Method for inspecting the retaining table

Abstract

To detect presence / absence of a foreign matter projecting from a holding surface.SOLUTION: There is provided an inspection method of a holding table for inspecting presence / absence of a foreign matter on a holding surface, in a processing device having a holding table having the holding surface capable of sucking and holding a workpiece, and an imaging unit which is arranged above the holding table and can image the workpiece sucked and held by the holding table. The method includes: a distribution creation step of creating distribution of brightness of a pixel in an image obtained by imaging one surface of a substrate sucked and held by the holding surface with the imaging unit; and a determination step of determining the presence / absence of the foreign matter on the holding surface, on the basis of the distribution of the brightness of the pixel in the image.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for inspecting a holding table in a processing apparatus having a holding table and an imaging unit, for inspecting whether or not there are foreign objects on the holding surface of the holding table. [Background technology]

[0002] Electronic devices such as mobile phones and personal computers are equipped with semiconductor device chips. Semiconductor device chips are manufactured, for example, by processing silicon wafers (workpieces) that include single-crystal silicon substrates.

[0003] To manufacture a semiconductor device chip, for example, multiple streets are first set up in a grid pattern on the surface side of a silicon wafer, and devices such as ICs (Integrated Circuits) are formed in each of the rectangular regions demarcated by the multiple streets.

[0004] Next, the silicon wafer is thinned by grinding the back side, and then the silicon wafer is cut along each street to divide it into multiple device chips. A cutting device is used when cutting the silicon wafer.

[0005] The cutting apparatus has a cylindrical spindle that can rotate at high speed, and a cutting blade having an annular cutting edge is attached to the tip of the spindle (see, for example, Patent Document 1). The cutting apparatus further includes a disc-shaped holding table for suction holding of a silicon wafer.

[0006] The holding table has a disc-shaped frame, with a circular recess formed in the upper part of the frame. A disc-shaped porous plate is fixed in the recess. The upper surfaces of the frame and the porous plate are flush and function as holding surfaces that attract and hold silicon wafers.

[0007] When cutting a silicon wafer with a cutting machine, for example, first, the back side of the silicon wafer is held in place by suction on the holding surface. Then, with the lower end of the high-speed rotating cutting blade positioned below the surface of the silicon wafer, the holding table is moved in a predetermined direction (processing feed direction). This cuts the silicon wafer.

[0008] However, if foreign matter such as cutting debris is present on the holding surface, unexpected cracks may occur in the silicon wafer during cutting. Specifically, the silicon wafer may crack due to the downward force applied by the suction pressure and the downward force applied to the silicon wafer by the cutting blade, and the upward force applied to the silicon wafer by foreign matter protruding from the holding surface.

[0009] Therefore, before suction-holding the silicon wafer on the holding surface, the holding surface is imaged with a microscope camera unit to inspect for the presence of foreign matter (see, for example, Patent Document 2). However, even when using a microscope camera unit, it can be difficult to detect foreign matter due to reasons such as the relatively small size of the foreign matter or the difficulty in distinguishing it from the pattern on the top surface of the porous plate. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Japanese Patent Publication No. 2000-87282 [Patent Document 2] Japanese Patent Publication No. 2000-216227 [Overview of the Initiative] [Problems that the invention aims to solve]

[0011] This invention has been made in view of the aforementioned problems, and aims to detect the presence or absence of foreign matter protruding from the holding surface. [Means for solving the problem]

[0012] According to one aspect of the present invention, a processing apparatus is provided comprising a holding table having a holding surface capable of holding a workpiece by suction, and an imaging unit disposed above the holding table and capable of imaging the workpiece held by the holding table, wherein the method for inspecting the holding table for the presence or absence of foreign matter on the holding surface is provided, comprising: a distribution creation step of creating a distribution of pixel brightness in an image obtained by imaging one surface of a substrate held by suction on the holding surface with the imaging unit, and a determination step of determining the presence or absence of foreign matter on the holding surface based on the pixel brightness distribution in the image.

[0013] According to another aspect of the present invention, A processing apparatus comprising a holding table having a holding surface capable of holding a workpiece by suction, and an imaging unit positioned above the holding table and capable of imaging the workpiece held by the holding table, wherein the method for inspecting the holding table for the presence or absence of foreign matter on the holding surface comprises: a distribution creation step of creating a distribution of pixel brightness in an image obtained by imaging one surface of a substrate held by suction on the holding surface with the imaging unit, and a determination step of determining the presence or absence of foreign matter on the holding surface based on the image, The image includes multiple images, and in the determination step, each image pixels in Based on the average brightness, the presence or absence of foreign matter on the holding surface is determined. A method for inspecting the retention table is provided. .

[0014] According to another aspect of the present invention, a processing apparatus is provided comprising a holding table having a holding surface capable of holding a workpiece by suction, and an imaging unit disposed above the holding table and capable of imaging the workpiece held by the holding table, wherein the method for inspecting the holding table for the presence or absence of foreign matter on the holding surface is provided, comprising: a distribution creation step of creating a distribution of pixel brightness in each of a plurality of first images obtained by imaging one surface of a substrate held by suction on the holding surface with the imaging unit; and a determination step of determining the presence or absence of foreign matter on the holding surface by comparing the distribution of pixel brightness in a second image pre-stored in the processing apparatus with the distribution of pixel brightness in each of the plurality of first images.

[0015] According to still another aspect of the present invention, in a processing apparatus having a holding table with a holding surface capable of sucking and holding a workpiece, and an imaging unit disposed above the holding table and capable of imaging the workpiece sucked and held by the holding table, there is provided an inspection method for the holding table for inspecting the presence or absence of foreign matter on the holding surface, the method including: a calculation step of calculating an average value of brightness of pixels in a first image obtained by imaging a predetermined region on one surface of a first substrate sucked and held on the holding surface with the imaging unit; and a determination step of determining the presence or absence of foreign matter on the holding surface by comparing an average value of brightness of pixels in a second image obtained by imaging a predetermined region on one surface of another substrate having a size corresponding to the workpiece and sucked and held on the holding surface with the imaging unit, with the average value of brightness of the predetermined region of the first substrate obtained in the calculation step.

Advantages of the Invention

[0016] In the inspection method for the holding table according to multiple aspects of the present invention, the presence or absence of foreign matter on the holding surface is determined based on the brightness of an image obtained by imaging one surface of a substrate sucked and held on the holding surface. Specifically, when foreign matter is present on the holding surface, the foreign matter protrudes from the holding surface, so that the region where the foreign matter is present and the periphery of that region become darker than the region where no foreign matter is present.

[0017] Therefore, even when the size of the foreign matter is relatively small, if the foreign matter protrudes from the holding surface, the foreign matter can be detected. Also, even when it is difficult to visually distinguish the pattern on the upper surface of the porous plate from the foreign matter, the presence or absence of foreign matter can be indirectly detected by imaging the substrate.

[0018] In this way, by imaging the shadow of the unevenness of the holding surface reflected on one surface of the substrate due to the foreign matter, the size of the foreign matter is exaggerated, so that even relatively small foreign matter can be more easily detected compared to the case where no substrate is used.

Brief Description of the Drawings

[0019] [Figure 1]This is a flowchart of the inspection method for a holding table according to the first embodiment. [Figure 2] This figure shows the process of imaging a workpiece held by suction on a holding surface free of foreign matter. [Figure 3] This figure shows the process of imaging a substrate that is held in place by suction on a holding surface containing foreign matter. [Figure 4] Figure 4(A) is an example of a composite image obtained by combining multiple unit images acquired by imaging a region without foreign matter, and Figure 4(B) is an example of a composite image obtained by combining multiple unit images acquired by imaging a region with foreign matter. [Figure 5] Figure 5(A) shows an example of the pixel brightness distribution in a composite image in a region without foreign matter, and Figure 5(B) shows an example of the pixel brightness distribution in a composite image in a region with foreign matter. [Figure 6] Figure 6(A) is a cross-sectional view of the workpiece and holding table when foreign matter is present, and Figure 6(B) shows how the workpiece cracks during cutting due to the foreign matter. [Figure 7] This is a flowchart illustrating the inspection method for the retaining table in a modified form. [Figure 8] This is a flowchart of the inspection method for the holding table according to the second embodiment. [Figure 9] This figure shows an example of a reference brightness distribution and the distributions of multiple brightness levels being compared. [Figure 10] This is a flowchart of the inspection method for the holding table according to the third embodiment. [Figure 11] This figure shows an example of the average value of a reference brightness and the average value of the brightness being compared. [Modes for carrying out the invention]

[0020] An embodiment of one aspect of the present invention will be described with reference to the attached drawings. In the first embodiment, the holding surface 4a of the holding table 4 of the cutting device (processing device) 2 (see Figure 2) is inspected to see whether or not foreign matter 11 such as cutting chips (see Figure 3) is present. Figure 1 is a flowchart of the inspection method for the holding table 4 according to the first embodiment.

[0021] In explaining the inspection method according to each step shown in Figure 1, we will first describe the cutting apparatus 2 with reference to Figures 2 and 3. Figure 2 shows the imaging of a workpiece 13 held by suction on a holding surface 4a that does not contain foreign matter 11, and Figure 3 shows the imaging of a substrate 15 held by suction on a holding surface 4a that contains foreign matter 11.

[0022] Note that the X-axis, Y-axis, and Z-axis directions shown in Figures 2 and 3 are mutually orthogonal directions. The X-axis direction is also called the machining feed direction, the Y-axis direction is called the indexing feed direction, and the Z-axis direction is called the cutting feed direction (up and down direction).

[0023] The cutting device 2 has a disc-shaped holding table 4 (also called a chuck table). The holding table 4 has a disc-shaped frame 4b made of metal. A disc-shaped recess is formed on the upper side of the frame 4b, and a disc-shaped porous plate 4c made of porous ceramics is fixed in this recess.

[0024] The upper surface of the frame 4b and the upper surface of the porous plate 4c are substantially flush, forming a substantially flat holding surface 4a. Multiple pores are formed between the upper and lower surfaces of the porous plate 4c, and when negative pressure is generated by a suction source 6 such as a vacuum pump, the negative pressure is transmitted to the porous plate 4c through the flow path of the frame 4b.

[0025] When a workpiece 13 (see Figure 2) or substrate 15 (see Figure 3) is placed on the holding surface 4a, and negative pressure is applied to the porous plate 4c, the workpiece 13 or substrate 15 is held in place by suction at the holding surface 4a.

[0026] The holding table 4 is supported by an X-axis movement mechanism (not shown) that moves the holding table 4 along the X-axis. Above the holding surface 4a, the cutting unit 8 is positioned. The cutting unit 8 has a spindle housing 10 whose longitudinal portion is positioned along the Y-axis.

[0027] A cylindrical spindle 12, whose longitudinal portion is aligned along the Y-axis, is rotatably housed in the spindle housing 10. A rotational drive source (not shown), such as a motor, is provided at one end of the spindle 12.

[0028] The other end of the spindle 12 protrudes outward from the spindle housing 10, and a cutting blade 14 having an annular cutting edge is mounted on this other end. The cutting blade 14 may be of the hubless type (i.e., washer type) or the hub type.

[0029] The spindle housing 10 is configured to be movable along the Y-axis and Z-axis directions by a Y-axis and Z-axis direction movement mechanism (not shown). An imaging unit 16 is provided at a predetermined position adjacent to the spindle housing 10 in the X-axis direction.

[0030] The imaging unit 16 is fixed to the spindle housing 10 and, like the cutting unit 8, is positioned above the holding surface 4a. The imaging unit 16, together with the spindle housing 10, is also movable along the Y-axis and Z-axis directions by a Y-axis and Z-axis direction movement mechanism.

[0031] The imaging unit 16 images the workpiece 13 and substrate 15 held by suction on the holding surface 4a. The imaging unit 16 includes a low-magnification microscope unit 16a and a high-magnification microscope unit (not shown). The high-magnification microscope unit is positioned further back in the plane of Figure 2 compared to the low-magnification microscope unit 16a.

[0032] The low-magnification microscope unit 16a includes a first lens (not shown) for low magnification, a first image sensor that focuses light from the first lens, and a first reflected light illuminator (not shown) that illuminates the imaging area.

[0033] The first image sensor may be a CMOS (Complementary Metal-Oxide-Semiconductor) image sensor or a CCD (Charge-Coupled Device) image sensor. The number of pixels of the first image sensor in this embodiment is approximately 300,000 (640 x 480) pixels.

[0034] When the image obtained using the first image sensor is a grayscale image, the pixel value of each pixel is represented by 256 gradations from 0 to 255. In contrast, when the image obtained using the first image sensor is a full-color image, one pixel has a pixel value that is represented by 256 gradations for each of the following colors, for example, R (red), G (green), and B (blue).

[0035] When imaging a workpiece 13 or substrate 15 held by suction on the holding surface 4a using the low-magnification microscope unit 16a, the resolution of the resulting image is 10 μm. Furthermore, the imaging field of view when the subject is in focus on the low-magnification microscope unit 16a is set to 5 mm × 5 mm. Therefore, the size of the image obtained using the low-magnification microscope unit 16a (hereinafter referred to as a unit image for convenience) is 5 mm × 5 mm.

[0036] In this embodiment, after capturing an image of the subject with the low-magnification microscope unit 16a, the imaging unit 16 is moved multiple times in the X-axis direction or the Y-axis direction, and 7 × 7 unit images are combined to obtain an image of size 35 mm × 35 mm (see Figures 4(A) and 4(B)).

[0037] For convenience, from now on, an image formed by combining multiple unit images will be referred to as a composite image. Of course, a composite image is constructed by appropriately arranging unit images that are adjacent to each other in the X-axis or Y-axis direction so that they constitute a part of the overall image of the subject.

[0038] Similarly, the high-magnification microscope unit includes a second lens (not shown) for high magnification, a second image sensor from which light from the second lens is focused, and a second reflected light illuminator (not shown) for illuminating the imaging area. The second image sensor is also a CMOS image sensor or a CCD image sensor.

[0039] The second image sensor also has approximately 300,000 (640 x 480) pixels. When imaging with the high-magnification microscope unit, the resolution of the resulting image is 0.5 μm, and the imaging field of view when focused on the subject is set to 0.25 mm x 0.25 mm. In other words, the size of the unit image is 0.25 mm x 0.25 mm.

[0040] Note that the pixel count, resolution, imaging field, and unit image size of the low-magnification microscope unit 16a and the high-magnification microscope unit are examples only and are not limited to the values ​​listed herein.

[0041] A control unit 18 that controls the operation of the cutting device 2 is connected to the imaging unit 16. The control unit 18 is composed of a computer that includes, for example, a processor (processing unit) represented by a CPU (Central Processing Unit) and memory (storage device).

[0042] Memory includes main memory such as DRAM (Dynamic Random Access Memory), SRAM (Static Random Access Memory), and ROM (Read Only Memory), and auxiliary memory such as flash memory, hard disk drives, and solid-state drives.

[0043] The auxiliary storage device stores software, including a predetermined program. The functions of the control unit 18 are realized by operating the processing unit and other components according to this software.

[0044] The control unit 18 has a distribution creation unit 20 which is realized by executing a first program stored in memory on the processor. The distribution creation unit 20 creates a distribution of pixel brightness (for example, a luminance distribution or a lightness distribution).

[0045] The distribution creation unit 20 of this embodiment creates a distribution of pixel brightness in composite images 30 and 32 (see Figures 4(A) and 4(B)) with a size of 35 mm × 35 mm, which are created by tiling seven unit images obtained in the imaging field (5 mm × 5 mm) of the low-magnification microscope unit 16a in the X-axis direction and seven in the Y-axis direction.

[0046] For example, as shown in Figure 3, when the imaging unit 16 images a region of one surface 15a of the substrate 15 that is held by suction on the holding surface 4a that does not contain foreign matter 11, a composite image 30 of a predetermined pattern shown in Figure 4(A) is obtained according to the shape of the device formed on the surface 15a.

[0047] The distribution creation unit 20 calculates a distribution curve fitted to the frequency distribution by calculating the mean (μ), standard deviation (σ), etc., in a frequency distribution where the horizontal axis is brightness (e.g., luminance or lightness) and the vertical axis is frequency.

[0048] For example, when the distribution creation unit 20 creates a distribution curve by fitting it to the frequency distribution of brightness of pixels constituting the composite image 30 shown in Figure 4(A), a first distribution curve 34 as shown in Figure 5(A) is obtained.

[0049] In contrast, when the imaging unit 16 images a convex region 15c (see Figure 3) on one surface 15a of the substrate 15 held by suction on the holding surface 4a, where the foreign object 11 is located, a composite image 32 shown in Figure 4(B) is obtained. In the composite image 32 of Figure 4(B), the areas that appear black (i.e., relatively dark) and the areas that appear white and shiny (i.e., relatively bright) correspond to the convex region 15c. For example, the foreign object 11 is located in the center of the dark area.

[0050] When the distribution creation unit 20 creates a distribution curve fitted to the frequency distribution of brightness of pixels constituting the composite image 32 shown in Figure 4(B), a second distribution curve 36 is obtained as shown in Figure 5(B). In the second distribution curve 36, there are peaks in the secondary distribution curves at positions corresponding to the brightness of the main distribution curve below μ-3σ.

[0051] The control unit 18 has a determination unit 22 which is realized by executing a second program stored in memory on the processor. The determination unit 22 in this embodiment determines whether or not there is a distribution curve having a peak at a brightness of μ-3σ or less (for example, low brightness or low lightness).

[0052] As shown in the composite image 32 of Figure 4(B), when foreign matter 11 is sandwiched between the holding surface 4a and the substrate 15, the light from the first incident illumination device is scattered, making it difficult for reflected light to return to the imaging unit 16. As a result, the number of dark pixels increases, as shown in the second distribution curve 36 of Figure 5(B).

[0053] The determination unit 22 of this embodiment determines the presence or absence of foreign matter 11 on the holding surface 4a by determining the presence or absence of a distribution curve having a peak at a brightness lower than μ-3σ, as shown in the second distribution curve 36 (i.e., based on the brightness distribution of the composite image 32).

[0054] However, the threshold used to determine the presence or absence of the foreign object 11 is not limited to μ-3σ. The threshold may be appropriately changed depending on the size of the foreign object 11, the size of the composite images 30 and 32, etc. μ-2σ, μ-σ, or other values ​​may also be used as the threshold.

[0055] In this embodiment, the presence or absence of foreign matter 11 on the holding surface 4a is determined based on the brightness distribution of an image obtained by imaging one surface 15a of the substrate 15 held by suction on the holding surface 4a. Specifically, if foreign matter 11 is present on the holding surface 4a, the foreign matter 11 protrudes from the holding surface 4a, causing the region where the foreign matter 11 is present and its surroundings to be darker than the region where the foreign matter 11 is not present.

[0056] Therefore, even if the size of the foreign object 11 is relatively small, if the foreign object 11 protrudes beyond the holding surface 4a, the foreign object 11 can be detected, and even if it is difficult to visually distinguish between the pattern on the upper surface of the porous plate 4c and the foreign object 11, the presence or absence of the foreign object 11 can be indirectly detected by imaging the substrate 15.

[0057] Next, the workpiece 13 and substrate 15 that are held by suction on the holding surface 4a will be described. The workpiece 13 has, for example, a disc-shaped single-crystal silicon substrate (silicon wafer). As the silicon wafer, a 12-inch wafer with a diameter of approximately 300 mm and a thickness of approximately 775 μm, or an 8-inch wafer with a diameter of approximately 200 mm and a thickness of approximately 725 μm can be used.

[0058] However, the diameter and thickness of the workpiece 13 are not limited to the two types described above. Devices such as ICs (Integrated Circuits), LEDs (Light Emitting Diodes), and MEMS (Micro Electro Mechanical Systems) (not shown) are formed on the surface 13a side of the workpiece 13.

[0059] In contrast, the substrate 15 includes a disc-shaped single-crystal silicon substrate (i.e., a so-called dummy wafer) having a size corresponding to the workpiece 13. In other words, the diameter and thickness of the substrate 15 are approximately the same as the diameter and thickness of the workpiece 13.

[0060] The substrate 15 may have a mirror wafer with one surface 15a that is mirror-finished. Dummy wafers and mirror wafers do not have devices formed on them. However, the substrate 15 may have a silicon wafer containing the same devices as the workpiece 13.

[0061] When cutting the workpiece 13, the back surface 13b is held by the holding surface 4a through suction. However, if foreign matter 11 is present between the workpiece 13 and the holding surface 4a, a convex region 15c is formed. Figure 6(A) is a cross-sectional view of the workpiece 13 and the holding table 4 when foreign matter 11 is present.

[0062] If the workpiece 13 is cut in this state, the workpiece 13 may crack due to the downward force applied by the suction pressure, the downward force applied to the workpiece 13 by the cutting blade 14, and the upward force applied to the workpiece 13 by the foreign matter 11 protruding from the holding surface 4a. Figure 6(B) shows how the workpiece 13 cracks during cutting due to the foreign matter 11.

[0063] Therefore, in this embodiment, before cutting the workpiece 13, foreign matter 11 on the holding surface 4a is inspected according to the flow chart shown in Figure 1. For example, foreign matter 11 is inspected before fully automatic cutting is performed on multiple workpieces 13 corresponding to one lot, or on multiple workpieces 13 contained in one cassette (not shown) that is fed into the cutting device 2.

[0064] Furthermore, inspection for foreign matter 11 may be performed each time a predetermined number of workpieces 13 are cut, or inspection for foreign matter 11 may be performed each time a workpiece 13 is cut. The substrate 15 used when inspecting for foreign matter 11 may be placed in an inspection cassette (not shown) different from the cassette described above and automatically transported to the cutting device 2, or it may be manually loaded into the cutting device 2 by an operator.

[0065] When inspecting for the presence or absence of foreign matter 11, first the substrate 15 is placed on the holding surface 4a, and the other surface 15b of the substrate 15 is held in place by suction on the holding surface 4a. If foreign matter 11 is present on the holding surface 4a, the substrate 15 deforms to conform to the irregularities formed by the foreign matter 11 and is held in place by suction on the holding surface 4a (see Figures 3 and 6(A)).

[0066] Then, the imaging unit 16 captures an image of approximately the entire surface 15a of the substrate 15. In this embodiment, as described above, the entire surface 15a is captured by obtaining multiple composite images, each with a size of 35 mm × 35 mm (for example, see composite image 30 in Figure 4(A) and composite image 32 in Figure 4(B)).

[0067] Figure 4(A) is an example of a composite image 30 obtained by combining multiple unit images (7×7) acquired by imaging a region where there is no foreign matter 11 between the substrate 15 and the retaining surface 4a, and Figure 4(B) is an example of a composite image 32 obtained by combining multiple unit images (7×7) acquired by imaging a region where there is foreign matter 11 between the substrate 15 and the retaining surface 4a.

[0068] Although the size (maximum length) of the foreign object 11 shown in Figure 4(B) in the XY plane view is approximately 100 μm, the size of the foreign object 11 is exaggerated by imaging the shadow of the unevenness of the holding surface 4a reflected on one surface 15a of the substrate 15 due to the foreign object 11. Therefore, even relatively small foreign objects 11 can be easily detected compared to when the substrate 15 is not used.

[0069] The square frames, triangles, etc., shown around the periphery of the composite images 30 and 32 are graphical user interfaces (GUIs) displayed on the touch panel (display input device) that displays the images acquired by the imaging unit 16. These GUIs are not included in the actual composite images 30 and 32.

[0070] Figure 5(A) shows an example of the pixel brightness distribution in a composite image 30 obtained by combining multiple unit images (7×7) acquired by imaging a region without foreign matter 11, and Figure 5(B) shows an example of the pixel brightness distribution in a composite image 32 obtained by combining multiple unit images (7×7) acquired by imaging a region with foreign matter 11.

[0071] In the distribution creation process S10, as shown in Figures 5(A) and 5(B), the distribution creation unit 20 creates a distribution curve that is fitted to the frequency distribution of brightness of the pixels that make up each of the composite image 30 and composite image 32.

[0072] After the distribution creation step S10, the determination unit 22 determines whether or not there is a distribution curve with a peak in brightness below a threshold (e.g., μ-3σ) (determination step S20). If there is no distribution curve with a peak below the threshold (NO in S30), the process ends.

[0073] In contrast, if there is a distribution curve with a peak below the threshold (YES in S30), the control unit 18 activates a touch panel, lamp, alarm, etc. (none of which are shown) to notify that there is a foreign object 11 on the holding surface 4a (notification step S40).

[0074] If a notification is received, the operator will clean the holding surface 4a or replace the holding table 4. For example, cleaning the holding surface 4a is performed by bringing a so-called cleaning wafer, which has a resin tape attached to one side of a dummy wafer or one side of a mirror wafer (the side opposite the mirror surface) to attract foreign matter 11, into contact with the holding surface 4a.

[0075] In this embodiment, the presence or absence of foreign matter 11 on the holding surface 4a is determined based on the brightness distribution of an image obtained by imaging one surface 15a of the substrate 15 held by suction on the holding surface 4a. Therefore, even if the size of the foreign matter 11 is relatively small, if the foreign matter 11 protrudes beyond the holding surface 4a, the foreign matter 11 can be detected. Furthermore, even if it is difficult to visually distinguish between the pattern on the upper surface of the porous plate 4c and the foreign matter 11, the presence or absence of foreign matter 11 can be indirectly detected by imaging the substrate 15.

[0076] In the distribution creation step S10 and determination step S20 described above, examples using a composite image were explained, but unit images may also be used. In addition, in the determination step S20, instead of determination based on a threshold, the presence or absence of foreign matter 11 can also be determined based on the average value (brightness distribution) of the pixel brightness in multiple images (composite image or unit image) of one surface 15a of the substrate 15.

[0077] Specifically, in the distribution creation process S10, the distribution creation unit 20 processes each image pixels in The average brightness is calculated. Next, in the determination step S20, if there is an image with an extremely low average value (YES in S31), the determination unit 22 determines that there is a foreign object 11 on the holding surface 4a and notifies the system of this (notification step S40).

[0078] Whether the average is extremely low or not depends, for example, on multiple comparison points. Pixels in an image The distribution creation unit 20 creates a frequency distribution of the average brightness, and the determination unit 22 makes a determination. In particular, the unit image pixels in When using the average brightness value, the image obtained by imaging the region containing the foreign object 11 will be generally dark, and the average brightness value will be significantly lower. Note that judgment may be made using methods other than frequency distribution.

[0079] In contrast, in the determination step S20, if there are no images with an extremely low average value (NO in S31), the determination unit 22 determines that there are no foreign objects 11 on the holding surface 4a. Figure 7 is a flowchart of the inspection method for the holding table 4 according to a modified example.

[0080] (Second Embodiment) Next, a second embodiment will be described. In the first embodiment described above, foreign matter 11 is detected by utilizing the brightness distribution in the image on one surface 15a of a single substrate 15.

[0081] In contrast, in the second embodiment, the presence or absence of foreign matter 11 on the holding surface 4a is detected by comparing the brightness distribution curve 38 (see Figure 9) of a reference image (second image) pre-stored in the memory of the control unit 18 with the brightness distribution curve 40-1 etc. (see Figure 9) of an image of one surface 15a (first image) obtained by imaging.

[0082] Figure 8 is a flowchart of the inspection method for the holding table 4 according to the second embodiment, and Figure 9 is a diagram showing an example of a reference brightness distribution curve 38 and multiple brightness distribution curves 40-1, etc., to be compared.

[0083] In the second embodiment, the memory of the control unit 18 stores a distribution curve 38 (see Figure 9) that shows the distribution of pixel brightness in a reference image (for example, a composite image 30) obtained by imaging a region free of foreign matter 11 from an image of one surface 15a of the substrate 15 held by suction on the holding surface 4a.

[0084] The distribution creation unit 20 creates distribution curves 40-1, 40-2, 40-3, 40-4…40-N that show the distribution of pixel brightness in each of the multiple first images (composite images) obtained by imaging one surface 15a of the substrate 15 held by suction on the holding surface 4a with the imaging unit 16 (distribution creation step S12). N is a natural number.

[0085] Then, the determination unit 22 compares the distribution curve 38 of the reference image (second image) with the distribution curves showing the brightness of pixels in each of the multiple first images to determine whether or not there is foreign matter 11 on the holding surface 4a (determination step S22).

[0086] For example, if the distribution curves 40-1...40-N have one peak, similar to the reference distribution curve 38, it is determined that there is no foreign matter 11 on the holding surface 4a. In other words, if there is a peak with approximately the same shape as the reference distribution curve 38 (NO in S32), the flow is terminated.

[0087] In contrast, in regions where an image corresponding to distribution curve 40-4, which has a shape clearly different from the reference distribution curve 38, is obtained, it is determined that foreign matter 11 is present. In this example, distribution curve 38 has one peak, while distribution curve 40-4 has multiple peaks, so the shapes of the distribution curves are different (YES in S32). In this case, the process proceeds to notification process S40.

[0088] From S40 onward, the procedure is the same as in the first embodiment, so the explanation will be omitted. In the second embodiment as well, even if the size of the foreign object 11 is relatively small, the foreign object 11 can be detected if it protrudes beyond the holding surface 4a. Furthermore, even if it is difficult to visually distinguish between the pattern on the upper surface of the porous plate 4c and the foreign object 11, the presence or absence of the foreign object 11 can be indirectly detected by imaging the substrate 15.

[0089] (Third Embodiment) Next, a third embodiment will be described. In the third embodiment, the foreign object 11 is detected using the average value of the brightness of multiple pixels that constitute an image of substantially the entire surface 15a of the substrate 15, rather than the brightness distribution of multiple pixels that constitute the composite images 30, 32, etc.

[0090] Figure 10 is a flowchart of the inspection method for the holding table 4 according to the third embodiment, and Figure 11 shows the average value μ of the reference brightness. A And the average value μ of the brightness being compared B The figure shows an example of this.

[0091] In the third embodiment, the memory of the control unit 18 contains the average value μ of pixel brightness in an image (second image) obtained by imaging a predetermined area of ​​one surface 15a of another substrate 15 that is held by suction on a holding surface 4a free of foreign matter 11. A (See Figure 11) This is stored in the memory of the control unit 18.

[0092] The predetermined region of one surface 15a is, for example, the entire device region in which the device is formed, but is not limited to this. The predetermined region of one surface 15a may be a region of one surface 15a corresponding to a composite image obtained by combining multiple unit images (for example, 20 mm × 20 mm or 30 mm × 30 mm).

[0093] Furthermore, a holding surface 4a free of foreign matter 11 can be achieved, for example, by using a new holding table 4, or by cleaning the holding surface 4a even if the holding table 4 is used. In addition, imaging of a predetermined area can be obtained by appropriately combining unit images.

[0094] The distribution creation unit 20 calculates the average value μ of pixel brightness in an image (first image) obtained by imaging a predetermined area (for example, the entire device area) of one surface 15a of a substrate 15 held by suction on the holding surface 4a with the imaging unit 16. B The result is calculated (calculation step S14).

[0095] Then, the determination unit 22 determines the image of the other board 15 that has been stored in advance. pixels in Average value of brightness μ A And the image of one substrate 15 obtained in calculation step S14 pixels in Average value of brightness μ BBy comparing [them], the presence or absence of the foreign matter 11 on the holding surface 4a is determined (determination step S24).

[0096] μ B is μ A If it is smaller than μ, there is a high possibility that there is foreign matter 11 between the one substrate 15 and the holding surface 4a. Therefore, μ B < μ A If it is in this case (YES in S34), the notification step S40 and the cleaning step S50 are sequentially performed. Note that μ A ≦ μ B If it is in this case (NO in S34), the flow is terminated.

[0097] Also in the third embodiment, even when the size of the foreign matter 11 is relatively small, if the foreign matter 11 protrudes from the holding surface 4a, the foreign matter 11 can be detected. Further, even when it is difficult to visually distinguish the pattern on the upper surface of the porous plate 4c from the foreign matter 11, the presence or absence of the foreign matter 11 can be indirectly detected by imaging the substrate 15.

[0098] In addition, the structures, methods, etc. according to the above-described embodiments can be appropriately changed and implemented as long as they do not deviate from the scope of the object of the present invention. For example, in the first and second embodiments, the number of unit images constituting the synthetic images 30, 32 is not limited to 7×7, and may be k×k (k is a natural number of 2 or more).

[0099] Also, the imaging unit 16 is not limited to the above-described low-magnification microscope unit 16a and high-magnification microscope unit, and may have a camera unit capable of imaging a region of 400 mm×400 mm in the XY plane in one imaging.

[0100] Such a wide-field camera unit is usually used for overall inspection for inspecting the entire surface 13a of the workpiece 13. However, in order to irradiate the entire surface 13a of the workpiece 13 with light substantially uniformly, it is preferable to adopt coaxial epi-illumination.

[0101] Incidentally, the contents described in the first to third embodiments above can be applied not only to the cutting device 2 but also to the grinding device (processing device) not shown. The grinding device has a disc-shaped holding table 4. The holding table 4 is configured to be rotatable around a predetermined rotation axis.

[0102] Above the holding table 4, a cylindrical spindle (not shown) is provided with its longitudinal portion aligned along the Z-axis direction. Near the upper end of the spindle, a rotational drive source (not shown), such as a motor, is provided to rotate the spindle.

[0103] A disc-shaped mount (not shown) is provided at the lower end of the spindle, and an annular grinding wheel (not shown) is mounted on the underside of the mount. The grinding wheel has an annular base made of aluminum alloy or the like. Multiple grinding wheels are arranged at approximately equal intervals along the circumferential direction of the base on the underside of the base.

[0104] When grinding a workpiece 13 with a grinding device, if foreign matter 11 is present on the holding surface 4a, the workpiece 13 is held by suction in a manner that conforms to the holding surface 4a, resulting in the formation of localized depressions in the workpiece 13 after grinding. Therefore, it is desirable to inspect the holding surface 4a for the presence or absence of foreign matter 11 even in the grinding device.

[0105] The first to third embodiments described above can also be applied to the inspection method of the holding surface 4a in the grinding device. In the cleaning process S50, self-grinding is performed by grinding the holding surface 4a with a grinding wheel while supplying grinding water such as pure water to the holding surface 4a. Self-grinding grinds the holding surface 4a and removes foreign matter 11 from the holding surface 4a. Of course, the holding table 4 itself may also be replaced.

[0106] In addition to the cutting device 2 and the grinding device, other processing devices such as a polishing device (not shown), a cutting tool device (not shown), and a spinner cleaning device (not shown) also have a holding table that is substantially the same as the holding table 4, so the first to third embodiments described above can be applied as a method for inspecting the holding surface.

[0107] The polishing device has almost the same configuration as the grinding device, but a disc-shaped polishing pad is attached to the lower end of the spindle via a mount. A disc-shaped cutting tool is attached to the lower end of the spindle of the cutting device via a mount.

[0108] The spinner cleaning device has a disc-shaped holding table that can rotate at high speed. Above the holding table, there is a cleaning nozzle capable of spraying cleaning water such as pure water. The cleaning nozzle is configured to reciprocate within a predetermined arc-shaped region above the holding surface that is substantially parallel to the holding surface.

[0109] When cleaning a so-called half-cut workpiece 13 with a spinner cleaning device, if there is foreign matter 11 on the holding surface, there is a possibility that the workpiece 13 may crack unexpectedly during cleaning. Therefore, it is preferable to apply the above inspection method to detect foreign matter 11 even during the cleaning process. [Explanation of symbols]

[0110] 2: Cutting equipment (processing equipment) 4: Holding table, 4a: Holding surface, 4b: Frame, 4c: Porous plate 6: Suction source, 8: Cutting unit, 10: Spindle housing, 12: Spindle 11: Foreign object 13: Workpiece, 13a: Front surface, 13b: Back surface 14: Cutting blade 15: Substrate, 15a: One side, 15b: Other side, convex area 15c 16: Imaging unit, 16a: Low-magnification microscope unit 18: Control unit, 20: Distribution creation unit, 22: Judgment unit 30,32: Composite image 34: First distribution curve, 36: Second distribution curve 38:Distribution curve 40-1,40-2,40-3,40-4,40-N:Distribution curve S10, S12: Distribution creation process S14: Calculation process S20, S22, S24: Judgment process S40: Notification Process S50: Cleaning process μ A ,μ B :Average value

Claims

1. A processing apparatus comprising a holding table having a holding surface capable of holding a workpiece by suction, and an imaging unit positioned above the holding table and capable of imaging the workpiece held by the holding table, wherein the method for inspecting the holding table for the presence or absence of foreign matter on the holding surface is as follows: A distribution creation step to create a distribution of pixel brightness in an image obtained by imaging one surface of a substrate held by suction on the holding surface with the imaging unit, A determination step of determining the presence or absence of foreign matter on the holding surface based on the brightness distribution of pixels in the image, A method for inspecting a holding table, characterized by comprising the following features.

2. A processing apparatus comprising a holding table having a holding surface capable of holding a workpiece by suction, and an imaging unit positioned above the holding table and capable of imaging the workpiece held by the holding table, wherein the method for inspecting the holding table for the presence or absence of foreign matter on the holding surface is as follows: A distribution creation step to create a distribution of pixel brightness in an image obtained by imaging one surface of a substrate held by suction on the holding surface with the imaging unit, The system includes a determination step of determining the presence or absence of foreign matter on the holding surface based on the image, The image in question contains multiple images, The inspection method for a retaining table is characterized in that, in the determination step, the presence or absence of foreign matter on the retaining surface is determined based on the average value of the brightness of pixels in each image.

3. A processing apparatus comprising a holding table having a holding surface capable of holding a workpiece by suction, and an imaging unit positioned above the holding table and capable of imaging the workpiece held by the holding table, wherein the method for inspecting the holding table for the presence or absence of foreign matter on the holding surface is as follows: A distribution creation step to create a distribution of pixel brightness in each of a plurality of first images obtained by imaging one surface of a substrate held by suction on the holding surface with the imaging unit, A determination step of determining the presence or absence of foreign matter on the holding surface by comparing the brightness distribution of pixels in a second image pre-stored in the processing apparatus with the brightness distribution of pixels in each of the plurality of first images, A method for inspecting a holding table, characterized by comprising the following features.

4. A processing apparatus comprising a holding table having a holding surface capable of holding a workpiece by suction, and an imaging unit positioned above the holding table and capable of imaging the workpiece held by the holding table, wherein the method for inspecting the holding table for the presence or absence of foreign matter on the holding surface is as follows: A calculation step of calculating the average value of pixel brightness in a first image obtained by imaging a predetermined area on one surface of a substrate held by suction on the holding surface with the imaging unit, A determination step to determine the presence or absence of foreign matter on the holding surface by comparing the average value of pixel brightness in a second image obtained by imaging a predetermined area on one surface of another substrate having a size corresponding to the workpiece and being held by suction on the holding surface with the imaging unit, with the average value of brightness of a predetermined area of ​​the first substrate obtained in the calculation step, A method for inspecting a holding table, characterized by comprising the following features.

Images