Method for Grinding Workpiece

Abstract

To provide a workpiece grinding method capable of reducing the probability of device breakage without significantly lengthening a time until grinding is completed when grinding a plate-shaped workpiece with a device on the front side from the back side.SOLUTION: A workpiece grinding method includes a first grinding step of grinding a workpiece from the back side to form a disk-shaped first thin plate portion and an annular first thick plate portion surrounding the first thin plate portion on the workpiece in a state in which the angle between the rotation axis of a first grinding wheel and the rotation axis of a first chuck table is adjusted such that the distance between the first grinding wheel and a first holding surface is wider on the outer edge side farther from the rotation axis of the first chuck table than on the center side closer to the rotation axis of the first chuck table.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a method for grinding a workpiece, which is applied when grinding a plate-shaped workpiece such as a wafer.

Background Art

[0002] In order to realize a small and lightweight device chip, the opportunity to thinly process a wafer on which a device such as an integrated circuit is provided on the surface side is increasing. For example, while holding the surface side of the wafer by a chuck table and rotating a grinding wheel on which a grindstone (grinding wheel) containing abrasive grains is fixed and the chuck table relative to each other, and supplying a liquid such as pure water, the grindstone is pressed against the back surface of the wafer, whereby the wafer can be ground and thinned.

[0003] By the way, when the entire wafer is thinned by the above method, the rigidity of the wafer is significantly reduced, making it difficult to handle the wafer in the subsequent process. Therefore, a technique has been proposed in which the central region (inner side) of the wafer provided with the device is ground and the outer edge region (outer side) is left as it is without being ground, so as to maintain the rigidity of the ground wafer at a sufficient height (see, for example, Patent Document 1).

[0004] In this technique, first, using a grinding wheel on which a grindstone containing abrasive grains of a certain size is fixed, the central region of the wafer is roughly ground to form a disk-shaped thin plate portion and an annular thick plate portion surrounding the thin plate portion on the wafer. In this way, by using a grinding wheel on which a grindstone containing large abrasive grains is fixed, the time required for grinding the wafer can be shortened compared to the case of using a grinding wheel on which a grindstone containing relatively small abrasive grains is fixed.

[0005] On the one hand, when a wafer is ground using a grinding wheel with a grinding stone containing large abrasive grains, a damaged layer including scratches and distortions caused by this grinding is generated on the surface side to be ground, and the mechanical strength (flexural strength) of the thin plate portion is likely to be insufficient. Therefore, after coarsely grinding the wafer, the thin plate portion is further ground using a grinding wheel with a grinding stone containing relatively small abrasive grains to remove the damaged layer.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] By the way, when the grinding wheel contacts the side surface of the thick plate portion or the like when grinding the thin plate portion to remove the damaged layer, the thick plate portion may be chipped. Therefore, when removing the damaged layer, only the region on the central side of the thin plate portion is ground so that the grinding wheel does not contact the thick plate portion. However, in this method, a damaged layer remains in the region on the outer edge side of the thin plate portion (the region close to the boundary with the thick plate portion). As a result, during subsequent conveyance or the like, cracks extend from the remaining damaged layer to the surface side of the wafer, and the device is likely to be damaged.

[0008] If the thin plate portion is thickened to sufficiently increase the distance from the surface - side device to the damaged layer, it is possible to prevent damage to the device caused by cracks extending from the damaged layer. However, in this case, in order to thin the thin plate portion to the final thickness, it is necessary to remove many parts of the wafer using a grinding wheel with a grinding stone containing relatively small abrasive grains and having a small amount that can be removed per unit time. That is, the time required to complete the grinding becomes significantly longer.

[0009] Therefore, an object of the present invention is to provide a method for grinding a work piece, when grinding a plate-shaped work piece having a device provided on the front surface side from the back surface side, capable of suppressing the probability of damage to the device without significantly increasing the time until grinding is completed.

Means for Solving the Problems

[0010] According to one aspect of the present invention, there is provided a method for grinding a workpiece, which uses a grinding wheel mounted on a rotating spindle to grind a plate-shaped workpiece having a plurality of devices provided on the front surface side from the back surface side opposite to the front surface, the method comprising: a pasting step of pasting a protection member on the front surface of the workpiece; a first grinding step in which the workpiece is held on a first holding surface of a first chuck table via the protection member, and while rotating the first grinding wheel provided with a first grinding stone containing abrasive grains and the first chuck table, the first grinding wheel and the first chuck table are relatively moved in a direction intersecting the first holding surface to grind the workpiece from the back surface side, and a first thin plate portion in a disc shape and a first thick plate portion in an annular shape surrounding the first thin plate portion are formed on the workpiece; after the first grinding step, a second grinding step in which the workpiece is held on a second holding surface of a second chuck table via the protection member, and while rotating the second grinding wheel provided with a second grinding stone containing smaller abrasive grains than the first grinding stone and the second chuck table, the second grinding wheel and the second chuck table are relatively moved in a direction intersecting the second holding surface to grind the first thin plate portion from the back surface side, and a second thin plate portion in a disc shape having a diameter smaller than that of the first thin plate portion and a second thick plate portion in an annular shape surrounding the second thin plate portion are formed on the first thin plate portion, wherein the angle formed by the rotation axis of the second grinding wheel and the rotation axis of the second chuck table is adjusted such that the difference between the distance on the central side close to the rotation axis of the second chuck table and the distance on the outer edge side far from the rotation axis of the second chuck table between the second grinding wheel and the second holding surface is smaller than the difference between the distance on the central side close to the rotation axis of the first chuck table and the distance on the outer edge side far from the rotation axis of the first chuck table between the first grinding wheel and the first holding surface.

[0011] Preferably, the first chuck table is used as the second chuck table. Also preferably, in the first grinding step, a first thin plate portion having a thickness such that cracks extending from a damaged layer including scratches or distortions generated on the outer edge side of the first thin plate portion in the first grinding step do not reach the device is formed.

Advantages of the Invention

[0012] In the method for grinding a workpiece according to one aspect of the present invention, the distance between the first grinding wheel including the first grinding stone containing abrasive grains and the first holding surface of the first chuck table is wider on the outer edge side far from the rotation axis of the first chuck table than on the central side close to the rotation axis of the first chuck table. With the angle formed by the rotation axis of the first grinding wheel and the rotation axis of the first chuck table adjusted, the workpiece is ground to form a disk-shaped first thin plate portion and an annular first thick plate portion surrounding the first thin plate portion on the workpiece. Therefore, the outer edge side of the first thin plate portion is thicker than the central side.

[0013] Then, thereafter, the difference between the distance on the central side close to the rotation axis of the second chuck table between the second grinding wheel including the second grinding stone containing abrasive grains smaller than the first grinding stone and the second holding surface of the second chuck table and the distance on the outer edge side far from the rotation axis of the second chuck table is smaller than the difference between the distance on the central side close to the rotation axis of the first chuck table between the first grinding wheel and the first holding surface and the distance on the outer edge side far from the rotation axis of the first chuck table. With the angle formed by the rotation axis of the second grinding wheel and the rotation axis of the second chuck table adjusted, the first thin plate portion is ground to form a disk-shaped second thin plate portion having a smaller diameter and a smaller thickness than the first thin plate portion and an annular second thick plate portion surrounding the second thin plate portion on the first thin plate portion. Therefore, while removing the damaged layer including scratches or distortions formed on the first thin plate portion, a second thin plate portion having a smaller difference in thickness between the outer edge side and the central side than the first thin plate portion can be formed.

[0014] Also, in the grinding method of the workpiece according to one aspect of the present invention, the outer edge side of the first thin plate portion remaining on the workpiece as the second thick plate portion is thicker than the central side of the first thin plate portion, and the distance from the damage layer formed in the second thick plate portion (that is, the outer edge side of the first thin plate portion) to the surface of the workpiece is sufficiently far. Therefore, when transporting the workpiece later, the possibility that cracks extend from the damage layer of the second thick plate portion to the surface side of the workpiece and the device is damaged is also reduced.

[0015] Furthermore, in the grinding method of the workpiece according to one aspect of the present invention, since the first thin plate portion with a thinner central side than the outer edge side is formed, compared with the case of processing the entire thick first thin plate portion into the second thin plate portion, the volume of the workpiece removed by the second grinding wheel is smaller. Therefore, even if the distance from the device to the damage layer of the second thick plate portion (the outer edge side of the first thin plate portion) is made sufficiently large, the time required to complete the grinding does not increase significantly. Thus, according to the grinding method of the workpiece according to one aspect of the present invention, the probability of device damage can be suppressed low without significantly increasing the time required to complete the grinding.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0017] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the method for grinding a workpiece according to this embodiment, first, a protective member is attached to a plate-shaped workpiece to be ground (attachment step). FIG. 1 is a perspective view schematically showing a state in which the protective member 21 is attached to the plate-shaped workpiece 11.

[0018] The workpiece 11 is typically a disk-shaped wafer made of a semiconductor such as silicon (Si). The surface 11a side of the workpiece 11 is divided into a plurality of small regions by a plurality of division planned lines (streets) 13 intersecting each other, and a device 15 such as an IC (Integrated Circuit) is formed in each small region. In this embodiment, a portion corresponding to the region (device region) where the device 15 of the workpiece 11 is formed is ground from the back surface 11b side opposite to the surface 11a to thin a part of the workpiece 11.

[0019] In this embodiment, a disk-shaped wafer made of a semiconductor such as silicon is used as the workpiece 11, but there is no limitation on the material, shape, structure, size, etc. of the workpiece 11. For example, a substrate made of other materials such as semiconductors, ceramics, resins, metals, etc. can also be used as the workpiece 11. Similarly, there is no limitation on the type, quantity, shape, structure, size, arrangement, etc. of the device 15.

[0020] The protective member 21 attached to the workpiece 11 is typically a circular tape (film), resin substrate, wafer of the same or different type as the workpiece 11, etc. having a diameter substantially equal to that of the workpiece 11. An adhesive layer (not shown) showing an adhesive force to the workpiece 11 is provided on the surface 21a side of the protective member 21.

[0021] Therefore, the protective member 21 can be attached to the workpiece 11 by bringing the surface 21a side of the protective member 21 into close contact with the workpiece 11. In the present embodiment, as shown in FIG. 1, the surface 21a side of the protective member 21 is brought into close contact with the surface 11a of the workpiece 11, and the protective member 21 is attached to the surface 11a of the workpiece 11. Thereby, when the workpiece 11 is ground from the back surface 11b side, the impact applied to the surface 11a can be mitigated, and the device 15 or the like can be protected.

[0022] After the protective member 21 is attached to the surface 11a of the workpiece 11, the workpiece 11 is held by the holding surface of the chuck table via the protective member 21 (holding step). That is, the back surface 21b side of the protective member 21 attached to the workpiece 11 is held by the chuck table. FIG. 2 is a cross-sectional view schematically showing a state in which the workpiece 11 is held by the chuck table 4 via the protective member 21. In each of the following steps, the grinding device 2 shown in FIG. 2 or the like is used.

[0023] The grinding device 2 includes a chuck table (first chuck table, second chuck table) 4 configured to hold the workpiece 11. The chuck table 4 includes, for example, a disk-shaped frame body 6 formed using ceramics, stainless steel, or the like. On the upper surface side of the frame body 6, a recess 6a having a circular opening at the upper end is formed. A holding plate 8 formed in a porous disk shape using ceramics or the like is fixed to the recess 6a.

[0024] The upper surface 8a of the holding plate 8 is configured in a shape corresponding to the side surface of a cone, for example, and functions as a holding surface for holding the protective member 21. In the present embodiment, the back surface 21b of the protective member 21 is brought into contact with this upper surface (first holding surface, second holding surface) 8a. The lower surface side of the holding plate 8 is connected to a suction source (not shown) such as an ejector via a flow path 6b provided inside the frame body 6 and a valve (not shown).

[0025] Therefore, the back surface 21b of the protection member 21 is brought into contact with the upper surface 8a of the holding plate 8 to open the valve and apply the negative pressure of the suction source, whereby the back surface 21b of the protection member 21 is sucked by the chuck table 4. That is, the workpiece 11 is held by the chuck table 4 via the protection member 21 attached to the surface 11a side.

[0026] Then, as shown in FIG. 2, the back surface 11b side of the workpiece 11 is exposed upward. In FIG. 2 and the like, the shape of the upper surface 8a of the holding plate 8 is exaggerated, but actually, the height difference (level difference) between the apex 8b of the upper surface 8a corresponding to the apex of the cone and the outer peripheral edge of the upper surface 8a is at most about 10 μm to 30 μm.

[0027] A rotary drive source (not shown) such as a motor is connected to the lower part of the frame body 6. The chuck table 4 rotates around a rotation axis along the vertical direction or a rotation axis slightly inclined with respect to the vertical direction so that the apex 8b becomes the center of rotation by the force generated by this rotary drive source. Further, the frame body 6 is supported by a chuck table moving mechanism (not shown), and the chuck table 4 moves in the horizontal direction by the force generated by this chuck table moving mechanism.

[0028] After the workpiece 11 is held by the chuck table 4 via the protection member 21, for example, the region corresponding to the region where the device 15 of the workpiece 11 is formed (device region) is roughly ground from the back surface 11b side (first grinding step). FIG. 3 is a cross-sectional view showing a state in which the workpiece 11 is roughly ground. In FIG. 3, for convenience of explanation, some elements are shown by the side surface.

[0029] As shown in FIG. 3 and the like, a first grinding unit (rough grinding unit) 10 is disposed above the chuck table 4 of the grinding device 2. The first grinding unit 10 includes, for example, a cylindrical spindle housing (not shown). A columnar spindle 12 is accommodated in the space inside the spindle housing.

[0030] At the lower end of the spindle 12, for example, a disc-shaped mount 14 with a smaller diameter than the workpiece 11 or the protective member 21 is provided. A plurality of holes (not shown) that penetrate the mount 14 in the thickness direction are formed on the outer peripheral portion of the mount 14, and bolts 16 or the like are inserted into each hole. On the lower surface of the mount 14, a disc-shaped first grinding wheel (rough grinding wheel) 18 having approximately the same diameter as the mount 14 is fixed by bolts 16 or the like.

[0031] The first grinding wheel 18 includes a disc-shaped wheel base 20 formed of a metal such as stainless steel or aluminum. A plurality of first grinding stones (rough grinding stones) 22 are fixed to the lower surface of the wheel base 20 along the circumferential direction of the wheel base 20. The first grinding stone 22 has a structure in which relatively large abrasive grains made of, for example, diamond are dispersed in a binder made of resin or the like.

[0032] When using the first grinding wheel 18 including the first grinding stone 22, while the amount of the workpiece 11 that can be removed per unit time increases, a damaged layer including scratches or distortion is likely to be formed on the ground surface side of the workpiece 11. On the upper end side of the spindle 12, a rotational drive source (not shown) such as a motor is connected. The first grinding wheel 18 rotates around a rotation axis along the vertical direction or a rotation axis slightly inclined with respect to the vertical direction by the force generated by this rotational drive source.

[0033] Near the first grinding wheel 18 or inside the first grinding wheel 18, a nozzle (not shown) is provided that is configured to supply a grinding liquid (typically water) to the first grinding stone 22 or the like. The spindle housing is supported, for example, by a first grinding unit moving mechanism (not shown), and the first grinding unit 10 moves in the vertical direction by the force generated by this first grinding unit moving mechanism.

[0034] When grinding the workpiece 11 with the first grinding unit 10 (the first grinding wheel 18), for example, the chuck table 4 is moved directly below the first grinding unit 10. Specifically, the chuck table moving mechanism horizontally moves the chuck table 4 so that the first grinding wheel 18 (all the first grinding wheels 22) is disposed directly above the region where the device 15 is formed.

[0035] Also, as shown in FIG. 3, the angle formed by the rotation axis of the first grinding wheel 18 and the rotation axis of the chuck table 4 is adjusted so that the distance between the first grinding wheel 18 (the first grinding wheel 22) and the chuck table 4 (the upper surface 8a of the holding plate 8) becomes wider on the outer edge side far from the rotation axis of the chuck table 4 than on the central side close to the rotation axis of the chuck table 4. Although there is no particular limitation on the method of adjustment, for example, it is preferable to adjust one or both of the inclination of the rotation axis of the chuck table 4 and the inclination of the rotation axis of the first grinding wheel 18.

[0036] In the present embodiment, after moving the chuck table 4 directly below the first grinding unit 10, the angle formed by the rotation axis of the first grinding wheel 18 and the rotation axis of the chuck table 4 is adjusted. However, after adjusting the angle formed by the rotation axis of the first grinding wheel 18 and the rotation axis of the chuck table 4, the chuck table 4 may be moved directly below the first grinding unit 10. Of course, the angle formed by the rotation axis of the first grinding wheel 18 and the rotation axis of the chuck table 4 may be adjusted before holding the workpiece 11 with the chuck table 4.

[0037] Then, the chuck table 4 and the first grinding wheel 18 are rotated respectively, and the first grinding unit 10 (the first grinding wheel 18) is lowered while supplying liquid from the nozzle. That is, the first grinding wheel 18 and the chuck table 4 are relatively moved in a direction intersecting the upper surface 8a, and the workpiece 11 is ground by the first grinding wheel 18. The speed at which the first grinding unit 10 is lowered (grinding feed rate) is adjusted within a range in which the first grinding wheel 22 is pressed against the workpiece 11 with an appropriate pressure.

[0038] FIG. 4 is a cross-sectional view schematically showing a part of the workpiece 11 after being ground by the first grinding wheel 18. As described above, by grinding the region corresponding to the region where the device 15 of the workpiece 11 is formed from the back surface 11b side, as shown in FIG. 4, a disk-shaped first thin plate portion 11c corresponding to the region where the device 15 is formed and an annular first thick plate portion 11d surrounding the first thin plate portion 11c can be formed on the workpiece 11.

[0039] In the present embodiment, as described above, the distance between the first grinding wheel 18 provided with the first grinding stone 22 containing abrasive grains and the upper surface 8a of the chuck table 4 is wider on the outer edge side far from the rotation axis of the chuck table 4 than on the central side close to the rotation axis of the chuck table 4. The workpiece 11 is being ground with the angle formed by the rotation axis of the first grinding wheel 18 and the rotation axis of the chuck table 4 adjusted. Therefore, the outer edge side of the first thin plate portion 11c is thicker than the central side.

[0040] Note that a damage layer 11e containing scratches or distortions is formed on the portion (grinding surface) on the back surface 11b side of the first thin plate portion 11c. Therefore, at least the outer edge side of the first thin plate portion 11c remaining on the workpiece 11 is desirably formed to have a thickness such that even if a crack extends from the damage layer 11e during subsequent conveyance or the like, the crack does not reach the device 15 on the surface 11a side. For example, when the workpiece 11 is a silicon wafer, by forming the outer edge side of the first thin plate portion 11c to have a thickness of 150 μm or more, preferably 200 μm or more, the crack extending from the damage layer 11e will not substantially reach the device 15.

[0041] There are no major restrictions on the specific grinding conditions. In order to achieve efficient grinding of the workpiece 11, it is advisable to set the rotation speed of the chuck table 4 to 100 rpm to 600 rpm, typically 300 rpm, and the rotation speed of the first grinding wheel 18 to 1000 rpm to 7000 rpm, typically 4500 rpm.

[0042] Also, it is advisable to set the descending speed of the first grinding unit 10 (first grinding wheel 18) to 0.8 μm / s to 10 μm / s. Furthermore, the descending speed of the first grinding unit 10 may be changed as the grinding progresses. Typically, three levels of speeds, 6.0 μm / s, 3.0 μm / s, and 1.0 μm / s, are set in order as the grinding progresses.

[0043] After grinding the workpiece 11 from the back surface 11b side to form a disc-shaped first thin plate portion 11c and an annular first thick plate portion 11d surrounding the first thin plate portion 11c, the first thin plate portion 11c is ground with higher precision from the back surface 11b side (second grinding step). FIG. 5 is a cross-sectional view showing how the workpiece 11 is ground with high precision. In FIG. 5, for convenience of explanation, some elements are shown by the side view.

[0044] As shown in FIG. 5, above the chuck table 4 of the grinding apparatus 2, a second grinding unit (finishing grinding unit) 24 different from the first grinding unit 10 is arranged. The second grinding unit 24 includes, for example, a cylindrical spindle housing (not shown). A columnar spindle 26 is accommodated in the space inside the spindle housing.

[0045] At the lower end of the spindle 26, for example, a disc-shaped mount 28 having a smaller diameter than the workpiece 11 and the protective member 21 is provided. A plurality of holes (not shown) penetrating the mount 28 in the thickness direction are formed in the outer peripheral portion of the mount 28, and bolts 30 and the like are inserted into each hole. A disc-shaped second grinding wheel (finishing grinding wheel) 32 having substantially the same diameter as the mount 28 is fixed to the lower surface of the mount 28 by bolts 30 and the like.

[0046] The second grinding wheel 32 includes a disc-shaped wheel base 34 formed of a metal such as stainless steel or aluminum. A plurality of second grinding wheels (finishing grinding wheels) 36 are fixed to the lower surface of the wheel base 34 along the circumferential direction of the wheel base 34. The second grinding wheel 36 has a structure in which small abrasive grains such as diamond are dispersed in a binder made of resin or the like. Specifically, the size (typically, the average particle size) of the abrasive grains included in the second grinding wheel 36 is smaller than the size of the abrasive grains included in the first grinding wheel 22.

[0047] When the second grinding wheel 32 including the second grinding wheel 36 is used, the amount of the workpiece 11 that can be removed per unit time decreases, while it becomes difficult to form a damaged layer including scratches or distortions on the ground surface side of the workpiece 11. A rotational drive source (not shown) such as a motor is connected to the upper end side of the spindle 26. The second grinding wheel 32 rotates around a rotation axis along the vertical direction or a rotation axis slightly inclined with respect to the vertical direction by the force generated by the rotational drive source.

[0048] A nozzle (not shown) configured to supply a grinding liquid (typically, water) to the second grinding wheel 36 or the like is provided beside the second grinding wheel 32 or inside the second grinding wheel 32. The spindle housing is supported by, for example, a second grinding unit moving mechanism (not shown), and the second grinding unit 24 moves in the vertical direction by the force generated by the second grinding unit moving mechanism.

[0049] When grinding the first thin plate portion 11c with the second grinding unit 24 (second grinding wheel 32), first, the chuck table 4 is moved directly below the second grinding unit 24. Specifically, the chuck table 4 is moved horizontally by a chuck table moving mechanism so that the second grinding wheel 32 (all the second grinding wheels 36) is disposed directly above the first thin plate portion 11c.

[0050] Further, as shown in FIG. 5, the difference between the distance on the central side closer to the rotation axis of the chuck table 4 between the second grinding wheel 32 (second grinding stone 36) and the chuck table 4 (upper surface 8a of the holding plate 8) and the distance on the outer edge side farther from the rotation axis of the chuck table 4 is made smaller than the difference between the distance on the central side closer to the rotation axis of the chuck table 4 between the first grinding wheel 18 (first grinding stone 22) and the chuck table 4 (upper surface 8a of the holding plate 8) and the distance on the outer edge side farther from the rotation axis of the chuck table 4 during the above-described rough grinding. The angle formed between the rotation axis of the second grinding wheel 32 and the rotation axis of the chuck table 4 is adjusted.

[0051] In the present embodiment, as shown in FIG. 5, the angle formed between the rotation axis of the second grinding wheel 32 and the rotation axis of the chuck table 4 is adjusted so that the difference between the distance on the central side closer to the rotation axis of the chuck table 4 between the second grinding wheel 32 (second grinding stone 36) and the chuck table 4 (upper surface 8a of the holding plate 8) and the distance on the outer edge side farther from the rotation axis of the chuck table 4 becomes sufficiently small (substantially zero). There is no particular limitation on the adjustment method, but for example, it is preferable to adjust one or both of the inclination of the rotation axis of the chuck table 4 and the inclination of the rotation axis of the second grinding wheel 32.

[0052] In the present embodiment, after moving the chuck table 4 directly below the second grinding unit 24, the angle formed between the rotation axis of the second grinding wheel 32 and the rotation axis of the chuck table 4 is adjusted. However, after adjusting the angle formed between the rotation axis of the second grinding wheel 32 and the rotation axis of the chuck table 4, the chuck table 4 may be moved directly below the second grinding unit 24. Of course, the angle formed between the rotation axis of the second grinding wheel 32 and the rotation axis of the chuck table 4 may be adjusted before holding the workpiece 11 by the chuck table 4.

[0053] Then, the chuck table 4 and the second grinding wheel 32 are rotated respectively, and while supplying liquid from the nozzle, the second grinding unit 24 (second grinding wheel 32) is lowered. That is, the second grinding wheel 32 and the chuck table 4 are relatively moved in a direction intersecting the upper surface 8a. The speed at which the second grinding unit 24 is lowered (grinding feed rate) is adjusted within a range in which the second grinding wheel 36 is pressed against the workpiece 11 with an appropriate pressure.

[0054] FIG. 6 is a cross-sectional view schematically showing a part of the workpiece 11 after the first thin plate portion 11c is ground by the second grinding wheel 32. As described above, by grinding the first thin plate portion 11c from the back surface 11b side, as shown in FIG. 6, a disk-shaped second thin plate portion 11f that is smaller in diameter and thinner than the first thin plate portion 11c and an annular second thick plate portion 11g surrounding the second thin plate portion 11f can be formed in the first thin plate portion 11c.

[0055] In the present embodiment, as described above, the distance on the central side close to the rotation axis of the chuck table 4 between the second grinding wheel 32 including the second grinding wheel 36 having smaller abrasive grains than the first grinding wheel 22 and the upper surface 8a of the chuck table 4, and the distance on the outer edge side far from the rotation axis of the chuck table 4, the difference between these distances, and the distance on the central side close to the rotation axis of the chuck table 4 between the first grinding wheel 18 and the upper surface 8a of the chuck table 4 during rough grinding, and the distance on the outer edge side far from the rotation axis of the chuck table 4, the difference between these distances, the angle formed by the rotation axis of the second grinding wheel 32 and the rotation axis of the chuck table 4 is adjusted so as to be smaller than the difference, and the first thin plate portion 11c is being ground. Therefore, while removing the damaged layer 11e including scratches or distortion formed in the first thin plate portion 11c, the second thin plate portion 11f having a smaller difference in thickness between the outer edge side and the central side than the first thin plate portion 11c can be formed.

[0056] There are no significant restrictions on the specific grinding conditions. To achieve efficient and precise grinding of the workpiece 11, it is advisable to set the rotational speed of the chuck table 4 to 100 rpm to 600 rpm, typically 300 rpm, and set the rotational speed of the second grinding wheel 32 to 1000 rpm to 7000 rpm, typically 4000 rpm.

[0057] In the grinding by this second grinding wheel 32, since the first thin plate portion 11c which is thinner on the central side than on the outer edge side is ground, compared with the case of processing the first thin plate portion with an overall thickness into the second thin plate portion, the volume of the workpiece 11 removed by the second grinding wheel 32 becomes smaller. Therefore, for example, at the stage of grinding the outer edge side of the first thin plate portion 11c, it is possible to increase the descending speed of the second grinding unit 24 compared with the case of grinding the first thin plate portion with an overall thickness.

[0058] For example, in the present embodiment, the descending speed of the second grinding unit 24 at the stage of grinding the outer edge side of the first thin plate portion 11c is set to 0.8 μm / s to 5.0 μm / s, and the descending speed of the second grinding unit 24 at the stage of grinding both the outer edge side and the central side of the first thin plate portion 11c is set to 0.1 μm / s to 0.8 μm / s.

[0059] That is, the descending speed of the second grinding unit 24 at the stage of grinding the outer edge side of the first thin plate portion 11c is made larger than the descending speed of the second grinding unit 24 at the stage of grinding both the outer edge side and the central side of the first thin plate portion 11c. Typically, in accordance with the progress of grinding, four-stage speeds of 1.5 μm / s, 1.3 μm / s, 0.6 μm / s, and 0.3 μm / s are sequentially set. Thereby, while shortening the time required for grinding and enhancing the efficiency, the amount of scratches and distortion formed in the second thin plate portion 11f can be made sufficiently small. That is, the generation of a new damaged layer can be prevented without significantly increasing the time required until the completion of grinding.

[0060] Note that although a damage layer 11e remains in the second thick plate portion 11g (on the outer edge side of the first thin plate portion 11c) that is not ground by the second grinding wheel 32, the distance from this damage layer 11e to the device 15 on the surface 11a side is sufficiently large. Therefore, the probability that a crack reaching the device 15 on the surface 11a side from the remaining damage layer 11e extends during subsequent conveyance or the like is also sufficiently low.

[0061] By the way, in order not to leave the damage layer 11e in the second thin plate portion 11f of the workpiece 11, it is necessary to sufficiently grind the workpiece 11 (the first thin plate portion 11c) using this second grinding wheel 32 (the second grinding stone 36). Specifically, when the thickness to be removed by the second grinding wheel 32 in order to completely remove the damage layer 11e is A or more, the thickness to be removed on the thinnest central side of the first thin plate portion 11c is A or more.

[0062] Therefore, assuming that the distance by which the second grinding wheel 32 is lowered during grinding (the thickness removed by grinding using the second grinding wheel 32) is B, in order not to leave the damage layer 11e in the second thin plate portion 11f, it is required to make the height difference between the outer edge side and the central side of the first thin plate portion 11c (B - A) or less. For example, when the grinding thickness A required to completely remove the damage layer 11e is 30 μm and the distance B by which the second grinding wheel 32 is lowered is 100 μm, the upper limit (B - A) of the height difference is 70 μm.

[0063] There is no major limitation on the lower limit of the height difference between the outer edge side and the central side of the first thin plate portion 11c. However, if this height difference becomes too small, it becomes difficult to increase the lowering speed of the second grinding unit 24, and the effect of the grinding method of the workpiece according to the present embodiment deteriorates. Therefore, the lower limit of the height difference is desirably about (B - A - 30 μm).

[0064] That is, in the above-described rough grinding (the first grinding step), it is desirable to adjust the angle formed by the rotation axis of the chuck table 4 and the rotation axis of the first grinding wheel 18 so that the height difference between the outer edge side and the central side of the formed first thin plate portion 11c is (B - A - 30 μm) to (B - A).

[0065] Next, examples and comparative examples conducted to confirm the effects of the grinding method of the workpiece according to the present embodiment will be described. In the examples and comparative examples, the grinding time required to grind a workpiece having a thickness of about 725 μm until a second thin plate portion having a thickness of about 100 μm was obtained was confirmed respectively. In the example, first, the workpiece 11 was ground using the first grinding wheel 18 to form a first thin plate portion 11c having a thickness of 200 μm and a first thick plate portion 11d having a thickness of 725 μm.

[0066] When grinding the workpiece 11, the speed at which the first grinding wheel 18 is lowered (grinding feed rate) was set in the order of 6.0 μm / s, 3.0 μm / s, and 1.0 μm / s as the grinding progressed. The distance by which the first grinding wheel 18 was lowered at each speed (that is, the thickness removed by grinding) was 465 μm at a speed of 6.0 μm / s, 30 μm at a speed of 3.0 μm / s, and 30 μm at a speed of 1.0 μm / s. The angle formed between the rotation axis of the chuck table 4 and the rotation axis of the first grinding wheel 18 was adjusted so that the height difference between the outer edge side and the central side of the first thin plate portion 11c was about 70 μm.

[0067] Thereafter, the first thin plate portion 11c was ground using the second grinding wheel 32 to form a second thin plate portion 11f having a thickness of about 100 μm. When grinding the first thin plate portion 11c, the speed at which the second grinding wheel 32 was lowered (grinding feed rate) was set in the order of 1.5 μm / s, 1.3 μm / s, 0.6 μm / s, and 0.3 μm / s as the grinding progressed. The distance by which the second grinding wheel 32 was lowered at each speed was 30 μm at a speed of 1.5 μm / s, 30 μm at a speed of 1.3 μm / s, 30 μm at a speed of 0.6 μm / s, and 10 μm at a speed of 0.3 μm / s. The angle formed between the rotation axis of the chuck table 4 and the rotation axis of the second grinding wheel 32 was adjusted so that the height difference between the outer edge side and the central side of the second thin plate portion 11f was substantially zero. In this example, the total grinding time was about 244 s.

[0068] Even in the comparative example, the workpiece was ground using the first grinding wheel 18 to form a first thin plate portion with a thickness of 200 μm and a first thick plate portion with a thickness of 725 μm. The speed (grinding feed rate) at which the first grinding wheel 18 was lowered when grinding the workpiece was set in the order of 6.0 μm / s, 3.0 μm / s, and 1.0 μm / s as the grinding progressed. The distances by which the first grinding wheel 18 was lowered at each speed were 465 μm at a speed of 6.0 μm / s, 30 μm at a speed of 3.0 μm / s, and 30 μm at a speed of 1.0 μm / s. However, the angle formed between the rotation axis of the chuck table 4 and the rotation axis of the first grinding wheel 18 was adjusted so that the height difference between the outer edge side and the central side of the first thin plate portion was substantially zero.

[0069] Thereafter, the first thin plate portion was ground using the second grinding wheel 32 to form a second thin plate portion with a thickness of approximately 100 μm. The speed (grinding feed rate) at which the second grinding wheel 32 was lowered when grinding the first thin plate portion was set in the order of 0.6 μm / s and 0.3 μm / s as the grinding progressed. The distances by which the second grinding wheel 32 was lowered at each speed were 90 μm at a speed of 0.6 μm / s and 10 μm at a speed of 0.3 μm / s. The angle formed between the rotation axis of the chuck table 4 and the rotation axis of the second grinding wheel 32 was adjusted so that the height difference between the outer edge side and the central side of the second thin plate portion was substantially zero. In the comparative example, the total grinding time was about 301 s. That is, in the example, the total grinding time was about 57 s shorter than in the comparative example.

[0070] As described above, in the grinding method of the workpiece according to the present embodiment, the distance between the first grinding wheel 18 including the first grinding stone 22 containing abrasive grains and the upper surface (first holding surface) 8a of the holding plate 8 of the chuck table (first chuck table) 4 is closer to the central side near the rotation axis of the chuck table (first chuck table) 4 than to the outer edge side far from the rotation axis of the chuck table (first chuck table) 4. The workpiece 11 is ground in a state where the angle formed by the rotation axis of the first grinding wheel 18 and the rotation axis of the chuck table (first chuck table) 4 is adjusted so as to be wider on the outer edge side far from the rotation axis of the chuck table (first chuck table) 4, and the disc-shaped first thin plate portion 11c and the annular first thick plate portion 11d surrounding the first thin plate portion 11c are formed on the workpiece 11. Therefore, the outer edge side of the first thin plate portion 11c becomes thicker than the central side.

[0071] Then, thereafter, the distance between the second grinding wheel 32 including the second grinding stone 36 containing abrasive grains smaller than those of the first grinding stone 22 and the upper surface (second holding surface) 8a of the holding plate 8 of the chuck table (second chuck table) 4 on the central side close to the rotation axis of the chuck table (second chuck table) 4, and the distance on the outer edge side far from the rotation axis of the chuck table (second chuck table) 4, The difference between the distance on the central side close to the rotation axis of the chuck table (first chuck table) 4 between the first grinding wheel 18 and the upper surface (first holding surface) 8a of the holding plate 8 of the chuck table (first chuck table) 4, and the distance on the outer edge side far from the rotation axis of the chuck table (first chuck table) 4, The first thin plate portion 11c is ground in a state where the angle formed by the rotation axis of the second grinding wheel 32 and the rotation axis of the chuck table (second chuck table) 4 is adjusted so as to be smaller than the difference, and the disc-shaped second thin plate portion 11f having a diameter smaller than that of the first thin plate portion 11c and thinner, and the annular second thick plate portion 11g surrounding the second thin plate portion 11f are formed on the first thin plate portion 11c. Therefore, while removing the damage layer 11e including scratches or distortion formed on the first thin plate portion 11c, a second thin plate portion 11f having a smaller difference in thickness between the outer edge side and the central side than the first thin plate portion 11c can be formed.

[0072] In addition, in the grinding method of the workpiece according to the present embodiment, the outer edge side of the first thin plate portion 11c remaining on the workpiece 11 as the second thick plate portion 11g is thicker than the central side of the first thin plate portion 11c, and the distance from the damage layer 11e formed in the second thick plate portion 11g (that is, the outer edge side of the first thin plate portion 11c) to the surface 11a of the workpiece 11 is sufficiently far. Therefore, when transporting the workpiece later, the possibility that a crack extends from the damage layer 11e of the second thick plate portion 11g to the surface 11a side of the workpiece 11 and the device 15 is damaged is also reduced.

[0073] Furthermore, in the grinding method of the workpiece according to the present embodiment, since the first thin plate portion 11c having a thinner central side than the outer edge side is formed, compared with the case where a thick first thin plate portion is processed into a second thin plate portion, the volume of the workpiece 11 removed by the second grinding wheel 32 becomes smaller. Therefore, even if the distance from the device 15 to the damage layer 11e of the second thick plate portion 11g (the outer edge side of the first thin plate portion 11c) is made sufficiently large, the time until grinding is completed does not become significantly longer. Thus, according to the grinding method of the workpiece according to the present embodiment, the probability of the device 15 being damaged can be suppressed low without significantly increasing the time until grinding is completed.

[0074] Note that the present invention is not limited to the description of the above-described embodiments and can be implemented with various modifications. For example, in the above-described embodiment, after grinding the workpiece 11 held by the chuck table 4 with the first grinding wheel 18, the workpiece 11 held by the same chuck table 4 is ground with the second grinding wheel 32. That is, the first chuck table when grinding the workpiece 11 with the first grinding wheel 18 is used as it is as the second chuck table when grinding the workpiece 11 with the second grinding wheel 32.

[0075] On the other hand, after grinding the workpiece 11 held by the chuck table 4 with the first grinding wheel 18, the workpiece 11 held by a chuck table different from the chuck table 4 can also be ground with the second grinding wheel 32. That is, the first chuck table when grinding the workpiece 11 with the first grinding wheel 18 and the second chuck table when grinding the workpiece 11 with the second grinding wheel 32 may be different. Similarly, the method for grinding a workpiece according to the present invention may be performed using a plurality of grinding devices.

[0076] In addition, the structures, methods, etc. according to the above-described embodiments and modifications can be appropriately changed and implemented as long as they do not deviate from the scope of the object of the present invention.

Explanation of Reference Numerals

[0077] 11: Workpiece 11a: Surface 11b: Back surface 11c: First thin plate portion 11d: First thick plate portion 11e: Damage layer 11f: Second thin plate portion 11g: Second thick plate portion 13: Scribing line (street) 15: Device 21: Protection member 21a: Surface 21b: Back surface 2: Grinding device 4: Chuck table (first chuck table, second chuck table) 6: Frame 6a: Recess 6b: Flow path 8: Holding plate 8a: Upper surface (first holding surface, second holding surface) 8b: Vertex 10: First grinding unit (rough grinding unit) 12: Spindle 14: Mount 16: Bolt 18: First grinding wheel (rough grinding wheel) 20: Wheel base 22: First grinding wheel (rough grinding wheel) 24: Second grinding unit (finish grinding unit) 26: Spindle 28: Mount 30: Bolt 32: Second grinding wheel (finish grinding wheel) 34: Wheel base 36: Second grinding stone (finish grinding stone)

Claims

1. A method for grinding a workpiece, which uses a grinding wheel mounted on a rotating spindle to grind a plate-shaped workpiece having a plurality of devices provided on a front surface side from a back surface side opposite to the front surface, comprising: an attaching step of attaching a protective member to the front surface of the workpiece; while the workpiece is held on a first holding surface of a first chuck table via the protective member, and while rotating a first grinding wheel having a first grinding stone containing abrasive grains and the first chuck table, and while relatively moving the first grinding wheel and the first chuck table in a direction intersecting the first holding surface, the first grinding step of grinding the workpiece from the back surface side so that a disk-shaped first thin plate portion and an annular first thick plate portion surrounding the first thin plate portion are formed on the workpiece, and the angle formed by the rotation axis of the first grinding wheel and the rotation axis of the first chuck table is adjusted such that the distance between the first grinding wheel and the first holding surface is wider on an outer edge side farther from the rotation axis of the first chuck table than on a central side closer to the rotation axis of the first chuck table; after the first grinding step, while the workpiece is held on a second holding surface of a second chuck table via the protective member, and while rotating a second grinding wheel having a second grinding stone containing abrasive grains smaller than those of the first grinding stone and the second chuck table, and while relatively moving the second grinding wheel and the second chuck table in a direction intersecting the second holding surface, the second grinding step of grinding the first thin plate portion from the back surface side so that a disk-shaped second thin plate portion having a diameter smaller than that of the first thin plate portion and thinner and an annular second thick plate portion surrounding the second thin plate portion are formed on the first thin plate portion, and the angle formed by the rotation axis of the second grinding wheel and the rotation axis of the second chuck table is adjusted such that the difference between the distance on a central side closer to the rotation axis of the second chuck table between the second grinding wheel and the second holding surface and the distance on an outer edge side farther from the rotation axis of the second chuck table is smaller than the difference between the distance on a central side closer to the rotation axis of the first chuck table between the first grinding wheel and the first holding surface and the distance on an outer edge side farther from the rotation axis of the first chuck table. A method for grinding a workpiece including the above steps.

2. The method for grinding a workpiece according to claim 1, wherein the first chuck table is used as the second chuck table.

3. The grinding method of the workpiece according to claim 1 or claim 2, wherein in the first grinding step, a first thin plate portion having a thickness such that cracks extending from a damaged layer including scratches or distortions generated on the outer edge side of the first thin plate portion in the first grinding step do not reach the device is formed.

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