Grinding method

Abstract

[Problem] To provide a grinding method that, compared to conventional grinding methods, requires less time and maximizes the usable area of ​​the product. [Solution] A grinding method applicable to grinding a circular plate-shaped workpiece having a first surface and a second surface opposite to the first surface from the second surface side, comprising: a first grinding step in which a first grinding stone contacts and grinds the workpiece, forming a first thin plate portion in the circular plate shape and a first thick plate portion in the annular shape surrounding the first thin plate portion; and a second grinding step in which a second grinding stone contacts the first thick plate portion and the first thin plate portion, grinding the workpiece, forming a second thin plate portion in the circular plate shape with a diameter greater than the first thin plate portion and a second thick plate portion in the annular shape surrounding the second thin plate portion. In the second grinding step, the second grinding stone contacts a region remaining on the second surface of the first thick plate portion, the region on the second surface being a region greater than the width of the second grinding stone separated from the inner edge of the second surface outwards.

Description

Technical Field

[0001] This invention relates to a grinding method applicable to grinding a workpiece in the form of a wafer-like disc. Prior Technology

[0002] In order to achieve small and lightweight component chips, there is an increasing opportunity to thin wafers with integrated circuits and other components on the front side. For example, the front side of the wafer is held by a chuck stage, and a grinding wheel containing abrasive grains is fixed to the chuck stage and rotates back and forth. While supplying liquid such as pure water, the grinding wheel is pressed against the back side of the wafer, thereby thinning the wafer.

[0003] However, if the wafer becomes thinner overall using the above method, its rigidity is also significantly reduced, making it difficult to process in subsequent steps. Therefore, a technique has been proposed that uses a grinding wheel with a diameter smaller than that of the wafer to grind the central (inner) area of ​​the wafer with components, while leaving the outer (outer) area un-grinded, thereby maintaining a high degree of rigidity of the wafer after grinding (for example, see Patent Document 1).

[0004] In this technology, firstly, a first grinding wheel is used to rough-grind the central area of ​​the wafer. In the thin, circular portion of the wafer and the annular thick portion surrounding the thin portion, the first grinding wheel is fixed with a grinding stone containing abrasive grains of a certain size. Thus, by using a grinding wheel with a grinding stone containing large abrasive grains, the time required for wafer grinding is shorter compared to using a grinding wheel with a grinding stone containing small abrasive grains.

[0005] On the other hand, if a grinding wheel with a fixed grinding stone containing large abrasive grains is used to rough grind the wafer, a damaged layer containing damage or deformation caused by the grinding stone will be formed on the ground surface, and the mechanical strength (flexural strength, etc.) of the thin plate portion is easily insufficient. Therefore, after rough grinding the wafer, the thin plate portion is further ground using a grinding wheel with a fixed grinding stone containing relatively small abrasive grains to remove the damaged layer. [Known Technical Documents] [Patent Literature]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2007-19461 Summary of the Invention

[0007] [The problem that the invention aims to solve] However, if the grinding wheel contacts the inner side of the thick plate when further grinding the thin plate to remove the damaging layer, the thick plate may chip. Therefore, when removing the damaging layer, the grinding wheel is not allowed to contact the thick plate, and only the central area of ​​the thin plate is ground. However, in this method, the damaging layer remains on the outer edge of the thin plate (the area near the boundary with the thick plate), making this area unusable for the product.

[0008] Therefore, the object of the present invention is to provide a grinding method that, when grinding a circular workpiece to form a thin plate portion and a thick plate portion, requires less time compared to conventional grinding methods and maximizes the effective area that can be used in the product.

[0009] [Technical means to solve the problem] According to one aspect of the present invention, a grinding method is provided, applicable to grinding a circular plate-shaped workpiece having a first surface and a second surface opposite to the first surface from the second surface, and comprising: a first grinding step in which a first grinding wheel and the workpiece are rotated relative to each other while moving relative to each other in a first direction intersecting the second surface, thereby causing a first grinding stone to contact the workpiece from the second surface side and grind the workpiece, wherein the workpiece forms a first thin plate portion in the circular plate shape and a first thick plate portion in the annular shape surrounding the first thin plate portion, wherein the first grinding wheel has a plurality of first grinding stones arranged in an annular region smaller than a first diameter of the workpiece, and the plurality of first grinding stones each contain abrasive grains; and a second grinding step in which, after the first grinding step, the second grinding wheel and the workpiece are rotated relative to each other in a first direction intersecting the second surface, thereby causing a first grinding stone to contact the workpiece from the second surface side and grind the workpiece. The second grinding wheel rotates and moves relative to the second direction intersecting the second surface, thereby causing the second grinding stone to contact the first thick plate portion and the first thin plate portion from the second surface side and grind the workpiece. A second thin plate portion with a diameter larger than the first thin plate portion and a second thick plate portion in an annular shape surrounding the second thin plate portion are formed in the workpiece. The second grinding wheel has a plurality of second grinding stones arranged in an annular region smaller than the second diameter of the workpiece. Compared with the first grinding stone, the plurality of second grinding stones contain smaller abrasive grains. In the second grinding step, the second grinding stone contacts the region remaining on the second surface of the first thick plate portion. The region on the second surface is the area greater than the width of the second grinding stone in the direction of the second diameter, which separates from the inner edge of the second surface outward.

[0010] Preferably, in the first grinding step, while the first grinding wheel and the workpiece are moved relative to each other in a direction perpendicular to the second surface, 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.

[0011] Furthermore, preferably, in the second grinding step, while the second grinding wheel and the workpiece are moved relative to each other 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 together in a direction parallel to the second surface.

[0012] [Invention Benefits] In one aspect of the grinding method of the present invention, after grinding the workpiece with a first grinding wheel equipped with a first grinding stone to form a first thin plate portion and a first thick plate portion, the first thin plate portion and the first thick plate portion are ground together with a second grinding wheel equipped with a second grinding stone to form a second thin plate portion and a second thick plate portion. The second grinding stone contains smaller abrasive grains than the first grinding stone, so the entire second thin plate portion becomes an effective area without the damaged layer caused by the first grinding stone.

[0013] Furthermore, since the volume of the portion of the first thick plate removed by the second grinding wheel is sufficiently small, the grinding time required is not significantly longer, for example, compared to conventional grinding methods where the second grinding wheel only grinds the central area of ​​the first thin plate while leaving the first thick plate completely un-ground. Therefore, according to one aspect of the grinding method of the present invention, compared to conventional grinding methods, a large amount of time is not required, and the effective area usable in the product is maximized.

[0014] Furthermore, in one aspect of the grinding method of the present invention, when the first thin plate portion and the first thick plate portion are ground together with the second grinding wheel, the second grinding stone contacts the area remaining on the second surface of the first thick plate portion. The area on the second surface is the area that is separated from the inner edge of the second surface by the width of the second grinding stone (the width of the second grinding stone in the direction of the second diameter) or more.

[0015] Therefore, since the point in time when the innermost part of the second grinding stone (located in the direction of the second diameter and the innermost part) contacts the first thick plate must exist, the wear of the inner part can be appropriately carried out in accordance with the wear of the outer part of the second grinding stone, thereby suppressing the partial wear that only occurs on the outer part of the second grinding stone. Simple Explanation of the Diagram

[0016] Figure 1 is a schematic perspective view showing the protective component being attached to a circular workpiece. Figure 2 is a schematic cross-sectional view showing the workpiece being held on the chuck table by a protective member. Figure 3 is a schematic cross-sectional view showing the beginning of the grinding of the workpiece by the first grinding wheel. Figure 4 is a schematic cross-sectional view showing the grinding of the workpiece by the first grinding wheel. Figure 5 is a schematic cross-sectional view of a portion of the workpiece after it has been ground by the first grinding wheel. Figure 6 is a schematic cross-sectional view showing the beginning of the grinding of the workpiece by the second grinding wheel. Figure 7 is a schematic cross-sectional view showing the grinding of the workpiece by the second grinding wheel. Figure 8 is a schematic cross-sectional view of a portion of the workpiece after it has been ground by the second grinding wheel. Figure 9 is a schematic cross-sectional view of a portion of the workpiece after being ground by the first grinding wheel in a modified grinding method. Figure 10 is a schematic cross-sectional view of a portion of the workpiece after being ground by the second grinding wheel in a modified grinding method. Implementation

[0017] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the grinding method of this embodiment, firstly, a protective member is attached to a circular plate-shaped workpiece that is to be ground (attachment step). FIG1 is a perspective view schematically showing the state in which the protective member 21 is attached to the circular plate-shaped workpiece 11.

[0018] The workpiece 11 is, for example, a wafer in the shape of a disc made of semiconductors such as silicon (Si). That is, the workpiece 11 has a circular front side (first side) 11a and a circular back side (second side) 11b opposite to the front side 11a. The front side 11a of the workpiece 11 is divided into multiple small regions by multiple intersecting dicing lines (pre-defined dividing lines) 13, and integrated circuit (IC) and other components 15 are formed in each small region.

[0019] In the grinding method of this embodiment, the portion of the workpiece 11 corresponding to the area where the element 15 is formed (element area) is ground from the back side 11b, and a portion of the workpiece 11 becomes thinner. That is, in the grinding method of this embodiment, the workpiece 11 is machined into a concave shape from the back side 11b.

[0020] Furthermore, although a wafer made of semiconductors such as silicon is used as the workpiece 11 in this embodiment, the material, shape, structure, and size of the workpiece 11 are not limited to this form. For example, a substrate made of other materials such as semiconductors, ceramics, resins, or metals can be used as the workpiece 11. Similarly, the type, number, shape, structure, size, and arrangement of the components 15 are not limited to the above-described form. The workpiece 11 may also be without components 15.

[0021] The protective member 21 attached to the workpiece 11 is typically a circular film (thin film) with a diameter approximately the same as that of the workpiece 11, a resin substrate, or a wafer of the same or different type as the workpiece 11. An adhesive layer is provided on the front side 21a of this protective member 21 to provide adhesion to the workpiece 11.

[0022] Therefore, as shown in FIG1, by making the front side 21a of the protective member 21 in close contact with the front side 11a of the workpiece 11, the protective member 21 is attached to the front side 11a of the workpiece 11. In this way, the impact applied to the front side 11a when grinding the workpiece 11 from the back side 11b is buffered by the protective member 21, thereby protecting the components 15, etc. of the workpiece 11.

[0023] After the protective member 21 is attached to the front surface 11a of the workpiece 11, the workpiece 11 is held on the chuck table through the protective member 21 (holding step). Figure 2 is a schematic cross-sectional view showing the state in which the workpiece 11 is held on the chuck table 4 of the grinding apparatus 2 through the protective member 21. Furthermore, in the following steps, the grinding apparatus 2 shown in Figure 2 is used.

[0024] The grinding apparatus 2 includes a chuck table 4 configured to hold the workpiece 11. The chuck table 4 comprises, for example, a circular plate-shaped frame 6 formed using a metal such as stainless steel. A recess 6a is formed on the upper surface of the frame 6, the recess 6a having a circular opening at its upper end. A retaining plate 8 is fixed to this recess 6a, the retaining plate 8 being a porous circular plate made of ceramic or the like.

[0025] The upper surface 8a of the retaining plate 8 is configured, for example, in a shape equivalent to the lateral side of a cone, and functions as a retaining surface for holding the workpiece 11, etc. Furthermore, the height difference (height difference) between the center 8b of the upper surface 8a of the retaining plate 8 (corresponding to the apex of the cone) and the outer periphery 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 contacts the upper surface (retaining surface) 8a of this retaining plate 8.

[0026] The lower surface of the retaining plate 8 is connected to a suction source (not shown) such as an injector through a flow path 6b provided inside the frame 6 and a valve (not shown) disposed outside the frame 6. Therefore, if the valve is opened and the suction source is subjected to negative pressure while the back surface 21b of the protective member 21 is in contact with the upper surface 8a of the retaining plate 8, the back surface 21b of the protective member 21 is attracted by the chuck table 4. That is, the workpiece 11 is held on the chuck table 4 with its back surface 11b exposed above through the protective member 21.

[0027] A rotary drive source (not shown) such as a motor is connected to the lower part of the frame 6. The chuck table 4 rotates about an axis in the vertical direction or an axis slightly inclined relative to the vertical direction, with the center 8b of the upper surface 8a as the center of rotation, using the force generated by this rotary drive source. Furthermore, the frame 6 is supported by a chuck table moving mechanism (not shown), and the chuck table 4 moves horizontally using the force generated by this chuck table moving mechanism.

[0028] After the workpiece 11 is held by the chuck table 4 through the protective member 21, the area of ​​the workpiece 11 corresponding to the area where the element 15 is formed (the element area) is rough-ground from the back side 11b (first grinding step). Figure 3 is a schematic cross-sectional view showing the state at which the grinding of the workpiece 11 begins, and Figure 4 is a schematic cross-sectional view showing the state during which the grinding of the workpiece 11 is performed. In addition, in Figures 3 and 4, the side view of a portion of the elements is shown for ease of explanation.

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

[0030] At the lower end of the spindle 12, for example, a circular plate-shaped mounting member 14 with a diameter smaller than that of the workpiece 11 is provided. A first grinding wheel (rough grinding wheel) 16 with a diameter approximately equal to that of the mounting member 14 is fixed to the lower surface of the mounting member 14 by bolts (not shown) or the like.

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

[0032] If the workpiece 11 is ground by the first grinding wheel 16 containing the first grinding stone 20, the amount of workpiece 11 that can be removed per unit time increases. On the other hand, it becomes easier to form a damaged layer containing damage or deformation on the ground surface of the workpiece 11. A rotary drive source (not shown) such as a motor is connected to the upper end of the spindle 12. The first grinding wheel 16 rotates about an axis in the vertical direction or an axis slightly inclined relative to the vertical direction by the force generated by this rotary drive source.

[0033] A nozzle (not shown) is provided next to or inside the first grinding wheel 16. The nozzle is configured to supply a grinding liquid (typically water) to the first grinding stone 20 or the like for grinding. The spindle housing is supported, for example, by a first grinding unit moving mechanism (not shown), by which the first grinding unit 10 moves vertically by the force generated by the first grinding unit moving mechanism.

[0034] When grinding the workpiece 11 with the first grinding unit 10 (first grinding wheel 16), firstly, the chuck table 4 is moved directly below the first grinding unit 10. More specifically, the chuck table moving mechanism moves the chuck table 4 horizontally such that the first grinding wheel 16 (all of the first grinding stones 20) is positioned directly above the area where the element 15 is formed.

[0035] Subsequently, the chuck table 4 and the first grinding wheel 16 rotate, and the first grinding unit 10 (first grinding wheel 16) descends. That is, the first grinding wheel 16 and the workpiece 11 rotate relative to each other while moving relative to each other in a vertical direction (first direction) intersecting the back surface 11b of the workpiece 11. At this time, liquid is supplied from the nozzle to the first grinding stone 20, etc. Thus, as shown in FIG3, the first grinding stone 20 contacts the workpiece 11 from the back surface 11b side, and the grinding of the workpiece 11 begins.

[0036] Furthermore, there are no significant limitations on specific grinding conditions. For example, in order 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 descent speed (grinding feed rate) of the first grinding unit 10 is set to 0.8 μm / s to 10 μm / s, typically 6.0 μm / s.

[0037] If the workpiece 11 is ground, as shown in FIG4, the portion of the workpiece 11 that is in contact with the first grinding stone 20 will become thinner, while maintaining the thickness of the remaining portion. That is, the portion of the workpiece 11 corresponding to the area where the element 15 is formed will become thinner, becoming a first thin plate portion 11c in the shape of a circular plate. Furthermore, the thickness of the portion of the workpiece 11 corresponding to the following area (outer peripheral area) will be maintained, becoming a first thick plate portion 11d in the shape of an annulus surrounding the first thin plate portion 11c, the area (outer peripheral area) surrounding the area where the element 15 is formed.

[0038] Figure 5 is a schematic cross-sectional view of a portion of the workpiece 11 after being ground by the first grinding wheel 16. As shown in Figure 5, a damaged layer 11e containing damage or deformation exists on the back side 11b side (ground surface) of the first thin plate portion 11c that has been ground by the first grinding stone 20 containing larger abrasive grains. Because the damaged layer 11e reduces the mechanical strength (flexural strength, etc.) of the workpiece 11, the area containing this damaged layer 11 cannot be used as a product.

[0039] Therefore, after grinding by 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 side 11b in a manner that removes the damaged layer 11e (second grinding step). Figure 6 is a schematic cross-sectional view showing the state of the workpiece 11 at the beginning of grinding, and Figure 7 is a schematic cross-sectional view showing the state of the workpiece 11 being ground. In addition, in Figures 6 and 7, the side view of some elements is shown for ease of explanation.

[0040] As shown in Figures 6 and 7, a second grinding unit (fine grinding unit) 30, different from the first grinding unit 10, is arranged above the chuck table 4 in the grinding apparatus 2. The second grinding unit 30 includes, for example, a cylindrical spindle housing (not shown). A cylindrical spindle 32 is accommodated in the space inside the spindle housing.

[0041] At the lower end of the spindle 32, for example, a circular plate-shaped mounting member 34 with a diameter smaller than that of the workpiece 11 is provided. A second grinding wheel (fine grinding wheel) 36 with a diameter approximately equal to that of the mounting member 34 is fixed to the lower surface of the mounting member 34 by bolts (not shown) or the like.

[0042] The second grinding wheel 36 includes an annular wheel base 38 formed of metals such as stainless steel and aluminum. Multiple second grinding stones (fine grinding stones) 40 are fixed to the annular lower surface of the wheel base 38 along its circumference. That is, the multiple second grinding stones 40 are arranged in an annular region with a diameter (second diameter) smaller than the workpiece 11.

[0043] Each of the second grinding stones 40 has, for example, the following structure: smaller abrasive grains, such as diamond, are dispersed in a binder made of resin or the like. Specifically, the size (typically the average grain size) of the abrasive grains contained in the second grinding stone 46 is smaller than the size of the abrasive grains contained in the first grinding stone 20.

[0044] If the workpiece 11 is ground with the second grinding wheel 36, which includes the second grinding stone 40, the amount of workpiece 11 removed per unit time is less than that when the workpiece 11 is ground with the first grinding wheel 16. On the other hand, it is difficult to create a destructive layer. A rotary drive source (not shown) such as a motor is connected to the upper end of the spindle 32. The second grinding wheel 36 rotates about an axis in the vertical direction or an axis slightly inclined relative to the vertical direction by the force generated by this rotary drive source.

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

[0046] When the workpiece 11 is being ground by the second grinding unit 30 (second grinding wheel 36), the chuck table 4 first moves to a position directly below the second grinding unit 30. More specifically, the chuck table moving mechanism moves the chuck table 4 horizontally such that any of the plurality of second grinding stones 40 of the second grinding wheel 36 is positioned directly above a region that is further outward than 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 4 is moved horizontally by the chuck table moving mechanism, which lowers the second grinding unit 30 so that the second grinding stone 40 can contact the area on the back surface 11b of the first thick plate portion 11d. The area on the back surface 11b is the area separated from the inner edge of the back surface 11b by a width W or more of the second grinding stone 40. Here, the width W of the second grinding stone 40 is the width of the second grinding stone 40 in the direction of the diameter of the annular area in which the second grinding stones 40 are arranged, and is, for example, about 1 mm to 5 mm.

[0048] Subsequently, the chuck table 4 and the second grinding wheel 36 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 relative to each other in a vertical direction (second direction) intersecting the back surface 11b of the workpiece 11. At this time, liquid is supplied from the nozzle to the second grinding stone 40, etc.

[0049] Thus, as shown in FIG6, the second grinding stone 40 contacts the first thick plate portion 11d from the back side 11b side and begins grinding the workpiece 11. As described above, in this embodiment, the second grinding stone 40 contacts a region existing on the back side 11b of the first thick plate portion 11d, the region on the back side 11b being a region of width W or more of the second grinding stone 40 separated from the inner edge of the back side 11b towards the outside.

[0050] That is, since the moment when the innermost part of the width W of the second grinding stone 40 contacts the first thick plate portion 11d must exist, the wear of the inner part can be appropriately carried out in accordance with the wear of the outer part of the second grinding stone 40, thereby suppressing the partial wear that only occurs on the outer part of the second grinding stone 40.

[0051] Furthermore, there are no major restrictions on specific grinding conditions. For example, in order to achieve efficient and high-precision 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] After the workpiece 11 is ground and the inner portion of the first thick plate portion 11d that is in contact with the second grinding stone 40 is removed, the second grinding stone 40 also contacts the first thin plate portion 11c. That is, in this embodiment, after only grinding the first thick plate portion 11d, the area including the first thin plate portion 11c (and the first thick plate portion 11d) is ground from the back side 11b.

[0053] Here, the grinding load applied to the second grinding stone 40 during the stage of grinding only the first thick plate portion 11d is less than the grinding load applied to the second grinding stone 40 during the stage of grinding the region including the first thin plate portion 11c. Therefore, compared to the stage of grinding the region including the first thin plate portion 11c, the descent speed (grinding feed rate) of the second grinding unit 30 can be increased during the stage of grinding only the first thick plate portion 11d.

[0054] For example, the descent speed of the second grinding unit 30 is set to 0.8 μm / s to 5.0 μm / s for the stage of grinding only the first thick plate portion 11d, and the descent speed of the second grinding unit 30 is set to 0.1 μm / s to 0.8 μm / s for the stage of grinding the region including the first thin plate portion 11c. In this way, by increasing the descent speed of the second grinding unit 30 in the stage of grinding only the first thick plate portion 11d, the grinding time required will not be significantly longer, for example, compared to conventional grinding methods that do not grind the first thick plate portion 11d.

[0055] If the workpiece 11 is further ground, as shown in FIG7, the portion of the workpiece 11 that is in contact with the second grinding stone 40 will become thinner, while maintaining the thickness of the remaining portion. That is, the portion of the workpiece 11 corresponding to the area where the element 15 is formed becomes thinner, becoming a second thin plate portion 11f in the shape of a circular plate. Furthermore, the thickness of the portion of the workpiece 11 corresponding to the following area (outer peripheral area) is maintained, becoming a second thick plate portion 11g in the shape of an annulus surrounding the second thin plate portion 11f, the area (outer peripheral area) surrounding the area where the element 15 is formed.

[0056] Figure 8 is a schematic cross-sectional view of a portion of the workpiece 11 after being ground by the second grinding wheel 36. As shown in Figure 8, no substantial damaging layer 11e remains on the back side 11b side (ground surface) of the second thin plate portion 11f ground by the second grinding stone 40 containing smaller abrasive grains. Therefore, the entire second thin plate portion 11f becomes an effective area usable in the product.

[0057] As shown in Figure 8, the edge of the second thin plate portion 11f is formed to a distance D further outward than the edge of the first thin plate portion 11c, where the distance D is a value greater than or equal to the width W of the second grinding stone 40. Similarly, the inner edge of the second thick plate portion 11g is formed to a distance D further outward than the inner edge of the first thick plate portion 11d. That is, 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, become equal to twice the distance D.

[0058] For example, as long as the area of ​​the workpiece 11 in which the element 15 is formed is included in the effective area, all of the element 15 can be used as a product. In this case, the diameter of the second thin plate portion 11f is greater than or equal to the diameter of the area in which the element 15 is formed. Therefore, the diameter of the first thin plate portion 11c may sometimes become smaller than the diameter of the area in which the element 15 is formed.

[0059] As described above, in the grinding method of this embodiment, after the workpiece 11 is ground by 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, the first thin plate portion 11c and the first thick plate portion 11d are ground together by the second grinding wheel 36 equipped with the second grinding stone 40 to form the second thin plate portion 11f and the second thick plate portion 11g. The second grinding stone 40 contains smaller abrasive grains than the first grinding stone 20. Therefore, the entire second thin plate portion 11f becomes an effective area without the damaged layer 11e caused by the first grinding stone 20.

[0060] 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 required is not significantly longer compared to conventional grinding methods where the second grinding wheel 36 only grinds the central area of ​​the first thin plate portion 11c while the first thick plate portion 11d is not ground at all. Therefore, the grinding method according to this embodiment requires less time compared to conventional grinding methods and maximizes the usable area in the product.

[0061] Furthermore, in the grinding method of this embodiment, when the first thin plate portion 11c and the first thick plate portion 11d are ground together with the second grinding wheel 36, the second grinding stone 40 is brought into contact with the area on the back surface 11b of the first thick plate portion 11d. The area on the back surface 11b is the area that is separated from the inner edge of the back surface (second surface) 11b by the width W of the second grinding stone 40 (the width of the second grinding stone 40 in the direction of the diameter (second diameter) of the annular area in which the second grinding stone 40 is arranged) from the outer edge.

[0062] Therefore, since the innermost part of the second grinding stone 40 (located in the direction of the diameter (second diameter) of the annular area where the second grinding stones 40 are arranged) must contact the first thick plate portion 11d at a certain point, the wear of the inner part can be appropriately carried out in accordance with the wear of the outer part of the second grinding stone 40, thereby suppressing the partial wear that only occurs on the outer part of the second grinding stone 40.

[0063] Furthermore, the present invention can be modified and implemented in various ways without being limited to the embodiments described above. As mentioned above, there is a deviation of more than the width W (distance D) of the second grinding stone 40 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.

[0064] Therefore, the diameter (first diameter) of the annular region of the first grinding stone 20 and the diameter (second diameter) of the annular region of the second grinding stone 40 may not be equal. For example, the diameter of the annular region of the second grinding stone 40 may be larger than the diameter of the annular region of the first grinding stone 20.

[0065] Furthermore, while grinding the workpiece 11 with the first grinding wheel 16, the first grinding wheel 16 and the workpiece 11 can be moved relative to each other in a direction perpendicular to the back surface 11b, while the center of rotation of the first grinding wheel 16 and the center of rotation of the workpiece 11 are brought closer together in a direction parallel to the back surface 11b. Figure 9 is a schematic cross-sectional view of a portion of the workpiece 11 after being ground by the first grinding wheel 16 in this modified grinding method.

[0066] As shown in Figure 9, in this modified example, the space defined by the first thin plate portion 11c and the first thick plate portion 11d forms an inverted frustum shape, and the inner side surface of the first thick plate portion 11d is inclined relative to the back surface 11b of the workpiece 11. That is, since the outer side surface of the first grinding stone 20 does not contact the workpiece 11, the uneven wear of the first grinding stone 20 can be suppressed.

[0067] Similarly, when grinding the workpiece 11 with the second grinding wheel 36, the second grinding wheel 36 and the workpiece 11 can be moved relative to each other in a direction perpendicular to the back surface 11b, while the center of rotation of the second grinding wheel 36 and the center of rotation of the workpiece 11 are brought closer together in a direction parallel to the back surface 11b. Figure 10 is a schematic cross-sectional view of a portion of the workpiece 11 after being ground by the second grinding wheel 36 in this modified grinding method.

[0068] As shown in Figure 10, in this modified example, the space defined by the second thin plate portion 11f and the second thick plate portion 11g forms an inverted frustum shape, and the inner side surface of the second thick plate portion 11g is inclined relative to the back surface 11b of the workpiece 11. That is, since the outer side surface of the second grinding stone 40 does not contact the workpiece 11, the uneven wear of the second grinding stone 40 can be further suppressed.

[0069] Furthermore, a grinding apparatus equipped with two chuck tables can also be used to grind the workpiece. The two chuck tables are: a chuck table that holds the workpiece 11 while it is being ground by the first grinding wheel 16; and another chuck table that holds the workpiece 11 while it is being ground by the second grinding wheel 36. Similarly, a grinding apparatus equipped with a first grinding unit 10 and another grinding apparatus equipped with a second grinding unit 30 can also be used to grind the workpiece 11.

[0070] Furthermore, the above-described embodiments and variations in construction and method can be appropriately modified and implemented as long as they do not depart from the purpose of this invention.

[0071] 11: Workpiece 11a: Front (First Side) 11b: Reverse side (second side) 11c: First thin plate section 11d: First thick plate section 11e: Destruction Layer 11f: Second thin plate section 11g: Second thickest plate section 13: Pre-defined dividing line (cutting track) 15: Components 21: Protective components 21a: Front 21b: Back 2:Grinding device 4: Chuck platform 6: Frame 6a: concave part 6b:Flow path 8: Holding plate 8a: Top surface (retaining surface) 8b: Center 10: First Grinding Unit (Rough Grinding Unit) 12: Spindle 14: Installation components 16: First grinding wheel (rough grinding wheel) 18: Wheel base platform 20: First grinding stone (coarse grinding stone) 30: Second Grinding Unit (Fine Grinding Unit) 32: Spindle 34: Installation components 36: Second grinding wheel (finishing grinding wheel) 38: Wheel base platform 40: Second grinding stone (fine grinding stone)

Claims

1. A grinding method applicable to grinding a circular plate-shaped workpiece having a first surface and a second surface opposite to the first surface from the second surface, comprising: a first grinding step in which a first grinding wheel having a plurality of first grinding stones arranged in an annular region smaller than a first diameter of the workpiece rotates relative to the workpiece while moving relative to it in a first direction intersecting the second surface, thereby causing the first grinding stones to contact the workpiece from the second surface side and grind the workpiece, wherein the workpiece forms a first thin plate portion in the shape of a circular plate and a first thick plate portion in the shape of an annular shape surrounding the first thin plate portion, wherein... The plurality of first grinding stones each contain abrasive grains; and a second grinding step, which, after the first grinding step, involves a second grinding wheel with a plurality of second grinding stones arranged in an annular region smaller than the second diameter of the workpiece, rotating relative to the workpiece while moving in a second direction intersecting the second surface, thereby causing the second grinding stones to contact the first thick plate portion and the first thin plate portion from the second surface side and grind the workpiece, resulting in a second thin plate portion with a diameter larger than the first thin plate portion and an annular second thick plate portion surrounding the second thin plate portion, wherein the plurality of second grinding stones each contain smaller abrasive grains than the first grinding stones. In the second grinding step, the second grinding stone is brought into contact with the area remaining on the second surface of the first thick plate portion. The area on the second surface is the area that is separated from the inner edge of the second surface by the width of the second grinding stone in the direction of the second diameter. While the second grinding wheel and the workpiece are moved relative to each other 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 together in a direction parallel to the second surface.

2. The grinding method as described in Request 1, wherein, In the first grinding step, while the first grinding wheel and the workpiece are moved relative to each other in a direction perpendicular to the second surface, 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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