Method for forming holder surface and grinding apparatus

Abstract

To prevent a ring-shaped recess from being formed on an outer periphery part of a porous member during self-grinding.SOLUTION: According to the invention, a first spindle (76), to which annular first grinding stones (80) are attached, and a second spindle (86), to which annular second grinding stones (90) are attached, are rotated to grind an upper surface of a chuck table (14), comprising a porous member (42) and a frame body (43) enclosing an outer periphery of the porous member, with the respective rotating grinding stones and form a holder surface (421) for suctioning and holding a wafer (W). The method for forming a holder surface includes: a first grinding step in which an axis (C1) of the chuck table is inclined relative to an axis (C21) of the first spindle at a first angle (θ1) and an entire upper surface of the frame body is ground with the first grinding stones; and a second grinding step in which the axis of the chuck table is inclined relative to an axis (C22) of the second spindle at a second angle (θ2), which is smaller than the first angle, and an entire upper surface of the porous member is ground with the second grinding stones.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a method for forming a holding surface for holding a wafer and a grinding apparatus. [Background technology]

[0002] Patent Document 1 discloses a grinding method in which the radius of a wafer held on a conical chuck table of a grinding device is ground with the underside of an annular grinding wheel. Furthermore, the grinding device of Patent Document 2 performs so-called self-grinding, in which the upper surface of the chuck table is ground with a grinding wheel after replacing the grinding wheel or chuck table, thereby forming the grinding surface of the grinding wheel parallel to the holding surface of the chuck table. The chuck table is composed of a porous member that forms the holding surface and a ring-shaped dense frame that surrounds the porous member. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-114573 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-237210 Summary of the Invention [Problem to be solved by the invention]

[0004] Because the porous member and the frame that make up the chuck table have different hardnesses, when self-grinding is performed, grinding of the porous member proceeds more easily than that of the frame. Therefore, after self-grinding, a ring-shaped depression forms on the outer periphery of the porous member, which is the boundary between the porous member and the frame. This results in a problem in that the outer periphery of the ground wafer held by the chuck table becomes slightly ring-shaped and convex at the location where the depression was formed.

[0005] The present invention has been made in consideration of these points, and one of its objects is to provide a method for forming a holding surface and a grinding device that can prevent the formation of a ring-shaped depression on the outer periphery of a porous member when the chuck table self-grinds. [Means for solving the problem]

[0006] One embodiment of the method of forming a holding surface of the present invention is a method of forming a holding surface that suction-holds a wafer by rotating a spindle equipped with an annular grinding wheel and grinding the upper surface of a chuck table composed of a porous member and an annular dense frame surrounding the outer periphery of the porous member with the rotating grinding wheel, the method comprising a first grinding step in which the axis of the chuck table is tilted at a predetermined first angle relative to the axis of the spindle and the entire upper surface of the frame is ground with the grinding wheel, and a second grinding step in which the axis of the chuck table is tilted at a second angle relative to the axis of the spindle that is smaller than the first angle and the entire upper surface of the porous member is ground with the grinding wheel.

[0007] One embodiment of the grinding apparatus of the present invention is a grinding apparatus that performs a method for forming a holding surface, and includes a chuck table that holds a wafer, a table spindle that rotates the chuck table, a grinding unit that grinds the wafer held on the chuck table with a grinding wheel attached to the spindle, and a control unit that sets the relative inclination between the table spindle and the first spindle to a first angle and a second angle that is smaller than the first angle. [Effects of the Invention]

[0008] According to the present invention, in the first grinding process and the second grinding process, in which the grinding stones have different abrasive grain sizes, the relative angle between the axis of the spindle and the axis of the chuck table is changed, and the grinding portion of the chuck table is changed as described above in the first grinding process and the second grinding process. This prevents the formation of a ring-shaped depression on the outer periphery of the porous member, which occurs when grinding of the porous member progresses more than that of the frame during self-grinding. As a result, when the wafer is held and ground on the chuck table after self-grinding, the formation of a convex portion corresponding to the ring-shaped depression on the wafer can be avoided, and the wafer can be ground to a uniform thickness. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic perspective view of a grinding device according to an embodiment; [Figure 2] FIG. 2 is a side view showing a chuck table, a table rotation mechanism, and an inclination adjustment mechanism. [Figure 3] FIG. 2 is a schematic perspective view showing a chuck table, a table rotation mechanism, and an inclination adjustment mechanism. [Figure 4] FIG. 2 is a cross-sectional view showing a part of the chuck table and the table spindle. [Figure 5] FIG. 10 is a plan cross-sectional view showing an example of the arrangement of the tilt adjustment mechanism. [Figure 6] FIG. [Figure 7] FIG. 4 is an explanatory diagram of a first grinding step. [Figure 8] FIG. 10 is an explanatory view of a second grinding step. DETAILED DESCRIPTION OF THE INVENTION

[0010] A grinding device according to an embodiment will now be described with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a grinding device according to an embodiment;

[0011] 1, the grinding apparatus 1 performs grinding on a wafer W, which is a workpiece formed in a substantially circular disk shape. The grinding apparatus 1 is configured to fully automatically perform a series of operations on the wafer W, including a loading process, grinding process, cleaning process, and unloading process. The wafer W is loaded into the grinding apparatus 1 while being housed in a cassette 13.

[0012] The X-axis, Y-axis, and Z-axis directions of the grinding apparatus 1 are perpendicular to one another. The X-axis and Y-axis directions are approximately horizontal, and the Z-axis direction is an up-down direction (vertical direction). Of the two arrows indicating the X-axis direction, the +X side is the front and the -X side is the rear. Of the two arrows indicating the Y-axis direction, the +Y side is the left and the -Y side is the right. Of the two arrows indicating the Z-axis direction, the +Z side is the up and the -Z side is the down.

[0013] Two cassettes 13, each capable of accommodating a plurality of wafers W, are placed on the front side of a base 10 of the grinding apparatus 1. One cassette 13 accommodates wafers W before grinding, and the other cassette 13 accommodates wafers W after grinding. A robot hand 11 is provided behind the cassettes 13 to move wafers W into and out of the cassettes 13.

[0014] A positioning mechanism 21 for placing the wafer W before grinding and a spinner cleaning device 12 for cleaning the ground wafer W are provided diagonally to the left and right of the robot hand 11. The robot hand 11 transports the wafer W before grinding from the cassette 13 to the positioning mechanism 21 and transports the ground wafer W from the spinner cleaning device 12 to the cassette 13.

[0015] The positioning mechanism 21 is configured by arranging a plurality of positioning pins 23 around the temporary placement table 22, which are movable toward and away from the center of the temporary placement table 22. In the positioning mechanism 21, the plurality of positioning pins 23 abut against the outer periphery of the wafer W placed on the temporary placement table 22, thereby positioning the center of the wafer W to the center of the temporary placement table 22.

[0016] The spinner cleaning device 12 cleans the ground wafer W by supplying a cleaning liquid from a cleaning nozzle 121 to the wafer W and rotating a spinner table 122 holding the wafer W at high speed by a motor (not shown).

[0017] Between the positioning mechanism 21 and the spinner cleaning device 12 in the Y-axis direction, there are provided a first transfer mechanism 15 that transfers the unground wafer W from the positioning mechanism 21 to the chuck table 14, and a second transfer mechanism 16 that transfers the ground wafer W from the chuck table 14 to the spinner cleaning device 12. The first transfer mechanism 15 and the second transfer mechanism 16 each use a transfer pad to suction-hold the wafer W from above, and transfer the wafer W by rotating the support arm that supports the transfer pad around an axis in the Z-axis direction and raising and lowering it in the Z-axis direction.

[0018] A rectangular opening extending in the X-axis direction is formed on the upper surface of the base 10 on the rear side of the grinding device 1. This opening is covered by a moving plate 17 that can move in the X-axis direction together with the chuck table 14, and a bellows-shaped waterproof cover 18.

[0019] A table moving mechanism 20 that moves the chuck table 14 in the X-axis direction is provided below the waterproof cover 18. The table moving mechanism 20 includes a pair of guide rails 25 extending in the X-axis direction and a ball screw 26, and a moving base 27 is supported so as to be movable along the guide rails 25. The ball screw 26 is threadedly engaged with a threaded portion (not shown) for movement, and when the ball screw 26 is rotated by operation of the motor 24, the moving base 27 moves in the X-axis direction.

[0020] In addition, below the waterproof cover 18, there are provided a table rotation mechanism 30 that rotates the chuck table 14, and an inclination adjustment mechanism 36 that can adjust the inclination of the chuck table 14. The table rotation mechanism 30 and the inclination adjustment mechanism 36 will be described later.

[0021] The chuck table 14 is composed of a disk-shaped porous member 42 and a frame 43 having an annular portion surrounding the outer periphery of the porous member 42 .

[0022] The porous member 42 is made of a porous material and has fine pores formed throughout. The upper surface of the porous member 42 constitutes a holding surface 421. The holding surface 421 holds the wafer W by suction using a suction source (not shown). The frame 43 is made of ceramics and is a dense body that is harder than the porous member 42 made of a porous material. The upper surface of the chuck table 14 is formed as a conical surface whose apex is located on the axis C1, which serves as the central axis of rotation, and which gradually becomes lower toward the outer periphery of the chuck table 14 (see FIG. 6). In FIG. 6, the inclination of the holding surface 421 relative to the horizontal direction and the inclination of the axis C1 relative to the vertical direction are exaggerated; in reality, the inclination is so slight that it is not discernible by visual inspection.

[0023] Next, the horizontal movement mechanism 50, the lifting mechanism 60, and the grinding mechanism 70 will be described. The horizontal movement mechanism 50 is disposed on the front side of the column 19 that is erected at the rear of the base 10. The horizontal movement mechanism 50 is provided so as to support the grinding mechanism 70 via two lifting mechanisms 60.

[0024] The horizontal movement mechanism 50 includes a pair of guide rails 51 disposed on the front side of the column 19 and extending in the Y-axis direction, a movable table 52 installed so as to be movable in the Y-axis direction relative to the pair of guide rails 51, and a ball screw 53 extending in the Y-axis direction and threadedly engaging with a threaded portion (not shown) of the movable table 52. Two movable tables 52 are provided side by side in the Y-axis direction. Each movable table 52 moves in the Y-axis direction as the ball screw 53 is rotated by the driving force of a motor 54 connected to one end of the ball screw 53.

[0025] The two lifting mechanisms 60 are configured similarly, and one is disposed in front of the movable table 52. The lifting mechanism 60 includes a pair of guide rails 61 that are disposed in front of the movable table 52 and extend in the Z-axis direction. The lifting mechanism 60 further includes a lifting table 62 that is installed so as to be movable in the Z-axis direction relative to the pair of guide rails 61, and a ball screw 63 that extends in the Z-axis direction and screws into a screw portion (not shown) of the lifting table 62. The ball screw 63 is rotated by the driving force of a motor 64 that is connected to one end of the ball screw 63, and thereby the lifting table 62 moves in the Z-axis direction.

[0026] The grinding mechanism 70 includes a first grinding unit (grinding unit) 71 supported by the right (-Y side) lifting mechanism 60 of the two lifting mechanisms 60, and a second grinding unit (grinding unit) 72 supported by the left (+Y side) lifting mechanism 60. The grinding mechanism 70 grinds the top surface of the wafer W held by suction on the holding surface 421 of the chuck table 14 with a first grinding wheel (grinding wheel) 80 and a second grinding wheel (grinding wheel) 90, which will be described later.

[0027] The first grinding unit 71 is attached to the front surface of the lift table 62 via a first holder 74, and rotatably supports a first spindle (spindle) 76 with respect to a first spindle housing 75 supported by the first holder 74. The first spindle 76 rotates around an axis C21 (see FIGS. 6 and 7) parallel to the Z-axis direction by the driving force of a first spindle motor 77.

[0028] A first mount 78 is connected to the lower end of the first spindle 76, and a first grinding wheel 79 is attached to the first mount 78. A plurality of first grinding wheels 80 are provided in an annular shape on the underside of the first grinding wheel 79. Thus, the plurality of first grinding wheels 80 are attached to the first spindle 76 via the first mount 78 and the first grinding wheel 79. The first grinding wheel 80 is, for example, a grinding wheel used for rough grinding, and is a grinding wheel containing relatively large abrasive grains. In other words, the first grinding unit 71, which performs grinding using the first grinding wheel 80, functions as a rough grinding mechanism for performing rough grinding on the wafer W.

[0029] The second grinding unit 72 is attached to the front surface of the lift table 62 via a second holder 84, and rotatably supports a second spindle (spindle) 86 with respect to a second spindle housing 85 supported by the second holder 84. The second spindle 86 rotates around an axis C22 (see FIG. 8) parallel to the Z-axis direction by the driving force of a second spindle motor 87.

[0030] A second mount 88 is connected to the lower end of the second spindle 86, and a second grinding wheel 89 is attached to the second mount 88. A plurality of second grinding wheels 90 are provided in an annular shape on the underside of the second grinding wheel 89. Thus, the plurality of second grinding wheels 90 are attached to the second spindle 86 via the second mount 88 and the second grinding wheel 89. The second grinding wheel 90 is, for example, a grinding wheel used for finish grinding, and contains relatively small abrasive grains, the abrasive grain size of which is smaller than that of the first grinding wheel 80. In other words, the second grinding unit 72, which performs grinding using the second grinding wheel 90, functions as a finish grinding mechanism for performing finish grinding on the wafer W.

[0031] A thickness measuring device 45 is provided on the base 10. The thickness measuring device 45 includes a first height gauge that measures the height position of the upper surface of the wafer W held on the holding surface 421 of the chuck table 14, and a second height gauge that measures the height position of the upper surface of the chuck table 14, and measures the thickness of the wafer W based on the difference between the measurement value of the first height gauge and the measurement value of the second height gauge.

[0032] The operation of each part of the grinding apparatus 1 is controlled by a control unit 95. The control unit 95 is configured to include a processor that executes various processes and a storage unit (memory) that stores various parameters, programs, etc. The storage unit of the control unit 95 stores, as part of a control program, programs for controlling the operation of, for example, the table movement mechanism 20, the table rotation mechanism 30, the tilt adjustment mechanism 36, the horizontal movement mechanism 50, the lift mechanism 60, and the grinding mechanism 70. Regarding the operation of each part of the grinding apparatus 1 described below, unless a control entity is specified, it is assumed that the operation is controlled by a control signal sent from the control unit 95.

[0033] 2 is a side view showing the chuck table, the table rotation mechanism, and the tilt adjustment mechanism. As shown in Fig. 2, the table rotation mechanism 30 that rotates the chuck table 14 includes a cylindrical table spindle 31 that is located below the frame 43 and has a common axis C1 with the chuck table 14.

[0034] Fig. 3 is a schematic perspective view showing the chuck table, the table rotation mechanism, and the tilt adjustment mechanism. As shown in Fig. 3, the table rotation mechanism 30 further includes a motor 32, a belt pulley 33 provided on the output shaft of the motor 32, and a transmission belt 34 wound around the belt pulley 33 and the table spindle 31. When the belt pulley 33 is rotationally driven by the motor 32, the rotational force is transmitted to the table spindle 31 via the transmission belt 34. Then, the table spindle 31, which shares an axis C1 with the chuck table 14, rotates, causing the chuck table 14 to rotate.

[0035] The tilt adjustment mechanism 36 is provided to be able to adjust the tilt of the table spindle 31 and the chuck table 14. The tilt adjustment mechanism 36 includes a support base 37, and a position adjustment unit 38 and a fixed support part 39 connected to the support base 37.

[0036] The support base 37 includes a cylindrical support tube portion 371 and a disk-shaped flange 372 formed by expanding the diameter of the lower portion of the support tube portion 371. The tilt adjustment mechanism 36 adjusts the tilt of the table spindle 31 by operating the position adjustment unit 38 to tilt the flange 372 with the fixed support portion 39 as a fulcrum.

[0037] Fig. 4 is a cross-sectional view showing a portion of the chuck table 14 and the table spindle 31. As shown in Fig. 4, the table spindle 31 is inserted into the support cylinder portion 371 of the support base 37. A bearing 373 arranged inside the support cylinder portion 371 contacts the outer peripheral surface of the table spindle 31, and the table spindle 31 is rotatably supported via the bearing 373.

[0038] 3, the position adjustment units 38 are provided at two or more locations at different positions in the circumferential direction of the support base 37, and each position adjustment unit 38 is connected to the flange 372. Each position adjustment unit 38 includes a cylindrical portion 381 fixed to the movable base 27, a movable shaft 382 penetrating the cylindrical portion 381, a motor 383 connected to the lower end of the movable shaft 382, ​​a male screw (not shown) formed on the tip of the movable shaft 382, ​​a female screw (not shown) formed on the flange 372 and into which the male screw is screwed, and a pressure applying portion 384 arranged on the upper part of the flange 372 and equipped with a spring that removes backlash between the male screw and the female screw.

[0039] The cylindrical portion 381 is fitted into a hole in the Z-axis direction formed in the movable table 27. In the position adjustment unit 38, the movable shaft 382 is rotated by the motor 383, whereby the flange 372, on which a female screw is formed by the thread action of each screw, changes its height position in the Z-axis direction.

[0040] Fig. 5 is a plan cross-sectional view showing an example of the arrangement of the position adjustment units 38 and the fixed support part 39. In the configuration of Fig. 5, two position adjustment units 38 and one fixed support part 39 are arranged at 120 degree intervals (equidistant intervals) in the circumferential direction. The fixed support part 39 supports the flange 372 at a constant height position. The two position adjustment units 38 are arranged to be able to operate independently to change the height position of the flange 372.

[0041] Next, an outline of the overall operation of the grinding apparatus 1 will be described. As shown in Fig. 1, in the grinding apparatus 1, an unground wafer W is taken out from a cassette 13 by a robot hand 11 and transported to a positioning mechanism 21. Next, the upper surface of the wafer W is suction-held by a transport pad of a first transport mechanism 15, and the wafer W is transported from the positioning mechanism 21 onto a chuck table 14 by the first transport mechanism 15. When the wafer W is delivered from the transport pad of the first transport mechanism 15, the chuck table 14 is positioned at a delivery position near the first transport mechanism 15 (toward the front in the X-axis direction) by driving a table moving mechanism 20.

[0042] When the wafer W is delivered to the chuck table 14 by the first transport mechanism 15, the wafer W is suction-held on the holding surface 421 of the chuck table 14. Thereafter, the table moving mechanism 20 moves the chuck table 14 backward, and the wafer W is positioned below the grinding mechanism 70.

[0043] In the grinding mechanism 70, the horizontal movement mechanism 50 positions the first grinding unit 71 above the chuck table 14, and the table rotation mechanism 30 rotates the chuck table 14 and the wafer W held by suction. Additionally, the lifting mechanism 60 lowers the first grinding unit 71 while the first spindle 76 rotates the first grinding wheel 80. In this way, the first grinding wheel 80 and the wafer W on the chuck table 14 are brought into contact with each other while rotating, thereby roughly grinding the top surface of the wafer W.

[0044] After the wafer W has been roughly ground, the horizontal movement mechanism 50 positions the second grinding unit 72 above the chuck table 14, and the table rotation mechanism 30 continues to rotate the chuck table 14 and the wafer W held by suction. Additionally, the second grinding unit 72 is lowered by the lifting mechanism 60, while the second grinding wheel 90 is rotated by the second spindle 86. In this manner, the second grinding wheel 90 and the wafer W on the chuck table 14 are brought into contact with each other while rotating, whereby the top surface of the wafer W is finish-ground, completing the grinding process of the wafer W.

[0045] After grinding is completed, the chuck table 14 is moved by the table moving mechanism 20, and the wafer W is returned to the delivery position. The ground wafer W is transported by the second transport mechanism 16 to the spinner cleaning device 12 and cleaned. After cleaning, the ground wafer W is stored in the cassette 13 by the robot hand 11.

[0046] Here, the grinding apparatus 1 performs a process called self-grinding, which grinds the upper surface of the chuck table 14 in advance. Self-grinding is performed, for example, when replacing the grinding wheels 79, 89 or after grinding the wafer W a predetermined number of times, and forms the holding surface 421 of the chuck table 14 so that it is parallel to the lower end surfaces (grinding surfaces) of the grinding stones 80, 90. A method for forming the holding surface 421 of the chuck table 14 by self-grinding in this embodiment will be described below.

[0047] The method for forming the holding surface 421 in this embodiment is carried out in the order of a preparatory grinding step, a first grinding step, and a second grinding step. Fig. 6 is an explanatory diagram of the preparatory grinding step, Fig. 7 is an explanatory diagram of the first grinding step, and Fig. 8 is an explanatory diagram of the second grinding step. Here, in each step, the axis C21 of the first spindle 76 and the axis C22 of the second spindle 86 are maintained parallel to the vertical direction (Z-axis direction), and the orientation of the axis C1 of the chuck table 14 (table spindle 31) is changed.

[0048] [Preparatory grinding process] As shown in FIG. 6, in the preparatory grinding step, the control unit 95 (see FIG. 1) controls the drive of the tilt adjustment mechanism 36 (see FIG. 2) to tilt the axis C1 of the chuck table 14 relative to the axis C21 of the first spindle 76 at a preparatory angle θ0. In this state, the table movement mechanism 20 and the horizontal movement mechanism 50 are driven to position the chuck table 14 below the first grinding unit 71. With this positioning, the outer periphery of the annularly arranged first grinding wheels 80 is maintained in a state where it passes directly above the axis C1 of the chuck table 14. The preparatory angle θ0 is the relative tilt between the table spindle 31 and the first spindle 76.

[0049] Thereafter, the table rotation mechanism 30 rotates the chuck table 14 about the axis C1, and the first spindle 76 rotates the first grinding wheel 80 about the axis C21. Then, the lifting mechanism 60 is driven to lower the first grinding unit 71, causing the rotating first grinding wheel 80 to come into contact with and press against the upper surface of the rotating chuck table 14. As a result, both the holding surface 421, which is the upper surface of the porous member 42 on the chuck table 14, and the upper surface of the frame 43 are ground, and the same conical surface is formed by these upper surfaces.

[0050] [First grinding process] After the preparatory grinding step is completed, the first grinding step is performed. As shown in FIG. 7 , in the first grinding step, the control unit 95 controls the tilt adjustment mechanism 36 to tilt the axis C1 of the chuck table 14 at a first angle θ1 relative to the axis C21 of the first spindle 76. The first angle θ1 is the relative tilt between the table spindle 31 and the first spindle 76. The first angle θ1 is set to a predetermined angle greater than the preparatory angle θ0. In this state, as in the preparatory grinding step, the chuck table 14 is positioned below the first grinding unit 71, and the outer periphery of the annularly arranged first grinding wheels 80 is maintained so as to pass directly above the axis C1 of the chuck table 14.

[0051] Thereafter, the table rotation mechanism 30 rotates the chuck table 14 around the axis C1, and the first grinding wheel 80 is rotated around the axis C21 by the first spindle 76. Then, the lifting mechanism 60 is driven to lower the first grinding unit 71, and the rotating first grinding wheel 80 comes into contact with and presses against the upper surface of the rotating chuck table 14 to perform grinding.

[0052] In this grinding, the first angle θ1 is set to be larger than the preparatory angle θ0, so the contact area between the first grinding stone 80 and the upper surface of the chuck table 14 is changed compared to the preparatory grinding process. Specifically, of the first grinding stone 80, a portion of the first grinding stone 80 closer to the axis C21 is brought into contact with the entire upper surface of the frame 43 of the chuck table 14. In other words, the first angle θ1 is set so that the first grinding stone 80 contacts only the upper surface of the frame 43 of the chuck table 14 and does not contact the upper surface (holding surface 421) of the porous member 42.

[0053] By tilting the chuck table 14 as described above, the entire upper surface of the frame body 43 is ground, but the porous member 42 is not ground, so that the conical surfaces formed have different taper angles on the upper surface of the frame body 43 and the upper surface of the porous member 42. More specifically, the upper surface of the frame body 43 is formed so as to have a smaller taper angle than the upper surface of the porous member 42.

[0054] [Second grinding process] After the first grinding step is completed, the second grinding step is performed. As shown in FIG. 8 , in the second grinding step, the control unit 95 controls the tilt adjustment mechanism 36 to tilt the axis C1 of the chuck table 14 relative to the axis C22 of the second spindle 86 at a second angle θ2. The second angle θ2 is the relative tilt between the table spindle 31 and the second spindle 86. The second angle θ2 is set to a predetermined angle smaller than the first angle θ1 and is set to be equal to or smaller than the preparation angle θ0 by a predetermined angle. In this state, the chuck table 14 is positioned below the second grinding unit 72, and the outer periphery of the annularly arranged second grinding wheels 90 is maintained so as to pass directly above the axis C1 of the chuck table 14.

[0055] Thereafter, the table rotation mechanism 30 rotates the chuck table 14 about the axis C1, and the second grinding wheel 90 is rotated about the axis C22 by the second spindle 86. Then, the second grinding unit 72 is lowered by driving the lifting mechanism 60, and the rotating second grinding wheel 90 comes into contact with and presses against the upper surface of the rotating chuck table 14 to perform grinding.

[0056] In this grinding, the second angle θ2 is set to be smaller than the first angle θ1, so the contact area between the second grinding wheel 90 and the upper surface of the chuck table 14 is changed compared to the contact area between the first grinding wheel 80 and the upper surface of the chuck table 14 in the first grinding step. Specifically, the second grinding wheel 90, excluding a portion closer to the axis C22, is brought into contact with the entire upper surface of the porous member 42 on the chuck table 14. In other words, the second angle θ2 is set so that the second grinding wheel 90 contacts only the upper surface (holding surface 421) of the porous member 42 on the chuck table 14 and does not contact the upper surface of the frame 43.

[0057] In the second grinding step, after the upper surface of the frame 43 and the upper surface of the porous member 42 are formed in the first grinding step so that the taper angles of the conical surfaces are different, grinding is performed with the chuck table 14 tilted as described above. This allows the holding surface 421, which is the entire upper surface of the porous member 42, to be finish-ground with the second grinding wheel 90 in the second grinding step, while preventing the upper surface of the frame 43 from being ground.

[0058] According to the above embodiment, the angle of the axis C1 of the chuck table 14 is changed between the first grinding process and the second grinding process of the self-grinding. By changing the angle in this way, the upper surface of the frame 43 is ground with the first grinding wheel 80 in the first grinding process, and the upper surface of the porous member 42 is ground with the second grinding wheel 90 in the second grinding process, thereby separating the grinding processes of the frame 43 and the porous member 42. Although the above embodiment includes the preparatory grinding step, the preparatory grinding step is not essential.

[0059] Here, in the past, the frame body and the porous member were ground simultaneously using self-grinding, so grinding of the porous member progressed more than that of the frame body, resulting in the formation of a ring-shaped depression on the outer periphery of the porous member.

[0060] In contrast to this, by performing the grinding steps of the frame 43 and the porous member 42 in separate orders as in the above embodiment, it is possible to prevent the grinding of the porous member 42 from progressing more rapidly than the frame 43, and to prevent a ring-shaped depression from being formed on the outer periphery of the porous member 42. This makes it possible to prevent a convex portion corresponding to the ring-shaped depression from being formed on the wafer W when grinding the wafer W after self-grinding, and allows the wafer W to be ground to a uniform thickness.

[0061] Furthermore, by preventing the formation of depressions in the outer periphery of the porous member 42, it is possible to reduce the unevenness of the upper surface of the chuck table 14. This makes it possible to avoid a situation in which grinding debris is interposed between the holding surface 421 and the wafer W due to such unevenness, and thus to prevent damage to the ground wafer W.

[0062] Furthermore, since the frame 43, which has a high hardness, is ground with the first grinding wheel 80, which has a large abrasive grain size, in the first grinding step, the grinding time in the first grinding step can be shortened. Also, in the second grinding step, the porous member 42, which has a low hardness, is ground with the second grinding wheel 90, which has a small abrasive grain size. As a result, compared to grinding the porous member 42 with the first grinding wheel 80, grinding with the second grinding wheel 90 takes longer. However, this has the effect of successfully smoothing the upper surface of the porous member 42. In the first grinding step, the frame 43 may be ground using the second grinding wheel 90, or the frame 43 may be ground using the second grinding wheel 90 in both the first grinding step and the second grinding step. Furthermore, in the second grinding step, the porous member 42 may be ground using the first grinding wheel 80, or the porous member 42 may be ground using the first grinding wheel 80 in both the first grinding step and the second grinding step. Alternatively, the frame 43 may be ground using the second grinding wheel 90 in the first grinding step, and the porous member 42 may be ground using the first grinding wheel 80 in the second grinding step.

[0063] Furthermore, by performing the preparatory grinding step, the upper surface of the porous member 42 and the upper surface of the frame 43 can be ground to form the same conical surface. The preparatory grinding step can be completed in a short time as a rough grinding step, since the angles of the upper surfaces of the porous member 42 and the frame 43 are adjusted by performing the first grinding step and the second grinding step thereafter. This prevents the formation of a recess on the outer periphery of the porous member 42 as in the conventional method, and in self-grinding after grinding the wafer W a predetermined number of times, the preparatory grinding step can be omitted and the first grinding step and the second grinding step can be performed.

[0064] The present invention is not limited to the above-described embodiments, and various modifications can be made. In the above-described embodiments, the size and shape shown in the accompanying drawings are not limited to these, and can be modified as appropriate within the scope of the effects of the present invention. In addition, the present invention can be modified as appropriate within the scope of the object of the present invention.

[0065] For example, the tilt adjustment mechanism 36 is not limited to the illustrated configuration example and can be modified in various ways. For example, the tilt adjustment mechanism 36 may be configured to include three or more position adjustment units 38, or to change the height of the flange 372 by sliding the movable shaft 382 in the Z-axis direction using a lever or the like without rotating the movable shaft 382.

[0066] As another example of the tilt adjustment mechanism 36, the first spindle 76 and the second spindle 86 may be tilted with respect to the Z-axis direction to change the relative tilt with respect to the table spindle 31. In such a configuration, the tilt adjustment mechanism 36 may be configured by a first tilt adjustment mechanism provided in the first grinding unit 71 and a second tilt adjustment mechanism provided in the second grinding unit 72. The first tilt adjustment mechanism tilts the axis C21 of the first spindle 76 with respect to the Z-axis direction to set the relative tilt between the axis C21 of the first spindle 76 and the axis C1 of the chuck table 14 to a first angle θ1. The second tilt adjustment mechanism tilts the axis C22 of the second spindle 86 with respect to the Z-axis direction to set the relative tilt between the axis C22 of the second spindle 86 and the axis C1 of the chuck table 14 to a second angle θ2.

[0067] In the present embodiment, the first and second grinding steps for forming the holding surface 421 may be performed using only one of the first grinding unit 71 and the second grinding unit 72. That is, the first grinding step may be performed using the first grinding wheel 80, and then the first grinding wheel 80 may be replaced with the second grinding wheel 90 to perform the second grinding step. Alternatively, the first grinding step may be performed using the second grinding wheel 90, and then the second grinding step may be performed by replacing the second grinding wheel 90 with the first grinding wheel 80. [Industrial Applicability]

[0068] As described above, the present invention has the effect of preventing the formation of a ring-shaped depression on the outer periphery of a porous member during self-grinding of a chuck table. [Explanation of symbols]

[0069] 1: Grinding equipment 14: Chuck table 31: Table spindle 36: Tilt adjustment mechanism 42: Porous material 421: Holding surface 43: Frame 71: First grinding unit (grinding unit) 72: Second grinding unit (grinding unit) 76: First spindle (spindle) 80: First grinding wheel (grinding wheel) 86: Second spindle (spindle) 90: Second grinding wheel (grinding wheel) 95: Control unit C1: Axial center C21: Axial center C22: Axial center W: wafer θ1: 1st angle θ2: 2nd angle

Claims

1. A method for forming a holding surface for suction-holding a wafer, comprising: rotating a spindle on which an annular grinding wheel is attached; and grinding an upper surface of a chuck table, which is composed of a porous member and an annular dense frame surrounding the outer periphery of the porous member, with the rotating grinding wheel; a first grinding step of relatively tilting the axis of the chuck table at a predetermined first angle with respect to the axis of the spindle and grinding the entire upper surface of the frame with a grinding wheel; a second grinding step in which the axis of the chuck table is tilted relative to the axis of the spindle at a second angle smaller than the first angle, and the entire upper surface of the porous member is ground with a grinding wheel.

2. 2. The method for forming a holding surface according to claim 1, wherein the second grinding step uses a grinding wheel having a smaller abrasive grain size than the grinding wheel used in the first grinding step.

3. A grinding apparatus for carrying out the method for forming a holding surface according to claim 1, a chuck table for holding a wafer, a table spindle for rotating the chuck table, and a grinding unit for grinding the wafer held on the chuck table with a grinding wheel attached to the spindle; an inclination adjustment mechanism that adjusts the relative inclination between the table spindle and the spindle to a first angle and a second angle smaller than the first angle; a control unit that sets the angle to the first angle when the grinding wheel is used to grind the frame, and sets the angle to the second angle when the grinding wheel is used to grind the porous member,

4. A grinding apparatus for carrying out the method for forming a holding surface according to claim 2, a chuck table for holding a wafer, a table spindle for rotating the chuck table, a first grinding unit for grinding the wafer held on the chuck table with a first grinding wheel attached to a first spindle, and a second grinding unit for grinding the wafer held on the chuck table with a second grinding wheel attached to a second spindle and having an abrasive grain size smaller than that of the first grinding wheel; an inclination adjustment mechanism that sets the relative inclination between the table spindle and the first spindle to a first angle and sets the relative inclination between the table spindle and the second spindle to a second angle that is smaller than the first angle; a control unit that sets the angle to a first angle when grinding the frame body with the first grinding wheel and to a second angle when grinding the porous member with the second grinding wheel, said grinding device comprising:

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