is impure crystal, the candidate impure crystal can be obtained at this time.

[0134] In this embodiment, the grayscale abnormal area recognition operation can be used to preliminarily extract the impurity crystal features, thereby reducing the processing complexity of the impurity crystal detection model and improving the efficiency of impurity crystal recognition. In addition, after the impurity crystal features are preliminarily extracted, the impurity crystal detection model can avoid misdetection of other areas, thereby improving the accuracy of impurity crystal detection.

[0135] After initially obtaining the candidate impurity crystals, some small stains may be coincidentally misjudged as impurity crystals due to their hexagonal appearance. However, after data collection and observation, it is difficult for large stains to present a hexagonal appearance. Therefore, the identification of stains and impurity crystals can be effectively carried out by controlling the area, which can avoid the situation where some small stains are misjudged as impurity crystals.

[0136] At this time, the attribute information of the miscellaneous crystal is set to include the area. When the target miscellaneous crystal is screened out from the candidate miscellaneous crystals using the attribute information of the candidate miscellaneous crystals, the area of ​​the candidate miscellaneous crystals may be calculated. The area may be determined by the number of pixels occupied by the miscellaneous crystals, or may be calculated by an AI model, depending on the actual configuration.

[0137] Then, candidate impurity crystals with an area greater than the area threshold are screened out and used as target impurity crystals. Specifically, since some small stains are easily misidentified as impurity crystals, but since the area of ​​the small stains is generally small, smaller than the area of ​​the impurity crystals, small stains with an area less than the area threshold can be excluded to obtain target impurity crystals.

[0138] The area threshold can be set according to actual conditions, such as 50 μm. 2 , 100μm 2 , 200μm 2 、300μm 2 , 400μm 2 Etc. For example, the area threshold can be set to 400 μm 2 , at this time the area can be less than 400μm 2 The small stains can be removed to avoid misidentification of small stains as stray crystals, thus improving the accuracy of stray crystal identification.

[0139] In this embodiment, the impure crystals marked as "impurity crystal defects to be confirmed" by the AI ​​model are re-judged through area card control. If the area is larger than the area threshold, it is judged as impure crystal, otherwise it is judged as other defects.

[0140] The area threshold can be adjusted in real time according to the situation of the impurity crystal capture. For example, if an impurity crystal with a similarity higher than the similarity threshold of the AI ​​model is smaller than 400μm in area, 2 The area threshold is stuck. In this case, you can adjust the area threshold down a bit, such as adjusting it to 200μm 2 , you can grab the miscellaneous crystals normally.

[0141] It should be noted that in addition to using the area to screen out impure crystals, impure crystals can also be screened out by combining the area with the length and width of the defects.

[0142] Through the above steps, the target impurity crystal can be screened out from the candidate impurity crystals. The schematic diagram of the target impurity crystal can be as follows: Figure 6 shown.

[0143] After obtaining the target impurity crystals, the impurity crystal detection result of the target polishing wafer can be determined based on the parameter information of the target impurity crystals. Specifically, the method includes the following steps:

[0144] 1) Calculating the distance between any two vertices of the target impurity crystal in the third image.

[0145] Specifically, the number of pixels occupied by the distance between any two vertices of the target impurity crystal in the third image is calculated, and the formula is: Among them, (x 2 ,y 2 )、(x 1 ,y 1) are the coordinates of any two vertex pixels of the target impurity crystal, and finally the distance between the two vertices can be obtained with d×pixel accuracy.

[0146] 2) The maximum distance is taken as the diameter of the target impurity crystal.

[0147] Specifically, the relative distances of all vertices of the target impurity crystal are traversed, and the maximum value of the distance is the required impurity crystal diameter.

[0148] 3) Counting the number of target impurity crystals in the target polished wafer.

[0149] In this embodiment, the number of identified target miscellaneous crystals is counted, and this number is the number of target miscellaneous crystals in the target polishing wafer.

[0150] 4) Determining the grade of the target polishing sheet based on the number and diameter of the target impurity crystals.

[0151] Specifically, the correspondence between the grade of the polishing sheet and the number and diameter of the impurity crystals in the polishing sheet can be preset according to actual needs. For example, if the impurity crystal diameter is less than 500 (μm) and the number of impurity crystals is less than 3, it is grade A, otherwise it is NG (unqualified) grade.

[0152] 5) The grade of the target polished sheet, the number, position and diameter of the target impurity crystals are used as impurity crystal detection results.

[0153] Specifically, after obtaining the grade of the target polished sheet, the number, position and diameter of the target impurity crystals, the grade of the target polished sheet, the number, position and diameter of the target impurity crystals can be summarized to obtain the impurity crystal detection result. The impurity crystal detection result can be output in the form of a chart, such as a MAP. The actual impurity crystal picture is output in the form of a picture, such as Figure 7 shown.

[0154] In this embodiment, by outputting the detection result of the impurity crystals, the relevant personnel can visually check the impurity crystals in the polishing sheet. The whole process only requires the polishing sheet to be placed on the stage manually, and the impurity crystal detection can be automatically performed and the detection result can be output, saving manpower. It can also simply and quickly detect the impurity crystal defects of the silicon carbide polishing sheet, avoid the waste of material and labor costs caused by subsequent invalid processing, improve the processing yield, and reduce costs.

[0155] To sum up, in this embodiment, polarized light is irradiated onto the polished wafer to be tested, an image is collected by a camera imaging device, and then artificial intelligence recognition and traditional algorithm card control are used to detect the stray crystal defect information under polarized reflection, thereby improving the accuracy of stray crystal judgment. The position, diameter, quantity and grading information of the stray crystals can be output, and the test results can be retained, reducing manual participation and improving the accuracy of stray crystal detection.

[0156] The present application also provides an electronic device, such as the above-mentioned processor. The electronic device is used to execute the above-mentioned method for detecting impurities in a polishing sheet. The structure of the electronic device is shown in FIG. Figure 8 As shown, it shows a schematic diagram of the structure of an electronic device suitable for implementing the embodiments of the present application. The electronic device in the embodiments of the present application may include but is not limited to fixed terminals such as mobile phones, notebook computers, PDAs (personal digital assistants), PADs (tablet computers), desktop computers, etc. Figure 8 The electronic device shown is merely an example and should not bring any limitation to the functions and scope of use of the embodiments of the present application.

[0157] like Figure 8 As shown, the electronic device may include a processing device (e.g., a central processing unit, a graphics processing unit, etc.) 601, which can perform various appropriate actions and processes according to a program stored in a read-only memory (ROM) 602 or a program loaded from a storage device 608 into a random access memory (RAM) 603. When the electronic device is powered on, various programs and data required for the operation of the electronic device are also stored in the RAM 603. The processing device 601, the ROM 602, and the RAM 603 are connected to each other via a bus 604. An input / output (I / O) interface 605 is also connected to the bus 604.

[0158] Typically, the following devices may be connected to the I / O interface 605: an input device 606 including, for example, a touch screen, a touch pad, a keyboard, a mouse, a camera, a microphone, an accelerometer, a gyroscope, etc.; an output device 607 including, for example, a liquid crystal display (LCD), a speaker, a vibrator, etc.; a storage device 608 including, for example, a memory card, a hard disk, etc.; and a communication device 609. The communication device 609 may allow the electronic device to communicate with other devices wirelessly or by wire to exchange data. Although Figure 8 An electronic device having various devices is shown, but it should be understood that it is not required to implement or possess all the devices shown. More or fewer devices may be implemented or possessed instead.

[0159] An embodiment of the present application also provides a computer program product including computer-readable instructions. When the computer-readable instructions are executed on an electronic device, the electronic device implements any of the methods for detecting impure crystals in a polishing sheet provided in the embodiments of the present application.

[0160] A computer-readable storage medium is also provided in an embodiment of the present application. The storage medium carries one or more computer programs. When the one or more computer programs are executed by an electronic device, the electronic device can implement any of the impurity crystal detection methods for polishing sheets provided in an embodiment of the present application.

[0161] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A polishing sheet impurity detection system, characterized in that: include: Polarized light transmission device, image acquisition device and processor; The polarized light transmission device is used to irradiate linear polarized light onto the target polishing sheet, so that the target polishing sheet reflects elliptically polarized light to the image acquisition device; The image acquisition device is used to acquire the image of the target polishing sheet to obtain a target image; The processor is used to perform a miscellaneous crystal detection operation on the target image to obtain candidate miscellaneous crystals, screen out target miscellaneous crystals from the candidate miscellaneous crystals using attribute information of the candidate miscellaneous crystals, and determine a miscellaneous crystal detection result of the target polishing sheet based on parameter information of the target miscellaneous crystals.

2. The impurity crystal detection system for a polishing sheet according to claim 1, characterized in that: The polarized light transmission device comprises: A light source, an analyzer, a polarizer and a beam splitter prism; the light source, the polarizer and the beam splitter prism are arranged in sequence, the analyzer is arranged above the beam splitter prism, and the analyzer and the polarizer are arranged vertically; The light output by the light source passes through the polarizer and the beam splitter prism in sequence to obtain linearly polarized light and irradiates the target polished sheet. The elliptically polarized light reflected by the target polished sheet passes through the beam splitter prism and the analyzer in sequence to be output to the image acquisition device.

3. The impurity crystal detection system for a polishing sheet according to claim 1, characterized in that: The target polishing sheet is arranged on a stage; The stage fixes the target polishing sheet via an outer ring foot and an inner ring foot; The loading platform is arranged on a guide rail so that the loading platform can move on the guide rail.

4. The impurity crystal detection system for a polishing sheet according to claim 3, characterized in that: The processor is further configured to: Controlling the outer ring foot of the loading platform to rise; Controlling the stage to move according to a preset step length and trajectory; wherein each time the stage moves, the image acquisition device acquires an image of the target polishing sheet to obtain a target image; After the loading platform finishes moving along the trajectory, the inner ring foot of the loading platform is controlled to rise, and the outer ring foot of the loading platform is controlled to fall; The stage is controlled to move so that the image acquisition device acquires the image of the target polishing sheet at the outer ring foot of the stage to obtain a target image.

5. The impurity crystal detection system for a polishing sheet according to claim 3, characterized in that: The stage controls the adsorption force between the stage and the target polishing sheet through an air pressure regulating device.

6. A method for detecting impurity crystals in a polishing sheet, characterized in that: A processor used in a mixed crystal detection system for a polishing sheet as claimed in any one of claims 1 to 5; The method for detecting the impurity crystals of the polishing sheet comprises: Performing a miscellaneous crystal detection operation on the target image to obtain candidate miscellaneous crystals; Screening out target impurity crystals from the candidate impurity crystals using the attribute information of the candidate impurity crystals; Based on the parameter information of the target miscellaneous crystals, a miscellaneous crystal detection result of the target polishing wafer is determined.

7. The method for detecting impurities in a polishing sheet according to claim 6, wherein: Performing a miscellaneous crystal detection operation on the target image to obtain candidate miscellaneous crystals includes: Based on the shooting order of the target images, performing a stitching operation on the target images to obtain a first image; Performing image noise reduction processing on the first image to obtain a second image; performing an image enhancement operation on the second image to obtain a third image; A miscellaneous crystal detection operation is performed on the third image using a miscellaneous crystal detection model to determine candidate miscellaneous crystals in the target polishing wafer.

8. The method for detecting impurities in a polishing sheet according to claim 7, wherein: Performing a miscellaneous crystal detection operation on the third image using a miscellaneous crystal detection model to determine candidate miscellaneous crystals in the target polishing wafer includes: Determining a grayscale abnormal area in the third image based on the grayscale value of each pixel in the third image; A miscellaneous crystal detection model is used to perform a miscellaneous crystal detection operation on the grayscale abnormal region to obtain a detection result of whether the grayscale abnormal region is a miscellaneous crystal, so as to determine the candidate miscellaneous crystals in the target polishing wafer using the detection result.

9. The method for detecting impurity crystals of a polishing sheet according to any one of claims 6 to 8, characterized in that: The attribute information includes area; and selecting target miscellaneous crystals from the candidate miscellaneous crystals by using the attribute information of the candidate miscellaneous crystals includes: Calculating the area of ​​the candidate impurity crystal; Candidate impurity crystals with an area greater than an area threshold are screened out and used as target impurity crystals.

10. The method for detecting impurity crystals of a polishing sheet according to claim 7, characterized in that: Determining the detection result of the target impurity crystals of the target polishing sheet based on the parameter information of the target impurity crystals includes: Calculating the distance between any two vertices of the target impurity crystal in the third image; The maximum distance is taken as the diameter of the target impurity crystal; Counting the number of target impurity crystals in the target polishing wafer; Determining the grade of the target polishing sheet based on the number and diameter of the target impurity crystals; The grade of the target polishing sheet, the number, position and diameter of the target miscellaneous crystals are taken as miscellaneous crystal detection results.

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