Grinding Method

Abstract

To finish a sparked-out wafer in a prescribed thickness.SOLUTION: A grinding grindstone 341 is lowered in the vertical direction to a holding surface 200 of a chuck table 2, and strain is generated in a chuck table 2 and a grinding mechanism 3 by imparting a vertical load to a wafer 10 by grinding an upper surface 100 while pushing the upper surface 100 of the wafer 10 held by the holding surface 200 by a lower surface of the grinding grindstone 341, and after grinding just before a thickness of the water 10 becomes a preset prescribed thickness, the upper surface 100 of the water 10 is ground by using a return of the strain, and the grind grindstone 341 is separated from the wafer 10 after a measured thickness of the wafer 10 becomes the preset prescribed thickness.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] A grinding device that holds a wafer such as a semiconductor wafer on the holding surface of a chuck table and grinds the wafer by bringing a grinding wheel into contact with the wafer calculates the difference between the measured height of the holding surface and the measured height of the top surface of the wafer as the wafer thickness, and continues grinding until the calculated thickness reaches a predetermined value (see, for example, Patent Document 1).

[0003] In the grinding process, the grinding wheel is moved toward the holding surface at a preset grinding feed rate, and when the wafer is formed to a predetermined thickness, a spark-out is performed to grind the wafer while the grinding wheel is stopped from descending, and then an escape cut is performed to slowly separate the grinding wheel from the wafer.The grinding wheel is then raised and retracted to finish grinding (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-073785 [Patent Document 2] Japanese Patent Application Publication No. 2020-131368 Summary of the Invention [Problem to be solved by the invention]

[0005] During grinding using a grinding wheel, the grinding device may be thermally deformed by the heat of the process, which can change the height of the holding surface and the height position of the grinding wheel during grinding. Furthermore, during grinding, a protective tape is attached to the wafer's held surface, but the amount of deformation of the protective tape when the grinding wheel is pressed against the wafer can vary from wafer to wafer. Furthermore, the load on the wafer can change depending on the remaining amount of grinding wheel. These factors result in different amounts of wafers being ground by spark-out or escape cut, resulting in different finished thicknesses for each wafer.

[0006] Therefore, in the grinding process using a grinding wheel, there is a problem to be solved in that the wafer that has undergone the spark-out process must be finished to a predetermined thickness. [Means for solving the problem]

[0007] The first invention is a method for grinding a wafer, in which a wafer held by a holding surface of a chuck table is ground by a grinding wheel attached to a grinding mechanism, the grinding wheel being lowered in a direction perpendicular to the holding surface, and the upper surface of the wafer held by the holding surface is ground while being pressed by the lower surface of the grinding wheel, thereby applying a vertical load to the wafer, causing distortions in mutually opposite directions in the perpendicular direction to the chuck table and the grinding mechanism, and the thickness of the wafer being ground, measured by a non-contact thickness measuring device, reaches a predetermined value. The method comprises a first grinding step in which the wafer is ground until it is just about to reach the predetermined thickness, and a second grinding step in which, after the first grinding step, the descent of the grinding wheel is stopped and the wafer is ground using the return of the distortion, and the grinding wheel is separated from the wafer when the thickness of the wafer measured by the thickness measuring device reaches the predetermined thickness, the amount of distortion in the perpendicular direction being determined in advance by experiment, and grinding is terminated in the first grinding step when the wafer thickness is thicker than the predetermined thickness and thinner than the sum of the predetermined thickness and the amount of distortion in the perpendicular direction. A second invention is a method for grinding a wafer, in which a wafer held by a holding surface of a chuck table is ground by a grinding wheel attached to a grinding mechanism, the method comprising: a third grinding step in which the grinding wheel is lowered in a direction perpendicular to the holding surface, and the upper surface of the wafer held by the holding surface is ground while being pressed by the lower surface of the grinding wheel, thereby applying a vertical load to the wafer, causing distortion in opposite directions in the direction perpendicular to the chuck table and the grinding mechanism, and grinding the wafer until the thickness of the wafer being ground, measured by a non-contact thickness gauge, reaches a predetermined thickness; and a fourth grinding step in which, after the third grinding step, the grinding wheel is raised at a predetermined ascending speed, the wafer is ground using the return of the distortion, and the grinding wheel is separated from the wafer when the thickness of the wafer, measured by the thickness gauge, reaches the predetermined thickness, the amount of distortion in the perpendicular direction being known in advance by experiment, 3 In the grinding step, grinding is terminated when the wafer thickness is greater than a predetermined thickness and less than the sum of the predetermined thickness and the amount of the distortion in the perpendicular direction. In the first grinding step, it is desirable to measure the vertical load with which the grinding wheel presses the wafer using a load measuring device, and to make the load measured by the load measuring device coincide with a preset load to keep the amount of distortion in the vertical direction constant. In the third grinding step, it is desirable to measure the vertical load with which the grinding wheel presses the wafer using a load measuring device, and to make the load measured by the load measuring device coincide with a preset load to keep the amount of distortion in the vertical direction constant. The rate of rise of the grinding wheel may be slower than the rate of return of the strain. [Effects of the Invention]

[0008] In the second and fourth grinding steps of the present invention, grinding is performed using the return of strain, so even if there are differences between wafers in thermal deformation of the grinding device due to processing heat during grinding, the amount of crushing of the protective tape, and the remaining amount of grinding wheels, the differences in processing heat during grinding of each wafer, the amount of crushing of the protective tape, and the remaining amount of grinding wheels can be absorbed by the return of strain. Therefore, the risk of errors in the finished thickness of the wafers due to differences between wafers in thermal deformation due to processing heat during grinding, the amount of crushing of the protective tape, and the remaining amount of grinding wheels can be reduced, and multiple wafers can be finished to a uniform thickness. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a perspective view showing an example of a grinding device. [Figure 2] 4 is a graph showing the relationship between the grinding time and the height of the lower surface (grinding surface) of the grinding wheel in the first embodiment. [Figure 3] 10 is a graph showing the relationship between the grinding time and the height of the lower surface (grinding surface) of the grinding wheel in the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] The grinding apparatus 1 shown in FIG. 1 is an apparatus that grinds a wafer 10 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 is movable in the Y-axis direction, and the grinding mechanism 3 is driven by a grinding feed mechanism 5 and is movable in the Z-axis direction.

[0011] 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 forms a holding surface 200 that holds the wafer. The holding surface 200 and the upper surface of the frame body 21 are flush with each other.

[0012] Below the chuck table 2 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 is provided a table base 23, which is supported at least at three points by three chuck support parts 24 (only two are shown in FIG. 1). Each chuck support part 24 is provided with a load measuring device 25 that measures the vertical load when the grinding mechanism 3 presses the wafer held by the holding surface 200. In addition, at least two chuck support parts 24 have the function of adjusting the height of the chuck table 2 and thereby adjusting the inclination of the holding surface 200.

[0013] 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.

[0014] The chuck table feed mechanism 4 includes a ball screw 40 having a rotation axis 400 in the Y-axis direction, a motor 41 that rotates the ball screw 40, a pair of guide rails 42 arranged parallel to the ball screw 40, and a slide plate 43 whose bottom is in sliding contact with the guide rails 42 and has a nut (not shown) inside that screws onto the ball screw 40. The chuck support 24 and the load measuring device 25 are 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. As the slide plate 43 moves in the Y-axis direction, the chuck table 2 also moves in the same direction. The frame 21 is rotatably supported by a base 27. A bellows 26 is connected to the side of the base 27 in the Y-axis direction. The chuck table 2 moves in the Y-axis direction as the bellows 26 expands and contracts.

[0015] The grinding feed mechanism 5 includes a ball screw 50 having a rotation axis 500 in the Z-axis direction, a motor 51 that rotates the ball screw 50, a pair of guide rails 52 arranged parallel to the ball screw 50, a lift plate 53 whose side is in sliding contact with the guide rails 52 and has a nut (not shown) inside that screws onto 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 that detects the position of the lift plate 53 in the Z-axis direction as a read value on the scale 55. When the ball screw 50 rotates, the lift plate 53 is guided by the guide rails 52 and moves in a direction perpendicular to the holding surface 200, and the grinding mechanism 3 also moves in the same direction, causing the grinding wheel 341 to approach or move 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.

[0016] A thickness gauge 6 is disposed on the side of the movement path of the chuck table 2 in the Y-axis direction to measure the thickness of the wafer held on the holding surface 200. The thickness gauge 6 is a non-contact type thickness gauge and includes a first measurement unit 61 that measures the height of the holding surface 200 and a second measurement unit 62 that measures the height of the upper surface 100 of the wafer 10 held on the holding surface 200, and measures the height of the wafer based on the difference in height between the first measurement unit 61 and the second measurement unit 62. The first measurement unit 61 and the second measurement unit 62 measure the height of the holding surface 200 and the upper surface 100 of the wafer 10 based on the time from when a laser beam is emitted downward to when the reflected light is received. Note that a contact type may also be used as the thickness gauge 6. In addition, the non-contact thickness measuring device can also be a spectroscopic interference measuring device that receives reflected light from the upper surface 100 of the wafer 10 held on the holding surface 200 and reflected light from the lower surface 101 of the wafer 10 to measure the thickness of the wafer 10.

[0017] The grinding device 1 includes a control unit 7 that controls the chuck table 2, grinding mechanism 3, chuck table feed mechanism 4, grinding feed mechanism 5, and thickness measuring device 6. The control unit 7 includes a CPU and a memory element.

[0018] 1. First embodiment (1) First grinding process When the upper surface 100 of the wafer 10 is ground using the grinding mechanism 3, a protective tape 11 is attached to the lower surface 101 of the wafer 10 to be ground. The protective tape 11 side is then suction-held on the holding surface 200 of the chuck table 2, and the upper surface 100 of the wafer 10 is exposed.

[0019] The chuck table 2 holding the wafer 10 on the holding surface 200 is rotated around the rotation axis 28, the spindle rotation mechanism 31 rotates the grinding wheel 34, and the grinding feed mechanism 5 lowers the grinding mechanism 3. At time T1, the height 81 of the lower surface (grinding surface) of the grinding wheel 341 shown by the solid line in Fig. 2 is the stage where the grinding wheel 341 is brought closer to the upper surface 100 of the wafer 10 before grinding, and is lowered at high speed.

[0020] Next, at time T2, the grinding feed rate is significantly reduced compared to time T1, and an air cut is performed in which the grinding wheel 341 is slowly brought closer to the upper surface 100 of the wafer 10. As a result, the lower surface (grinding surface) of the grinding wheel 341 gradually comes into contact with the upper surface 100 of the wafer 10, and the load value 82 indicated by the dashed line in FIG. 2 increases. This load value 82 is a value measured by a load measuring device 25 (not shown) disposed below the chuck table 2 in FIG. 1, and indicates the force with which the grinding wheel 341 presses the wafer 10. During grinding, the load value 82 is constantly measured by the load measuring device 25, and the control unit 7 adjusts the grinding feed rate so that the load value 82 measured by the load measuring device 25 matches a predetermined set load value.

[0021] At time T3, the grinding mechanism 3 continues to descend in a direction perpendicular to the holding surface 200 at the same speed as at time T2, and grinding is performed while the lower surface of the grinding wheel 341 is maintained in contact with the upper surface 100 of the wafer 10. During this time, the load value 82 continues to gradually increase. At time T3, the grinding wheel 341 descends in a direction perpendicular to the holding surface 200, and the lower surface of the grinding wheel 341 presses against and grinds the upper surface 100 of the wafer 10 held on the holding surface 200, applying a vertical load to the wafer 10.

[0022] At time T4 after time T3, the grinding feed rate is made slightly slower than at time T3 and the grinding mechanism 3 is lowered, and just before the wafer 10 reaches the predetermined finished thickness, for example, when the wafer 10 reaches a state that is about 1 to 2 μm thicker than the predetermined finished thickness, the lowering of the grinding mechanism 3 is stopped.

[0023] (2) Second grinding process At time T5, grinding (spark out) is performed with the descent of the grinding wheel 341 stopped. At times T3 and T4, when the grinding wheel 341 is lowered and brought into contact with the upper surface 100 of the wafer 10 to perform grinding, distortion occurs in the grinding apparatus 1 due to the grinding wheel 341 being pressed against the wafer 10. Specifically, the chuck table 2 sinks downward and the grinding mechanism 3 is pushed back upward. Meanwhile, when the descent of the grinding wheel 341 is stopped at time T5, the distortion returns (springback), and during spark out, the lower surface of the grinding wheel 341 comes into contact with the upper surface 100 of the wafer 10 to perform grinding. Then, when the measurement value of the thickness gauge 6 reaches a predetermined thickness during this grinding, the grinding at time T5 ends. At time T5, the load value 82 decreases as grinding progresses, and when the distortion is completely restored, grinding ends, the grinding wheel 341 and the upper surface 100 of the wafer 10 no longer come into contact, and the load value 82 becomes zero.

[0024] When the grinding at time T5 is completed, the process moves to time T7, the grinding mechanism 3 is raised at high speed to separate the grinding wheel 341 from the wafer 70, and the grinding is completed.

[0025] Even if there are differences between wafers 10 in the thermal deformation of the grinding device 1 due to processing heat during grinding or the amount of crushing of the protective tape 11, in the second grinding process, spark-out is performed to grind the wafers 10 while measuring the thickness of the wafers 10 by utilizing the return of distortion.This makes it possible to absorb differences in the amount of grinding in spark-out due to differences in processing heat during grinding of each wafer 10, differences in the amount of crushing of each protective tape 11, and differences in the remaining amount of grinding wheel 341, thereby reducing the risk of errors in the finished thickness of the wafers 10 caused by differences between wafers 10 in the thermal deformation due to processing heat during grinding, differences in the amount of crushing of the protective tape 11, and differences in the remaining amount of grinding wheel 341.

[0026] 2. Second embodiment (1) Third grinding process The upper surface 100 of the wafer 10 is ground using the grinding apparatus 1 shown in Figure 1. A protective tape 11 is attached to the lower surface 101 of the wafer 10, and the protective tape 11 side is suction-held on the holding surface 200 of the chuck table 2, leaving the upper surface 100 of the wafer 10 exposed. Specific implementation details of this step are the same as those of times T1 to T4 in the first embodiment, as shown in Figure 3. During grinding, the load value 84 is constantly measured by the load measuring device 25, and the control unit 7 adjusts the grinding feed rate so that the measured value of the load measuring device 25 matches a predetermined set load value.

[0027] (2) Fourth grinding process After time T4, at time T6, grinding (spark out) is performed while gradually raising the grinding wheel 341. The absolute value of the raising speed of the grinding wheel 341 here is smaller than the lowering speed at time T4, e.g., 0.1 μm / sec. At times T3 and T4, when grinding is performed while the grinding wheel 341 is lowered, the grinding wheel 341 is pressed against the wafer 10, causing the chuck table 2 to sink downward and the grinding mechanism 3 to be pushed back upward, resulting in distortion of the grinding apparatus 1. Therefore, at time T5, the distortion returns (springback). At time T6, the grinding wheel 341 is slowly raised, but by making the raising speed of the grinding wheel 341 slower than the distortion return speed, the lower surface of the grinding wheel 341 comes into contact with the upper surface 100 of the wafer 10 during the return, thereby performing grinding. When the measurement value of the thickness gauge 6 reaches a predetermined thickness through this grinding, the grinding is terminated at time T6. At time T6, the load value 84 decreases as the grinding progresses, and when the distortion is completely restored, the grinding is terminated, the grinding wheel 341 and the upper surface 100 of the wafer 10 no longer come into contact, and the load value 84 becomes 0.

[0028] When the grinding at time T6 is completed, the process moves to time T7, at which the grinding mechanism 3 is raised at high speed to separate the grinding wheel 341 from the wafer 70, thereby completing the grinding.

[0029] Even if there are differences between wafers 10 in the thermal deformation of the grinding device 1 due to the processing heat during grinding, the amount of crushing of the protective tape 11, and the remaining amount of grinding wheel 341, by performing spark-out using the return of distortion in the fourth grinding process, the differences in the processing heat during grinding of each wafer 10, the differences in the amount of crushing of each protective tape 11, and the differences in the remaining amount of grinding wheel 341 can be absorbed by the return of distortion, thereby reducing the risk of errors in the finished thickness of the wafers 10 caused by differences between wafers 10 in the thermal deformation due to the processing heat during grinding, the differences in the amount of crushing of the protective tape 11, and the remaining amount of grinding wheel 341.

[0030] In the fourth grinding step, the grinding wheel 341 is raised at time T6, while the strain of the grinding mechanism 3 returns downward, so that grinding can be performed efficiently at time T6.

[0031] In the grinding apparatus 1 shown in FIG. 1, the load measuring device 25 is provided below the chuck table 2, but the load measuring device may be provided on the grinding mechanism 3 side.

[0032] By understanding the amount of distortion that occurs in the first grinding step and the third grinding step in advance through experiments, the amount of distortion that will be restored in the second grinding step and the fourth grinding step can be determined. Knowing the amount of restoration of distortion then makes it possible to determine at what thickness the wafer 10 should be ground in the first grinding step and the third grinding step, compared to a predetermined thickness, thereby improving the accuracy of the finished thickness after grinding in the second grinding step and the fourth grinding step. [Explanation of symbols]

[0033] 1: Grinding device 10: Wafer 100: Top surface 101: Bottom surface 11: Protective tape 2: Chuck table 20: Suction part 200: Holding surface 21: Frame 22: Chuck rotation mechanism 23: Table base 24: Chuck support 25: Load measuring device 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 board 5: Grinding feed mechanism 50: Ball screw 500: Rotating shaft 51: Motor 52: Guide rail 53: Lifting plate 54: Holder 55: Scale 56: Reading unit 6: Thickness measuring device 61: First measuring section 62: Second measuring section 7: Control unit

Claims

1. A wafer grinding method for grinding a wafer held by a holding surface of a chuck table with a grinding wheel attached to a grinding mechanism, comprising: a first grinding step in which the grinding wheel is lowered in a direction perpendicular to the holding surface, and the upper surface of the wafer held by the holding surface is ground while being pressed by the lower surface of the grinding wheel, thereby applying a vertical load to the wafer and causing distortions in opposite directions in the perpendicular direction to the chuck table and the grinding mechanism, and grinding the wafer until the thickness of the wafer being ground, as measured by a non-contact thickness measuring device, immediately reaches a predetermined thickness; a second grinding step in which, after the first grinding step, the descent of the grinding wheel is stopped, the upper surface of the wafer is ground using the recovery of the distortion, and when the thickness of the wafer measured by the thickness measuring device reaches the predetermined thickness, the grinding wheel is separated from the wafer; It consists of the amount of the strain in the perpendicular direction is known in advance by experiment, In the first grinding step, grinding is terminated when the wafer thickness is greater than a predetermined thickness and less than the sum of the predetermined thickness and the amount of distortion in the perpendicular direction. Wafer grinding method.

2. A wafer grinding method for grinding a wafer held by a holding surface of a chuck table with a grinding wheel attached to a grinding mechanism, comprising: a third grinding step in which the grinding wheel is lowered in a direction perpendicular to the holding surface, and the upper surface of the wafer held by the holding surface is ground while being pressed by the lower surface of the grinding wheel, thereby applying a vertical load to the wafer and causing distortions in mutually opposite directions in the perpendicular direction to the chuck table and the grinding mechanism, and grinding the wafer until the thickness of the wafer being ground, as measured by a non-contact thickness measuring device, immediately reaches a predetermined thickness; a fourth grinding step in which, after the third grinding step, the grinding wheel is raised at a preset ascending speed, the upper surface of the wafer is ground using the return of the strain, and when the thickness of the wafer measured by the thickness measuring device reaches the predetermined thickness, the grinding wheel is separated from the wafer; It consists of the amount of the strain in the perpendicular direction is known in advance by experiment, In the third grinding step, grinding is terminated when the wafer thickness is greater than a predetermined thickness and less than the sum of the predetermined thickness and the amount of distortion in the perpendicular direction. Wafer grinding method.

3. 2. The wafer grinding method according to claim 1, wherein in the first grinding step, a vertical load with which the grinding wheel presses the wafer is measured by a load measuring device, and the load measured by the load measuring device is made to coincide with a preset load to make the amount of distortion in the vertical direction constant.

4. A method for grinding a wafer as described in claim 2, wherein in the third grinding step, the vertical load with which the grinding wheel presses the wafer is measured by a load measuring device, and the load measured by the load measuring device is made to match a predetermined set load, thereby making the amount of distortion in the vertical direction constant.

5. 3. The method for grinding a wafer according to claim 2, wherein the ascending speed of the grinding wheel is slower than the returning speed of the strain.

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