Correction Rate Calculation Method

Abstract

To grind a sectional shape of a wafer into a prescribed sectional shape within less time.SOLUTION: A correction factor calculation method comprises: a first trial grinding step of grinding a wafer 41; a first sectional shape recognition step of measuring thicknesses of the ground wafer 41 at three places and recognizing a first sectional shape of the wafer 41; an inclination changing step of changing inclination at a first value 81 so that a sectional shape of a next wafer 41 can be a finish sectional shape; a second trial grinding step of grinding the wafer 41 held on a holding surface 200 changed in the inclination changing step; a second sectional recognition step of measuring the thicknesses of the wafer 41 ground in the second trial grinding step at the three places and recognizing a second sectional shape of the wafer 41; and an inclination change correction factor calculation step of calculating an inclination change correction factor from an inclination change correction factor=the first value / (the first value-the second value) so that a sectional shape of a next ground wafer can be the finish sectional shape.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a correction factor calculation method. [Background technology]

[0002] A grinding machine uses an annular grinding wheel to grind a wafer held on the holding surface of a chuck table. The grinding machine grinds the wafer by bringing the underside of the grinding wheel into contact with the radius of the wafer. For example, to make the thickness of the ground wafer uniform, the tilt of the chuck table is adjusted so that the underside of the grinding wheel and the radius of the holding surface are parallel.

[0003] Therefore, in the grinding device, as disclosed in Patent Documents 1 and 2, the lengths of two of the at least three support pillars that support the chuck table are configured to be extendable, and the inclination of the holding surface is adjusted by changing the length of the support pillars. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-264913 [Patent Document 2] Patent No. 5788304 Summary of the Invention [Problem to be solved by the invention]

[0005] However, if the grinding wheel itself is changed or grinding conditions such as the grinding feed rate and rotation speed of the grinding wheel are changed, the thickness of the wafer will no longer be uniform if the tilt of the holding surface is maintained. In other words, even with the same type of grinding wheel, the bond hardness and abrasive grain concentration are slightly different. Therefore, when the grinding wheel is changed, the vertical load applied to the wafer also changes. Furthermore, changing the grinding conditions also changes the vertical load applied to the wafer. In this way, if the vertical load applied to the wafer changes when grinding the wafer to a specified thickness, the parallelism between the bottom surface of the grinding wheel and the holding surface changes. Therefore, when the grinding wheel or grinding conditions are changed, it is difficult to achieve a uniform thickness in the ground wafer if the inclination of the holding surface is maintained.

[0006] Therefore, in the technology disclosed in Patent Document 1, the thickness of the ground wafer is measured and the tilt of the holding surface is corrected, and then the wafer is ground again, the wafer thickness is measured, the tilt of the holding surface is corrected again, and the wafer is ground again. In this way, with this technology, the grinding process, wafer thickness measurement, and tilt correction of the holding surface are repeated many times to make the wafers have a uniform thickness. Therefore, it takes a lot of time to make the wafers have a uniform thickness. In addition, in the technology disclosed in Patent Document 2, the thickness of the wafer being ground is measured along the radial direction before the wafer reaches a predetermined thickness, and the tilt of the chuck table is corrected. The remaining grinding is then performed to grind the wafer to the predetermined thickness. However, the grinding load applied to the support columns during grinding before measuring the wafer's thickness along the radial direction is different from the grinding load applied to the support columns during grinding until the wafer reaches the predetermined thickness after the tilt is corrected. This makes it difficult to correct the tilt of the holding surface and achieve a uniform in-plane thickness (uniform cross-sectional shape) of the wafer before grinding to the predetermined thickness. Therefore, to achieve a uniform wafer thickness, the wafer must be ground again to correct the tilt of the holding surface, which takes a lot of time.

[0007] Therefore, there is a problem of grinding the wafer into a predetermined cross-sectional shape in a short time. [Means for solving the problem]

[0008] The correction factor calculation method of the present invention is a method for calculating a correction factor in wafer grinding using a grinding device comprising: a chuck table that holds a wafer by a holding surface; a grinding mechanism that grinds the wafer by the underside of an annular grinding wheel disposed at the tip of a spindle; and an inclination change mechanism that changes the inclination of the holding surface relative to the underside of the grinding wheel, wherein the underside of the grinding wheel is brought into contact with a radial portion of the wafer held on the holding surface to grind the wafer, the method comprising: a first test grinding step in which the wafer held on the holding surface is ground by the grinding wheel; and a first cross-sectional shape recognition step in which thicknesses of the wafer ground in the first test grinding step are measured at three locations: the center, the outer periphery, and an intermediate point between the center and the outer periphery, to recognize a first cross-sectional shape of the wafer. the first cross-sectional shape recognized in the first cross-sectional shape recognition step; Finished cross-sectional shape From the difference with a tilt changing step of acquiring a first value based on the first cross-sectional shape and changing the tilt of the holding surface using the first value; a second test grinding step of grinding the wafer held on the holding surface of the chuck table having the tilt changed in the tilt changing step with the grinding wheel; and a second cross-sectional shape recognition step of measuring the thicknesses of the three locations of the wafer ground in the second test grinding step and recognizing a second cross-sectional shape of the wafer. the second cross-sectional shape recognized in the second cross-sectional shape recognition step; The finished cross-sectional shape From the difference with The method further includes a tilt change correction factor calculation step of obtaining a second value based on the second cross-sectional shape, and using the second value and the first value to calculate a tilt change correction factor from the following formula: tilt change correction factor = first value / (first value - second value). Furthermore, the wafer grinding method of the present invention is a wafer grinding method that uses the above-mentioned correction factor calculation method to grind a wafer by bringing the lower surface of the grinding wheel into contact with a radial portion of the wafer held on the holding surface, and includes a tilting step of tilting the holding surface by an angle corresponding to a value obtained by multiplying the first value obtained in the tilt changing step by the tilt change correction factor calculated in the tilt change correction factor calculation step, and a grinding step of grinding the wafer held on the holding surface tilted in the tilting step to a predetermined thickness by the grinding wheel. [Effects of the Invention]

[0009] In the correction factor calculation method of the present invention, two trial grinding steps, a first trial grinding step and a subsequent second trial grinding step after changing the tilt, are performed using a grinding mechanism to calculate a tilt change correction factor for obtaining a good tilt of the holding surface. Then, when grinding a similar wafer under the same grinding conditions, the tilt change correction factor is used to change the tilt of the holding surface of the chuck table. This allows the wafer to be ground to a finished cross-sectional shape. In this way, with the correction factor calculation method of the present invention, the wafer can be ground to the finished cross-sectional shape after two trial grindings, which means that the wafer can be ground to the finished cross-sectional shape in a shorter total time than with conventional techniques that require repeated grinding and tilt correction of the holding surface. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 2 is a perspective view illustrating the entire grinding device. [Figure 2] FIG. 3 is a cross-sectional view showing a first grinding mechanism, a chuck table, and a third thickness measurement unit. [Figure 3] FIG. 2 is a cross-sectional view of the chuck table. [Figure 4] FIG. 1A is a plan view of the chuck table, and FIG. 1B is an explanatory diagram of the tilt angle. [Figure 5] FIG. 2 is a cross-sectional view of a wafer. [Figure 6] FIG. 2 is a cross-sectional view showing a first grinding mechanism and a wafer held on a chuck table. [Figure 7] FIG. 10 is a cross-sectional view showing a third thickness measurement unit and a wafer. [Figure 8] FIG. 2 is a cross-sectional view showing a first grinding mechanism and a wafer held on a chuck table. [Figure 9] FIG. 10 is a cross-sectional view showing a third thickness measurement unit and a wafer. [Figure 10] FIG. 2 is a cross-sectional view showing a first grinding mechanism and a wafer held on a chuck table. [Figure 11] FIG. 10 is a cross-sectional view of the wafer after the first test grinding. [Figure 12] FIG. 10 is a cross-sectional view showing a wafer after first trial grinding and a wafer having a finished cross-sectional shape superimposed on each other. [Figure 13] FIG. 10 is a cross-sectional view of the wafer after the second test grinding. [Figure 14] FIG. 10 is a cross-sectional view showing a wafer after second trial grinding and a wafer having a finished cross-sectional shape superimposed on each other. DETAILED DESCRIPTION OF THE INVENTION

[0011] 1 holds wafers 41 on holding surfaces 200 of a plurality of chuck tables 2, and grinds the wafers 41 using a first grinding mechanism 31 and a second grinding mechanism 32. The wafers 41 are, for example, disk-shaped semiconductor wafers. As shown in FIG. 1, the grinding device 1 includes a base 10 extending in the Y-axis direction.

[0012] A first cassette 701 is disposed on the −Y direction side and the +X direction side of the base 10. The first cassette 701 has a plurality of shelves (not shown) for storing wafers 41. Each shelf of the first cassette 701 stores, for example, unprocessed wafers 41. A second cassette 702 is disposed on the −X direction side of the first cassette 701. The second cassette 702 also has a plurality of shelves (not shown) for storing wafers 41. The second cassette 702 stores, for example, processed wafers 41.

[0013] A robot 71 is disposed on the +Y side of the first cassette 701. A temporary placement area 720 where unprocessed wafers 41 are temporarily placed is provided on the +X side of the movable range of the robot 71. A cleaning mechanism 73 that cleans the processed wafers 41 is disposed on the -X side of the movable range of the robot 71.

[0014] The robot 71 takes out the wafers 41 stored in the first cassette 701 and transports them to the temporary storage area 720. The robot 71 also stores the processed wafers 41 from the cleaning mechanism 73 into the second cassette 702.

[0015] An alignment mechanism 72 is disposed in the temporary placement area 720. The alignment mechanism 72 aligns the wafer 41 that is carried out from the first cassette 701 and placed in the temporary placement area 720.

[0016] A turntable 5 is disposed on the +Y direction side of the temporary placement area 720. Three chuck tables 2 are disposed on the turntable 5 in the circumferential direction at intervals of 120 degrees around the center of the turntable 5. Each chuck table 2 is supported by the turntable 5 so as to be able to revolve.

[0017] The turntable 5 is connected to a turntable rotation mechanism (not shown) and is rotatable around a rotation axis in the Z-axis direction that passes through the center of the turntable 5. By rotating the turntable 5, each chuck table 2 is positioned below the first transport mechanism 741, below the first grinding mechanism 31, and below the second grinding mechanism 32.

[0018] Each chuck table 2 includes a disk-shaped suction portion 20 and a frame 21 that supports the suction portion 20. The holding surface 200 of the chuck table 2 is formed in the shape of a cone with its center 201 as its apex. The upper surface of the suction portion 20 is the holding surface 200 on which the wafer 41 is held, and the upper surface 210 of the frame 21 is formed flush with the holding surface 200.

[0019] A suction source (not shown) is connected to the holding surface 200. When the suction source is activated while the wafer 41 is placed on the holding surface 200, the chuck table 2 suction-holds the wafer 41 with the holding surface 200.

[0020] A first transport mechanism 741 is disposed at a position adjacent to the temporary placement area 720. The first transport mechanism 741 transports the wafer 41, which has been aligned to a predetermined position by the alignment mechanism 72, to the holding surface 200 of the chuck table 2, which is disposed near the alignment mechanism 72.

[0021] A second transfer mechanism 742 is disposed on the −X direction side of the first transfer mechanism 741. The second transfer mechanism 742 transfers the ground wafer 41 from the holding surface 200 of the chuck table 2 to the cleaning mechanism 73.

[0022] A first column 11 is erected on the +Y direction side and +X direction side of the base 10, and a second column 12 is erected on the −X direction side of the first column 11.

[0023] A first grinding mechanism 31 is disposed on a side surface of the first column 11 on the -Y direction side, and a second grinding mechanism 32 is disposed on a side surface of the second column 12 on the -Y direction side. The first grinding mechanism 31 is, for example, a rough grinding mechanism that roughly grinds the wafers 41, and the second grinding mechanism 32 is, for example, a finish grinding mechanism that finish grinds the wafers 41.

[0024] As shown in FIG. 2 , the first grinding mechanism 31 includes a spindle 39 having a first rotation axis 351 in the Z-axis direction, a housing 33 that rotatably supports the spindle 39, a spindle motor 30 connected to the upper end of the spindle 39 and rotating the spindle 39, a mount 38 fixed to the lower end of the spindle 39, and a first grinding wheel 341 disposed at the tip of the spindle 39 via the mount 38. A grinding wheel 34 is attached to the mount 38. The grinding wheel 34 includes a base 37 and a plurality of first grinding wheels 341 each having a substantially rectangular parallelepiped shape and arranged in a ring shape on the lower surface of the base 37. A lower surface 343 of the first grinding wheel 341 is a grinding surface that contacts the wafer 41. The first grinding wheel 341 is, for example, a rough grinding wheel.

[0025] 1, the first grinding mechanism 31 includes an elevating mechanism 36 for raising and lowering the grinding wheel 34. The elevating mechanism 36 includes a ball screw 360 having a rotation axis in the Z-axis direction, a guide rail 361 disposed parallel to the ball screw 360, a Z-axis motor 362 connected to the ball screw 360 and rotating the ball screw 360, and an elevating plate 363 whose internal nut is threaded onto the ball screw 360 and whose side is in sliding contact with the guide rail 361.

[0026] In the first grinding mechanism 31, as the ball screw 360 is driven by the Z-axis motor 362 to rotate, the lifting plate 363 moves up and down in the Z-axis direction while being guided by the guide rails 361. When the lifting plate 363 moves up and down in the Z-axis direction, the housing 33 moves up and down. At the same time, the spindle 39 supported by the housing 33 and the grinding wheel 34 attached to the tip of the spindle 39 via a mount 38 move up and down in the Z-axis direction.

[0027] The second grinding mechanism 32 has a configuration similar to that of the first grinding mechanism 31. However, the spindle 39 provided in the second grinding mechanism 32 has a second rotation axis 352 in the Z-axis direction different from the first rotation axis 351. The second grinding mechanism 32 also has a second grinding wheel 342 different from the first grinding wheel 341 provided in the first grinding mechanism 31. The second grinding wheel 342 is, for example, a finish grinding wheel.

[0028] The grinding apparatus 1 includes a contact-type first thickness measurement unit 91 disposed on the +X direction side of the base 10. The first thickness measurement unit 91 is disposed near the first grinding mechanism 31. The first thickness measurement unit 91 includes a holding surface height gauge 98 that measures the height of the holding surface 200 of the chuck table 2, and an upper surface height gauge 99 that measures the height of the upper surface 410 of the wafer 41.

[0029] In the first thickness measurement unit 91, with the wafer 41 held on the holding surface 200 of the chuck table 2 positioned below the first grinding mechanism 31, the holding surface height gauge 98 comes into contact with the upper surface 210 of the frame 21 to measure the height of the holding surface 200, and the upper surface height gauge 99 comes into contact with the upper surface 410 of the wafer 41 to measure the height of the upper surface 410 of the wafer 41. Then, the first thickness measurement unit 91 measures the difference between the measurement value of the height of the holding surface 200 measured by the holding surface height gauge 98 and the measurement value of the height of the upper surface 410 of the wafer 41 measured by the upper surface height gauge 99 as the thickness of the wafer 41.

[0030] The grinding apparatus 1 includes a second thickness measurement unit 92 disposed on the −X direction side of the base 10. The second thickness measurement unit 92 is disposed near the second grinding mechanism 32 and is configured similarly to the first thickness measurement unit 91. The second thickness measurement unit 92 measures the thickness of the wafer 41 when the chuck table 2, with the wafer 41 held on the holding surface 200, is positioned below the second grinding mechanism 32.

[0031] A non-contact third thickness measuring unit 93 is disposed adjacent to the second thickness measuring unit 92 to measure the thickness of the wafer 41 held on the holding surface 200 of the chuck table 2 positioned below the second grinding mechanism 32.

[0032] 2, the third thickness measurement unit 93 includes a stand 95 and an arm 94 extending from the stand 95 in a substantially horizontal direction, and a measurement unit 930 is supported on the arm 94. The measurement unit 930 measures the thickness of multiple locations on the wafer 41 from above the wafer 41 held on the holding surface 200 of the chuck table 2 in a non-contact manner.

[0033] The measurement unit 930 includes a first sensor 931, a second sensor 932, and a third sensor 933. Each sensor irradiates measurement light onto the wafer 41 held on the holding surface 200 of the chuck table 2. Then, the sensor receives the light reflected by the upper surface 410 and the lower surface 414 of the wafer 41, and measures the thickness of the wafer 41 for each portion from the difference in the timing at which the light is received. The first sensor 931 measures the thickness of the center 411 of the wafer 41, the second sensor 932 measures the thickness of the middle 412 between the center 411 and the outer periphery 413 of the wafer 41, and the third sensor 933 measures the thickness of the outer periphery 413. Here, the middle 412 between the center 411 and the outer periphery 413 of the wafer 41 means a position that is equidistant from the center 411 and the outer periphery 413 on a line connecting the center 411 and the outer periphery 413 of the wafer 41. The distance between the center 411 and the middle 412 and the distance between the middle 412 and the outer periphery 413 correspond to ½ the radius of the wafer 41.

[0034] That is, the third thickness measuring unit 93 measures the thickness of the wafer 41 at least at three locations: the center 411 , the outer periphery 413 , and the intermediate portion 412 between the center 411 and the outer periphery 413 .

[0035] In addition, the arm unit 94 can rotate horizontally around the stand 95 as a rotation axis. When the arm unit 94 rotates above the wafer 41 held on the holding surface 200, each sensor moves above the wafer 41. In addition, the measuring unit 930 may be equipped with only the first sensor 931, and may measure the thickness of at least three locations of the wafer 41: the center 411, the outer periphery 413, and the middle 412 between the center 411 and the outer periphery 413, by rotating the arm unit 94 around the stand 95 as a pivot axis.

[0036] 3, the turntable 5 has a turntable body 50 and a cover plate 502 that covers the turntable body 50. The grinding device 1 also has an inclination change mechanism 22 on the turntable body 50 that changes the inclination of the holding surface 200 relative to the lower surface 343 of the first grinding wheel 341 and the lower surface 344 of the second grinding wheel 342.

[0037] The tilt change mechanism 22 includes a support base 23. The support base 23 has a cylindrical support tube portion 230 and a disk-shaped flange portion 231 that supports the support tube portion 230. A lower surface 2311 of the flange portion 231 and the holding surface 200 are parallel to each other.

[0038] The tilt change mechanism 22 includes a first adjustment unit 241, a second adjustment unit 242, and a fixed shaft 26, which are arranged at intervals of 120 degrees around the center of the flange portion 231.

[0039] The first adjustment unit 241 includes a shaft 243 extending in a substantially vertical direction, a nut 246 provided on the flange portion 231 , and a drive portion 247 that drives the shaft 243 .

[0040] The shaft 243 is provided so as to penetrate the upper surface 500 of the turntable main body 50. A male thread is formed near the upper end of the shaft 243, and is screwed into a nut 246 arranged on the flange portion 231. The lower end side of the shaft 243 extends to an accommodation space 59 formed inside the turntable main body 50. A drive unit 247 is provided in the accommodation space 59, and the lower end of the shaft 243 is connected to the drive unit 247.

[0041] Furthermore, a fastener 245 is provided on the upper surface 500 of the turntable body 50. The fastener 245 supports the shaft 243 so that it can rotate. The drive unit 247 includes a motor 248 that rotates the shaft 243 and a reducer 249 that reduces the rotation speed of the shaft 243 .

[0042] The second adjustment unit 242 has the same configuration as the first adjustment unit 241.

[0043] In the first adjustment unit 241, when the motor 248 rotates the shaft 243, the nut 246 threaded onto the top of the shaft 243 moves up and down, as well as the portion of the flange portion 231 through which the shaft 243 passes (the nut 246 of the first adjustment unit 241). That is, as shown in FIGS. 3 and 4(a) and (b), the nut 246 of the first adjustment unit 241 moves up and down about the straight line 28 connecting the contact point (second contact point) 49 between the nut 246 of the second adjustment unit 242 and the flange portion 231 and the upper end 260 of the fixed shaft 26. This changes the inclination of the holding surface 200.

[0044] 4(b) shows the lower surface 2311 of the flange portion 231. The nut 246 of the first adjustment unit 241 moves up and down around the straight line 28 as an axis, thereby changing the distance L between the nut 246 of the first adjustment unit 241 and the upper surface 500 of the turntable main body 50. Accordingly, the tilt angle θ of the holding surface 200 changes.

[0045] That is, as shown in FIG. 4(b), the difference between this distance L and the distance L1 between the nut 246 of the second adjustment unit 242 and the upper end 260 of the fixed shaft 26 and the upper surface 500 (L < L1 in FIG. 4(b)) is L1 - L. Using this difference (L1 - L) and the length M of the perpendicular line 29 drawn from the contact point (the first contact point) 48 between the flange portion 231 of the nut 246 of the first adjustment unit 241 to the straight line 28, the inclination angle θ can be calculated by sinθ = (L1 - L) / M. Conversely, the distance L can also be calculated from the inclination angle θ. Note that the length of the straight line 291 is also M, and the straight line 292 connecting the ends of the straight line 29 and the straight line 291 is slightly inclined. However, in the above calculation, for the sake of convenience, it is calculated as if it is not inclined.

[0046] Also, the second adjustment unit 242 changes the inclination of the holding surface 200 of the chuck table 2 by moving the nut 246 of the second adjustment unit 242 up and down. In this way, by changing the height of the nut 246 of the first adjustment unit 241 or the height of the nut 246 of the second adjustment unit 242, the inclination of the holding surface 200 of the chuck table 2 is changed. Note that, as shown in FIG. 4(a), for the sake of convenience, the fixed shaft 26, the first adjustment unit 241, and the second adjustment unit 242 are illustrated as being arranged inside the chuck table 2, but they may be arranged at the vertices of an equilateral triangle centered on the center 201 of the holding surface 200 of the chuck table 2 and may be arranged directly below the outer periphery 203 of the holding surface 200. Also, as shown in FIG. 4(a), a grinding area 202 of an arc connecting the outer periphery 203 and the center 201 of the holding surface 200 is arranged so as to straddle the straight line 28. Therefore, when the inclination of the holding surface 200 is changed by reducing the distance L by the first adjustment unit 241, the portion 204 on the center side of the holding surface 200 from the straight line 28 in the grinding area 202 drops below the straight line 28, and the inclination changes in the direction in which the portion 205 on the outer periphery side of the holding surface 200 from the straight line 28 rises.

[0047] 3, a chuck table rotation mechanism 27 is connected to the chuck table 2. The chuck table rotation mechanism 27 can rotate the chuck table 2 around a rotation axis 25 of the chuck table 2.

[0048] The cover plate 502 of the turntable 5 has a circular opening 504, and the holding surface 200 of the chuck table 2 is exposed upward through the opening 504. The cover plate 502 has a function of protecting the tilt changing mechanism 22.

[0049] As shown in FIG. 1, the grinding apparatus 1 includes a control unit 97 that controls various operations of the grinding apparatus 1.

[0050] The control unit 97 has the function of recognizing the cross-sectional shape of the wafer 41 based on the thickness of the center 411 of the wafer 41, the thickness of the outer periphery 413, and the thickness of the middle 412 between the center 411 and the outer periphery 413 measured by the third thickness measurement unit 93.

[0051] Here, the cross-sectional shape of the wafer 41 is determined according to the shape of the upper surface 410 of the wafer 41. The cross-sectional shape is characterized by the difference (hereinafter referred to as the thickness difference) between the thinnest part of the wafer 41 and the thickest part of the wafer 41. This thickness difference is also referred to as the TTV (Total Thickness Variation). The cross-sectional shape of the wafer 41 is recognized by the thickness of the center 411 of the wafer 41, the thickness of the outer periphery 413 of the wafer 41, and the thickness of the intermediate portion 412 between the center 411 and the outer periphery 413 of the wafer 41.

[0052] Furthermore, the control unit 97 has a function of storing the finished cross-sectional shape of the wafer 41. The finished cross-sectional shape means the desired cross-sectional shape of the wafer 41. The operator can set the thickness of the center 411 of the wafer 41, the thickness of the outer periphery 413, and the thickness of the intermediate portion 412 between the center 411 and the outer periphery 413, thereby setting the finished cross-sectional shape of the wafer 41 and storing it in the control unit 97. If the finished cross-sectional shape has a uniform thickness, the same value is set for these three thickness values.

[0053] Hereinafter, there will be described a method for calculating a tilt change correction factor by the grinding apparatus 1 shown in Fig. 1. This method for calculating a tilt change correction factor is used when the grinding conditions are changed. In the tilt change correction factor calculation method, first, in the first trial grinding step, the wafer 41 is subjected to a first trial grinding.

[0054] (First test grinding process) In the first trial grinding step, for example, an operator sets the finished cross-sectional shape of the wafer 41 in advance and stores it in the control unit 97. Fig. 5 shows a wafer 41 having the finished cross-sectional shape. Here, the finished cross-sectional shape is a shape with a uniform thickness, and the upper surface 410 of the wafer 41 having the finished cross-sectional shape is a flat surface 430. The finished cross-sectional shape may be a concave shape in which the thickness of the center 411 of the wafer 41 is thinner than that of the outer periphery 413, or a convex shape in which the thickness of the center 411 of the wafer 41 is thicker than that of the outer periphery 413.

[0055] As shown in FIG. 6, when the first trial grinding step is performed, the distance between the nut 246 of the first adjustment unit 241 and the upper surface 500 of the turntable body 50 (distance L shown in FIG. 4(b)) is an initial value of 80. In the first test grinding step, the control unit 97 causes the robot 71 shown in FIG. 1 to extract the wafers 41 stored in the first cassette 701 and place them in the temporary placement area 720. Then, the control unit 97 causes the alignment mechanism 72 to align the wafers 41 placed in the temporary placement area 720.

[0056] In addition, the control unit 97 rotates the turntable 5 using a turntable rotation mechanism (not shown) to position one of the three chuck tables 2 supported on the turntable 5 near the first transport mechanism 741.

[0057] Then, the control unit 97 places the wafer 41 on the holding surface 200 of the chuck table 2 positioned near the first transport mechanism 741 using the first transport mechanism 741, and activates the suction source. As a result, the holding surface 200 of the chuck table 2 holds the wafer 41 by suction.

[0058] Next, the control unit 97 rotates the turntable 5 counterclockwise by 120 degrees to position the wafer 41, which is suction-held on the holding surface 200 of the chuck table 2, below the first grinding mechanism 31. At this time, the rotation of the turntable 5 adjusts the horizontal positional relationship between the lower surface 343 of the first grinding wheel 341 and the wafer 41 held on the holding surface 200 so that the lower surface 343 of the first grinding wheel 341 overlaps the radial portion of the wafer 41 held on the holding surface 200.

[0059] At this time, the other two chuck tables 2 supported by the turntable 5 are positioned below the second grinding mechanism 32 and in the vicinity of the first transfer mechanism 741.

[0060] In addition, the control unit 97 rotates the chuck table 2 using the chuck table rotation mechanism 27 to rotate the wafer 41 held on the holding surface 200 of the chuck table 2, and also rotates the first grinding wheel 341 using the spindle motor 30.

[0061] Then, while the wafer 41 and the first grinding wheel 341 held on the holding surface 200 are rotating, the control unit 97 causes the lifting mechanism 36 to lower the first grinding wheel 341 in the −Z direction. As a result, the lower surface 343 of the first grinding wheel 341 comes into contact with the radial portion of the wafer 41 held on the holding surface 200, as shown in FIG. Then, with the lower surface 343 of the first grinding wheel 341 in contact with the radial portion of the wafer 41, the control unit 97 further lowers the first grinding wheel 341 in the -Z direction, thereby roughly grinding the wafer 41 held on the holding surface 200 with the first grinding wheel 341.

[0062] During rough grinding of the wafer 41 by the first grinding wheel 341, the thickness is measured by the first thickness measurement unit 91 shown in Fig. 1. Then, when the wafer 41 has been rough ground to a predetermined thickness, rough grinding of the wafer 41 is terminated.

[0063] Thereafter, the control unit 97 raises the first grinding wheel 341 in the +Z direction to separate it from the wafer 41. Then, the turntable 5 is rotated counterclockwise by 120 degrees to revolve the chuck table 2, thereby positioning the wafer 41 held on the holding surface 200 positioned below the first grinding mechanism 31 below the second grinding mechanism 32.

[0064] Then, as in the case of rough grinding of the wafer 41 by the first grinding mechanism 31, the control unit 97 rotates the wafer 41 and the second grinding wheel 342 on the holding surface 200, while using the lifting mechanism 36 to lower the second grinding wheel 342 in the -Z direction, so that the lower surface 344 of the second grinding wheel 342 comes into contact with the radial portion of the wafer 41 held on the holding surface 200. Furthermore, the control unit 97 causes the second grinding wheel 342 to lower in the −Z direction, thereby finish-grinding the wafer 41 held on the holding surface 200 with the second grinding wheel 342 .

[0065] While the wafer 41 is being finish-ground by the second grinding wheel 342, the thickness is measured by the second thickness measurement unit 92. Then, when the wafer 41 has been finish-ground to a predetermined thickness, the finish grinding of the wafer 41 is terminated. The wafer 41 may be finish-ground to a predetermined thickness while measuring the thickness of the wafer 41 using the third thickness measurement unit 93. When the wafer 41 is ground while measuring the thickness with the third thickness measurement unit 93, the second thickness measurement unit 92 may not be provided.

[0066] (First cross-sectional shape recognition process) Next, as shown in Fig. 7, the control unit 97 measures the thickness of the wafer 41 after grinding at three locations: the thickness at the center 411, the thickness at the outer periphery 413, and the intermediate thickness 412 between the center 411 and the outer periphery 413, using the first sensor 931, the second sensor 932, and the third sensor 933 of the third thickness measurement unit 93. Then, the control unit 97 recognizes a first cross-sectional shape, which is the cross-sectional shape of the wafer 41 ground in the first trial grinding step, from the measured thicknesses at the three locations. Furthermore, the control unit 97 calculates a first thickness difference 61, which is the thickness difference of the wafer 41 ground in the first grinding step, using the recognized first cross-sectional shape and a preset finished cross-sectional shape. The first thickness difference 61 is determined at three locations: the center 411 of the wafer 41, the outer periphery 413, and the intermediate portion 412 between the center 411 and the outer periphery 413.

[0067] (Tilt change process) Thereafter, the control unit 97 acquires a first value 81 based on the first thickness difference 61 so that the cross-sectional shape of the next wafer 41 to be ground will be the predetermined finished cross-sectional shape, and uses the first value 81 to change the inclination of the holding surface 200 of the chuck table 2 by changing the height of the nut 246 of the first adjustment unit 241.

[0068] The first value 81 is the distance between the nut 246 of the first adjustment unit 241 and the upper surface 500 of the turntable body 50, adjusted so that the cross-sectional shape of the next wafer 41 to be ground will be the finished cross-sectional shape, as shown in Figure 8.

[0069] The first value 81 is a factor that determines the inclination of the holding surface 200, and the inclination of the chuck table 2 is determined according to the first value 81. The cross-sectional shape of the wafer 41 after grinding is determined according to the inclination of the chuck table 2. Therefore, the first value 81 is mathematically related to the cross-sectional shape of the wafer 41 after grinding.

[0070] In the tilt changing step, the control unit 97 determines the tilt angle θ at which the first thickness difference 61 is eliminated when the next wafer 41 held by the holding surface 200 is ground. For example, based on the first thickness difference 61 of the wafer 41, the control unit 97 determines the tilt angle θ of the holding surface 200 at which the first thickness difference 61 is eliminated when the next wafer 41 held by the holding surface 200 is ground. Furthermore, the control unit 97 acquires a first value 81, which is the distance between the nut 246 and the upper surface 500 of the turntable body 50, according to the obtained tilt angle θ.

[0071] Then, the control unit 97 changes the height of the nut 246 of the first adjustment unit 241 to the first value 81. To achieve this, the control unit 97 rotates the shaft 243 of the first adjustment unit 241 an appropriate number of rotations using, for example, the motor 248 of the drive unit 247 of the first adjustment unit 241 shown in FIG. As a result, the inclination of the holding surface 200 of the chuck table 2 is changed as shown in FIG.

[0072] (Second test grinding process) In the second trial grinding process, a wafer 41 different from the wafer 41 ground in the first trial grinding process is held on the holding surface 200 of the chuck table 2 whose inclination has been changed in the inclination change process, and a second trial grinding is performed.

[0073] In the second test grinding step, similarly to the first test grinding step, the control unit 97 causes the robot 71 shown in FIG. 1 to extract the unprocessed wafer 41 from the first cassette 701 and place it in the temporary placement area 720, and aligns it with the alignment mechanism 72. Then, the control unit 97 causes the first transport mechanism 741 to transport the wafer 41 to the holding surface 200 of the chuck table 2 located near the first transport mechanism 741. Then, the control unit 97 activates the suction source, thereby holding the wafer 41 on the holding surface 200 of the chuck table 2 whose tilt has been changed in the tilt changing step.

[0074] When the wafer 41 to be ground in the second trial grinding process is transported to the holding surface 200 of the chuck table 2, the wafer 41 is held on the holding surface 200 of the chuck table 2 that held the wafer 41 in the first trial grinding process.

[0075] After holding the wafer 41 on the holding surface 200 of the chuck table 2, the control unit 97 rotates the turntable 5 counterclockwise by 120 degrees to position the wafer 41 held on the holding surface 200 below the first grinding mechanism 31.

[0076] 7, the control unit 97 causes the first grinding mechanism 31 to roughly grind the wafer 41. The rough grinding of the wafer 41 by the first grinding wheel 341 is performed in the same manner as the rough grinding of the wafer 41 by the first grinding wheel 341 in the first trial grinding step.

[0077] Thereafter, the control unit 97 rotates the turntable 5 counterclockwise by 120 degrees to position the wafer 41 below the second grinding mechanism 32. Then, the control unit 97 finish-grinds the wafer 41 with the second grinding wheel 342. The finish-grinding of the wafer 41 with the second grinding wheel 342 is performed in the same manner as the finish-grinding of the wafer 41 with the second grinding wheel 342 in the first trial grinding step.

[0078] (Second cross-sectional shape recognition process) 9, the control unit 97 uses the third thickness measurement unit 93 to measure the thickness of the wafer 41 ground in the second test grinding process at three locations: the thickness at the center 411, the thickness at the outer periphery 413, and a middle portion 412 between the center 411 and the outer periphery 413, and recognizes a second cross-sectional shape, which is the cross-sectional shape of the wafer 41 finish-ground in the second test grinding process. Furthermore, the control unit 97 calculates a second thickness difference 62, which is the thickness difference of the wafer 41 ground in the second grinding process, based on the recognized second cross-sectional shape. The second thickness difference 62 is calculated at the center 411 of the wafer 41, the outer periphery 413, and the intermediate portion 412 between the center 411 and the outer periphery 413.

[0079] Thus, even if the height of the nut 246 of the first adjustment unit 241 and the height of the nut of the second adjustment unit 242 are changed so as to eliminate the first thickness difference 61 (see FIG. 7) in the tilt changing step, the upper surface 410 of the wafer 41 may not be flat after the second trial grinding step, and a second thickness difference 62 may occur in the wafer 41. One of the causes of this is related to deformation (distortion) of the device that occurs depending on the grinding conditions.

[0080] (Slope change correction rate calculation process) Therefore, the control unit 97 acquires the second value 82 shown in FIG. 10 based on the second cross-sectional shape so that the cross-sectional shape of the wafer 41 to be ground next will be the finished cross-sectional shape (the upper surface 410 of the wafer 41 will be flat), and calculates the tilt change correction factor R1 using the second value 82 and the first value 81.

[0081] Here, the second value 82 shown in Figure 10 is the difference between the adjustment distance 83, which is the distance between the nut 246 and the upper surface 500 of the turntable body 50 so that the cross-sectional shape of the next ground wafer 41 becomes the finished cross-sectional shape, and the first value 81, which is the distance between the nut 246 of the first adjustment unit 241 and the upper surface 500 of the turntable body 50 in the second trial grinding process.

[0082] To obtain the second value 82, the control unit 97 obtains the inclination of the holding surface 200 according to the second thickness difference 62. That is, the control unit 97 obtains the inclination angle θ of the holding surface 200 such that the second thickness difference 62 will be eliminated the next time the wafer 41 held by the holding surface 200 is ground. Furthermore, the control unit 97 obtains an adjustment distance 83, which is the distance between the nut 246 and the upper surface 500 of the turntable body 50, according to the inclination angle θ. Furthermore, the control unit 97 obtains a value (a value representing the height deficiency relative to the first value 81) by subtracting the first value 81 from the adjustment distance 83, as the second value 82.

[0083] Furthermore, the control unit 97 uses the second value 82 and the first value 81 to calculate the slope change correction rate R1 from the following formula. Slope change correction rate R1 = first value 81 / (first value 81 - second value 82)

[0084] Thereafter, the control unit 97 grinds the next wafer 41 as the target for actual grinding after the trial grinding. At this time, first, the amount of change in the tilt of the holding surface 200 is corrected using the tilt change correction factor R1 calculated from the above formula.

[0085] When correcting the change amount of the inclination of the holding surface 200, the control unit 97, for example, rotates the shaft 243 of the first adjustment unit 241 by an amount of rotation R1 times the amount of rotation of the shaft 243 of the first adjustment unit 241 in the above-mentioned inclination change process from a state in which the inclination of the holding surface 200 is not changed, thereby setting the distance between the nut 246 of the first adjustment unit 241 and the upper surface 500 of the turntable main body 50 to an adjustment distance 83.

[0086] Then, the control unit 97 holds the wafer 41 on the holding surface 200 of the chuck table 2, and performs rough grinding by the first grinding mechanism 31 and finish grinding by the second grinding mechanism 32. This makes it possible to shape the cross-sectional shape of the wafer 41 into the finished cross-sectional shape.

[0087] As described above, the control unit 97 performs two trial grinding processes, the first trial grinding process and the subsequent second trial grinding process after the tilt change, and calculates the tilt change correction coefficient R1 for obtaining a good tilt of the holding surface 200. When grinding a similar wafer 41 under the same grinding conditions, the control unit 97 changes the tilt of the holding surface 200 of the chuck table 2 by rotating the wafer 41 by an amount of rotation that is a value obtained by multiplying the amount of rotation of the shaft 243 for changing the tilt of the holding surface 200 in the tilt change process by this tilt change correction coefficient R1. Thereafter, the control unit 97 grinds the actual wafer 41 to grind the wafer 41 into a finished cross-sectional shape. In this way, in this embodiment, the wafer 41 can be ground to the finished cross-sectional shape after two trial grindings. Therefore, compared to the conventional technology in which the grinding process and the correction of the tilt of the holding surface 200 were repeated many times, the wafer 41 can be ground to the finished cross-sectional shape in a shorter total time.

[0088] The calculation of the inclination change correction rate R1 may be performed not only when the grinding conditions are changed, but also when the grinding wheel 34 is replaced.

[0089] Furthermore, the cross-sectional shape of the wafer 41 may be characterized by the difference between the thickness of the center 411 and the thickness of the outer periphery 413 of the wafer 41, with the thickness of the center 411 being used as a reference. In this case, the first cross-sectional shape is recognized by calculating the difference between the thickness of the center 411 and the thickness of the outer periphery 413 of the wafer 41.

[0090] The control unit 97 may also set the finished cross-sectional shape to a cone shape with a small thickness near the center 411. The control unit 97 may also set the finished cross-sectional shape to a dome shape with a large thickness near the center 411.

[0091] The first value 81 may also be the distance between the nut 246 of the second adjustment unit 242 and the upper surface 500 of the turntable body 50 such that the cross-sectional shape of the wafer 41 to be ground next becomes the finished cross-sectional shape. The second value 82 may also be the difference between the first value 81 determined in this way and the distance between the nut 246 of the second adjustment unit 242 and the upper surface 500 of the turntable body 50 that can actually make the cross-sectional shape of the wafer 41 become the finished cross-sectional shape. In this case, the control unit 97 may change the second height by using the second adjustment unit 242 instead of the first adjustment unit 241, thereby changing the inclination of the holding surface 200.

[0092] The grinding apparatus 1 can also finish the wafer 41 into a finished cross-sectional shape as follows. First, the control unit 97 performs a first test grinding of the wafer 41 using the first grinding wheel 341 and the second grinding wheel 342 shown in FIG. 1. As a result, the cross-sectional shape of the wafer 41 becomes the cross-sectional shape shown in FIG. 11. Then, the control unit 97 uses the third thickness measurement unit 93 to measure the thickness of the center 411 of the wafer 41, the thickness of the outer periphery 413, and the thickness of a middle point 412 between the center 411 and the outer periphery 413, and recognizes the cross-sectional shape of the wafer 41 after the first test grinding based on the results.

[0093] Furthermore, the finished cross-sectional shape of the wafer 41 is set in advance by the operator and stored in the control unit 97 .

[0094] Then, the control unit 97 compares the recognized cross-sectional shape of the wafer 41 with the finished cross-sectional shape of the wafer 41. Specifically, as shown in Fig. 12, the control unit 97 compares the thickness of the center 411 of the wafer 41 after the first trial grinding with the thickness of the wafer 41 having the finished cross-sectional shape, and calculates a third thickness difference D1, which is the difference between them. Here, the third thickness difference D1 is assumed to be 1.2 µm.

[0095] Thereafter, the control unit 97 changes the inclination of the holding surface 200 of the chuck table 2 so that the wafer 42 to be ground next has the finished cross-sectional shape. Specifically, for example, the control unit 97 causes the motor 248 of the first adjustment unit 241 shown in FIG. 6 to rotate the shaft 243, thereby raising the height of the nut 246 of the first adjustment unit 241.

[0096] Next, the control unit 97 performs a second trial grinding of the wafer 41 using the first grinding wheel 341 and the second grinding wheel 342. As a result, the wafer 41 is ground into the cross-sectional shape shown in Fig. 13. Thereafter, the control unit 97 measures the thickness of the center 411 of the wafer 41, the thickness of the outer periphery 413, and the thickness of the intermediate portion 412 between the center 411 and the outer periphery 413 using the third thickness measurement unit 93, and recognizes the cross-sectional shape of the wafer 41 after the second trial grinding based on the results.

[0097] Thereafter, the control unit 97 compares the recognized cross-sectional shape of the wafer 41 after the second trial grinding with the finished cross-sectional shape of the wafer 41. Specifically, as shown in Fig. 14, the control unit 97 compares the thickness of the center 411 of the wafer 41 after the second trial grinding with the thickness of the wafer 41 having the finished cross-sectional shape, and calculates the difference, a fourth thickness difference D2. Here, the fourth thickness difference D2 is assumed to be 0.4 µm.

[0098] Next, the control unit 97 calculates the correction ratio R2 by substituting the third thickness difference D1 and the fourth thickness difference D2 into the formula expressed as correction ratio R2=(D1+D2) / D1, whereby the correction ratio R2 is calculated as R2=1.33.

[0099] Then, the control unit 97 again changes the inclination of the holding surface 200 from the state before the inclination change. Here, the control unit 97 performs the operation for changing the inclination using an amount of movement obtained by multiplying the amount of movement when changing the inclination of the holding surface 200 performed before the above-mentioned second test grinding by R2=1.33. Specifically, for example, the control unit 97 increases the rotation amount of the motor 248 of the first adjustment unit 241 by 1.33 times compared to when the inclination was changed before the second trial grinding, and raises the height of the nut 246 of the first adjustment unit 241 by 1.33 times compared to when the inclination was changed. As a result, the control unit 97 changes the inclination of the holding surface 200 of the chuck table 2 to 1.33 times the inclination when the inclination was changed.

[0100] Thereafter, the control unit 97 grinds the wafer 41 using the first grinding wheel 341 and the second grinding wheel 342. This allows the wafer 41 to be finished into a finished cross-sectional shape.

[0101] The calculation formula for the correction ratio R2 can also be expressed as R2=1 / (third thickness difference D1 / fourth thickness difference D2)+1.

[0102] 2, the arm 94 can be rotated to move the first sensor 931, the second sensor 932, and the third sensor 933 to positions other than the vicinity of the center 411, the middle 412, and the outer periphery 413 of the wafer 41, thereby measuring the thickness of the wafer 41 at positions other than the center 411, the middle 412, and the outer periphery 413. Therefore, in this embodiment, the control unit 97 may be configured to use the third thickness measurement unit 93 to measure the thickness of the wafer 41 at positions other than the three positions of the center 411, the outer periphery 413, and the middle 412 between the center 411 and the outer periphery 413. The control unit 97 may also use the third thickness measurement unit 93 to measure the thickness of four or more positions on the wafer 41. [Explanation of symbols]

[0103] 1: Grinding device 2: Chuck table 10: Base 11: 1st column 12: 2nd column 20: Suction unit 21: Frame 22: Tilt change mechanism 23: Support base 25: Rotating shaft 26: Fixed shaft 27: Chuck table rotation mechanism 200: Holding surface 201: Center 202: Grinding area 203: Outer periphery 204: Center portion 205: Outer periphery portion 210: Upper surface 230: Support cylinder portion 231: Flange portion 241: First adjustment unit 242: Second adjustment unit 243: Shaft 245: Fastener 246: Nut 247: Drive unit 248: Motor 249: Reducer 30: Spindle motor 31: First grinding mechanism 32: Second grinding mechanism 33: Housing 34: Grinding wheel 36: Lifting mechanism 37: Base 38: Mount 39: Spindle 341: First grinding wheel 342: Second grinding wheel 343: Bottom surface 344: Bottom surface 351: 1st rotation axis 352: 2nd rotation axis 360: Ball screw 361: Guide rail 362: Z-axis motor 363: Lifting plate 41: Wafer 42: Wafer 410: Top surface 411: Center 412: Middle 413: Outer 430: Flat surface 5: Turntable 50: Turntable body 502: Cover plate 59: Storage space 500: Top surface 61: First thickness difference 62: Second thickness difference 71: Robot 72: Alignment mechanism 73: Cleaning mechanism 701: 1st cassette 702: 2nd cassette 720: Temporary placement area 741: First transport mechanism 742: Second transport mechanism 80: Initial value 81: First value 82: Second value 83: Adjustment distance 91: First thickness measurement unit 92: Second thickness measurement unit 93: Third thickness measurement unit 94: Arm unit 95: Stand 97: Control unit 98: Support surface height gauge 99: Upper surface height gauge 930: Measuring unit 931: First sensor 932: Second sensor 933: Third sensor D1: Third thickness difference D2: Fourth thickness difference R1: Inclination change correction rate R2: Correction ratio

Claims

1. A method for calculating a correction factor in grinding a wafer using a grinding device comprising: a chuck table that holds a wafer by a holding surface; a grinding mechanism that grinds the wafer by a lower surface of an annular grinding wheel disposed at a tip of a spindle; and an inclination changing mechanism that changes the inclination of the holding surface with respect to the lower surface of the grinding wheel, the method comprising the steps of: bringing the lower surface of the grinding wheel into contact with a radial portion of the wafer held by the holding surface to grind the wafer, the method comprising the steps of: a first test grinding step of grinding the wafer held on the holding surface by the grinding wheel; a first cross-sectional shape recognition step of measuring thicknesses of the wafer ground in the first trial grinding step at three locations, i.e., a center, an outer periphery, and an intermediate location between the center and the outer periphery, to recognize a first cross-sectional shape of the wafer; a tilt changing step of acquiring a first value based on the first cross-sectional shape from a difference between the first cross-sectional shape recognized in the first cross-sectional shape recognition step and a finish cross-sectional shape, and changing a tilt of the holding surface by the first value; a second test grinding step of grinding the wafer held on the holding surface of the chuck table having the inclination changed in the inclination changing step by the grinding wheel; a second cross-sectional shape recognition step of measuring the thicknesses of the three locations of the wafer ground in the second trial grinding step to recognize a second cross-sectional shape of the wafer; a gradient change correction factor calculation step of acquiring a second value based on the second cross-sectional shape from a difference between the second cross-sectional shape recognized in the second cross-sectional shape recognition step and the finished cross-sectional shape, and calculating a gradient change correction factor from the following formula using the second value and the first value; Tilt change correction rate=the first value / (the first value−the second value) A correction factor calculation method comprising:

2. A method for grinding a wafer, comprising: using the correction factor calculation method according to claim 1; bringing a lower surface of the grinding wheel into contact with a radius portion of the wafer held on the holding surface to grind the wafer; a tilting step of tilting the holding surface by an angle corresponding to a value obtained by multiplying the first value obtained in the tilt changing step by the tilt change correction factor calculated in the tilt change correction factor calculation step; a grinding step of grinding the wafer held on the holding surface tilted in the tilting step to a predetermined thickness by the grinding wheel; A method for grinding a wafer comprising the steps of:

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