JP5486405B2 - Wafer center position detection method - Google Patents

Description

  The present invention relates to a method for determining the center position of a wafer.

  In recent years, with the thinning and miniaturization of electrical equipment, wafers are required to be thinner and, for example, ground to 100 μm or less. Conventionally, chamfering has been applied to the outer periphery of a wafer in order to prevent cracking and dust generation during the manufacturing process. Therefore, when the wafer is thinly ground, a chamfered portion on the outer periphery is formed in a knife edge shape (eave shape). If the chamfered portion on the outer periphery of the wafer is formed in a knife edge shape, there arises a problem that the wafer is damaged due to chipping from the outer periphery. In order to solve this problem, a method has been proposed in which the chamfered portion of the outer periphery of the wafer is previously removed by cutting in the circumferential direction with a cutting blade, and then the back surface of the wafer is ground (see, for example, Patent Document 1).

  When the outer peripheral portion of the semiconductor wafer is cut in the circumferential direction by the cutting blade, if the center of the semiconductor wafer and the center of rotation of the chuck table that is the holding means for the semiconductor wafer do not exactly coincide, The width of the cut part is not constant. However, when the semiconductor wafer is placed on the chuck table by the transfer device, generally, an error in positional accuracy of about ± 1 mm is inevitably generated. When such an error occurs, the semiconductor wafer is eccentrically rotated with respect to the chuck table when the outer peripheral portion of the semiconductor wafer is cut, so that the width of the portion to be cut in the outer peripheral portion is not constant. That is, there is a problem that a circle on the same distance from the center of the semiconductor wafer cannot be cut.

  Therefore, the three peripheral edges of the wafer placed on the chuck table are imaged by the imaging means, the center position of the wafer is calculated from the coordinate position of the three points, and the deviation amount between the center position of the wafer and the center position of the chuck table A method is adopted in which the cutting blade is moved so as to correct the deviation, and the wafer is cut in the circumferential direction at the same distance from the center position of the wafer (see, for example, Patent Document 2).

JP 2000-173961 A JP 2006-93333 A

  However, even if it is attempted to detect the outer peripheral edge of the wafer by the imaging means, an accurate edge is not always detected by image processing depending on the dirt on the chuck table, the remaining cutting water, or the state of the wafer. For this reason, if the processing position is obtained based on the calculated center position coordinates of the wafer, the processing position may be significantly shifted.

  The present invention has been made in view of the above points, and an object of the present invention is to detect the outer periphery of a wafer by image processing and calculate the center position of the wafer based on the result. It is an object to provide a wafer center position detection method capable of accurately detecting the wafer center position by avoiding erroneous calculation of the wafer center position due to the erroneous recognition.

The present invention provides a processing apparatus including a rotatable chuck table having a holding upper surface for holding a semiconductor wafer and an imaging unit for imaging the upper surface of the semiconductor wafer held on the holding upper surface of the chuck table. A wafer detection method for detecting a center position of a mounted semiconductor wafer, comprising: a wafer mounting step for mounting a wafer on a holding upper surface of a chuck table; and an arbitrary four or more N points on an outer peripheral edge of the wafer. An edge position coordinate detection step for detecting N edge position coordinates by imaging using an image pickup means, and obtaining a combination of three _N C ₃ edge position coordinates out of the _N edge position coordinates, for each combination. center position locus calculating the center position coordinates of the _N C ₃ ways to calculate the center position coordinates of the wafer based on the three-point edge position coordinates A calculation step, a determining step variation of the center position coordinates whether greater than a predetermined threshold value of the calculated _N C ₃ types of wafers, the _N C ₃ ways in the determination step of the center position coordinates A re-detection step of determining that any of the N edge position coordinates detected when the variation is larger than the threshold value is erroneously recognized and performing the edge position coordinate detection step again; In the determination step, when the variation in the _N C ₃ center position coordinates is smaller than the threshold value, it is determined that all the N edge position coordinates detected are normal, and the average of the _N C ₃ center position coordinates is determined. It consists of a center position coordinate at the time of machining and a center position coordinate determination step for determining the value.

  In the present invention, four or more position coordinates of the outer peripheral edge of the wafer are detected, all combinations of the three position coordinates are obtained from the detected position coordinate values of the plurality of outer peripheral edges, and the center position coordinates are calculated for each combination. The variation of the calculated center position coordinates is calculated, and when there is a variation of a predetermined threshold value or more, it is determined that the edge position coordinates are misrecognized, and the edge position coordinates are detected again. It is possible to prevent the wafer center position from being erroneously calculated due to erroneous recognition by processing, and to accurately detect the wafer center position.

It is explanatory drawing which shows an example of a structure of a cutting device typically. It is a front view which shows the state with which the wafer was hold | maintained at the chuck table. It is a flowchart which shows the method of calculating | requiring the center position coordinate of a wafer. It is a front view which shows the state which images the edge of a wafer. It is explanatory drawing which shows an example of the image at the time of edge detection. It is explanatory drawing which shows the example of a successful calculation of the center position coordinate of a wafer. It is explanatory drawing which shows the example of a failure of calculation of the center position coordinate of a wafer. It is a front view which shows the state which cuts the chamfer part of a wafer outer periphery. It is explanatory drawing which shows the eccentricity of the center of a wafer, and the center of a chuck table. It is explanatory drawing which shows the state which cuts the chamfer part of a wafer outer periphery in case there exists eccentricity of the center of a wafer and the center of a chuck table. It is sectional drawing which shows schematically the wafer by which the chamfered part was cut. It is explanatory drawing which shows the state which forms a recessed part in the back surface of a wafer.

  A cutting apparatus 1 shown in FIG. 1 is an example of a processing apparatus to which the present invention is applied. A chuck table 2 having a holding upper surface 20 that holds a semiconductor wafer 5 and a semiconductor held on the holding upper surface 20 of the chuck table 2. An imaging means 3 for imaging the upper surface of the wafer 5 and a cutting means 4 for cutting the wafer 5 held on the chuck table 2 are provided. The chuck table 2 is movable in the X direction, and the imaging means 3 and the cutting means 4 are movable in the Y direction and the Z direction (direction perpendicular to the paper surface in FIG. 1). The imaging unit 3 and the cutting unit are integrally formed, and are configured to move in the Y direction and the Z direction in conjunction with each other.

  The cutting means 4 is configured by attaching a cutting blade 41 to the tip of a spindle 40 having an axis in the Y direction. The imaging means 3 includes an objective lens 30 that faces the wafer 5 held on the chuck table 2, and a reference line 30 a is formed on the objective lens 30. The reference line 30a is located on the extension line of the cutting blade 41 in the X direction.

  An X scale 21 for recognizing the position of the chuck table 2 in the X direction is disposed in the X direction, which is the moving direction of the chuck table 2, and the imaging means 3 and the cutting means 4 in the moving direction of the imaging means 3 and the cutting means 4. A Y scale 42 for recognizing the position of the means 4 in the Y direction is provided. The chuck table 2 is provided with a sensor 22 for reading the distance from the origin X0 of the X scale 21, and the cutting means 4 is provided with a sensor 43 for reading the distance of the Y scale 42 from the origin Y0. Has been.

  The operations of the chuck table 2, the imaging unit 3 and the cutting unit 4 are controlled by the control unit 6. The value read by the sensor 22 is recognized by the control means 6 as the X coordinate of the chuck table 2, and the value read by the sensor 43 is recognized as the Y coordinate of the imaging means 3 and the cutting means 4. The control means 6 can store information necessary for control in the storage means 7 and can read and use it as necessary.

  In the following, a method for detecting the center position of the wafer 5 shown in FIG. 2 will be described with reference to the flowchart shown in FIG. The wafer 5 shown in FIG. 2 has a top surface 50 as a device formation surface. A chamfering process is performed on the outer periphery of the wafer 5 to form a chamfered portion 51, and an outermost peripheral portion of the chamfered portion 51 formed in the largest diameter is an edge 52. The wafer 5 is placed on the holding upper surface 20 of the chuck table 2 and sucked and held (wafer placing step). In the present embodiment, the wafer 5 is held on the chuck table 2 with the upper surface 50 of the wafer 5 exposed upward.

  Next, the position coordinates of any four points on the edge 52 of the wafer 5 are obtained. As shown in FIG. 4, the vicinity of the edge 52 is imaged from above by the imaging means 4. Then, for example, an image 8 shown in FIG. 5 is acquired. Here, in the image 8, the light quantity of the image pickup means 4 is adjusted so that the wafer 5 is black and the surrounding chuck table 2 is white and the contrast becomes clear.

  Imaging is performed while appropriately fine-adjusting the position of the chuck table 2 in the X direction and the position of the imaging means 3 in the Y direction, and as shown in FIG. 5, the first location of the edge 52 at the center of the objective lens 30 of the imaging means 3 When E1 is imaged, the control means 6 detects the first location by image processing (known various edge detection methods) such as recognizing a portion in the image information where the pixel value has changed by a certain threshold value or more as an edge. Edge E1 is detected. Since the chamfered portion 51 is formed on the wafer 5, the contrast between the edge 52 and the chuck table 2 around the edge 52 is not clearly shown, and is affected by the state of the holding upper surface 20 of the chuck table 2. False recognition is likely to occur during edge recognition. Image 8 in FIG. 5 shows an example in which the boundary 53 between the upper surface 50 and the chamfered portion 51 is erroneously recognized as an edge. The control means 6 reads the values of the X scale 21 and the Y scale 42 read by the sensors 22 and 43 shown in FIG. 1 when the edge is recognized, and uses the value of the X scale 21 as the X coordinate of the first location E1, Y The value of the scale 42 is stored in the storage means 7 as the Y coordinate of the first location E1.

  While moving the chuck table 2 in the X direction and moving the imaging means 3 in the Y direction, coordinates are similarly obtained for the other three edges E2, E3, and E4 of the edge 52 shown in FIG. The coordinates of E1, E2, E3, and E4 are (X1, Y1), (X2, Y2), (X3, Y3), and (X4, Y4), respectively. The value of each coordinate is memorize | stored in the memory | storage means 7 by the control means 6 (edge position coordinate detection step). Note that the number of locations for obtaining coordinates may be any number as long as it is four or more.

Next, the control means 6 selects three from E1 to E4 and obtains all the combinations, that is, ₄ C _three combinations. When the number of locations for which coordinates are obtained is n, _n C _three combinations are obtained. In the present embodiment, four combinations of E1-E2-E3, E1-E2-E4, E2-E3-E4, and E1-E3-E4 are obtained. Then, each of these four combinations is a triangle, and the center of the circumscribed circle of each triangle is obtained. Specifically, the coordinates of the following four points are obtained (center position coordinate calculation step).
The center O ₁ (a ₁ , b ₁ ) of the circumscribed circle of the triangle E1-E2-E3,
The center O ₂ (a ₂ , b ₂ ) of the circumscribed circle of the triangle E1-E2-E4
The center O ₃ (a ₃ , b ₃ ) of the circumscribed circle of the triangle E2-E3-E4,
The center O ₄ (a ₄ , b ₄ ) of the circumscribed circle of the triangle E1-E3-E4

For example, the coordinates (a ₁ , b ₁ ) of O ₁ can be obtained by the following (Expression 1) and (Expression 2), respectively. The X coordinate and Y coordinate of O ₂ , O ₃ , and O ₄ can be similarly obtained.

If the coordinates (X1, Y1), (X2, Y2), (X3, Y3), (X4, Y4) of E1, E2, E3, and E4 are accurately determined without error, the above O ₁ , O ₂ , O ₃ , and O ₄ should match, but an error may actually occur. Therefore, the variation in the positions of O _{1 to} O ₄ is obtained, and it is determined whether or not the obtained variation is larger than a predetermined threshold value. (Judgment step). The predetermined threshold value is determined based on an allowable value of eccentricity at the time of wafer processing performed later, and is stored in the storage unit 7.

O ₁ variation in the position of the ~ O _{4 is,} O 1 the distance between two points in all combinations of two points among the four points of the ~ O _{4, i.e., O 1 -O 2, O 1} -O 3, O It obtains all _{1 -O 4, O 2 -O 3} , O 2 -O 4, O 3 -O 4 distance d1~d6 from the coordinate values, smaller than d1~d6 all predetermined threshold, E1 to E4 It is determined that the position coordinate detection is normal. That is, if O1 to O4 are included in the circle Aum indicating the threshold shown in FIG. 6, it is determined that the coordinates of E1 to E4 are within the allowable range even if there is an error. Note that it is also possible to determine whether the position coordinate detection of E1 to E4 is normal based on whether the standard deviation is within a predetermined range, not the distance between the two points.

_{Meanwhile, O 1 -O 2, O 1} -O 3, O 1 -O 4, O 2 -O 3, O 2 -O 4, of the O 3 Distance -O ₄ d1 to d6, the threshold even one If there is an excess, as shown in FIG. 7, any one of O _{1 to} O ₄ is located outside the circle Aum, so that it is erroneously recognized as one of the four edges E1 to E4. Therefore, it is determined that the obtained center position of the wafer has an error exceeding the allowable range. That is, since there is a high possibility of erroneous recognition at the edge recognition stage, in this case, the edge position coordinate detection step, the center position coordinate calculation step, and the determination step are performed again (redetection step).

When the distances d1 to d6 of O ₁ -O ₂ , O ₁ -O ₃ , O ₁ -O ₄ , O ₂ -O ₃ , O ₂ -O ₄ , and O ₃ -O ₄ are all within a predetermined allowable value , O _{1 to} O ₄ are averaged with respect to the X and Y coordinates, and the average value Ow (Xw, Yw) is determined as the rotation center position coordinate at the time of subsequent processing (center position coordinate determination step).

  As described above, in the edge position coordinate detection step, four or more position coordinates of the outer peripheral edge of the wafer are detected, and in the center position coordinate calculation step, all combinations of the three position coordinates are detected from the detected position coordinate values of the plurality of edges. Find the center position coordinates for each combination, calculate the variation of the calculated center position coordinates, and if there is a variation greater than a predetermined threshold in the determination step, there is an erroneous recognition of the edge position coordinates Since the determination is performed and the edge position coordinates are detected again, the wafer center position can be prevented from being erroneously calculated due to erroneous recognition by image processing, and the wafer center position can be accurately detected.

  In the center position coordinate calculation step, the center of the circumscribed circle of the four triangles is obtained, and in the determination step, it is determined whether the variation in the position is within a predetermined range. The radius of the circle may be obtained, and it may be determined whether or not there is an erroneous recognition of the edge depending on whether the variation in the length of each radius is within a predetermined range. The predetermined threshold value at that time is determined based on, for example, tolerance such as SEMI standard of the outer diameter of the wafer (0.5 mm in diameter for an 8-inch wafer) and stored in the storage means 7.

  Next, a case where the chamfered portion 51 of the wafer 5 is removed using the obtained coordinate information of the center Ow (Xw, Yw) of the wafer 5 will be described. As shown in FIG. 8, the wafer 5 is held as it is on the chuck table 2 in the holding state of the wafer 5 when O1 to O4 are obtained. On the other hand, in the cutting means 3, a cutting blade 41 having a blade thickness (for example, 2 to 3 mm) substantially equal to the chamfered portion 51 of the wafer 5 is mounted on the spindle 40.

  Then, while rotating the chuck table 2, the cutting blade 41 is positioned at a position displaced from the Ow (Xw, Yw) by the radius of the wafer W in the Y direction, and the cutting blade 41 is lowered while rotating, as shown in FIG. Then, the chamfered portion 51 of the wafer 5 is shaved to a predetermined thickness from the upper surface 50 side in the circumferential direction. At this time, if there is an eccentricity between the rotation center Oc (Xc, Yc) of the chuck table 2 and the center Ow (Xw, Yw) of the wafer 5 as shown in FIG. Cutting is performed while moving 41 in the Y direction, and control is performed so that the distance from the center Ow of the wafer 5 to the cutting position of the cutting blade 41 is always constant. Specifically, the control is performed as follows.

  The eccentricity between the rotation center Oc (Xc, Yc) of the chuck table 2 and the center Ow (Xw, Yw) of the wafer 5 is constituted by the eccentric distance d and the eccentric angle φ shown in FIG. A method for obtaining the eccentric distance d and the eccentric distance φ will be described below. The eccentric distance d is a linear distance on the XY plane between the center Ow (Xw, Yw) of the wafer 5 and the rotation center Oc (Xc, Yc) of the chuck table 2, and the eccentric angle φ is This is an angle formed by a line segment connecting the center Ow (Xw, Yw) and the rotation center Oc (Xc, Yc) of the chuck table 2 with the X axis on the XY plane.

  For the eccentric distance d and the eccentric angle φ, the coordinates (Xw, Yw) of the center position Ow of the wafer 5 and the coordinates (Xc, Yc) of the rotation center Oc of the chuck table 2 are expressed by the following (Expression 3) and (Expression 4). Each is calculated by substitution.

  At the time of cutting, the chamfered portion 51 is cut in the circumferential direction by rotating the chuck table 2 once and cutting the cutting edge of the cutting blade 41 into the chamfered portion 51 of the wafer 5. At this time, even if the eccentricity is present, cutting is performed while moving the cutting blade 41 in the Y-axis direction so that the distance from the center Ow (Xw, Yw) of the wafer 5 to the cutting position of the cutting blade 41 is always constant. I do.

  Specifically, the position Yb in the Y-axis direction of the cutting blade 41 shown in FIG. 10 (the Y coordinate of the position B where the cutting edge of the cutting blade 41 cuts into the wafer 5) is expressed by the following (formula 5). , Cutting is performed while moving the cutting blade 22 in the Y-axis direction.

  In the above (Expression 5), r is a finished radius r inside the wafer 5 after removing the chamfered portion shown in FIG. The calculation method of (Formula 5) is as described in JP-A-2006-93333.

  As described above, by obtaining the center Ow (Xw, Yw) of the wafer 5 and performing cutting in consideration of the eccentricity between the Ow and the rotation center Oc (Xc, Yc) of the chuck table 2, The chamfered portion 51 can be removed with a constant cutting width in the circumferential direction.

  When the chamfered portion 51 is scraped off from the upper surface 50 side in this way, even if the back surface is ground and thinned later, the outer peripheral portion does not become a sharp shape, so that no chipping occurs from the outer periphery of the wafer 5.

  The technique for obtaining the center position of the wafer described above can also be used when the recess 90a is formed by grinding the back surface 90 while leaving the peripheral edge 9a of the wafer 9 as shown in FIG. Such grinding is performed in order to facilitate handling such as conveyance of the wafer 9 after back grinding.

  The wafer 9 is sucked and held by the holding upper surface 20 of the chuck table 2. A grinding means 10 is disposed above the chuck table 2. The grinding means 10 is configured by attaching a grinding wheel 101 to the lower end of a spindle 100 having a vertical axis, and the grinding wheel 101 includes a plurality of grinding wheels 101a fixed in an annular shape. ing.

  When the back surface 90 of the wafer 9 is ground, control is performed so that the rotation trajectory of the grinding wheel 101 a passes through the center of the wafer 9. The radius of the rotation trajectory of the grinding wheel 101a is slightly larger than the radius of the recess 90a. Since the center of the wafer 9 can be obtained by the same method as described above, it is possible to control the rotation trajectory of the grinding wheel 101 a so as to always pass through the center of the wafer 9.

1: Cutting device 2: Chuck table 20: Holding upper surface 21: X scale 22: Sensor 3: Imaging means 30: Objective lens 30a: Reference line 4: Cutting means 40: Spindle 41: Cutting blade 42: Y scale 43: Sensor 5 : Wafer 50: Upper surface 51: Chamfered portion 52: Edge 53: Boundary 6: Control means 7: Storage means 8: Image 9: Wafer 9a: Peripheral portion 90: Back surface 90a: Concave portion 10: Grinding means 100: Spindle 101: Grinding wheel 101a: grinding wheel

Claims (1)

In a processing apparatus comprising a rotatable chuck table having a holding upper surface for holding a semiconductor wafer and imaging means for imaging the upper surface of the semiconductor wafer held on the holding upper surface of the chuck table, the processing device is mounted on the holding upper surface. A wafer detection method for detecting the center position of the placed semiconductor wafer,
A wafer mounting step of mounting the wafer on the holding upper surface of the chuck table;
An edge position coordinate detection step of imaging any four or more N locations on the outer peripheral edge of the wafer with the imaging means, and detecting the N edge position coordinates by image processing;
Seeking a combination of _N C ₃ types of edge coordinates three points out of the N pieces of the edge position coordinates, the center position coordinates of the wafer based on the edge position coordinates three points was calculated for each combination, _N C A center position coordinate calculating step for calculating _three kinds of center position coordinates;
A determination step of determining whether or not the calculated variation in the center position coordinates of the _N C ₃ wafers is greater than a predetermined threshold;
If it is determined in the determination step that the variation in the _N C ₃ center position coordinates is larger than the threshold value, one of the detected N edge position coordinates is erroneously recognized. A re-detection step of determining that the edge position coordinates are detected again,
When the variation of the _N C ₃ center position coordinates is smaller than the threshold value in the determination step, it is determined that all the detected N edge position coordinates are normal, and the _N C ₃ A center position coordinate determining step for determining an average value of the center position coordinates as a center position coordinate at the time of machining;
A wafer center position detection method comprising:

Images