Wafer visual inspection device and wafer visual inspection method

Abstract

To provide a wafer visual inspection device and a wafer visual inspection method capable of improving quality of a wafer having a film.SOLUTION: A wafer visual inspection device 10 includes an input section 14 for acquiring an image of a wafer surface, and a control section 12 for detecting gradation abnormality on the wafer surface on the basis of the image of the wafer surface. The control section 12 performs an operation of calculating a brightness average value of pixels arranged in the main scanning direction at each position in the sub-scanning direction and calculating an absolute value of a slope of an approximate straight line of a profile of the brightness average value along the sub-scanning direction in an annular range in which a distance from the center of the wafer surface is equal to or greater than a first distance in the image of the wafer surface by setting the main scanning direction to at least two directions. The control section determines that a gradation abnormality occurs on the wafer surface when the maximum value of an absolute value of a slope of the brightness average value when the main scanning direction is set to each of at least two directions is equal to or larger than a slope threshold value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a wafer visual inspection apparatus and a wafer visual inspection method. [Background technology]

[0002] Conventionally, there is known a method for evaluating the back surface of a wafer, which detects and evaluates polishing irregularities, cloudiness, scratches, and particles (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5433201 Summary of the Invention [Problem to be solved by the invention]

[0004] Defects on the film-coated surface of bare wafers (film-coated wafers) are more difficult to detect than defects on bare wafers due to the influence of the film on the wafer. There is a need to improve the quality of film-coated wafers by detecting defects on the film-coated surface of wafers.

[0005] Therefore, an object of the present disclosure is to propose a wafer appearance inspection apparatus and a wafer appearance inspection method that can improve the quality of film-coated wafers. [Means for solving the problem]

[0006] One embodiment of the present disclosure that solves the above problem is as follows. [1] an input unit that acquires an image of a wafer surface; and a control unit that detects a gradation abnormality on the wafer surface based on the image of the wafer surface, The control unit calculating an average brightness value of pixels aligned in a main scanning direction at each position in a sub-scanning direction within an annular range of the image of the wafer surface that is a first distance or more from the center of the wafer surface, and calculating an absolute value of a slope of an approximation line of a profile of the average brightness values ​​along the sub-scanning direction, while setting the main scanning direction to at least two directions; determining that a gradation abnormality has occurred on the wafer surface when the maximum absolute value of the gradient of the average brightness value when the main scanning direction is set to each of at least two directions is equal to or greater than a gradient threshold value; Visual inspection equipment. [2] The appearance inspection apparatus described in [1] above, wherein the annular range is a range whose distance from the center of the wafer surface is equal to or greater than the first distance and equal to or less than a second distance that is longer than the first distance. [3] The control unit of the visual inspection device described in [1] or [2] above outputs an alert regarding the wafer processing device that captured the image of the wafer surface when the amount of drop in the profile of the average brightness value along the sub-scanning direction from the approximate straight line of the profile of the average brightness value when the absolute value of the slope of the average brightness value is at its maximum is less than a drop threshold. [4] acquiring an image of the wafer surface; calculating an average brightness value of pixels aligned in a main scanning direction at each position in a sub-scanning direction in an annular range of the image of the wafer surface that is a first distance or more from the center of the wafer surface, and calculating an absolute value of a slope of an approximation line of a profile of the average brightness values ​​along the sub-scanning direction, while setting the main scanning direction to at least two directions; determining that a gradation abnormality has occurred on the wafer surface when the maximum absolute value of the gradient of the brightness average value is equal to or greater than a gradient threshold value; A visual inspection method including: [Effects of the Invention]

[0007] According to the wafer visual inspection apparatus and wafer visual inspection method of the present disclosure, the quality of film-coated wafers can be improved. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a block diagram illustrating a configuration example of a visual inspection system according to the present disclosure. [Figure 2] FIG. 10 is a diagram showing an example of an entire image generated based on part images. [Figure 3] FIG. 10 is a diagram illustrating an example of a brightness-enhanced image. [Figure 4] FIG. 10 is a diagram illustrating an example of a scanning direction in which an average brightness value is calculated. [Figure 5] FIG. 10 is a diagram illustrating an example of division of an area. [Figure 6A] 1 shows the luminance profile of sample A. [Figure 6B] 10 is a luminance profile of sample B. [Figure 6C] 10 is a luminance profile of sample C. [Figure 7] 10 is a bar graph showing the gradient of the luminance profile of each sample. [Figure 8] 10 is a flowchart illustrating an example of a procedure for generating a luminance profile in the appearance inspection method according to the present disclosure. [Figure 9] 10 is a flowchart illustrating an example of a procedure for determining gradation defects of a wafer based on a brightness profile in the visual inspection method according to the present disclosure. [Figure 10] 10 is a flowchart illustrating an example of a procedure for outputting an alert regarding a wafer manufacturing device based on a luminance profile in the visual inspection method according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0009] (Configuration example of wafer appearance inspection device 10) Hereinafter, a wafer visual inspection system 100 and a visual inspection apparatus 10 according to an embodiment of the present disclosure will be described with reference to the drawings. As shown in Fig. 1, the wafer visual inspection system 100 includes the visual inspection 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 visual inspection apparatus 10.

[0010] The visual inspection system 100 may inspect the appearance of a wafer surface, including the front or back surface of a wafer. Wafers include silicon wafers and the like. The visual inspection system 100 inspects the appearance of a wafer surface in which a thin film, such as a CVD (Chemical Vapor Deposition) film, is formed on a polished wafer or an epitaxial wafer. The type of thin film may be, for example, an oxide film, such as a silicon oxide film, or a nitride film, such as a silicon nitride film. The type of thin film is not limited to an oxide film or a nitride film, and may be various other materials. The thickness of the thin film may be, for example, approximately 250 nm to 450 nm. The thickness of the thin film may be 250 nm or less, or 450 nm or more.

[0011] Here, subtle variations in the thickness of a thin film along a certain direction on the wafer surface can sometimes be recognized as subtle color variations along a certain direction when the wafer surface is visually inspected, i.e., gradation. If the color variation along a certain direction on the wafer surface is significant, the wafer is determined to have a gradation anomaly. In other words, a gradation anomaly is an anomaly in which the appearance of the wafer surface changes along a certain direction. Gradation anomalies can occur due to abnormalities in the supply of source gases or abnormal temperature distribution in the film-forming equipment that forms the thin film. Gradation anomalies are difficult to detect by pattern recognition from images of the wafer surface. Below, we describe an appearance inspection system 100 that inspects the appearance of the backside of a wafer on which a thin film has been formed for gradation anomalies.

[0012] In the visual inspection system 100, a wafer is transported by a transport device 30 to an imaging device 20, which then photographs the front or back surface of the wafer. The imaging device 20 outputs the photographed image of the wafer to the visual inspection device 10. The visual inspection device 10 inspects the appearance of the front or back surface of the wafer based on the image of the wafer.

[0013] The appearance inspection apparatus 10 includes a control unit 12, an input unit 14, and an output unit 16. The control unit 12 controls each component of the appearance inspection apparatus 10. The control unit 12 acquires information or data such as an image of a wafer from the input unit 14. The control unit 12 outputs processing results based on the information or data via the output unit 16. The control unit 12 may include at least one processor. The processor may execute programs that realize various functions of the control unit 12. The processor may be realized as a single integrated circuit. An integrated circuit is also called an IC (Integrated Circuit). The processor may be realized as multiple integrated circuits and discrete circuits that are connected to each other in a communicative manner. The processor may be realized based on various other known technologies.

[0014] The control unit 12 may further include a memory unit. The memory unit stores, for example, an image of the wafer or a visual inspection result based on the image of the wafer. 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.

[0015] The input unit 14 acquires an image of the wafer from the imaging device 20 and outputs it to the control unit 12. The output unit 16 outputs information or data relating to the processing results in the control unit 12.

[0016] The input unit 14 or the output unit 16 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 conveying 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.

[0017] The input unit 14 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 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.

[0018] The output unit 16 may include, for example, a display device that outputs visual information such as images, characters, or graphics. The display device may be configured to 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 be configured to include displays of various other types. The display device may be configured to include a light-emitting device such as an LED (Light Emitting Diode) or an LD (Laser Diode). The display device may be configured to include various other devices. The output unit 16 may also include an audio output device such as a speaker.

[0019] The imaging device 20 is configured to include, for example, a camera or an imaging element. The imaging device 20 captures an image of the wafer surface, including the front or back surface of the wafer. The imaging device 20 may include a light source that emits illumination light to illuminate the wafer surface. The imaging device 20 may include, for example, an LED or a halogen lamp as the light source. The light source may be configured to be able to change the illuminance of the illumination light in at least two stages. 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 multiple light-emitting devices.

[0020] In the visual inspection system 100 according to the present disclosure, the imaging device 20 captures images of the wafer surface divided into multiple regions along the radial and circumferential directions of the wafer. The imaging device 20 is configured as multiple cameras or imaging elements arranged in the radial direction of the wafer. The imaging device 20 may include a stage on which the wafer is placed. The imaging device 20 may rotate the placed wafer by rotating the stage. The imaging device 20 may capture images of the wafer surface divided into multiple regions along the circumferential direction of the wafer by capturing images of the rotating wafer from a fixed camera or imaging element. The imaging device 20 may capture images of the wafer surface divided into multiple regions along the circumferential direction of the wafer by moving the camera or imaging element along the circumferential direction of the wafer relative to the wafer placed on the stage. The regions may partially overlap along the radial or circumferential direction. The images captured of each region are also referred to as part images. The imaging device 20 outputs the part images to the visual inspection device 10. Furthermore, the imaging device 20 outputs to the appearance inspection device 10 information specifying the relationship between the part image and the position within the wafer surface where the part image was captured, in association with the part image.

[0021] The imaging device 20 may be configured to image the entire wafer surface in one go.

[0022] The transport device 30 transports the wafer to the imaging device 20. The transport device 30 may transport the wafer onto a stage of the imaging device 20. The transport device 30 may also transport the wafer from the imaging device 20 after the imaging device 20 has completed photographing the wafer. The transport device 30 may include an arm that is moved by a driving device such as a motor. The transport device 30 may include a hand or a suction unit that holds the wafer.

[0023] (Example of operation of the visual inspection system 100) In the visual inspection system 100, the imaging device 20 captures part images of the wafer surface by appropriately setting the illuminance of the illumination light. The illuminance of the illumination light can be set based on the type or thickness of the thin film formed on the wafer surface. The illuminance of the illumination light may be set, for example, between 100,000 lux and 500,000 lux. The illuminance of the illumination light may be set to less than 100,000 lux or to 500,000 lux or more. The illuminance of the illumination light may be set as the power input to the light source. The power input to the light source may be set, for example, between 100 watts (W) and 500 watts (W). The power input to the light source may be set to less than 100 watts or to 500 watts or more.

[0024] Control unit 12 of visual inspection apparatus 10 acquires part images of the wafer surface illuminated with illumination light of each illuminance level by imaging device 20 from input unit 14. Based on information specifying the positions on the wafer surface where the part images were acquired, control unit 12 arranges the acquired part images at each imaging position, thereby generating an overall image 40 that appears to be an image of the entire wafer surface, as shown in FIG. 2, for example.

[0025] In FIG. 2, the entire image 40 includes a first part image 41, a second part image 42, a third part image 43, a fourth part image 44, and a fifth part image 45. The first part image 41 corresponds to an image obtained by dividing an area located on the outermost periphery of the wafer surface into multiple areas along the circumferential direction. The second part image 42, the third part image 43, and the fourth part image 44 correspond to images obtained by dividing an area located on the second, third, and fourth periphery inside the outermost periphery of the wafer surface into multiple areas along the circumferential direction, respectively. The fifth part image 45 corresponds to an image obtained by capturing an area located at the center of the wafer surface. The arrangement of the part images in the entire image 40 is not limited to the example of FIG. 2 and may be changed to various other arrangements.

[0026] The control unit 12 may remove noise from the overall image 40 when generating the overall image 40 or after generating the overall image 40. The noise may be, for example, an image of particles contained in each part image. Particles are a general term for foreign matter attached to the wafer surface.

[0027] If there is an area where the wafer surface is not photographed between each of the part images constituting the entire image 40, the control unit 12 may interpolate the image between each of the part images. The control unit 12 may interpolate the image using an algorithm for interpolating missing parts of the image. The algorithm for interpolating missing parts of the image may include various algorithms, such as an algorithm using a neural network.

[0028] The control unit 12 may enhance the brightness of the overall image 40 to generate a brightness-enhanced image 50 as illustrated in FIG. 3. The brightness enhancement may be performed, for example, by multiplying the brightness of each pixel of the overall image 40 by a common magnification factor. The brightness-enhanced image 50 as illustrated in FIG. 3 is generated by tripling the brightness of each pixel of the overall image 40 as illustrated in FIG. 2. In the brightness-enhanced image 50, the arrangement of the first part image 41, the second part image 42, the third part image 43, the fourth part image 44, and the fifth part image 45 is maintained.

[0029] The control unit 12 sets a scanning direction in the entire image 40 or the brightness-enhanced image 50, and calculates the average brightness value of each pixel in the entire image 40 or the brightness-enhanced image 50. Hereinafter, the calculation of the average brightness value of each pixel in the entire image 40 will be described with reference to FIG.

[0030] The control unit 12 sets a main scanning direction and a sub-scanning direction for the entire image 40. The main scanning direction and the sub-scanning direction intersect each other. In the present disclosure, the main scanning direction and the sub-scanning direction are orthogonal to each other. The control unit 12 calculates the average luminance value of pixels arranged on a scanning line, which is a straight line along the main scanning direction. The control unit 12 moves the scanning line to multiple positions along the sub-scanning direction and calculates the average luminance value of pixels arranged on the scanning line at each position. In FIG. 4, multiple arrows extending vertically from top to bottom correspond to multiple scanning lines moved along the sub-scanning direction. The control unit 12 generates a luminance profile that represents the change in the average luminance value along the sub-scanning direction by correlating the positions in the sub-scanning direction of the scanning lines used to calculate the average luminance value with the calculation result of the average luminance value. The luminance profile is expressed as a graph (see FIG. 6A, etc.) that correlates the average luminance value of pixels on the scanning line with each position in the sub-scanning direction.

[0031] The control unit 12 changes the main scanning direction and the sub-scanning direction to different directions, moves the scanning line aligned with the changed main scanning direction to multiple positions along the changed sub-scanning direction, and calculates the average luminance value of the pixels aligned on the scanning line at each position. In other words, the control unit 12 rotates the scanning line to generate a luminance profile. The control unit 12 changes the main scanning direction in at least two directions and generates a luminance profile for each direction. In the present disclosure, the control unit 12 rotates the main scanning direction up to 180 degrees in 10-degree increments and generates a luminance profile for each main scanning direction. The angle increments of the main scanning direction are not limited to 10 degrees. The angle increments of the main scanning direction may be set to an angle corresponding to the circumferential position when the part image is arranged.

[0032] The control unit 12 may rotate the image for which the average brightness value is to be calculated by a plurality of angles while fixing the main scanning direction and the sub-scanning direction, and generate a brightness profile for the image at each angle.

[0033] As illustrated in FIG. 5, the control unit 12 divides the wafer surface into a first region 51, a second region 52, and a third region 53. The first region 51 is a region located on the outermost periphery of the wafer surface, and its distance from the center of the wafer surface, i.e., its radius, is greater than R2. The third region 53 is a region located in the center of the wafer surface, and its distance from the center of the wafer surface, i.e., its radius, is smaller than R1. The second region 52 is a region located between the first region 51 and the third region 53, and its distance from the center of the wafer surface, i.e., its radius, is greater than or equal to R1 and less than R2.

[0034] In the present disclosure, the first region 51 is the region of the first part image 41 in Fig. 2 or 3. The second region 52 is the region of the second part image 42 and the third part image 43. The third region 53 is the region of the fourth part image 44 and the fifth part image 45.

[0035] In the present disclosure, the control unit 12 calculates the average luminance value using only pixels located in the second region 52 of the wafer surface, i.e., excluding pixels located in the first region 51 and the third region 53. The control unit 12 may calculate the average luminance value using pixels located in the first region 51 and the second region 52 of the wafer surface, i.e., excluding pixels located in the third region 53. The control unit 12 may calculate the average luminance value using pixels located in the second region 52 and the third region 53 of the wafer surface, i.e., excluding pixels located in the first region 51. The control unit 12 may calculate the average luminance value using all pixels on the wafer surface.

[0036] As described above, the control unit 12 sets the main scanning direction to multiple directions and generates a luminance profile for each direction. The control unit 12 approximates the luminance profile in each direction with a straight line and calculates the absolute value of the slope of the approximated line. A large absolute value of the slope of the luminance profile's approximated line corresponds to a large change in the luminance of the image of the wafer surface in the sub-scanning direction. As described above, a gradation abnormality on the wafer is determined based on the degree to which the appearance of the wafer surface changes in a certain direction. Therefore, the control unit 12 determines the luminance profile when the absolute value of the slope of the approximated line is maximum. The control unit 12 may also determine the main scanning direction when the absolute value of the slope of the approximated line is maximum.

[0037] Figures 6A, 6B, and 6C show the brightness profiles generated from images of the wafer surfaces of samples A, B, and C, where the absolute value of the slope of the approximation line is maximum. The horizontal axis of the brightness profile graph represents each position in the sub-scanning direction, and the vertical axis represents the average brightness value of pixels in the main scanning direction. The brightness profile is represented by a solid line. The approximation line of the brightness profile is represented by a dashed line. Samples A, B, and C are different wafers included in the same lot of film formation equipment. F1 and F2 displayed in the brightness profile of each sample will be described later.

[0038] The control unit 12 determines whether or not there is a gradation abnormality based on the maximum absolute value of the slope of the approximated line. The control unit 12 determines that there is a gradation abnormality when the maximum absolute value of the slope of the approximated line is equal to or greater than the slope threshold, and determines that there is no gradation abnormality when the maximum absolute value of the slope of the approximated line is less than the slope threshold. The slope threshold is set by correlating the result of an inspector visually inspecting a wafer to determine whether or not there is a gradation abnormality with the maximum absolute value of the slope of the approximated line calculated when the wafer is inspected by the visual inspection device 10.

[0039] FIG. 7 shows a bar graph representing the maximum absolute value of the slope of the average brightness values ​​calculated for each of samples A, B, and C. The vertical axis of the bar graph represents the maximum absolute value of the slope of the average brightness values. Here, sample A is a non-defective wafer that was visually inspected by an inspector and determined to have no gradation abnormality. On the other hand, samples B and C are defective wafers that were visually inspected by an inspector and determined to have gradation abnormality. The control unit 12 sets the slope threshold to a value that is greater than the maximum absolute value of the slope of the average brightness values ​​of sample A, which is a non-defective product, and smaller than the maximum absolute value of the slope of the average brightness values ​​of samples B and C, which are defective products. By setting the slope threshold in this manner, the visual inspection apparatus 10 can detect gradation abnormalities on the wafer surface.

[0040] A possible method for detecting gradation anomalies in a comparative example is to create a template of gradation anomalies and match it with an image of the wafer surface to detect gradation anomalies. However, because gradation anomalies appear in a variety of ways, it is difficult to create a template that can increase the probability of correctly detecting wafers with gradation anomalies and reduce the probability of erroneously determining that wafers without gradation anomalies have gradation anomalies.

[0041] On the other hand, the visual inspection apparatus 10 according to the present disclosure generates luminance profiles of a wafer in multiple directions, calculates the maximum absolute value of the slope of the luminance profile, and can efficiently determine gradation abnormalities based on the calculated value. In other words, the visual inspection apparatus 10 according to the present disclosure makes it possible to replace inspection of gradation abnormalities, which was previously performed visually by an inspector, with inspection by a device by using a new index, the maximum absolute value of the slope of the luminance profile. As a result, the quality of film-coated wafers can be improved.

[0042] Furthermore, the visual inspection apparatus 10 according to the present disclosure generates a brightness profile by calculating the average brightness value in a range excluding pixels near the center of the wafer surface. Pixels near the center of the wafer surface are prone to detecting variations in the film growth process. Detecting gradation anomalies using a brightness profile generated from the average brightness value in a range excluding pixels near the center of the wafer surface eliminates the influence of variations in the film growth process. As a result, the accuracy of detecting gradation anomalies can be improved.

[0043] Furthermore, the visual inspection apparatus 10 according to the present disclosure may generate a brightness profile by calculating the average brightness value in a range excluding pixels near the periphery of the wafer surface. Pixels near the periphery of the wafer surface are prone to detecting variations in the film growth process. Detecting gradation anomalies using a brightness profile generated from the average brightness value in a range excluding pixels near the periphery of the wafer surface eliminates the influence of variations in the film growth process. As a result, the accuracy of detecting gradation anomalies can be improved.

[0044] The brightness profiles shown in Figures 6A, 6B, and 6C each have two significant dips relative to the approximate line. These dips in the brightness profile may reflect the state of the equipment, such as uneven transport speeds in processing equipment for film deposition on wafers.

[0045] The control unit 12 may calculate the maximum value of the drop in the luminance profile relative to the approximate line at both ends of the luminance profile. The drop in the luminance profile at each position in the sub-scanning direction is calculated by subtracting the luminance profile from the approximate line. The lower the luminance value of the luminance profile, the larger the calculated drop. In each of the luminance profiles in FIGS. 6A, 6B, and 6C, the maximum value of the drop near the left end of the luminance profile is represented by F1, and the maximum value of the drop near the right end of the luminance profile is represented by F2.

[0046] When at least one of F1 and F2 is equal to or greater than the drop threshold, the control unit 12 may determine that some abnormality or a sign of an abnormality has occurred in the wafer processing equipment, and output an alert regarding the processing equipment. When both F1 and F2 are equal to or greater than the drop threshold, the control unit 12 may determine that some abnormality or a sign of an abnormality has occurred in the wafer processing equipment, and output an alert regarding the processing equipment.

[0047] Fluctuations in film thickness, expressed as a drop in the brightness profile, are difficult to detect by visual inspection of the wafer. The visual inspection device 10 according to the present disclosure can detect abnormalities or signs of abnormalities that are difficult to detect by visual inspection of the wafer by outputting an alert related to the processing device based on the drop in the brightness profile. As a result, the quality of film-coated wafers can be improved.

[0048] (Example of visual inspection procedure) The control unit 12 of the appearance inspection apparatus 10 may execute an appearance inspection method including the steps of the flowcharts exemplified in Fig. 8, Fig. 9, or Fig. 10. The appearance inspection method may be realized as an appearance inspection program executed by a processor constituting the control unit 12. The appearance inspection program may be stored in a non-transitory computer-readable medium.

[0049] Referring to FIG. 8, the control unit 12 generates an overall image 40 (step S1). The control unit 12 may generate the overall image 40 based on part images, or may generate the overall image 40 by capturing the wafer surface once. The control unit 12 removes noise from the overall image 40 (step S2). The control unit 12 may remove images of particles as noise. The control unit 12 performs brightness enhancement on the overall image 40 to generate a brightness-enhanced image 50 (step S3).

[0050] The control unit 12 sets the scanning direction (step S4). When the control unit 12 generates a luminance profile of the entire image 40 in the next step S5, the control unit 12 sets the main scanning direction and the sub-scanning direction for the entire image 40. When the control unit 12 generates a luminance profile of the luminance-enhanced image 50 in the next step S5, the control unit 12 sets the main scanning direction and the sub-scanning direction for the luminance-enhanced image 50.

[0051] The control unit 12 calculates the average luminance value in the scanning direction set in step S4 to generate a luminance profile (step S5). The control unit 12 determines whether generation of luminance profiles has been completed in all planned directions (step S6). For example, if it is planned to generate luminance profiles in each direction by rotating the scanning direction in 10-degree increments, the control unit 12 determines that generation of luminance profiles has been completed in all directions when luminance profiles have been generated by changing the scanning direction to all 18 rotation angles from 0 to 170 degrees. If generation of luminance profiles has not been completed in all planned directions (step S6: NO), the control unit 12 returns to the scanning direction setting procedure in step S4 and changes the scanning direction. If generation of luminance profiles has been completed in all planned directions (step S6: YES), the control unit 12 ends execution of the procedure in the flowchart of FIG. 8.

[0052] The control unit 12 may not execute the procedure of step S2 or S3 in the example of the procedure in the flowchart of FIG.

[0053] 9, the control unit 12 calculates the slope of the luminance profile in each direction using the luminance profile in each direction generated by executing the procedure of the flowchart in FIG. 8 (step S11). The control unit 12 determines an approximate line of the luminance profile and calculates the slope of the approximate line as the slope of the luminance profile. The control unit 12 calculates the maximum value from the absolute value of the slope of the luminance profile in each direction (step S12).

[0054] The control unit 12 determines whether the maximum absolute value of the slope of the luminance profile is less than the slope threshold (step S13). If the maximum absolute value of the slope of the luminance profile is less than the slope threshold (step S13: YES), the control unit 12 determines that the gradation of the wafer being inspected is OK, i.e., that there is no gradation abnormality (step S14). If the maximum absolute value of the slope of the luminance profile is not less than the slope threshold (step S13: NO), i.e., if the maximum absolute value of the slope of the luminance profile is equal to or greater than the slope threshold, the control unit 12 determines that the gradation of the wafer being inspected is poor (step S15). The control unit 12 outputs the determination result of step S14 or S15 (step S16). After executing step S16, the control unit 12 ends the execution of the procedure of the flowchart in FIG. 9.

[0055] 10, the control unit 12 calculates the amount of drop in the luminance profile using the luminance profile when the absolute value of the slope of the luminance profile is maximum (step S21). The control unit 12 determines whether the amount of drop in the luminance profile is equal to or greater than a drop threshold (step S22). If the amount of drop in the luminance profile is equal to or greater than the drop threshold (step S22: YES), the control unit 12 outputs an alert related to the device (step S23). After executing the procedure of step S23, the control unit 12 ends execution of the procedure of the flowchart of FIG. 10. If the amount of drop in the luminance profile is not equal to or greater than the drop threshold (step S22: NO), that is, if the amount of drop in the luminance profile is less than the drop threshold, the control unit 12 ends execution of the procedure of the flowchart of FIG. 10 without outputting an alert related to the device.

[0056] The control unit 12 may independently execute the determination of gradation abnormality according to the procedure of the flowchart in FIG. 9 and the determination of an alert regarding the device according to the procedure of the flowchart in FIG.

[0057] As described above, the visual inspection system 100, visual inspection device 10, and visual inspection method according to this embodiment can detect gradation abnormalities on the wafer surface of a film-coated wafer. Furthermore, abnormalities or signs of abnormalities in the wafer processing device can be detected. As a result, the quality of film-coated wafers can be improved.

[0058] 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.

[0059] The graphs included in this disclosure are schematic and do not necessarily correspond to the actual scale. [Industrial Applicability]

[0060] According to the embodiments of the present disclosure, the quality of the film-coated wafer can be improved. [Explanation of symbols]

[0061] 100 Visual Inspection System 10 Appearance inspection device (12: control unit, 14: input unit, 16: output unit) 20 Imaging device 30 Conveyor device 40 Overall image (41-45: 1st to 5th part images) 50 Brightness-enhanced images 51, 52, 53 Domain 1, Domain 2, Domain 3

Claims

1. an input unit that acquires an image of a wafer surface; and a control unit that detects a gradation abnormality on the wafer surface based on the image of the wafer surface, The control unit calculating an average brightness value of pixels aligned in a main scanning direction at each position in a sub-scanning direction within an annular range of the image of the wafer surface that is a first distance or more from the center of the wafer surface, and calculating an absolute value of a slope of an approximation line of a profile of the average brightness values ​​along the sub-scanning direction, while setting the main scanning direction to at least two directions; determining that a gradation abnormality has occurred on the wafer surface when the maximum absolute value of the gradient of the average brightness value when the main scanning direction is set to each of at least two directions is equal to or greater than a gradient threshold value; Visual inspection equipment.

2. 2. The visual inspection apparatus according to claim 1, wherein the annular range is a range whose distance from the center of the wafer surface is equal to or greater than the first distance and equal to or less than a second distance that is longer than the first distance.

3. 3. The visual inspection device of claim 1, wherein the control unit outputs an alert regarding a wafer processing device that captured the image of the wafer surface when the amount of drop in the profile of the average brightness values ​​along the sub-scanning direction from an approximate straight line of the profile of the average brightness values ​​when the absolute value of the slope of the average brightness values ​​is at its maximum value is less than a drop threshold.

4. acquiring an image of the wafer surface; calculating an average brightness value of pixels aligned in a main scanning direction at each position in a sub-scanning direction in an annular range of the image of the wafer surface that is a first distance or more from the center of the wafer surface, and calculating an absolute value of a slope of an approximation line of a profile of the average brightness values ​​along the sub-scanning direction, while setting the main scanning direction to at least two directions; determining that a gradation abnormality has occurred on the wafer surface when the maximum absolute value of the gradient of the brightness average value is equal to or greater than a gradient threshold value; A visual inspection method including:

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