Grinding Method

Abstract

To provide a grinding method which does not require a considerably longer time in comparison with a conventional grinding method and in which an effective region that can be used for products can be maximally secured.SOLUTION: A grinding method which is applied in grinding a discoid work-piece which has a first surface and a second surface at the opposite side to the first surface when grinding it beginning from the second surface side, includes: a first grinding step of grinding the work-piece while bringing a first grinding stone into contact with the work-piece to form on the work-piece a discoid first thin plate part and an annular first thick plate part surrounding the first thin plate part; and a second grinding step of grinding the work-piece while bringing a second grinding stone into contact with the first thick plate part and the first thin plate part to form on the work-piece a discoid second thin plate part which is larger in diameter and thinner than the first thin plate part and an annular second thick plate part surrounding the second thin plate part, where in the second grinding step, the second grinding stone is brought into contact with a region on the second surface away by a width of the second grinding stone or more from an inner edge of the second surface remaining in the first thick plate part toward the outside.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a grinding method that is applied when grinding a disk-shaped workpiece such as a wafer. [Background technology]

[0002] In order to realize small and lightweight device chips, there are increasing opportunities to thin wafers on which devices such as integrated circuits are mounted on the front side. For example, the front side of the wafer is held by a chuck table, and the chuck table and a grinding wheel with a grinding stone containing abrasive grains fixed thereto 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, thereby grinding the wafer to thin it.

[0003] However, when the entire wafer is thinned by the above-mentioned method, the rigidity of the wafer is also significantly reduced, making it difficult to handle the wafer in subsequent processes. Therefore, a technology has been proposed in which a grinding wheel with a smaller diameter than the wafer is used to grind the central (inner) region of the wafer where devices are provided, and the outer edge (outer) region is left unground, thereby maintaining high rigidity of the wafer after grinding (see, for example, Patent Document 1).

[0004] In this technique, the central region of the wafer is first roughly ground with a first grinding wheel to which a grinding stone containing a relatively large abrasive grain is fixed, thereby forming a disk-shaped thin plate portion and an annular thick plate portion surrounding the thin plate portion on the wafer. In this way, using a grinding wheel to which a grinding stone containing a large abrasive grain is fixed reduces the time required to grind the wafer compared to using a grinding wheel to which a grinding stone containing a small abrasive grain is fixed.

[0005] On the other hand, when a wafer is roughly ground using a grinding wheel with a fixed grinding stone containing large abrasive grains, a damaged layer containing scratches and distortions caused by the grinding stone is formed on the ground surface, and the mechanical strength (transverse strength, etc.) of the thin plate portion is likely to be insufficient. Therefore, after the wafer is roughly ground, the damaged layer is removed by further grinding the thin plate portion using a grinding wheel with a fixed grinding stone containing relatively small abrasive grains. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-19461 Summary of the Invention [Problem to be solved by the invention]

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

[0008] The present invention has been made in view of the above problems, and its object is to provide a grinding method that, when grinding a disk-shaped workpiece to form a thin plate portion and a thick plate portion, does not require a significantly longer time than conventional grinding methods, and maximizes the effective area that can be used for the product. [Means for solving the problem]

[0009] According to one aspect of the present invention, there is provided a grinding method applied when grinding a disk-shaped workpiece having a first surface and a second surface opposite to the first surface from the second surface side, the method including a first grinding step in which a first grinding wheel in which a plurality of first grinding stones, each containing abrasive grains, are arranged in an annular region having a first diameter smaller than that of the workpiece, and the workpiece are moved relatively to each other in a first direction intersecting the second surface while rotating relative to each other, thereby bringing the first grinding stones into contact with the workpiece from the second surface side to grind the workpiece and form a disk-shaped first thin plate portion and an annular first thick plate portion surrounding the first thin plate portion in the workpiece; and after the first grinding step, grinding the workpiece with a first grinding wheel in which a plurality of first grinding stones, each containing abrasive grains smaller than that of the first grinding stones, are arranged in an annular region having a first diameter smaller than that of the workpiece. and a second grinding step in which a second grinding wheel having a plurality of second grinding stones arranged in an annular region having a second diameter smaller than that of the workpiece and the workpiece are moved relatively in a second direction intersecting with the second surface while rotating relative to each other, thereby bringing the second grinding stone into contact with the first thick plate portion and the first thin plate portion from the second surface side to grind the workpiece, thereby forming a second thin plate portion that is disc-shaped and has a larger diameter than the first thin plate portion and an annular second thick plate portion surrounding the second thin plate portion on the workpiece, wherein in the second grinding step, the second grinding stone is brought into contact with an area on the second surface away from an inner edge of the second surface remaining on the first thick plate portion toward the outside by a distance equal to or greater than the width of the second grinding stone in the direction of the second diameter. While the second grinding wheel and the workpiece are relatively moved in a direction perpendicular to the second surface, the center of rotation of the second grinding wheel and the center of rotation of the workpiece are brought closer to each other in a direction parallel to the second surface. A grinding method is provided.

[0010] Preferably, in the first grinding step, the first grinding wheel and the workpiece are moved relatively in a direction perpendicular to the second surface, while the center of rotation of the first grinding wheel and the center of rotation of the workpiece are brought closer together in a direction parallel to the second surface. [Effects of the Invention]

[0012] In a grinding method according to one aspect of the present invention, a workpiece is ground with a first grinding wheel having a first grinding stone to form a first thin plate portion and a first thick plate portion, and then the first thin plate portion is ground together with the first thick plate portion with a second grinding wheel having a second grinding stone that contains smaller abrasive grains than the first grinding stone to form a second thin plate portion and a second thick plate portion, so that the entire second thin plate portion becomes an effective area that is free of a layer damaged by the first grinding stone.

[0013] Furthermore, because the volume of the portion of the first thick plate portion removed by the second grinding wheel is sufficiently small, the time required for grinding is not significantly longer than, for example, a conventional grinding method in which only the central region of the first thin plate portion is ground with the second grinding wheel and the first thick plate portion is not ground at all with the second grinding wheel. Thus, the grinding method according to one aspect of the present invention maximizes the effective area that can be used for the product without requiring a significantly longer grinding time than conventional grinding methods.

[0014] In addition, in a grinding method according to one aspect of the present invention, when the first thin plate portion is ground together with the first thick plate portion with the second grinding wheel, the second grinding wheel contacts an area on the second surface that is further away from the inner edge of the second surface remaining on the first thick plate portion toward the outside than the width of the second grinding wheel (the width of the second grinding wheel in the direction of the second diameter).

[0015] As a result, there is always a timing when the innermost part of the second grinding wheel (the part located most inward in the direction of the second diameter) comes into contact with the first thick plate part, so that the wear of the inner part of the second grinding wheel can be made to progress appropriately in accordance with the wear of the outer part, and the progression of uneven wear in which only the outer part of the second grinding wheel wears can be suppressed. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a perspective view schematically showing how 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 a workpiece is held on a chuck table via a protective member. [Figure 3]FIG. 3 is a cross-sectional view that schematically shows how grinding of the workpiece by the first grinding wheel begins. [Figure 4] FIG. 4 is a cross-sectional view schematically showing how 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 that schematically shows how grinding of the workpiece by the second grinding wheel begins. [Figure 7] FIG. 7 is a cross-sectional view schematically showing how 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 after being ground by the first grinding wheel in the grinding method according to the modified example. [Figure 10] FIG. 10 is a cross-sectional view schematically showing a part of the workpiece after being ground by the second grinding wheel in the grinding method according to the modified example. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. In the grinding method according to this embodiment, first, a protective member is attached to a disk-shaped workpiece to be ground (attaching step). Fig. 1 is a perspective view schematically showing how a protective member 21 is attached to a disk-shaped workpiece 11.

[0018] The workpiece 11 is, for example, a disk-shaped wafer made of a semiconductor such as silicon (Si). That is, the workpiece 11 has a circular front surface (first surface) 11a and a circular back surface (second surface) 11b opposite the front surface 11a. The front surface 11a side of the workpiece 11 is divided into a plurality of small regions by a plurality of intersecting streets (planned division lines) 13, and a device 15 such as an integrated circuit (IC) is formed in each small region.

[0019] In the grinding method according to this embodiment, a portion of the workpiece 11 corresponding to a region where the device 15 is formed (device region) is ground from the back surface 11b side, thinning a portion of the workpiece 11. That is, in the grinding method according to this embodiment, the workpiece 11 is machined into a concave shape from the back surface 11b side.

[0020] In this embodiment, a disk-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, a substrate made of other semiconductors, ceramics, resin, metal, etc. may be used as the workpiece 11. Similarly, the type, number, shape, structure, size, arrangement, etc. of the devices 15 are not limited to the above embodiment. The devices 15 do not have to be formed on the workpiece 11.

[0021] The protective member 21 attached to the workpiece 11 is typically a circular tape (film) having a diameter roughly equal to that of the workpiece 11, a resin substrate, a wafer of the same or different type as the workpiece 11, etc. An adhesive layer that exhibits adhesive strength to the workpiece 11 is provided on the front surface 21a side of this protective member 21.

[0022] 1, the front surface 21a of the protective member 21 is brought into close contact with the front surface 11a of the workpiece 11, whereby the protective member 21 is attached to the front surface 11a of the workpiece 11. As a result, the protective member 21 absorbs the impact applied to the front surface 11a when the workpiece 11 is ground from the back surface 11b side, and the device 15 of the workpiece 11 and the like are protected.

[0023] 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). Fig. 2 is a cross-sectional view that schematically shows how the workpiece 11 is held on the chuck table 4 of the grinding device 2 via the protective member 21. Note that the grinding device 2 shown in Fig. 2 and other figures is used in each of the following steps.

[0024] The grinding device 2 is equipped with a chuck table 4 configured to hold a workpiece 11. The chuck table 4 includes a disk-shaped frame 6 made of a metal such as stainless steel. A recess 6a having a circular opening at its upper end is formed on the upper surface of the frame 6. A porous disk-shaped holding plate 8 made of ceramics or the like is fixed to this recess 6a.

[0025] 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 workpiece 11, etc. The difference in height (height difference) between the center 8b of the upper surface 8a of the holding plate 8, which corresponds to the apex of the cone, and the outer periphery of the upper surface 8a of the holding plate 8 is approximately 10 μm to 30 μm. In this embodiment, the back surface 21b of the protective member 21 comes into contact with the upper surface (holding surface) 8a of the holding plate 8.

[0026] 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 6 and a valve (not shown) arranged 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 holding plate 8, the back surface 21b of the protective member 21 is sucked by the chuck table 4. In other words, the workpiece 11 is held on the chuck table 4 via the protective member 21 so that the back surface 11b is exposed upward.

[0027] A rotational drive source (not shown), such as a motor, is connected to the lower part of the frame 6. The force generated by this rotational drive source causes the chuck table 4 to rotate about an axis along the vertical direction or an axis slightly tilted relative to the vertical direction, with the center 8b of the upper surface 8a as the center of rotation. The frame 6 is also supported by a chuck table moving mechanism (not shown), and the force generated by this chuck table moving mechanism causes the chuck table 4 to move horizontally.

[0028] After the workpiece 11 is held by the chuck table 4 via the protective member 21, an area of ​​the workpiece 11 corresponding to an area where the device 15 is formed (device area) is roughly ground from the back surface 11b side (first grinding step). Fig. 3 is a cross-sectional view showing a state where grinding of the workpiece 11 is started, and Fig. 4 is a cross-sectional view showing a state where grinding of the workpiece 11 progresses. Note that for the sake of convenience, Figs. 3 and 4 show side views of some elements.

[0029] 3 and 4, 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 housed in the space inside the spindle housing.

[0030] A disk-shaped mount 14 having a diameter smaller than that of the workpiece 11 is provided at the lower end of the spindle 12. A circular first grinding wheel (coarse grinding wheel) 16 having a diameter roughly equal to that of the mount 14 is fixed to the underside of the mount 14 with bolts (not shown) or the like.

[0031] The first grinding wheel 16 includes an annular wheel base 18 made of metal such as stainless steel or aluminum. A plurality of first grinding stones (rough grinding stones) 20 are fixed to the annular lower surface of the wheel base 18 along the circumferential direction of the wheel base 18. That is, the plurality of first grinding stones 20 are arranged in an annular region having a diameter (first diameter) smaller than the diameter of the workpiece 11. Each first grinding stone 20 has a structure in which large abrasive grains made of, for example, diamond or the like are dispersed in a binder made of resin or the like.

[0032] When the workpiece 11 is ground with the first grinding wheel 16 including this first grinding stone 20, a larger amount of the workpiece 11 can be removed per unit time, but a damaged layer containing scratches or distortion is more likely to form on the grinding surface 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 that is aligned vertically or slightly tilted relative to the vertical direction by the force generated by this rotational drive source.

[0033] A nozzle (not shown) configured to supply a grinding liquid (typically water) to the first grinding stone 20 and the like is provided near the first grinding wheel 16 or inside the first grinding wheel 16. 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 a force generated by this first grinding unit moving mechanism.

[0034] When grinding the workpiece 11 with the first grinding unit 10 (first grinding wheel 16), the chuck table 4 first moves to a position directly below the first grinding unit 10. More specifically, the chuck table moving mechanism moves the chuck table 4 in the horizontal direction so that the first grinding wheel 16 (all first grinding wheels 20) are positioned directly above the area where the device 15 is formed.

[0035] Thereafter, the chuck table 4 and the first grinding wheel 16 each rotate, and the first grinding unit 10 (first grinding wheel 16) descends. That is, the first grinding wheel 16 and the workpiece 11 move relatively in a vertical direction (first direction) intersecting the back surface 11b of the workpiece 11 while rotating relative to each other. At this time, liquid is supplied from a nozzle to the first grinding wheel 20, etc. As a result, as shown in FIG. 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.

[0036] There are no significant limitations on the specific grinding conditions. For example, to achieve efficient grinding of the workpiece 11, the rotation speed of the chuck table 4 is set to 100 rpm to 600 rpm, typically 300 rpm, the rotation speed of the first grinding wheel 16 is set to 1000 rpm to 7000 rpm, typically 4500 rpm, and the descending speed of the first grinding unit 10 (grinding feed rate) is set to 0.8 μm / s to 10 μm / s, typically 6.0 μm / s.

[0037] As grinding of the workpiece 11 progresses, as shown in Fig. 4, the portion of the workpiece 11 that has come into contact with the first grinding wheel 20 becomes thinner, while the thickness of the remaining portion is maintained. That is, the portion of the workpiece 11 corresponding to the region where the device 15 is formed becomes thinner, becoming a disk-shaped first thin portion 11c. Furthermore, the thickness of the portion of the workpiece 11 corresponding to the region (outer peripheral region) surrounding the region where the device 15 is formed is maintained, becoming an annular first thick portion 11d surrounding the first thin portion 11c.

[0038] 5 is a cross-sectional view schematically showing a portion of the workpiece 11 after being ground by the first grinding wheel 16. As shown in FIG. 5, a damaged layer 11e containing scratches or distortion exists in the portion (ground surface) on the back surface 11b side of the first thin plate portion 11c that has been ground by the first grinding stone 20 containing larger abrasive grains. The damaged layer 11e reduces the mechanical strength (transverse strength, etc.) of the workpiece 11, and therefore the region where this damaged layer 11e exists cannot be used as a product.

[0039] 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 from the back surface 11b side so as to remove the damaged layer 11e (second grinding step). Fig. 6 is a cross-sectional view showing a state in which grinding of the workpiece 11 is started, and Fig. 7 is a cross-sectional view showing a state in which grinding of the workpiece 11 progresses. Note that Figs. 6 and 7 show side views of some elements for ease of explanation.

[0040] 6 and 7, a second grinding unit (finish grinding unit) 30, which is separate from the first grinding unit 10, is disposed above the chuck table 4 of the grinding device 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.

[0041] A disk-shaped mount 34 having a diameter smaller than that of the workpiece 11 is provided at the lower end of the spindle 32. A circular second grinding wheel (finish grinding wheel) 36 having approximately the same diameter as the mount 34 is fixed to the underside of the mount 34 with bolts (not shown) or the like.

[0042] The second grinding wheel 36 includes an annular wheel base 38 made of metal such as stainless steel or aluminum. A plurality of second grinding stones (finish grinding stones) 40 are fixed to the annular lower surface of the wheel base 38 along the circumferential direction of the wheel base 38. In other words, the plurality of second grinding stones 40 are arranged in an annular region having a diameter (second diameter) smaller than that of the workpiece 11.

[0043] Each second grinding wheel 40 has a structure in which small abrasive grains made of, for example, diamond or the like are dispersed in a binder made of resin or the like. Specifically, the size (typically, average particle size) of the abrasive grains contained in the second grinding wheel 46 is smaller than the size of the abrasive grains contained in the first grinding wheel 20.

[0044] When the workpiece 11 is ground with the second grinding wheel 36 including this second grinding stone 40, the amount of workpiece 11 that can be removed per unit time is smaller than when the workpiece 11 is ground with the first grinding wheel 16, but damaged layers are less likely to be generated. 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 that is vertical or slightly tilted relative to the vertical by the force generated by this rotational drive source.

[0045] A nozzle (not shown) configured to supply a grinding liquid (typically, water) to the second grinding stone 40 and the like is provided near the second grinding wheel 36 or inside the second grinding wheel 36. The spindle housing is supported, for example, by a second grinding unit moving mechanism (not shown), and the second grinding unit 30 moves in the vertical direction by a force generated by this second grinding unit moving mechanism.

[0046] When the workpiece 11 is ground by the second grinding unit 30 (second grinding wheel 36), first, the chuck table 4 moves to a position directly below the second grinding unit 30. More specifically, the chuck table moving mechanism moves the chuck table 4 in the horizontal direction so that one of the plurality of second grinding stones 40 of the second grinding wheel 36 is positioned directly above an area outside the inner edge of the first thick plate portion 11d (the outer edge of the first thin plate portion 11c).

[0047] In this embodiment, the chuck table moving mechanism moves the chuck table 4 in the horizontal direction so that the second grinding unit 30 moves down to bring the second grinding wheel 40 into contact with an area on the back surface 11b that is located in the first thick plate portion 11d and that is spaced outward from the inner edge of the back surface 11b by at least the width W of the second grinding wheel 40. Here, the width W of the second grinding wheel 40 is the width of the second grinding wheel 40 in the direction of the diameter of the annular area in which the second grinding wheels 40 are arranged, and is, for example, about 1 mm to 5 mm.

[0048] Thereafter, the chuck table 4 and the second grinding wheel 36 each rotate, and the second grinding unit 30 (second grinding wheel 36) descends. That is, the second grinding wheel 36 and the workpiece 11 rotate relative to each other while moving relatively in a vertical direction (second direction) intersecting with the back surface 11b of the workpiece 11. At this time, liquid is supplied from a nozzle to the second grinding stone 40 and the like.

[0049] 6, the second grinding wheel 40 comes into contact with the first thick plate portion 11d from the back surface 11b side, and grinding of the workpiece 11 is started. As described above, in this embodiment, the second grinding wheel 40 comes into contact with an area on the back surface 11b that is apart from the inner edge of the back surface 11b present in the first thick plate portion 11d toward the outside by a distance equal to or greater than the width W of the second grinding wheel 40.

[0050] In other words, there is always a timing when the innermost part of the second grinding wheel 40 in the direction of width W comes into contact with the first thick plate portion 11d, so the wear of the inner part of the second grinding wheel 40 can be made to progress appropriately in accordance with the wear of the outer part, and the progress of uneven wear in which only the outer part of the second grinding wheel 40 wears can be suppressed.

[0051] There are no significant limitations on the specific grinding conditions. For example, to achieve efficient and highly accurate grinding of the workpiece 11, the rotation speed of the chuck table 4 is set to 100 rpm to 600 rpm, typically 300 rpm, and the rotation speed of the second grinding wheel 36 is set to 1000 rpm to 7000 rpm, typically 4000 rpm.

[0052] As grinding of the workpiece 11 progresses, after the inner portion of the first thick portion 11d that contacts the second grinding wheel 40 has been removed, the second grinding wheel 40 also contacts the first thin portion 11c. That is, in this embodiment, after only the first thick portion 11d has been ground, the region including the first thin portion 11c (and the first thick portion 11d) is ground from the back surface 11b side.

[0053] Here, the grinding load on the second grinding wheel 40 when only the first thick portion 11d is ground is smaller than the grinding load on the second grinding wheel 40 when the region including the first thin portion 11c is ground. Therefore, when only the first thick portion 11d is ground, it is possible to increase the speed at which the second grinding unit 30 descends (grinding feed rate) compared to when the region including the first thin portion 11c is ground.

[0054] For example, the speed of the second grinding unit 30 descending when only the first thick portion 11d is ground is set to 0.8 μm / s to 5.0 μm / s, and the speed of the second grinding unit 30 descending when the region including the first thin portion 11c is ground is set to 0.1 μm / s to 0.8 μm / s. By increasing the speed of the second grinding unit 30 descending when only the first thick portion 11d is ground, the time required for grinding does not become significantly longer than, for example, a conventional grinding method in which the first thick portion 11d is not ground.

[0055] As grinding of the workpiece 11 progresses further, the portion of the workpiece 11 that has come into contact with the second grinding wheel 40 becomes thinner, while the thickness of the remaining portion is maintained, as shown in Fig. 7. That is, the portion of the workpiece 11 corresponding to the region where the device 15 is formed becomes thinner, forming a disk-shaped second thin portion 11f. Also, the thickness of the portion of the workpiece 11 corresponding to the region (peripheral region) surrounding the region where the device 15 is formed is maintained, forming an annular second thick portion 11g surrounding the second thin portion 11f.

[0056] 8 is a cross-sectional view schematically showing a portion of the workpiece 11 after being ground by the second grinding wheel 36. As shown in FIG. 8, no substantial damaged layer 11e remains on the back surface 11b side (ground surface) of the second thin plate portion 11f that has been ground by the second grinding stone 40 containing smaller abrasive grains. Therefore, the entire second thin plate portion 11f becomes an effective area that can be used for the product.

[0057] 8, the edge of the second thin plate portion 11f is formed outward from the edge of the first thin plate portion 11c by a distance D that is equal to or greater than the width W of the second grinding wheel 40, and the inner edge of the second thick plate portion 11g is formed outward from the inner edge of the first thick plate portion 11d by the distance D. In other words, the difference between the diameter of the second thin plate portion 11f and the diameter of the first thin plate portion 11c and the difference between the width of the second thick plate portion 11g and the width of the first thick plate portion 11d are equal to twice the distance D.

[0058] For example, if the area of ​​the workpiece 11 where the devices 15 are formed is included in the effective area, all of the devices 15 can be used as products. In this case, the diameter of the second thin plate portion 11f is equal to or greater than the diameter of the area where the devices 15 are formed. Therefore, the diameter of the first thin plate portion 11c may be smaller than the diameter of the area where the devices 15 are formed.

[0059] As described above, in the grinding method of this embodiment, the workpiece 11 is ground with the first grinding wheel 16 equipped with the first grinding stone 20 to form the first thin plate portion 11c and the first thick plate portion 11d, and then the first thin plate portion 11c is ground together with the first thick plate portion 11d with the second grinding wheel 36 equipped with the second grinding stone 40 containing smaller abrasive grains than the first grinding stone 20 to form the second thin plate portion 11f and the second thick plate portion 11g, so that the entire second thin plate portion 11f becomes an effective area that is free of the damaged layer 11e caused by the first grinding stone 20.

[0060] Furthermore, because the volume of the portion of the first thick portion 11d removed by the second grinding wheel 36 is sufficiently small, the time required for grinding is not significantly longer than, for example, a conventional grinding method in which only the central region of the first thin portion 11c is ground by the second grinding wheel 36 and the first thick portion 11d is not ground at all by the second grinding wheel 36. Therefore, the grinding method of this embodiment maximizes the effective area that can be used for the product without requiring a significantly longer time than conventional grinding methods.

[0061] Furthermore, in the grinding method according to this embodiment, when the second grinding wheel 36 grinds the first thin plate portion 11c together with the first thick plate portion 11d, the second grinding wheel 40 contacts an area on the back surface 11b that is away from the inner edge of the back surface (second surface) 11b present on the first thick plate portion 11d toward the outside by a distance greater than the width W of the second grinding wheel 40 (the width of the second grinding wheel 40 in the direction of the diameter (second diameter) of the annular area in which the second grinding wheel 40 is arranged).

[0062] As a result, there is always a timing when the innermost part of the second grinding wheel 40 (the part located innermost in the direction of the diameter (second diameter) of the annular area in which the second grinding wheels 40 are arranged) comes into contact with the first thick plate portion 11d, so that the wear of the inner part of the second grinding wheel 40 can be made to progress appropriately in accordance with the wear of the outer part, and the progress of uneven wear in which only the outer part of the second grinding wheel 40 wears can be suppressed.

[0063] The present invention is not limited to the above-described embodiment and can be practiced with various modifications. As described above, there is a deviation (distance D) between the position of the first grinding wheel 16 relative to the workpiece 11 and the position of the second grinding wheel 36 relative to the workpiece 11 that is equal to or greater than the width W of the second grinding stone 40.

[0064] Therefore, the diameter (first diameter) of the annular region in which the first grinding wheels 20 are arranged and the diameter (second diameter) of the annular region in which the second grinding wheels 40 are arranged do not necessarily have to be equal. For example, the diameter of the annular region in which the second grinding wheels 40 are arranged may be larger than the diameter of the annular region in which the first grinding wheels 20 are arranged.

[0065] Furthermore, when the workpiece 11 is ground with the first grinding wheel 16, the center of rotation of the first grinding wheel 16 and the center of rotation of the workpiece 11 may be brought closer to each other in a direction parallel to the back surface 11b while the first grinding wheel 16 and the workpiece 11 are moved relatively in a direction perpendicular to the back surface 11b. Fig. 9 is a cross-sectional view schematically showing a part of the workpiece 11 after being ground with the first grinding wheel 16 in the grinding method according to this modified example.

[0066] 9, in this modification, the inner side surface of the first thick portion 11d is inclined with respect to the back surface 11b of the workpiece 11 so that the space defined by the first thin portion 11c and the first thick portion 11d has an inverted truncated cone shape. In other words, the outer side surface of the first grinding wheel 20 does not come into contact with the workpiece 11, so that the progression of uneven wear of the first grinding wheel 20 can be suppressed.

[0067] Similarly, when the workpiece 11 is ground with the second grinding wheel 36, the center of rotation of the second grinding wheel 36 and the center of rotation of the workpiece 11 may be brought closer to each other in a direction parallel to the back surface 11b while the second grinding wheel 36 and the workpiece 11 are moved relatively in a direction perpendicular to the back surface 11b. Fig. 10 is a cross-sectional view schematically showing a part of the workpiece 11 after being ground with the second grinding wheel 36 in the grinding method according to this modified example.

[0068] 10, in this modification, the inner side surface of the second thick portion 11g is inclined with respect to the back surface 11b of the workpiece 11 so that the space defined by the second thin portion 11f and the second thick portion 11g has an inverted truncated cone shape. In other words, the outer side surface of the second grinding wheel 40 does not come into contact with the workpiece 11, so that the progression of uneven wear of the second grinding wheel 40 can be further suppressed.

[0069] Furthermore, the workpiece 11 may be ground using a grinding apparatus that includes a chuck table that holds the workpiece 11 when the workpiece 11 is ground by the first grinding wheel 16, and another chuck table that holds the workpiece 11 when the workpiece 11 is ground by the second grinding wheel 36. Similarly, the workpiece 11 may be ground using a grinding apparatus that includes the first grinding unit 10 and another grinding apparatus that includes the second grinding unit 30.

[0070] In addition, the structures, methods, etc. according to the above-described embodiments and modifications may be modified as appropriate without departing from the scope of the present invention. [Explanation of symbols]

[0071] 11: Workpiece 11a: Surface (first side) 11b: Back side (second side) 11c: 1st thin plate part 11d: First thick plate section 11e: Damage Layer 11f: 2nd thin plate part 11g: Second thick plate section 13: Planned division line (street) 15: Device 21: Protective material 21a: Surface 21b: Back side 2: Grinding equipment 4: Chuck table 6: Frame 6a: Recess 6b: Flow path 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: No. 1 grinding wheel (rough grinding wheel) 30: Second grinding unit (finish grinding unit) 32: Spindle 34: Mount 36: Second grinding wheel (finish grinding wheel) 38: Wheel base 40: Second grinding wheel (finishing grinding wheel)

Claims

1. A grinding method applied when grinding a disk-shaped workpiece having a first surface and a second surface opposite to the first surface from the second surface side, a first grinding step in which a first grinding wheel, in which a plurality of first grinding stones each containing abrasive grains are arranged in an annular region having a first diameter smaller than that of the workpiece, and the workpiece are moved relatively in a first direction intersecting with the second surface while rotating relative to each other, thereby bringing the first grinding stones into contact with the workpiece from the second surface side to grind the workpiece, thereby forming a disk-shaped first thin plate portion and an annular first thick plate portion surrounding the first thin plate portion on the workpiece; and a second grinding step after the first grinding step, in which a second grinding wheel, in which a plurality of second grinding wheels each containing smaller abrasive grains than the first grinding wheels are arranged in an annular region having a second diameter smaller than that of the workpiece, and the workpiece are moved relatively in a second direction intersecting with the second surface while rotating relative to each other, thereby bringing the second grinding wheels into contact with the first thick plate portion and the first thin plate portion from the second surface side to grind the workpiece, thereby forming, on the workpiece, a second thin plate portion that is circular and thinner in diameter than the first thin plate portion and an annular second thick plate portion surrounding the second thin plate portion, In the second grinding step, the second grinding wheel is brought into contact with an area on the second surface that is spaced apart from the inner edge of the second surface remaining on the first thick plate portion toward the outside by a distance equal to or greater than the width of the second grinding wheel in the direction of the second diameter, and the second grinding wheel and the workpiece are moved relatively in a direction perpendicular to the second surface, while the center of rotation of the second grinding wheel and the center of rotation of the workpiece are brought closer together in a direction parallel to the second surface.

2. 2. The grinding method according to claim 1, wherein in the first grinding step, the first grinding wheel and the workpiece are moved relatively in a direction perpendicular to the second surface while the center of rotation of the first grinding wheel and the center of rotation of the workpiece are brought closer together in a direction parallel to the second surface.

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