JP2009300287A - Surface defect inspection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect a surface defect of a workpiece with high accuracy. <P>SOLUTION: A surface defect inspection device includes a differential interference image acquisition part 2 containing a differential interference optical system for forming a differential interference optical image of the workpiece 1 and a photographing part for acquiring a differential interference image by photographing the differential interference optical image, and a processing part 3 for processing the differential interference image and detecting the defect on the surface of the workpiece. The processing part 3 includes an image rotating processing means for performing an image rotating processing of rotating the differential interference image obtained by the photographing part or an image obtained by performing a predetermined processing thereto in accordance with the displacement between the shear direction the differential interference optical system and the arranged direction of one of the pixel in the photographing part. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a surface defect inspection apparatus that automatically detects defects on the surface of an object to be inspected such as a substrate, a mirror, and a mask, or allows an inspector to detect the defects.

2. Description of the Related Art Conventionally, a technique for detecting minute foreign matters attached on a sample surface using differential interference is known (for example, Patent Document 1 below). In this conventional method, the illumination light is irradiated onto the sample surface via the differential interference optical system, and the intensity of the differential interference light generated when there is unevenness on the sample surface is detected by the light receiving element. When the value exceeds a predetermined threshold value, it is determined as a foreign substance, thereby detecting a minute foreign substance adhering to the sample surface.
JP 61-260211

  In view of the above-described conventional method of detecting minute foreign matter (convex) adhering to the sample surface using differential interference, scratches (recesses) that are defects on the surface of the inspection object are detected using differential interference. It is obvious that it can be detected. And if the defect (depression) which is a defect on the surface of the object to be inspected is detected using the differential interference method, the concave shape and the convex shape can be distinguished from each other according to the differential interference method. Since it is possible to distinguish a scratch from a dust having a convex shape, it is possible to reduce false detection and increase the accuracy of defect detection. However, in such a defect detection method using the differential interference method, if no consideration is given to the shear direction of the differential interference optical system (sometimes referred to as “shear direction”) as in the conventional method, A defect on the surface of the inspection object cannot be detected with high accuracy.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a surface defect inspection apparatus capable of detecting defects on the surface of an object to be inspected with high accuracy.

  In order to solve the above problem, a surface defect inspection apparatus according to a first aspect of the present invention captures a differential interference optical system that forms a differential interference optical image of an inspection object and the differential interference optical image to obtain a differential interference image. A differential interference image acquisition unit having an imaging unit to be obtained; and a processing unit that processes the differential interference image to detect a defect on the surface of the inspection object. The processing unit is configured to determine the differential interference image obtained by the imaging unit or a predetermined value for the differential interference image according to a shift between a shear direction of the differential interference optical system and one arrangement direction of pixels in the imaging unit. Image rotation processing means for performing image rotation processing for rotating the image subjected to the pre-processing.

  The surface defect inspection apparatus according to a second aspect of the present invention is the surface defect inspection apparatus according to the first aspect, wherein the processing unit is arranged in a direction corresponding to the shear direction in the image subjected to the image rotation processing by the image rotation processing means. A defect on the surface of the object to be inspected is detected based on the data of the aligned pixel columns.

  The surface defect inspection apparatus according to a third aspect of the present invention is the surface defect inspection apparatus according to the second aspect, wherein the processing unit is determined to be a concave portion based on data of the pixel column, as a necessary condition. It detects defects on the surface of an object.

  A surface defect inspection apparatus according to a fourth aspect of the present invention includes a differential interference optical system that forms a differential interference optical image of an object to be inspected, and a differential having an imaging unit that captures the differential interference optical image and obtains a differential interference image. An interference image acquisition unit and a processing unit that processes the differential interference image and detects defects on the surface of the inspection object. (I) differential image acquisition means for obtaining a differential image obtained by taking a difference between the differential interference image obtained by the imaging unit and a low-pass image obtained by filtering the differential interference image with a low-pass filter; (Ii) noise reduction processing means for performing noise reduction processing for reducing the value of a pixel having an absolute value smaller than a predetermined threshold to zero in the difference image; and (iii) shear direction of the differential interference optical system and the imaging Image rotation processing means for performing image rotation processing for rotating the difference image on which the noise reduction processing has been performed in accordance with a shift between one arrangement direction of pixels in the unit, and (iv) the image rotation processing means The post-processing data acquisition unit obtains post-processing data of the pixel row from the original data of the pixel row arranged in a direction corresponding to the shear direction in the image subjected to the image rotation processing. The value of the post-processing data of each pixel in the pixel column is the number of pixels in which the value of the original data is not zero among a plurality of continuous pixels within a predetermined range in the pixel column including the pixel. If the number of pixels in which the original data value is not zero among the plurality of consecutive pixels is greater than the predetermined number, the number of pixels in the pixel row is less than the predetermined number. And a post-processing data acquisition means for making the sum of the post-processing data value of the pixel adjacent to one side and the original data value of the pixel. The processing unit detects a defect on the surface of the inspection object on the condition that it is determined to be a recess based on post-processing data of the pixel column obtained by the post-processing data acquisition unit.

  A surface defect inspection apparatus according to a fifth aspect of the present invention includes a differential interference optical system that forms a differential interference optical image of an object to be inspected, and a differential having an imaging unit that captures the differential interference optical image and obtains a differential interference image. An interference image acquisition unit, a processing unit that performs a predetermined process on the differential interference image, and a display unit that displays an image after the predetermined process obtained by the processing unit. The processing unit is configured to determine the differential interference image obtained by the imaging unit or a predetermined value for the differential interference image according to a shift between a shear direction of the differential interference optical system and one arrangement direction of pixels in the imaging unit. Image rotation processing means for performing image rotation processing for rotating the image subjected to the pre-processing.

  The surface defect inspection apparatus according to a sixth aspect of the present invention is the surface defect inspection apparatus according to the fifth aspect, wherein the processing unit is arranged in a direction corresponding to the shear direction in the image subjected to the image rotation processing by the image rotation processing means. It has a means for processing for each data of each pixel row arranged, and the display section displays an image composed of the data of each pixel row processed by the means for processing.

  The surface defect inspection apparatus according to a seventh aspect of the present invention is the surface defect inspection apparatus according to the fifth aspect, wherein the processing unit is arranged in a direction corresponding to the shear direction in the image subjected to the image rotation processing by the image rotation processing means. Means for processing each data of each pixel row arranged, and image reverse rotation processing for rotating an image composed of the data of each pixel row processed by the processing means in the reverse direction by the same angle as the image rotation processing The image reverse rotation processing means for performing the image reverse rotation processing means, and the display unit displays the image subjected to the image reverse rotation processing.

  A surface defect inspection apparatus according to an eighth aspect of the present invention includes a differential interference optical system that forms a differential interference optical image of an object to be inspected and a differential imaging unit that captures the differential interference optical image and obtains a differential interference image. An interference image acquisition unit and a processing unit that processes the differential interference image and detects defects on the surface of the inspection object. The processing unit includes: (i) a difference image acquisition unit that obtains a difference image obtained by taking a difference between the differential interference image obtained by the imaging unit and a low-pass image obtained from the differential interference image; and (ii) the difference Noise reduction processing means for performing noise reduction processing for setting the value of a pixel having an absolute value smaller than a predetermined threshold to zero in an image; (iii) the shear direction of the differential interference optical system and one of the pixels in the imaging unit Image rotation processing means for performing image rotation processing for rotating the difference image on which the noise reduction processing has been performed in accordance with a deviation from the arrangement direction; and (iv) the image rotation processing is performed by the image rotation processing means. Post-processing data acquisition means for obtaining post-processing data of each pixel column from the original data of each pixel column arranged in a direction corresponding to the shear direction in the performed image, and for each pixel column The value of the post-processing data of each pixel in the pixel column is determined by the number of pixels in which the value of the original data is not zero among a plurality of continuous pixels within a predetermined range in the pixel column including the pixel. If the number of pixels in which the original data value is not zero among the plurality of consecutive pixels is greater than the predetermined number, the number of pixels in the pixel row is less than the predetermined number. And a post-processing data acquisition means for making the sum of the post-processing data value of the pixel adjacent to one side and the original data value of the pixel. The display unit displays an image composed of the post-processing data of each image sequence obtained by the post-processing data acquisition unit.

  A surface defect inspection apparatus according to a ninth aspect of the present invention includes a differential interference optical system that forms a differential interference optical image of an object to be inspected and a differential imaging unit that captures the differential interference optical image and obtains a differential interference image. An interference image acquisition unit and a processing unit that processes the differential interference image and detects defects on the surface of the inspection object. The processing unit includes: (i) a difference image acquisition unit that obtains a difference image obtained by taking a difference between the differential interference image obtained by the imaging unit and a low-pass image obtained from the differential interference image; and (ii) the difference Noise reduction processing means for performing noise reduction processing for setting the value of a pixel having an absolute value smaller than a predetermined threshold to zero in an image; (iii) the shear direction of the differential interference optical system and one of the pixels in the imaging unit Image rotation processing means for performing image rotation processing for rotating the difference image on which the noise reduction processing has been performed in accordance with a deviation from the arrangement direction; and (iv) the image rotation processing is performed by the image rotation processing means. Post-processing data acquisition means for obtaining post-processing data of each pixel column from the original data of each pixel column arranged in a direction corresponding to the shear direction in the performed image, and for each pixel column The value of the post-processing data of each pixel in the pixel column is determined by the number of pixels in which the value of the original data is not zero among a plurality of continuous pixels within a predetermined range in the pixel column including the pixel. If the number of pixels in which the original data value is not zero among the plurality of consecutive pixels is greater than the predetermined number, the number of pixels in the pixel row is less than the predetermined number. Post-processing data acquisition means for making the sum of the value of the post-processing data of the pixel adjacent to one side and the value of the original data of the pixel, and (v) each of the obtained by the post-processing data acquisition means Image reverse rotation processing means for performing image reverse rotation processing for rotating an image composed of the processed data of the image sequence in the reverse direction by the same angle as the image rotation processing. The display unit displays an image obtained by the reverse rotation processing unit.

  A surface defect inspection apparatus according to a tenth aspect of the present invention includes: (i) a differential interference optical system that forms a differential interference optical image of an inspection object; and an imaging unit that captures the differential interference optical image and obtains a differential interference image. (Ii) the shear direction of the differential interference optical system and the defect candidate direction on the surface of the inspection object detected in advance are in a state of being perpendicular to each other. A rotation unit that rotates at least a part of the differential interference image acquisition unit and / or the inspection object; and (iii) based on the differential interference image captured by the differential interference image acquisition unit in the vertical state, And a processing unit for detecting defects on the surface of the inspection object.

  A surface defect inspection apparatus according to an eleventh aspect of the present invention includes, in the tenth aspect, means for detecting the candidate and its direction based on a differential interference image previously captured by the differential interference image acquisition unit. It is a thing.

  The surface defect inspection apparatus according to a twelfth aspect of the present invention is the surface defect inspection apparatus according to the tenth or eleventh aspect, wherein the processing unit in the differential interference image captured by the differential interference image acquisition unit in the vertical state. Index value acquisition means for obtaining an index value corresponding to the contrast of the candidate along the shear direction, and determination means for determining whether the candidate is a defect on the surface of the inspection object based on the index value; It is what has.

  In the first to twelfth aspects, when the object to be inspected is a transparent body, any surface defect on the surface of the transparent body, the surface near the differential interference image acquisition unit and the surface far from the differential interference image acquisition unit. Can also be detected.

  ADVANTAGE OF THE INVENTION According to this invention, the surface defect inspection apparatus which can detect the defect of the surface of a to-be-inspected object with high precision can be provided.

  Hereinafter, a surface defect inspection apparatus according to the present invention will be described with reference to the drawings.

  [First Embodiment]

  FIG. 1 is a schematic configuration diagram schematically showing a surface defect inspection apparatus according to a first embodiment of the present invention. For convenience of explanation, as shown in FIG. 1, an X axis, a Y axis, and a Z axis that are orthogonal to each other are defined. The surface of the inspection object 1 is parallel to the XY plane.

  The surface defect inspection apparatus according to the present embodiment is configured to inspect defects on the surface on the + Z side of an inspection object 1 such as a glass substrate or a mirror or a mask, and a differential interference image of the inspection object 1 is obtained. A differential interference image acquisition unit 2 to be obtained, a processing unit 3, a control unit 4, a moving mechanism 5, a display unit 6, and an operation unit 7 are provided.

  In the present embodiment, the differential interference image acquisition unit 2 is configured as a differential interference microscope, and includes a light source 11, an illumination optical system 12, a polarizer 13, a Nomarski prism 14, an objective lens 15, and a half mirror 16. It has an analyzer 17, an imaging lens 18, and an image sensor 19 such as a CCD. A portion of the differential interference image acquisition unit 2 excluding the image sensor 19 constitutes a differential interference optical system that forms a differential interference optical image of the inspection object 1. The imaging element 19 constitutes an imaging unit that captures a differential interference optical image formed by the differential interference optical system to obtain a differential interference image.

  The light from the light source 11 may be, for example, monochromatic light or light having a predetermined wavelength width limited to some extent. The light from the light source 11 is converted into linearly polarized light by the polarizer 13 via the illumination optical system 12, bent by the half mirror 16, and further divided into two light beams by the Nomarski prism 14. As is well known, the Nomarski prism 14 is made of a birefringent crystal and has a refraction angle different depending on the polarization direction. These two light beams are incident on a slightly different point on the surface of the inspection object 1 on the + Z side by the objective lens 15, and the reflected light on the surface is again joined by the Nomarski prism 14, and the half mirror 16 and After passing through the analyzer 17, a differential interference optical image of the inspection object 1 is formed on the image sensor 19 by the imaging lens 18. This differential interference optical image is converted into an electric signal by the image pickup device 19 and picked up. Although not shown in the drawing, in the present embodiment, one arrangement direction of the pixels of the image sensor 19 is the X-axis direction, and another arrangement direction of the pixels of the image sensor 19 is the Y-axis direction. The imaging operation by the imaging element 19 is performed by a command from the control unit 4. Since this differential interference optical system detects the phase difference of light between two points slightly separated from each other, the obtained differential interference optical image is very sensitive to the step. The direction between the two points is determined by the orientation of the Nomarski prism 14 and is called a shear direction or shear direction. In the present embodiment, the shear direction of the differential interference optical system is deviated from one arrangement direction (X-axis direction) of the pixels of the image sensor 19. When the light from the light source 11 is monochromatic light or light having a predetermined wavelength width limited to some extent, the shape difference between the concave and convex shapes on the surface of the inspection object 1 is distinguished depending on how the light and darkness is added in the differential interference optical image. be able to.

  In the present embodiment, the moving mechanism 5 moves the entire differential interference image acquisition unit 2 two-dimensionally in a plane parallel to the XY plane under the control of the control unit 4. The display unit 6 is composed of a liquid crystal panel or the like and displays inspection results and the like. The operation unit 7 supplies an operation start command and the like to the control unit 4 by a human operation. The processing unit 3 processes the differential interference image obtained by the differential interference image acquisition unit 2 under the control of the control unit 4 to detect the result on the surface of the inspection object 1.

  FIG. 2 is a schematic flowchart showing an example of a specific operation of the surface defect inspection apparatus according to the present embodiment.

  When the operation start is instructed by the operation unit 7, as shown in FIG. 2, the control unit 4 controls the moving mechanism 5 so that the differential interference image acquisition unit 2 as a whole has a field of view of the inspection object 1. It moves so that it may become the first to-be-inspected area (step S1).

  Next, the control unit 4 causes the imaging element 19 of the differential interference image acquisition unit 2 to capture a differential interference optical image of the first inspection area of the inspection object 1 and obtains a differential interference image from the differential interference image acquisition unit 2 ( Step S2). An example of a part of the differential interference image obtained from the differential interference image acquisition unit 2 (a region in the vicinity of a linear scratch (concave)) is schematically shown in FIG. The diagonal linear figure in FIG. 3 is equivalent to the linear flaw (recessed part). As shown in FIG. 3, in this differential interference image, the shear direction 100 is shifted by an angle θ1 with respect to the X-axis direction (the direction in which one pixel is arranged). In this example, the flaw direction (the flaw extending direction) 101 is assumed to be orthogonal to the shear direction 100. Of course, the flaw direction varies depending on the flaw.

  Next, the processing unit 3 applies a Gaussian filter, for example, to the differential interference image obtained in step S2 to obtain a low-pass image (step S3). Subsequently, the processing unit 3 obtains a difference image obtained by taking a difference between the differential interference image obtained in step S2 and the low-pass image obtained in step S3 (step S4). In the difference image obtained in step S4, noise reduction processing is performed to make the value of a pixel whose absolute value is smaller than the predetermined threshold th zero (step S5). Thereby, the influence of random noise is reduced. In the present embodiment, the processes in steps S3 to S5 are pre-processes performed on the differential interference image obtained in step S2.

  Thereafter, the processing unit 3 uses the differential image subjected to the noise reduction process in step S5 as the shear direction 100 of the differential interference optical system of the differential interference image acquisition unit 2 and one arrangement direction (X-axis direction) of the image sensor 19. Image rotation processing is performed so that the shear direction 100 is rotated by affine transformation or the like so that the shear direction 100 matches the X-axis direction (step S6). FIG. 4 schematically shows an example of a partial region of the image that has undergone the image rotation processing in step S6 (an example corresponding to FIG. 3). However, in order to facilitate understanding, in FIG. 4, the differential interference image that has not undergone the processes of steps S <b> 3 to S <b> 5 is illustrated as being rotated. In the case of the example of FIG. 3, as shown in FIG. 4, a process of rotating the image counterclockwise by an angle θ1 is performed. In this image rotation process, it is desirable to perform interpolation by a method such as bilinear interpolation so as not to change the shape of the original image (image before rotation) as much as possible. Note that after step S2, image rotation processing may be performed on the differential interference image obtained in step S2, and then processing in steps S3 to S5 may be performed on the image after the rotation processing.

  Next, the processing unit 3 obtains post-processing data of the pixel row from the original data of the pixel row arranged in the direction corresponding to the shear direction 100 (X-axis direction) in the image subjected to the image rotation processing in step S6. (Steps S7 to S11). In this processing, the value Valb (x, y) of the post-processing data of each pixel (the XY coordinate of the pixel is (x, y)) of the pixel column (the pixel row whose Y coordinate is y) is The value of the original data (the value in the image obtained in step S6) among a plurality of (in this case, 2r + 1) pixels within a predetermined range x−r ≦ x ≦ x + r in the pixel row including the pixel. When the number of non-zero pixels is equal to or less than a predetermined number n, the number is set to zero, and the number of pixels whose original data value is not zero among the plurality of consecutive (here, 2r + 1) pixels is the predetermined number. When the number is larger than n, the value Valb (x−1, y) of the post-processing data of the pixel adjacent to the pixel on one side with respect to the pixel in the pixel column and the value Vala of the original data of the pixel The sum Valb (x-1, y) + Vala (x, y) with x, y) is set.

  That is, after step S6, the processing unit 3 initially sets the X coordinate value x to the minimum value, and then sequentially sets the maximum value (steps S10 and S11). Sometimes steps S7 to S9 are performed. In step S7, the processing unit 3 determines the number of pixels whose original data value is not zero among 2r + 1 consecutive pixels in which the X coordinate value of the Y coordinate value y currently targeted for processing is from x−r to x + r. It is determined whether it is a predetermined number n or less. If it is equal to or less than the predetermined number n, the processing unit 3 sets the value Valb (x, y) of the post-processing data to zero in step S9, and proceeds to step S10. On the other hand, if it is not less than the predetermined number n (if it is larger than the predetermined number n), in step S8, the processing unit 3 sets the value Valb (x, y) of the processed data to the value Valb of the processed data on the left side. The sum Valb (x-1, y) + Vala (x, y) of (x-1, y) and the original data value Vala (x, y) of the pixel (x, y) is set, and the process proceeds to step S10. .

  FIG. 5 schematically shows an example of original data (data in the image obtained in step S6) of a pixel column at a certain Y coordinate value in the vicinity of a scratch (concave portion). FIG. 6 shows post-processing data obtained from the original data of the pixel column at a certain Y coordinate value shown in FIG. In this example, when the post-processing data shown in FIG. 6 is obtained from the original data shown in FIG. 5, r = 1 and n = 1. Since the values of the pixels arranged in the X-axis direction are cumulatively added in step S8, the processed data shown in FIG. 6 is scratched (as if the differential image was integrated and returned to the original image). It is a pseudo representation of the shape (height) of the recess. In the present embodiment, step S8 is not always performed, but step S7 is performed when the determination in step S7 is performed and the number is n or less. Therefore, noise caused by the quantization error of the differential interference image or the like is eliminated. The influence can be reduced. If step S8 is performed without always performing step S9, a phenomenon occurs in which the quantization error included in each pixel is greatly influenced as it goes to the right pixel. Actual scratches (concave portions) and dust (convex portions) are not so large with respect to the resolution, and there is almost no region having a constant height. Therefore, if the determination in step S7 is performed and n or less, step S9 is performed. If the value is “0”, that is, if the region where the height change is “0” continues, “0”. It is supposed to be considered. In FIG. 5, the pixel value of x = 3 and the pixel value of x = 29 are affected by noise and are not zero, but in those cases, it is determined as yes in step S7, and the process of step S9 is performed. Therefore, the influence of the noise does not appear in the processed data in FIG. The values of r and n described above may be set as appropriate in consideration of the size of the scratch to be detected.

  FIG. 7 schematically illustrates an example of original data (data in the image obtained in step S6) of a pixel column at a certain Y coordinate value in the vicinity of dust (convex portion). FIG. 8 shows post-processing data obtained from the original data of the pixel column at a certain Y coordinate value shown in FIG. In this example, when the post-process data shown in FIG. 6 is obtained from the original data shown in FIG. 7, r = 1 and n = 1, as in the case of FIG. Since the values of the pixels lined up in the X-axis direction are cumulatively added in step S8, the processed data shown in FIG. 6 is treated as dust (as if the differential image was integrated and returned to the original image). It is a pseudo representation of the shape (height) of the convex portion.

  5 to 8, when the setting of the differential interference optical system in the differential interference image acquisition unit 2 is concave, the image obtained in step S6 becomes darker as it goes from the -X side to the + X side. In the case where the image becomes brighter and convex, the image obtained in step S6 is set to become brighter and darker as it goes from the -X side to the + X side. Depending on the setting of the differential interference optical system, etc., the light / dark situation is reversed.

  Then, the processing unit 3 performs the processes of steps S7 to S11 for all the rows (y) (that is, for all the pixel columns in the direction corresponding to the shear direction 100) (steps S12 and S13). An image made up of the processed data is obtained.

  After that, the processing unit 3 determines that the pixel value in the image is negative (in the case shown in FIGS. 5 to 8, in the case of the light / dark situation) from the image including the post-processing data of each pixel column obtained in this way. A region that is positive in the case of setting to reverse is detected as a scratch (concave portion) as a defect of the inspection object 1 (step S14). A defect having a concave shape and a dust having a convex shape have different pixel values, so that they are distinguished from each other, and only a defect having a concave shape is detected as a defect.

  In the present embodiment, in this manner, the concave portions are formed based on the data of the pixel columns arranged in the direction corresponding to the shear direction 100 in the image subjected to the image rotation processing in step S6 (that is, here, As a necessary condition, it is determined that a defect on the surface of the inspection object 1 is detected.

  Thereafter, the processing unit 3 determines whether or not the inspection of all the inspection regions of the inspection object 1 has been completed (that is, whether or not the processing of steps S2 to S14 has been completed for all the inspection regions) (step S15). ). If not completed, the control unit 4 controls the moving mechanism 5 to move the entire differential interference image acquisition unit 2 so that its field of view is the next inspection area of the inspection object 1 ( Step S16), and then returns to Step S2. On the other hand, if the inspection of all the areas to be inspected is completed, the process proceeds to step S17.

  In step S <b> 17, the processing unit 3 outputs the presence / absence of defects, the number and positions of defects, and the like as inspection results to the outside and displays them on the display unit 6. As a result, the series of operations is completed. Note that only the presence or absence of defects may be output as the inspection result. In the present embodiment, it is not always necessary to display the inspection result on the display unit 6.

  In this embodiment, as can be understood from Steps S6, S8, and S14 described above, a defect having a concave shape can be obtained by examining the state of light and darkness along the shear direction 100 in the differential interference image. It is detected as a defect on the surface of the inspection object 1 by distinguishing it from dust. Therefore, according to the present embodiment, since the defect detection is performed in consideration of the shear direction 100 as described above, the surface of the inspection object 1 can be detected with high accuracy.

  In the present embodiment, the process along the shear direction 100 in the differential interference image is performed after the image rotation process of step S6, so the process along the shear direction 100 is as simple as step S8. Addition processing is sufficient, and the processing becomes extremely simple and the processing speed can be increased. If step S6 is not performed and processing along the shear direction 100 comparable to step S8 is performed, extremely complicated calculations must be performed, and the processing speed must be reduced.

  By the way, depending on the direction of the scratch with respect to the shear direction 100 of the differential interference optical system of the differential interference image acquisition unit 2, the contrast of the scratch along the shear direction 100 in the differential interference image changes. Therefore, for example, in the present embodiment, not only the differential interference image acquisition unit 2 is moved two-dimensionally in a plane parallel to the XY plane, but the differential interference image acquisition unit 2 is moved around the optical axis of the objective lens 15. The movement mechanism 5 may be configured so as to be able to rotate, and the processes of steps S1 to S16 described above may be performed in each state where the differential interference image acquisition unit 2 is positioned at a plurality of rotation positions. Thereby, the defect (scratch) detection result of step S14 is obtained at each rotational position, and by obtaining the logical sum of the obtained results, it is possible to avoid missing the scratch (recess). Defects can be detected with higher accuracy. Furthermore, when it is desired to detect dust (convex parts), the post-processing data of each pixel row obtained by the processing of steps S7 to S12 in each state where the differential interference image acquisition unit 2 is positioned at a plurality of rotational positions. In an image consisting of a region where the pixel value is positive (in the case of FIG. 5 to FIG. 8; however, in the case where the light / dark situation is reversed, it is negative) It is preferable to obtain a logical product of the detection results obtained by detecting them as concave portions. Since the dust is hardly affected by the viewing direction, the same contrast is obtained even if it is rotated. As a result, factors other than dust can be deleted. Needless to say, instead of rotating the differential interference image acquisition unit 2, the inspection object 1 may be rotated.

  [Second Embodiment]

  As can be seen from the above description, the surface defect inspection apparatus according to the first embodiment is configured to automatically detect defects on the surface of the inspection object 1 without depending on the judgment of the inspector. Yes.

  The surface defect inspection apparatus according to the second embodiment of the present invention displays an image after performing predetermined processing on the differential interference image, and displays the determination of the detection of the defect on the surface of the inspection object 1. The surface defect inspection apparatus according to the first embodiment is modified so that it is left to the inspector who has seen the above. Specifically, the surface defect inspection apparatus according to the present embodiment is different from the surface defect inspection apparatus according to the first embodiment only in the points described below.

  In the present embodiment, the moving mechanism 5 not only moves the differential interference image acquisition unit 2 two-dimensionally in a plane parallel to the XY plane, but also moves the differential interference image acquisition unit 2 around the optical axis of the objective lens 15. It is configured so that it can be rotated. Needless to say, instead of enabling the differential interference image acquisition unit 2 to rotate, the inspection object 1 may be rotated.

  FIG. 9 is a schematic flowchart showing an example of a specific operation of the surface defect inspection apparatus according to the second embodiment of the present invention. 9, steps that are the same as or correspond to steps in FIG. 2 are given the same reference numerals, and redundant descriptions thereof are omitted.

  In the present embodiment, the processing unit 3 performs reverse image rotation in which an image composed of post-process data of each pixel column obtained by the processes in steps S7 to S12 is rotated in the reverse direction by the same angle as the image rotation process in step S6. Processing is performed (step S21).

  Next, the image subjected to the image reverse rotation process of step S21 is displayed on the display unit 6 (step S22). At this time, the differential interference image acquired in step S <b> 2 may also be displayed on the display unit 6. In this case, since the inspector can compare the original differential interference image and the image after the processing of steps S3 to S21, the defect (flaw) on the surface of the inspection object 1 is detected with higher accuracy. be able to. In the present embodiment, since the image that has been subjected to the image reverse rotation process of step S21 is displayed instead of the image itself that is the processed data of each pixel column obtained by the processes of steps S7 to S12, the original differentiation is performed. The interference image and the image subjected to the image reverse rotation process are also images at the same rotation position, and it is easy to compare the two. However, an image made up of post-process data of each pixel column obtained by the processes of steps S7 to S12 may be displayed on the display unit 6 as it is without performing the image reverse rotation process of step S21.

  The inspector looks at the image displayed on the display unit 6 in step S22 and detects the presence or absence, position, etc., of the surface of the inspection object 1 (scratches). At this time, the display image is a pseudo representation of the shape (height) of scratches (concave portions) and dust (convex portions) by the processing of steps S7 to S12. It is possible to distinguish a flaw having the shape from the dust having a convex shape and accurately detect it as a defect on the surface of the inspection object 1.

  Thereafter, the processing unit 3 waits for an operation performed by the inspector to the effect that the inspection of the region to be inspected is completed by the operation unit 7 (step S23). When the operation is performed, the process proceeds to step S15.

  According to the present embodiment, an image that has undergone processing along the shear direction 100 (particularly step S8) in the differential interference image is displayed on the display unit 6, and a processed image that takes the shear direction 100 into consideration is presented to the examiner. Therefore, the inspector can detect the result of the surface of the inspection object 1 with high accuracy.

  In the present embodiment, the process along the shear direction 100 in the differential interference image is performed after the image rotation process of step S6, so the process along the shear direction 100 is as simple as step S8. Addition processing is sufficient, and the processing becomes extremely simple and the processing speed can be increased. If step S6 is not performed and processing along the shear direction 100 comparable to step S8 is performed, extremely complicated calculations must be performed, and the processing speed must be reduced.

  For example, in the present embodiment, not only the differential interference image acquisition unit 2 is moved two-dimensionally in a plane parallel to the XY plane, but the differential interference image acquisition unit 2 is moved around the optical axis of the objective lens 15. The moving mechanism 5 may be configured so that it can be rotated, and the processing of the steps shown in FIG. 9 may be performed in each state where the differential interference image acquisition unit 2 is positioned at a plurality of rotational positions. As a result, the inspector obtains the detection results of defects (scratches) at each rotational position, and obtains the logical sum of the obtained results, thereby avoiding missing of the scratches (recesses). Defects can be detected with higher accuracy.

  [Third Embodiment]

  The surface defect inspection apparatus according to the third embodiment of the present invention is different from the surface defect inspection apparatus according to the first embodiment only in the points described below.

  In the present embodiment, the moving mechanism 5 not only moves the differential interference image acquisition unit 2 two-dimensionally in a plane parallel to the XY plane, but also moves the differential interference image acquisition unit 2 around the optical axis of the objective lens 15. It is configured so that it can be rotated. Needless to say, instead of enabling the differential interference image acquisition unit 2 to rotate, the inspection object 1 may be rotated.

  10 and 11 are schematic flowcharts showing an example of specific operation of the surface defect inspection apparatus according to the third embodiment of the present invention. 10, steps that are the same as or correspond to steps in FIG. 2 are given the same reference numerals, and redundant descriptions thereof are omitted.

  In the present embodiment, in step S40, the processing unit 3 performs exactly the same detection process as in step S14 in FIG. 2 described above, but what is detected as a defect (scratch) of the inspection object 1 in step S14, It is detected as a defect (scratch) candidate for the inspection object 1.

  Thereafter, the processing unit 3 determines whether there is a defect candidate detected in step S40 (step S41). If there is a defect candidate, the processing unit 3 sets the first defect candidate among the defect candidates detected in step S40 as a processing target (step S42). On the other hand, if there is no defect candidate, the processing unit 3 proceeds to step S51.

  After step S42, the processing unit 3 calculates a defect candidate direction (direction in which the defect candidate extends) 101 currently set as a processing target (step S43). The processing unit 3 calculates, for example, a moment feature (inertial main axis direction) as the defect candidate direction 101. Here, the X-axis direction (one pixel alignment direction), the Y-axis direction (another pixel alignment direction), the defect candidate direction 101 in the differential interference image acquired in step S2, and the differential interference image. An example of the relationship with the shear direction 100 of the differential interference optical system of the acquisition unit 2 is schematically shown in FIG. In the example shown in FIG. 12A, in this differential interference image, the defect candidate direction 101 is shifted from the angle perpendicular to the shear direction 100 by an angle θ2. In the example shown in FIG. 12A, in this differential interference image, the shear direction 100 is shifted by an angle θ1 with respect to the X-axis direction (the direction in which one pixel is arranged).

  Next, the control unit 4 controls the moving mechanism 5 so that the shear direction 100 and the defect candidate direction 101 obtained in step S43 are perpendicular to each other, thereby controlling the entire differential interference image acquisition unit 2. Rotate (step S44). When the differential interference image shown in step S2 has the relationship shown in FIG. 12A, the differential interference image acquisition unit 2 is rotated by an angle θ2 in step S44, as shown in FIG. The shear direction 100 and the defect candidate direction 101 are orthogonal to each other. In addition, instead of rotating the entire differential interference image acquisition unit 2, the inspection object 1 may be rotated, or the shear direction can be changed by changing the orientation of the Nomarski prism 14 and the analyzer which are part of the differential interference optical system. 100 may be rotated. Next, in this state, the control unit 4 causes the imaging element 19 of the differential interference image acquisition unit 2 to capture a differential interference optical image of the inspection object 1, and obtains a differential interference image from the differential interference image acquisition unit 2 (step S45). ). FIG. 12B shows the X-axis direction (one pixel alignment direction), the Y-axis direction (another pixel alignment direction), and the defect candidate direction 101 in the differential interference image acquired in step S45. FIG. 6 is a diagram schematically illustrating an example of a relationship between a differential interference optical system of the differential interference image acquisition unit 2 and a shear direction 100. FIG. 12B shows the defect candidate direction 101 as if it was rotated by an angle θ2 with respect to FIG. 12A for convenience of drawing.

  Thereafter, the processing unit 3 determines the direction of the defect candidate for the defect candidate region (this region is known by the processing of step S40) that is the current processing target in the differential interference image obtained in step S45. By performing projection (projection) on 101, a one-dimensional signal in the shear direction 100 is acquired (step S46). Here, the maximum value of this one-dimensional signal is set to max and the minimum value is set to min. Next, the processing unit 3 calculates the contrast of the one-dimensional signal obtained in step S46 by the equation (max−min) / (max + min) (step S47).

  As described above, the scratch contrast along the shear direction 100 in the differential interference image changes depending on the scratch direction 101 with respect to the shear direction 100 of the differential interference optical system of the differential interference image acquisition unit 2. Further, this contrast changes depending on the depth of the scratch, and increases as the depth of the scratch increases. Thus, the contrast varies depending on both the depth of the scratch and the direction 101 of the scratch relative to the shear direction 100. Therefore, in the state where the scratch direction 101 is different from the shear direction 100, even if the scratch depth is the same, the contrast is variously different, and the scratch is evaluated by evaluating the contrast. Depth cannot be assessed. On the other hand, in the present embodiment, the differential interference image obtained in step S45 is obtained in a state where the shear direction 100 and the defect candidate direction 101 are orthogonal to each other, and therefore the differential obtained in step S45. The contrast of the scratch along the shear direction 100 in the interference image appropriately reflects the depth of the scratch, and the depth of the scratch can be appropriately evaluated based on this contrast. The contrast of the one-dimensional signal obtained in step S46 = (max−min) / (max + min) becomes an index value corresponding to the scratch contrast along the shear direction 100 in the differential interference image obtained in step S45. Yes. Therefore, by evaluating the contrast of the one-dimensional signal obtained in step S46, it is possible to appropriately evaluate the depth of the scratch.

  After step S47, the processing unit 3 determines whether or not the defect candidate is a defect based on the contrast of the one-dimensional signal obtained in step S46 (step S48). Specifically, for example, when the contrast of the one-dimensional signal obtained in step S46 is equal to or smaller than a predetermined threshold, the processing unit 3 can evaluate that the depth of the scratch is shallower than the predetermined value. The defect candidate may be determined not to be a defect. On the other hand, when the contrast of the one-dimensional signal obtained in step S46 is greater than or equal to a predetermined threshold, the processing unit 3 can evaluate that the depth of the scratch is deeper than the predetermined value. What is necessary is just to determine with a defect, and the said defect candidate is detected as a defect of the surface of the to-be-inspected object 1. FIG.

  Next, the processing unit 3 determines whether there is a defect candidate that has not been determined in step S48 among the defect candidates detected in step S40 (step S49). If there is an undetermined defect candidate, the processing unit 3 sets the next defect candidate among the defect candidates detected in step S40 as a processing target (step S50), and then returns to step S43. On the other hand, if there is no undetermined defect candidate, the process proceeds to step S51.

  In step S51, the processing unit 3 determines whether or not the inspection of all the inspection regions of the inspection object 1 has been completed (that is, whether or not the processing of steps S2 to S49 has been completed for all the inspection regions) ( Step S51). If not completed, the control unit 4 controls the moving mechanism 5 to move the entire differential interference image acquisition unit 2 so that its field of view is the next inspection area of the inspection object 1 ( Step S52) and then return to Step S2. On the other hand, if the inspection of all the areas to be inspected is completed, the process proceeds to step S53.

  In step S <b> 53, the processing unit 3 outputs the presence / absence of defects, the number and positions of defects, and the like as inspection results to the outside and displays them on the display unit 6. As a result, the series of operations is completed. Note that only the presence or absence of defects may be output as the inspection result.

  In the present embodiment, as described above, for the defect candidates obtained in advance, in the present embodiment, in the differential interference image obtained in step S45 with the shear direction 100 and the defect candidate direction 101 orthogonal to each other, An index value corresponding to the scratch contrast along the shear direction 100 is obtained (step S47), and based on this, it is determined whether or not the defect candidate is a defect, and the defect is detected. 1 surface defects can be detected.

  [Fourth Embodiment]

  FIG. 13 is a schematic flowchart showing an example of a specific operation of the surface defect inspection apparatus according to the fourth embodiment of the present invention. In FIG. 13, steps that are the same as or correspond to steps in FIGS.

  The surface defect inspection apparatus according to the present embodiment is different from the surface defect inspection apparatus according to the third embodiment in the third embodiment described above from the differential interference image obtained in step S2. In the present embodiment, the defect candidates on the surface of the inspection object 1 are detected by performing the processes of steps S3 to S40 in FIG. 10, whereas in the present embodiment, the differential interference image obtained in step S2 The only difference is that a defect candidate on the surface of the inspection object 1 is detected by a process different from that of the third embodiment.

  In the present embodiment, in step S60, for example, the processing unit 3 binarizes and labels the differential interference image obtained in step S2, performs feature extraction of the shape of the labeling region, and extracts the feature. By comparing with a preset feature, a defect candidate on the surface of the inspection object 1 is detected.

  Also in the present embodiment, as in the third embodiment, defect candidates obtained in advance are obtained in step S45 in the present embodiment in a state where the shear direction 100 and the defect candidate direction 101 are orthogonal to each other. In the obtained differential interference image, an index value corresponding to the scratch contrast along the shear direction 100 is obtained (step S47), and based on this, it is determined whether or not the defect candidate is a defect and the defect is detected. It is possible to detect defects on the surface of the inspection object 1 with high accuracy.

  In the present embodiment, the relationship between the directions in the differential interference image obtained in step S2 is the same as that in FIG. 12A, and the relationship between the directions in the differential interference image obtained in step S45 is as shown in FIG. ). In the present embodiment, instead of this, for example, the relationship between the directions in the differential interference image obtained in step S2 is the same as that in FIG. 14A, and the direction of each direction in the differential interference image obtained in S45. The relationship may be the same as in FIG. In FIG. 12, the shear direction 100 is shifted by an angle θ1 with respect to the X-axis direction (one pixel arrangement direction), whereas in FIG. 14, the shear direction 100 coincides with the X-axis direction. In FIG. 14, elements that are the same as or correspond to the elements in FIG.

  Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments.

It is a schematic block diagram which shows typically the surface defect inspection apparatus by the 1st Embodiment of this invention. It is a schematic flowchart which shows an example of the specific operation | movement of the surface defect inspection apparatus shown in FIG. It is a figure which shows typically the example of the one part area | region of a differential interference image. It is a figure which shows typically the example of the one part area | region of the image in which the image rotation process was performed. It is a figure which shows typically the example of the original data of the pixel row in a certain Y coordinate value in the vicinity of a crack (concave part). It is a figure which shows the post-process data obtained from the original data of the pixel row in a certain Y coordinate value shown in FIG. It is a figure which shows typically the example of the original data of the pixel row in a certain Y coordinate value in the vicinity of dust (convex part). It is a figure which shows the post-process data obtained from the original data of the pixel row in a certain Y coordinate value shown in FIG. It is a schematic flowchart which shows an example of the specific operation | movement of the surface defect inspection apparatus by the 2nd Embodiment of this invention. It is a schematic flowchart which shows an example of the specific operation | movement of the surface defect inspection apparatus by the 3rd Embodiment of this invention. It is another schematic flowchart which shows an example of the specific operation | movement of the surface defect inspection apparatus by the 3rd Embodiment of this invention. It is a figure which shows an example of the relationship of each direction in a differential interference image. It is a schematic flowchart which shows an example of the specific operation | movement of the surface defect inspection apparatus by the 4th Embodiment of this invention. It is a figure which shows the other example of the relationship of each direction in a differential interference image.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inspection object 2 Differential interference image acquisition part 3 Processing part 4 Control part 5 Movement mechanism 6 Display part 7 Operation part

Claims (12)

A differential interference image acquisition unit having a differential interference optical system that forms a differential interference optical image of an object to be inspected, and an imaging unit that captures the differential interference optical image and obtains a differential interference image;
A processing unit that processes the differential interference image and detects defects on the surface of the inspection object;
With
The processing unit is configured to determine the differential interference image obtained by the imaging unit or a predetermined value for the differential interference image according to a shift between a shear direction of the differential interference optical system and one arrangement direction of pixels in the imaging unit. An apparatus for inspecting a surface defect, comprising image rotation processing means for performing image rotation processing for rotating an image subjected to the preprocessing.   The processing unit detects a defect on the surface of the inspection object based on data of pixel rows arranged in a direction corresponding to the shear direction in the image subjected to the image rotation processing by the image rotation processing unit. The surface defect inspection apparatus according to claim 1.   3. The surface defect inspection according to claim 2, wherein the processing unit detects a defect on the surface of the inspection object on the condition that it is determined as a recess based on data of the pixel column. apparatus. A differential interference image acquisition unit having a differential interference optical system that forms a differential interference optical image of an object to be inspected, and an imaging unit that captures the differential interference optical image and obtains a differential interference image;
A processing unit that processes the differential interference image and detects defects on the surface of the inspection object;
With
(I) differential image acquisition means for obtaining a differential image obtained by taking a difference between the differential interference image obtained by the imaging unit and a low-pass image obtained by filtering the differential interference image with a low-pass filter; (Ii) noise reduction processing means for performing noise reduction processing for reducing the value of a pixel having an absolute value smaller than a predetermined threshold to zero in the difference image; and (iii) shear direction of the differential interference optical system and the imaging Image rotation processing means for performing image rotation processing for rotating the difference image on which the noise reduction processing has been performed in accordance with a shift between one arrangement direction of pixels in the unit, and (iv) the image rotation processing means The post-processing data acquisition unit obtains post-processing data of the pixel row from the original data of the pixel row arranged in a direction corresponding to the shear direction in the image subjected to the image rotation processing. The value of the post-processing data of each pixel in the pixel column is the number of pixels in which the value of the original data is not zero among a plurality of continuous pixels within a predetermined range in the pixel column including the pixel. If the number of pixels in which the original data value is not zero among the plurality of consecutive pixels is greater than the predetermined number, the number of pixels in the pixel row is less than the predetermined number. A post-processing data acquisition means for making the sum of the value of the post-processing data of a pixel adjacent to one side and the value of the original data of the pixel,
The processing unit detects a defect on the surface of the inspection object on the condition that it is determined to be a recess based on the post-processing data of the pixel row obtained by the post-processing data acquisition unit,
A surface defect inspection apparatus. A differential interference image acquisition unit having a differential interference optical system that forms a differential interference optical image of an object to be inspected, and an imaging unit that captures the differential interference optical image and obtains a differential interference image;
A processing unit that performs a predetermined process on the differential interference image;
A display unit for displaying an image after the predetermined processing obtained by the processing unit;
With
The processing unit is configured to determine the differential interference image obtained by the imaging unit or a predetermined value for the differential interference image according to a shift between a shear direction of the differential interference optical system and one arrangement direction of pixels in the imaging unit. An apparatus for inspecting a surface defect, comprising image rotation processing means for performing image rotation processing for rotating an image subjected to the preprocessing. The processing unit includes means for processing each pixel row data arranged in a direction corresponding to the shear direction in the image subjected to the image rotation processing by the image rotation processing means,
The surface defect inspection apparatus according to claim 5, wherein the display unit displays an image including data of each pixel column processed by the processing unit. The processing section is processed by means for processing each pixel row data arranged in a direction corresponding to the shear direction in the image subjected to the image rotation processing by the image rotation processing means, and by the processing means. Image reverse rotation processing means for performing image reverse rotation processing for rotating an image composed of data of each pixel column in the reverse direction by the same angle as the image rotation processing,
The surface defect inspection apparatus according to claim 5, wherein the display unit displays an image on which the image reverse rotation process has been performed. A differential interference image acquisition unit having a differential interference optical system that forms a differential interference optical image of an object to be inspected, and an imaging unit that captures the differential interference optical image and obtains a differential interference image;
A processing unit that processes the differential interference image and detects defects on the surface of the inspection object;
With
The processing unit includes: (i) a difference image acquisition unit that obtains a difference image obtained by taking a difference between the differential interference image obtained by the imaging unit and a low-pass image obtained from the differential interference image; and (ii) the difference Noise reduction processing means for performing noise reduction processing for setting the value of a pixel having an absolute value smaller than a predetermined threshold to zero in an image; (iii) the shear direction of the differential interference optical system and one of the pixels in the imaging unit Image rotation processing means for performing image rotation processing for rotating the difference image on which the noise reduction processing has been performed in accordance with a deviation from the arrangement direction; and (iv) the image rotation processing is performed by the image rotation processing means. Post-processing data acquisition means for obtaining post-processing data of each pixel column from the original data of each pixel column arranged in a direction corresponding to the shear direction in the performed image, and for each pixel column The value of the post-processing data of each pixel in the pixel column is determined by the number of pixels in which the value of the original data is not zero among a plurality of continuous pixels within a predetermined range in the pixel column including the pixel. If the number of pixels in which the original data value is not zero among the plurality of consecutive pixels is greater than the predetermined number, the number of pixels in the pixel row is less than the predetermined number. A post-processing data acquisition means for making the sum of the value of the post-processing data of a pixel adjacent to one side and the value of the original data of the pixel,
The surface defect inspection apparatus, wherein the display unit displays an image composed of the post-processing data of each image sequence obtained by the post-processing data acquisition unit. A differential interference image acquisition unit having a differential interference optical system that forms a differential interference optical image of an object to be inspected, and an imaging unit that captures the differential interference optical image and obtains a differential interference image;
A processing unit that processes the differential interference image and detects defects on the surface of the inspection object;
With
The processing unit includes: (i) a difference image acquisition unit that obtains a difference image obtained by taking a difference between the differential interference image obtained by the imaging unit and a low-pass image obtained from the differential interference image; and (ii) the difference Noise reduction processing means for performing noise reduction processing for setting the value of a pixel having an absolute value smaller than a predetermined threshold to zero in an image; (iii) the shear direction of the differential interference optical system and one of the pixels in the imaging unit Image rotation processing means for performing image rotation processing for rotating the difference image on which the noise reduction processing has been performed in accordance with a deviation from the arrangement direction; and (iv) the image rotation processing is performed by the image rotation processing means. Post-processing data acquisition means for obtaining post-processing data of each pixel column from the original data of each pixel column arranged in a direction corresponding to the shear direction in the performed image, and for each pixel column The value of the post-processing data of each pixel in the pixel column is determined by the number of pixels in which the value of the original data is not zero among a plurality of continuous pixels within a predetermined range in the pixel column including the pixel. If the number of pixels in which the original data value is not zero among the plurality of consecutive pixels is greater than the predetermined number, the number of pixels in the pixel row is less than the predetermined number. Post-processing data acquisition means for making the sum of the value of the post-processing data of the pixel adjacent to one side and the value of the original data of the pixel, and (v) each of the obtained by the post-processing data acquisition means Image reverse rotation processing means for performing image reverse rotation processing for rotating an image composed of the processed data of the image sequence in the reverse direction by the same angle as the image rotation processing;
The surface defect inspection apparatus, wherein the display unit displays an image obtained by the reverse rotation processing means. A differential interference image acquisition unit having a differential interference optical system that forms a differential interference optical image of an object to be inspected, and an imaging unit that captures the differential interference optical image and obtains a differential interference image;
At least a part of the differential interference image acquisition unit and / or so that the shear direction of the differential interference optical system and a direction of a defect candidate on the surface of the inspection object detected in advance are perpendicular to each other. A rotating unit for rotating the object to be inspected;
Based on the differential interference image captured by the differential interference image acquisition unit in the vertical state, a processing unit that detects defects on the surface of the inspection object;
A surface defect inspection apparatus comprising:   11. The surface defect inspection apparatus according to claim 10, further comprising means for detecting the candidate and its direction based on a differential interference image previously captured by the differential interference image acquisition unit.   The processing unit includes an index value acquisition unit that acquires an index value according to a contrast along the shear direction of the candidate in the differential interference image captured by the differential interference image acquisition unit in the vertical state; and the index The surface defect inspection apparatus according to claim 10, further comprising: a determination unit that determines whether the candidate is a defect on the surface of the inspection object based on a value.

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