METHOD FOR FORMING A HOLDER SURFACE, AND GRINDING APPARATUS

Abstract

A method for forming a holder surface of a chuck table by rotating a spindle, to which an annular grinding stone is attached, and grinding an upper surface of the chuck table with the grinding stone rotated along with the spindle. The chuck table includes a porous member and a frame having a dense body in an annular shape. The method includes a first grinding process including tilting an axis of the chuck table with respect to an axis of the spindle relatively at a predetermined first angle and grinding an entire upper surface of the frame with the grinding stone, and a second grinding process including tilting the axis of the chuck table with respect to the axis of the spindle relatively at a second angle, which is smaller than the first angle, and grinding an entire upper surface of the porous member with the grinding stone.

Claims

1. A method for forming a holder surface of a chuck table to suction and hold a wafer thereon by rotating a spindle, to which an annular grinding stone is attached, and grinding an upper surface of the chuck table with the grinding stone rotated along with the spindle, the chuck table being composed of a porous member and a frame having a dense body in an annular shape surrounding an outer circumference of the porous member, the method comprising: a first grinding process including tilting an axis of the chuck table with respect to an axis of the spindle relatively at a predetermined first angle and grinding an entire upper surface of the frame with the grinding stone; and a second grinding process including tilting the axis of the chuck table with respect to the axis of the spindle relatively at a second angle, the second angle being smaller than the first angle, and grinding an entire upper surface of the porous member with the grinding stone.

2. The method according to claim 1, wherein a grain diameter of the grinding stone to be used in the second grinding process is smaller than a grain diameter of the grinding stone used in the first grinding process.

3. A grinding apparatus configured to form the holder surface of the chuck table in the method according to claim 1, comprising: the chuck table configured to hold the wafer; a table spindle configured to rotate the chuck table; a grinding unit configured to grind the wafer held on the chuck table with the grinding stone attached to the spindle; a tilt-adjusting assembly configured to adjust relative inclination between the table spindle and the spindle to one of the first angle or the second angle; and a controller configured to control the tilt-adjusting assembly to form the first angle for grinding the frame with the grinding stone and to form the second angle for grinding the porous member with the grinding stone.

4. A grinding apparatus configured to form the holder surface of the chuck table by rotating the spindle, the spindle including a first spindle and a second spindle, and by grinding the upper surface of the chuck table with the grinding stone, the grinding stone including a first grinding stone and a second griding stone, in the method according to claim 2, the grinding apparatus comprising: the chuck table configured to hold the wafer; a table spindle configured to rotate the chuck table; a first grinding unit configured to grind the wafer held on the chuck table with the first grinding stone attached to the first spindle; a second grinding unit configured to grind the wafer held on the chuck table with the second grinding stone, of which grain diameter is smaller than a grain diameter of the first grinding stone, the second grinding stone being attached to the second spindle; a tilt-adjusting assembly configured to adjust relative inclination between the table spindle and the first spindle to the first angle and relative inclination between the table spindle and the second spindle to the second angle; and a controller configured to control the tilt-adjusting assembly to form the first angle for grinding the frame with the first grinding stone and to form the second angle for grinding the porous member with the second grinding stone.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 is a schematic perspective view of the grinding apparatus according to an embodiment of the present disclosure.

[0010] FIG. 2 is a side view of a chuck table, a table-rotating assembly, and a tilt-adjusting assembly.

[0011] FIG. 3 is a schematic perspective view of the chuck table, the table-rotating assembly, and the tilt-adjusting assembly.

[0012] FIG. 4 is a cross-sectional partial view of the chuck table and a table spindle.

[0013] FIG. 5 is a cross-sectional plan view of an exemplary arrangement of the tilt-adjusting assembly.

[0014] FIG. 6 illustrates a preparatory grinding process.

[0015] FIG. 7 illustrates a first grinding process.

[0016] FIG. 8 illustrates a second grinding process.

DESCRIPTION OF EMBODIMENTS

[0017] A grinding apparatus according to an embodiment of the present disclosure will be described below with reference to the accompanying drawings. FIG. 1 is a schematic perspective view of the grinding apparatus according to the embodiment of the present disclosure.

[0018] As shown in FIG. 1, a grinding apparatus 1 may grind and process a wafer W, which is a workpiece to be processed, formed in a substantially circular shape of a disk. The grinding apparatus 1 is configured to perform a series of operations including a loading process, a grinding process, a cleaning process, and an unloading process with the wafer W fully automatically. To load the grinding apparatus 1 with the wafer W, a cassette 13 containing the wafer W is set in the grinding apparatus 1.

[0019] In the grinding apparatus 1, an X-axis direction, a Y-axis direction, and a Z-axis direction are orthogonal to one another. The X-axis direction and the Y-axis direction are substantially horizontal directions, and the Z-axis direction is an up-down direction (vertical direction). A +X side and a X side, which are one and the opposite sides as pointed by a bidirectional arrow along the X-axis direction, are a frontward side and a rearward side, respectively. A +Y side and a Y side, which are one and the opposite sides as pointed by a bidirectional arrow along the Y-axis direction, are a leftward side and a rightward side, respectively. A +Z side and a Z side, which are one and the opposite sides as pointed by a bidirectional arrow along the Z-axis direction, is an upper side and a lower side, respectively.

[0020] On the frontward side to a base 10 of the grinding apparatus 1, two cassettes 13 that may each store a plurality of wafers W are placed. One of the cassettes 13 may store the wafers W before grinding, and the other of the cassettes 13 may store the wafers W after grinding. At a rearward position with respect to the cassettes 13, a robot hand 11 that may pick up the wafer W from one of the cassettes 13 or may place the wafer W back in the other of the cassettes 13 is provided.

[0021] At a rightward-rear position and a leftward-rear position with respect to the robot hand 11, respectively, provided are a positioning assembly 21, on which the wafer W before grinding may be placed, and a spinner-cleaning device 12, which may clean the wafer W after grinding. The robot hand 11 may convey the wafer W before grinding from the cassette 13 to the positioning assembly 21 and convey the wafer W after grinding from the spinner-cleaning device 12 to the cassette 13.

[0022] The positioning assembly 21 includes a plurality of positioning pins 23, which are arranged around a temporary placement table 22 and are movable inward toward or outward from a center of the temporary placement table 22. With the wafer W placed on the temporary placement table 22 in the positioning assembly 21, by moving the plurality of positioning pins 23 to respectively contact an outer circumference of the wafer W, a center of the wafer W is located at the center of the temporary placement table 22.

[0023] The spinner-cleaning device 12 may clean the wafer W having been ground by supplying a cleaning solution from a cleaning nozzle 121 to the wafer W and rotating a spinner table 122 holding the wafer W at a high speed by a motor, which is not shown.

[0024] Between the positioning assembly 21 and the spinner-cleaning device 12 in the Y-axis direction, provided are a first conveyer assembly 15, which may convey the wafer W before grinding from the positioning assembly 21 to a chuck table 14, and a second conveyer assembly 16, which may convey the wafer W after grinding from the chuck table 14 to the spinner-cleaning device 12. The first conveyer assembly 15 and the second conveyer assembly 16 each have a conveyer pad, which suctions and holds the wafer W from above, and a supporting arm supporting the conveyer pad. The first conveyer assembly 15 and the second conveyer assembly 16 may convey the wafer W by operating the supporting arm supporting the conveyer pad to rotate on an axis extending in the Z-axis direction and move up or down in the Z-axis direction.

[0025] On an upper surface of the base 10 on the rearward side in the grinding apparatus 1, an opening in a rectangular form elongated in the X-axis direction is formed. The opening is covered by a movable plate 17, which is movable in the X-axis direction along with the chuck table 14, and a waterproof cover 18 having a form of bellows.

[0026] Below the waterproof cover 18, provided is a table-movable assembly 20 that may move the chuck table 14 in the X-axis direction. The table-movable assembly 20 includes a pair of guide rails 25 extending in the X-axis direction and a ball screw 26, and a movable table 27 is supported on the guide rails 25 movably along the guide rails 25. The ball screw 26 is screwed to a screw thread (not shown) in the movable table 27, and when the ball screw 26 is rotated by a motor 24, the movable table 27 moves in the X-axis direction.

[0027] Below the waterproof cover 18, provided are a table-rotating assembly 30, which may rotate and drive the chuck table 14, and a tilt-adjusting assembly 36, which may adjust inclination of the chuck table 14. The table-rotating assembly 30 and the tilt-adjusting assembly 36 will be described further below.

[0028] The chuck table 14 is composed of a disk-shaped porous member 42 and a frame 43 including an annular portion that surrounds an outer periphery of the porous member 42.

[0029] The porous member 42 is made of a porous material and has fine pores formed throughout. An upper surface of the porous member 42 forms a holder surface 421. The holder surface 421 suctions and thereby holds the wafer W by a suction source, which is not shown. The frame 43 is formed of ceramics and is composed of a dense body, of which hardness is higher than the porous member 42 made of the porous material. An upper surface of the chuck table 14 is formed as a conical surface, of which apex is located on an axis C1 being a rotation axis of the chuck table 14, and which descends gradually toward an outer periphery of the chuck table 14 (see FIG. 6). Note that, in FIG. 6, inclination of the holder surface 421 with respect to the horizontal direction and inclination of the axis C1 with respect to the vertical direction are depicted in an exaggerated manner; however, the inclinations in reality are slight enough not to be visually recognizable.

[0030] Next, a horizontal movable assembly 50, lift/lower assemblies 60, and a grinding assembly 70 will be described. The horizontal movable assembly 50 is located on a frontward side or a column 19, which stands at a rearward position on the base 10. On the horizontal movable assembly 50, the grinding assembly 70 is supported via two lift/lower assemblies 60.

[0031] The horizontal movable assembly 50 includes a pair of guide rails 51 arranged on the frontward side of the column 19 and extending in the Y-axis direction, movable tables 52 arranged on the pair of guide rails 51 movably in the Y-axis direction, and a ball screw 53 extending in the Y-axis direction and screwed to a screw thread (not shown) formed in the movable tables 52. The two movable tables 52 are arranged side by side along the Y-axis direction. The movable tables 52 are movable in the Y-axis direction by rotation of the ball screw 53, which is rotatable by a driving force of a motor 54 coupled to an end of the ball screw 53.

[0032] The two lift/lower assemblies 60 are similarly configured and are each arranged on a frontward side of a respective one of the movable tables 52. Each lift/lower assembly 60 has a pair of guide rails 61 arranged on the frontward side of the movable table 52 and extending in the Z-axis direction. Furthermore, the lift/lower assembly 60 has a lift/lower table 62, which is arranged on the pair of guide rails 61 movably in the Z-axis direction, and a ball screw 63 extending in the Z-axis direction and screwed to a screw thread (not shown) formed in the lift/lower table 62. The lift/lower table 62 are movable in the Z-axis direction by rotation of the ball screw 63, which is rotatable by a driving force of a motor 64 coupled to one end of the ball screw 63.

[0033] The grinding assembly 70 includes a first grinding unit (grinding unit) 71 supported by one of the lift/lower assemblies 60 on the right (Y side) and a second grinding unit (grinding unit) 72 supported by the other of the lift/lower assemblies 60 on the left (+Y side). The grinding assembly 70 may grind an upper surface of the wafer W suctioned and held on the holder surface 421 of the chuck table 14 with a first grinding stone (grinding stone) 80 and a second grinding stone (grinding stone) 90, which will be described further below.

[0034] The first grinding unit 71 is mounted on a frontward side of the lift/lower table 62 via a first holder 74 and supports a first spindle (spindle) 76 rotatably with respect to a first spindle housing 75 supported by the first holder 74. The first spindle 76 may rotate on an axis C21, which is parallel to the Z-axis direction (see FIGS. 6 and 7) by a driving force of a first spindle motor 77.

[0035] The first spindle 76 is coupled with a first mount 78 at a lower end thereof, and to the first mount 78, a first grinding wheel 79 is attached. On a lower surface of the first grinding wheel 79, the first grinding stone 80, including a plurality of first grinding stones 80 arranged annularly, is provided. As such, the plurality of first grinding stones 80 are attached to the first spindle 76 via the first mount 78 and the first grinding wheel 79. The first grinding stones 80 may be, for example, grinding stones that are usable in rough grinding, and a size of abrasive grains contained therein is relatively large. In other words, the first grinding unit 71 that may grind the workpiece with the first grinding stones 80 may function as a rough-grinding assembly that may grind the wafer W roughly.

[0036] The second grinding unit 72 is mounted on a frontward side of the lift/lower table 62 via a second holder 84 and supports a second spindle (spindle) 86 rotatably with respect to a second spindle housing 85 supported by the second holder 84. The second spindle 86 may rotate on an axis C22 (see FIG. 8), which is parallel to the Z-axis direction by a driving force of a second spindle motor 87.

[0037] The second spindle 86 is coupled with a second mount 88 at a lower end thereof, and to the second mount 88, a second grinding wheel 89 is attached. On a lower surface of the second grinding wheel 89, the second grinding stone 90, including a plurality of second grinding stones 90 arranged annularly, is provided. As such, the plurality of second grinding stones 90 are attached to the second spindle 86 via the second mount 88 and the second grinding wheel 89. The second grinding stones 90 may be, for example, grinding stones that are usable in finish grinding, and a size of abrasive grains contained therein is relatively small, and a grain diameter of the second grinding stones is smaller than a grain diameter of the first grinding stones 80. In other words, the second grinding unit 72 that may grind the workpiece with the second grinding stones 90 may function as a finish-grinding assembly that may finely grind to finish the wafer W.

[0038] On the base 10, a thickness-measuring device 45 is provided. The thickness-measuring device 45 includes a first height gauge for measuring a height position of the upper surface of the wafer W held on the holder surface 421 of the chuck table 14 and a second height gauge for measuring a height position of the upper surface of the chuck table 14. Based on a difference between a value measured with the first height gauge and a value measured with the second height gauge, a thickness of the wafer W is measured.

[0039] Operations of the components in the grinding apparatus I are controlled by a controller 95. The controller 95 includes a processor that may execute various processes and a memory (memory) storing various parameters and programs. The memory of the controller 95 may store, as parts of the control programs, for example, programs for controlling the operations of the table-movable assembly 20, the table-rotating assembly 30, the tilt-adjusting assembly 36, the horizontal movable assembly 50, the lift/lower assemblies 60, and the grinding assembly 70. For the operation of each component in the grinding apparatus 1 described below, when no explicit entity is specified as a subject to control the operation, it is assumed that the operation is controlled by signals output from the controller 95.

[0040] FIG. 2 is a side view of the chuck table 14, the table-rotating assembly 30, and the tilt-adjusting assembly 36. As shown in FIG. 2, the table-rotating assembly 30 that may drive the chuck table 14 to rotate includes a cylindrical table spindle 31, of which axis C1 is common with the chuck table 14, located below the frame 43.

[0041] FIG. 3 is a schematic perspective view of the chuck table 14, the table-rotating assembly 30, and the tilt-adjusting assembly 36. As shown in FIG. 3, the table-rotating assembly 30 further includes a motor 32, a belt pulley 33 provided to an output shaft of the motor 32, and a transmission belt 34 wound around the belt pulley 33 and the table spindle 31. When the motor 32 drives the belt pulley 33 to rotate, the rotational force is transmitted to the table spindle 31 via the transmission belt 34, and the table spindle 31 having the same axis C1 as the chuck table 14 rotates.

[0042] The tilt-adjusting assembly 36 is provided to adjust inclination of the table spindle 31 and chuck table 14. The tilt-adjusting assembly 36 includes a support stand 37, position-adjusting units 38, and a fixed support 39 connected to the support stand 37.

[0043] The support stand 37 includes a cylindrically-shaped support cylinder 371 and a disc-shaped flange 372, which is a lower part of the support cylinder 371 expanded radially. The tilt-adjusting assembly 36 adjusts the inclination of the table spindle 31 by operating the position-adjusting units 38 to tilt the flange 372 using the fixed support 39 as a fulcrum.

[0044] FIG. 4 is a cross-sectional partial view of the chuck table 14 and the table spindle 31. As shown in FIG. 4, the table spindle 31 is inserted in the support cylinder 371 of the support stand 37. A bearing 373 arranged inside the support cylinder 371 is in contact with an outer circumferential surface of the table spindle 31, and the table spindle 31 is rotatably supported through the bearing 373.

[0045] Referring back to FIG. 3, at different positions in a circumferential direction of the support stand 37, at least two position-adjusting units 38 are provided and are connected to the flange 372. Each position-adjusting unit 38 includes a cylinder 381 fixed to the movable table 27, a movable shaft 382 penetrating the cylinder 381, a motor 383 connected to a lower end of the movable shaft 382, a male screw (not shown) formed at a tip end of the movable shaft 382, a female screw (not shown) formed on the flange 372 to be screwed with the male screw, and a pressurizer 384 located on the flange 372 and having a spring that provides backlash between the male screw and the female screw.

[0046] The cylinder 381 is fitted in a hole formed through the movable table 27 in the Z-axis direction. In the position-adjusting unit 38, as the motor 383 rotates and drives the movable shaft 382, a height position of the flange 372, in which the female screw is formed, may change in the Z-axis direction.

[0047] FIG. 5 is a cross-sectional plan view of an exemplary arrangement of the position-adjusting units 38 and the fixed support 39. According to the configuration shown in FIG. 5, two position-adjusting units 38 and one fixing support 39 are arranged at intervals by 120 degrees (equally spaced) in the circumferential direction. The fixed support 39 supports the flange 372 at a constant height position. The two position-adjusting units 38 may operate individually to change the height position of the flange 372.

[0048] Next, an overall operation of the grinding apparatus 1 will be explained briefly. As shown in FIG. 1, in the grinding apparatus 1, an unground wafer W is picked up from the cassette 13 and conveyed to the positioning assembly 21 by the robot hand 11. Next, the upper surface of the wafer W is suctioned and held by the conveyer pad of the first conveyer assembly 15, and the wafer W is conveyed from the positioning assembly 21 to the chuck table 14 by the first conveyer assembly 15. For passing the wafer W from the conveyer pad of the first conveyer assembly 15 to the chuck table 14, the chuck table 14 is driven by the table-movable assembly 20 and located at a load/unload position in proximity to (frontward in the X-axis direction) the first conveyer assembly 15.

[0049] When the wafer W is passed to the chuck table 14 by the first conveyer assembly 15, the wafer W is suctioned and held on the holder surface 421 of the chuck table 14. Thereafter, the chuck table 14 is moved rearward by the table-movable assembly 20, and the wafer W is located below the grinding assembly 70.

[0050] In the grinding assembly 70, the horizontal movable assembly 50 locates the first grinding unit 71 above the chuck table 14, and the table-rotating assembly 30 rotates the chuck table 14 and the wafer W being held and suctioned thereon. The lift/lower assembly 60 lowers the first grinding unit 71 and rotates the first grinding stones 80 through the first spindle 76. As such, the first grinding stones 80 and the wafer W on the chuck table 14 are moved to rotate respectively and contact each other, thereby grinding the upper surface of the wafer W roughly.

[0051] After grinding the wafer W roughly, the horizontal movable assembly 50 locates the second grinding unit 72 above the chuck table 14, and the table-rotating assembly 30 continuously rotates the chuck table 14 and the wafer W held and suctioned thereon. Moreover, the lift/lower assembly 60 lowers the second grinding unit 72 and rotates the second grinding stones 90 through the second spindle 86. As such, the second grinding stones 90 and the wafer W on the chuck table 14 are moved to rotate respectively and contact each other, thereby grinding to finish the upper surface of the wafer W, and grinding of the wafer W is completed.

[0052] After grinding is completed, the table-movable assembly 20 is operated to move the chuck table 14 to return to the load/unload position. The wafer W having been ground is conveyed by the second conveyer assembly 16 to the spinner-cleaning device 12 and cleaned thereby. After cleaning, the wafer W having been ground is stored in the cassette 13 by the robot hand 11.

[0053] According to the grinding apparatus 1 described herein, a process called self-grinding to preparatorily grind the upper surface of the chuck table 14 is performed. Self-grinding may be performed, for example, after replacing the first and/or second grinding wheels 79, 89 or after grinding the wafers W a predetermined number of times so that the holder surface 421 of the chuck table 14 is formed to be parallel to the lower surfaces (grinding surfaces) of the first and second grinding stones 80, 90. The following describes a method for forming the holder surface 421 of the chuck table 14 by self-grinding according to the present embodiment.

[0054] The method for forming the holder surface 421 according to the present embodiment is implemented by performing steps including a preparatory grinding process, a first grinding process, and a second grinding process in this given order. FIG. 6 illustrates the preparatory grinding process, FIG. 7 illustrates the first grinding process, and FIG. 8 illustrates the second grinding process. According to the present embodiment, in each of the processes, 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), but the axis C1 of the chuck table 14 (table spindle 31) is reoriented.

Preparatory Grinding Process

[0055] As shown in FIG. 6, in the preparatory grinding process, the controller 95 (see FIG. 1) controls and drives the tilt-adjusting assembly 36 (see FIG. 2) so that the axis C1 of the chuck table 14 is tilted relatively to the axis C21 of the first spindle 76 at a preparation angle 0. Under this condition, the table-movable assembly 20 and the horizontal movable assembly 50 are driven to locate the chuck table 14 below the first grinding unit 71. At this position, outer circumferential edges of the annularly arranged first grinding stones 80 are maintained to pass directly above the axis C1 of the chuck table 14. The preparation angle 0 is a relative inclination between the table spindle 31 and the first spindle 76.

[0056] Thereafter, the table-rotating assembly 30 is operated to rotate the chuck table 14 on the axis C1, and the first spindle 76 is driven to rotate the first grinding stones 80 on the axis C21. Moreover, the lift/lower assembly 60 is driven to lower the first grinding unit 71 to press the rotating first grinding stones 80 against the upper surface of the rotating chuck table 14. Thereby, the holder surface 421 being the upper surface of the porous member 42 in the chuck table 14 and the upper surface of the frame 43 are mutually ground and form the identical conical surfaces.

First Grinding Process

[0057] After completion of the preparatory grinding process, the first grinding process is performed. As shown in FIG. 7, in the first grinding process, the controller 95 controls and drives the tilt-adjusting assembly 36 so that the axis C1 of the chuck table 14 is tilted relatively to the axis C21 of the first spindle 76 at a first angle 1. The first angle 1 is a relative inclination between the table spindle 31 and the first spindle 76. The first angle 1 is set to be greater than the preparation angle 0 by a predetermined angle. Under this condition, similarly to the preparatory grinding process, the chuck table 14 is located below the first grinding unit 71, and the outer circumferential edges of the annularly arranged first grinding stones 80 are maintained to pass directly above the axis C1 of the chuck table 14.

[0058] Thereafter, the table-rotating assembly 30 is operated to rotate the chuck table 14 on the axis C1, and the first spindle 76 is driven to rotate the first grinding stones 80 on the axis C21. Moreover, the lift/lower assembly 60 is driven to lower the first grinding unit 71 to press the rotating first grinding stones 80 against the upper surface of the rotating chuck table 14 to grind the upper surface of the chuck table 14.

[0059] In this grinding process, the first angle 1 is set to be greater than the preparation angle 0; therefore, a contact area between the first grinding stones 80 and the upper surface of the chuck table 14 is changed compared to the contact area in the preparation grinding process. In particular, a part of the first grinding stones 80 closer to the axis C21 is caused to contact the entire upper surface of the frame 43 of the chuck table 14. In other words, the first angle 1 is set to an angle that enables the first grinding stones 80 to contact, within the chuck table 14, solely the upper surface of the frame 43 but not to contact the upper surface (holder surface 421) of the porous member 42.

[0060] By tilting the chuck table 14 as described above, the entire upper surface of the frame 43 is ground, but the porous member 42 is not ground; therefore, the upper surface of the frame 43 and the upper surface of the porous member 42 are formed to have respective conical surfaces, of which taper angles are different. More specifically, the upper surface of the frame 43 is formed to have a taper angle smaller than a taper angle of the upper surface of the porous member 42.

Second Grinding Process

[0061] After completion of the first grinding process, the second grinding process is performed. As shown in FIG. 8, in the second grinding process, the controller 95 controls and drives the tilt-adjusting assembly 36 so that the axis C1 of the chuck table 14 is tilted relatively to the axis C22 of the second spindle 86 at a second angle 2. The second angle 2 is a relative inclination between the table spindle 31 and the second spindle 86. The second angle 2 is set to be smaller than the first angle 1 by a predetermined angle and to be equal to or smaller than the preparation angle 0 by a predetermined angle. Under this condition, the chuck table 14 is located below the second grinding unit 72, and outer circumferential edges of the annularly arranged second grinding stones 90 are maintained to pass directly above the axis C1 of the chuck table 14.

[0062] Thereafter, the table-rotating assembly 30 is operated to rotate the chuck table 14 on the axis C1, and the second spindle 86 is driven to rotate the second grinding stones 90 on the axis C22. Moreover, the lift/lower assembly 60 is driven to lower the second grinding unit 72 to press the rotating second grinding stones 90 against the upper surface of the rotating chuck table 14 to grind the upper surface of the chuck table 14.

[0063] In this grinding process, the second angle 2 is set to be smaller than the first angle 1; therefore, a contact area between the second grinding stones 90 and the upper surface of the chuck table 14 is changed compared to the contact area between the first grinding stones 80 and the upper surface of the chuck table 14 in the first grinding process. In particular, a part of the second grinding stones 90, excluding a part closer to the axis C22, is caused to contact the entire upper surface of the porous member 42 in the chuck table 14. In other words, the second angle 2 is set to an angle that enables the second grinding stones 90 to contact, within the chuck table 14, merely the upper surface of the porous member 42 (holder surface 421) but not to contact the upper surface of the frame 43.

[0064] In the second grinding process, which is after forming the upper surface of the frame 43 and the upper surface of the porous member 42 to have the respective conical surfaces at the different taper angles in the first grinding process, the chuck table 14 is ground in the orientation tilted as described above. As such, while the upper surface of the frame 43 is prevented from being ground, the holder surface 421 forming the entire upper surface of the porous member 42 may be ground to be finished with the second grinding stones 90.

[0065] 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 in the self-grinding operation. With the changed angles, the process to grind the frame 43 and the porous member 42 is separated into the first grinding process, in which the upper surface of the frame 43 is ground with the first grinding stones 80, and the second grinding process, in which the upper surface of the porous member 42 is ground with the second grinding stones 90. Note that, although the above embodiment includes the preparatory grinding process, the preparatory grinding process is not necessarily required.

[0066] Conventionally, the frame and the porous member are ground simultaneously in self-grinding; therefore, grinding of the porous member may progress ahead compared to grinding of the frame, resulting to form a ring-shaped concavity on the circumferential portion of the porous member.

[0067] In contrast, by separating the processes of grinding the frame 43 and the porous member 42 and performing in sequence, as those in the above embodiment, progression of grinding of the porous member 42 ahead compared to the frame 43 may be prevented, and the porous member 42 may prevent the ring-shaped concavity from being formed on the circumferential portion thereof. Accordingly, after self-grinding, when the wafer W is ground, the wafer W may prevent the convexity corresponding to the form of ring-shaped concavity from being formed thereon, and the wafer W may be ground to an even thickness.

[0068] Moreover, as the porous member 42 is enabled to avoid the concavity from being formed at the circumferential portion thereof, unevenness of the upper surface of the chuck table 14 may be reduced. Therefore, intervention of grinding debris between the holder surface 421 and the wafer W due to such unevenness of the upper surface of the chuck table 14 may be avoided, and the wafer W being ground may be prevented from being damaged.

[0069] Furthermore, in the first grinding process, the frame 43 having a higher degree of hardness is ground with the first grinding stones 80 having the larger grain diameter; therefore, the time for grinding in the first grinding process may be shortened. Meanwhile, in the second grinding process, the porous member 42 having a lower degree of hardness is ground with the second grinding stones 90 having the smaller grain diameter. Accordingly, the time for grinding the porous member 42 with the second grinding stones 90 may be longer compared to a hypothetical case in which the porous member 42 is ground with the first grinding stones 80. However, it provides an effect of smoothing the upper surface of the porous member 42 preferably. Optionally, in the first grinding step, the frame 43 may be ground with the second grinding stones 90, therefore grinding may be done with the second grinding stones 90 in both the first grinding process and the second grinding process. Furthermore, optionally, in the second grinding step, the porous member 42 may be ground with the first grinding stones 80, therefore grinding may be done with the first grinding stones 80 in both the first grinding process and the second grinding process. Moreover, optionally, the frame 43 may be ground with the second grinding stones 90 in the first grinding process, and the porous member 42 may be ground with the first grinding stones 80 in the second grinding process.

[0070] Furthermore, the preparatory grinding process enables the upper surface of the porous member 42 and the upper surface of the frame 43 to be ground to align with the same conical surface. The preparatory grinding process may be provided to end in a short time as a process of rough grinding, considering that the angles of the upper surfaces of the porous member 42 and the frame 43 are finely adjusted later by performing the first grinding process and the second grinding process. Therefore, unlike the conventional method, the porous member 42 may prevent the ring-shaped concavity from being formed in the circumferential portion thereof. Moreover, optionally, in the self-grinding operation after grinding the wafers W for a predetermined number of times, the first grinding process and the second grinding process may be performed while the preparatory grinding process is omitted.

[0071] Embodiment of the present disclosure may not necessarily be limited to the configuration described above but may be modified in various ways. In the embodiment described above, sizes or forms of the components illustrated in the accompanying drawings are not limited thereto but may be modified optionally within the scope of the effects of the present disclosure. Moreover, the embodiment may be modified optionally without departing from the scope of the object of the present disclosure.

[0072] For example, the tilt-adjusting assembly 36 may not necessarily be limited to the exemplary configuration as illustrated but may be modified in various ways. For example, the tilt-adjusting assembly 36 may have three or more position-adjusting units 38 or may be configured to change the height of the flange 372 not by rotating but by sliding the movable shaft 382 in the Z-axis direction using, for example, leverage.

[0073] For another example of the tilt-adjusting assembly 36, the first spindle 76 and the second spindle 86 may be tilted with respect to the Z-axis direction so that the inclination between the table spindle 31 and the first spindle 76 and the inclination between the table spindle 31 and the second spindle 86 are relatively changeable. In this configuration, for example, the tilt-adjusting assembly 36 may be configured to have a first tilt-adjusting assembly provided to the first grinding unit 71 and a second tilt-adjusting assembly provided to the second grinding unit 72. The first tilt-adjusting assembly may have the axis C21 of the first spindle 76 inclining with respect to the Z-axis direction so that the relative inclination between the axis C21 of the first spindle 76 and the axis C1 of the chuck table 14 forms the first angle 1. The second tilt-adjusting assembly may have the axis C22 of the second spindle 86 inclining with respect to the Z-axis direction so that the relative inclination between the axis C22 of the second spindle 86 and the axis C1 of the chuck table 14 forms the second angle 2.

[0074] For another example, in the first and second grinding processes to form the holder surface 421 in the present embodiment, either one of the first grinding unit 71 or the second grinding unit 72 may be used. In other words, the first grinding process may be performed with the first grinding stones 80, and the first grinding stones 80 may be replaced with the second grinding stones 90 for performing the second grinding process thereafter. Alternatively, the first grinding process may be performed with the second grinding stones 90, and the second grinding stones 90 may be replaced with the first grinding stones 80 for performing the second grinding process thereafter.

INDUSTRIAL APPLICABILITY

[0075] As explained above, the present disclosure provides the effect such that a ring-shaped concavity may be prevented from being formed on a circumferential portion of a porous member during self-grinding of a chuck table.