Grinding method for workpieces

Abstract

To provide a grinding method of a workpiece which can inhibit occurrence of chips at an outer periphery part of the workpiece.SOLUTION: A grinding method of a workpiece includes: a holding step 101 in which a workpiece is held on a holding table; a center part grinding step 102 in which a center part of the workpiece is ground to a predetermined thickness to form a recessed part with a first grinding wheel having an outer diameter smaller than that of the workpiece; and an outer periphery part grinding step 103 in which the first grinding wheel is relatively moved from the recessed part to an outer periphery area of a holding surface of the holding table to grind an outer periphery part of the workpiece surrounding the recessed part after the center part grinding step 102 is performed.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] When grinding a warped workpiece, in the conventional processing method, it was considered necessary to first adsorb the workpiece on a holding table. Therefore, in order to adsorb it on the holding table, a mechanism is provided on the transfer arm to press the outer peripheral portion of the workpiece against the holding table (see, for example, Patent Document 1), the number of pumps is increased to increase the suction force of the holding table, the suction path of the holding surface is divided into a center and an outer periphery, and even if the outer periphery floats from the holding surface along the outer periphery, the center does not leak, and the outer peripheral side is pressed by a transfer arm or the like to enable vacuuming. Therefore, solutions such as forming a dedicated vacuum path for the outer periphery have been taken.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, workpieces with large warpage have emerged, and there are also cases where the entire surface of the workpiece cannot be adsorbed even if the transfer and holding surfaces are improved.

[0005] If grinding proceeds in a state where the outer peripheral portion is floating, and the grinding wheel hits the outer peripheral portion, there is a risk of chipping on the outer peripheral portion.

[0006] An object of the present invention is to provide a method for grinding a workpiece that can suppress the occurrence of chipping on the outer peripheral portion of the workpiece.

Means for Solving the Problems

[0007] To solve the above-mentioned problems and achieve the objective, the present invention provides a workpiece grinding method comprising: a holding step of holding the workpiece on a holding table; a central grinding step of grinding the central part of the workpiece to a predetermined thickness to form a recess using a first grinding wheel having an outer diameter smaller than that of the workpiece; and an outer peripheral grinding step of moving the first grinding wheel relatively from the recess to the outer peripheral region of the holding surface of the holding table, after performing the central grinding step, to grind the outer peripheral part of the workpiece surrounding the recess. The holding table has a holding surface divided into an outer region for holding the outer periphery and a central region for holding the central part, and suction paths that independently connect the outer region and the central region to a suction source, and the holding step generates a suction force in the central region and holds the central part of the workpiece. It is characterized by the following.

[0009] In the aforementioned method for grinding the workpiece, the central grinding step and the outer peripheral grinding step may be performed repeatedly.

[0010] The above-mentioned method for grinding a workpiece may also include an outer periphery suction step in which, at a predetermined timing after starting the outer periphery grinding step, while maintaining the suction force in the central region, an additional suction force is generated in the outer periphery region to adsorb the thinned outer periphery of the workpiece to the outer periphery region, and a full-surface grinding step in which, after performing the outer periphery suction step, the entire surface of the workpiece is ground with the first grinding wheel or a second grinding wheel different from the first grinding wheel to thin the workpiece to a desired final thickness.

[0011] In the aforementioned method for grinding a workpiece, the first grinding wheel may have an outer diameter smaller than the central region.

[0012] In the aforementioned method for grinding a workpiece, the second grinding wheel used in the full-surface grinding step may have a larger outer diameter than the first grinding wheel. [Effects of the Invention]

[0013] The present invention has the effect of suppressing the occurrence of chipping on the outer circumference of a workpiece. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 is a perspective view showing an example of the configuration of a workpiece to be processed in the grinding method for workpieces according to Embodiment 1. [Figure 2] Figure 2 is a flowchart showing the flow of the grinding method for a workpiece according to Embodiment 1. [Figure 3] Figure 3 is a schematic side view showing a partial cross-section of the holding step in the workpiece grinding method shown in Figure 2. [Figure 4] Figure 4 is a schematic side view showing a partial cross-section of the central grinding step of the workpiece grinding method shown in Figure 2. [Figure 5] Figure 5 is a schematic side view showing a partial cross-section immediately after the start of the outer periphery grinding step in the workpiece grinding method shown in Figure 2. [Figure 6] Figure 6 is a schematic side view showing a partial cross-section of the workpiece grinding method shown in Figure 2, just before the end of the outer circumference grinding step. [Figure 7] Figure 7 is a flowchart showing the flow of the grinding method for a workpiece according to Embodiment 2. [Figure 8] Figure 8 is a schematic side view showing a partial cross-section of the workpiece grinding method shown in Figure 7, just before the completion of the first outer circumference grinding step. [Figure 9] Figure 9 is a schematic side view showing a partial cross-section of the workpiece retraction step in the grinding method of the workpiece shown in Figure 7. [Figure 10] Figure 10 is a schematic side view showing a partial cross-section of the central grinding preparation step of the workpiece grinding method shown in Figure 7. [Figure 11] Figure 11 is a flowchart showing the flow of the grinding method for a workpiece according to Embodiment 3. [Figure 12] Figure 12 is a schematic side view showing a partial cross-section of the outer periphery suction step of the workpiece grinding method shown in Figure 11. [Figure 13] Figure 13 is a schematic side view showing a partial cross-section of the full-surface grinding step of the workpiece grinding method shown in Figure 11. [Figure 14]FIG. 14 is a side view schematically showing a holding step of a workpiece grinding method according to a modification of Embodiment 1, Embodiment 2, and Embodiment 3 in a partial cross section.

Embodiments for Carrying Out the Invention

[0015] The embodiments (embodiments) for carrying out the present invention will be described in detail with reference to the drawings. The present invention is not limited by the contents described in the following embodiments. Further, the constituent elements described below include those that can be easily assumed by those skilled in the art and those that are substantially the same. Furthermore, the configurations described below can be combined as appropriate. Also, various omissions, substitutions, or changes in the configuration can be made without departing from the gist of the present invention.

[0016] 〔Embodiment 1〕 The grinding method of the workpiece according to Embodiment 1 of the present invention will be described based on the drawings. FIG. 1 is a perspective view showing a configuration example of a workpiece to be processed in the grinding method of the workpiece according to Embodiment 1. FIG. 2 is a flowchart showing the flow of the grinding method of the workpiece according to Embodiment 1.

[0017] (Workpiece) The grinding method of the workpiece according to Embodiment 1 is a method of grinding the workpiece 1 shown in FIG. 1. The workpiece 1 to be processed in the grinding method of the workpiece according to Embodiment 1 is a disk-shaped semiconductor wafer or optical device wafer having a substrate 2 made of silicon, sapphire, gallium arsenide, SiC (silicon carbide), or the like. As shown in FIG. 1, a plurality of division planned lines 4 intersecting each other are set on the surface 3 of the workpiece 1, and a device 5 is formed in a region partitioned by the division planned lines 4.

[0018] Device 5 is, for example, an integrated circuit such as an IC (Integrated Circuit) or LSI (Large Scale Integration), an image sensor such as a CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor), or a memory (semiconductor memory device).

[0019] Furthermore, in Embodiment 1, the workpiece 1 includes a central portion 8 and an outer peripheral portion 9 located further outward than the central portion 8, with the outer peripheral portion 9 being more curved in the thickness direction than the central portion 8 (Note that Figure 1 omits the curvature of the workpiece 1). The central portion 8 is the region that includes the center of the workpiece 1 in a plan view, and the outer peripheral portion 9 is the region that is further outward than the central portion 8 and includes the outer edge of the workpiece 1. The outer peripheral portion 9 may or may not have a device 5 formed on its surface 3.

[0020] In Embodiment 1, the workpiece 1 is the wafer described above, but in the present invention, it is not limited to a wafer and may be various workpieces such as a package substrate comprising a substrate on which a plurality of device chips are arranged and a molded resin in which the plurality of device chips on the substrate are molded and sealed. Furthermore, in the present invention, the workpiece 1 may be a wafer on which no devices 5 are formed on the surface 3.

[0021] (Method for grinding workpieces) The first embodiment of the workpiece grinding method involves grinding the back surface 7 of the back surface 3 of the workpiece 1 to thin the workpiece 1 to a desired final thickness 6. As shown in Figure 2, the workpiece grinding method comprises a holding step 101, a central grinding step 102, and an outer peripheral grinding step 103.

[0022] (Holding step) Figure 3 is a schematic side view showing a partial cross-section of the holding step of the workpiece grinding method shown in Figure 2. The holding step 101 is the step of holding the workpiece 1 on the holding surface 25 of the holding table 21 of the grinding device 20. The holding table 21 comprises a disc-shaped porous member 22 and a frame 23 provided with a circular recess 24 into which the porous member 22 is fitted and mounted.

[0023] The porous member 22 is made of a porous material such as porous ceramic. The upper surface of the porous member 22 is formed flat along the horizontal direction and is the holding surface 25 for holding the workpiece 1. The holding table 21 has the holding surface 25, which is the upper surface of the porous member 22, and the upper surface of the frame 23 arranged on the same plane.

[0024] Furthermore, in Embodiment 1, the holding table 21 is divided into an outer peripheral region 251 that holds the outer peripheral portion 9 of the workpiece 1 and a central region 252 that holds the central portion 8 of the workpiece 1. In Embodiment 1, a partition member 26 made of porous ceramic, non-permeable resin, or non-permeable glass, etc., which has lower permeability than other parts of the porous member 22, is embedded in the porous member 22 between the outer peripheral region 251 and the central region 252, and the holding surface 25 is divided into the outer peripheral region 251 and the central region 252. Thus, the holding table 21 has a holding surface 25 divided into an outer peripheral region 251 and a central region 252.

[0025] Furthermore, the holding table 21 has suction paths 27 and 28 that independently connect the outer peripheral region 251 of the holding surface 25 and the central region 252 of the holding surface 25 to the suction source 29. Each of the suction paths 27 and 28 is provided with an on / off valve 271 and 281. Suction path 27 opens on the bottom surface of the recess 24 at a position on the outer peripheral side of the partition wall member 26, and suction path 28 opens on the bottom surface of the recess 24 at a position on the inner peripheral side of the partition wall member 26.

[0026] In Embodiment 1, in the holding step 101, the workpiece 1, to which the support member 10 is attached to the surface 3, is placed on the holding surface 25 of the holding table 21 of the grinding device 20. At this time, the outer periphery 9 of the workpiece 1 is located on the outer peripheral region 251, and the central portion 8 of the workpiece 1 is located on the central region 252. In Embodiment 1, in the holding step 101, the grinding device 20 opens the on-off valve 281 with the on-off valve 271 closed, generating a suction force only in the central region 252 of the holding surface 25, and holding the central portion 8 of the workpiece 1 in the central region 252 by suction.

[0027] In Embodiment 1, the support member 10 is an adhesive tape having a base layer that is flexible and non-adhesive, and an adhesive layer laminated on the base layer that is flexible and adhesive. However, the present invention is not limited to adhesive tape. In the present invention, the support member 10 may be a sheet made of a thermoplastic resin that does not have an adhesive layer. In the case of a non-adhesive sheet, the support member 10 is preferably a polyolefin sheet, a polyethylene sheet, a polypropylene sheet, or a polystyrene sheet, and is attached to the workpiece 1 by heat pressing.

[0028] (Central grinding step) Figure 4 is a schematic side view showing a partial cross-section of the central grinding step of the workpiece grinding method shown in Figure 2. The central grinding step 102 is a step in which the central part 8 of the workpiece 1 is ground to a predetermined thickness using a first grinding wheel 30 whose outer diameter is smaller than the outer diameter of the workpiece 1, thereby forming a partial recess 11 on the back surface 7.

[0029] In Embodiment 1, the first grinding wheel 30 has an outer diameter smaller than the outer diameter of the workpiece 1. It comprises a disc-shaped wheel base 31 smaller than the outer diameter of the central region 252 of the workpiece 1, and a plurality of grinding wheels 32 provided on the outer edge of the wheel base 31. Thus, the diameter of the circle formed by the outer edges of the plurality of grinding wheels 32 (corresponding to the outer diameter of the first grinding wheel 30) is smaller than the outer diameter of the workpiece 1 and the outer diameter of the central region 252 of the workpiece 1. The central region 252 holds the central part 8 of the workpiece 1, but since the central part 8 has less curvature than the outer peripheral part 9, it is held by attraction to the holding surface 25. Since the outer diameter of the first grinding wheel 30 is smaller than the central region 252, only the region held by the holding surface 25 can be ground. Therefore, there is no risk of the first grinding wheel 30 colliding with the portion of the workpiece 1 that has warped and lifted away from the holding surface 25, thus preventing damage to the workpiece 1.

[0030] Furthermore, in Embodiment 1, the outer diameter of the first grinding wheel 30 is larger than the radius of the central portion 8 of the workpiece 1. In this invention, the objective is to grind the central portion 8, which is held by suction on the holding surface 25, first, without grinding the outer peripheral portion 9 that is warped and floating away from the holding surface 25. Therefore, it is preferable that the outer diameter of the first grinding wheel 30 is less than or equal to the outer diameter of the central region 252 of the workpiece 1. However, since the warping around the central region 252 is also small, and grinding can be performed without damaging the workpiece 1 even if it is not held by suction, it is sufficient that the outer diameter is smaller than the outer diameter of the workpiece 1. In addition, in this invention, the outer diameter of the first grinding wheel 30 may be limited to the radius of the central portion 8 of the workpiece 1.

[0031] In Embodiment 1, during the central grinding step 102, the grinding device 20 positions the axis of the holding table 21 and the axis 34 of the spindle 33, which has the first grinding wheel 30 attached to its lower end, parallel to each other and spaced apart, and positions the grinding wheel 32 of the first grinding wheel 30 above the central part 8 of the back surface 7 of the workpiece 1 held on the holding table 21. In Embodiment 1, during the central grinding step 102, the grinding device 20 rotates the holding table 21 around its axis and moves the first grinding wheel 30 downward while supplying grinding water to the workpiece 1 and rotating the first grinding wheel 30 around its axis 34.

[0032] In Embodiment 1, in the central grinding step 102, the grinding device 20 grinds the back surface 7 of the workpiece 1 with the grinding wheels 32 by bringing a plurality of grinding wheels 32, which are provided on the outer edge of the wheel base 31, close to the holding table 21 at a predetermined feed rate, as shown in Figure 4. In Embodiment 1, in the central grinding step 102, the grinding device 20 grinds the central part 8 of the workpiece 1 to a final thickness 6, thinning it and forming a partially recessed area 11 on the back surface 7 of the workpiece 1. Note that in Embodiment 1, since the outer diameter of the first grinding wheel 30 is larger than the radius of the central part 8 of the workpiece 1, the area near the axis of the central part 8 on the back surface 7 of the workpiece 1 is not ground, and the recessed area 11 is formed in an annular shape.

[0033] (Outer circumference grinding step) Figure 5 is a schematic side view showing a partial cross-section immediately after the start of the outer peripheral grinding step of the workpiece grinding method shown in Figure 2. Figure 6 is a schematic side view showing a partial cross-section immediately before the end of the outer peripheral grinding step of the workpiece grinding method shown in Figure 2. The outer peripheral grinding step 103 is a step in which, after the central grinding step 102 is performed, the first grinding wheel 30 is moved relative to the outer peripheral region 251 of the holding surface 25 of the holding table 21, and the outer peripheral portion 9 of the workpiece 1 surrounding the recess 11 is ground.

[0034] In Embodiment 1, during the outer peripheral grinding step 103, as shown in Figure 5, the grinding device 20 moves the first grinding wheel 30 relative to the holding table 21 along the holding surface 25 toward the outer peripheral region 251 of the holding surface 25 of the holding table 21, while maintaining the distance of the grinding wheel 32 from the holding surface 25 at the end of the central grinding step 102, thereby grinding the outer peripheral portion 9 of the workpiece 1 from the inner surface side of the recess 11. During the outer peripheral grinding step 103, the first grinding wheel 30 grinds while moving, removing the unground area near the axis of the central portion 8 of the workpiece 1 shown in Figure 4. In the outer peripheral grinding step 103, finally, as shown in Figure 6, the grinding wheel 32 of the first grinding wheel 30 is moved relative to the holding surface 25 to the outer edge of the workpiece 1, thinning the outer peripheral portion 9 of the workpiece 1 to the final thickness 6.

[0035] In Embodiment 1, during the outer peripheral grinding step 103, the grinding device 20 moves the first grinding wheel 30 50 mm relative to the outer peripheral region 251 of the holding surface 25 of the holding table 21.

[0036] In the workpiece grinding method according to Embodiment 1 described above, a recess 11 is formed in the central part 8 of the back surface 7 of the workpiece 1 in the central part grinding step 102, and then in the outer peripheral grinding step 103, the inner surface of the recess 11 is ground toward the outer edge of the workpiece 1. Therefore, even if the outer peripheral part 9 of the workpiece 1 is lifted from the holding surface 25, the first grinding wheel 30 is pressed against the inner surface of the recess 11, so the outer peripheral part 9 is ground while being pressed against the holding surface 25 by the first grinding wheel 30. For this reason, in the workpiece grinding method according to Embodiment 1, even if the outer peripheral part 9 of the workpiece 1 is lifted from the holding surface 25, the first grinding wheel 30 can be prevented from colliding with the outer peripheral part 9 of the workpiece 1, and chipping of the outer peripheral part 9 can be prevented.

[0037] As a result, the grinding method for a workpiece according to Embodiment 1 has the effect of suppressing the occurrence of chipping on the outer circumference 9 of the workpiece 1.

[0038] [Embodiment 2] A method for grinding a workpiece according to Embodiment 2 of the present invention will be described with reference to the drawings. Figure 7 is a flowchart showing the flow of the workpiece grinding method according to Embodiment 2. Figure 8 is a schematic side view showing a partial cross-section just before the end of the first outer peripheral grinding step of the workpiece grinding method shown in Figure 7. Figure 9 is a schematic side view showing a partial cross-section of the retraction step of the workpiece grinding method shown in Figure 7. Figure 10 is a schematic side view showing a partial cross-section of the central grinding preparation step of the workpiece grinding method shown in Figure 7. Note that in Figures 7, 8, 9, and 10, parts identical to those in Embodiment 1 are denoted by the same reference numerals and their descriptions are omitted.

[0039] The workpiece grinding method according to Embodiment 2 is the same as Embodiment 1, except that in the first central grinding step 102, the central part 8 of the workpiece 1 is ground to a predetermined thickness 12 (shown in Figure 8) that is thicker than the final thickness 6, and as shown in Figure 7, the central grinding step 102 and the outer peripheral grinding step 103 are repeated multiple times to gradually thin the entire surface of the workpiece 1 to the final thickness 6, and the method includes a retraction step 105 and a central grinding preparation step 106.

[0040] In the workpiece grinding method according to Embodiment 2, the grinding device 20 grinds the central part 8 of the workpiece 1 to a predetermined thickness 12 that is thicker than the final thickness 6 in the first central part grinding step 102, and in the first outer peripheral grinding step 103, while maintaining the distance of the grinding wheel 32 from the holding surface 25 at the end of the first central part grinding step 102, the first grinding wheel 30 is moved relative to the holding table 21 along the holding surface 25 toward the outer peripheral region 251 of the holding surface 25 of the holding table 21, thereby grinding the outer peripheral part 9 of the workpiece 1 from the inner surface side of the recess 11. In Embodiment 2, in the outer peripheral grinding step 103, as shown in Figure 8, when the grinding wheel 32 of the first grinding wheel 30 is positioned on the outer edge of the workpiece 1, the grinding device 20 determines whether or not the workpiece 1 has been thinned to the final thickness 6 (step 104). In Embodiment 2, if the grinding device 20 determines that the workpiece 1 has not been thinned to the final thickness 6 (Step 104: No), the device proceeds to the retraction step 105.

[0041] In Embodiment 2, the retraction step 105 is the step of raising the first grinding wheel 30 so that the grinding wheel 32 is at a height where it does not come into contact with the workpiece 1, i.e., above the back surface 7 of the workpiece 1. In Embodiment 2, in the retraction step 105, as shown in Figure 9, the grinding device 20 raises the first grinding wheel 30 relative to the holding table 21.

[0042] In Embodiment 2, the central grinding preparation step 106 is the step of positioning the first grinding wheel 30 above the central portion 8 of the back surface 7 of the workpiece 1. In Embodiment 2, in the central grinding preparation step 106, as shown in Figure 10, the grinding device 20 moves the first grinding wheel 30 relative to the holding table 21 along the holding surface 25, positioning the first grinding wheel 30 above the central portion 8 of the back surface 7 of the workpiece 1 held on the holding table 21, and then returns to the central grinding step 102.

[0043] In Embodiment 2, in the central grinding step 102, the grinding device 20 thins the central part 8 of the workpiece 1 by a predetermined distance, such as 10 μm or 100 μm, in each run, and in the outer peripheral grinding step 103, the workpiece is thinned by the same predetermined distance as in the central grinding step 102, in each run. In Embodiment 2, after the outer peripheral grinding step 103, the grinding device 20 determines that the workpiece 1 has been thinned to a final thickness 6 (step 104: Yes), and the process ends. Thus, in Embodiment 2, the central grinding step 102 and the outer peripheral grinding step 103 are repeatedly performed until the thickness of the workpiece 1 reaches a final thickness of 6.

[0044] In the workpiece grinding method according to Embodiment 2, a recess 11 is formed in the central part 8 of the back surface 7 of the workpiece 1 in the central part grinding step 102, and then in the outer peripheral grinding step 103, the inner surface of the recess 11 is ground toward the outer edge of the workpiece 1. This suppresses collision of the first grinding wheel 30 with the outer peripheral 9 of the workpiece 1, and suppresses chipping of the outer peripheral 9. As a result, the workpiece grinding method according to Embodiment 2 has the effect of suppressing chipping of the outer peripheral 9 of the workpiece 1, similar to Embodiment 1.

[0045] [Embodiment 3] A method for grinding a workpiece according to Embodiment 3 of the present invention will be described with reference to the drawings. Figure 11 is a flowchart showing the flow of the workpiece grinding method according to Embodiment 3. Figure 12 is a schematic side view showing a partial cross-section of the outer peripheral suction step of the workpiece grinding method shown in Figure 11. Figure 13 is a schematic side view showing a partial cross-section of the full surface grinding step of the workpiece grinding method shown in Figure 11. In Figures 11, 12, and 13, the same reference numerals are used for parts that are the same as those in Embodiment 1, and their descriptions are omitted.

[0046] The workpiece grinding method according to Embodiment 3 is equivalent to Embodiment 1, except that in the central grinding step 102, the central part 8 of the workpiece 1 is ground to a first-stage finishing thickness 13 (shown in Figure 12) which is thicker than the final thickness 6, and the method includes an outer peripheral suction step 107 and a full-surface grinding step 108, which are performed after the outer peripheral grinding step 103, as shown in Figure 11.

[0047] In the workpiece grinding method according to Embodiment 3, the grinding device 20 grinds the central part 8 of the workpiece 1 to a first-stage finishing thickness 13 that is thicker than the final thickness 6 in the central part grinding step 102, and in the outer peripheral part grinding step 103, while maintaining the distance of the grinding wheel 32 from the holding surface 25 at the end of the central part grinding step 102, the first grinding wheel 30 is moved relative to the holding table 21 along the holding surface 25 toward the outer peripheral region 251 of the holding surface 25 of the holding table 21, thereby grinding the outer peripheral part 9 of the workpiece 1 from the inner side of the recess 11. The first-stage finishing thickness 13 is the thickness of the workpiece 1 that allows the outer peripheral part 9 to be thinned, reducing warping and enabling the outer peripheral part 9 to be held by attraction in the outer peripheral region 251 of the holding table 21.

[0048] In Embodiment 3, the outer periphery suction step 107 is a step in which, at a predetermined timing after the start of the outer periphery grinding step 103, while maintaining the suction force in the central region 252, an additional suction force is generated in the outer periphery region 251, and the outer periphery 9 of the thinned workpiece 1 is attracted to the outer periphery region 251. In Embodiment 3, in the outer periphery suction step 107, after the completion of the outer periphery grinding step 103 at a predetermined timing, the grinding device 20 opens the on-off valve 271 with the on-off valve 281 open, generates a suction force in the outer periphery region 251 of the holding surface 25, and attracts and holds the outer periphery 9 of the workpiece 1 to the outer periphery region 251 as shown in Figure 12.

[0049] In Embodiment 3, the full-surface grinding step 108 is a step in which, after the outer peripheral adsorption step 107 is performed, the entire surface of the back surface 7 of the workpiece 1 is ground with a second grinding wheel 40 different from the first grinding wheel 30, thereby thinning the workpiece 1 to a desired final thickness 6. The second grinding wheel 40 comprises a disc-shaped wheel base 41 whose radius is larger than the radius of the workpiece 1, and a plurality of grinding wheels 42 provided on the outer edge of the wheel base 41. Thus, in the second grinding wheel 40, the radius of the circle formed by the outer edges of the plurality of grinding wheels 42 (corresponding to the radius of the second grinding wheel 40) is larger than the radius of the workpiece 1.

[0050] In Embodiment 3, during the full-surface grinding step 108, the grinding device 20 positions the axis of the holding table 21 and the axis 44 of the spindle 43, which has a second grinding wheel 40 attached to its lower end, parallel to each other and spaced apart, and positions the grinding wheel 42 of the second grinding wheel 40 above the central part 8 of the back surface 7 of the workpiece 1 held on the holding table 21. In Embodiment 3, during the full-surface grinding step 108, the grinding device 20 rotates the holding table 21 around its axis and grinds the entire back surface 7 of the workpiece 1 by rotating the second grinding wheel 40 around its axis while supplying grinding water to the workpiece 1 and moving the second grinding wheel 40 downwards.

[0051] In Embodiment 3, in the full-surface grinding step 108, the grinding device 20 grinds the entire surface of the back surface 7 of the workpiece 1 with the grinding wheels 42 by bringing a plurality of grinding wheels 42, which are provided on the outer edge of the wheel base 41 of the second grinding wheel 40, close to the holding table 21 at a predetermined feed rate, as shown in Figure 13. In addition, in the present invention, although the grinding time is longer than in Embodiment 3, the grinding device 20 may also grind the entire surface of the back surface 7 of the workpiece 1 with the first grinding wheel 30 in the full-surface grinding step 108.

[0052] In the workpiece grinding method according to Embodiment 3, a recess 11 is formed in the central part 8 of the back surface 7 of the workpiece 1 in the central part grinding step 102, and then in the outer peripheral grinding step 103, the inner surface of the recess 11 is ground toward the outer edge of the workpiece 1. This suppresses collision of the first grinding wheel 30 with the outer peripheral 9 of the workpiece 1, thereby suppressing chipping of the outer peripheral 9. As a result, the workpiece grinding method according to Embodiment 3 has the effect of suppressing chipping of the outer peripheral 9 of the workpiece 1, similar to Embodiment 1. Furthermore, in Embodiment 3, by performing full-surface grinding with a second grinding wheel 40 having a radius greater than or equal to the radius of the workpiece 1, the entire surface can be ground without relatively moving the holding surface 25 and the second grinding wheel 40 during grinding. Therefore, compared to grinding the entire surface of the workpiece 1 to the final thickness 6 with a first grinding wheel 30 having an outer diameter smaller than the radius of the workpiece 1, the grinding time can be reduced.

[0053] In addition, in Embodiment 3 of the present invention, the grinding device 20 may repeat the central grinding step 102 and the outer peripheral grinding step 103 multiple times, similar to Embodiment 2, by grinding the central part 8 of the workpiece 1 to a predetermined thickness 12 that is thicker than the first stage finishing thickness 13 in the first central grinding step 102.

[0054] Furthermore, in the present invention, in embodiments 1 to 3, the outer periphery suction step 107 may be performed during the outer periphery grinding step 103 (corresponding to a predetermined timing). In particular, in the present invention, when the central grinding step 102 and the outer periphery grinding step 103 are repeated multiple times, the outer periphery suction step 107 may be performed after these steps have been performed a predetermined number of times (corresponding to a predetermined timing).

[0055] [Variation] A method for grinding a workpiece according to modifications of Embodiments 1, 2, and 3 of the present invention will be described with reference to the drawings. Figure 14 is a schematic side view showing a holding step of the workpiece grinding method according to modifications of Embodiments 1, 2, and 3 in a partial cross-section. In addition, the same reference numerals are used for the same parts as in Embodiment 1 in Figure 14, and their description is omitted.

[0056] The modified method for grinding a workpiece is the same as in Embodiment 1, except that the holding table 21 does not have a partition member 26 embedded in the porous member 22, the holding surface 25 is not divided into a central region 252 and an outer peripheral region 251, and only one suction path 28-1 is provided that connects the holding surface 25 to the suction source 29. The suction path 28-1 is provided with an on / off valve 281-1.

[0057] In the modified example, in the holding step 101, the workpiece 1, to which the support member 10 is attached to the surface 3, is placed on the holding surface 25 of the holding table 21 of the grinding device 20. At this time, as in Embodiment 1, the outer periphery 9 of the workpiece 1 is located on the outer peripheral region 251, and the central part 8 of the workpiece 1 is located on the central region 252. In Embodiment 1, in the holding step 101, the grinding device 20 opens the on / off valve 281-1 to generate a suction force across the entire holding surface 25, and in the case of a warped workpiece 1, the central part 8 is held in the central region 252 by suction, as shown in Figure 14. Note that in the modified example, when the full-surface grinding step 108 is performed as in Embodiment 3, the outer peripheral suction step 107 is not performed.

[0058] In the modified workpiece grinding method, a recess 11 is formed in the central part 8 of the back surface 7 of the workpiece 1 in the central part grinding step 102, and then in the outer peripheral grinding step 103, the inner surface of the recess 11 is ground toward the outer edge of the workpiece 1. This suppresses collision of the first grinding wheel 30 with the outer peripheral 9 of the workpiece 1, and prevents chipping of the outer peripheral 9. As a result, the modified workpiece grinding method has the effect of suppressing chipping of the outer peripheral 9 of the workpiece 1, similar to Embodiment 1.

[0059] Furthermore, in the modified workpiece grinding method, since an attractive force is generated across the entire holding surface 25 in the holding step 101, grinding the outer periphery 9 in the outer periphery grinding step 103 to alleviate warping makes it possible to hold the outer periphery 9 of the workpiece 1 by attraction to the holding surface 25. As a result, the modified workpiece grinding method can suppress the first grinding wheel 30 from colliding with the outer periphery 9 of the workpiece 1, and can suppress chipping of the outer periphery 9.

[0060] Although the embodiments of the present invention have been described with reference to a warped workpiece 1, the present invention is also effective for non-warped workpieces 1. This is because, not limited to warping of the workpiece 1, the outer edge of the workpiece 1 is usually chamfered into a rounded shape and is slightly raised from the holding surface 25, making it prone to flapping during grinding due to the intrusion of grinding fluid and collision with the grinding wheel. Furthermore, even if the chamfered portion of the workpiece 1 has been removed beforehand, there is a risk of chipping occurring in the workpiece 1 starting from the outer periphery as the grinding wheel collides with it from the outer periphery. Therefore, the present invention, which forms a recess 11 in the central part 8 of the workpiece 1 and applies the grinding wheel to the inner surface of the recess 11 to widen the grinding area and grind the outer periphery 9, prevents damage to the workpiece 1 starting from the outer periphery 9, where the holding force is unstable, because the grinding wheel does not come into contact with the outer periphery 9. It should be noted that the present invention is not limited to the above embodiments. That is, it can be implemented with various modifications without departing from the core of the present invention. [Explanation of symbols]

[0061] 1 Workpiece 6. Final thickness (specified thickness) 8 Central part 9 Outer periphery 11 recess 12. Specified thickness 21 Holding Table 25 Holding surface 27,28 Suction route 29 Suction source 30. First grinding wheel 40. Second grinding wheel 101 Holding step 102 Central grinding step 103 Outer circumference grinding step 107 Peripheral Adsorption Step 108 Full surface grinding step 251 Outer area 252 Central area

Claims

1. A method for grinding a workpiece, A holding step in which the workpiece is held on a holding table, A central grinding step is performed using a first grinding wheel with an outer diameter smaller than that of the workpiece to grind the central part of the workpiece to a predetermined thickness and form a recess. After the central grinding step is performed, the first grinding wheel is moved relative to the outer peripheral region of the holding surface of the holding table from the recess, and the outer peripheral portion of the workpiece surrounding the recess is ground in an outer peripheral grinding step. Equipped with, The holding table is, A retaining surface divided into an outer peripheral region that holds the outer peripheral portion and a central region that holds the central portion, It has a suction path that connects the outer peripheral region and the central region to a suction source independently, The method for grinding a workpiece is characterized in that the holding step generates an attractive force in the central region and holds the central part of the workpiece.

2. The method for grinding a workpiece according to claim 1, characterized in that the central grinding step and the outer peripheral grinding step are repeatedly performed.

3. An outer periphery suction step is performed, starting from the outer periphery grinding step, and at a predetermined timing, while maintaining the suction force in the central region, an additional suction force is generated in the outer periphery region, thereby adsorbing the thinned outer periphery of the workpiece to the outer periphery region. After the outer periphery suction step, the entire surface of the workpiece is ground with the first grinding wheel or a second grinding wheel different from the first grinding wheel to thin the workpiece to the desired final thickness in a full surface grinding step, A method for grinding a workpiece according to claim 1, characterized by comprising the following features.

4. The method for grinding a workpiece according to claim 1, characterized in that the first grinding wheel has an outer diameter smaller than the central region.

5. The method for grinding a workpiece according to claim 3, characterized in that the second grinding wheel used in the full-surface grinding step has a larger outer diameter than the first grinding wheel.

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