Grinding method for workpieces

Abstract

This invention provides a grinding method for a workpiece that can prevent dulling and uneven wear of the grinding wheel. [Solution] The first grinding step (S20) involves grinding the workpiece (10) to form a curved surface (11) while the rotation axis of the grinding wheel (42) is tilted relative to the rotation axis (22) of the holding surface (21) of the chuck table (20) that holds the workpiece (10), and leaving a flat surface (12) on at least one of the center or outer circumference of the workpiece (10) that is not in contact with the grinding wheel (41) of the grinding wheel (42). The second grinding step (S30) involves bringing the grinding wheel (51) of the grinding wheel (52) into contact with the flat surface (12) and then grinding the workpiece (10) to a predetermined thickness.

Description

Technical Field

[0001] The present invention relates to a method for grinding a workpiece.

Background Art

[0002] With the miniaturization of semiconductor devices progressing, wafers (workpieces) on which semiconductor devices are formed are, for example, ground to a thickness of 100 μm or less. The thinner the wafer, the more likely it is that warping occurs in the wafer after grinding due to grinding distortion generated on the grinding surface, and it is also more likely to be damaged, making it difficult to handle during conveyance and subsequent processes. A so-called TAIKO (registered trademark) grinding technique is used in which only the area excluding the outer peripheral edge of the wafer is ground to form a circular recess corresponding to the device area on the back surface of the wafer and an annular convex portion corresponding to the outer peripheral surplus area (see, for example, Patent Document 1).

[0003] On the other hand, when grinding a workpiece with a high grinding load, there is a problem that the grinding wheel becomes clogged and the grinding force decreases. In the grinding method described in Patent Document 2, the workpiece is ground into a concave shape with a rough grinding wheel to reduce the volume of the workpiece removed by the finish grinding wheel, and the rough grinding surface is exposed during grinding with the second grinding wheel so that the second grinding wheel contacts the rough grinding surface, thereby preventing clogging of the grinding wheel during finish grinding.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the method described in Patent Document 2, there was a problem in that the grinding wheel, which grinds the concave workpiece, had to make contact with the workpiece surface which was not flat, resulting in uneven wear of the grinding wheel.

[0006] This invention has been made in view of the above points, and aims to provide a grinding method that can prevent dulling and uneven wear of the grinding wheel. [Means for solving the problem]

[0007] A method for grinding a workpiece according to one aspect of the present invention includes a first grinding step in which the workpiece is ground with the rotation axis of a first grinding wheel tilted relative to the rotation axis of the holding surface of a holding table that holds the workpiece, thereby forming a curved surface on the workpiece and leaving a flat surface on at least one of the center or outer circumference of the workpiece that does not come into contact with the grinding wheel portion of the first grinding wheel. The method also includes a second grinding step in which the grinding wheel portion of a second grinding wheel is brought into contact with the flat surface, and the workpiece is ground to a predetermined thickness. [Effects of the Invention]

[0008] According to the present invention, it is possible to prevent dulling and uneven wear of the grinding wheel during the grinding of a workpiece. [Brief explanation of the drawing]

[0009] [Figure 1] This is a perspective view of the workpiece (wafer) according to the first embodiment. [Figure 2] This is a perspective view showing an example of the configuration of a grinding unit according to the first embodiment. [Figure 3] This is a flowchart showing the flow of the grinding method for a workpiece according to the first embodiment. [Figure 4] This is a diagram illustrating the pre-grinding step according to the first embodiment. [Figure 5] This is a diagram illustrating the pre-grinding step according to the first embodiment. [Figure 6] This is a diagram illustrating the first grinding step according to the first embodiment. [Figure 7] It is a cross-sectional view for explaining a workpiece after a first grinding step according to the first embodiment. [Figure 8] It is a diagram for explaining a second grinding step according to the first embodiment. [Figure 9] It is a diagram for explaining a contact surface between a grinding wheel portion and a flat surface in the second grinding step of the first embodiment. [Figure 10] It is a diagram for explaining a second grinding step according to a comparative example. [Figure 11] It is a diagram for explaining a contact surface between a grinding wheel portion and a flat surface in the second grinding step of the comparative example. [Figure 12] It is a diagram for explaining a second grinding step according to the first embodiment. [Figure 13] It is a diagram for explaining a second grinding step according to the first embodiment. [Figure 14] It is a diagram for explaining a pre-grinding step according to the second embodiment. [Figure 15] It is a diagram for explaining a pre-grinding step according to the second embodiment. [Figure 16] It is a diagram for explaining a first grinding step according to the second embodiment. [Figure 17] It is a cross-sectional view for explaining a workpiece after a first grinding step according to the second embodiment. [Figure 18] It is a diagram for explaining a second grinding step according to the second embodiment. [Figure 19] It is a diagram for explaining a second grinding step according to the second embodiment.

MODE FOR CARRYING OUT THE INVENTION

[0010] Hereinafter, embodiments will be described with reference to the drawings. (First Embodiment)

[0011] FIG. 1 is a perspective view of a workpiece (wafer) according to the first embodiment. The workpiece 10 is, for example, a wafer such as a disk-shaped semiconductor wafer with silicon as the base material, or an optical device wafer with sapphire, SiC (silicon carbide), etc. as the base material.

[0012] As shown in FIG. 1, the wafer 10 has a device region 103 and an outer peripheral surplus region 104 surrounding the device region 103 on the surface 105. In the device region 103, devices 107 are formed in regions partitioned by a plurality of division planned lines 106 that intersect each other. The device 107 is an integrated circuit such as an IC (Integrated Circuit) or LSI (Large Scale Integration). The outer peripheral surplus region 104 is a region that surrounds the device region 103 on the surface 105 of the wafer 10 and in which no device 107 is formed. A film such as an oxide film or a nitride film may be formed on the back surface 101 side of the wafer 10.

[0013] Next, a grinding unit used for grinding the workpiece 10 will be described. FIG. 2 is a perspective view showing a configuration example of the grinding unit according to the first embodiment. In the present embodiment, the grinding unit 30 is used for the pre-grinding step, the first grinding step, and the second grinding step described later.

[0014] The grinding unit 30 includes a columnar spindle 36. A rotational drive source (not shown) such as a motor for rotating the spindle 36 is connected to the base end portion (upper end portion) of the spindle 36. When the rotational drive source is driven, the spindle 36 rotates around the rotation axis �5.

[0015] A disk-shaped wheel mount 33 made of metal or the like is fixed to the tip end portion (lower end portion) of the spindle 36. A grinding wheel corresponding to the purpose of grinding is mounted at the lower end of the wheel mount 33. In the present embodiment, any one of the grinding wheel 32, the grinding wheel 42, and the grinding wheel 52 is mounted.

[0016] The grinding wheel 32, which serves as the third grinding wheel, has an annular base 34 and a plurality of grinding wheels 31 fixed to the lower surface of the annular base 34. The annular base 34 is made of a metal such as aluminum or stainless steel and is formed to be approximately the same diameter as the wheel mount 33. The upper surface of the annular base 34 is fixed to the lower surface of the wheel mount 33.

[0017] Multiple grinding wheels 31 are arranged circumferentially around the outer edge of the annular base 34. The lower surface of each grinding wheel 31 constitutes a grinding surface 311 for grinding the wafer 10. For example, the grinding wheels 31 are formed in a rectangular parallelepiped shape and arranged in an annular pattern at roughly equal intervals along the circumferential direction of the annular base 34. That is, the grinding surfaces 311 of the multiple grinding wheels 31 form an annular shape. Each grinding wheel 31 contains abrasive grains made of diamond, cBN (cubic boron nitride), etc., and a binder (bonding material) such as a metal bond, resin bond, or vitrified bond to fix the abrasive grains. However, there are no restrictions on the material, shape, structure, size, etc., of the grinding wheel 31. The number of grinding wheels 31 can also be set arbitrarily.

[0018] The first grinding wheel, the grinding wheel 42, has an annular base 34 and a plurality of grinding wheels 41 fixed to the lower surface of the annular base 34. The lower surface of the grinding wheels 41 constitutes a grinding surface 411 for grinding the workpiece 10. The plurality of grinding wheels 41 are arranged in an annular shape at roughly equal intervals along the circumferential direction of the annular base 34, similar to the grinding wheel 31. The abrasive grains of the grinding wheels 41 are equivalent to those of the grinding wheel 31.

[0019] The grinding wheel 52, which serves as the second grinding wheel, has an annular base 34 and a plurality of grinding wheels 51 fixed to the lower surface of the annular base 34. The lower surface of the grinding wheels 51 constitutes a grinding surface 511 for grinding the workpiece 10. The plurality of grinding wheels 51 are arranged in an annular shape at roughly equal intervals along the circumferential direction of the annular base 34, similar to the grinding wheel 31. The abrasive grains of the grinding wheels 51 are finer than the abrasive grains of the grinding wheels 31 and 41.

[0020] The grinding wheels 32, 42, and 52 rotate around the rotation axis 35 by power transmitted from a rotation drive source (not shown) via the spindle 36 and wheel mount 33. That is, the rotation axis 35 of the spindle 36 corresponds to the rotation axis of the wheel mount 33 and the grinding wheels 32, 42, and 52. When the grinding wheels 32, 42, and 52 are rotated, the multiple grinding wheels 31, 41, and 51 each revolve along an annular trajectory (path) that is roughly parallel to the plane perpendicular to the rotation axis 35, with the rotation axis 35 as the center. The grinding wheel 32 is formed such that the outermost diameter 316 of the rotational trajectory of the multiple grinding wheels 31, that is, the annular outer diameter formed by the grinding surfaces 311 of the multiple grinding wheels 31, satisfies the following condition: The multiple grinding wheels 31 are arranged such that the diameter 316 is greater than the radius 108 of the device region 103 of the workpiece 10 and less than the diameter of the device region 103.

[0021] Similar to the grinding wheel 32, the grinding wheels 42 and 52 are formed such that the outermost diameters 416 and 516 of the rotational trajectories of the multiple grinding wheels 41 and 51 are greater than the radius 108 of the device region 103 of the workpiece 10 and smaller than the diameter of the device region 103. In the following description, the lengths of the grinding surfaces 311, 411, and 511 in the direction from the center of the annular base 34 toward the outer circumference are referred to as the widths 312, 412, and 512 of the grinding surfaces 311, 411, and 511.

[0022] Next, the grinding method in this embodiment will be described with reference to Figure 3. Figure 3 is a flowchart showing the flow of the grinding method for a workpiece according to the first embodiment. The grinding method for a workpiece according to this embodiment includes three steps, as shown in Figure 3. Each step will be described in detail below.

[0023] First, in the pre-grinding step, the back surface of the workpiece is ground to a predetermined thickness (S10). Figures 4 and 5 illustrate the pre-grinding step according to the first embodiment. In this embodiment, in the pre-grinding step, the back surface 101 of the workpiece 10 corresponding to the device region 103 is ground with the grinding wheel 32 to form a circular recess 13. Since the grinding wheel 32 uses a grinding wheel 31 with coarse abrasive grains, so-called rough grinding is performed in the pre-grinding step.

[0024] First, as shown in Figure 4, the workpiece 10 is held by the chuck table 20, which acts as a holding table. Specifically, the workpiece 10 is placed on the chuck table 20 so that its surface 105 is in contact with the upper surface (holding surface) 21 of the chuck table 20, and the workpiece 10 is sucked and held to the chuck table 20 by a suction mechanism (not shown) provided on the chuck table 20. In other words, the back surface 101 of the workpiece 10 is exposed.

[0025] Furthermore, protective material such as tape may be attached to the surface 105 of the workpiece 10 to protect the device 107. If protective material is attached, the workpiece 10 is held in the chuck table 20 such that the protective material and the holding surface 21 of the chuck table 20 are in contact. A rotational drive source (not shown), such as a motor, is connected to the lower surface of the chuck table 20 to rotate the chuck table 20. When the rotational drive source is driven, the chuck table 20 rotates around the rotation axis 22.

[0026] Meanwhile, the grinding unit 30 has a grinding wheel 32 attached to the lower end of the wheel mount 33, and is positioned above the chuck table 20 such that the grinding surface 311 of the grinding wheel 31 faces the back surface 101 of the workpiece 10.

[0027] Next, as shown in Figure 5, the grinding unit 30 is lowered so that the grinding surface 311 of the grinding wheel 31 comes into contact with the back surface 101 of the workpiece 10. At this time, the grinding surface 311 of the grinding wheel 31 is adjusted to be parallel to the holding surface 21 of the chuck table 20. That is, the rotation axis 35 of the grinding wheel 32 and the rotation axis 22 of the chuck table 20 are adjusted to be in the same direction. Then, the chuck table 20 is rotated and the grinding wheel 32 is rotated while being lowered. As a result, the back surface 101 of the workpiece 10 corresponding to the device region 103 is ground by the grinding wheel 31. At this time, the operation of the grinding unit 30 is controlled so that the grinding surface 311 of the grinding wheel 31 does not come into contact with the back surface 101 of the workpiece 10 corresponding to the outer peripheral excess region 104. The back surface 101 of the workpiece 10 is ground to a predetermined depth.

[0028] Once the pre-grinding steps described above are completed, an annular protrusion 14 is formed on the back surface 101 of the workpiece 10 corresponding to the outer peripheral excess region 104, and a circular recess 13 is formed on the back surface 101 of the workpiece 10 corresponding to the device region 103.

[0029] Next, in the first grinding step, the back surface of the workpiece is further ground to form a curved shape (S20). Figures 6 and 7 illustrate the first grinding step according to the first embodiment. In this embodiment, in the first grinding step, the back surface 101 of the workpiece 10 corresponding to the device region 103 is ground with the grinding wheel 42 to form a curved surface 11 and a flat surface 12.

[0030] As shown in Figure 6, in the first grinding step, a grinding unit 30 is used, in which a grinding wheel 42 is mounted on the lower end of a wheel mount 33. Since the grinding wheel 42 uses a grinding disc 41 with coarse abrasive grains, so-called rough grinding is performed in the first grinding step. When the grinding surface 311 of the grinding disc 31 is brought into contact with the back surface 101 (bottom surface of the circular recess 13) of the workpiece 10, the grinding unit 30 is positioned such that the rotation axis 35 of the grinding wheel 42 has a predetermined inclination with respect to the rotation axis 22 of the chuck table 20. Figure 6 shows, as an example, a case in which the grinding unit 30 is positioned such that the rotation axis 35 has a predetermined inclination in the front-to-back direction of the paper with respect to the rotation axis 22. Alternatively, the inclination of the rotation axis 22 may be adjusted by adjusting the position of the chuck table 20 without changing the inclination of the rotation axis 35 of the grinding wheel 42.

[0031] Then, the chuck table 20 is rotated, and the grinding wheel 42 is rotated and lowered. At this time, the position and inclination of the grinding unit 30 are adjusted so that the central part of the radius of the bottom surface of the circular recess 13 makes contact with the grinding wheel 41 first. The central part of the radius of the bottom surface of the circular recess 13 is the midpoint between the center of the bottom surface of the circular recess 13 and the outer circumference of the bottom surface of the circular recess 13. Also, when viewed from above the holding surface 21, the center of the bottom surface of the circular recess 13 is approximately the same as the center 110 of the back surface 101 of the workpiece 10. Furthermore, the outer circumference of the circular recess 13 is approximately the same as the outer circumference of the device region 103 of the workpiece 10.

[0032] Next, the chuck table 20 is rotated, and the grinding wheel 42 is rotated and lowered. This causes the bottom surface of the circular recess 13 to be ground by the grinding wheel 41. In this grinding, as shown in Figure 6, the central part of the radius of the bottom surface of the circular recess 13 is the first to contact the grinding wheel 41, that is, before the central and outer sides of the bottom surface of the circular recess 13. Therefore, grinding starts from the central part of the radius, and the back surface 101 of the workpiece 10 is ground so that the area to be ground gradually expands to the central and outer sides of the circular recess 13. At this time, the central region (a circular region with a radius of a predetermined distance from the center) and the annular region from the outer circumference of the circular recess 13 to a predetermined distance are left as flat surfaces 12 without being ground. Specifically, grinding is performed so that the widths 121 and 122 of the two flat surfaces 12 are wider than the width 512 of the grinding wheel 51.

[0033] Once the first grinding step described above is completed, as shown in Figure 7, in the cross-section of the workpiece 10, a flat surface 12 having a predetermined width from the outer circumference of the circular recess 13 and a flat surface 12 having a predetermined width in the central region of the circular recess 13 are formed inside the annular protrusion 14. In addition, a bowl-shaped curved surface 11 is formed in the region sandwiched between the two flat surfaces 12.

[0034] Finally, in the second grinding step, the back surface of the workpiece is further ground to form a circular recess 131 inside the annular protrusion 14 (S30). The circular recess 131 has approximately the same diameter as the circular recess 13 formed in the pre-grinding step and is formed deeper than the circular recess 13. Figures 8, 12, and 13 illustrate the second grinding step according to the first embodiment. In this embodiment, in the second grinding step, the back surface 101 of the workpiece 10 corresponding to the device region 103 is ground with a grinding wheel 52 to form a circular recess 131 (shown in Figure 13) with a flat bottom surface.

[0035] As shown in Figure 8, in the second grinding step, a grinding unit 30 is used, in which a grinding wheel 52 is mounted on the lower end of a wheel mount 33. Since the grinding wheel 52 uses a grinding disc 51 with finer abrasive grains than in the first grinding step, so-called finish grinding is performed in the second grinding step. The grinding surface 511 of the grinding disc 51 is brought into contact with the flat surface 12 of the workpiece 10. At this time, the grinding surface 511 of the grinding disc 51 is adjusted to be parallel to the holding surface 21 of the chuck table 20. That is, the rotation axis 35 of the grinding wheel 52 and the rotation axis 22 of the chuck table 20 are adjusted to be in the same direction.

[0036] Figure 9 illustrates the contact surface between the grinding wheel and the flat surface in the second grinding step of the first embodiment. In Figure 9, the area on the grinding surface 511 that is in contact with the workpiece 10 and where grinding is performed is indicated by shading. In the first grinding step, the widths 121 and 122 of the flat surface 12 are wider than the width 512 of the grinding surface 511. Therefore, according to the grinding method of the embodiment, from the start of grinding in the second grinding step, the entire surface of the grinding surface 511 of the grinding wheel 51 in the area in contact with the workpiece comes into contact with the flat surface 12 and grinding can be performed. Thus, uneven wear of the grinding wheel 51 can be prevented.

[0037] The uneven wear of the grinding wheel will be explained using a comparative example. Figure 10 is a diagram illustrating the second grinding step in the comparative example. Figure 11 is a diagram illustrating the contact surface between the grinding wheel and the flat surface in the second grinding step of the comparative example. Figures 10 and 11 show the state at the start of the second grinding step. In the grinding method of the comparative example, grinding is performed in the first grinding step until the curved surface 11 reaches the center or outer circumference of the circular recess 13. As a result, a flat surface 12 is not formed on the workpiece 10. If the second grinding step is started in this state, only a portion of the grinding surface 511 can contact the curved surface 11 and be ground. As a result, the portion of the grinding surface 511 that contacts the curved surface 11 wears down, while the portion that does not contact the curved surface 11 does not wear down, causing uneven wear of the grinding wheel 51.

[0038] In contrast, in this embodiment, the entire surface of the grinding surface 511 comes into contact with the flat surface 12 from the start of grinding in the second grinding step. As grinding progresses while the grinding unit 30 is lowered, grinding by the grinding surface 511 progresses from the outer circumference of the curved surface 11 towards the center, and the area of ​​the flat surface 12 expands. Specifically, as shown in Figure 12, the width of the flat surface 12 in the central part of the circular recess 13 expands toward the outer circumference, and the width of the flat surface 12 in the outer circumference of the circular recess 13 expands toward the center, and the area of ​​the flat surface 12 expands. The curved surface 11 is processed with a grinding wheel 41 that has a coarser particle size than the grinding wheel 51, so the surface is formed roughly. For this reason, by processing the curved surface 11 in the second grinding step, the grinding surface 511 is continuously dressed, and the wear of the grinding wheel 51 can be prevented.

[0039] After the curved surface 11 has been completely ground down and the inside of the annular protrusion 14 is covered by the flat surface 12, forming a circular recess 131 as shown in Figure 12, grinding of the bottom surface of the circular recess 131 is continued using the grinding wheel 52. When the thickness of the bottom surface of the circular recess 131 reaches a predetermined thickness, the second grinding step is terminated.

[0040] As described above, according to this embodiment, in the first grinding step, when grinding the back surface 101 of the workpiece 10 using a coarse grinding wheel 41, a flat surface 12 having a predetermined width is formed from the outer circumference of the device region 103, and a flat surface 12 having a predetermined width is formed in the central region of the device region 103. Then, a bowl-shaped curved surface 11 is formed in the region sandwiched between the two flat surfaces 12. At this time, the widths 121 and 122 of the flat surfaces 12 are formed to be wider than the width 512 of the grinding wheel 51 used in the second grinding step. As a result, in the second grinding step that is performed thereafter, the entire surface of the grinding surface 511 can be in contact with the flat surfaces 12 from the start of grinding. Therefore, uneven wear of the grinding wheel 51 can be prevented. In addition, by forming a bowl-shaped curved surface 11 between the two flat surfaces 12, the dressing effect is continued during the second grinding, and the wear of the grinding wheel 51 can be prevented. Furthermore, by performing so-called TAIKO grinding, in which an annular protrusion 14 is formed on the back surface 101 corresponding to the excess outer peripheral region 104 in the pre-grinding step, and a circular recess 131 is formed inside the annular protrusion 14 in the first and second grinding steps, warping of the workpiece 10 can be suppressed.

[0041] In the above description, flat surfaces 12 are formed in the central and peripheral regions of the circular recess 13, but only one of them may be used. Also, since the diameter 316 of the grinding wheel 32 and the roughness of the grinding wheel 31 are approximately the same as the diameter 416 of the grinding wheel 42 and the roughness of the grinding wheel 41, the grinding wheel 32 may be used in the first grinding step, or the grinding wheel 42 may be used in the pre-grinding step. By performing the pre-grinding step and the first grinding step with the same grinding wheel 32 (or grinding wheel 42), the time required to change the grinding wheel can be reduced, and the grinding time can be reduced. Furthermore, although the above states that the abrasive grains of grinding wheel 51 are finer than those of grinding wheel 41, the abrasive grains of grinding wheel 41 may be made to be the same fineness as those of grinding wheel 51. In this case, grinding wheel 52 may be used in the first grinding step, or grinding wheel 42 may be used in the second grinding step. Moreover, the abrasive grains of grinding wheel 51 may be made to be the same coarseness as those of grinding wheels 31 and 41. (Second embodiment)

[0042] The workpiece grinding method according to this embodiment differs from the first embodiment in that the entire back surface of the workpiece is ground in the pre-grinding step, and an annular protrusion is formed in the second grinding step. The flow of the workpiece grinding method according to this embodiment is the same as that of the first embodiment shown in Figure 3. The differences from the first embodiment will be described below.

[0043] First, the pre-grinding step (S10) will be described. Figures 14 and 15 illustrate the pre-grinding step according to the second embodiment. As shown in Figure 14, the diameter 316 of the grinding wheel 32 used for pre-grinding in this embodiment is larger than the diameter of the device area 103, and multiple grinding wheels 31 are arranged accordingly.

[0044] As shown in Figure 15, the chuck table 20 is rotated while the grinding wheel 32 is rotated and lowered. This grinds the workpiece 10 with the grinding wheel 31 until it reaches a predetermined thickness. The rotation axis 22 of the chuck table 20 and the rotation axis 35 of the spindle 36 are positioned differently on the front and back sides of the paper in Figure 15. When viewed from above the holding surface 21, the grinding wheel 31 passes through the center 110 of the back surface 101 of the workpiece 10 during grinding. Since the chuck table 20 is conical, the actual machining area is the radial portion of the chuck table.

[0045] In the subsequent first grinding step (S20), a wheel with the same diameter 416 as the grinding wheel 42 used in the first embodiment is used. Figure 16 is a diagram illustrating the first grinding step according to the second embodiment. Unlike the first embodiment, the circular recess 13 is not formed in the pre-grinding step. Therefore, in the first grinding step of this embodiment, when the grinding surface 411 of the grinding wheel 41 is brought into contact with the back surface 101 of the workpiece 10, the position and inclination of the grinding unit 30 are adjusted so that the central part of the radius of the circular region of the back surface 101 corresponding to the device region 103 contacts the grinding wheel 41 first. From this state, grinding is carried out in the same manner as in the first embodiment, and the central region (a circular region with a radius of a predetermined distance from the center 110 of the back surface 101) and the annular region from the outer circumference of the back surface 101 to a predetermined distance are left as a flat surface 12 without grinding. Specifically, the back surface 101 is ground so that the width 121 of the outer peripheral flat surface 12 is greater than the sum of the width of the outer peripheral excess area 104 and the width 512 of the grinding wheel 51, and the width 122 of the central flat surface 12 is greater than the width 512 of the grinding wheel 51.

[0046] Figure 17 is a cross-sectional view illustrating the workpiece after the first grinding step according to the second embodiment. When the first grinding step described above is completed, as shown in Figure 17, a flat surface 12 having a predetermined width is formed on the outer circumference of the back surface 101 and another flat surface 12 having a predetermined width is formed in the central region of the back surface 101 in the cross-section of the diameter of the workpiece 10. In addition, a bowl-shaped curved surface 11 is formed in the region sandwiched between the two flat surfaces 12.

[0047] Finally, the second grinding step (S30) will be described. In this embodiment, the second grinding is performed using a wheel with the same diameter 516 as the grinding wheel 52 used in the first embodiment. Figures 18 and 19 illustrate the second grinding step according to the second embodiment. As shown in Figure 18, the grinding surface 511 of the grinding wheel 51 is brought into contact with the flat surface 12 of the workpiece 10, and the grinding wheel 52 is rotated and lowered. At this time, the operation of the grinding unit 30 is controlled so that the grinding surface 511 of the grinding wheel 51 does not come into contact with the flat surface 12 corresponding to the outer peripheral excess region 104. As grinding progresses, the curved surface 11 is completely ground, and as shown in Figure 19, the back surface 101 corresponding to the device region 103 becomes flat, and a circular recess 131 is formed. The flat surface 12 corresponding to the outer peripheral excess region 104 remains unground in the second grinding step, forming an annular protrusion 14. When the thickness of the bottom surface of the circular recess 131 reaches a predetermined thickness, the second grinding step is terminated.

[0048] As described above, even if the entire surface of the back surface 101 is ground using a large-diameter grinding wheel 32 in the pre-grinding step, the same effects as in the first embodiment can be obtained. That is, uneven wear of the grinding wheel 51 and dulling of the grinding wheel 51 can be prevented. Furthermore, in the second grinding step, by performing so-called TAIKO grinding, which forms an annular protrusion 14 on the back surface 101 corresponding to the excess outer peripheral region 104, warping of the workpiece 10 can be suppressed. (Third embodiment)

[0049] The workpiece grinding method according to this embodiment differs from the second embodiment in that a grinding wheel with a large diameter is used in the first grinding step. That is, the first grinding step of this embodiment uses a grinding wheel 42 in which a plurality of grinding wheels 41 are arranged such that its diameter 416 is larger than the diameter of the device region 103.

[0050] The flow of the grinding method for the workpiece according to this embodiment, the processing method at each step, and the shape of the workpiece after each step are the same as those of the second embodiment described above, so their explanation will be omitted.

[0051] As described above, even if the entire surface of the back surface 101 is ground using a larger diameter grinding wheel 42 in the first grinding step, the same effects as in the second embodiment can be obtained. That is, uneven wear of the grinding wheel 51 and dulling of the grinding wheel 51 can be prevented. Furthermore, in the second grinding step, by performing so-called TAIKO grinding, which forms an annular protrusion 14 on the back surface 101 corresponding to the excess outer peripheral region 104, warping of the workpiece 10 can be suppressed. Also, since the diameter 316 of the grinding wheel 32 and the roughness of the grinding wheel 31 are substantially the same as the diameter 416 of the grinding wheel 42 and the roughness of the grinding wheel 41, the grinding wheel 32 may be used in the first grinding step, or the grinding wheel 42 may be used in the pre-grinding step. By performing the pre-grinding step and the first grinding step with the same grinding wheel 32 (or grinding wheel 42), the time required to change the grinding wheel can be reduced, and the grinding time can be reduced.

[0052] While several embodiments of the present invention have been described, these embodiments are provided as examples only and are not intended to limit the scope of the invention. These novel embodiments can be implemented in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. Furthermore, a flat surface is defined as being at least flatter than the curved surface intentionally formed in the first grinding step, and does not need to be perfectly flat. The flat surface is the same surface as the back surface 101 that was processed before the first grinding step was performed, and it is sufficient if it is flatter than the curved surface. [Industrial applicability]

[0053] As described above, the workpiece grinding method of the present invention has the effect of preventing uneven wear and dulling of the grinding wheel used in the second grinding stage when grinding is performed in two stages: first grinding (e.g., rough grinding) and second grinding (e.g., finish grinding). [Explanation of Symbols]

[0054] 10 Workpiece (wafer) 11 Curved surface 12 flat surface 13 Circular recess 14 Annular protrusion 20 Chuck Table 21 Top surface (holding surface) 22 Rotation axis 30 Grinding Units 31, 41, 51 grinding wheels 316, 416, 516 diameter 32, 42, 52 grinding wheels 33 Wheel Mount 34 Ring base 35 Rotation axis 36 spindles 101 Back side 103 Device Area 104 Peripheral surplus area 105 Surface 106 planned division lines 107 devices 108 radius 110 center 131 Circular recess 311, 411, 511 Grinding surface

Claims

1. A method for grinding a workpiece, The rotation axis of the first grinding wheel is positioned on the holding surface of the holding table that holds the workpiece. The workpiece is ground while tilted relative to the axis of rotation. A curved surface is formed on the workpiece, At least one of the center and outer circumference of the workpiece, A first grinding step that leaves a flat surface that does not come into contact with the grinding wheel portion of the first grinding wheel, After bringing the grinding wheel portion of the second grinding wheel into contact with the flat surface, A second grinding step in which the workpiece is ground to a predetermined thickness, A method for grinding a workpiece, comprising the following components.

2. The flat surface is, The second grinding wheel is characterized by having a width greater than or equal to the width of the grinding wheel portion. A method for grinding a workpiece according to claim 1.

3. Before the first grinding step, It further includes a pre-grinding step in which the workpiece is thinned to a predetermined thickness using a third grinding wheel. A method for grinding a workpiece according to claim 1.

4. The workpiece has a device region and an outer peripheral excess region surrounding the device region. The diameter of the outermost circumference of the rotational trajectory of the grinding wheel portion of the first grinding wheel, the second grinding wheel, and the third grinding wheel is characterized in that it is greater than the radius of the device region and less than the diameter of the device region. A method for grinding a workpiece according to claim 1.

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