Grinding Equipment

Abstract

To reduce variations in cross-sectional shape of a ground wafer, regardless of types of grinding devices and types of grinding stones.SOLUTION: A grinding device, when a load measured or a load current value of a spindle measured during grinding does not match a preset value, changes a rotation speed of the spindle so that the load or the load current value of the spindle matches the preset value. This can set the rotation speed of the spindle, regardless of types of grinding devices and types of grinding stones, correspondingly to the difference in the types, so that the load or the load current value of the spindle is held constant, which can reduce variations in cross-sectional shape of a wafer.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a grinding apparatus for grinding a wafer. [Background technology]

[0002] In a grinding device that grinds a wafer using a grinding wheel, a wafer is held on the holding surface of a chuck table, the chuck table is rotated around the center of the holding surface, and an annular grinding wheel attached to the tip of a spindle is positioned above the wafer so that its orbit passes through the center of rotation of the wafer held by the holding surface. The rotating grinding wheel is then moved (grinding feed) in a direction approaching the holding surface to grind the upper surface of the wafer. Grinding conditions such as the spindle rotation speed, chuck table rotation speed, and grinding feed speed are set in the grinding device, and the wafer is ground under those grinding conditions (see, for example, Patent Document 1). The grinding conditions are determined according to the type of wafer and grinding wheel, and even when a different grinding device is used, the grinding process is performed under the same grinding conditions as long as the wafer to be ground and the grinding wheel used are the same. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-131368 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, when the grinding device is different, the cross-sectional shape of the ground wafer (in-plane thickness of the wafer) differs slightly due to differences in the grinding device, which means that even if the grinding conditions are the same, the cross-sectional shape of the wafer will not be the same. In addition, even if the grinding wheel is replaced using the same grinding device, the cross-sectional shape of the ground wafer may differ slightly even if the new grinding wheel is the same type as the old one. In other words, even if the grinding wheel is replaced using the same grinding device, there is a problem that the cross-sectional shape of the wafer will not be the same. Therefore, there is a problem to be solved in terms of reducing the variation in the cross-sectional shape of the ground wafer even when there are differences in the grinding device and grinding wheel. [Means for solving the problem]

[0005] The present invention provides a grinding device comprising a chuck table for holding a wafer on a holding surface, a chuck rotation mechanism for rotating the chuck table about a chuck rotation axis passing through the center of the holding surface, a grinding mechanism for grinding the wafer held on the holding surface by the underside of an annular grinding wheel arranged at the tip of a spindle, a spindle rotation mechanism for rotating the spindle, a grinding feed mechanism for moving the grinding wheel toward and away from the holding surface in a direction perpendicular to the holding surface, and a control unit, and the grinding device measures the force with which the grinding wheel is pressed against the wafer held by the holding surface. The control unit has a load sensor for measuring the rotational speed of the spindle, and a first memory unit for storing the rotational speed of the spindle, and measures the load with the load sensor during grinding processing. If the measured load does not match a preset load, the spindle rotational speed is changed so that the load during grinding processing matches the preset load. The spindle rotational speed at which the load becomes the preset load is stored in the first memory unit. Next, the spindle is rotated at the spindle rotational speed stored in the first memory unit to grind the wafer from the wafer held on the holding surface. The present invention also provides a grinding device comprising a chuck table for holding a wafer on a holding surface, a chuck rotation mechanism for rotating the chuck table about a chuck rotation axis passing through the center of the holding surface, a grinding mechanism for grinding the wafer held on the holding surface by the underside of an annular grinding wheel disposed at the tip of a spindle, a spindle rotation mechanism for rotating the spindle, a grinding feed mechanism for moving the grinding wheel toward and away from the holding surface in a direction perpendicular to the holding surface, and a control unit, wherein the grinding device further comprises a load sensor for measuring the force with which the grinding wheel is pressed against the wafer held by the holding surface. and a load data table showing the relationship between the load and the spindle rotation speed, the control unit has a first selection unit which selects a spindle rotation speed from the load data table, and measures the load with the load sensor during grinding processing, and if the measured load does not match a preset load, the load data table is referenced and the first selection unit selects a spindle rotation speed at which the measured load becomes the preset load, and then rotates the spindle at the spindle rotation speed selected by the first selection unit to grind the wafer from the wafer held on the holding surface. In the above grinding apparatus, the control unit may maintain the load measured by the load sensor at a preset load while changing the rotational speed of the spindle within a range including the spindle rotational speed stored in the first memory unit or the spindle rotational speed selected by the first selection unit.

[0006] The present invention provides a grinding device comprising: a chuck table for holding a wafer on a holding surface; a chuck rotation mechanism for rotating the chuck table about a chuck rotation axis passing through the center of the holding surface; a grinding mechanism for grinding the wafer held on the holding surface by the underside of an annular grinding wheel disposed at the tip of a spindle; a spindle rotation mechanism for rotating the spindle; a grinding feed mechanism for moving the grinding wheel toward and away from the holding surface in a direction perpendicular to the holding surface; and a control unit, the grinding device further comprising: a load current value measuring unit for measuring a load current value of the spindle, the control unit comprising: and a second memory unit that stores the spindle rotation speed, the load current value is measured by the load current value measuring unit during grinding processing, and if the measured load current value does not match the preset load current value, the spindle rotation speed is changed so that the load current value during grinding processing matches the preset load current value, and the spindle rotation speed at which the load current value becomes the preset load current value is stored in the second memory unit, and then the spindle is rotated at the spindle rotation speed stored in the second memory unit to grind the wafer from the wafer held on the holding surface. The present invention also relates to a grinding device comprising a chuck table for holding a wafer on a holding surface, a chuck rotation mechanism for rotating the chuck table about a chuck rotation axis passing through the center of the holding surface, a grinding mechanism for grinding the wafer held on the holding surface by the underside of an annular grinding wheel arranged at the tip of a spindle, a spindle rotation mechanism for rotating the spindle, a grinding feed mechanism for moving the grinding wheel toward and away from the holding surface in a direction perpendicular to the holding surface, and a control unit, the grinding device comprising a load current value measurement unit for measuring a load current value of the spindle, and a control unit for controlling a load current value and a spindle rotation mechanism ... and a load current value data table showing the relationship between the load current value and the spindle rotation speed, the control unit having a second selection unit which selects a spindle rotation speed, the load current value measurement unit measures the load current value during grinding, and if the measured load current value does not match a preset load current value, the load current value data table is referenced and the second selection unit selects a spindle rotation speed at which the measured load current value becomes the preset load current value, and then the spindle is rotated at the spindle rotation speed selected by the second selection unit from the wafer held on the holding surface to grind the wafer. In the above grinding device, the control unit may be configured to maintain the load current value measured by the load current value measuring unit at a preset load current value while changing the rotational speed of the spindle within a range including the spindle rotational speed stored in the second memory unit or the spindle rotational speed selected by the second selection unit.

[0007] Furthermore, when no corresponding spindle rotation speed is found when referring to the load data table or the load current value data table, the lower or upper limit spindle rotation speed in the load data table or the load current value data table may be selected to change the rotation speed of the chuck table. Effect of the Invention

[0008] In the present invention, when the measured load does not match the preset load, the spindle rotation speed is changed so that the two loads match. Therefore, even if there are differences in the grinding device or grinding wheel, the spindle rotation speed is determined in response to the differences, and the load is constant, thereby reducing the variation in the cross-sectional shape of the wafer. In addition, a load data table showing the relationship between load and spindle rotation speed is provided, and when the measured load does not match a preset load, the spindle rotation speed corresponding to the measured load value in the load data table is selected, thereby quickly controlling the load value to match the set value and reducing variation in the cross-sectional shape of the wafer. Furthermore, by adjusting the spindle rotation speed so that the load value becomes the desired set value, and then further varying the spindle rotation speed within a range that includes that spindle rotation speed while maintaining the measured load at a pre-set value, the load can be maintained at a constant value with greater precision, thereby further reducing the variation in the cross-sectional shape of the wafer.

[0009] In the present invention, taking into consideration that the load current value of the spindle is also a factor that affects the cross-sectional shape of the wafer, like the load, if the measured load current value does not match a preset load current value, the spindle rotation speed is changed so that the two load current values ​​match. Therefore, even if there are differences in the grinding device or grinding wheel, the spindle rotation speed is determined in response to those differences, and the load current value is constant, thereby reducing the variation in the cross-sectional shape of the wafer. In addition, a load current value data table showing the relationship between the load current value and the spindle rotation speed is provided, and when the measured load current value does not match a preset load current value, the spindle rotation speed corresponding to the measured load current value in the load current value data table is selected, thereby quickly controlling the load current value to match the set value and reducing the variation in the cross-sectional shape of the wafer. Furthermore, by adjusting the spindle rotation speed so that the load current value becomes the desired set value, and then further changing the spindle rotation speed within a range including that spindle rotation speed while maintaining the measured load current at a pre-set value, the load current value can be maintained at a constant value with greater precision, thereby further reducing variation in the cross-sectional shape of the wafer.

[0010] When there is no corresponding spindle rotation speed in the load data table or the load current value data table, by setting the upper or lower limit spindle rotation speed of these tables and changing the rotation speed of the chuck table, it is possible to reduce the variation in the cross-sectional shape of the wafer corresponding to the measured load or load current even when the measured load or load current is in a range not covered by the load data table or the load current value data table. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a perspective view showing a first embodiment of a grinding device. [Diagram 2] 4 is a graph showing the change in height of the grinding surface of a grinding wheel during wafer grinding. [Diagram 3] 4 is a flowchart showing a first control example in the first embodiment. [Figure 4] 6 is a flowchart showing a second control example in the first embodiment. [Diagram 5] 13 is a table showing an example of a load data table used in the second control example in the first embodiment. [Figure 6] 13 is a flowchart showing a process specific to a third control example in the first embodiment. [Figure 7] 13 is a flowchart showing a process specific to a fourth control example in the first embodiment. [Figure 8] 13 is a table showing an example of a chuck rotation speed data table used in the fourth control example in the first embodiment. [Figure 9] FIG. 4 is a perspective view showing a second embodiment of the grinding device. [Figure 10] 13 is a flowchart showing a fifth control example in the second embodiment. [Figure 11] 13 is a flowchart showing a sixth control example in the second embodiment. [Figure 12] 13 is a table showing an example of a load current value data table used in the sixth control example in the second embodiment. [Figure 13] 13 is a flowchart showing a process specific to a seventh control example in the second embodiment. [Figure 14] 13 is a flowchart showing a process specific to an eighth control example in the second embodiment. [Figure 15] 13 is a table showing an example of a chuck rotation speed data table used in the eighth control example in the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] 1. First embodiment The grinding apparatus 1 shown in FIG. 1 is an apparatus that grinds a wafer held on a chuck table 2 using a grinding mechanism 3. The chuck table 2 is driven by a chuck table feed mechanism 4 and can move in the Y-axis direction, and the grinding mechanism 3 is driven by a grinding feed mechanism 5 and can move in the Z-axis direction.

[0013] The chuck table 2 includes a suction part 20 formed of a porous member and a frame body 21 that supports the suction part 20. The surface of the suction part 20 constitutes a holding surface 200 that holds a wafer. The holding surface 200 and the upper surface of the frame body 21 are flush with each other.

[0014] Below the chuck table 2, there is provided a chuck rotation mechanism 22 that rotates the chuck table 2 about a chuck rotation axis 28 that passes through the center of the holding surface 200. Above the chuck rotation mechanism 22, there is provided a table base 23, which is supported at least at three points by three chuck supports 24 (only two are shown in FIG. 1). Each chuck support 24 is provided with a load sensor 25 that measures, as a load, the force with which a grinding wheel 341 is pressed against a wafer held by the holding surface 200. In addition, at least two chuck supports 24 have a function of adjusting the height of the chuck table 2 to adjust the inclination of the holding surface 200.

[0015] The grinding mechanism 3 includes a spindle 30 having a rotation axis 300 in the Z-axis direction, a spindle rotation mechanism 31 that rotates the spindle 30, a spindle housing 32 that rotatably supports the spindle 30, a mount 33 connected to the lower end of the spindle 30, and a grinding wheel 34 attached to the mount 33. When the spindle rotation mechanism 31 rotates the spindle 30, the grinding wheel 34 also rotates. The grinding wheel 34 is composed of a base 340 fixed to the mount 33, and a plurality of grinding stones 341 fixed in an annular shape to the lower surface of the base 340.

[0016] The chuck table feed mechanism 4 includes a ball screw 40 having a rotation shaft 400 in the Y-axis direction, a motor 41 for rotating the ball screw 40, a pair of guide rails 42 arranged in parallel with the ball screw 40, and a slide plate 43 having a bottom part in sliding contact with the guide rails 42 and a nut (not shown) screwed to the ball screw 40. A load sensor 25 is arranged above the slide plate 43. When the ball screw 40 rotates, the slide plate 43 moves in the Y-axis direction while being guided by the guide rails 42, and the chuck table 2 also moves in the same direction as the slide plate 43 moves in the Y-axis direction. The frame 21 is rotatably supported by a base 27, and a bellows 26 is connected to a side part of the base 27 in the Y-axis direction, and the chuck table 2 moves in the Y-axis direction with the expansion and contraction of the bellows 26.

[0017] The grinding feed mechanism 5 includes a ball screw 50 having a rotating shaft 500 in the Z-axis direction, a motor 51 for rotating the ball screw 50, a pair of guide rails 52 arranged parallel to the ball screw 50, a lift plate 53 having a side portion in sliding contact with the guide rails 52 and having a nut (not shown) therein that is screwed into the ball screw 50, a holder 54 connected to the lift plate 53 and supporting the spindle housing 32, a scale 55 arranged along the guide rails 52, and a reading unit 56 for detecting the position of the lift plate 53 in the Z-axis direction as a read value of the scale 55. When the ball screw 50 rotates, the lift plate 53 is guided by the guide rails 52 to move in a direction perpendicular to the holding surface 200, and the grinding mechanism 3 also moves in the same direction accordingly, and the grinding wheel 341 approaches or moves away from the holding surface 200. The position of the grinding mechanism 3 in the Z-axis direction is detected by the reading unit 56. The position of the grinding mechanism 3 in the Z-axis direction may be recognized by the read value of the encoder of the motor 51.

[0018] A thickness measuring unit 6 for measuring the thickness of a wafer held on the holding surface 200 is disposed on the side of the movement path of the chuck table 2 in the Y-axis direction. The thickness measuring unit 6 includes a first gauge 61 for measuring the height of the holding surface 200 and a second gauge 62 for measuring the height of the upper surface of the wafer held on the holding surface 200, and measures the height of the wafer based on the difference in height between the first gauge 61 and the second gauge 62.

[0019] The control unit 7 includes a CPU and a memory element. The chuck table 2, the grinding mechanism 3, the chuck table feed mechanism 4, and the grinding feed mechanism 5 operate under the control of the control unit 7.

[0020] The control unit 7 includes a set load value memory unit 71 in which a predetermined load value during grinding is pre-stored, a spindle rotation speed control unit 72 which controls the rotation speed of the spindle 30 so that the actual load value measured by the load sensor 25 during grinding becomes the load value stored in the set load value memory unit 71, and a first memory unit 73 which stores the spindle rotation speed when the actual load becomes the load value stored in the set load value memory unit 71.

[0021] The grinding device 1 has a load data table memory unit 91 that stores a load data table showing the relationship between load and spindle rotation speed, and the control unit 7 has a first selection unit 74 that refers to the contents of the load data table memory unit 91 and selects the spindle rotation speed corresponding to the measurement value of the load sensor 25.

[0022] In addition, the grinding device 1 has a chuck rotational speed data table storage unit 92 that stores a chuck rotational speed data table indicating the relationship between the rotational speed of the chuck table 2 and the load, and the control unit 7 is equipped with a chuck table rotational speed control unit 75 that changes the rotational speed of the chuck table 2 in response to the measurement value of the load sensor 25.

[0023] A protective tape 11 is attached to the bottom surface of the wafer 10 to be ground, and the protective tape 11 side is held on the holding surface 200 of the chuck table 2. Then, the chuck table 2 is moved in the +Y direction to position the wafer 10 below the grinding mechanism 3, the chuck table 2 is rotated, the spindle rotation mechanism 31 of the grinding mechanism 3 rotates the spindle 30, and the grinding feed mechanism 5 lowers the grinding mechanism 3. Then, the bottom surface of the grinding wheel 341 arranged at the tip of the spindle 30 comes into contact with the top surface of the wafer 10, and grinding begins. When the wafer 10 has been finished to a predetermined thickness, the grinding mechanism 3 is raised to end grinding. It is not necessary to attach the protective tape 11 to the lower surface of the wafer 10 .

[0024] The lifting and lowering operation of the grinding mechanism 3 from before the start of grinding to the end of grinding is divided into seven stages, T1 to T7, shown in FIG. 2. T1 is a stage in which the grinding mechanism 3 is lowered at high speed from the retreat position in order to move the grinding wheel 341 closer to the upper surface of the wafer 10 more quickly, and T2 is a stage called air cut just before the grinding wheel 341 contacts the upper surface of the wafer 10. T3 to T5 are all stages in which the grinding wheel 341 contacts the upper surface of the wafer 10 and grinding is performed, T3 is a stage in which grinding is performed under a relatively high first grinding feed rate, T4 is a stage in which grinding is performed under a second grinding feed rate that is slower than the first grinding feed rate, and T5 is the final stage in which the descent of the grinding mechanism 3 is stopped and grinding is performed, which is a stage called spark out. T6 is a stage in which the grinding mechanism 3 is slowly raised to end grinding, and T7 is a stage in which the grinding mechanism 3 is raised at high speed and returned to the retreat position.

[0025] In the final finishing stage T30 of the grinding process T3 at the first grinding feed rate, for example, any of the controls shown in the following first to fourth control examples is performed.

[0026] (1-1) First control example The following description will be given with reference to the flowchart shown in FIG. First, an ideal load value during grinding in the finish stage T30 is stored in the set load value storage unit 71 of the control unit 7 (step 101). This load value is a load value that is empirically considered to be optimal for finish grinding in relation to the type of grinding wheel 341 used, the material of the wafer 10 to be ground, and the grinding feed rate determined accordingly.

[0027] In the finishing stage T30, the grinding mechanism 3 is stopped from descending by the grinding feed mechanism 5, and the spindle rotation mechanism 31 continues to rotate the spindle 30 to perform grinding (step 102). The control unit 7 reads the load measurement value of the load sensor 25 (step 103) and determines whether the measurement value matches the predetermined load value set in the set load value storage unit 71 (step 104). If the two load values ​​match, the load value stored in the set load value storage unit 71 is stored in the first storage unit 73 (step 105). On the other hand, if they do not match, the spindle rotation speed control unit 72 changes the rotation speed of the spindle 30 (step 106). Specifically, if the measurement value of the load sensor 25 is greater than the predetermined load value stored in the set load value storage unit 71, the rotation speed of the spindle 30 is slowed down, and if the measurement value of the load sensor is smaller than the predetermined load value stored in the set load value storage unit 71, the rotation speed of the spindle 30 is increased. Then, grinding is performed while changing the spindle rotation speed (step 102), and the load value of the load sensor 25 is measured (step 103). When the two load values ​​match, the spindle rotation speed at that time is stored in the first memory unit 73 (step 105).

[0028] When the spindle rotation speed is thus stored in the first storage unit 73, the wafer 10 is removed from the holding surface 200, and another wafer 10 is held on the holding surface 200. Then, the grinding mechanism 3 is lowered by the same control as in T1 to T5 shown in FIG. 2, and in the finishing stage T30, the spindle rotation speed control unit 72 grinds the wafer 10 while maintaining the rotation speed of the spindle 30 at the speed stored in the first storage unit 73 (step 107). Then, the thickness measurement unit 6 monitors whether the total value of the thickness of the wafer 10 and the protective tape 11 has reached a predetermined thickness (step 108), and when the total value reaches the predetermined thickness, the grinding feed mechanism 5 raises the grinding mechanism 3, and grinding is completed. Similarly, a finishing stage T40 may be provided at the end of the grinding process T4 at the second grinding feed rate to measure the load and control the spindle rotation speed so as to achieve a predetermined load. It should be noted that a finishing stage T50 may be provided during the spark out T5 to measure the load and control the spindle rotation speed to achieve a predetermined load.

[0029] Conventionally, the load value was set to a predetermined value only by controlling the grinding feed rate using the correspondence relationship between the grinding feed rate and the load value that was grasped by experience, so the load value may not be the predetermined value due to differences in the equipment, the grinding wheel lot, etc. However, according to this first control example, a load value corresponding to an ideal grinding feed rate that is grasped by experience is first set, the spindle rotation speed is changed so that the measured value by the load sensor 25 becomes the set load value, the spindle rotation speed when the measured value by the load sensor 25 matches the set load value is stored, and the spindle 30 is rotated at the stored spindle rotation speed to perform grinding, so that even if there are differences in the equipment or the grinding wheel lot, the spindle rotation speed is determined in response to the differences. Therefore, the variation in the cross-sectional shape of the wafer can be reduced.

[0030] (1-2) Second control example The following description will be given with reference to the flowchart shown in FIG. An ideal load value during grinding in the finish stage T30 is stored in the set load value storage unit 71 of the control unit 7 (step 201). This load value is a load value that is empirically considered to be optimal for finish grinding in relation to the type of grinding wheel 341 used, the material of the wafer 10 to be ground, and the grinding feed rate determined accordingly.

[0031] In the finishing stage T30, with the descent of the grinding mechanism 3 by the grinding feed mechanism 5 stopped, the spindle rotation mechanism 31 keeps the spindle 30 rotating while grinding is being performed (step 202), while the control unit 7 reads the load measurement value of the load sensor 25 (step 203) and judges whether the measurement value matches the predetermined load value set in the set load value storage unit 71 (step 204). Then, if the two load values ​​match, grinding of the next wafer 10 is started (step 205). On the other hand, if the two load values ​​do not match, the contents stored in the load data table storage unit 91 are referred to. The load data table storage unit 91 stores, for example, a load data table 910 shown in Fig. 5. This load data table 910 was obtained by a grinding experiment using a specific grinding wheel under a specific grinding feed rate, with the left column showing the measured values ​​by the load sensor 25 and the right column showing the spindle rotation speed for making the load value 35N from the measured values. For example, when the measured value by the load sensor 25 is 30N, the spindle rotation speed should be set to 1200 rpm in order to make the measurement 35N. The first selection unit 74 reads the measured value of the load sensor 25, and selects the value of the spindle rotation speed corresponding to the measured value in the load data table 910. For example, if the load stored in the set load value storage unit 71 is 35 N and the measured value of the load sensor 25 is 32 N, 1400 rpm is selected as the spindle rotation speed (step 206). Then, the wafer 10 is removed from the holding surface 200, and another wafer 10 is held on the holding surface 200. Then, the grinding mechanism 3 is lowered by the same control as T1 to T5 shown in FIG. 2, and in the finishing stage T30, the spindle rotation speed control unit 72 performs grinding at a spindle rotation speed of 1400 rpm (step 205). The load data table 910 is prepared for each target load value and each grinding feed rate, and is stored in the load data table storage unit 91.

[0032] In the finishing stage T30, the thickness measuring unit 6 monitors whether the total thickness of the wafer 10 and the protective tape 11 has reached a predetermined thickness (step 207), and when that total thickness reaches the predetermined thickness, the grinding feed mechanism 5 raises the grinding mechanism 3, thereby completing the grinding.

[0033] According to this second control example, first, an ideal load value that is understood from experience is set, and if the measured value by the load sensor 25 does not match the set load value, the load data table is referenced to determine the spindle rotation speed for changing the measured load value to the set load value, and grinding is performed under the determined spindle rotation speed, so that even if there are differences between machines or between grinding wheel lots, the load value can be quickly set to a predetermined value in response to the differences. Therefore, the variation in the cross-sectional shape of the wafer can be reduced. The second control example may be applied to the finishing stages T40 and T50.

[0034] (1-3) Third control example This third control example is an example in which the processing shown in the flowchart of FIG. 6 is performed between steps 107 and 108 in the first control example shown in FIG. 3, or between steps 205 and 207 in the second control example shown in FIG. 4.

[0035] As shown in Fig. 6, even after step 107 in the first control example or after step 205 in the second control example, that is, even in the grinding in the finishing stage T30 after adjusting the spindle rotation speed once according to the measured load value, the control unit 7 reads the measured value of the load sensor 25 and judges whether the measured value matches the load value stored in the set load value storage unit 71 (step 301). If the two load values ​​match, the process is terminated, and if they do not match, the spindle rotation speed is changed within a range including the spindle rotation speed selected by the first selection unit 74 until they match (step 302). This process is performed until the grinding in the finishing stage T30 is completed. This allows the load value to be controlled with higher precision, so that the variation in the cross-sectional shape of the wafer 10 can be further reduced. The third control example may be applied to the finishing stages T40 and T50.

[0036] (1-4) Fourth control example The fourth control example is an example of processing performed when there is no corresponding spindle rotation speed when referring to the load data table 910 shown in Fig. 5 in step 206 of the second control example shown in Fig. 4. That is, the fourth control example is a modification of step 206 of the second control example, and is an example of performing the processing shown in the flowchart of Fig. 7.

[0037] The control unit 7 refers to the load data table 910 shown in FIG. 5 (step 401) and judges whether there is a spindle rotation speed corresponding to the measured load (step 402). If there is a corresponding spindle rotation speed, the first selection unit 74 selects that spindle rotation speed and performs finishing stage T30 grinding on the next wafer 10 under the same conditions (step 205 in FIG. 4). On the other hand, if there is no corresponding spindle rotation speed, the first selection unit 74 selects the upper or lower limit spindle rotation speed of the load data table 910. For example, if the load value set in the set load value storage unit 71 is 35 N while the measured value by the load sensor 25 is 28 N, the first selection unit 74 selects the lower limit 1200 rpn, which is the spindle rotation speed corresponding to 30 N (step 403).

[0038] Next, the control unit 7 refers to the chuck rotation speed data table 920 shown in FIG. 8 (step 404). This chuck rotation speed data table 920 was obtained by a grinding experiment using a specific grinding wheel under a specific grinding feed rate, and indicates the change in load relative to the change in rotation speed of the chuck table 2. The control unit 7 obtains the difference between the measurement value by the load sensor 25 and the load value corresponding to the spindle rotation speed selected by the first selection unit 74 as the load change amount, and obtains the chuck table rotation speed change amount corresponding to the load change amount. In the above example, since the load change amount is 30N-28N=2N, 20 rpm is selected in the chuck rotation speed data table 920 as the chuck table rotation speed change amount corresponding to the load change amount 2N. If the initial rotation speed of the chuck table 2 is 200 rpm, 200 rpm+20 rpm=220 rpm is selected as the chuck table rotation speed. The chuck table rotation speed control unit 75 of the control unit 7 changes the rotation speed of the chuck table 2 to 220 rpm (step 405). Next, grinding in the finishing stage T30 is continued under these conditions (step 205 in FIG. 4).

[0039] In the fourth control example, even if the measurement value of the load sensor 25 is outside the range of the load data table 910 and therefore the spindle rotation speed cannot be set corresponding to the measured load, by changing the rotation speed of the chuck table 2, it is possible to perform grinding under the conditions of the load value stored in the set load value memory unit 71. Therefore, even if the measured load value is significantly different from the load value stored in the set load value memory unit 71, it is possible to reduce the variation in the cross-sectional shape of the wafer 10. Depending on the grinding wheel, the load can be increased by slowing down the rotational speed of the spindle or the rotational speed of the chuck table, and it is a good idea to set in advance in the device the change in load in response to a change in the rotational speed of the spindle or the change in load in response to a change in the rotational speed of the chuck table for each grinding wheel. The fourth control example may be applied to the finishing stages T40 and T50.

[0040] 2. Second embodiment 9 is an apparatus that grinds a wafer held on a chuck table 2 using a grinding mechanism 3, similar to the grinding apparatus 1 shown in Fig. 1, and the chuck table 2 is driven by a chuck table feed mechanism 4 to be movable in the Y-axis direction, and the grinding mechanism 3 is driven by a grinding feed mechanism 5 to be movable in the Z-axis direction. Below, parts that differ from the grinding apparatus 1 will be described, and parts that are configured similarly will be given the same reference numerals and their description will be omitted.

[0041] The grinding apparatus 100 has a control unit 8 that controls the chuck table 2, the grinding mechanism 3, the chuck table feed mechanism 4, and the grinding feed mechanism 5. The control unit 8 includes a CPU and a memory element.

[0042] The control unit 8 includes a set load current value memory unit 81 in which a predetermined spindle load current value during grinding is pre-stored, a spindle rotation speed control unit 82 which controls the rotation speed of the spindle 30 so that the actual load current value measured by the load current value measuring unit 95 during grinding becomes the load current value stored in the set load current value memory unit 81, and a second memory unit 83 which stores the spindle rotation speed when the actual load current value becomes the load current value stored in the set load current value memory unit 81.

[0043] The grinding device 1 has a load current value data table memory unit 93 that stores a load current value data table showing the relationship between the load current value and the spindle rotation speed, and the control unit 8 has a second selection unit 84 that refers to the contents of the load current value data table memory unit 93 and selects the spindle rotation speed corresponding to the measurement value of the load current value measuring unit 95.

[0044] In addition, the grinding device 1 has a chuck rotational speed data table storage unit 94 that stores a chuck rotational speed data table indicating the relationship between the rotational speed of the chuck table 2 and the load, and the control unit 8 is equipped with a chuck table rotational speed control unit 85 that changes the rotational speed of the chuck table 2 in response to the measurement value of the load current value measuring unit 95.

[0045] (2-1) Fifth control example The following description will be given with reference to the flowchart shown in FIG. First, an ideal load value during grinding in the finishing stage T30 is stored in the set load current value storage unit 81 of the control unit 8 (step 501). This load current value is a load current value that is empirically considered optimal in relation to the type of grinding wheel 341 used, the material of the wafer 10 to be ground, and the grinding feed rate determined accordingly.

[0046] In the finishing stage T30, the descent of the grinding mechanism 3 by the grinding feed mechanism 5 is stopped, and the spindle rotation mechanism 31 maintains the state of rotating the spindle 30 to perform grinding (step 502), while the control unit 8 reads the measured value in the load current value measurement unit 95 (step 503) and judges whether it matches the predetermined load current value set in the set load current value storage unit 81 (step 504). Then, if both load current values ​​match, the load current value stored in the set load current value storage unit 81 is stored in the second storage unit 83 (step 505). On the other hand, if they do not match, the spindle rotation speed control unit 72 changes the rotation speed of the spindle 30 (step 506). Specifically, if the measurement value of the load current value measuring unit 95 is greater than the predetermined load current value stored in the set load current value storage unit 81, the rotation speed of the spindle 30 is slowed down, and if the measurement value of the load current value measuring unit 95 is less than the predetermined load value stored in the set load current value storage unit 81, the rotation speed of the spindle 30 is increased. Then, grinding is performed while changing the spindle rotation speed (step 502), and the load current value is measured by the load current value measuring unit 95 (step 503). When the two load values ​​match, the spindle rotation speed at that time is stored in the second storage unit 83 (step 505).

[0047] Once the spindle rotation speed is stored in the second storage unit 83 in this manner, the wafer 10 is removed from the holding surface 200, and another wafer 10 is held on the holding surface 200. Then, the grinding mechanism 3 is lowered by the same control as that of T1 to T5 shown in Fig. 2, and in the finishing stage T30, the spindle rotation speed control unit 82 grinds the wafer 10 while maintaining the rotation speed of the spindle 30 at the speed stored in the second storage unit 83 (step 507).

[0048] Then, the thickness measuring unit 6 monitors whether the total thickness of the wafer 10 and the protective tape 11 has reached a predetermined thickness (step 508), and when that total thickness reaches the predetermined thickness, the grinding feed mechanism 5 raises the grinding mechanism 3, thereby completing the grinding.

[0049] According to the fifth control example, an ideal load current value that is understood from experience is first set, and then the spindle rotation speed when the value measured by the load current value measuring unit 95 reaches the set load current value is stored, and grinding is performed by rotating the spindle 30 at the stored spindle rotation speed, so that even if there are differences between machines or between grinding wheel lots, the spindle rotation speed can be adjusted to accommodate those differences. Therefore, the variation in the cross-sectional shape of the wafer can be reduced. The fifth control example may be applied to the finishing stages T40 and T50.

[0050] (2-2) 6th control example The following description will be given with reference to the flow chart shown in FIG. First, an ideal load current value during grinding in the finishing stage T30 is stored in the set load current value storage unit 81 of the control unit 8 (step 601). This load current value is a load current value that is empirically considered optimal in relation to the type of grinding wheel 341 used, the material of the wafer 10 to be ground, and the grinding feed rate determined accordingly.

[0051] In the finishing stage T30, with the descent of the grinding mechanism 3 by the grinding feed mechanism 5 stopped, the spindle rotation mechanism 31 keeps the spindle 30 rotating to perform grinding (step 602), while the control unit 8 reads the measurement value in the load current value measuring unit 95 (step 603) and determines whether it matches the predetermined load current value set in the set load current value storage unit 81 (step 604). Then, if both load current values ​​match, grinding of the next wafer 10 is started (step 605). On the other hand, if the two load current values ​​do not match, the contents stored in the load current value data table storage unit 93 are referred to. The load current value data table storage unit 93 stores, for example, a load current value data table 930 shown in Fig. 12. This load current value data table 930 was obtained by a grinding experiment using a specific grinding wheel at a specific grinding feed rate, with the left column showing values ​​measured by the load current value measurement unit 95 and the right column showing the spindle rotation speed at which the load current value becomes 7 A based on the measured values. The second selection unit 84 reads the measured value of the load current value measurement unit 95, and selects the value of the spindle rotation speed corresponding to the measured value in the load current value data table 930. For example, when the measured value by the load current value measurement unit 95 is 6.7 A, the spindle rotation speed may be set to 1400 rpm in order to make the measured value 7 A. When the load stored in the set load current value storage unit 81 is 7 [A] and the measured value by the load current value measurement unit 95 is 6.7 A, the spindle rotation speed is selected to be 1400 rpm (step 606). Then, the spindle rotation speed control unit 72 continues grinding at the spindle rotation speed (step 605).

[0052] During the grinding of the wafer 10 in the finishing stage T30, the thickness measuring unit 6 monitors whether the total thickness of the wafer 10 and the protective tape 11 has reached a predetermined thickness (step 607), and when that total thickness reaches the predetermined thickness, the grinding feed mechanism 5 raises the grinding mechanism 3, thereby ending the grinding.

[0053] According to the sixth control example, first, an ideal load current value known from experience is set, and if the measured value by the load current value measuring unit 95 does not match the set load current value, the spindle rotation speed for changing the measured load current value to the set load current value is calculated by referring to the load current value data table 930, and grinding is performed at the calculated spindle rotation speed, so that even if there are differences between machines or between grinding wheel lots, the spindle rotation speed can be adjusted to accommodate those differences. Therefore, the cross-sectional shape of the wafer can be made constant. The sixth control example may be applied to the finishing stages T40 and T50.

[0054] (2-3) Seventh control example The seventh control example is an example in which the processing shown in the flowchart in FIG. 13 is performed between steps 507 and 508 in the fifth control example shown in FIG. 10, or between steps 605 and 607 in the sixth control example shown in FIG. 11.

[0055] As shown in Fig. 13, even after step 507 in the fifth control example or after step 605 in the sixth control example, that is, even while grinding is being performed by adjusting the spindle rotation speed once according to the measured value of the load current, the control unit 8 reads the measured value of the load current value measuring unit 95 and judges whether the measured value coincides with the load current value stored in the set load current value storage unit 81 (step 701). If they coincide, the process is terminated, and if they do not coincide, the spindle rotation speed is changed until the load current value coincides within a range including the load current value selected by the second selection unit 84 (step 702). This process is performed until the grinding in the finishing stage T30 is completed. This allows the spindle rotation speed to be controlled with higher precision, so that the variation in the cross-sectional shape of the wafer 10 can be further reduced. The seventh control example may be applied to the finishing stages T40 and T50.

[0056] (2-4) 8th control example The eighth control example is an example of processing performed when there is no corresponding spindle rotation speed when referring to the load current value data table 930 shown in Fig. 12 in step 606 of the sixth control example shown in Fig. 11. That is, the eighth control example is a modification of step 606 of the sixth control example, and is an example of performing the processing shown in the flowchart of Fig. 14.

[0057] The control unit 8 refers to the load current value data table 930 shown in Fig. 12 (step 801) and determines whether there is a spindle rotation speed corresponding to the measured load current value (step 802). If there is a corresponding spindle rotation speed, the second selection unit 84 selects that spindle rotation speed, and grinding of the finishing stage T30 is performed on the next wafer 10 under the same conditions (step 605 in Fig. 11). On the other hand, if there is no corresponding spindle rotation speed, the second selection unit 84 selects the upper or lower limit spindle rotation speed of the load current value data table 930. For example, if the load current value set in the set load current value storage unit 81 is 7 A and the load current value measured by the load current value measuring unit 95 is 8 A, the second selection unit 84 selects the upper limit of 2200 rpm, which is the spindle rotation speed corresponding to 7.5 A (step 803).

[0058] Next, the control unit 7 refers to a chuck rotation speed data table 940 shown in FIG. 15 (step 804). This chuck rotation speed data table 940 was obtained by a grinding experiment using a specific grinding wheel under a specific grinding feed rate, and indicates the change in the load current value with respect to the change in the rotation speed of the chuck table 2. The control unit 8 obtains the difference between the measured value by the load current value measurement unit 95 and the load current value corresponding to the spindle rotation speed selected by the second selection unit 84 as the load current value change amount, and obtains the chuck table rotation speed change amount corresponding to the load current value change amount. In the above example, since the load current value change amount is 7A-7.5A=-0.5A, -5 is selected as the chuck table rotation speed change amount corresponding to the load current value change amount -0.5A in the chuck rotation speed data table 940. If the initial rotation speed of the chuck table 2 is 200 rpm, 195 rpm is selected as the chuck table rotation speed. The chuck table rotation speed control unit 85 of the control unit 8 changes the rotation speed of the chuck table 2 to 195 rpm (step 805). Next, grinding is continued under these conditions (step 605 in FIG. 5).

[0059] In the eighth control example, even if the measurement value in the load current value measuring unit 95 is outside the range of the load current value data table 930 and therefore the spindle rotation speed cannot be set corresponding to the measured value of the load current, by changing the rotation speed of the chuck table 2, it is possible to perform grinding under the load current value stored in the set load current value memory unit 81. Therefore, even if the measured value of the load current is significantly different from the load current value stored in the set load current value memory unit 81, the variation in the cross-sectional shape of the wafer 10 can be reduced. The eighth control example may be applied to the finishing stages T40 and T50.

[0060] As described above, in the fifth to eighth control examples, the load current value of the spindle 30 is also a factor that affects the grinding quality, just like the load, and by keeping the load current value constant, the spindle rotation speed is kept constant, thereby reducing the variation in the cross-sectional shape of the wafer 10, just as in the case where the grinding load is kept constant.

[0061] Moreover, in any of the control examples, it is possible to reduce the variation in the cross-sectional shape of the wafer 10. The load during grinding is usually adjusted by controlling the grinding feed speed by the grinding feed mechanism 5, and fine control exceeding the resolution of the ball screw 50 constituting the grinding feed mechanism 5 was impossible, but in the present invention, by adjusting the load or load current value through control of the spindle rotation speed, fine control that is not possible by adjusting only the grinding feed speed is possible.

[0062] In the grinding apparatus 1 of the first embodiment, the load sensor 25 is provided below the chuck table 2, but the load sensor may be provided on the grinding mechanism 3 side. Also, the grinding apparatus 100 of the second embodiment does not need to be provided with the load sensor 25. [Explanation of symbols]

[0063] 1, 100: Grinding equipment 2: Chuck table 20: Suction part 200: Holding surface 21: Frame 22: Chuck rotation mechanism 23: Table base 24: Chuck support 25: Load sensor 26: Bellows 27: Base 28: Chuck rotation axis 3: Grinding mechanism 30: Spindle 300: Rotating shaft 31: Spindle rotation mechanism 32: Spindle housing 33: Mount 34: Grinding wheel 340: Base 341: Grinding stone 4: Chuck table feed mechanism 40: Ball screw 400: Rotating shaft 41: Motor 42: Guide rail 43: Slide plate 5: Grinding feed mechanism 50: Ball screw 500: Rotating shaft 51: Motor 52: Guide rail 53: Lift plate 54: Holder 55: Scale 56: Reading unit 6: Thickness measuring section 61: First gauge 62: Second gauge 7, 8: Control section 71: Set load value storage unit 72: Spindle rotation speed control unit 73: First storage unit 74: First selection unit 75: Chuck table rotation speed control unit 81: Set load current memory unit 82: Spindle rotation speed control unit 83: Second memory unit 84: second selection unit 85: chuck table rotation speed control unit 91: Load data table storage unit 910: Load data table 92: Chuck rotation speed data table storage section 920: Chuck rotation speed data table 93: Load current value data table storage unit 930: Load current value data table 94: Chuck rotation speed data table storage section 940: Chuck rotation speed data table 95: Load current measurement section 10: Wafer 11: Protective tape

Claims

1. a chuck table that holds a wafer on a holding surface, a chuck rotation mechanism that rotates the chuck table about a chuck rotation axis that passes through the center of the holding surface, a grinding mechanism that grinds the wafer held on the holding surface by an underside of an annular grinding wheel disposed at the tip of a spindle, a spindle rotation mechanism that rotates the spindle, a grinding feed mechanism that moves the grinding wheel toward and away from the holding surface in a direction perpendicular to the holding surface, and a control unit, a load sensor for measuring a force with which the grinding wheel is pressed against the wafer held by the holding surface; the control unit includes a first storage unit that stores the rotation speed of the spindle, measures a load with the load sensor during grinding, and if the measured load does not match a preset load, changes the spindle rotation speed so that the load during grinding matches the preset load, and stores in the first storage unit the spindle rotation speed when the load becomes the preset load; Next, the grinding apparatus rotates the spindle at the spindle rotation speed stored in the first storage unit to grind the wafer from the wafer held on the holding surface.

2. a chuck table that holds a wafer on a holding surface, a chuck rotation mechanism that rotates the chuck table about a chuck rotation axis that passes through the center of the holding surface, a grinding mechanism that grinds the wafer held on the holding surface by an underside of an annular grinding wheel disposed at the tip of a spindle, a spindle rotation mechanism that rotates the spindle, a grinding feed mechanism that moves the grinding wheel toward and away from the holding surface in a direction perpendicular to the holding surface, and a control unit, a load sensor for measuring a force with which the grinding wheel is pressed against the wafer held by the holding surface; a load data table showing a relationship between the load and the spindle rotation speed; The control unit includes a first selection unit that selects a spindle rotation speed from the load data table, measures a load with the load sensor during grinding, and when the measured load does not match a preset load, refers to the load data table, and the first selection unit selects a spindle rotation speed at which the measured load becomes the preset load; Next, the grinding apparatus rotates the spindle at the spindle rotation speed selected by the first selection unit to grind the wafer from the wafer held on the holding surface.

3. The control unit changes the rotation speed of the spindle within a range including the spindle rotation speed stored in the first storage unit or the spindle rotation speed selected by the first selection unit, while maintaining the load measured by the load sensor at a preset load. The grinding apparatus according to claim 1 or 2.

4. a chuck table that holds a wafer on a holding surface, a chuck rotation mechanism that rotates the chuck table about a chuck rotation axis that passes through the center of the holding surface, a grinding mechanism that grinds the wafer held on the holding surface by an underside of an annular grinding wheel disposed at the tip of a spindle, a spindle rotation mechanism that rotates the spindle, a grinding feed mechanism that moves the grinding wheel toward and away from the holding surface in a direction perpendicular to the holding surface, and a control unit, a load current value measuring unit for measuring a load current value of the spindle; the control unit includes a second storage unit that stores a spindle rotation speed, measures a load current value by the load current value measurement unit during grinding, and when the measured load current value does not match a preset load current value, changes the spindle rotation speed so that the load current value during grinding matches the preset load current value, and stores in the second storage unit the spindle rotation speed at which the load current value becomes the preset load current value; Next, the grinding apparatus rotates the spindle at the spindle rotation speed stored in the second storage section to grind the wafer from the wafer held on the holding surface.

5. a chuck table that holds a wafer on a holding surface, a chuck rotation mechanism that rotates the chuck table about a chuck rotation axis that passes through the center of the holding surface, a grinding mechanism that grinds the wafer held on the holding surface by an underside of an annular grinding wheel disposed at the tip of a spindle, a spindle rotation mechanism that rotates the spindle, a grinding feed mechanism that moves the grinding wheel toward and away from the holding surface in a direction perpendicular to the holding surface, and a control unit, a load current value measuring unit for measuring a load current value of the spindle; a load current value data table showing a relationship between the load current value and the spindle rotation speed, The control unit includes a second selection unit which selects a spindle rotation speed, and measures a load current value by the load current value measurement unit during grinding. When the measured load current value does not match a preset load current value, the load current value data table is referenced, and the second selection unit selects a spindle rotation speed at which the measured load current value becomes the preset load current value. Next, the grinding apparatus rotates the spindle at the spindle rotation speed selected by the second selection unit to grind the wafer from the wafer held on the holding surface.

6. the control unit changes the rotation speed of the spindle within a range including the spindle rotation speed stored in the second storage unit or the spindle rotation speed selected by the second selection unit, while maintaining the load current value measured by the load current value measurement unit at a preset load current value. The grinding apparatus according to claim 4 or 5.

7. When the load data table or the load current value data table is referred to and there is no corresponding spindle rotation speed, Select the lower or upper limit spindle rotation speed of the load data table or the load current value data table, The rotation speed of the chuck table is changed. The grinding apparatus according to claim 2 or 5.

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