Grinding method for wafer

Abstract

To provide a grinding method for wafers capable of grinding a wafer to a predetermined thickness without temporarily stopping grinding to change the tilt of a chuck table.SOLUTION: There is provided a grinding method for wafers in which a lower surface of an annular grinding stone (12) is brought into contact with a radius area on an upper surface of a wafer (W) that is held on a conical holding surface (32) of a chuck table (10) and a rotating wafer is ground by a rotating grinding stone, the wafer being rotated by an arc-shaped grinding area (K). The grinding method includes: a tilt change step of changing the tilt of the holding surface in a direction that approaches the holding surface of the chuck table with respect to a lower surface of the grinding stone at an intermediate part in the grinding area, from a state where the lower surface of the grinding stone and the holding surface of the chuck table are parallel with each other in the grinding area; and a grinding step of, after the tilt change step, grinding the wafer to a finish thickness while supplying cooling water (M) at a predetermined temperature from the outside of the grinding stone to an upper surface center of the wafer.SELECTED DRAWING: Figure 5

Description

[Technical field]

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

[0002] As disclosed in Patent Document 1, when grinding wafers with a grinding device, the grinding process is stopped midway so that the wafer ground by the grinding wheel has a uniform thickness, and the thickness of the wafer is measured. After that, the inclination of the chuck table is adjusted to grind the wafer to a preset finishing thickness.

[0003] The grinding device arranges grinding wheels in a ring shape on the underside of the grinding wheel, and performs grinding while rotating the chuck table that holds the wafer and the grinding wheel relative to each other. The chuck table is gently conical with the center of rotation as its apex, and the grinding wheel is positioned so that it passes through the center of rotation of the chuck table during grinding. Therefore, the area of ​​the wafer that comes into contact with the grinding wheel changes in the circumferential direction (rotation direction) with the relative rotation of the chuck table and the grinding wheel except for the central part of the wafer, while the grinding wheel always comes into contact with the central part of the wafer. As a result, the central part of the wafer is ground away more, which can cause a dent.

[0004] As a countermeasure, the center of the conical holding surface of the chuck table is flattened to prevent the formation of a dent in the center of the ground wafer, as disclosed in Patent Document 2. By flattening the center of the holding surface, the contact of the grinding wheel with the center of the wafer is mitigated, preventing the formation of a dent. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2013-119123 A [Patent Document 2] JP 2019-130637 A Summary of the Invention [Problem to be solved by the invention]

[0006] If the grinding process is temporarily stopped and the inclination of the chuck table is changed every time a wafer is ground, as in Patent Document 1, the time required for the grinding process increases, resulting in poor manufacturing efficiency.

[0007] When forming a holding surface with a flat center on the chuck table as in Patent Document 2, two grinding processes are performed: a grinding process to form a conical surface and a grinding process to form a flat surface in the center of the cone. This requires the inclination of the chuck table to be changed midway, resulting in a problem that it takes a long time to form the holding surface.

[0008] Therefore, there is a need for a method of grinding a wafer that can grind the wafer to a predetermined thickness without temporarily stopping the grinding process and changing the inclination of the chuck table. [Means for solving the problem]

[0009] One aspect of the present invention is a method for grinding a wafer, in which the lower surface of an annular grinding wheel is brought into contact with a radial region of the upper surface of a wafer held on a conical holding surface of a chuck table, and the wafer, which rotates through an arc-shaped grinding area, is ground with the rotating grinding wheel, the method comprising: a tilt changing step of changing the inclination of the holding surface in a direction that brings the holding surface of the chuck table closer to the lower surface of the grinding wheel in an intermediate portion of the grinding area from a state in which the lower surface of the grinding wheel and the holding surface of the chuck table are parallel in the grinding area; and a grinding step of grinding the wafer to a finishing thickness while supplying cooling water of a predetermined temperature from the outside of the grinding wheel to the center of the upper surface of the wafer after the tilt changing step. Effect of the Invention

[0010] According to the wafer grinding method of the present invention, the adjustment of the relative inclination relationship between the holding surface and the grinding wheel in the inclination changing step prevents the center of the upper surface of the wafer from being ground excessively, and furthermore, the supply of cooling water to the center of the upper surface of the wafer suppresses thermal expansion of the center of the upper surface of the wafer, making it possible to grind the wafer to a predetermined thickness without causing a recess in the central portion of the wafer. After the relative inclination relationship between the holding surface and the grinding wheel is set in the inclination changing step, the grinding step can be performed without temporarily stopping the grinding process, thereby preventing the grinding process from taking a long time and realizing efficient wafer processing. [Brief description of the drawings]

[0011] [Figure 1] FIG. [Diagram 2] 1 is a top view showing a chuck table and a grinding wheel of a grinding apparatus to which a grinding method according to a first embodiment is applied. [Diagram 3] 3 is a cross-sectional view of a portion of the grinding apparatus taken along line AA in FIG. 2. [Figure 4] 3 is a cross-sectional view showing an inclination changing step of the first embodiment taken along the line BB in FIG. 2. [Diagram 5] 3 is a cross-sectional view showing an inclination changing step of the first embodiment taken along the line BB in FIG. 2. [Figure 6] 3 is a cross-sectional view showing a grinding process at a position along the line AA in FIG. 2. [Figure 7] FIG. 11 is a top view showing a chuck table and a grinding wheel of a grinding apparatus to which a grinding method according to a second embodiment is applied. [Figure 8] 8 is a cross-sectional view taken along line CC in FIG. 7, illustrating a tilt changing step in the second embodiment. [Figure 9] 8 is a cross-sectional view taken along line CC in FIG. 7, illustrating a tilt changing step in the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] 1 to 6, a first embodiment of a grinding apparatus 1 according to the present embodiment and a method for grinding a wafer performed by the grinding apparatus 1 will be described. The X-axis direction, Y-axis direction, and Z-axis direction in the grinding apparatus 1 are perpendicular to each other. The X-axis direction and Y-axis direction are approximately horizontal, and the Z-axis direction is a vertical direction.

[0013] The grinding apparatus 1 is an apparatus that grinds the upper surface of a wafer W held on a chuck table 10 with a grinding wheel 12 of a grinding mechanism 11. The wafer W is a semiconductor wafer made of, for example, silicon. Note that the material and type of the wafer W are not limited to this.

[0014] 3 to 6, a protective member H is formed on the bottom surface of the wafer W to be ground by the grinding device 1. The protective member H is formed by supplying an ultraviolet-curable liquid resin or a thermosetting liquid resin onto a sheet, pressing the bottom surface of the wafer W against the liquid resin to spread it out, and then curing the liquid resin by irradiating it with ultraviolet rays or applying heat.

[0015] The grinding apparatus 1 includes a control unit 2 that is configured with a processor that executes various processes, a memory that stores programs, etc. The grinding apparatus 1 is configured to perform a series of operations such as loading and grinding of the wafer W under the control of the control unit 2.

[0016] 1, a rectangular opening 14 extending in the Y-axis direction is formed in the upper surface of the base 13 of the grinding device 1. The opening 14 is covered by a movable plate 15 movable in the Y-axis direction together with the chuck table 10, and bellows-shaped waterproof covers 16 provided on both sides of the movable plate 15.

[0017] A table moving mechanism 20 that moves the chuck table 10 in the Y-axis direction is provided inside the base 13. The table moving mechanism 20 includes a pair of guide rails 21 and a ball screw 22 extending in the Y-axis direction, and a slide portion 23 that supports the chuck table 10 is supported so as to be movable in the Y-axis direction along the guide rails 21. The ball screw 22 is screwed into a screw portion (not shown) of the slide portion 23, and when the ball screw 22 is rotated by a motor 24 connected to one end of the ball screw 22, the chuck table 10 and the moving plate 15 move in the Y-axis direction together with the slide portion 23.

[0018] The chuck table 10 can be moved in the Y-axis direction by the table moving mechanism 20 to a transfer position on the -Y-axis side and a processing position on the +Y-axis side. The processing position of the chuck table 10 is a position where the wafer W held on the chuck table 10 can be ground by a grinding wheel 12 of a grinding mechanism 11.

[0019] 3 to 6, the chuck table 10 includes a frame 30 and a disk-shaped porous plate 31 attached in a recess on the upper surface side of the frame 30. The porous plate 31 is made of a porous material such as ceramics, and has fine pores formed all over. With the porous plate 31 attached in the recess of the frame 30, the upper surface of the frame 30 and the upper surface of the porous plate 31 are flush with each other. The upper surface of the frame 30 and the upper surface of the porous plate 31 form a holding surface 32 on which a wafer W is placed and held.

[0020] The chuck table 10 is formed with a suction passage 33 that communicates with the bottom of the porous plate 31. The suction passage 33 is connected to a suction source 34 via an open / close valve. When the open / close valve is opened to operate the suction source 34, air in the porous plate 31 is sucked through the suction passage 33, and a suction force acts on the holding surface 32. The wafer W can be sucked and held on the holding surface 32 by this suction force.

[0021] The holding surface 32 of the chuck table 10 has a gentle cone shape with a center Qa (FIGS. 2, 3, and 6) as its apex. The wafer W is held on the chuck table 10 in a cone shape following the holding surface 32. The center of the wafer W held on the holding surface 32 approximately coincides with the center Qa of the chuck table 10.

[0022] As shown in FIG. 1, the chuck table 10 is configured to be rotatable by a table rotation mechanism 35. A frame 30 of the chuck table 10 is connected to a chuck spindle 36. The chuck spindle 36 is rotatably supported via a bearing disposed inside a cylindrical support base 37. The table rotation mechanism 35 transmits the rotation of an output shaft of a motor (not shown) to the chuck spindle 36 via a pulley 38 and a belt 39, and rotates the chuck table 10 by the rotation of the chuck spindle 36. The rotation axis Pa (FIGS. 3 and 6) of the chuck table 10 is a line that passes through a center Qa of the holding surface 32 and extends in the height direction of the conical holding surface 32.

[0023] The inclination of the chuck table 10 can be adjusted by an inclination adjustment mechanism 40. As shown in FIG. 2, the inclination adjustment mechanism 40 includes a fixed shaft 41, a first chuck adjustment shaft 42, and a second chuck adjustment shaft 43, which are arranged at approximately equal intervals in the circumferential direction of the chuck table 10. The fixed shaft 41 supports the support base 37 at a constant height position relative to the slide portion 23. The first chuck adjustment shaft 42 and the second chuck adjustment shaft 43 can be operated individually to change the height, thereby changing the height position of the support base 37 relative to the slide portion 23. Note that the inclination adjustment mechanism 40 is shown in a simplified form in FIGS. 3 to 6.

[0024] The tilt adjustment mechanism 40 adjusts the tilt of the chuck table 10 connected to the chuck spindle 36 by operating the first chuck adjustment shaft 42 and the second chuck adjustment shaft 43 to tilt the support base 37 around the fixed shaft 41 as a fulcrum. By appropriately selecting the adjustment direction and adjustment amount of the height of each of the first chuck adjustment shaft 42 and the second chuck adjustment shaft 43, the tilt direction and magnitude of the chuck table 10 can be changed as desired.

[0025] A height detection unit 45 is provided on the base 13 near the chuck table 10. The height detection unit 45 includes two measurement probes, a probe 46 and a probe 47. The probe 46 is provided at a position where it can come into contact with the top surface of the wafer W held on the chuck table 10 and measure the height of the top surface of the wafer W. The probe 47 is provided at a position where it can come into contact with the top surface of the frame 30 that constitutes the holding surface 32 and measure the height of the holding surface 32. The control unit 2 calculates the thickness of the wafer W based on the difference between the top surface height of the wafer W measured by the probe 46 and the height of the holding surface 32 measured by the probe 47.

[0026] Moreover, the height detection unit 45 can measure the thickness at a plurality of positions on the wafer W by changing the position of the probe 46 that contacts the top surface of the wafer W, thereby detecting the variation in the thickness of the wafer W. For example, the thickness can be measured at the center, outer periphery, and intermediate position in the radial direction of the wafer W to detect the tendency of the variation in thickness in the radial direction of the wafer W.

[0027] Next, a description will be given of the grinding mechanism 11. A column 17 erected on the upper surface of the base 13 is provided with a lifting mechanism 50 that moves the grinding mechanism 11 toward and away from the chuck table 10 (in the Z-axis direction).

[0028] The lifting mechanism 50 includes a pair of guide rails 51 disposed on the front side of the column 17 and extending in the Z-axis direction, a lifting table 52 supported movably in the Z-axis direction via the pair of guide rails 51, a ball screw 53 extending in the Z-axis direction and screwed into a screwing portion of the lifting table 52, and a motor 54 that rotates the ball screw 53. The drive amount of the motor 54 is detected by an encoder 55.

[0029] When the ball screw 53 is rotated by the drive of the motor 54, the lift table 52 moves in the Z-axis direction. The grinding mechanism 11 is attached to the front surface of the lift table 52 via a housing 56, and the grinding mechanism 11 moves up and down together with the lift table 52 in the Z-axis direction.

[0030] The grinding mechanism 11 includes a spindle unit 57 supported via a housing 56. The spindle unit 57 is, for example, an air spindle, and rotatably supports a spindle 58 inside the casing via high-pressure air. The spindle 58 extends in the Z-axis direction, and a mount 59 is connected to the lower end of the spindle 58 protruding downward from the housing 56. A grinding wheel 60 is attached to the lower part of the mount 59, and a plurality of grinding wheels 12 are arranged in an annular shape on the lower surface of the grinding wheel 60. When the spindle 58 is driven to rotate by the spindle unit 57, the grinding wheel 60 supported via the mount 59 rotates, and the grinding wheels 12 rotate together with the grinding wheel 60.

[0031] The rotation axis Pb (FIGS. 4 and 5) of the spindle 58 is a line that passes through the center Qb (FIG. 2) of the grinding wheel 60 and extends in the Z-axis direction. The spindle unit 57 is supported by the housing 56 via three fixed shafts 61 (FIG. 2) that are positioned so as to surround the rotation axis Pb. Although not shown in the figure, there is a space in the Z-axis direction between a downward support surface provided on the spindle unit 57 and the bottom surface of the housing 56, and the three fixed shafts 61 are disposed in this space.

[0032] The grinding apparatus 1 is provided with a cooling water nozzle 65 in the vicinity of the chuck table 10. The cooling water nozzle 65 is connected to a cooling water source 66 via a cooling water supply passage, and the cooling water M supplied from the cooling water source 66 is sprayed from the cooling water nozzle 65 (see FIG. 6).

[0033] The cooling water nozzle 65 is located above and on the outer periphery side of the chuck table 10, with the opening at the tip facing the center Qa of the holding surface 32. The cooling water nozzle 65 thus positioned supplies cooling water M from the outside of the grinding wheel 60 and the grinding stone 12 toward the center of the upper surface of the wafer W during grinding processing.

[0034] A series of steps for grinding the wafer W using the grinding apparatus 1 configured as above will be described. Note that, unless a control entity is specified for the operation of each part of the grinding apparatus 1, the operation is assumed to be controlled by a control signal sent from the control unit 2.

[0035] The chuck table 10 is positioned at a delivery position on the -Y direction side, and the wafer W is transported to the chuck table 10 using a transport mechanism (not shown). A protective member H is formed on the underside of the wafer W to be transported to the grinding device 1. The transport mechanism positions the suction pad above the chuck table 10 while the upper surface of the wafer W is suction-held by the suction pad. Then, the suction pad is lowered to bring the protective member H covering the underside of the wafer W close to the holding surface 32 of the chuck table 10.

[0036] The suction source 34 is operated to open the on-off valve, and a suction force is applied to the holding surface 32 of the chuck table 10. When the protective member H is placed on the holding surface 32, the protective member H is held in close contact with the holding surface 32 by the suction force acting on the holding surface 32. In other words, the wafer W is held on the holding surface 32 of the chuck table 10 via the protective member H. The suction force acting on the holding surface 32 causes the wafer W to assume a shape conforming to the holding surface 32 as a whole, and the wafer W is prevented from floating up from the holding surface 32. The chuck table 10 holding the wafer W by suction is moved in the +Y direction by the table moving mechanism 20, and is positioned at a processing position below the grinding mechanism 11.

[0037] The grinding method of the present invention is not limited to grinding a wafer having a protective member formed thereon, but can also be applied to grinding a wafer having no protective member formed thereon. For example, the lower surface of the wafer not covered with a protective member may be placed and held on the holding surface 32 of the chuck table 10.

[0038] 2, when the chuck table 10 is positioned at the processing position, the center Qa of the holding surface 32 and the center Qb of the grinding wheel 60 are shifted from each other so that the grinding wheels 12 pass over the center Qa of the holding surface 32 when the grinding wheel 60 is rotated. With this arrangement, when the grinding wheel 60 is rotated, the annularly arranged grinding wheels 12 move along a radial region extending from the outer periphery to the center of the wafer W held on the holding surface 32 of the chuck table 10.

[0039] Since the holding surface 32 of the chuck table 10 has a gentle cone shape with the center Qa as the apex, the wafer W is held on the chuck table 10 in a cone shape following the holding surface 32. Then, the inclination of the chuck table 10 is adjusted using the inclination adjustment mechanism 40 so that the radial region of the upper surface of the wafer W is approximately parallel to the lower surface of the grinding wheel 12, as shown in FIG.

[0040] The tilt adjustment of the chuck table 10 using the tilt adjustment mechanism 40 can be performed automatically by the control unit 2 controlling the operation of the first chuck adjustment shaft 42 and the second chuck adjustment shaft 43. Alternatively, an operator operating the grinding device 1 may manually operate the first chuck adjustment shaft 42 and the second chuck adjustment shaft 43.

[0041] With the chuck table 10 set in this manner, the grinding wheel 60 is rotated by the spindle unit 57, and the grinding mechanism 11 is lowered by the lifting mechanism 50 to bring the lower surface of the grinding wheel 12 into contact with the upper surface of the wafer W. The table rotation mechanism 35 rotates the chuck table 10, causing the wafer W on the chuck table 10 and the grinding wheel 60 to rotate relatively. Then, the upper surface of the wafer W is ground while the grinding wheel 12 is pressed against the wafer W. During the grinding process, the chuck table 10 and the wafer W are rotated in a rotation direction Ra shown in FIG. 2, and the grinding wheel 60 and the grinding wheel 12 are rotated in a rotation direction Rb shown in FIG. 2.

[0042] The grinding wheel 12 comes into contact with a radial region extending from the center of the wafer W (center Qa of the holding surface 32) to the outer periphery, and grinds the wafer W in an arc-shaped grinding region K shown in Figures 1 and 2. By rotating the chuck table 10, the grinding region K changes in the circumferential direction of the wafer W, and the entire upper surface of the wafer W can be ground by the grinding wheel 12. In the top view of Figure 2, one end of the grinding region K overlaps with the center Qa of the holding surface 32, and the other end of the grinding region K overlaps with a support position by the fixed shaft 41 (a position that serves as a fulcrum when the tilt adjustment mechanism 40 adjusts the tilt).

[0043] The thickness of the wafer W is measured using the height detection unit 45, and when the wafer W is ground to the desired thickness, the grinding mechanism 11 is raised by the lifting mechanism 50 to move the grinding wheel 12 away from the wafer W on the chuck table 10, thereby completing the grinding process.

[0044] After the grinding process, the table moving mechanism 20 moves the chuck table 10 to the transfer position on the -Y direction side. Also, the open / close valve is closed to release communication between the suction source 34 and the porous plate 31, so that the suction force is not applied to the wafer W from the holding surface 32 of the chuck table 10. This makes it possible to transfer the wafer W from the chuck table 10 to the transfer mechanism.

[0045] Incidentally, when grinding a conical wafer W conforming to the holding surface 32 of the chuck table 10 with the grinding wheel 12, the lower surface of the grinding wheel 12 and the holding surface 32 of the chuck table 10 are set to be parallel in the grinding region K. However, with this setting alone, there is a risk that the thickness of the wafer W ground with the grinding wheel 12 will not be uniform.

[0046] In the grinding region K, the center of the wafer W corresponding to the center Qa of the holding surface 32 is the apex of a cone, and therefore the lower surface of the grinding wheel 12 always contacts the center of the wafer W during grinding, regardless of the change in position of the wafer W in the rotational direction of the chuck table 10. In contrast, in the grinding region K, other than the center of the wafer W, the range of the wafer W that contacts the grinding wheel 12 changes sequentially in the circumferential direction (the rotational direction of the chuck table 10) as the chuck table 10 and the grinding wheel 60 rotate relative to each other.

[0047] In addition, since the wafer W held in a conical shape has a circumferential length that increases from the radial center toward the outer periphery, the circumferential length over which the grinding wheel 12 contacts the wafer W per unit rotation angle of the chuck table 10 is relatively small at the radial center of the wafer W and relatively large at the outer periphery of the wafer W.

[0048] For these reasons, when the wafer W is ground with the grinding wheel 12, the central portion of the wafer W tends to be ground more, and the uneven grinding amount causes a dent in the central portion of the wafer W. As described above, the grinding rate by the grinding wheel 12 is not uniform over the entire grinding region K, which is one of the reasons why the ground wafer W has an uneven thickness.

[0049] In addition, the central portion of the wafer W, where the grinding rate is high, is prone to temperature rise due to friction between the grinding wheel 12 and the wafer W, and the wafer W expands due to heat, increasing the load received from the grinding wheel 12. In other words, the thermal expansion of the wafer W during grinding is also a cause of the central portion of the wafer W being excessively ground.

[0050] As an example of a conventional grinding method for making the thickness of the wafer ground by a grinding wheel uniform, a method is known in which the grinding process is stopped midway, the thickness of the wafer is measured, and the inclination of the chuck table is changed so as to correct the deviation in the thickness of the wafer W found by the measurement, and the wafer is ground to a preset finishing thickness. This grinding method has a problem that the grinding time is long because the inclination of the chuck table is changed after the grinding process is paused. In particular, if the grinding process is paused and the inclination of the chuck table is adjusted every time an individual wafer is ground, the time required for grinding multiple wafers becomes very long.

[0051] As another example of a different conventional grinding method, a method is known in which the center of the conical holding surface of the chuck table is flattened in order to prevent a depression from occurring in the central portion of the wafer. By flattening the center of the holding surface, the tendency for the central portion of the wafer to be excessively ground can be suppressed when the wafer is ground. When forming such a holding surface, a grinding process is first performed on the porous plate that constitutes the holding surface of the chuck table to form a conical surface, and then a grinding process is performed to form a flat surface in the center, which is a two-stage grinding process, and therefore there is a problem that it takes a long time to form the holding surface of the chuck table.

[0052] The method for grinding a wafer according to the present embodiment solves the above problems and efficiently grinds the wafer W to a uniform thickness, and the details thereof will be described below. In the grinding method according to the first embodiment, the tilt changing step, which will be described later, is performed by adjusting the tilt of the chuck table 10 using the tilt adjustment mechanism 40.

[0053] [Initial setting process] In the initial setting step, the inclination of the chuck table 10 is adjusted using the inclination adjustment mechanism 40 so that the lower surface of the grinding wheel 12 and the holding surface 32 of the chuck table 10 are parallel in the grinding region K. By changing the heights of the first chuck adjustment shaft 42 and the second chuck adjustment shaft 43, the chuck table 10 tilts about the fixed shaft 41 as a fulcrum, and the direction and magnitude of the inclination of the holding surface 32 can be appropriately adjusted. Fig. 3 shows the relative inclination relationship between the chuck table 10 and the grinding mechanism 11 after the initial setting step has been performed.

[0054] In addition, since the grinding region K is arc-shaped and the holding surface 32 of the chuck table 10 is cone-shaped, the region of the holding surface 32 along the grinding region K is not located on a plane. In other words, even if the inclination of the holding surface 32 is adjusted, the lower surface of the grinding wheel 12 and the holding surface 32 do not become completely parallel over the entire grinding region K. Strictly speaking, in the initial setting process, the inclination of the chuck table 10 is adjusted so that the radial region along the imaginary straight line La (FIG. 2) connecting the center Qa of the holding surface 32, which is one end of the grinding region K, and the outer periphery (support position by the fixed shaft 41) of the holding surface 32, which is the other end, becomes parallel to the lower surface of the grinding wheel 12. By adjusting in this way, in the grinding region K, the lower surface of the grinding wheel 12 and the holding surface 32 become in a positional relationship that is approximately parallel.

[0055] The height adjustment operations of the first chuck adjustment shaft 42 and the second chuck adjustment shaft 43 in the initial setting step can be automatically performed under the control of the control unit 2. Alternatively, the operator who operates the grinding device 1 may manually perform the height adjustment operations of the first chuck adjustment shaft 42 and the second chuck adjustment shaft 43.

[0056] The chuck table 10, whose inclination was set in the initial setting process, is positioned at the delivery position on the -Y direction side, and the wafer W is held on the holding surface 32 via the protective member H. The suction source 34 is operated to open the open / close valve, and a suction force is applied to the holding surface 32 of the chuck table 10. The table movement mechanism 20 is operated to move the chuck table 10, which has the wafer W held by suction on the holding surface 32, to the processing position on the +Y direction side. At the processing position, the chuck table 10 is positioned so that the grinding wheel 12 passes over the center Qa of the chuck table 10.

[0057] In the initial setting step, the tilt of the chuck table 10 may be adjusted using the tilt adjustment mechanism 40 after the wafer W is first held on the holding surface 32 of the chuck table 10 .

[0058] [Measurement process] Following the initial setting process, a measurement process is performed. In the measurement process, grinding (test grinding) of the upper surface of the wafer W is performed by the grinding wheel 12 at the tilt position of the chuck table 10 set in the initial setting process, and the thickness tendency of the wafer W in the radial direction is measured using the height detection unit 45. The thickness tendency of the wafer W in the radial direction refers to the state of variation in the wafer thickness for each position in the radial direction of the wafer W.

[0059] In the measurement process, the control unit 2 rotates the grinding wheel 60 using the spindle unit 57, lowers the grinding mechanism 11 using the lifting mechanism 50 to bring the lower surface of the grinding wheel 12 into contact with the upper surface of the wafer W, and rotates the chuck table 10 using the table rotation mechanism 35 to grind the upper surface of the wafer W while pressing the grinding wheel 12 against the wafer W.

[0060] During grinding in the measurement process, cooling water M is supplied from a cooling water source 66 to a cooling water nozzle 65, and the cooling water M is sprayed from the cooling water nozzle 65 toward the center of the top surface of the wafer W. During grinding, the temperature rises due to friction between the grinding wheel 12 and the wafer W. The cooling water M is set to a predetermined temperature that reduces the rise in temperature due to friction at the grinding point, and the cooling water M supplied from the cooling water nozzle 65 cools the center of the top surface of the wafer W. The cooling effect of the cooling water M suppresses thermal expansion of the central portion of the wafer W.

[0061] After performing a predetermined amount of test grinding, the control unit 2 causes the height detection unit 45 to measure the thickness of the wafer W. More specifically, the thickness of the wafer W is measured so as to determine at least the presence or absence of a dent in the central portion of the wafer W, and the amount of the dent if a dent exists. For example, the height detection unit 45 may be caused to measure the thickness at multiple points in the radial direction of the wafer W, and the thickness trend of the wafer W may be calculated from the thicknesses measured at the multiple points, thereby making it possible to determine the state of the dent in the central portion of the wafer W.

[0062] [Tilt change process] Following the measurement step, an inclination change step is performed. In the inclination change step, the inclination of the holding surface 32 of the chuck table 10 is changed from a state in which the lower surface of the grinding wheel 12 and the holding surface 32 of the chuck table 10 are parallel in the grinding region K (strictly speaking, the radial region along the straight line La) to a direction in which the holding surface 32 of the chuck table 10 approaches the lower surface of the grinding wheel 12 in the intermediate portion of the grinding region K.

[0063] 2, 4, and 5 show point Sa, a specific position on the holding surface 32 at the centroid of the grinding region K, which is the region where the lower surface of the grinding wheel 12 contacts the wafer W. Note that point Sa also refers to the centroid of the grinding region K on the lower surface of the grinding wheel 12. Also, a point at a specific position on the upper surface of the wafer W that is held on the holding surface 32 and ground is also referred to as point Sa.

[0064] FIG. 4 shows the chuck table 10 before the inclination is changed. In the example of FIG. 4, the support position of the chuck table 10 by the first chuck adjustment shaft 42 and the support position of the chuck table 10 by the second chuck adjustment shaft 43 are at the same height, and the chuck table 10 is configured to be approximately symmetrical with respect to the line La shown in FIG. 2. That is, in the cross section shown in FIG. 4, the holding surface 32 of the chuck table 10 has a curved mountain shape with the highest point along the line La. The imaginary plane Va shown in FIG. 4 is parallel to the lower surface of the grinding wheel 12 and is at the same height as the line La. The point Sa on the holding surface 32 is located slightly below the imaginary plane Va.

[0065] 2, the fixed shaft 41, the first chuck adjustment shaft 42, and the second chuck adjustment shaft 43 constituting the inclination adjustment mechanism 40 are disposed at approximately equal intervals in the circumferential direction of the chuck table 10, and the center Qa of the holding surface 32 is located approximately at the center of an equilateral triangle with the fixed shaft 41, the first chuck adjustment shaft 42, and the second chuck adjustment shaft 43 as vertices. The first chuck adjustment shaft 42 and the second chuck adjustment shaft 43 are disposed approximately symmetrically in one and the other regions sandwiching the straight line La. Therefore, when the height of one of the first chuck adjustment shaft 42 and the second chuck adjustment shaft 43 is increased and the height of the other is decreased, the inclination of the chuck table 10 changes with the straight line La as an axis.

[0066] Since the intermediate portion of the grinding region K is located on the second chuck adjustment axis 43 side with respect to the straight line La, by increasing the height of the second chuck adjustment axis 43 and decreasing the height of the first chuck adjustment axis 42, the chuck table 10 is tilted in the direction of the arrow Ta in Fig. 4 and changed to the orientation shown in Fig. 5. As a result, in the intermediate portion of the grinding region K, the holding surface 32 of the chuck table 10 (for example, the position of point Sa shown in Figs. 4 and 5) approaches the lower surface of the grinding wheel 12.

[0067] When the inclination of the chuck table 10 is changed as described above, in the subsequent grinding process, the state of contact of the grinding wheel 12 with the upper surface of the wafer W on the holding surface 32 changes in the intermediate portion of the grinding region K. More specifically, as the point Sa on the holding surface 32 approaches the lower surface of the grinding wheel 12 in the inclination changing process, more of the wafer W is likely to be ground in the intermediate portion of the grinding region K in the grinding process. In other words, the grinding rate of the central portion of the wafer W and the intermediate portion in the radial direction is equalized, and excessive grinding of the central portion of the wafer W can be prevented.

[0068] For example, if the inclination of the chuck table 10 is changed until the height position of the point Sa on the holding surface 32 reaches the height position of the virtual plane Va shown in Fig. 4, the load with which the grinding wheel 12 is pressed against the central part of the wafer W and the load with which the grinding wheel 12 is pressed against the radial middle part of the wafer W in the subsequent grinding process will be approximately equal. However, since the grinding wheel 12 is always in contact with the central part of the wafer W in the grinding process, even if the contact load of the grinding wheel 12 is approximately equal, the grinding rate of the central part of the wafer W tends to be relatively large due to the difference in the contact time with the grinding wheel 12. Therefore, in the inclination changing process, the height position of the point Sa on the holding surface 32 is adjusted to be closer to the lower surface of the grinding wheel 12 (adjustment to relatively reduce the grinding rate of the central part of the wafer W) as necessary, and the grinding rates of the central part of the wafer W and the radial middle part are equalized.

[0069] It should be noted that, at the stage when the initial setting process is performed, the inclination of the chuck table 10 along the line BB in Fig. 2 may differ from the inclination shown in Fig. 4. For example, at the stage when the initial setting process is performed, the inclination angle of the chuck table 10 may be close to the state in Fig. 5. In this case as well, if the measurement process reveals thickness variations such as a dent in the central portion of the wafer W, the inclination changing process is performed to eliminate the variations.

[0070] The control unit 2 calculates the amount of tilt change for making the wafer W have a uniform thickness without causing a recess in the central portion of the wafer W, based on the thickness data of the wafer W obtained from the measurement result by the height detection unit 45 in the measurement process. In this embodiment, the control unit 2 calculates the amount of tilt change of the chuck table 10 by the tilt adjustment mechanism 40. The calculated amount of tilt change of the chuck table 10 is stored in the memory of the control unit 2.

[0071] In the tilt changing process, the chuck table 10 is tilted by the calculated tilt change amount. The height adjustment operations of the first chuck adjustment shaft 42 and the second chuck adjustment shaft 43 in the tilt changing process can be automatically executed under the control of the control unit 2.

[0072] Alternatively, in the inclination changing step, an operator operating the grinding apparatus 1 may manually perform the height adjustment operation of the first chuck adjustment axis 42 and the second chuck adjustment axis 43. When performing the height adjustment operation manually, the control unit 2 displays information on the adjustment amount of the first chuck adjustment axis 42 and the second chuck adjustment axis 43 based on the calculated amount of inclination change on a display unit (not shown) or the like provided in the grinding apparatus 1, and the operator performs the height adjustment operation by referring to the displayed information.

[0073] [Grinding process] After the tilt changing step, a grinding step is performed in which the wafers W are ground to a finishing thickness. The initial setting step, measurement step, and tilt changing step described above are performed as preparation steps before grinding each wafer W. After the tilt of the chuck table 10 is set in the tilt changing step, the setting is maintained and multiple wafers W are ground.

[0074] 6 shows a state in which the grinding process is being performed. The control unit 2 rotates the grinding wheel 60 using the spindle unit 57, lowers the grinding mechanism 11 using the lifting mechanism 50 so that the lower surface of the grinding wheel 12 comes into contact with the upper surface of the wafer W, and rotates the chuck table 10 using the table rotation mechanism 35 to grind the upper surface of the wafer W while pressing the grinding wheel 12 against the wafer W.

[0075] As a result of changing the inclination of the holding surface 32 of the chuck table 10 in the inclination changing process, in the grinding process, the grinding rate in the grinding region K in the radial direction of the wafer W is equalized. More specifically, in the inclination changing process, the inclination is changed in a direction that brings the central part of the holding surface 32 of the chuck table 10 in the radial direction (grinding region K) closer to the lower surface of the grinding wheel 12, so that a difference in the amount of grinding is unlikely to occur between the central part of the wafer W and the parts other than the central part.

[0076] 6, in the grinding process, the control unit 2 controls the cooling water nozzle 65 to supply cooling water M toward the center of the upper surface of the wafer W. The cooling water M at a predetermined temperature (a temperature that reduces the temperature increased by friction between the grinding wheel 12 and the wafer W) supplied from the cooling water nozzle 65 cools the center of the upper surface of the wafer W. The cooling effect of the cooling water M suppresses thermal expansion of the central portion of the wafer W. In particular, the cooling water nozzle 65 is disposed outside the grinding mechanism 11, and by supplying the cooling water M from the outside of the grinding wheel 12, the center of the upper surface of the wafer W can be efficiently cooled.

[0077] For these reasons, the central portion of the wafer W is not excessively ground in the grinding process, and grinding processing can be achieved that does not cause a recess in the central portion of the wafer W. In other words, it is possible to suppress the variation in thickness of the wafer W and grind it to a uniform finished thickness.

[0078] In both the measurement process and the grinding process, the wafer W is ground by supplying cooling water M from the cooling water nozzle 65 to the center of the upper surface of the wafer W. Therefore, the amount of change in tilt of the chuck table 10 set in the tilt changing process is set in anticipation of the effect of suppressing thermal expansion of the wafer W by the cooling water M. By making the conditions related to cooling the wafer W during grinding the same in both the measurement process and the grinding process, the amount of change in tilt in the tilt changing process can be optimized for the actual grinding process performed while supplying cooling water M.

[0079] When grinding a plurality of wafers W with common processing conditions, the initial setting process, thickness tendency measuring process, and tilt changing process are performed only on the wafer W that is the judgment reference (for example, the first wafer W or every nth wafer W), and the other wafers W can be held on the chuck table 10 after the tilt has been changed in the tilt changing process and only the grinding process is performed. Therefore, it is possible to efficiently achieve uniform thickness of the ground wafers W without the need for the time and effort of temporarily stopping the grinding process and changing the tilt of the chuck table 10 every time each wafer W is ground.

[0080] In addition, since no processing is performed to flatten the center of the holding surface 32 of the chuck table 10, it is possible to prevent a depression from being formed in the central portion of the wafer W, which has the advantage that it does not take much time to form the holding surface 32.

[0081] In the grinding method of the first embodiment described above, the inclination changing step is performed by adjusting the inclination of the chuck table 10 using the inclination adjustment mechanism 40. Next, a grinding method of the second embodiment in which the inclination changing step is performed by adjusting the inclination on the grinding mechanism 11 side will be described with reference to Figs. 7 to 9.

[0082] In the grinding device 1 for carrying out the grinding method of the second embodiment, the grinding mechanism 11 is provided with an inclination adjustment mechanism 70. The configuration other than the inclination adjustment mechanism 70 is common to the first embodiment, and detailed description of the parts common to the first embodiment will be omitted.

[0083] The inclination adjustment mechanism 70 supports the spindle unit 57 so as to change the inclination thereof relative to the housing 56. As shown in Fig. 7, the inclination adjustment mechanism 70 includes a first fixed shaft 71, a second fixed shaft 72, and a spindle adjustment shaft 73, which are arranged at approximately equal intervals in the circumferential direction of the grinding wheel 60. As shown in Figs. 8 and 9, there is a space in the Z-axis direction between a downward support surface 74 provided on the spindle unit 57 and a bottom surface portion 75 of the housing 56, and the first fixed shaft 71, the second fixed shaft 72, and the spindle adjustment shaft 73 are arranged in this space.

[0084] The first fixed shaft 71 and the second fixed shaft 72 support the spindle unit 57 at a constant height position relative to the housing 56. The spindle adjustment shaft 73 is operable to change the height, and can change the height position of the spindle unit 57 relative to the housing 56.

[0085] The tilt adjustment mechanism 70 adjusts the tilt of the grinding wheel 60 connected to the spindle unit 57 via the spindle 58 and mount 59 by operating the spindle adjustment shaft 73 to tilt the spindle unit 57 about an imaginary straight line Lb (FIG. 7) connecting the first fixed shaft 71 and the second fixed shaft 72. By selecting the adjustment direction and adjustment amount of the height of the spindle adjustment shaft 73, the tilt direction and magnitude of the tilt of the grinding wheel 60 can be changed as desired.

[0086] The straight line Lb, which is the axis of the tilt adjustment mechanism 70 changing the tilt of the grinding wheel 60, is parallel to the above-mentioned straight line La (the straight line connecting the center Qa of the holding surface 32 of the chuck table 10 and the support position by the fixed shaft 41). Therefore, when the tilt adjustment mechanism 70 changes the tilt of the grinding wheel 60 about the straight line Lb as the axis, the distance between the lower surface of the grinding wheel 12 and the holding surface 32 of the chuck table 10 changes in the intermediate portion of the grinding region K, similar to the case where the tilt adjustment mechanism 40 changes the tilt of the chuck table 10 about the straight line La as the axis in the grinding method of the first embodiment.

[0087] 7 to 9 show point Sb, which is a specific position on the underside of the grinding wheel 12 at the centroid of the grinding region K, which is the region where the underside of the grinding wheel 12 contacts the wafer W. Note that point Sb also refers to the centroid of the grinding region K of the holding surface 32 and the wafer W. In the tilt changing step, the tilt of the grinding wheel 60 is changed in a direction that brings point Sb on the underside of the grinding wheel 12 closer to the holding surface 32 of the chuck table 10. FIG. 8 shows the state of the grinding wheel 60 before the tilt is changed, and FIG. 9 shows the state of the grinding wheel 60 after the tilt is changed.

[0088] Since the intermediate portion of the grinding region K is located on the opposite side of the spindle adjustment shaft 73 with respect to the straight line Lb, by raising the height of the support position of the spindle unit 57 by the spindle adjustment shaft 73, the grinding wheel 60 is tilted in the direction of the arrow Tb in Fig. 8, and is changed to the orientation shown in Fig. 9. As a result, in the intermediate portion of the grinding region K, the lower surface of the grinding stone 12 (for example, the position of point Sb shown in Figs. 8 and 9) approaches the holding surface 32 of the chuck table 10.

[0089] When the inclination of the grinding wheel 60 and the grinding wheel 12 is changed as described above, the state of contact of the grinding wheel 12 with the upper surface of the wafer W on the holding surface 32 changes in the middle part of the grinding region K during the grinding process. In particular, as the point Sb of the grinding wheel 12 is brought closer to the holding surface 32 during the inclination changing process, the wafer W is more likely to be ground in the middle part of the grinding region K during the grinding process. In other words, the grinding rate of the central part of the wafer W and the middle part in the radial direction is equalized, and excessive grinding of the central part of the wafer W can be prevented.

[0090] When changing the inclination of the grinding wheel 12 in the grinding mechanism 11 in the inclination changing step, it is also possible to use an inclination adjustment mechanism having a different form from the inclination adjustment mechanism 70 described above. For example, of the three fixed shafts 61 shown in Fig. 2, two fixed shafts 61 are configured as spindle adjustment shafts that can change the height position of the spindle unit 57. Then, by adjusting these two spindle adjustment shafts, the inclination of the spindle 58 can be changed, and the distance between the lower surface of the grinding wheel 12 and the holding surface 32 of the chuck table 10 may be adjusted so that the distance at the point Sa is smaller than the distance at other points.

[0091] The grinding method of the second embodiment is performed in the same manner as the grinding method of the first embodiment, except for the operation in the inclination changing step described above. Therefore, in the grinding step after the inclination changing step, if grinding is performed while supplying cooling water M from the cooling water nozzle 65 toward the center of the upper surface of the wafer W, the thickness of the ground wafer W can be made uniform without causing a recess in the central portion of the wafer W.

[0092] As can be seen from the above embodiments, in the tilt changing step, the tilt of the wafer W side held by the chuck table 10 may be changed, or the tilt of the grinding wheel 12 side supported by the grinding wheel 60 may be changed. In the present invention, changing the tilt of the holding surface 32 of the chuck table 10 in a direction to bring the holding surface 32 of the chuck table 10 closer to the lower surface of the grinding wheel 12 in the middle part of the grinding region K means relatively changing the tilt of the lower surface of the grinding wheel 12 and the holding surface 32, and it is sufficient to change the tilt of at least one of the lower surface of the grinding wheel 12 and the holding surface 32. In other words, the present invention is not limited to the first embodiment in which the chuck table 10 is tilted.

[0093] In addition, in each embodiment, the tilt changing step changes the tilt of either the chuck table 10 or the grinding wheel 60 selectively, but it is also possible to change the tilt of both the chuck table 10 and the grinding wheel 60. For example, it is also possible to allocate a part of the tilt change amount calculated as a result of the measurement step to changing the tilt of the grinding wheel 60, and allocate the remainder to changing the tilt of the chuck table 10.

[0094] Although the above-mentioned embodiments are applied as a grinding method for preventing a recess in the central portion of the wafer W, it is also possible to apply the above-mentioned technique related to the inclination change for the purpose of preventing a convex shape in the central portion and grinding the wafer W to a predetermined thickness when a convex shape is formed in the central portion of the wafer W. For example, by inclining the chuck table 10 in the direction opposite to the direction of the arrow Ta in FIG. 4 or by inclining the grinding wheel 60 in the direction opposite to the direction of the arrow Tb in FIG. 8, the grinding rate in the radial middle portion of the wafer W becomes relatively lower and the grinding rate in the central portion of the wafer W becomes relatively higher. Therefore, by performing such inclination change on the chuck table 10 or the grinding wheel 60, it is possible to prevent a convex shape from being formed in the central portion of the wafer W.

[0095] The embodiments of the present invention are not limited to the above-mentioned embodiments and modifications, and may be modified, substituted, or altered in various ways without departing from the spirit of the technical idea of ​​the present invention. Furthermore, if the technical idea of ​​the present invention can be realized in a different way due to technological progress or a different derived technology, the present invention may be implemented using that method. Therefore, the claims cover all embodiments that may be included within the scope of the technical idea of ​​the present invention. [Industrial Applicability]

[0096] As described above, the wafer grinding method of the present invention makes it possible to grind wafers to a predetermined uniform thickness without the need to measure the wafer thickness and adjust the inclination of the chuck table during the grinding process, or to change the shape of the holding surface of the chuck table before the grinding process, thereby achieving improved wafer production efficiency and improved quality. [Explanation of symbols]

[0097] 1: Grinding equipment 2: Control section 10: Chuck table 11: Grinding mechanism 12: Grinding wheel 13: Foundation 20: Table movement mechanism 30: Frame 31:Porous plate 32: Holding surface 34: Suction source 35: Table rotation mechanism 36: Chuck spindle 37: Support stand 40: Tilt adjustment mechanism 41: Fixed axis 42: First chuck adjustment axis 43: Second chuck adjustment axis 45: Height detection unit 50: Lifting mechanism 52: Lift table 56: Housing 57: Spindle unit 58: Spindle 59: Mount 60: Grinding wheel 61: Fixed axis 65: Cooling water nozzle 66: Cooling water source 70: Tilt adjustment mechanism 71: 1st fixed axis 72:Second fixed axis 73: Spindle adjustment shaft H: Protective material K: Grinding area M: Cooling water Qa: Center of holding surface Qb: Center of the grinding wheel W: Wafer

Claims

[Claim 1] A method for grinding a wafer, comprising contacting a lower surface of an annular grinding wheel with a radial region of an upper surface of a wafer held on a conical holding surface of a chuck table, and grinding the rotating wafer with the rotating grinding wheel by an arc-shaped grinding region, comprising: an inclination changing process for changing an inclination of the holding surface of the chuck table from a state in which the lower surface of the grinding wheel and the holding surface of the chuck table are parallel to each other in the grinding region, in a direction in which the holding surface of the chuck table approaches the lower surface of the grinding wheel in an intermediate portion of the grinding region; a grinding step of grinding the wafer to a finishing thickness while supplying cooling water at a predetermined temperature from the outside of the grinding wheel to the center of the upper surface of the wafer after the tilt changing step; A method for grinding a wafer comprising the steps of:

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