JP7185510B2 - Center detection method - Google Patents

Description

The present invention relates to a center detection method.

In the edge trimming process, the chamfered portion on the outer periphery of the wafer is removed along the circumferential direction. In this edge trimming process, it is required to equalize the width (length in the radial direction) of the removed portion on the outer periphery of the wafer. Therefore, the center of the wafer is recognized and the deviation between the center of the wafer and the rotation axis of the holding table is corrected (see Patent Document 1).

Moreover, there is the following method for recognizing the center of the wafer (see Patent Documents 2 and 3). That is, at least three locations on the outer circumference of the wafer are imaged, and outer edge pixels, which are pixels indicating the outer edge of the wafer in each captured image, are found. Then, the center of the wafer is calculated from the coordinate values of the three peripheral edge pixels.
In this method, when finding the outer edge of the wafer, the captured image is binarized and the boundary between the black pixels and the white pixels is recognized as the outer edge pixel.

JP-A-2006-93333 Japanese Patent No. 5486405 JP 2015-102389 A

When the captured image is binarized, pixels are classified into black or white based on preset threshold values, so the outer peripheral edge of the wafer may be mistaken. In addition, when light is reflected at a portion near the outer edge of the wafer, this portion may appear whitish, and when a shadow forms outside the outer edge of the wafer, this portion may appear dark. These can be the cause of erroneous recognition of the outer edge of the wafer.

An object of the present invention is to prevent erroneous recognition of the outer peripheral edge of a wafer when detecting the center of the wafer.

A center detection method (this center detection method) of the present invention is a center detection method for detecting the center of a disk-shaped workpiece, and a surface defined by an X coordinate on the X axis and a Y coordinate on the Y axis is detected. a holding step of holding the disk-shaped work on a holding table having a rotating shaft, and an imaging means having an imaging element having a plurality of pixels arranged in parallel with the X-axis and the Y-axis. A positioning step of positioning the outer circumference of the plate-shaped work and acquiring an image of the outer circumference by imaging with an imaging means; A line sensor setting step of setting in an outer circumference image, and brightness and darkness output from each pixel of the line sensor in a state in which the pixels corresponding to the outer circumference of the disk-shaped work in the outer circumference image divide the line sensor into two equal parts. obtain a value, calculate the slope value of the brightness value distribution with respect to the X-axis as a reference slope value by the least squares method, and set a slope value that is less than the reference slope value and close to the reference slope value as a threshold value. a threshold value setting step, and while moving the line sensor toward the disk-shaped work one pixel at a time in the X-axis direction in the outer peripheral image, obtaining a light-dark value output from each pixel of the line sensor; a slope value calculation step of calculating a slope value with respect to the X-axis in the brightness value distribution by the square method; Calculate the average value of the minimum and maximum output brightness values, and obtain the coordinates of the pixels of the line sensor having brightness values closest to the average value as the coordinates of the outer periphery of the disk-shaped workpiece. A coordinate determination step, rotating the disk-shaped work, performing the inclination value calculation step and the outer peripheral coordinate determination step at least three times to acquire at least three outer peripheral coordinates, and to these three outer peripheral coordinates and a center coordinate calculation step of calculating the center coordinates of the disk-shaped work based on the above.

In this center detection method, in the slope value calculation step, the average value of the brightness values of a plurality of pixels surrounding each pixel forming the line sensor may be used as the brightness value output from each pixel forming the line sensor. good.

In this center detection method, in the line sensor setting step, a plurality of line sensors arranged in the Y-axis direction are set in the peripheral image, and in the inclination value calculation step, an inclination value is calculated for each of the plurality of line sensors. In the outer peripheral coordinate determination step, the outer peripheral coordinates of the disk-shaped work are acquired for each of the plurality of line sensors, and further, the distance from each outer peripheral coordinate to the coordinate of the rotation axis of the holding table is the first 1 distance is calculated, a group of peripheral coordinates to which the calculated first distance approximates is created, and any peripheral coordinate of the group to which the largest number of peripheral coordinates belong is determined as the peripheral coordinate of the disk-shaped work. may

In this center detection method, a line sensor extending in the X-axis direction is moved by one pixel in the X-axis direction, and each time the line sensor is moved, a brightness value output from each pixel of the line sensor is obtained; The outer peripheral coordinates of the disk-shaped workpiece are determined based on the inclination value with respect to the X-axis in the brightness value distribution. Therefore, in this center detection method, the coordinates of the circumference of the disk-shaped workpiece can be determined without binarizing the captured image. Therefore, it is possible to avoid erroneous recognition of the outer circumference of the disc-shaped workpiece due to an error in the binarization process.

In addition, by using the average value of the brightness values of a plurality of pixels surrounding this pixel as the brightness value of the pixel of the line sensor, the brightness value of the pixel of the line sensor deviates from the original value due to the influence of unnecessary light. can also suppress its impact.

In addition, by using a plurality of line sensors to determine the outer peripheral coordinates by majority vote, the brightness value of one line sensor may be erroneously detected due to the influence of unnecessary light, etc., resulting in the acquisition of erroneous outer peripheral coordinates. However, the impact can be reduced.

It is a perspective view showing a wafer according to the present embodiment. 2 is a cross-sectional view of the wafer shown in FIG. 1; FIG. 1 is a perspective view showing a cutting device for processing wafers; FIG. FIG. 4 is an explanatory diagram showing an embodiment of a positioning process; FIG. 4 is an explanatory diagram showing an example of an initial image obtained in a positioning process; FIG. 5 is an explanatory diagram showing an example of an outer circumference image obtained in a positioning process; 5 is a graph showing an example of the relationship between the position of each pixel of the line sensor and the brightness value output from each pixel; FIG. 10 is an explanatory diagram showing an example of movement of the line sensor in the slope value calculation process; 4 is a flow chart showing operations of a slope value calculation process and a peripheral coordinate determination process; 7 is a graph showing an example of a distribution of brightness values of a line sensor and a regression line when the line sensor is set at a position where all pixels of the line sensor are pixels corresponding to a frame; 4 is a graph showing an example of the distribution of light and dark values of a line sensor and a regression line when the line sensor is set at a position where many pixels of the line sensor are pixels corresponding to a wafer; 9 is a graph showing an example of the distribution of brightness values when it is determined that the slope value is equal to or greater than the threshold; FIG. 11 is an explanatory diagram showing a modified example regarding calculation of the brightness value of the line sensor; It is an explanatory view showing a modification using a plurality of line sensors. FIG. 15 is a graph showing the distribution of a plurality of peripheral coordinates obtained in the modified example of FIG. 14; FIG. It is explanatory drawing which shows a light quantity adjustment process.

A processing method (main processing method) according to the present embodiment is a method for processing a wafer, which is an example of a disk-shaped workpiece, and includes a center detection method for detecting the center of the wafer.

As shown in FIG. 1, the device D is formed on the front surface Wa of the disk-shaped wafer W. As shown in FIG. The back surface Wb of the wafer W does not have the device D and is a surface to be ground with a grinding wheel or the like.

As shown in FIG. 2, the edge WE of the wafer W is chamfered in an arc shape from the front surface Wa to the back surface Wb. 2, the devices D provided on the front surface Wa of the wafer W are omitted. Moreover, in this embodiment, the color of the wafer W is black.

In this processing method, the front surface Wa side of the edge WE of such a wafer W is removed (edge trimming processing). Therefore, in this processing method, a cutting device 1 as shown in FIG. 3 is used. As shown in FIG. 3, the cutting device 1 rotates and cuts the cutting blade 63 provided in the cutting unit 6 into the wafer W held on the holding surface 302 of the holding table 30 to perform edge trimming. It is a device that applies
The cutting device 1 includes a base 10 , a portal column 14 erected on the base 10 , and a controller 7 for controlling each member of the cutting device 1 .

An X-axis feeding means 11 is arranged on the base 10 . The X-axis direction feeding means 11 moves the holding table 30 along the cutting feeding direction (X-axis direction). The X-axis direction feeding means 11 includes a pair of guide rails 111 extending in the X-axis direction, an X-axis table 113 placed on the guide rails 111, a ball screw 110 extending parallel to the guide rails 111, and a motor for rotating the ball screw 110. 112 included.

A pair of guide rails 111 are arranged on the upper surface of the base 10 in parallel with the X-axis direction. The X-axis table 113 is installed on a pair of guide rails 111 so as to be slidable along these guide rails 111 . A holding unit 3 is placed on the X-axis table 113 .

The ball screw 110 is screwed into a nut portion (not shown) provided on the bottom side of the X-axis table 113 . The motor 112 is connected to one end of the ball screw 110 and drives the ball screw 110 to rotate. By rotationally driving the ball screw 110, the X-axis table 113 and the holding portion 3 move along the guide rail 111 along the X-axis direction, which is the feed direction for cutting.

The holding unit 3 has a holding table 30 that holds the wafer W thereon. The holding table 30 has a θ table 31 that is a rotating shaft that supports and rotates the holding table 30 .

The holding table 30 is a member for sucking and holding the wafer W shown in FIG. 1, and is formed in a disc shape. The holding table 30 includes a suction portion 300 containing a porous material and a white frame 301 supporting the suction portion 300 .

The suction unit 300 communicates with a suction source (not shown) and has a holding surface 302 that is an exposed surface. The holding surface 302 has a circular shape slightly smaller than the wafer W and is flush with the upper surface of the frame 301 . The suction unit 300 sucks and holds the wafer W with the holding surface 302 . In this embodiment, the upper surface of the frame 301 forming the surface of the holding table 30 and the position on the holding surface 302 are defined by the X coordinate on the X axis and the Y coordinate on the Y axis.

The holding table 30 is supported by a θ table 31 arranged on the bottom side of the holding table 30 . The θ table 31 is provided on the upper surface of the X-axis table 113 so as to be rotatable within the XY plane. Therefore, the θ table 31 can support the holding table 30 and rotate the holding table 30 within the XY plane.

A portal column 14 is erected on the rear side (−X direction side) of the base 10 so as to straddle the X-axis direction feeding means 11 . A cutting portion moving mechanism 13 for moving the cutting portion 6 is provided on the front surface (the surface on the +X direction side) of the portal column 14 . The cutting portion moving mechanism 13 feeds the cutting portion 6 in the Y-axis direction as well as in the Z-axis direction. The cutting part moving mechanism 13 includes a Y-axis direction moving means 12 for moving the cutting part 6 in the index feed direction (Y-axis direction) and a Z-axis direction movement means for moving the cutting part 6 in the cutting feed direction (Z-axis direction). Means 16 are provided.

The Y-axis direction moving means 12 is arranged on the front surface of the portal column 14 . The Y-axis direction moving means 12 reciprocates the Z-axis direction moving means 16 and the cutting portion 6 in the Y-axis direction. The Y-axis direction is a direction orthogonal to the holding surface direction (horizontal direction) with respect to the X-axis direction.

The Y-axis direction moving means 12 includes a pair of guide rails 121 extending in the Y-axis direction, a Y-axis table 123 placed on the guide rails 121, a ball screw 120 extending parallel to the guide rails 121, and a motor for rotating the ball screw 120. 122 included.

A pair of guide rails 121 are arranged in front of the portal column 14 in parallel with the Y-axis direction. The Y-axis table 123 is installed on a pair of guide rails 121 so as to be slidable along these guide rails 121 . The Z-axis moving means 16 and the cutting section 6 are mounted on the Y-axis table 123 .

The ball screw 120 is screwed into a nut portion (not shown) provided on the back side of the Y-axis table 123 . The motor 122 is connected to one end of the ball screw 120 and drives the ball screw 120 to rotate. By rotationally driving the ball screw 120, the Y-axis table 123, the Z-axis direction moving means 16, and the cutting portion 6 move along the guide rail 121 in the Y-axis direction, which is the index feed direction.

The Z-axis direction moving means 16 reciprocates the cutting portion 6 in the Z-axis direction (vertical direction). The Z-axis direction is a direction orthogonal to the X-axis direction and the Y-axis direction and orthogonal to the holding surface 302 of the holding table 30 .

The Z-axis direction moving means 16 includes a pair of guide rails 161 extending in the Z-axis direction, a support member 163 mounted on the guide rails 161, a ball screw 160 extending parallel to the guide rails 161, and a motor 162 for rotating the ball screw 160. contains.

A pair of guide rails 161 are arranged on the Y-axis table 123 in parallel with the Z-axis direction. The support member 163 is installed on a pair of guide rails 161 so as to be slidable along these guide rails 161 . A cutting part 6 is attached to the lower end of the support member 163 .

The ball screw 120 is screwed into a nut portion (not shown) provided on the back side of the support member 163 . The motor 162 is connected to one end of the ball screw 160 and drives the ball screw 160 to rotate. By rotationally driving the ball screw 160, the support member 163 and the cutting portion 6 move along the guide rail 161 in the Z-axis direction, which is the feed direction.

3, the cutting unit 6 includes a housing 61 provided at the lower end of the support member 163, a rotating shaft 60 extending in the Y-axis direction, a cutting blade 63 attached to the rotating shaft 60, and a motor (not shown) that drives the rotating shaft 60 .
Rotating shaft 60 is rotatably supported by housing 61 . The cutting blade 63 also rotates at high speed by rotating the rotary shaft 60 with the motor.

Furthermore, the cutting section 6 has an imaging means 65 on the front surface of the housing 61 . The imaging means 65 is attached to the front surface of the housing 61 . The imaging means 65 has an imaging element, and the imaging element has a plurality of pixels arranged in parallel with the X-axis and the Y-axis. The imaging means 65 is configured to take an image of an area below the imaging means 65 along the -Z-axis direction as an imaging area. The imaging area of the imaging means 65 can be set by the X-axis direction feeding means 11 , the cutting portion moving mechanism 13 and the θ table 31 . The imaging means 65 can image the wafer W placed on the holding surface 302 and its vicinity, for example. The image captured by the imaging means 65 is, for example, a 256-gradation grayscale image in this embodiment.

The control unit 7 has a memory 71 that stores various data and programs. The control unit 7 executes various processes and centrally controls each component of the cutting device 1 .
For example, the controller 7 receives detection results from various detectors (not shown). Furthermore, the control unit 7 controls the X-axis direction feeding means 11 (motor 112), the cutting portion moving mechanism 13 (motor 122 and motor 162), and the θ table 31 so that the cutting blade 63 of the cutting unit 6 cuts. The position of the wafer W and the imaging area of the imaging means 65 are determined. Further, the control unit 7 controls the motor of the cutting unit 6 to cut the wafer W, and controls the imaging unit 65 to capture an image of the imaging area.

The machining method using the cutting apparatus 1 shown in FIG. 3 will be described below.
(1) Holding Step In this step, the user places the wafer W on the holding surface 302 of the holding table 30 . Then, the control unit 7 controls a suction source (not shown) to transmit a suction force to the holding surface 302 , whereby the holding surface 302 holds the wafer W by suction. As described above, the positions on the upper surface of the frame 301 forming the surface of the holding table 30 and the holding surface 302 are defined by the X coordinate and the Y coordinate.

(2) Positioning process In this process, first, the control unit 7 controls the X-axis direction feeding means 11, the cutting part moving mechanism 13, and the θ table 31 so that the imaging area of the imaging means 65 as shown in FIG. is set so that the edge WE of the wafer W and the frame 301 of the holding table 30 are included in this area. After that, the control section 7 controls the imaging means 65 to capture an image of this imaging region. As a result, an initial image as shown in FIG. 5 is captured.

In this initial image, the upper left pixel FP corresponding to the frame 301 that is the background member is shown in white corresponding to the color of the frame 301 . On the other hand, the pixels WP from the upper right to the lower left corresponding to the wafer W are shown in black corresponding to the color of the wafer W. FIG. Furthermore, the gray pixels SP formed on the boundaries between the black pixels WP and the white pixels FP are shadows of the wafer W formed on the frame 301 . A white line formed in the black pixel WP is a boundary line B set in the imaging means 65 .

Next, the control unit 7 controls the X-axis direction feeding means 11, the cutting part moving mechanism 13, and the θ table 31 to set the imaging area of the imaging means 65 so that the boundary line B overlaps the gray pixel SP. Then, the imaging means 65 is controlled to take an image of this imaging area. As a result, an outer peripheral image including the edge WE of the wafer W and the frame 301 of the holding table 30 as shown in FIG. 6 is captured.

(3) Line sensor setting process In this process, the control unit 7 sets the line sensor LS on the peripheral image as shown in FIG. The line sensor LS is composed of, for example, a row of pixels arranged along the X-axis direction. The number of pixels forming the line sensor LS is less than half the number of pixels in the X-axis direction (the number of pixels in the peripheral image shown in FIG. 6 in the X-axis direction) in the imaging element (imaging area) of the imaging means 65. Yes, for example 20 pixels.

(4) Threshold setting step In this step, the control unit 7 sets the position of the line sensor LS on the outer circumference image to a position (reference position) such that pixels corresponding to the outer circumference of the wafer W bisect the line sensor LS. set to In this state, the control unit 7 acquires the brightness value output from each pixel of the line sensor LS.
Note that the reference position is obtained by obtaining the inclination value with respect to the X axis in the distribution of brightness values output from each pixel of the line sensor LS each time the line sensor LS is moved in the X-axis direction by one pixel, and the inclination value is maximized. It may be the position of the line sensor LS when it becomes.

When the line sensor LS is at the reference position, the left side of the line sensor LS is the pixel FP corresponding to the frame 301, the right side is the pixel WP corresponding to the wafer W, and the center is the gray pixel SP. Therefore, the relationship between each pixel of the line sensor LS and the brightness value output from each pixel fluctuates as shown in FIG. Then, the control unit 7 creates a regression line RL by the method of least squares, and calculates a reference tilt value θ0 which is a tilt value with respect to the X axis in the distribution of brightness values of the line sensor LS at the reference position.

Furthermore, the control unit 7 sets a threshold value that is less than the reference inclination value θ0 and is close to the reference inclination value θ0 or the reference inclination value θ0. The threshold is, for example, a value obtained by multiplying the reference tilt value θ0 by 0.8.
It should be noted that the threshold value is obtained by one line sensor on the peripheral image.
Also, one threshold may be used for at least three peripheral images obtained by imaging at least three locations, or a different threshold may be used for each peripheral image.

(5) Inclination Value Calculation Step and Periphery Coordinates Determination Step In the inclination value calculation step, the control unit 7 first determines the position of the line sensor LS on the perimeter image as shown in FIG. is the pixel FP corresponding to the frame 301 . After that, the control unit 7 moves the line sensor LS toward the pixel WP corresponding to the wafer W pixel by pixel in the X-axis direction on the peripheral image, as indicated by an arrow A in FIG.

Then, as shown in FIG. 9, the control unit 7 acquires the brightness value output from each pixel of the line sensor LS each time the line sensor LS is moved (S1). Further, the control unit 7 calculates the inclination value of the brightness value distribution with respect to the X-axis by the method of least squares (S2).

For example, when the line sensor LS is set at a position where all the pixels are pixels FP corresponding to the frame 301, the distribution of the brightness values of the line sensor LS and the regression line RL are as shown in FIG. It becomes a straight line substantially parallel to the X-axis.
On the other hand, when the line sensor LS is set to the right beyond the reference position, that is, when the line sensor LS is set at a position where many pixels are the pixels WP corresponding to the wafer W, the line sensor LS , and the regression line RL are shown in FIG.

Then, each time the control unit 7 calculates the tilt value, as shown in FIG. 9, the control unit 7 determines whether or not the calculated tilt value is equal to or greater than the threshold set in the threshold setting step (S3). . When the controller 7 determines that the calculated tilt value is less than the threshold value (S3; N), it returns to S1 to continue moving the line sensor LS and calculating the tilt value.

On the other hand, when the control unit 7 determines that the calculated tilt value is equal to or greater than the threshold value (S3; Y), the control unit 7 calculates the average value of the minimum and maximum brightness values output from each pixel of the line sensor LS. Calculate (S4). Then, the control unit 7 specifies a pixel having a brightness value closest to the calculated average value from among the pixels of the line sensor LS, and converts the coordinates of the pixel to the outer peripheral coordinates of the wafer W (the edge WE of the wafer W). (see FIG. 1)) (S5).

For example, when it is determined that the slope value is greater than or equal to the threshold value, a distribution of brightness values as shown in FIG. 12 is obtained. The control unit 7 calculates the average value of the brightness values by dividing the sum of the maximum value Bmax and the minimum value Bmin of the brightness values by two. Then, the control unit 7 specifies the pixel of the line sensor LS that outputs the brightness value closest to this average value from the X coordinate (Xe in FIG. 12) corresponding to the average value ((Bmax+minimum value Bmin)/2). do. Then, the control unit 7 specifies the X coordinate and the Y coordinate of the specified pixel based on the position of the line sensor LS in the imaging area, and acquires them as the outer peripheral coordinates of the wafer W. FIG.

(6) Center Coordinate Calculation Step Next, the control unit 7 controls the θ table 31 to rotate the wafer W together with the holding table 30 holding it by a predetermined angle. Then, the control unit 7 executes the above-described positioning process, line sensor setting process, threshold value setting process, inclination value calculation process, and outer peripheral coordinate determination process. In this way, the control unit 7 rotates the wafer W by a predetermined angle and performs the positioning process, the line sensor setting process, the threshold value setting process, the tilt value calculation process, and the outer peripheral coordinate determination process at least three times. That is, the control unit 7 acquires at least three peripheral images, and sets a threshold according to each peripheral image. After performing the slope value calculation step, the control unit 7 uses the set threshold value to perform the outer peripheral coordinate determination step. Thereby, the control unit 7 acquires the outer circumference coordinates of at least three locations. Then, the center coordinates of the wafer W are calculated based on the coordinates of the outer circumference of the wafer W at these three locations.

Any known method may be used as a method of calculating the center coordinates. For example, the control unit 7 creates two straight lines connecting two adjacent points in the three selected points, and obtains the perpendicular bisectors of these two straight lines. Then, the control unit 7 can calculate the center of the wafer W as the intersection of the two perpendicular bisectors.
After rotating the wafer W by a predetermined angle, the control unit 7 performs the positioning step, the line sensor setting step, the tilt value calculating step, and the outer peripheral coordinate determining step without performing the threshold value setting step. , at least three perimeter coordinates may be obtained. In this case, the controller 7 can use the threshold value set in the first threshold value setting step in the second and subsequent outer peripheral coordinate determination steps.

(7) Edge removal step In this step, the control unit 7 determines the amount of deviation between the center of the wafer W calculated in the center coordinate calculation step and the rotation axis that is the center of the holding table 30 (hereinafter referred to as the amount of center deviation). Ask. Then, the control unit 7 causes the rotating cutting blade 63 to cut the edge WE on the front surface Wa of the wafer W while rotating the holding table 30 by the θ table 31 shown in FIG.

At this time, the controller 7 moves the cutting blade 63 in the Y-axis direction based on the amount of center shift and the outer peripheral coordinates of the wafer W. As shown in FIG. Thereby, the control unit 7 can cut the edge WE of the wafer W from the center position of the wafer W with substantially the same width along the circumferential direction. For the position control of the cutting blade 63 according to the amount of center shift, a known method such as that described in Patent Document 1 can be used.
In this manner, the control unit 7 removes the front surface Wa side of the edge WE of the wafer W (edge trimming). The cutting blade 63 used has, for example, a flat cutting edge.

As described above, in this processing method, the line sensor LS extending in the X-axis direction is moved by one pixel in the X-axis direction. values, and furthermore, the slope value with respect to the X-axis in the brightness value distribution is calculated. Then, based on this tilt value, the outer peripheral coordinates, which are the coordinates of the edge WE of the wafer W, are determined. Therefore, in this processing method, the outer peripheral coordinates can be determined without binarizing the captured image. Therefore, erroneous recognition of the edge WE due to an error in the binarization process can be avoided.

Note that in the present embodiment, the brightness value output from each pixel forming the line sensor LS is acquired in the slope value calculation step. At this time, as shown in FIG. 13, the control unit 7 selects a plurality of pixels (for example, 20 pixels in the X-axis direction and 20 pixels in the Y-axis direction) surrounding each pixel constituting the line sensor LS. pixels) may be set. Then, the control unit 7 may use the average value of the brightness values of the plurality of pixels included in the pixel group PG as the brightness value output from each pixel.

In this regard, the brightness value of the pixels of the line sensor LS may deviate from the original value due to the influence of unnecessary light (unnecessary light) that irradiates the frame 301 and the wafer W from the outside. In the above configuration, since the average value of the brightness values of the pixel group surrounding the pixel is used, it is possible to suppress the influence of unnecessary light as described above.

Further, in the present embodiment, the controller 7 calculates the tilt value using one line sensor LS in the tilt value calculation step. Alternatively, as shown in FIG. 14, a plurality of (n number of) line sensors LS (LS1 to LSn) arranged with a shift in the Y-axis direction may be used.

In this case, in the slope value calculation process, the control unit 7 calculates the slope value for each of the plurality of line sensors LS. Then, in the outer peripheral coordinate determination step, the control unit 7 acquires the outer peripheral coordinates of the wafer W for each of the plurality of line sensors LS.

Furthermore, the control unit 7 calculates a first distance, which is the distance from the outer peripheral coordinates to the coordinates of the rotation axis, which is the center of the holding table 30, for each outer peripheral coordinate. Thereby, the first distance corresponding to each outer circumference coordinate is calculated. Then, the control unit 7 creates a group of peripheral coordinates such that the calculated first distances are approximate. That is, the control unit 7 divides the outer circumference coordinates into groups according to the first distance. Then, the control unit 7 determines one of the outer peripheral coordinates of the group to which the largest number of outer peripheral coordinates belong as the outer peripheral coordinates of the wafer W. FIG.

For example, in the example shown in FIG. 15, the outer coordinates are divided into a group G1 corresponding to a certain first distance D1 and a group G1 corresponding to a first distance D2 shorter than the first distance D1. In this example, the control unit 7 determines one of the outer peripheral coordinates belonging to the group G1 (one or more) as the outer peripheral coordinate of the wafer W. FIG.
In FIG. 15, the first distance of each outer coordinate is shown using the position of the line sensor LS (LS1 to LSn) in the Y-axis direction corresponding to each outer coordinate.

In this regard, as described above, due to the influence of unnecessary light illuminating the frame 301 and the wafer W, the brightness values of the pixels of the line sensor LS are erroneously detected, resulting in erroneous outer peripheral coordinates being determined. there is a possibility. In the method shown in FIG. 14, a plurality of line sensors LS are used to determine the outer peripheral coordinates by majority vote. It is possible to suppress the influence of unnecessary light as described above.

Moreover, in this embodiment, the wafer W shown in FIGS. 1 and 2 is used as the disk-shaped workpiece. Alternatively, a laminated substrate may be used as the disk-shaped work. The bonded substrate includes a disk-shaped support substrate and a wafer having a diameter smaller than that of the support substrate, which is bonded onto the support substrate. In this case, in this processing method, the coordinates of the periphery of the wafer of the bonded substrate can be obtained, and the coordinates of the center thereof can be calculated.

In this case, since the present processing method uses the gradient value in the distribution of the light and dark values of the line sensor LS, the outer peripheral edge of the support substrate, which has a color different from that of the wafer, can be distinguished from the outer peripheral edge of the wafer. . Therefore, similarly to the example shown in this embodiment, the outer peripheral edges of the wafers in the bonded substrate can be cut along the circumferential direction with substantially the same width from the center position of the wafers.

Further, in this embodiment, from the initial image shown in FIG. Set the line B to overlap the gray pixel SP. At this time, for example, the control unit 7 may superimpose the boundary line B on the gray pixel SP based on an instruction from the user who is visually observing the positions of the boundary line B and the pixel SP. Alternatively, the user may directly control the X-axis feeding means 11, the cutting portion moving mechanism 13, and the driving device of the θ table 31 so that the boundary line B overlaps the gray pixel SP.

Further, after the boundary line B is superimposed on the gray pixel SP, a light amount adjustment step of adjusting the light amount of the imaging means 65 may be performed. This step may be performed based on the result of visual observation by the user, or may be performed by the control section 7 .

For example, the control unit 7 stores a plurality of types (for example, 100 types) of light amount patterns in the memory 71 in advance. The light quantity pattern is distinguished, for example, by the ratio of epi-illumination and oblique illumination and the intensity of each illumination.

Then, as shown in FIG. 16, the control unit 7 sets the first light amount check area RA within the black pixel WP corresponding to the wafer W, and sets the second light amount check area within the white pixel FP corresponding to the frame 301. Set the region RB. Furthermore, the control unit 7 sets a first check area RC1 that is in contact with the boundary line B and includes the first light intensity check area RA. Similarly, the control unit 7 sets a second check area RC2 that is in contact with the boundary line B and includes the second light intensity check area RB. The size of the first check area RC1 and the second check area RC2 is, for example, 10×10 pixels.

The control unit 7 changes the first check area RC1 and the second check area RC along the boundary line B with respect to the light intensity pattern of one imaging unit 65, and displays a plurality of first check areas RC1 and second check areas RC2. Get the intensity value in the . The control unit 7 acquires such brightness values for a plurality of light intensity patterns. Then, the control unit 7 specifies a light amount pattern that maximizes the difference between the brightness value in the first check area RC1 and the brightness value in the second check area RC2, and uses this light amount pattern to perform imaging. Imaging is performed by means 65, and each step of the present processing method is performed.

According to this, since the difference between the brightness values on both sides of the boundary line B can be increased, the difference between the brightness values in each pixel of the line sensor LS can be increased in the threshold value setting process, the slope value calculation process, and the outer peripheral coordinate determination process. can be done. As a result, it is possible to increase the change in the slope value (the angle between the regression line RL and the X axis) according to the position of the line sensor LS in the brightness value distribution as shown in FIG. This makes it possible to improve the accuracy of comparison between the slope value and the threshold.

1: cutting device, 3: holding unit, 6: cutting unit, 7: control unit, 71: memory,
11: X-axis direction feeding means, 12: Y-axis direction moving means, 16: Z-axis direction moving means,
63: cutting blade, 65: imaging means,
30: holding table, 31: θ table,
300: adsorption part, 301: frame, 302: holding surface,
LS: line sensor,
W: wafer, WE: edge,

Claims (3)

A center detection method for detecting the center of a disk-shaped workpiece,
a holding step of holding the disk-shaped work on a holding table having a surface defined by the X coordinate on the X axis and the Y coordinate on the Y axis and having a rotating shaft;
An imaging means having an imaging element having a plurality of pixels arranged in parallel with the X-axis and the Y-axis is positioned on the outer circumference of the disk-shaped work, and the imaging means performs imaging to obtain an outer circumference image. process and
a line sensor setting step of setting a line sensor having a number of pixels less than half of a plurality of pixels aligned in the X-axis direction in the peripheral image;
With the pixels corresponding to the outer circumference of the disk-shaped work in the outer circumference image dividing the line sensor into two equal parts, the brightness value output from each pixel of the line sensor is obtained, and the brightness is calculated by the method of least squares. a threshold value setting step of calculating a slope value with respect to the X-axis in the value distribution as a reference slope value, and setting a slope value that is less than the reference slope value and close to the reference slope value as a threshold value;
While moving the line sensor toward the disk-shaped work one pixel at a time in the X-axis direction in the peripheral image, the brightness value output from each pixel of the line sensor is acquired, and the brightness value is obtained by the least squares method. a slope value calculation step of calculating a slope value with respect to the X-axis in the value distribution;
When the slope value calculated in the slope value calculation step is equal to or greater than the threshold value, the average value of the minimum value and the maximum value of the brightness values output from the pixels of the line sensor is calculated, and the average value is a peripheral coordinate determination step of acquiring the coordinates of the pixels of the line sensor having the closest brightness value as the peripheral coordinates of the disk-shaped work;
The disk-shaped workpiece is rotated, the inclination value calculating step and the outer peripheral coordinate determining step are performed at least three times to acquire at least three outer peripheral coordinates, and based on these three outer peripheral coordinates, the circle a center coordinate calculation step of calculating the center coordinates of the plate-shaped work;
A center detection method including. In the slope value calculating step, an average value of brightness values of a plurality of pixels surrounding each pixel constituting the line sensor is used as a brightness value output from each pixel constituting the line sensor;
The center detection method according to claim 1. In the line sensor setting step, a plurality of line sensors arranged in the Y-axis direction are set in the peripheral image;
In the slope value calculation step, a slope value is calculated for each of the plurality of line sensors,
In the peripheral coordinate determining step, the peripheral coordinates of the disk-shaped work are acquired for each of the plurality of line sensors, and a first distance, which is the distance from each peripheral coordinate to the coordinates of the rotation axis of the holding table, is calculated. calculating, creating a group of peripheral coordinates to which the calculated first distance is approximate, and determining any peripheral coordinate of the group to which the largest number of peripheral coordinates belong as the peripheral coordinates of the disk-shaped work;
3. The center detection method according to claim 1 or 2.

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