Grinding method for workpieces

Abstract

To provide a work-piece grinding method that can sufficiently secure an effective region that can be used for a product, without requiring a time remarkably longer in comparison with a time required in a conventional method.SOLUTION: A work-piece grinding method, which is applied in grinding a work-piece in a disk-shape having a first surface and a second surface at the opposite side of the first surface, includes: a first grinding step of grinding the work-piece by bringing a first grinding stone into contact with the work-piece from the second surface side so as to form, on the work-piece, a first thin plate part in a disk-shape and a first thick plate part in an annular shape surrounding the first thin plate part, at least a portion of an inner side surface of which is inclined with respect to the second surface; and a second grinding step of bringing a second grinding stone into contact with either of the first thin plate part and the portion of the inclined side surface of the first thick plate part, from the second surface side, and then bringing the grinding stone into contact with the other of the first thin plate part and the portion of the side surface of the first thick plate part, and grinding the work-piece so that the portion of the inclined side surface of the first thick plate part is partially removed, so as to form, on the work-piece, a second thin plate part in a disk-shape which is larger in diameter and thinner than the first thin plate part and a second thick plate part in an annular shape surrounding the second thin plate part.SELECTED DRAWING: Figure 6

Description

Technical Field

[0005]

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

Background Art

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

[0003] By the way, when the entire wafer becomes thin by the above method, the rigidity of the wafer also significantly decreases, making it difficult to handle the wafer in subsequent processes. Therefore, a technique has been proposed to maintain high rigidity of the wafer after grinding by using a grinding wheel having a diameter smaller than that of the wafer to grind the central region (inner region) of the wafer provided with the device and leaving the outer edge region (outer region) unground (see, for example, Patent Document 1).

[0004] In this technique, first, the central region of the wafer is roughly ground with a first grinding wheel on which a grinding stone containing relatively large abrasive grains is fixed, and a disk-shaped thin plate portion and an annular thick plate portion surrounding the thin plate portion are formed on the wafer. Thus, by using a grinding wheel on which a grinding stone containing large abrasive grains is fixed, the time required for grinding the wafer is shorter than when using a grinding wheel on which a grinding stone containing small abrasive grains is fixed.

[0005] On the other hand, when a wafer is roughly ground using a grinding wheel with a grinding wheel containing large abrasive grains, a damage layer containing scratches and distortions caused by the grinding wheel is formed on the ground surface, making it easy for the mechanical strength (flexural strength, etc.) of the thin wafer portion to be insufficient. Therefore, after roughly grinding the wafer, the thin wafer portion is further ground using a grinding wheel with a grinding wheel containing relatively small abrasive grains to remove the damage layer. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2007-19461 [Overview of the project] [Problems that the invention aims to solve]

[0007] Incidentally, when further grinding the thin plate portion to remove the damaged layer, if the grinding wheel comes into contact with the sharp inner side of the thick plate portion, this thick plate portion may chip. Therefore, when removing the damaged layer, only the central area of ​​the thin plate portion was ground to prevent the grinding wheel from coming into contact with the thick plate portion. However, with this method, the damaged layer remains in the outer edge area of ​​the thin plate portion (the area close to the boundary with the thick plate portion), making the outer edge area of ​​the thin plate portion unusable in the product.

[0008] Therefore, the object of the present invention is to provide a method for grinding a disc-shaped workpiece to form a thin plate portion and a thick plate portion, which does not require significantly longer time than conventional methods and ensures a sufficient usable area for the product. [Means for solving the problem]

[0009] According to one aspect of the present invention, a method for grinding a workpiece is applied when grinding a disc-shaped workpiece having a first surface and a second surface opposite to the first surface, comprising: a first grinding step in which a plurality of first grinding wheels, each containing abrasive grains, are arranged in an annular region having a first diameter smaller than the workpiece, and the workpiece is moved relative to each other while rotating, thereby bringing the first grinding wheels into contact with the workpiece from the second surface side to grind the workpiece, and forming a disc-shaped first thin plate portion and an annular first thick plate portion surrounding the first thin plate portion, with at least a portion of the inner side surface including the end on the first thin plate portion side inclined with respect to the second surface, and after the first grinding step The second grinding step includes: a second grinding wheel in which a plurality of second grinding wheels, each containing abrasive grains with an average particle size smaller than that of the first grinding wheel, are arranged in an annular region with a second diameter smaller than that of the workpiece, and the workpiece, are moved relative to each other while rotating, thereby bringing the second grinding wheel into contact with one of the first thin plate portion and a portion of the side surface of the first thick plate portion from the second surface side, and then into contact with the other of the first thin plate portion and a portion of the side surface of the first thick plate portion, thereby grinding the workpiece so that the portion of the side surface of the first thick plate portion is partially removed, thereby forming a disc-shaped second thin plate portion that is larger in diameter and thinner than the first thin plate portion, and an annular second thick plate portion surrounding the second thin plate portion, on the workpiece. In the first grinding step, the first grinding wheel and the workpiece are moved relative to each other in a direction inclined with respect to the second surface, so as to bring the center of rotation of the first grinding wheel closer to the center of rotation of the workpiece. A method for grinding a workpiece is provided. According to another aspect of the present invention, a method for grinding a disc-shaped workpiece having a first surface and a second surface opposite to the first surface is provided, wherein a first grinding wheel, each containing abrasive grains, is arranged in an annular region having a first diameter smaller than the workpiece, and the workpiece is moved relative to each other while rotating, thereby bringing the first grinding wheel into contact with the workpiece from the second surface side and grinding the workpiece, and the disc A first grinding step in which a first thin plate portion and an annular first thick plate portion surrounding the first thin plate portion, with at least a portion of the inner side surface including the end on the first thin plate portion side inclined with respect to the second surface, are formed on the workpiece; and after the first grinding step, a second grinding wheel in which a plurality of second grinding wheels, each containing abrasive grains with an average particle size smaller than that of the first grinding wheel, are arranged in an annular region with a second diameter smaller than that of the workpiece, and the workpiece is rotated relative to each other. By moving it symmetrically, the second grinding wheel is brought into contact with one of the first thin plate portion and the part of the side surface of the first thick plate portion from the second surface side, and then brought into contact with the other of the first thin plate portion and the part of the side surface of the first thick plate portion, thereby grinding the workpiece so that the part of the side surface of the first thick plate portion is partially removed, forming a disc-shaped second thin plate portion that is larger in diameter and thinner than the first thin plate portion, and an annular second thick plate portion surrounding the second thin plate portion, in the workpiece, a second grinding step, A method for grinding a workpiece is provided, which includes, in the first grinding step, moving the first grinding wheel and the workpiece relatively in a direction intersecting the second surface so that the center of rotation of the first grinding wheel does not approach the center of rotation of the workpiece, and then moving the first grinding wheel and the workpiece relatively in a direction inclined with respect to the second surface so that the center of rotation of the first grinding wheel approaches the center of rotation of the workpiece.

[0010] According to yet another aspect of the present invention, a method for grinding a workpiece that is applied when grinding a disc-shaped workpiece having a first surface and a second surface opposite to the first surface, comprising: a first grinding wheel in which a plurality of first grinding wheels, each containing abrasive grains, are arranged in an annular region having a first diameter smaller than the workpiece, and the workpiece, are moved relative to each other while rotating, thereby bringing the first grinding wheels into contact with the workpiece from the second surface side and grinding the workpiece, and grinding the disc-shaped first thin plate portion, A first grinding step in which an annular first thick plate portion surrounds the first thin plate portion and a portion of the inner side surface, including at least the end on the first thin plate portion side, is inclined with respect to the second surface, is formed on the workpiece; and after the first grinding step, a second grinding wheel is formed in which a plurality of second grinding wheels, each containing abrasive grains with an average particle size smaller than that of the first grinding wheel, are arranged in an annular region with a second diameter smaller than that of the workpiece, and the workpiece is moved relative to each other while rotating, thereby grinding the second grinding wheel The second grinding step includes bringing a tool into contact with one of the first thin plate portion and the portion of the side surface of the first thick plate portion from the second surface side, and then bringing it into contact with the other of the first thin plate portion and the portion of the side surface of the first thick plate portion, thereby grinding the workpiece so that the portion of the side surface of the first thick plate portion is partially removed, thereby forming a disc-shaped second thin plate portion that is larger in diameter and thinner than the first thin plate portion, and an annular second thick plate portion surrounding the second thin plate portion, wherein in the second grinding step, relative to the center of rotation of the workpiece, A method for grinding a workpiece is provided, which involves moving the second grinding wheel and the workpiece relative to each other in a direction intersecting the second surface so as not to move the center of rotation of the second grinding wheel away from the center of rotation of the workpiece, thereby grinding at least the first thin plate portion, and then moving the second grinding wheel and the workpiece relative to each other in a direction along the second surface so as to move the center of rotation of the second grinding wheel away from the center of rotation of the workpiece, thereby partially removing at least a portion of the side surface of the first thick plate portion.

[0011] According to another aspect of the present invention, a method for grinding a workpiece that is applied when grinding a disc-shaped workpiece having a first surface and a second surface opposite to the first surface, wherein a first grinding wheel, each having a plurality of first grinding wheels containing abrasive grains arranged in an annular region having a first diameter smaller than the workpiece, and the workpiece are moved relative to each other while rotating, thereby bringing the first grinding wheels into contact with the workpiece from the second surface side and grinding the workpiece, thereby grinding the disc-shaped first thin plate portion and the A first grinding step in which an annular first thick plate portion surrounds a first thin plate portion and a portion of the inner side surface, including at least the end on the first thin plate portion side, is inclined with respect to the second surface, is formed on the workpiece; and after the first grinding step, a second grinding wheel is formed in which a plurality of second grinding wheels, each containing abrasive grains with an average particle size smaller than that of the first grinding wheel, are arranged in an annular region with a second diameter smaller than that of the workpiece, and the workpiece is moved relative to each other while rotating, thereby grinding the second grinding wheel The second grinding step includes bringing the first thin plate portion and a portion of the side surface of the first thick plate portion into contact with one of them from the second surface side, and then bringing the first thin plate portion and a portion of the side surface of the first thick plate portion into contact with the other of them, thereby grinding the workpiece so that the portion of the side surface of the first thick plate portion is partially removed, thereby forming a disc-shaped second thin plate portion that is larger in diameter and thinner than the first thin plate portion, and an annular second thick plate portion surrounding the second thin plate portion, wherein the second grinding step is performed with respect to the center of rotation of the workpiece. A method for grinding a workpiece is provided, which involves moving the second grinding wheel and the workpiece relative to each other in a direction along the second surface so as to move away from the center of rotation of the second grinding wheel, thereby partially removing at least a portion of the side surface of the first thick plate portion, and then moving the second grinding wheel and the workpiece relative to each other in a direction intersecting the second surface so as not to move away from the center of rotation of the workpiece, thereby grinding at least the first thin plate portion.

[0012] Preferably, in the second grinding step, the second grinding wheel and the workpiece are moved relative to each other in a direction inclined with respect to the second surface, such that the center of rotation of the second grinding wheel is moved away from the center of rotation of the workpiece.

[0013] Furthermore, in the second grinding step, the second grinding wheel and the workpiece may be moved relative to each other in a direction intersecting the second surface so as not to move the center of rotation of the second grinding wheel away from the center of rotation of the workpiece, thereby grinding at least the first thin plate portion. After that, the second grinding wheel and the workpiece may be moved relative to each other in a direction along the second surface so as to move the center of rotation of the second grinding wheel away from the center of rotation of the workpiece, thereby partially removing at least a portion of the side surface of the first thick plate portion.

[0014] Furthermore, in the second grinding step, the second grinding wheel and the workpiece may be moved relative to each other in a direction along the second surface so as to move the center of rotation of the second grinding wheel away from the center of rotation of the workpiece, thereby partially removing at least a portion of the side surface of the first thick plate portion. Then, the second grinding wheel and the workpiece may be moved relative to each other in a direction intersecting the second surface so as not to move the center of rotation of the second grinding wheel away from the center of rotation of the workpiece, thereby grinding at least the first thin plate portion. [Effects of the Invention]

[0015] In a method for grinding a workpiece according to one aspect of the present invention, first, the workpiece is ground with a first grinding wheel equipped with a first grinding wheel to form a first thin plate portion and an annular first thick plate portion in which at least a part of the inner side surface is inclined. Then, the second grinding wheel of a second grinding wheel, which is equipped with a second grinding wheel containing abrasive grains with a smaller average particle size than the first grinding wheel, is brought into contact with one of the first thin plate portion and a part of the inclined side surface of the first thick plate portion, and then into contact with the other of the first thin plate portion and a part of the inclined side surface of the first thick plate portion, thereby grinding the workpiece so that a part of the inclined side surface of the first thick plate portion is partially removed, forming a second thin plate portion and a second thick plate portion.

[0016] Therefore, the entire second thin plate portion becomes an effective region without a damaged layer caused by the first grinding wheel. Also, at this time, since the first thick plate portion is ground so that a part of the inclined side surface is partially removed, unlike the case where the second grinding wheel is brought into contact with the upright side surface to grind the first thick plate portion from the side, the possibility of the first thick plate portion chipping is reduced.

[0017] And since the volume of the portion of the first thick plate portion removed by the second grinding wheel is sufficiently small, for example, even when compared with a conventional method in which only the central region of the first thin plate portion is ground by the second grinding wheel and the first thick plate portion is not ground at all by the second grinding wheel, the time required for grinding does not become significantly longer. Therefore, according to the grinding method of the workpiece according to one aspect of the present invention, an effective region that can be used for the product is sufficiently ensured without requiring a significantly longer time compared to the conventional method.

Brief Description of the Drawings

[0018] [Figure 1] FIG. 1 is a perspective view schematically showing a state in which a protective member is attached to a disk-shaped workpiece. [Figure 2] FIG. 2 is a cross-sectional view schematically showing a state in which the workpiece is held by a chuck table via a protective member. [Figure 3] FIG. 3 is a cross-sectional view schematically showing a state in which grinding of the workpiece by the first grinding wheel is started. [Figure 4] FIG. 4 is a cross-sectional view schematically showing a state in which grinding of the workpiece by the first grinding wheel progresses. [Figure 5] FIG. 5 is a cross-sectional view schematically showing a part of the workpiece after being ground by the first grinding wheel. [Figure 6] FIG. 6 is a cross-sectional view schematically showing a state in which grinding of the workpiece by the second grinding wheel is started. [Figure 7] FIG. 7 is a cross-sectional view schematically showing a state in which grinding of the workpiece by the second grinding wheel progresses. [Figure 8]FIG. 8 is a cross-sectional view schematically showing a part of the workpiece after being ground by the second grinding wheel. [Figure 9] FIG. 9 is a cross-sectional view schematically showing a part of the workpiece being ground by the second grinding wheel in the grinding method of the workpiece according to the first modification. [Figure 10] FIG. 10 is a cross-sectional view schematically showing a part of the workpiece after being ground by the first grinding wheel in the grinding method of the workpiece according to the second modification. [Figure 11] FIG. 11 is a cross-sectional view schematically showing a part of the workpiece after being ground by the second grinding wheel in the grinding method of the workpiece according to the second modification.

MODE FOR CARRYING OUT THE INVENTION

[0019] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the grinding method of the workpiece according to the present embodiment, by grinding the central (inner) region of the disc-shaped workpiece to be ground, a concave workpiece in which this region becomes thin is obtained. Specifically, first, a protective member is attached to the workpiece (attachment step). FIG. 1 is a perspective view schematically showing a state where the protective member 21 is attached to the disc-shaped workpiece 11.

[0020] As shown in FIG. 1, the workpiece 11 is, for example, a disc-shaped wafer made of a semiconductor such as silicon (Si). That is, the workpiece 11 has a circular surface (first surface) 11a and a circular back surface (second surface) 11b opposite to the surface 11a. The surface 11a side of the workpiece 11 is partitioned into a plurality of small regions by a plurality of streets (division planned lines) 13 intersecting each other, and devices 15 such as integrated circuits (ICs) are formed in each small region.

[0021] In the workpiece grinding method according to this embodiment, the portion of the workpiece 11 corresponding to the region where the device 15 is formed (device region) is ground from the back surface 11b side, while the remaining annular region (outer peripheral region) is not ground. In other words, the workpiece 11 is processed into a concave shape from the back surface 11b side.

[0022] In this embodiment, a disc-shaped wafer made of a semiconductor such as silicon is used as the workpiece 11, but the material, shape, structure, size, etc. of the workpiece 11 are not limited to this embodiment. For example, substrates made of other semiconductors, ceramics, resins, metals, etc. can be used as the workpiece 11. Similarly, the type, quantity, shape, structure, size, arrangement, etc. of the devices 15 are not limited to the above embodiment. The workpiece 11 does not need to have devices 15 formed on it.

[0023] The protective member 21 attached to the workpiece 11 is typically a circular tape (film) with a diameter roughly the same as the workpiece 11, a resin substrate, or a wafer of the same or different type as the workpiece 11. In other words, the protective member 21 has a circular surface 21a and a circular back surface 21b opposite to the surface 21a. For example, an adhesive layer is provided on the surface 21a side of the protective member 21 to indicate adhesion to the workpiece 11.

[0024] Then, as shown in Figure 1, when the surface 21a side of the protective member 21 is brought into close contact with the surface 11a of the workpiece 11, the protective member 21 is attached to the surface 11a of the workpiece 11. As a result, the impact applied to the surface 11a when grinding the workpiece 11 from the back side 11b is mitigated by the protective member 21, and the device 15, etc. of the workpiece 11 is protected. However, if the device 15 is not formed on the workpiece 11, the protective member 21 does not necessarily have to be attached to the workpiece 11.

[0025] After the protective member 21 is attached to the surface 11a of the workpiece 11, the workpiece 11 is held on the chuck table via the protective member 21 (holding step). Figure 2 is a schematic cross-sectional view showing how the workpiece 11 is held on the chuck table 4 of the grinding device 2 via the protective member 21. The grinding device 2 shown in Figure 2, etc., is used in each of the following steps.

[0026] The grinding apparatus 2 includes a chuck table 4 configured to hold a workpiece 11. The chuck table 4 includes a disc-shaped frame 6 formed, for example, from ceramics. A recess 6a with a circular opening at its upper end is formed on the upper side of the frame 6. A porous disc-shaped holding plate 8, formed from ceramics or the like, is fixed to this recess 6a.

[0027] The upper surface 8a of the retaining plate 8 is configured to have a shape corresponding to, for example, the side surface of a cone, and functions as a retaining surface for holding the workpiece 11 or the like. The height difference (height difference) between the center 8b of the upper surface 8a of the retaining plate 8, which corresponds to the apex of the cone, and the outer edge of the upper surface 8a of the retaining plate 8 is approximately 10 μm to 30 μm. In this embodiment, the back surface 21b of the protective member 21 is in contact with the upper surface (retaining surface) 8a of the retaining plate 8.

[0028] The lower surface of the retaining plate 8 is connected to a suction source (not shown), such as an ejector, via a flow path 6b provided inside the frame 6 or a valve (not shown) located outside the frame 6. Therefore, when the valve is opened and negative pressure from the suction source is applied with the back surface 21b of the protective member 21 in contact with the upper surface 8a of the retaining plate 8, the back surface 21b of the protective member 21 is sucked by the chuck table 4.

[0029] In other words, the workpiece 11 is held on the chuck table 4 via the protective member 21 so that its back surface 11b is exposed upwards. If the protective member 21 is not attached to the surface 11a of the workpiece 11, the surface 11a of the workpiece 11 can be brought into direct contact with the upper surface 8a of the holding plate 8, the valve can be opened, and the negative pressure from the suction source can be applied.

[0030] A rotational drive source (not shown), such as a motor, is connected to the lower part of the frame 6. The chuck table 4 rotates around an axis aligned with the vertical direction, or an axis slightly inclined with respect to the vertical direction, due to the force generated by this rotational drive source, such that the center 8b of the upper surface 8a becomes the center of rotation. The frame 6 is also supported by a chuck table movement mechanism (not shown), such as a ball screw type or a turntable rotation type, and the chuck table 4 moves horizontally due to the force generated by this chuck table movement mechanism.

[0031] After the workpiece 11 is held in the chuck table 4, the area of ​​the workpiece 11 corresponding to the area where the device 15 is formed (device area) is roughly ground from the back surface 11b side (first grinding step). Figure 3 is a schematic cross-sectional view showing the start of grinding of the workpiece 11, and Figure 4 is a schematic cross-sectional view showing the progress of grinding of the workpiece 11. Note that in Figures 3 and 4, the sides of some elements are shown for the sake of explanation.

[0032] As shown in Figures 3 and 4, a first grinding unit (rough grinding unit) 10 is positioned above the chuck table 4 of the grinding apparatus 2. The first grinding unit 10 includes, for example, a cylindrical spindle housing (not shown). A columnar spindle 12 is housed in the space inside the spindle housing.

[0033] A disc-shaped mount 14, for example, with a smaller diameter than the workpiece 11, is provided at the lower end of the spindle 12. An annular first grinding wheel (rough grinding wheel) 16, with a diameter approximately equal to that of the mount 14, is fixed to the lower surface of the mount 14 with bolts (not shown) or the like.

[0034] The first grinding wheel 16 includes an annular wheel base 18 formed from a metal such as stainless steel or aluminum. Multiple first grinding wheels (coarse grinding wheels) 20 are provided on the annular lower surface of the wheel base 18 along the circumferential direction of the wheel base 18. Specifically, the multiple first grinding wheels 20 are arranged in an annular region with a diameter (first diameter) smaller than the workpiece 11. Each first grinding wheel 20 has a structure in which larger abrasive grains, such as diamond, are dispersed in a binder such as resin.

[0035] Therefore, when the workpiece 11 is ground with the first grinding wheel 16 including the first grinding wheel 20, the amount of workpiece 11 that can be removed per unit time increases, while a damage layer containing scratches or distortions is more likely to form on the grinding surface side of the workpiece 11. A rotational drive source (not shown), such as a motor, is connected to the upper end of the spindle 12. The first grinding wheel 16 rotates around an axis aligned with the vertical direction, or an axis slightly inclined with respect to the vertical direction, due to the force generated by this rotational drive source.

[0036] A nozzle (not shown) is provided next to or inside the first grinding wheel 16, configured to supply a grinding fluid (typically water) to the first grinding wheel 20, etc. The spindle housing is supported by, for example, a ball screw type first grinding unit moving mechanism (not shown), and the first grinding unit 10 moves vertically due to the force generated by this first grinding unit moving mechanism.

[0037] When grinding the workpiece 11 with the first grinding unit 10 (first grinding wheel 16), the chuck table moving mechanism first moves the chuck table 4 directly below the first grinding unit 10. More specifically, the chuck table moving mechanism moves the chuck table 4 horizontally so that the first grinding wheel 16 (all first grinding wheels 20) is positioned directly above the area where the device 15 is formed.

[0038] Then, as shown in Figure 3, the rotational drive source connected to the frame 6 and the rotational drive source connected to the spindle 12 rotate the chuck table 4 and the first grinding wheel 16 respectively, while the first grinding unit moving mechanism lowers the first grinding unit 10 (first grinding wheel 16). As a result, as shown in Figure 3, the first grinding wheel 20 comes into contact with the workpiece 11 from the back surface 11b side, and grinding of the workpiece 11 begins. Liquid is supplied to the workpiece 11 and the first grinding wheel 20, etc., from a nozzle.

[0039] Furthermore, in this embodiment, as shown in Figure 3, while the workpiece 11 is being ground by the first grinding wheel 16, the chuck table moving mechanism moves the chuck table 4 horizontally so that the center of rotation of the workpiece 11 and the center of rotation of the first grinding wheel 16 are brought closer together. In other words, the first grinding wheel 16 and the workpiece 11 move relative to each other in a direction inclined with respect to the back surface 11b so that the center of rotation of the first grinding wheel 16 is closer to the center of rotation of the workpiece 11 (so that the horizontal distance between the center of rotation of the workpiece 11 and the center of rotation of the first grinding wheel 16 is reduced).

[0040] As the grinding of the workpiece 11 progresses through the above-described operation, as shown in Figure 4, the portion of the workpiece 11 in contact with the first grinding wheel 20 becomes thinner, while the thickness of the remaining portion of the workpiece 11 is maintained. In other words, the portion of the workpiece 11 corresponding to the area where the device 15 is formed becomes thinner, forming a disc-shaped first thin plate portion 11c. Furthermore, the thickness of the portion of the workpiece 11 corresponding to the area surrounding the area where the device 15 is formed (outer peripheral area) is maintained, forming an annular first thick plate portion 11d surrounding the first thin plate portion 11c.

[0041] As described above, in this embodiment, the first grinding wheel 16 and the workpiece 11 move relative to each other in a direction inclined with respect to the back surface 11b. Therefore, as shown in Figure 4, the first grinding wheel 16 removes the inverted frustoconical region on the back surface 11b side of the workpiece 11. In other words, the inner side surface 11e of the first thick plate portion 11d becomes inclined with respect to the back surface 11b.

[0042] There are no major restrictions on the specific grinding conditions. For example, to achieve efficient grinding of the workpiece 11, the rotational speed of the chuck table 4 is set to 100 rpm to 600 rpm, typically 300 rpm, and the rotational speed of the first grinding wheel 16 is set to 1000 rpm to 7000 rpm, typically 4500 rpm.

[0043] Furthermore, the speed at which the first grinding unit 10 descends (grinding feed rate) when the first grinding wheel 20 is in contact with the workpiece 11 is set to 0.8 μm / s to 10 μm / s, typically 6.0 μm / s, and the relative horizontal distance between the first grinding wheel 16 and the workpiece 11 from the time the first grinding wheel 20 makes contact with the workpiece 11 until grinding is completed is set to 50 μm to 1000 μm, typically 400 μm.

[0044] Figure 5 is a schematic cross-sectional view showing a portion of the workpiece 11 after grinding by the first grinding wheel 16. As shown in Figure 5, a damaged layer 11f containing scratches or distortion exists on the back surface 11b of the first thin plate portion 11c (the ground surface) that has been ground by the first grinding wheel 20 containing larger abrasive grains. Since the damaged layer 11f reduces the mechanical strength (flexural strength, etc.) of the workpiece 11, the region where this damaged layer 11f exists cannot be used as a product.

[0045] Therefore, after grinding with the first grinding wheel 16, the first thin plate portion 11c and the first thick plate portion 11d are ground with higher precision so that the damaged layer 11f is removed (second grinding step). Figure 6 is a schematic cross-sectional view showing the start of grinding of the workpiece 11, and Figure 7 is a schematic cross-sectional view showing the progress of grinding of the workpiece 11. Note that in Figures 6 and 7, the sides of some elements are shown for the sake of explanation.

[0046] As shown in Figures 6 and 7, a second grinding unit (finish grinding unit) 30, separate from the first grinding unit 10, is positioned above the chuck table 4 of the grinding apparatus 2. The second grinding unit 30 includes, for example, a cylindrical spindle housing (not shown). A columnar spindle 32 is housed in the space inside the spindle housing.

[0047] A disc-shaped mount 34, for example, smaller in diameter than the workpiece 11, is provided at the lower end of the spindle 32. An annular second grinding wheel (finishing grinding wheel) 36, which has a diameter approximately equal to that of the mount 34, is fixed to the lower surface of the mount 34 with bolts (not shown) or the like.

[0048] The second grinding wheel 36 includes an annular wheel base 38 formed from a metal such as stainless steel or aluminum. Multiple second grinding wheels (finishing grinding wheels) 40 are provided on the annular lower surface of the wheel base 38, along the circumferential direction of the wheel base 38. Specifically, the multiple second grinding wheels 40 are arranged in an annular region with a diameter smaller than the workpiece 11 (second diameter).

[0049] Each second grinding wheel 40 has a structure in which small abrasive grains, such as diamond, are dispersed in a binder made of resin or the like. In other words, the size (average particle size) of the abrasive grains contained in the second grinding wheel 40 is smaller than the size (average particle size) of the abrasive grains contained in the first grinding wheel 20.

[0050] When the workpiece 11 is ground with the second grinding wheel 36, which includes the second grinding wheel 40, the amount of workpiece 11 that can be removed per unit time is less than when the workpiece 11 is ground with the first grinding wheel 16, but a damage layer 11f is less likely to occur. A rotational drive source (not shown), such as a motor, is connected to the upper end of the spindle 32. The second grinding wheel 36 rotates around an axis aligned with the vertical direction, or an axis slightly inclined with respect to the vertical direction, due to the force generated by this rotational drive source.

[0051] A nozzle (not shown) is provided next to or inside the second grinding wheel 36, configured to supply a grinding fluid (typically water) to the second grinding wheel 40, etc. The spindle housing is supported by, for example, a ball screw type second grinding unit moving mechanism (not shown), and the second grinding unit 30 moves vertically due to the force generated by this second grinding unit moving mechanism.

[0052] When grinding the workpiece 11 with the second grinding unit 30 (second grinding wheel 36), the chuck table moving mechanism first moves the chuck table 4 directly below the second grinding unit 30. More specifically, the chuck table moving mechanism moves the chuck table 4 horizontally so that the second grinding wheel 36 (all of the second grinding wheels 40) is positioned directly above the first thin plate portion 11c.

[0053] Then, as shown in Figure 6, the rotational drive source connected to the frame 6 and the rotational drive source connected to the spindle 12 rotate the chuck table 4 and the first grinding wheel 16 respectively, while the second grinding unit moving mechanism lowers the second grinding unit 30 (second grinding wheel 36). As a result, as shown in Figure 6, the second grinding wheel 40 comes into contact with the workpiece 11 (first thin plate portion 11c) from the back surface 11b side, and grinding of the workpiece 11 begins. Liquid is supplied to the workpiece 11 and the second grinding wheel 40, etc., from a nozzle.

[0054] Furthermore, in this embodiment, as shown in Figure 6, while the workpiece 11 is being ground by the second grinding wheel 36, the chuck table moving mechanism moves the chuck table 4 horizontally so as to move the center of rotation of the workpiece 11 away from the center of rotation of the second grinding wheel 36. In other words, the second grinding wheel 36 and the workpiece 11 move relative to each other in a direction inclined with respect to the back surface 11b so that the center of rotation of the second grinding wheel 36 moves away from the center of rotation of the workpiece 11 (so that the horizontal distance between the center of rotation of the workpiece 11 and the center of rotation of the second grinding wheel 36 increases).

[0055] As the grinding of the workpiece 11 progresses through the above-described operation, the second grinding wheel 40 first contacts the first thin plate portion 11c from the back surface 11b side, and then contacts the inclined side surface 11e of the first thick plate portion 11d. As a result, as shown in Figure 7, the first thin plate portion 11c is ground on the lower surface of the second grinding wheel 40, and the damaged layer 11f of this first thin plate portion 11c is removed. In addition, the inside of the first thick plate portion 11d is ground on the outer side surface of the second grinding wheel 40, and the inclined side surface 11e of the first thick plate portion 11d is partially removed along with the damaged layer 11f.

[0056] There are no major restrictions on the specific grinding conditions. For example, to achieve efficient and highly accurate grinding of the workpiece 11, the rotational speed of the chuck table 4 is set to 100 rpm to 600 rpm, typically 300 rpm, and the rotational speed of the second grinding wheel 36 is set to 1000 rpm to 7000 rpm, typically 4000 rpm.

[0057] Furthermore, the speed at which the second grinding unit 30 descends (grinding feed rate) when the second grinding wheel 40 is in contact with the workpiece 11 is set to 0.1 μm / s to 0.8 μm / s, typically 0.6 μm / s, and the relative horizontal distance between the second grinding wheel 36 and the workpiece 11 from the time the second grinding wheel 40 makes contact with the workpiece 11 until grinding is completed is set to 50 μm to 1000 μm, typically 300 μm.

[0058] Figure 8 is a schematic cross-sectional view showing a portion of the workpiece 11 after grinding by the second grinding wheel 36. As shown in Figure 8, the first thin plate portion 11c and the portion where the side surface 11e of the first thick plate portion 11d has been removed form a disc-shaped second thin plate portion 11g, and the remaining portion of the first thick plate portion 11d becomes an annular second thick plate portion 11h surrounding the second thin plate portion 11g. In other words, the second thin plate portion 11g is larger in diameter and thinner than the first thin plate portion 11c.

[0059] As described above, in the workpiece grinding method according to this embodiment, first, the workpiece 11 is ground with a first grinding wheel 16 equipped with a first grinding wheel 20 to form a first thin plate portion 11c and an annular first thick plate portion 11d with an inclined inner side surface 11e. Then, the second grinding wheel 40 of the second grinding wheel 36, which is equipped with abrasive grains with a smaller average particle size than the first grinding wheel 20, is brought into contact with the first thin plate portion 11c and then into contact with the inclined side surface 11e of the first thick plate portion 11d, grinding the workpiece 11 so that a part of the side surface 11e of the first thick plate portion 11d is partially removed, thereby forming a second thin plate portion 11g and a second thick plate portion 11h.

[0060] Therefore, the entire second thin plate portion 11g becomes an effective area free from the damage layer 11f caused by the first grinding wheel 20. Furthermore, since the first thick plate portion 11d is ground in such a way that a portion of the inclined side surface 11e is partially removed, the possibility of the first thick plate portion 11d chipping is reduced, unlike when the second grinding wheel 40 is brought into contact with the sharp side surface and the first thick plate portion 11d is ground from the side.

[0061] Furthermore, since the volume of the portion of the first thick plate portion 11d removed by the second grinding wheel 36 is sufficiently small, the grinding time will not be significantly longer compared to, for example, a conventional method in which only the central region of the first thin plate portion 11c is ground by the second grinding wheel 36 and the first thick plate portion 11d is not ground at all by the second grinding wheel 36. Therefore, according to the workpiece grinding method of this embodiment, a sufficient usable area for the product can be secured without requiring significantly longer time compared to conventional methods.

[0062] Although a damaged layer 11f remains on the second thick plate portion 11h along with a part of the inclined side surface 11e, the region where this damaged layer 11f exists is sufficiently far from the second thin plate portion 11g along the thickness direction of the workpiece 11. Therefore, the damaged layer 11f does not adversely affect the device 15 of the second thin plate portion 11g.

[0063] It should be noted that the present invention is not limited to the embodiments described above and can be implemented with various modifications. For example, in the embodiments described above, the workpiece 11 is ground by lowering the first grinding wheel 16 and the second grinding unit 30 and moving the chuck table 4 horizontally, but the manner in which each part moves is not limited thereto.

[0064] For example, the workpiece 11 may be ground by moving the first grinding unit 10 and the second grinding unit 30 horizontally and raising the chuck table 4. Alternatively, the workpiece 11 may be ground by lowering the first grinding unit 10 and the second grinding unit 30 and moving them horizontally. Similarly, the workpiece 11 may be ground by moving the chuck table 4 horizontally and raising it.

[0065] Furthermore, in the embodiment described above, the second grinding wheel 36 and the workpiece 11 move relative to each other in a direction inclined with respect to the back surface 11b such that the center of rotation of the second grinding wheel 36 moves away from the center of rotation of the workpiece 11. However, the manner in which the relative movement between the second grinding wheel 36 and the workpiece 11 occurs is not limited to this.

[0066] If the second grinding wheel 40 contacts one of the first thin plate portion 11c and a part of the side surface 11e of the first thick plate portion 11d from the back surface 11b side, and then contacts the other of the first thin plate portion 11c and a part of the side surface 11e of the first thick plate portion 11d, thereby partially removing a part of the side surface 11e of the first thick plate portion 11d, then the manner of relative movement between the second grinding wheel 36 and the workpiece 11 can be freely changed.

[0067] Figure 9 is a schematic cross-sectional view showing a portion of the workpiece 11 being ground by the second grinding wheel 36 in the first modified example of the workpiece grinding method. In the first modified example of the workpiece grinding method, for example, the second grinding wheel 36 and the workpiece 11 are moved relative to each other in a direction intersecting the back surface 11b so that the center of rotation of the second grinding wheel 36 does not move away from the center of rotation of the workpiece 11 (so that the horizontal distance between the center of rotation of the workpiece 11 and the center of rotation of the second grinding wheel 36 does not become large), and at least the first thin plate portion 11c is ground. Typically, the second grinding wheel 36 and the workpiece 11 are moved relative to each other in a direction perpendicular to the back surface 11b.

[0068] This results in a disc-shaped intermediate thin plate portion 11i that is thinner than the first thin plate portion 11c, and an annular intermediate thick plate portion 11j surrounding the intermediate thin plate portion 11i, as shown in Figure 9. The diameter of the intermediate thin plate portion 11i is less than or equal to the diameter of the first thin plate portion 11c. In other words, at this stage, a portion of the first thin plate portion 11c adjacent to the first thick plate portion 11d may remain unground. In that case, the unground portion of the first thin plate portion 11c and the first thick plate portion 11d become the intermediate thick plate portion 11j.

[0069] After the intermediate thin plate portion 11i is formed from which the damaged layer 11f has been removed, the second grinding wheel 36 and the workpiece 11 are moved relative to each other in a direction along the back surface 11b so as to move the center of rotation of the second grinding wheel 36 away from the center of rotation of the workpiece 11 (so as to increase the horizontal distance between the center of rotation of the workpiece 11 and the center of rotation of the second grinding wheel 36), thereby partially removing at least the side surface 11e (side surface 11e of the first thick plate portion 11d) remaining on the intermediate thick plate portion 11j.

[0070] This results in a disc-shaped second thin plate portion 11g and an annular second thick plate portion 11h surrounding the second thin plate portion 11g, as shown in Figure 8. Note that other parts of the workpiece grinding method according to the first modified example (excluding grinding with the second grinding wheel 36) may be the same as those in the workpiece grinding method according to the embodiment described above.

[0071] Alternatively, instead of the above-described manner of movement, the second grinding wheel 36 and the workpiece 11 may be moved relative to each other in a direction along the back surface 11b so that the center of rotation of the second grinding wheel 36 is moved away from the center of rotation of the workpiece 11 (so that the horizontal distance between the center of rotation of the workpiece 11 and the center of rotation of the second grinding wheel 36 is increased), and at least the side surface 11e of the first thick plate portion 11d is partially removed. Then, the second grinding wheel 36 and the workpiece 11 may be moved relative to each other in a direction intersecting the back surface 11b so that the center of rotation of the second grinding wheel 36 is not moved away from the center of rotation of the workpiece 11 (so that the horizontal distance between the center of rotation of the workpiece 11 and the center of rotation of the second grinding wheel 36 is not increased), and at least the first thin plate portion 11c may be ground.

[0072] In this case as well, the final result is a disc-shaped second thin plate portion 11g and an annular second thick plate portion 11h surrounding the second thin plate portion 11g, as shown in Figure 8. Other parts of the grinding method for the workpiece (excluding grinding with the second grinding wheel 36) may be the same as in the embodiment described above.

[0073] Furthermore, in the above-described embodiment, the first grinding wheel 16 and the workpiece 11 move relative to each other in a direction inclined with respect to the back surface 11b such that the center of rotation of the first grinding wheel 16 approaches the center of rotation of the workpiece 11. However, the manner of relative movement between the first grinding wheel 16 and the workpiece 11 is not limited to this. As long as a disc-shaped first thin plate portion and an annular first thick plate portion surrounding the first thin plate portion, with at least a part of its inner side surface inclined with respect to the back surface 11b are obtained, the manner of relative movement between the second grinding wheel 36 and the workpiece 11 can be freely changed.

[0074] Figure 10 is a schematic cross-sectional view showing a portion of the workpiece 11 after grinding by the first grinding wheel 16 in the workpiece grinding method according to the second modified example. In the workpiece grinding method according to the second modified example, the first grinding wheel 16 and the workpiece 11 move relative to each other in a direction intersecting the back surface 11b so that the center of rotation of the first grinding wheel 16 does not approach the center of rotation of the workpiece 11 (so that the horizontal distance between the center of rotation of the workpiece 11 and the center of rotation of the first grinding wheel 16 does not become small). Typically, the first grinding wheel 16 and the workpiece 11 are moved relative to each other in a direction perpendicular to the back surface 11b.

[0075] Then, the first grinding wheel 16 and the workpiece 11 move relative to each other in a direction inclined with respect to the back surface 11b, so that the center of rotation of the first grinding wheel 16 is brought closer to the center of rotation of the workpiece 11 (so that the horizontal distance between the center of rotation of the workpiece 11 and the center of rotation of the first grinding wheel 16 is reduced). As a result, a disc-shaped first thin plate portion 11k and an annular first thick plate portion 11l surrounding the first thin plate portion 11k are obtained, as shown in Figure 10.

[0076] In the second modified example, the damage layer 11f of the workpiece 11 is then removed using the second grinding wheel 36, similar to the embodiments and the first modified example described above. Figure 11 is a schematic cross-sectional view showing a portion of the workpiece 11 after grinding with the second grinding wheel 36 in the workpiece grinding method according to the second modified example.

[0077] In this case, the final result is a disc-shaped second thin plate portion 11m, which is larger in diameter and thinner than the first thin plate portion 11k, as shown in Figure 11, and an annular second thick plate portion 11n surrounding the second thin plate portion 11m. Other parts of the grinding method for the workpiece (excluding grinding with the first grinding wheel 16) may be the same as in the embodiments and first modified examples described above.

[0078] Furthermore, in the embodiments and variations described above, the workpiece 11 may be ground using a grinding apparatus comprising a chuck table for holding the workpiece 11 when it is ground by the first grinding wheel 16, and another chuck table for holding the workpiece 11 when it is ground by the second grinding wheel 36. Similarly, the workpiece 11 may be ground using a grinding apparatus comprising a first grinding unit 10 and another grinding apparatus comprising a second grinding unit 30.

[0079] Furthermore, the structures, methods, etc., of the embodiments and their respective modifications described above may be modified as appropriate, as long as they do not deviate from the scope of the present invention. [Explanation of Symbols]

[0080] 11: Workpiece 11a: Surface (first side) 11b: Back side (second side) 11c: 1st thin plate part 11d: First thick plate section 11e: Side 11f: Damage layer 11g: 2nd thin plate part 11h: Second thick plate section 11i: Intermediate thin plate part 11j: Intermediate thick plate section 11k: 1st thin plate part 11l: First thick plate section 11m: 2nd thin plate part 11n: Second thick plate section 13: Planned division line (street) 15: Device 21: Protective component 21a: Surface 21b: Back side 2: Grinding equipment 4: Chuck Table 6: Frame 6a: recess 6b: Flow channel 8: Holding plate 8a:Top surface (holding surface) 8b: Center 10: First grinding unit (rough grinding unit) 12: Spindle 14: Mount 16: First grinding wheel (rough grinding wheel) 18: Wheel base 20: First grinding wheel (coarse grinding wheel) 30: Second grinding unit (finishing grinding unit) 32: Spindle 34: Mount 36: Second grinding wheel (finishing grinding wheel) 38: Wheel base 40: Second grinding wheel (finishing grinding wheel)

Claims

1. A method for grinding a workpiece that is applied when grinding a disc-shaped workpiece having a first surface and a second surface opposite to the first surface, A first grinding step involves rotating a first grinding wheel, in which a plurality of first grinding wheels, each containing abrasive grains, are arranged in an annular region having a first diameter smaller than the workpiece, and moving the workpiece and the first grinding wheel relative to each other while rotating them, thereby bringing the first grinding wheels into contact with the workpiece from the second surface side and grinding the workpiece, thereby forming a disc-shaped first thin plate portion and an annular first thick plate portion surrounding the first thin plate portion, with at least a portion of the inner side surface, including the end on the first thin plate portion side, inclined with respect to the second surface, on the workpiece. The second grinding step includes, after the first grinding step, moving the workpiece and a second grinding wheel, each containing abrasive grains with an average particle size smaller than the first grinding wheel, arranged in an annular region with a second diameter smaller than the workpiece, while rotating them relative to each other, thereby bringing the second grinding wheel into contact with one of the first thin plate portion and a portion of the side surface of the first thick plate portion from the second surface side, and then into contact with the other of the first thin plate portion and a portion of the side surface of the first thick plate portion, thereby grinding the workpiece so that the portion of the side surface of the first thick plate portion is partially removed, and forming a disc-shaped second thin plate portion that is larger in diameter and thinner than the first thin plate portion, and an annular second thick plate portion surrounding the second thin plate portion on the workpiece. A method for grinding a workpiece, wherein in the first grinding step, the first grinding wheel and the workpiece are moved relative to each other in a direction inclined with respect to the second surface, so as to bring the center of rotation of the first grinding wheel closer to the center of rotation of the workpiece.

2. A method for grinding a workpiece that is applied when grinding a disc-shaped workpiece having a first surface and a second surface opposite to the first surface, A first grinding step involves rotating a first grinding wheel, in which a plurality of first grinding wheels, each containing abrasive grains, are arranged in an annular region having a first diameter smaller than the workpiece, and moving the workpiece and the first grinding wheel relative to each other while rotating them, thereby bringing the first grinding wheels into contact with the workpiece from the second surface side and grinding the workpiece, thereby forming a disc-shaped first thin plate portion and an annular first thick plate portion surrounding the first thin plate portion, with at least a portion of the inner side surface, including the end on the first thin plate portion side, inclined with respect to the second surface, on the workpiece. The second grinding step includes, after the first grinding step, moving the workpiece and a second grinding wheel, each containing abrasive grains with an average particle size smaller than the first grinding wheel, arranged in an annular region with a second diameter smaller than the workpiece, while rotating them relative to each other, thereby bringing the second grinding wheel into contact with one of the first thin plate portion and a portion of the side surface of the first thick plate portion from the second surface side, and then into contact with the other of the first thin plate portion and a portion of the side surface of the first thick plate portion, thereby grinding the workpiece so that the portion of the side surface of the first thick plate portion is partially removed, and forming a disc-shaped second thin plate portion that is larger in diameter and thinner than the first thin plate portion, and an annular second thick plate portion surrounding the second thin plate portion on the workpiece. A method for grinding a workpiece, wherein in the first grinding step, the first grinding wheel and the workpiece are moved relatively in a direction intersecting the second surface so as not to bring the center of rotation of the first grinding wheel close to the center of rotation of the workpiece, and then the first grinding wheel and the workpiece are moved relatively in a direction inclined with respect to the second surface so as to bring the center of rotation of the first grinding wheel close to the center of rotation of the workpiece.

3. A method for grinding a workpiece that is applied when grinding a disc-shaped workpiece having a first surface and a second surface opposite to the first surface, A first grinding step involves rotating a first grinding wheel, in which a plurality of first grinding wheels, each containing abrasive grains, are arranged in an annular region having a first diameter smaller than the workpiece, and moving the workpiece and the first grinding wheel relative to each other while rotating them, thereby bringing the first grinding wheels into contact with the workpiece from the second surface side and grinding the workpiece, thereby forming a disc-shaped first thin plate portion and an annular first thick plate portion surrounding the first thin plate portion, with at least a portion of the inner side surface, including the end on the first thin plate portion side, inclined with respect to the second surface, on the workpiece. The second grinding step includes, after the first grinding step, moving the workpiece and a second grinding wheel, each containing abrasive grains with an average particle size smaller than the first grinding wheel, arranged in an annular region with a second diameter smaller than the workpiece, while rotating them relative to each other, thereby bringing the second grinding wheel into contact with one of the first thin plate portion and a portion of the side surface of the first thick plate portion from the second surface side, and then into contact with the other of the first thin plate portion and a portion of the side surface of the first thick plate portion, thereby grinding the workpiece so that the portion of the side surface of the first thick plate portion is partially removed, and forming a disc-shaped second thin plate portion that is larger in diameter and thinner than the first thin plate portion, and an annular second thick plate portion surrounding the second thin plate portion on the workpiece. A method for grinding a workpiece, wherein in the second grinding step, the second grinding wheel and the workpiece are moved relative to each other in a direction intersecting the second surface so as not to move the center of rotation of the second grinding wheel away from the center of rotation of the workpiece, and at least the first thin plate portion is ground, and then the second grinding wheel and the workpiece are moved relative to each other in a direction along the second surface so as to move the center of rotation of the second grinding wheel away from the center of rotation of the workpiece, thereby partially removing at least a portion of the side surface of the first thick plate portion.

4. A method for grinding a workpiece that is applied when grinding a disc-shaped workpiece having a first surface and a second surface opposite to the first surface, A first grinding step involves rotating a first grinding wheel, in which a plurality of first grinding wheels, each containing abrasive grains, are arranged in an annular region having a first diameter smaller than the workpiece, and moving the workpiece and the first grinding wheel relative to each other while rotating them, thereby bringing the first grinding wheels into contact with the workpiece from the second surface side and grinding the workpiece, thereby forming a disc-shaped first thin plate portion and an annular first thick plate portion surrounding the first thin plate portion, with at least a portion of the inner side surface, including the end on the first thin plate portion side, inclined with respect to the second surface, on the workpiece. The second grinding step includes, after the first grinding step, moving the workpiece and a second grinding wheel, each containing abrasive grains with an average particle size smaller than the first grinding wheel, arranged in an annular region with a second diameter smaller than the workpiece, while rotating them relative to each other, thereby bringing the second grinding wheel into contact with one of the first thin plate portion and a portion of the side surface of the first thick plate portion from the second surface side, and then into contact with the other of the first thin plate portion and a portion of the side surface of the first thick plate portion, thereby grinding the workpiece so that the portion of the side surface of the first thick plate portion is partially removed, and forming a disc-shaped second thin plate portion that is larger in diameter and thinner than the first thin plate portion, and an annular second thick plate portion surrounding the second thin plate portion on the workpiece. A method for grinding a workpiece, wherein in the second grinding step, the second grinding wheel and the workpiece are moved relative to each other in a direction along the second surface so as to move the center of rotation of the second grinding wheel away from the center of rotation of the workpiece, thereby partially removing at least a portion of the side surface of the first thick plate portion, and then the second grinding wheel and the workpiece are moved relative to each other in a direction intersecting the second surface so as not to move the center of rotation of the second grinding wheel away from the center of rotation of the workpiece, thereby grinding at least the first thin plate portion.

5. A method for grinding a workpiece according to claim 1 or 2, wherein in the second grinding step, the second grinding wheel and the workpiece are moved relative to each other in a direction inclined with respect to the second surface, such that the center of rotation of the second grinding wheel is moved away from the center of rotation of the workpiece.

6. A method for grinding a workpiece according to claim 1 or 2, wherein in the second grinding step, the second grinding wheel and the workpiece are moved relative to each other in a direction intersecting the second surface so as not to move the center of rotation of the second grinding wheel away from the center of rotation of the workpiece, and after grinding at least the first thin plate portion, the second grinding wheel and the workpiece are moved relative to each other in a direction along the second surface so as to move the center of rotation of the second grinding wheel away from the center of rotation of the workpiece, thereby partially removing at least a portion of the side surface of the first thick plate portion.

7. A method for grinding a workpiece according to claim 1 or 2, wherein in the second grinding step, the second grinding wheel and the workpiece are moved relative to each other in a direction along the second surface so as to move the center of rotation of the second grinding wheel away from the center of rotation of the workpiece, thereby partially removing at least a portion of the side surface of the first thick plate portion, and then the second grinding wheel and the workpiece are moved relative to each other in a direction intersecting the second surface so as not to move the center of rotation of the second grinding wheel away from the center of rotation of the workpiece, thereby grinding at least the first thin plate portion.

Images