Method for grinding a workpiece

Abstract

To suppress generation of grinding defects in grinding to form a ring-shaped reinforcement in the back surface of a workpiece.SOLUTION: A method of grinding a workpiece is performed to form a disk-shaped recess and a ring-shaped reinforcement surrounding the recess by grinding a predetermined region corresponding to a device region on a back surface of the workpiece having the device region and an outer peripheral surplus region surrounding the device region on a front surface. The method of grinding the workpiece comprises the steps of: grind-feeding a grinding unit to grind the predetermined region while rotating a spindle without rotating a chuck table holding the workpiece so as to form a groove in the back surface of the workpiece; starting rotation of the chuck table while maintaining the rotation of the spindle so as to grind side walls of the groove, thereby removing the groove; and grind-feeding the grinding unit while rotating the spindle and the chuck table so as to grind the predetermined region, thereby forming the recess and the ring-shaped reinforcement.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for grinding a workpiece, the method comprising grinding a predetermined area on the back side of the workpiece having a device area and a peripheral excess area surrounding the device area on the front side thereof, the predetermined area corresponding to the device area, to form a disk-shaped recess and a ring-shaped reinforcing portion surrounding the recess. [Background technology]

[0002] In order to reduce the weight and thickness of device chips mounted on electronic devices, a wafer (workpiece) with multiple devices formed on its surface is sometimes ground using a grinding device to thin the workpiece to, for example, 100 μm or less.

[0003] However, if the workpiece is thinned too much, it becomes difficult to transport the workpiece after thinning, etc. Therefore, a grinding method is known in which a predetermined area on the back side of the workpiece corresponding to a device area on the front side on which multiple devices are formed is ground to form a disk-shaped recess and a ring-shaped reinforcing part surrounding the recess (see, for example, Patent Document 1).

[0004] This grinding method is called TAIKO (registered trademark). By forming a ring-shaped reinforcing part on the outer periphery of the workpiece, the warping of the workpiece can be reduced and the strength of the workpiece can be improved compared to a workpiece whose entire back side is uniformly thinned. In addition, cracks of the workpiece originating from the outer periphery can be suppressed.

[0005] In order to form the ring-shaped reinforcing portion, a grinding wheel having an outer diameter smaller than that of the workpiece is used. The grinding wheel has an annular wheel base, and a plurality of segment-shaped grinding stones are fixed to one side of the wheel base along the circumferential direction of the wheel base.

[0006] The grinding wheel has a smaller diameter and fewer grinding stones than a normal grinding wheel used for grinding the entire back surface uniformly. Furthermore, the peripheral speed during grinding is slower than that of a normal grinding wheel, so the amount of work per grinding stone is greater than that of a normal grinding wheel.

[0007] Therefore, compared to the grinding stones in normal grinding wheels, the grinding ability of the grinding stone is more likely to decrease, and the grinding stone is more likely to be in poor condition due to glazing, chipping, clogging, etc. For example, if a relatively hard oxide film is formed on the back side of the workpiece, grinding defects are more likely to occur due to the decrease in grinding ability. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2007-19461 A Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been made in consideration of the above problems, and aims to provide a grinding method that can suppress the occurrence of grinding defects in grinding to form a ring-shaped reinforcing portion on the back side of a workpiece. [Means for solving the problem]

[0010] According to one aspect of the present invention, there is provided a method for grinding a workpiece, the method comprising: a chuck table for holding a workpiece; and a grinding unit for grinding the workpiece held by the chuck table while rotating the grinding wheel around the spindle, the grinding wheel including a spindle and having a plurality of grinding stones arranged in a ring shape, the grinding wheel being attached to the spindle and the workpiece being ground. The grinding wheel is used to grind a predetermined region on the back side of the workpiece, the back side of the workpiece having a device region on a front side on which a plurality of devices are formed and a peripheral excess region surrounding the device region, the predetermined region corresponding to the device region, to form a disk-shaped recess and a ring-shaped reinforcing portion surrounding the recess, the method comprising the steps of: not rotating the chuck table holding the workpiece; a groove forming step of grinding the predetermined region by feeding the grinding unit in a grinding feed while rotating the spindle in a state where the predetermined region is ground to form an arc-shaped or annular groove having a depth less than the finishing thickness on the back surface of the workpiece; a groove removing step of, after the groove forming step, starting rotation of the chuck table while keeping the spindle rotating, to grind the side wall of the groove and remove the groove from the workpiece; and a recess forming step of, after the groove removing step, grinding the grinding unit in a grinding feed while rotating the spindle and the chuck table, to grind the predetermined region corresponding to the device region to form the recess and to form the ring-shaped reinforcing portion surrounding the recess.

[0011] Preferably, in the groove removing step, the chuck table is rotated while the grinding unit is moved in grinding feed. Effect of the Invention

[0012] In one embodiment of the method for grinding a workpiece according to the present invention, the grinding unit is fed to grind the workpiece while rotating the spindle, without rotating the chuck table holding the workpiece, thereby forming an arc-shaped or annular groove having a depth that does not reach the finishing thickness on the back surface of the workpiece (groove forming step).

[0013] After the groove forming step, the rotation of the chuck table is started while the spindle is rotating, thereby grinding the sidewall of the groove and removing the groove from the workpiece (groove removing step).Furthermore, after the groove removing step, the grinding unit is fed for grinding while rotating the spindle and the chuck table, thereby grinding a predetermined area corresponding to the device area to form a recess and a ring-shaped reinforcing part surrounding the recess (recess forming step).

[0014] In the groove forming step, grinding is mainly performed on the bottom surface of the grinding wheel, but in the groove removing step, grinding can be mainly performed on the side surface of the grinding wheel. Therefore, in the groove removing step, deterioration of the condition of the bottom surface of the grinding wheel (i.e., reduction in grinding ability) can be reduced compared to when the entire back side of the workpiece is ground mainly on the bottom surface of the grinding wheel.

[0015] In the recess forming step after the groove removing step, the entire predetermined area on the back side of the workpiece from which the grooves have been removed is ground. In the recess forming step, grinding is mainly performed on the bottom surface of the grinding wheel, and grinding can be performed in a state in which the condition of the bottom surface of the grinding wheel is not deteriorated to a great extent. Therefore, even if a relatively hard oxide film is formed on the back side of the workpiece, grinding defects of the workpiece can be suppressed. [Brief description of the drawings]

[0016] [Figure 1] FIG. [Diagram 2] FIG. 2 is a flow diagram of a grinding method. [Diagram 3] FIG. 4 is a partial cross-sectional side view showing a groove forming step. [Figure 4] FIG. 4(A) is a top view of the workpiece etc. in the groove forming step, and FIG. 4(B) is a top view of the workpiece showing the grooves formed in the groove forming step. [Diagram 5] FIG. 11 is a partial cross-sectional side view showing a groove removing step. [Figure 6] FIG. 11 is a top view of a workpiece etc. in a groove removing step. [Figure 7]FIG. 4 is a partial cross-sectional side view showing a recess forming step. [Figure 8] FIG. 2 is a cross-sectional view of the workpiece after grinding. [Figure 9] FIG. 11 is a top view of the workpiece showing the grooves formed in the groove forming step of the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] An embodiment according to one aspect of the present invention will be described with reference to the accompanying drawings. First, a workpiece 11 to be ground in the first embodiment will be described with reference to Fig. 1. Fig. 1 is a perspective view of the workpiece 11 and the like.

[0018] The workpiece 11 in this embodiment is a disk-shaped silicon wafer having a predetermined diameter (e.g., a diameter of about 200 mm). The workpiece 11 has a front surface 11a and a back surface 11b, and the length from the front surface 11a to the back surface 11b (i.e., the thickness of the workpiece 11) is a predetermined value (e.g., 725 μm) of 200 μm to 800 μm.

[0019] A thermal oxide film (not shown) having a thickness of about 2000 Å to 3000 Å is formed on the entire back surface 11b. A plurality of division lines 13 are set in a lattice pattern on the front surface 11a. A device 15 such as an IC (Integrated Circuit) is formed on the front surface 11a side of a rectangular region partitioned by the plurality of division lines 13.

[0020] There are no limitations on the type, material, size, shape, structure, etc. of the workpiece 11. The workpiece 11 may be a wafer or substrate made of a compound semiconductor other than silicon (GaN, SiC, etc.), glass, ceramics, resin, metal, etc. Furthermore, there are no limitations on the type, number, shape, structure, size, arrangement, etc. of the devices 15 formed on the workpiece 11.

[0021] A device region 17a in which a plurality of devices 15 are formed is surrounded by a substantially flat, annular peripheral excess region 17b in which no devices 15 are formed, around the device region 17a in a plan view.

[0022] Before grinding the workpiece 11, a circular resin protective tape 19 is attached to the front surface 11a in order to reduce damage to the device 15 during grinding. This forms a workpiece unit 21 in which the workpiece 11 and the protective tape 19 are laminated.

[0023] When grinding the workpiece 11, a predetermined region 17d (see FIG. 8) on the back surface 11b corresponding to the device region 17a is ground to a predetermined depth, thereby forming a disk-shaped recess 11c and a ring-shaped reinforcing portion 11d surrounding the side of the recess 11c, as shown in FIG.

[0024] Next, a grinding device 2 used for grinding a workpiece 11 will be described with reference to Fig. 3. The +Z direction and -Z direction shown in Fig. 3 are directions parallel to the Z-axis direction and opposite to each other. For example, the +Z direction is the upward direction, and the -Z direction is the downward direction.

[0025] 3 are directions parallel to the X-axis direction perpendicular to the Z-axis direction and opposite to each other, and the +Y and -Y directions are directions parallel to the Y-axis direction perpendicular to the Z-axis direction and the X-axis direction and opposite to each other. For example, the XY plane is parallel to the horizontal plane.

[0026] 3, the grinding device 2 includes a disk-shaped chuck table 4 that suction-holds the front surface 11a side of the workpiece 11. The chuck table 4 has a disk-shaped frame body made of ceramics.

[0027] A disk-shaped recess (not shown) is formed in the center of the frame. A predetermined flow path (not shown) is formed inside the frame. One end of the predetermined flow path is exposed to the recess, and the other end of the predetermined flow path is connected to a suction source (not shown) such as an ejector.

[0028] A porous plate (not shown) made of porous ceramics is fixed in the recess of the frame. Negative pressure from the suction source is transmitted to the upper surface of the porous plate. The upper surface of the porous plate and the upper surface of the frame are flush with each other, and function as a holding surface 4a that holds the workpiece 11 by suction.

[0029] Furthermore, the annular region between the outer peripheral end and center of the holding surface 4a is recessed more than the outer peripheral end and center of the holding surface 4a, and the annular region has a so-called biconcave shape when viewed in a cross-section of the chuck table 4 in the radial direction of the holding surface 4a.

[0030] However, since the depth of the recess is, for example, about 1 μm to 20 μm, the holding surface 4a is shown as substantially flat for convenience in Fig. 3. In the subsequent drawings, the holding surface 4a is also shown as substantially flat for convenience.

[0031] The chuck table 4 can rotate around a predetermined rotation axis 4b (see FIG. 5) by a rotation drive source (not shown) such as a motor provided below the chuck table 4. The rotation axis 4b is inclined at a predetermined angle with respect to the Z-axis direction within the XZ plane so that the outer circumferential end portion on the +X direction side of the holding surface 4a is slightly higher than the outer circumferential end portion on the -X direction side of the holding surface 4a.

[0032] Returning to Fig. 3, a description will be given of other components of the grinding device 2. A grinding unit 6 is disposed above the chuck table 4. The grinding unit 6 has a cylindrical spindle housing (not shown).

[0033] A ball screw type grinding feed mechanism (not shown) that moves the grinding unit 6 along the Z-axis direction is connected to the spindle housing. A part of a cylindrical spindle 8 is rotatably held inside the spindle housing.

[0034] The spindle 8 in this embodiment is disposed approximately parallel to the Z-axis direction. A rotation drive source (not shown) such as a motor is provided at the upper end of the spindle 8, and a disk-shaped mount 10 is fixed to the lower end of the spindle 8.

[0035] An annular grinding wheel 12 is attached to the underside of the mount 10. The grinding wheel 12 has an annular wheel base 14 made of a metal such as an aluminum alloy. The upper side of the wheel base 14 is fixed to the underside of the mount 10.

[0036] The grinding wheel 12 mounted on the spindle 8 in this manner is rotatable about the spindle 8. On the underside of the wheel base 14, a plurality of segment-shaped grinding wheels 16 are arranged in an annular shape along the circumferential direction of the wheel base 14.

[0037] The outer diameter of the area formed by the tracks of the grinding wheels 16 is approximately half the diameter of the back surface 11b. Next, a method for grinding the workpiece 11 using the grinding device 2 will be described. Figure 2 is a flow chart of the grinding method.

[0038] 3, the front surface 11a side of the workpiece 11 is suction-held by the holding surface 4a via the protective tape 19. At this time, the workpiece 11 is deformed according to the shape of the holding surface 4a (holding step S10). After the holding step S10, the groove forming step S20 is performed.

[0039] In the groove forming step S20, while the chuck table 4 on which the workpiece 11 is held by suction is not rotated (i.e., is stationary), the spindle 8 is rotated at a predetermined rotation speed while the grinding unit 6 is fed along the Z-axis direction for grinding.

[0040] In this embodiment, the predetermined rotation speed of the spindle 8 is set to 4000 rpm, and the grinding feed speed is set to 3.0 μm / s. Fig. 3 is a partially sectional side view showing the groove forming step S20. Note that in Fig. 3, the protective tape 19 is omitted for convenience.

[0041] Fig. 4(A) is a top view of the workpiece 11 in the groove forming step S20. In Fig. 4(A), a boundary region 17c on the back surface 11b side, which corresponds to the boundary between the device region 17a and the peripheral excess region 17b, is shown by a dashed line. The inside of this boundary region 17c is the above-mentioned predetermined region 17d.

[0042] In the groove forming step S20 of this embodiment, a region of the predetermined region 17d on the back surface 11b that corresponds to the movement trajectory of the grinding wheel 16 is ground to form an annular groove 11e passing through the center 11b1 of the back surface 11b. Fig. 4(B) is a top view of the workpiece 11 showing the groove 11e formed in the groove forming step S20.

[0043] The trench 11e formed in the trench forming step S20 has a predetermined depth that is deeper than the thickness of the oxide film formed on the back surface 11b side and does not reach the finished thickness 11f (see FIG. 8) of the device region 17a.

[0044] For example, the oxide film is 0.2 μm to 0.3 μm. When the grinding feed rate is 3.0 μm / s, when grinding is performed for 1 s after the lower surface of the grinding wheel 16 comes into contact with the back surface 11b, the grinding wheel 16 breaks through the oxide film, and a groove 11e having a depth of 3.0 μm to the deepest bottom is formed.

[0045] Since the finished thickness 11f is, for example, 100 μm, the depth of the groove 11e does not reach the finished thickness 11f. After the groove forming step S20, the chuck table 4 starts to rotate while the spindle 8 is rotating at a predetermined rotation speed (groove removing step S30).

[0046] In the groove removing step S30, the groove 11e is removed from the workpiece 11 by grinding the inner peripheral side wall 11e1 and the outer peripheral side wall 11e2 of the groove 11e, as shown in FIGS.

[0047] In the groove removing step S30, for example, the rotation of the chuck table 4 is started and finally increased to 300 rpm. In the groove removing step S30 of this embodiment, the chuck table 4 is rotated while the grinding unit 6 is fed downward for grinding at a speed of 3.0 μm / s, but the chuck table 4 may be rotated without grinding feed.

[0048] Fig. 5 is a partially sectional side view showing the groove removing step S30, and Fig. 6 is a top view of the workpiece 11 etc. in the groove removing step S30. In Fig. 6, arrows are used to diagrammatically show how the inner peripheral side wall 11e1 and the outer peripheral side wall 11e2 of the groove 11e are ground.

[0049] In the groove forming step S20, grinding is performed mainly on the bottom surface of the grinding wheel 16, whereas in the groove removing step S30, grinding can be performed mainly on the side surfaces (inner peripheral side surface and outer peripheral side surface) of the grinding wheel 16.

[0050] Therefore, in the groove removing step S30, deterioration of the condition of the bottom surface of the grinding wheel 16 (ie, reduction in grinding ability) can be reduced compared to when the entire back surface 11b side is ground mainly with the bottom surface of the grinding wheel 16.

[0051] Furthermore, in this embodiment, by performing the groove removing step S30, the predetermined region 17d can be ground using both the inner peripheral side surface and the outer peripheral side surface of the grinding wheel 16. Therefore, the load on the side surface of the grinding wheel 16 can be reduced compared to the case where only one of the inner peripheral side surface and the outer peripheral side surface of the grinding wheel 16 is used for grinding in the groove removing step S30.

[0052] After the groove removing step S30, the grinding unit 6 is fed for grinding while continuing to rotate the spindle 8 and the chuck table 4. For example, the grinding unit 6 is fed for grinding at 3.0 μm / s while the spindle 8 is rotated at 4000 rpm and the chuck table 4 is rotated at 300 rpm.

[0053] After the predetermined region 17d is ground until the thickness of the ground portion reaches a predetermined finish thickness 11f, the grinding feed is stopped. In this manner, the recess 11c shown in Fig. 7 is formed, and the ring-shaped reinforcing portion 11d surrounding the recess 11c is formed (recess formation step S40). Fig. 7 is a partially sectional side view showing the recess formation step S40, and Fig. 8 is a sectional view of the workpiece 11 after grinding.

[0054] In the recess forming step S40, grinding is mainly performed on the bottom surface of the grinding wheel 16, and in particular, grinding can be performed in a state where the degree of deterioration of the condition of the bottom surface of the grinding wheel 16 is reduced. Therefore, even if a relatively hard oxide film is formed on the back surface 11b side, the occurrence of grinding defects of the workpiece 11 can be suppressed.

[0055] Next, a second embodiment will be described. In the second embodiment, the steps from the holding step S10 to the recess forming step S40 are also performed in this order. However, since the inclination of the rotation axis 4b of the chuck table 4 in the second embodiment is larger than that of the rotation axis 4b in the first embodiment, the position of the outer circumferential end of the holding surface 4a on the +X direction side is higher than that in the first embodiment.

[0056] Therefore, in the groove forming step S20 in the second embodiment, a semicircular groove 11e passing through a center 11b1, rather than a circular groove, is formed on the +X direction side of the back surface 11b. Fig. 9 is a top view of the workpiece 11 showing the semicircular groove 11e formed in the groove forming step S20 in the second embodiment.

[0057] The second embodiment differs from the first embodiment in that a semicircular arc-shaped groove 11e is formed in groove forming step S20. However, in the second embodiment, groove removing step S30 and recess forming step S40 can be performed in the same manner as in the first embodiment.

[0058] The shape of the groove 11e formed in the groove forming step S20 of the second embodiment may be an arc shape having a predetermined central angle. By forming the arc-shaped or semicircular-shaped groove 11e in the groove forming step S20 of the second embodiment, the load on the bottom surface of the grinding wheel 16 can be reduced compared to the case where the annular groove 11e is formed.

[0059] In the groove removing step S30 of the second embodiment, deterioration of the condition of the bottom surface of the grinding wheel 16 (i.e., reduction in grinding ability) can also be reduced compared to when the entire back surface 11b side is ground mainly with the bottom surface of the grinding wheel 16.

[0060] Also, in the recess forming step S40 of the second embodiment, grinding can be performed in a state where the degree of deterioration of the condition of the bottom surface of the grinding wheel 16 is reduced. Therefore, even if a relatively hard oxide film is formed on the back surface 11b side, the occurrence of grinding defects of the workpiece 11 can be suppressed.

[0061] In addition, the structures, methods, and the like according to the above-described embodiments can be modified as appropriate without departing from the scope of the object of the present invention. [Explanation of symbols]

[0062] 2: grinding device, 4: chuck table, 4a: holding surface, 4b: rotating shaft 6: Grinding unit, 8: Spindle, 10: Mount 11: Workpiece, 11a: Front surface, 11b: Back surface, 11b1: Center 11c: recess, 11d: ring-shaped reinforcing part 11e: groove, 11e1: inner peripheral side wall, 11e2: outer peripheral side wall, 11f: finishing thickness 12: Grinding wheel, 14: Wheel base, 16: Grinding stone 13: Planned division line, 15: Device 17a: device region, 17b: peripheral surplus region, 17c: boundary region, 17d: predetermined region 19: protective tape, 21: workpiece unit

Claims

1. A chuck table for holding the workpiece; a grinding unit including a spindle, a grinding wheel having a plurality of grinding stones arranged in an annular manner attached to the spindle, and configured to grind the workpiece held by the chuck table while rotating the grinding wheel around the spindle; a grinding method for a workpiece, the method comprising: grinding a predetermined area of ​​a back surface side of the workpiece, the back surface side of the workpiece having a device area on which a plurality of devices are formed and an outer peripheral excess area surrounding the device area, with the grinding wheel, to form a disk-shaped recess and a ring-shaped reinforcing part surrounding the recess, the method comprising: a groove forming step of grinding the predetermined area by feeding the grinding unit while rotating the spindle while not rotating the chuck table holding the workpiece, thereby forming an arc-shaped or annular groove having a depth less than the finishing thickness on the back side of the workpiece; a groove removing step of, after the groove forming step, starting rotation of the chuck table while keeping the spindle rotating, grinding a side wall of the groove and removing the groove from the workpiece; a recess forming step of grinding the specified area corresponding to the device area to form the recess and to form the ring-shaped reinforcement portion surrounding the recess by rotating the spindle and the chuck table while grinding and feeding the grinding unit after the groove removing step.

2. 2. The method for grinding a workpiece according to claim 1, wherein in said groove removing step, said chuck table is rotated while said grinding unit is fed for grinding.

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