Imaging apparatus

Abstract

To reduce labor for adjusting sensitivity in an imaging device for inspecting a wafer.SOLUTION: The sensitivity adjustment device is provided with a line sensor (21) in which a plurality of imaging elements (22) are arranged in the radial direction of a wafer (W) held on a holding table (11), a rotation mechanism (16) for relatively rotating the holding table and the line sensor, a horizontal movement mechanism (30) for relatively moving the holding table and the line sensor in the horizontal plane, and a sensitivity adjustment control unit (42) for adjusting the sensitivity of each imaging element, wherein the sensitivity adjustment control unit is provided with a belt-like image generation unit (43) for imaging at least two locations of the relatively rotating wafer and forming a belt-like image (50) with the horizontal axis as the longitudinal direction of the line sensor and the vertical axis as the rotation direction of the line sensor with respect to the holding table, a calculation unit (44) for calculating the average value or the median value of the brightness of each imaging element in the belt-like image, and a leveling correction unit (45) for leveling the value of each imaging element calculated by the calculation unit.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an imaging device used for inspecting wafers. [Background technology]

[0002] As disclosed in Patent Documents 1 and 2, in an inspection device for inspecting wafers after grinding, a table holding a wafer whose upper surface has been ground with a grinding wheel is rotated while a line sensor extending in the radial direction of the wafer above the wafer is moved in the radial direction of the wafer, and the ground surface of the wafer is imaged using the line sensor in a spiral trajectory to obtain an image of the entire ground surface of the wafer, and inspection is performed based on the image. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-075554 [Patent Document 2] Japanese Patent Application Publication No. 2019-032260 Summary of the Invention [Problem to be solved by the invention]

[0004] Because the roughness of the ground wafer surface varies depending on processing conditions such as the abrasive grain size of the grinding stone or the hardness of the wafer, inspection equipment that inspects wafers using captured images requires sensitivity adjustment (gain adjustment) of the line sensor when acquiring the captured image. Conventionally, a portion of the ground wafer surface is imaged and the sensitivity of the line sensor is adjusted based on the image results, but this sensitivity adjustment work is performed by the operator, which is time-consuming and problematic.

[0005] Therefore, there is a demand for an imaging device for inspecting wafers that allows sensitivity adjustment without requiring the operator to take time and effort. [Means for solving the problem]

[0006] One aspect of the present invention is an imaging device comprising: a holding table for holding a wafer ground with a grinding wheel; a line sensor having a plurality of imaging elements arranged in the radial direction of the wafer with a length equal to or less than the radius of the wafer; a rotation mechanism for rotating the holding table and the line sensor relatively on an axis passing through the center of the holding table; and a horizontal movement mechanism for moving the holding table and the line sensor relatively in a horizontal plane in the direction of the arrangement of the imaging elements of the line sensor, the imaging device comprising: a sensitivity adjustment control unit for adjusting the sensitivity of each of the imaging elements; the sensitivity adjustment control unit for imaging at least two locations on the wafer rotated by the rotation mechanism and held on the holding table, and forming a band-shaped image with the horizontal axis being the longitudinal direction of the line sensor and the vertical axis being the rotation direction of the line sensor relative to the holding table; a calculation unit for calculating the average or median brightness of each of the imaging elements in the band-shaped image; and a leveling correction unit for leveling the values ​​for each of the imaging elements calculated by the calculation unit. [Effects of the Invention]

[0007] According to the imaging device of the present invention, sensitivity adjustment can be performed without requiring the operator to take time and effort. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a plan view of an imaging device for wafer inspection. [Figure 2] FIG. 2 is a diagram showing the imaging device as viewed along the X-axis direction. [Figure 3] FIG. 2 is a view of the imaging device as seen along the Y-axis direction. [Figure 4] FIG. 10 is a diagram illustrating sensitivity adjustment of a line sensor. DETAILED DESCRIPTION OF THE INVENTION

[0009] 1 to 3 show an imaging device 10 according to this embodiment. The imaging device 10 constitutes an inspection device that images a ground surface Wa, which is the top surface of a wafer W (see FIGS. 2 and 3) ground by a grinding device, to obtain an image of the entire ground surface Wa, and inspects the processing results (such as grinding marks) based on the image. The imaging device 10 includes a holding table 11 for holding the wafer W, an imaging unit 20 for imaging the wafer W on the holding table 11, and a control unit 40 for controlling each component. The X-, Y-, and Z-axes of the imaging device 10 are perpendicular to one another. The X- and Y-axes are horizontal directions, and the Z-axis is the up-and-down direction.

[0010] The imaging device 10 may be configured as part of the grinding device, or may be configured as a device independent of the grinding device. When the imaging device 10 is part of the grinding device, the holding table 11 that holds the wafer W, which is the object to be inspected, may be a chuck table that holds the wafer W during grinding, or, if the grinding device is equipped with a spinner cleaning unit that sprays cleaning water onto the wafer W held on the spinner table to clean the wafer W, the spinner table may be the spinner table. When the imaging device 10 is a device independent of the grinding device, the wafer W after grinding in the grinding device is transported to the imaging device 10 and held on the holding table 11.

[0011] 2 and 3, the holding table 11 includes a frame 12 supported on a base (not shown), and a disk-shaped porous plate 13 attached to a recess on the upper surface of the frame 12. The porous plate 13 is made of a porous material such as ceramics, and has fine pores formed throughout. With the porous plate 13 attached to the recess of the frame 12, the upper surfaces of the frame 12 and the porous plate 13 are flush with each other, forming a holding surface on which the wafer W is placed and held.

[0012] The holding table 11 is provided with a suction path 14 that communicates with the bottom of the porous plate 13, and the suction path 14 is connected to a suction source 15. When the suction source 15 is operated, air inside the porous plate 13 is sucked through the suction path 14, and a suction force acts on the upper surface of the porous plate 13. This suction force allows the wafer W to be sucked and held on the holding surface of the holding table 11.

[0013] Holding table 11 can be rotated around an axis that passes through center C (see FIG. 1) of holding table 11 and extends in the Z-axis direction by rotation mechanism 16. Rotation mechanism 16 includes motor 17 that generates power to rotate holding table 11, and encoder 18 that detects the amount of rotation of motor 17, and can manage the amount of rotation (rotation angle) of holding table 11 based on the detection signal of encoder 18.

[0014] The imaging unit 20 is disposed above the holding table 11. The imaging unit 20 includes a line sensor 21 consisting of an imaging element array in which a plurality of imaging elements 22 (see FIG. 4) are arranged. The direction in which the imaging elements 22 are arranged is the radial direction of the holding table 11, which is the longitudinal direction of the line sensor 21. In this embodiment, the X-axis direction is the longitudinal direction of the line sensor 21. The longitudinal length of the line sensor 21 is equal to or less than the radius of the wafer W. The imaging element 22 is a semiconductor device such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor), which photoelectrically converts light received on its light-receiving surface and outputs an electrical signal corresponding to the intensity (brightness) of the received light. The imaging unit 20 is capable of capturing an image of a rectangular area below using the line sensor 21.

[0015] The imaging unit 20 includes an illumination unit 23 arranged along the line sensor 21. A pair of illumination units 23 are arranged on both sides of the line sensor 21 in the Y-axis direction. Note that FIG. 4 illustrates only one of the illumination units 23 located on one side of the line sensor 21. As shown in FIG. 4, each illumination unit 23 is configured with multiple light sources 24 arranged in the longitudinal direction of the line sensor 21. Light emitted from each light source 24 is expanded by a lens or the like to irradiate a linear range extending in the X-axis direction. Each light source 24 is configured by an LED (Light Emitting Diode) or the like that emits light of a predetermined wavelength suitable for imaging the wafer W.

[0016] 2, each illumination unit 23 is configured to irradiate linear light L emitted from a plurality of light sources 24 obliquely downward so as to be tilted in the Y-axis direction, illuminating an imaging area directly below the line sensor 21. The illumination light from the illumination unit 23 is reflected by the grinding surface Wa (upper surface) of the wafer W held on the holding table 11, and the reflected light passes through an optical system (not shown) of the line sensor 21 and enters each imaging element 22.

[0017] The imaging device 10 includes an X-axis movement mechanism 30 that moves the imaging unit 20 in the X-axis direction, a Y-axis movement mechanism 31 that moves the imaging unit 20 in the Y-axis direction, and a Z-axis movement mechanism 32 that moves the imaging unit 20 in the Z-axis direction. The X-axis movement mechanism 30 movably supports an X-axis slider 34 via an X-axis guide member 33 extending in the X-axis direction, and moves the X-axis slider 34 in the X-axis direction using a drive source such as a motor. The Y-axis movement mechanism 31 movably supports a Y-axis slider 36 via a Y-axis guide member 35 extending in the Y-axis direction, and moves the Y-axis slider 36 in the Y-axis direction using a drive source such as a motor. The Z-axis movement mechanism 32 movably supports a Z-axis slider 38 via a Z-axis guide member 37 extending in the Z-axis direction, and moves the Z-axis slider 38 in the Z-axis direction using a drive source such as a motor. The Y-axis guide member 35 is supported on a base (not shown). The Y-axis slider 36 supports the X-axis guide member 33, the X-axis slider 34 supports the Z-axis guide member 37, and the Z-axis slider 38 supports the imaging unit 20. The X-axis movement mechanism 30 constitutes a horizontal movement mechanism that moves the holding table 11 and the imaging unit 20 relatively on a horizontal plane in the arrangement direction of the imaging elements 22 (the longitudinal direction of the line sensor 21).

[0018] The control unit 40 is composed of hardware such as a processor that executes arithmetic processing, a memory that stores control programs, and a communication interface that sends control signals to each part of the imaging device 10. The control unit 40 controls each part of the imaging device 10. The control unit 40 includes an image processing circuit 41, which processes image signals output from each imaging element 22 of the line sensor 21 and converts them into data in an image format, thereby generating a captured image.

[0019] In the imaging device 10 configured as described above, when imaging and inspecting the wafer W using the imaging unit 20, the underside of the wafer W, with the grinding surface Wa facing upward, is suction-held on the holding surface of the holding table 11, as shown in FIGS. 2 and 3. The control unit 40 operates the X-axis movement mechanism 30 and the Y-axis movement mechanism 31 to adjust the horizontal position (X-axis and Y-axis directions) of the imaging unit 20 relative to the holding table 11, and position one longitudinal end of the line sensor 21 above the center C of the holding table 11. This positions the multiple imaging elements 22 in the radial direction of the wafer W. The control unit 40 also operates the Z-axis movement mechanism 32 to adjust the vertical position (Z-axis direction) of the imaging unit 20 relative to the holding table 11, and aligns the focal position of the line sensor 21 with the grinding surface Wa of the wafer W. Then, illumination light from the illumination unit 23 is irradiated toward an imaging area (area directly below the line sensor 21) where the line sensor 21 images the grinding surface Wa.

[0020] After preparation in this manner, the control unit 40 operates the rotation mechanism 16 to rotate the holding table 11, while moving the imaging unit 20 at a constant speed in the X-axis direction from the center C of the holding surface of the holding table 11 outward, causing the line sensor 21 to image the grinding surface Wa of the wafer W. As a result, the entire grinding surface Wa of the wafer W is imaged in a spiral shape by the line sensor 21, which has a length equal to or less than the radius of the holding surface of the holding table 11. Then, the image processing circuit 41 of the control unit 40 combines the spiral images imaged by the line sensor 21 to obtain a circular image of the entire grinding surface Wa of the wafer W.

[0021] Alternatively, the control unit 40 may cause the line sensor 21 to capture an image without moving the imaging unit 20 until the holding table 11 has made one rotation, then move the imaging unit 20 in the X-axis direction, and then rotate the holding table 11 once again to capture an image, repeating this process. As a result, multiple annular ranges are captured on the grinding surface Wa of the wafer W, like tree rings. Then, the image processing circuit 41 of the control unit 40 combines the captured multiple annular images to obtain a circular image of the entire grinding surface Wa of the wafer W.

[0022] In the imaging unit 20, it is difficult for the illumination light from the illumination unit 23 to illuminate the entire imaging area of ​​the line sensor 21 in the X-axis direction with completely uniform light intensity. Therefore, variations in illumination intensity may result in partial differences in brightness of the image captured along the longitudinal direction of the line sensor 21, potentially affecting accurate inspection of the grinding surface Wa of the wafer W. To prevent this problem, the imaging device 10 of this embodiment is configured and controlled to adjust the sensitivity of each imaging element 22 based on the image captured by the line sensor 21 of the grinding surface Wa of the wafer W. This sensitivity adjustment of the imaging elements 22 is controlled by a sensitivity adjustment control unit 42, which is a functional block of the control unit 40. The sensitivity adjustment control unit 42 includes a band-shaped image generation unit 43, a calculation unit 44, and a leveling correction unit 45.

[0023] The band-shaped image generating unit 43 of the sensitivity adjustment control unit 42 rotates the holding table 11 using the rotation mechanism 16, and causes the imaging unit 20 to capture images of at least two locations on the wafer W held on the holding table 11 (at least two locations in the circumferential direction of the wafer W), forming a band-shaped image whose horizontal axis is the longitudinal direction of the line sensor 21 and whose vertical axis is the rotation direction of the line sensor 21 with respect to the holding table 11 (the relative rotation direction between the holding table 11 and the imaging unit 20). The position of the wafer W that is imaged when forming the band-shaped image is, for example, near the middle of the wafer W in the radial direction (see FIG. 3).

[0024] The band-shaped image 50 shown in FIG. 4 is obtained by outputting 360° (360 images) of image data of the wafer W captured by the line sensor 21 of the imaging unit 20 as a band-shaped image indicated by the horizontal and vertical axes, while changing the angle of the line sensor 21 relative to the holding table 11 in 1° increments under the control of the band-shaped image generating unit 43. The band-shaped image generating unit 43 controls the line sensor 21 of the imaging unit 20 to capture images at positions every 1° in the rotational direction of the holding table 11, while detecting the rotational angle of the holding table 11 connected to the motor 17 using the encoder 18. Each grid in the band-shaped image 50, divided along the horizontal axis, indicates an imaging position in the radial direction (X-axis direction) of the wafer W corresponding to each imaging element 22. Each grid in the band-shaped image 50, divided along the vertical axis, indicates an imaging position every 1° in the rotational direction of the holding table 11 and the imaging unit 20. In other words, the band-shaped image 50 is a circular image consisting of 360 images captured in a predetermined radial range (a range corresponding to the length of the line sensor 21) of the wafer W on the holding table 11, one circumference of the wafer W, converted into a matrix as shown in Figure 4, and the images in each grid of the band-shaped image 50 represent different locations in the radial and circumferential directions of the wafer W.

[0025] In the band-shaped image generating unit 43, a band-shaped image is formed by capturing images of multiple locations on the wafer W held on the holding table 11, thereby obtaining information for grasping the brightness trends of the images captured by each image sensor 22. A band-shaped image can be formed by capturing images of at least two locations on the wafer W. However, if too few locations on the wafer W are captured when forming the band-shaped image, the brightness of the captured locations, which have foreign matter such as water droplets or dust attached and have a different light reflectance from the original wafer W, will differ significantly from the brightness of the other captured locations, which have no foreign matter attached and correspond to the reflectance of the wafer W. This makes it difficult to obtain accurate brightness information. Therefore, it is desirable to capture images of as many locations on the wafer W as possible within the range that does not increase the processing time excessively, and to form a band-shaped image that includes as much sample image information as possible. The band-shaped image 50 shown in FIG. 4 is an image of the entire circumference of the wafer W at 1° intervals in the relative rotation direction of the line sensor 21 with respect to the holding table 11. By referring to this band-shaped image 50 and performing processing by the calculation unit 44 and the leveling correction unit 45 described below, it is possible to eliminate the influence of localized foreign matter adhesion and adjust the sensitivity of the image sensor 22 with extremely high precision.

[0026] The calculation unit 44 of the sensitivity adjustment control unit 42 calculates the average or median brightness value for each image sensor 22 in the band-shaped image generated by the band-shaped image generation unit 43. For example, in the processing example shown in FIG. 4 , a series of grid images (images obtained by dividing a circumference into 360 parts, each 1°) captured by each image sensor 22 and arranged along the vertical axis of the band-shaped image 50 are extracted as one image group G, and the calculation unit 44 calculates the average brightness value for the image group G. For example, the average brightness value for the image group G can be obtained by accumulating the brightness values ​​of each grid image included in one image group G and dividing the accumulated brightness value by 360. The pre-adjustment graph 51 shown in FIG. 4 is a graph plotting the average brightness values ​​of the multiple image groups G corresponding to the multiple image sensors 22. The horizontal axis of the pre-adjustment graph 51 indicates the position of each image sensor 22 in the radial direction of the wafer W, and the vertical axis of the pre-adjustment graph 51 indicates the average brightness value of the image groups G corresponding to each image sensor 22.

[0027] The calculation unit 44 may calculate the median value of the brightness of the image group G for each image sensor 22. In this case, the vertical axis direction of the pre-adjustment graph 51 indicates the median value of the brightness of the image group G.

[0028] 4 shows that the average brightness of the image group G captured by the image sensors 22 at both ends of the longitudinal direction of the line sensor 21 is lower than the average brightness of the image group G captured by the image sensors 22 in other regions (intermediate regions excluding both ends of the longitudinal direction of the line sensor 21). This is because, as shown in FIG. 4, the arrangement of the light sources 24 in the illumination unit 23 is biased toward the center of the longitudinal direction of the line sensor 21, and the intensity of the illumination light from the illumination unit 23 is likely to be relatively low near both ends of the longitudinal direction of the line sensor 21.

[0029] Even if light source 24 is placed near an end of line sensor 21 in the longitudinal direction, it is difficult to achieve a completely uniform illuminance of illumination light over the entire longitudinal direction of line sensor 21 due to constraints on the light distribution characteristics of the optical system in illumination unit 23 (such as a reduction in the amount of peripheral light in a light distribution lens). Therefore, it is difficult to avoid variations in brightness occurring at each position of multiple image pickup elements 22 in the longitudinal direction of line sensor 21 simply by devising the configuration of illumination unit 23 or light emission control of light source 24.

[0030] The leveling correction unit 45 of the sensitivity adjustment control unit 42 performs a process of leveling the values ​​calculated by the calculation unit 44 for each image sensor 22. FIG. 4 shows a first example of the leveling process. In the first example, the leveling correction unit 45 adjusts the sensitivity of the image sensors 22 and increases the light-receiving sensitivity of the image sensors 22 that are found to have a low average (or median) brightness value for the image group G, i.e., the image sensors 22 at both ends of the line sensor 21 in the longitudinal direction. The image sensors 22 with increased light-receiving sensitivity are set to detect equivalent brightness values ​​with a smaller amount of received light than the other image sensors 22. Therefore, the brightness values ​​for each image sensor 22 are leveled, as shown in the post-adjustment graph 52 in FIG. 4. Therefore, even if the imaging unit 20 has variations in illumination intensity along the longitudinal direction of the line sensor 21, the imaging unit 20 can capture an image of the ground surface Wa of the wafer W while eliminating the effects of the variations, thereby improving inspection accuracy.

[0031] As a second example of the leveling process performed by the leveling correction unit 45, an image sensor 22 (in the example of FIG. 4, the image sensor 22 at both ends of the line sensor 21 in the longitudinal direction) that is found to have a low average (or median) brightness value of the image group G may not be used to capture images of the wafer W during inspection. That is, the image processing circuit 41 of the control unit 40 processes the image signal output from the image sensor 22 so as not to accept the image signal, thereby managing the image signal not to be reflected in the image formation of the grinding surface Wa of the wafer W. In other words, the line sensor 21 of the imaging unit 20 is treated as a line sensor with a shorter length (a line sensor with a smaller number of image sensors 22) than the actual configuration. Since a typical imaging unit tends to produce images with lower brightness at both ends of the line sensor in the longitudinal direction, as shown in the pre-adjustment graph 51 of FIG. 4, the leveling process in the second example can be applied. That is, in addition to the leveling process in the first example, the leveling process in the second example is also included in the sensitivity adjustment of the image sensor 22 in a broad sense.

[0032] If an image group G with low brightness exists at a position midway along the longitudinal direction of the line sensor 21, performing the leveling process of the second example in which the image signals of the image sensor 22 corresponding to that image group G are omitted from the image formation may result in a hole in the image due to part of the grinding surface Wa not being captured during inspection of the wafer W. Therefore, in this case, it is preferable to apply the leveling process of the first example described above.

[0033] 4 increases the sensitivity of some of the imaging elements 22 for which the brightness of the captured image group G is low, but if the brightness of the image group G captured by some of the imaging elements 22 is high, it may also be possible to decrease the sensitivity of those imaging elements 22. It is also possible to perform both the process of increasing the sensitivity of the imaging elements 22 for which the brightness of the image group G is relatively low and the process of decreasing the sensitivity of the imaging elements 22 for which the brightness of the image group G is relatively high.

[0034] In order to accurately inspect the grinding surface Wa of the wafer W using the image captured by the imaging unit 20, regardless of which of the above-mentioned sensitivity adjustment methods is used in the leveling process, it is necessary to prevent overexposure (blown-out highlights) or underexposure (crushed shadows) from occurring in the images captured by all of the imaging elements 22 of the grinding surface Wa of the wafer W after the leveling process. By referring to the brightness fluctuation range of all the grids in the belt-like image 50 shown in FIG. 4, information regarding the appropriate sensitivity range of the imaging elements 22 that does not cause overexposure or underexposure when the entire grinding surface Wa of the wafer W is captured can be obtained. Then, in the leveling process performed by the leveling correction unit 45, the sensitivity of each imaging element 22 after the leveling process is adjusted so that it falls within the appropriate sensitivity range. For example, if the sensitivity of each image sensor 22 after sensitivity adjustment in the post-adjustment graph 52 shown in Fig. 4 exceeds the appropriate sensitivity range (is too high), the sensitivity can be brought within the appropriate sensitivity range by performing leveling processing to lower the sensitivity of the image sensor 22 with a relatively high brightness. By performing the processing as described above, it is possible to perform both sensitivity adjustment (gain adjustment) for setting the overall line sensor 21 to an appropriate sensitivity depending on the reflectance of the ground surface Wa of the wafer W to be inspected, and leveling processing for correcting variations in brightness of the captured image for each image sensor 22.

[0035] The above series of sensitivity adjustments performed using the sensitivity adjustment control unit 42 is preferably performed whenever the type of wafer W to be inspected or the processing conditions are changed. Alternatively, the sensitivity adjustments using the sensitivity adjustment control unit 42 may be performed periodically whenever a predetermined time has elapsed or when the number of inspected wafers W reaches a predetermined number.

[0036] As described above, the imaging device 10 of this embodiment automatically adjusts the sensitivity of the line sensor 21 equipped with multiple imaging elements 22 without any effort on the part of the operator, and in particular, it equalizes the brightness of the images from each imaging element 22, thereby eliminating bias in the inspection conditions in the imaging unit 20 and enabling highly accurate inspection of the wafer W.

[0037] In the above explanation, the variation in brightness of the captured images (image group G) for each image sensor 22 in the pre-adjustment graph 51 in FIG. 4 is attributed to variation in illumination intensity at the illumination unit 23 of the imaging unit 20. However, variations in brightness of the captured images for each image sensor 22 may occur due to factors other than illumination intensity. For example, if there are inherent differences in the light-receiving sensitivity of each image sensor 22, even if illumination light with uniform illuminance is distributed over the entire longitudinal direction of the line sensor 21, the amount of reflected light of the illumination light to the image sensor 22 may differ due to differences in the size of the unevenness of the grinding surface Wa, resulting in non-uniform brightness of the captured images for each image sensor 22. Even in such a case, as in the imaging device 10 described above, the leveling correction unit 45 performs a process of leveling the values ​​calculated by the calculation unit 44 for each image sensor 22, thereby enabling inspection of the wafer W with the sensitivity of the line sensor 21 automatically optimized.

[0038] In the above embodiment, an image of a ground wafer W is captured, but this device may also be used to capture an image of the polished surface of a wafer W. When the polished surface of the wafer is captured using a line sensor to obtain an image of the entire surface to be polished and an inspection is performed based on the image, the burden on the operator can be reduced and highly accurate inspection can be achieved efficiently by automatically adjusting the sensitivity of the imaging element as described above.

[0039] The embodiments of the present invention are not limited to the above-described embodiments and modifications, and may be variously changed, substituted, or modified without departing from the spirit of the technical idea of ​​the present invention. Furthermore, if the technical idea of ​​the present invention can be realized in a different way due to technological advances or other derived technologies, it may be implemented using that method. Therefore, the claims cover all embodiments that may fall within the scope of the technical idea of ​​the present invention. [Industrial Applicability]

[0040] According to the imaging device of the present invention, the sensitivity of the line sensor is automatically adjusted, thereby reducing the workload of the operator and contributing to efficient and highly accurate wafer inspection. [Explanation of symbols]

[0041] 10: Imaging device 11: Holding table 16: Rotation mechanism 20: Imaging unit 21: Line sensor 22: Image sensor 23: Lighting Department 24:Light source 30:X-axis movement mechanism (horizontal movement mechanism) 31:Y-axis movement mechanism 32:Z-axis movement mechanism 40: Control unit 41: Image processing circuit 42: Sensitivity adjustment control section 43: Band image generation unit 44: Calculation section 45: Equalization correction section 50: Strip image W: wafer Wa: Surface to be ground

Claims

[Claim 1] an imaging device comprising: a holding table for holding a wafer; a line sensor having a plurality of imaging elements arranged in the radial direction of the wafer with a length equal to or less than the radius of the wafer; a rotation mechanism for relatively rotating the holding table and the line sensor on an axis passing through the center of the holding table; and a horizontal movement mechanism for relatively moving the holding table and the line sensor in a horizontal plane in the direction of the arrangement of the imaging elements of the line sensor, a sensitivity adjustment control unit that adjusts the sensitivity of each of the image pickup elements; The sensitivity adjustment control unit a band-shaped image generating unit that captures images of at least two locations on the wafer rotated by the rotation mechanism and held on the holding table, and forms a band-shaped image whose horizontal axis is the longitudinal direction of the line sensor and whose vertical axis is the rotation direction of the line sensor relative to the holding table; a calculation unit that calculates an average value or a median value of brightness for each of the image pickup elements in the belt-like image; a leveling correction unit that levels the values ​​calculated for each imaging element by the calculation unit; An imaging device comprising:

Images