Chuck table, grinding apparatus, and method for forming a holding surface

Abstract

To grind a warped wafer to reduce its thickness to a uniform thickness.SOLUTION: Air is supplied to an elastic tube 20 provided between a center suction part 17, configured to hold a center part of a wafer 100, and an outer periphery holding part 18, configured to hold an outer periphery part, to bring an upper end of the elastic tube into contact with a lower surface 100b of the wafer 100 in which an outer periphery is warped, and an upper surface 100a of the wafer 100 is ground with grind stones 57 to weaken a warping force of the wafer 100. Air in the elastic tube 20 is discharged and the lower surface 100b of the wafer 100 is held with a center holding surface 21 and an outer periphery holding surface 22 to grind the upper surface 100a of the wafer 100. Air is supplied to the elastic tube 20 to bring the elastic tube 20 into contact with the lower surface 100b of the wafer 100 suctioned and held by the center holding surface 21 and the outer periphery holding surface 22, and the upper surface 100a of the wafer 100 is ground with the grind stones 57 to reduce a thickness of the wafer 100 to a predetermined thickness.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a chuck table for sucking and holding a wafer, a grinding apparatus provided with the chuck table, and a method for forming a holding surface of the chuck table.

Background Art

[0002] For example, in Patent Documents 1 and 2 below, as a chuck table for holding a wafer having an element whose outer periphery warps upward from the center, a suction surface for sucking the central portion of the lower surface of the wafer and an annular elastic member for contacting the lower surface of the outer peripheral portion of the wafer outside the suction surface are arranged.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] When the wafer held on the above chuck table is ground with a grinding wheel, the elastic member in contact with the outer peripheral portion of the lower surface of the wafer is crushed by the grinding load. Therefore, there is a problem that the thickness of the portion of the ground wafer that was in contact with the elastic member becomes thick in an annular shape.

[0005] Therefore, when grinding a warped wafer, there is a problem of forming the wafer to have a uniform thickness.

Means for Solving the Problems

[0006] The first invention is a chuck table for holding the lower surface of a wafer by suction in order to grind the upper surface of the wafer, which has an element in which the outer circumference is curved upward from the central portion, with a grinding wheel, comprising: a central suction portion that holds the central portion of the lower surface of the wafer by suction with a central holding surface; an outer periphery suction portion that holds the outer circumference of the lower surface of the wafer by suction with an outer periphery holding surface that is flush with the central holding surface; an annular elastic tube that fits into an annular groove formed between the central suction portion and the outer periphery suction portion; and a frame body having a recess that accommodates the central suction portion, the annular groove and the outer periphery suction portion, the upper surface of the recess being flush with the outer periphery holding surface, wherein the frame body comprises a central suction passage that connects the central suction portion to a suction source, an outer periphery suction passage that connects the outer periphery suction portion to a suction source and an air supply passage that connects the elastic tube to an air source. The second invention is a grinding apparatus comprising: a chuck table according to claim 1 for suction holding the lower surface of a wafer having an element in which the outer circumference is curved higher than the central portion; a grinding mechanism for grinding the upper surface of the wafer held by suction on the chuck table with a grinding wheel; a thickness measuring instrument for measuring the thickness of the wafer; and a control unit, wherein the apparatus is equipped with a shape adjustment mechanism that changes the shape of the elastic tube by supplying air into the inside of the elastic tube and changes the height of the upper end of the elastic tube in the vertical direction of the central holding surface, and the control unit supplies air into the inside of the elastic tube by the shape adjustment mechanism and holds the wafer held by suction on the central holding surface with its outer circumference curved upward, and the central holding The device comprises: a first control unit that brings the upper end of the elastic tube into contact with the lower surface outside the portion held by the surface; a second control unit that grinds the upper surface of the wafer with the grinding wheel to reduce the force that causes the outer peripheral portion of the wafer to warp; a third control unit that uses the shape adjustment mechanism to expel air from inside the elastic tube and uses the outer peripheral holding surface to attract and hold the lower surface of the outer peripheral portion of the wafer held by the central holding surface; and a fourth control unit that uses the shape adjustment mechanism to supply air to the inside of the elastic tube, brings the elastic tube into contact with the lower surface of the wafer that is attracted and held by the central holding surface and the outer peripheral holding surface, and grinds the upper surface of the wafer with the grinding wheel to grind the entire wafer to a predetermined thickness. This grinding apparatus may be equipped with an outer peripheral nozzle that supplies water to the outer peripheral portion of the wafer, and the second control unit may cause the outer peripheral nozzle to supply water to the outer peripheral holding surface. The third invention is a method for forming a holding surface of a chuck table attached to the grinding apparatus, comprising: a grinding wheel mounting step of mounting a holding surface grinding wheel for grinding the upper surface of the chuck table to the grinding mechanism; a pressure adjustment step of adjusting the air pressure inside the elastic tube by the shape adjustment mechanism using an upper surface height measuring instrument to measure the height of the upper surface of the chuck table so that the upper surface of the elastic tube becomes flush with the central holding surface or the outer peripheral holding surface; and a holding surface grinding step of grinding the central holding surface, the upper surface of the elastic tube, and the outer peripheral holding surface using the holding surface grinding wheel while maintaining the pressure value adjusted in the pressure adjustment step. [Effects of the Invention]

[0007] The chuck table of the present invention has an elastic tube fitted into the annular groove between the central suction section and the outer peripheral suction section. By bringing the elastic tube into contact with the underside of the wafer, which is curved upwards on the outer peripheral side, the wafer can be held in suction without air leakage, at least in the central suction section. Furthermore, by adjusting the height of the upper end of the elastic tube, the thickness distribution (longitudinal cross-sectional shape) of the wafer being ground can be adjusted. In the grinding apparatus of the present invention, an elastic tube is fitted into an annular groove between a central suction section that holds the center of the wafer by suction and an outer suction section that holds the outer periphery by suction. By bringing the upper end of the elastic tube into contact with the lower surface of the wafer and grinding the upper surface of the wafer, the wafer's warping can be reduced. Subsequently, by lowering the upper end of the elastic tube and holding the lower surface of the wafer by suction at the central and outer periphery holding surfaces and grinding the upper surface, the wafer's thickness can be made uniform. Therefore, it is no longer necessary to perform the complicated operation of grinding on a chuck table formed on the outer periphery to reduce warping, and then transferring the wafer to a chuck table without an elastic member for further grinding, thus shortening the grinding time. [Brief explanation of the drawing]

[0008] [Figure 1] This is a perspective view showing an example of a grinding machine. [Figure 2]This is a perspective view showing an example of a chuck table and base. [Figure 3] This is a longitudinal cross-sectional view showing an example of a chuck table. [Figure 4] This is a schematic cross-sectional view showing the self-grinding state of the holding surface of the chuck table. [Figure 5] This is a schematic cross-sectional view showing a wafer with its outer edge curved upwards being held in a grinding machine. [Figure 6] This is a schematic cross-sectional view showing the state in which the wafer is ground by contacting the upper end of an elastic tube with the lower surface of the wafer, which is curved upwards on its outer edge. [Figure 7] This is a schematic cross-sectional view showing the state in which the upper end of the elastic tube is lowered to grind the wafer. [Figure 8] This is a schematic cross-sectional view showing the process of grinding a wafer to form a uniform thickness. [Modes for carrying out the invention]

[0009] The grinding apparatus 1 shown in Figure 1 comprises a chuck table 10 for holding a wafer 100, a grinding mechanism 50 for grinding the wafer 100 held on the chuck table 10, a grinding feed mechanism 60 for moving the grinding mechanism 50 toward or away from the chuck table 10, a horizontal movement mechanism 70 for moving the chuck table 10 horizontally, and a thickness measuring instrument 80 for measuring the thickness of the wafer 100.

[0010] As shown in Figure 2, the chuck table 10 comprises a frame 11 having a recess 12 and a suction member 16 housed in the recess 12.

[0011] The frame 11 has a peripheral edge 14 that is formed to be lower than its upper surface 13, and the peripheral edge 14 has a plurality of through holes 15 that penetrate in the thickness direction and are formed at predetermined intervals in the circumferential direction.

[0012] The attracting member 16 includes a central attracting portion 17 that attracts and holds the central portion of the wafer 100, an outer peripheral attracting portion 18 that attracts and holds the outer peripheral portion of the wafer 100, an annular groove 19 formed between the central attracting portion 17 and the outer peripheral attracting portion 18, and an annular elastic tube 20 fitted into the annular groove 19. The upper surface of the central attracting portion 17 constitutes a central holding surface 21 that attracts and holds the central portion of the lower surface of the wafer, and the upper surface of the outer peripheral attracting portion 18 constitutes an outer peripheral holding surface 22 that attracts and holds the outer peripheral portion of the lower surface 100b of the wafer 100.

[0013] The chuck table 10 is fixed to the base 30 shown in FIG. 2. The base 30 is formed to have the same diameter as the chuck table 10, and a plurality of screw holes 31 corresponding to the through holes 15 formed in the frame body 11 are formed in the peripheral portion. By screwing a screw (not shown) inserted through the through hole 15 of the frame body 11 into the screw hole 31, the chuck table 10 is fixed to the base 30.

[0014] An annular central attracting groove 32 is formed in the base 30 at a position corresponding to the central attracting portion 17 of the chuck table 10. A central attracting flow path 33 opens at the bottom surface of the central attracting groove 32. An air supply flow path 34 opens at a position on the outer peripheral side of the central attracting groove 32 and corresponding to the annular groove 19 in which the elastic tube 20 of the chuck table 10 is accommodated. An annular outer peripheral attracting groove 35 is formed on the outer peripheral side of the air supply flow path 34. The outer peripheral attracting groove 35 is formed at a position corresponding to the outer peripheral attracting portion 18 of the chuck table 10. An outer peripheral attracting flow path 36 opens at the bottom surface of the outer peripheral attracting groove 35.

[0015] As shown in FIG. 3, the central holding surface 21 and the outer peripheral holding surface 22 are formed on a conical surface having the center of the chuck table 10 as the apex. An air space 23 into which air is injected is formed inside the elastic tube 20, and the air space 23 communicates with an air supply path 24 formed in the frame body 11, and the air supply path 24 opens at an air supply port 25 on the lower surface of the frame body 11.

[0016] The frame body 11 is formed with a central suction passage 26 that communicates with the central suction portion 17 of the chuck table 10. The central suction passage 26 opens at a central suction port 27 on the lower surface of the frame body 11.

[0017] The frame body 11 is formed with an outer peripheral suction passage 28 that communicates with the outer peripheral suction portion 18 of the chuck table 10. The outer peripheral suction passage 28 opens at an outer peripheral suction port 29 on the lower surface of the frame body 11.

[0018] As shown in FIG. 4, when the chuck table 10 is fixed to the base 30, the central suction port 27 of the frame body 11 communicates with the central suction passage 33 of the base 30, the outer peripheral suction port 29 of the frame body 11 communicates with the outer peripheral suction passage 36 of the base 30, and the air supply port 25 of the frame body 11 communicates with the air supply passage 34 of the base 30.

[0019] The central suction passage 33 is connected to a suction source 39 via a central suction pipe 37 and an on-off valve 38. A pressure gauge 40 is connected to the central suction pipe 37. The outer peripheral suction passage 36 is connected to a suction source 39 via an outer peripheral suction pipe 41 and an on-off valve 42. A pressure gauge 43 is connected to the outer peripheral suction pipe 41. The air supply passage 34 is connected to an air source 47 via an air supply pipe 44, a pressure regulating valve 45, and an on-off valve 46. By sending air from the air source 47 to the air space 23 of the elastic tube 20 via the pressure regulating valve 45 and the on-off valve 46 or by discharging air from the on-off valve 46, the shape of the elastic tube 20 can be changed, and the height of the upper surface of the elastic tube 20 can be changed in a direction perpendicular to the central holding surface 21. Therefore, the pressure regulating valve 45, the on-off valve 46, and the air source 47 constitute a shape adjusting mechanism 48.

[0020] As shown in Figure 1, the grinding mechanism 50 includes a spindle 51 extending in the Z-axis direction, a spindle housing 52 that rotatably supports the spindle 51, a motor 53 that rotationally drives the spindle 51, a mount 54 connected to the lower end of the spindle 51, and a grinding wheel 55 mounted on the mount 54. The grinding wheel 55 consists of a base 56 fixed to the mount 54 and a plurality of grinding wheels 57 fixed in an annular shape to the lower surface of the base 56. When the motor 53 rotates the spindle 51, the grinding wheel 55 also rotates.

[0021] The grinding feed mechanism 60 includes a ball screw 61 extending in the Z-axis direction, a pair of guide rails 62 arranged parallel to the ball screw 61, a motor 63 for rotating the ball screw 61 in forward and reverse directions, a lifting plate 64 equipped with a nut that screws onto the ball screw 61 and whose rear side (+Y side) slides against the guide rail 62, and a holder 65 connected to the lifting plate 64 and supporting the spindle housing 52. When the motor 763 rotates the ball screw 61 in forward and reverse directions, the lifting plate 64 moves up and down, causing the grinding mechanism 50 to move up and down.

[0022] The base 30 to which the chuck table 10 shown in Figure 2 is fixed is connected to the rotary drive mechanism 49 shown in Figure 1, and is rotatable. Also, as shown in Figure 1, the rotary drive mechanism 49 is fixed to the slide plate 74.

[0023] The horizontal movement mechanism 70 includes a ball screw 71 extending in the Y-axis direction, a pair of guide rails 72 arranged parallel to the ball screw 71, a motor 73 for rotating the ball screw 71 in forward and reverse directions, and a slide plate 74 equipped with a nut that screws onto the ball screw 71 and whose lower side (-Z side) slides against the guide rail 72. When the motor 73 rotates the ball screw 71 in forward and reverse directions, the slide plate 74 slides in the Y-axis direction, and together with the slide plate 74, the chuck table 10 and the rotary drive mechanism 49 move in the Y-axis direction.

[0024] The chuck table 10 is covered by a cover 75, and bellows 76 are connected to the +Y and -Y sides of the cover 75. When the slide plate 74 is moved in the Y-axis direction by the horizontal movement mechanism 70, the rotation drive mechanism 49, the base 30, and the chuck table 10 also move in the Y-axis direction accordingly.

[0025] A thickness measuring device 80 for measuring the thickness of the wafer 100 is positioned to the side of the Y-axis movement path of the chuck table 10. The thickness measuring device 80 includes a top surface height measuring device 81 for measuring the height of the top surface 100a of the wafer 100, and a holding surface height measuring device 82 for measuring the height of the top surface 13 of the frame 11, and the height of the central holding surface 21 and the outer peripheral holding surface 22 which are formed flush with the top surface 13. The thickness of the wafer 100 is determined by calculating the difference between the measurement value of the top surface height measuring device 81 and the measurement value of the holding surface height measuring device 82.

[0026] 1 Self-grinding Before grinding the upper surface 100a of the wafer 100, the central holding surface 21 of the chuck table 10, the outer periphery holding surface 22, and the elastic tube 20 are self-ground. This self-grinding process is carried out with air supplied to the elastic tube 20, and after self-grinding, the central holding surface 21, the outer periphery holding surface 22, and the upper surface of the elastic tube 20 become flush.

[0027] (1) Grinding wheel mounting process First, as shown in Figure 1, the grinding wheel 55 is mounted on the mount 54. Here, the grinding wheel 55 is a surface grinding wheel for grinding the central holding surface 21 and the outer periphery holding surface 22 of the chuck table 10. Although not shown, for example, the mount 54 has a through hole, and the base 56 of the grinding wheel 55 has a screw hole. The grinding wheel 55 is fixed to the mount 54 by inserting a screw (not shown) from above the mount 54 and screwing it into the screw hole in the base 56.

[0028] (2) Pressure adjustment process Next, the chuck table 10 is positioned to the side of the thickness measuring instrument 80 by the horizontal movement mechanism 70, the tip of the top surface height measuring instrument 81 is brought into contact with the top surface of the elastic tube 20, and the tip of the holding surface height measuring instrument 82 is brought into contact with, for example, the outer peripheral holding surface 22. While measuring the height of the top surface of the elastic tube 20, the control unit 90 opens the on / off valve 46 shown in Figure 4 to connect the air source 47 with the air space 23 of the elastic tube 20, and controls the pressure regulating valve 45 to adjust the air pressure inside the air space 23 so that the top surface of the elastic tube 20 becomes flush with the outer peripheral holding surface 22. The pressure regulating valve 45 then maintains the pressure when the top surface of the elastic tube 20 and the outer peripheral holding surface 22 become flush. Alternatively, the tip of the top surface height measuring instrument 81 may be brought into contact with the central holding surface 21, and the tip of the holding surface height measuring instrument 82 may be brought into contact with the upper surface of the elastic tube 20, and the air pressure inside the air space 23 may be adjusted so that the upper surface of the elastic tube 20 is flush with the upper surface of the central holding surface 21.

[0029] (3) Grinding process of the holding surface Next, while maintaining the pressure in the air space 23 when the upper surface of the elastic tube 20 is flush with the central holding surface 21 or the outer periphery holding surface 22, the rotation drive mechanism 49 shown in Figure 1 rotates the chuck table 10, the motor 53 of the grinding mechanism 50 rotates the spindle 51, and the motor 63 of the grinding feed mechanism 60 rotates the ball screw 61, causing the grinding mechanism 50, with the grinding wheel 55 rotating, to descend, and the rotating grinding wheel 57 to come into contact with the central holding surface 21, the outer periphery holding surface 22, and the upper surface of the elastic tube 20 of the chuck table 10 to perform grinding. As a result, the central holding surface 21, the outer periphery holding surface 22, and the elastic tube 20 become flush.

[0030] 2. Wafer grinding As shown in Figure 5, the bottom surface 100b of the wafer 100 is placed on the central holding surface 21, the outer peripheral holding surface 22, and the upper end of the elastic tube 20, which have been made flush by self-grinding. Then, the control unit 90 opens the on / off valve 38 to connect the central suction unit 17 and the suction source 39. Because the outer peripheral side of the wafer 100 is warped upward, there is a gap between the outer peripheral portion of the central holding surface 21 and the bottom surface 100b of the wafer 100, causing suction force to leak at the central holding surface 21.

[0031] Therefore, under the control of the first control unit 91, the on / off valve 46 constituting the shape adjustment mechanism 48 is opened to supply air to the air space 23 of the elastic tube 20, thereby raising the upper end of the elastic tube 20 and bringing it into contact with the lower surface 100b of the wafer 100. Since the upper end of the elastic tube 20 contacts the lower surface 100b of the wafer 100 outside the central holding surface 21, air leakage at the central holding surface 21 is eliminated. Consequently, the wafer 100 is held more stably compared to before the upper end of the elastic tube 20 contacts the lower surface 100b of the wafer 100. As the outer edge of the wafer 100 is curved upwards, the central portion of the lower surface of the wafer 100 is held in place by suction only by the central holding surface 21. Alternatively, the negative pressure on the central holding surface 21 may be monitored to recognize when the upper end of the elastic tube 20 has come into contact with the lower surface 100b of the wafer 100. In other words, an increase in the negative pressure value on the central holding surface 21 indicates that the elastic tube 20 has come into contact with the lower surface 100b of the wafer 100. Then, the air pressure in the air space 23 of the elastic tube 20 may be reduced, and the wafer 100 may be forcibly held by the suction force of the central holding surface 21. In other words, the air pressure in the air space 23 of the elastic tube 20 may be reduced until the negative pressure value of the central holding surface 21 begins to change in the positive direction, bringing the entire surface of the central holding surface 21 closer to the bottom surface 100b of the wafer 100.

[0032] From that state, as shown in Figure 6, under the control of the second control unit 92, the rotation drive mechanism 49 is driven to rotate the chuck table 10, the motor 53 constituting the grinding mechanism 50 is driven to rotate the grinding wheel 55, and the motor 63 constituting the grinding feed mechanism 60 is driven to lower the grinding mechanism 50. As a result, the grinding wheel 57 comes into contact with the outer periphery of the upper surface 100a of the wafer 100, and grinding is performed on the upper surface 100a while pressing down on the wafer 100 from above and reducing the upward bending force. Since more of the outer periphery of the upper surface 100a of the wafer 100 is ground, the wafer 100 is formed thinner on the outer side.

[0033] Alternatively, an outer peripheral nozzle 83 may be positioned outside the outer peripheral suction section 18, and under the control of the second control unit 92, water supplied from the water source 84 may be ejected from the outer peripheral nozzle 83 towards the gap between the outer peripheral holding surface 22 and the lower surface 100b of the wafer 100. This forms a water seal at the contact point between the upper end of the elastic tube 20 and the lower surface of the wafer 100, preventing air leakage at the central holding surface 21 and further stabilizing the wafer 100's holding state. Furthermore, grinding debris can be prevented from entering the gap, thus preventing it from adhering to the outer peripheral holding surface 22. Alternatively, the outer peripheral suction section 18 and the suction source 39 may be connected, water may be supplied from the outer peripheral nozzle 83, and the upper surface 100a of the wafer 100 may be ground while sucking water from the outer peripheral suction surface.

[0034] In this way, grinding continues with leakage prevented at the central holding surface 21, and under the control of the third control unit 93, the pressure regulating valve 45 constituting the shape adjustment mechanism 48 discharges the air from the air space 23 of the elastic tube 20, connecting the outer peripheral holding surface 22 to the suction source, and as shown in Figure 7, the height of the upper end of the elastic tube 20 is adjusted to match the height of the central holding surface 21, and the lower surface 100b of the wafer 100 is held by suction at the central holding surface 21 and the outer peripheral holding surface 22. As a result, the lower surface 100b of the wafer 100 is held by suction following the central holding surface 21 and the outer peripheral holding surface 22. When discharging air from the air space 23 of the elastic tube 20, water may be supplied to the outer peripheral holding surface 22 from the outer peripheral nozzle 83.

[0035] Alternatively, a nozzle 85 may be provided that sprays water downward from above the outer periphery of the wafer 100. Under the control of the third control unit 93, as shown in Figure 7, water supplied from the water source 84 to the nozzle 85 may be sprayed toward the outer periphery of the wafer 100 toward the outer periphery holding surface 22, thereby pressing the outer periphery of the wafer 100 downward and causing the lower surface 100b of the wafer 100 to be attracted and held by the outer periphery holding surface 22.

[0036] Next, under the control of the fourth control unit 94, the pressure regulating valve 45 constituting the shape adjustment mechanism 48 is adjusted to supply air to the air space 23 of the elastic tube 20. As shown in Figure 8, the upper end of the elastic tube 20 is brought into contact with the lower surface 100b of the wafer 100, which is held by the central holding surface 21 and the outer peripheral holding surface 22. The lower surface 100b of the wafer 100 is supported by the central holding surface 21, the outer peripheral holding surface 22, and the upper end of the elastic tube 20 so that the wafer 100 does not become concave in an annular shape at the annular contact portion, and the upper surface 100a of the wafer 100 is ground by the grinding wheel 57. When the thickness measurement of the wafer 100 by the thickness measuring instrument 80 reaches a predetermined thickness, the grinding feed mechanism 60 raises the grinding mechanism 50 to end the grinding. Furthermore, although the thickness measuring instrument 80 measures the thickness of the portion of the wafer 100 held on the central holding surface 21, an additional thickness measuring instrument may be added to measure the thickness of the portion held on the outer peripheral holding surface 22. Using this additional thickness measuring instrument, for example, under the control of the second control unit 92, only the thickness of the outer peripheral portion of the wafer 100 held on the outer peripheral holding surface 22 may be measured, and it may be determined that the upward warping force has weakened due to the change in thickness. Under the control of the third control unit 93, it may be determined that the outer peripheral holding surface 22 has attracted and held the lower surface of the wafer 100 because the upper surface height of the outer peripheral portion of the wafer 100 held on the outer peripheral holding surface 22 has decreased. Under the control of the fourth control unit 94, the thickness of the portion held on the central holding surface 21 and the thickness of the portion held on the outer peripheral holding surface 22 may be measured. In other words, grinding may be performed until the values ​​of the two thickness measuring instruments match and a predetermined thickness is achieved. Furthermore, if the thickness of the portion held by the outer peripheral holding surface 22 is smaller than a preset finish thickness, the machining process may be terminated without performing grinding by the fourth control unit 94. Furthermore, under the control of the third control unit 93, whether or not the outer peripheral holding surface 22 is suction-holding the lower surface 100b of the wafer 100 may be determined by monitoring the negative pressure value (suction force) of the outer peripheral holding surface 22. Furthermore, under the control of the second control unit 92, the on / off valve 42 is opened to connect the outer peripheral suction unit 18 and the suction source 39, and water is supplied from the outer peripheral nozzle 83 to the outer peripheral holding surface 22 to grind the outer peripheral portion of the wafer 100. As the outer peripheral portion of the wafer 100 is ground and its upper surface height decreases, when the thickness of the outer peripheral portion of the wafer 100 becomes smaller than the thickness of the central portion of the wafer 100, the third control unit 93 may determine that the outer peripheral holding surface 22 is suction-holding the lower surface 100b of the wafer 100.

[0037] During grinding under the control of the fourth control unit 94, the lower surface 100b of the wafer 100 is held by suction from the central holding surface 21 and the outer peripheral holding surface 22, and the upper end of the elastic tube 20 is in contact with the lower surface 100b of the wafer 100 between the central holding surface 21 and the outer peripheral holding surface 22 so as not to lift the wafer 100, thereby enabling the wafer 100 to be formed to a uniform thickness. Alternatively, instead of the elastic tube 20, a ring-shaped elastic member and a lifting mechanism for raising and lowering the ring-shaped elastic member may be provided, and the upper end of the elastic member may be brought into contact with the lower surface of the wafer 100, which is held in place by suction from the central holding surface 21 and the outer peripheral holding surface 22.

[0038] As described above, in the grinding apparatus 1, since the elastic tube 20 is fitted into the annular groove 19 between the central suction part 17 that holds the center of the wafer 100 by suction and the outer peripheral suction part 18 that holds the outer peripheral, the elastic tube 20 is brought into contact with the lower surface 100b of the wafer 100, which is warped on the outer peripheral side, and the outer peripheral side of the wafer 100 is pressed and ground by the grinding wheel 57, thereby reducing the warping of the wafer 100. Then, by lowering the upper end of the elastic tube 20 and holding the lower surface 100b of the wafer 100 by suction at the central holding surface 21 and the outer peripheral holding surface 22, the upper surface 100a is ground, thereby making the thickness of the wafer 100 uniform. Therefore, it is not necessary to perform the complicated work of grinding on a chuck table formed on the outer peripheral side to reduce warping, and then transferring it to a chuck table without an elastic member for further grinding, and the grinding time can be shortened. [Explanation of symbols]

[0039] 1: Grinding device 10: Chuck table, 11: Frame, 12: Recess, 13: Top surface, 14: Peripheral edge, 15: Through hole, 16: Suction member, 17: Central suction part, 18: Outer peripheral suction part, 19: Annular groove, 20: Elastic tube, 21: Central retaining surface, 22: Outer peripheral retaining surface, 23: Air space, 24: Air supply path, 25: Air supply port, 26: Central suction path, 27: Central suction port, 28: Outer perimeter suction passage, 29: Outer perimeter suction port, 30: Base, 31: Screw hole, 32: Central suction groove, 33: Central suction channel, 34: Air supply channel, 35: Outer perimeter suction groove, 36: Outer perimeter suction channel, 37: Central suction tube, 38: On / off valve, 39: Suction source, 40: Pressure gauge, 41: Outer suction tube, 42: On / off valve, 42: On / off valve, 43: Pressure gauge, 44: Air supply pipe, 45: Pressure regulating valve, 46: On / off valve, 47: Air source, 48: Shape adjustment mechanism, 49: Rotary drive mechanism, 50: Grinding mechanism, 51: Spindle, 52: Spindle housing, 53: Motor, 54: Mount, 55: Grinding wheel, 56: Base, 57: Grinding wheel, 60: Grinding feed mechanism, 61: Ball screw, 62: Guide rail, 63: Motor, 64: Lifting plate, 65: Holder, 70: Horizontal movement mechanism, 71: Ball screw, 72: Guide rail, 73: Motor, 74: Sliding plate, 75: Cover, 76: Bellows 80: Thickness measuring instrument, 81: Top surface height measuring instrument, 82: Holding surface height measuring instrument, 83: Outer nozzle, 83: Nozzle, 84: Water source, 85: Nozzle 90: Control unit, 91: First control unit, 92: Second control unit, 93: Third control unit, 94: Fourth Control Unit 100: Wafer, 100a: Top surface, 100b: Bottom surface

Claims

1. A chuck table that holds the bottom surface of a wafer by suction in order to grind the top surface of a wafer having an element where the outer edge is curved upward from the central part with a grinding wheel, The device comprises a central suction section that holds the central portion of the lower surface of the wafer by suction with a central holding surface, an outer periphery suction section that holds the outer periphery of the lower surface of the wafer by suction with an outer periphery holding surface flush with the central holding surface, an annular elastic tube that fits into an annular groove formed between the central suction section and the outer periphery suction section, and a frame having a recess that accommodates the central suction section, the annular groove, and the outer periphery suction section, with the upper surface of the recess being flush with the outer periphery holding surface. The frame comprises a central suction passage connecting the central suction section to a suction source, an outer suction passage connecting the outer suction section to a suction source, and an air supply passage connecting the elastic tube to an air source. Chuck table.

2. A grinding apparatus comprising: a chuck table according to claim 1 for suction holding the lower surface of a wafer having an element in which the outer periphery is curved higher than the central part; a grinding mechanism for grinding the upper surface of the wafer held by suction on the chuck table with a grinding wheel; a thickness measuring instrument for measuring the thickness of the wafer; and a control unit, The elastic tube is equipped with a shape adjustment mechanism that changes the shape of the elastic tube by supplying air inside the elastic tube, thereby changing the height of the upper end of the elastic tube in the vertical direction of the central holding surface. The control unit is A first control unit that supplies air into the elastic tube by the shape adjustment mechanism and brings the upper end of the elastic tube into contact with the lower surface outside the portion held by the central holding surface of the wafer, which is held by the central holding surface and has its outer circumference curved upwards. A second control unit that grinds the upper surface of the wafer with the grinding wheel to reduce the force that causes the outer periphery of the wafer to warp, A third control unit that uses the shape adjustment mechanism to expel air from inside the elastic tube and holds the lower surface of the outer periphery of the wafer, which is held by the central holding surface, by suction with the outer periphery holding surface, A fourth control unit that supplies air into the elastic tube by the shape adjustment mechanism, brings the elastic tube into contact with the lower surface of the wafer held by suction on the central holding surface and the outer peripheral holding surface, and grinds the upper surface of the wafer with the grinding wheel to grind the entire wafer to a predetermined thickness, A grinding device equipped with the following features.

3. It is equipped with an outer nozzle that supplies water to the outer edge of the wafer. The second control unit causes water to be supplied from the outer peripheral nozzle to the outer peripheral holding surface. The grinding apparatus according to claim 2.

4. A method for forming a holding surface of a chuck table attached to a grinding apparatus according to claim 2, A grinding wheel mounting step is to attach a holding surface grinding wheel to the grinding mechanism for grinding the upper surface of the chuck table, A pressure adjustment step involves using a top surface height measuring device to measure the height of the top surface of the chuck table, and adjusting the air pressure inside the elastic tube by the shape adjustment mechanism so that the top surface of the elastic tube becomes flush with the central holding surface or the outer peripheral holding surface. A retaining surface grinding step is performed by grinding the central retaining surface, the upper surface of the elastic tube, and the outer retaining surface using the retaining surface grinding wheel while maintaining the pressure value adjusted in the pressure adjustment step. A method for forming a retaining surface comprising the following features.

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