JP2024074423A - Method for grinding a workpiece - Google Patents

Abstract

The present invention reduces deterioration of the condition of a second grinding wheel.
[Solution] A method for grinding a workpiece includes a first grinding step of grinding a workpiece with a first grinding wheel having a plurality of first grinding stones, and a second grinding step of grinding the workpiece with a second grinding wheel having a plurality of second grinding stones, each of which has abrasive grains with an average grain size smaller than the average grain size of the abrasive grains of each of the first grinding stones. The first grinding step includes an upper surface grinding step of grinding the upper surface side of the workpiece while rotating the first grinding wheel and a first chuck table, and a groove forming step of grinding the workpiece while rotating the first grinding wheel and not rotating the first chuck table, to form a first arc-shaped groove having a first depth and a second arc-shaped groove having a second depth different from the first depth in the workpiece. In the second grinding step, the workpiece is ground with the second grinding wheel so as to remove the first groove and the second groove.
[Selected Figure] Figure 1

Description

The present invention relates to a method for grinding a workpiece using a grinding wheel.

When grinding hard wafers, such as silicon single crystal substrates with a relatively high impurity concentration or hard material substrates with a higher hardness than silicon single crystal substrates, with a grinding wheel, the condition of the grinding stone fixed to the grinding wheel is likely to deteriorate. When the condition of the grinding stone deteriorates, problems such as a sudden increase in the current value for driving the spindle to which the grinding wheel is attached occur.

This problem is particularly likely to occur when grinding hard wafers using a finishing grinding wheel (second grinding wheel) that includes multiple finishing grinding wheels (second grinding wheels), each of which has a smaller average grain size than the average grain size of the rough grinding wheel (first grinding wheel).

To address this issue, a method is known in which a grinding wheel is inserted into the outer periphery of the workpiece to grind only the outer periphery, and then the inclination of the chuck table that holds the workpiece by suction is gradually changed to grind the entire workpiece, thereby uniformly thinning the workpiece (see, for example, Patent Document 1).

However, with the above-mentioned method, for example, it is necessary to change the inclination of the chuck table while a load is being applied to the chuck table from the grinding wheel, so modifications to the normal inclination adjustment mechanism that adjusts the inclination of the chuck table to give it high rigidity are necessary. In order to avoid such modifications, some kind of ingenuity is required to reduce the deterioration of the condition of the grinding wheel during grinding, instead of modifying the inclination adjustment mechanism, etc.

JP 2011-206867 A

The present invention was made in consideration of these problems, and aims to reduce deterioration of the condition of the second grinding wheel when grinding a workpiece with a second grinding wheel that includes a second grinding wheel having abrasive grains with an average grain size smaller than the average grain size of the abrasive grains of each of the first grinding wheels after grinding the workpiece with a first grinding wheel.

According to one aspect of the present invention, a method for grinding a workpiece includes a first grinding step in which a first grinding wheel having a plurality of first grinding wheels arranged in an annular manner on the underside of a first wheel base and a disk-shaped first chuck table having a circular first holding surface are moved relatively along the rotation axis direction of the first grinding wheel to grind the workpiece, and after the first grinding step, a second grinding step in which a second grinding wheel having a plurality of second grinding wheels each having a smaller average grain size than the average grain size of the abrasive grains of each of the first grinding wheels and a disk-shaped second chuck table having a circular second holding surface are moved relatively along the rotation axis direction of the second grinding wheel to grind the workpiece, and the first grinding step includes a second grinding step in which the first grinding wheel and the first chuck table are moved relatively along the rotation axis direction of the second grinding wheel to grind the workpiece. The method includes a groove forming step including: an upper surface grinding step of grinding the upper surface side of the workpiece while rotating the first grinding wheel and the table; a first groove forming step of grinding the workpiece while rotating the first grinding wheel and not rotating the first chuck table to form a first arc-shaped groove having a first depth in the workpiece; and a second groove forming step of grinding the workpiece after the first groove forming step by rotating the first grinding wheel and not rotating the first chuck table to grind at least a part of a region different from the first groove to form a second arc-shaped groove having a second depth different from the first depth in the workpiece, and in the second grinding step, the workpiece is ground with the second grinding wheel so as to remove the first groove and the second groove.

In a second grinding step of the grinding method according to one aspect of the present invention, the workpiece is ground with a second grinding wheel so as to remove a first groove having a first depth and a second groove having a second depth different from the first depth, which are formed in the workpiece in the first grinding step.

Therefore, in the second grinding step, the second grinding wheel can be dressed in stages using the first and second grooves, reducing deterioration of the condition of the second grinding wheel.

FIG. 2 is a flow diagram of a method for grinding a workpiece. FIG. 2 is a partial cross-sectional side view of the grinding device. FIG. 3A is a partially sectional side view showing the upper surface grinding step, and FIG. 3B is a perspective view showing the upper surface grinding step. FIG. 4A is a top view showing the first groove forming step, and FIG. 4B is a top view of the workpiece in which the first groove has been formed. FIG. 5A is a top view of the workpiece after the groove forming step, and FIG. 5B is a graph showing an example of an outline of the depth of each groove. FIG. 6A is a top view showing the second grinding step, and FIG. 6B is a partially sectional side view of the second grinding device. 13 is a graph showing an outline of another example of the depth of each groove. FIG. 11 is a top view of the workpiece after a groove forming step according to a second modified example.

An embodiment of one aspect of the present invention will be described with reference to the attached drawings. FIG. 1 is a flow diagram of a method for grinding a disk-shaped workpiece 11 (see FIG. 2). In this embodiment, the workpiece 11 is ground according to the flow shown in FIG. 1.

The workpiece 11 in this embodiment has a disk-shaped silicon single crystal substrate. The silicon single crystal substrate may have a relatively low concentration of impurities (i.e., the resistivity may be greater than 0.1 Ω·cm and less than or equal to 40.0 Ω·cm), or may have a relatively high concentration of impurities (i.e., the resistivity may be greater than or equal to 0.001 Ω·cm and less than or equal to 0.1 Ω·cm).

The workpiece 11 may have a compound semiconductor single crystal substrate instead of a silicon single crystal substrate. The compound semiconductor single crystal substrate is, for example, a single crystal substrate made of gallium nitride (GaN), silicon carbide (SiC), etc., but is not limited to these materials. The workpiece 11 may have a single crystal sapphire substrate.

On the surface 11a side of the workpiece 11, a number of planned division lines (not shown) are set in a grid pattern, and devices (not shown) such as ICs (Integrated Circuits) are formed in each small area partitioned by the planned division lines. There are no restrictions on the type, number, shape, structure, size, arrangement, etc. of the devices. It is not necessary for devices to be formed on the surface 11a side.

By grinding the back surface 11b, which is located opposite the front surface 11a, the workpiece 11 is uniformly thinned. If a device is formed on the front surface 11a, a resin protective member 13 (see FIG. 2) of approximately the same diameter as the workpiece 11 is attached to the front surface 11a before grinding the workpiece 11.

The protective member 13 is, for example, a tape having a base layer and an adhesive layer, and the adhesive layer of the tape is attached to the surface 11a side. By attaching the protective member 13 to the surface 11a side, it is possible to reduce the impact on the device during grinding.

The protective member 13 may be a sheet having a base layer without an adhesive layer. In this case, the protective member 13 is attached to the surface 11a by thermocompression bonding. After the protective member 13 is attached to the surface 11a, the workpiece 11 is ground using the first grinding device 2 (see FIG. 2) and the second grinding device 50 (see FIG. 6(A)).

The first grinding device 2 and the second grinding device 50 are each a so-called manual grinder. The structures of the first grinding device 2 and the second grinding device 50 are substantially the same, so we will first explain the configuration of the first grinding device 2 with reference to Figure 2.

Figure 2 is a partially cross-sectional side view of the first grinding device 2. In Figure 2, the X-axis direction and the Y-axis direction form a horizontal plane and are perpendicular to each other. The Z-axis direction (up-down direction, height direction) is perpendicular to the XY plane.

The first grinding device 2 includes a base 4 that supports or houses each component. A rectangular parallelepiped recess 4a having a longitudinal portion arranged along the X-axis direction is formed on the upper surface side of the base 4. A ball screw type movement mechanism 6 is provided in the recess 4a.

The moving mechanism 6 has a pair of guide rails (not shown) arranged approximately parallel to the X-axis direction. The pair of guide rails is fixed to the base 4. A moving plate 8 is slidably attached to the upper side of the pair of guide rails.

A nut portion 10 is provided on the underside of the moving plate 8. A screw shaft 12 is rotatably connected to the nut portion 10 via a number of balls (not shown). The screw shaft 12 is disposed between a pair of guide rails along the X-axis direction.

A motor 14 such as a stepping motor or a pulse motor is connected to one end of the screw shaft 12. When the screw shaft 12 is rotated by the motor 14, the moving plate 8 moves along the X-axis direction. A first chuck table 16, which is disk-shaped, is disposed above the moving plate 8.

The first chuck table 16 has a disk-shaped frame made of non-porous ceramics. A disk-shaped recess is formed in the upper part of the frame. A disk-shaped porous plate made of porous ceramics and having an outer diameter approximately the same as the inner diameter of the recess is fixed in this recess.

A groove, a tube, etc. are formed in the bottom of the frame. Negative pressure generated by a suction source (not shown) such as a vacuum pump is transmitted to the upper surface of the porous plate via the groove, the tube, etc. The upper surface of the frame and the upper surface of the porous plate are approximately flush with each other.

The upper surface of the frame and the upper surface of the porous plate form a circular first holding surface 16a. The first holding surface 16a has a conical shape with the radial center 16c (see FIG. 3(A)) protruding by about 20 μm from the outer periphery, but since this protrusion is minute, the first holding surface 16a is shown as approximately flat in FIG. 2. Note that the protrusion of the center 16c is exaggerated in FIG. 3(A).

When negative pressure is applied to the porous plate while the workpiece 11 is placed on the first holding surface 16a, the workpiece 11 deforms to conform to the shape of the first holding surface 16a and is held by suction on the first holding surface 16a via the protective member 13.

The first chuck table 16 is rotatably supported by an annular table base 18 via a bearing (not shown). A through hole (not shown) is formed in the radial center of the table base 18, and the rotation shaft 16b of the first chuck table 16 is inserted into this through hole.

A driven pulley (not shown) is fixed to the lower end of the rotating shaft 16b. The driven pulley is connected via an endless belt (not shown) to a drive pulley (not shown) that is fixed to the output shaft of a rotation drive source (not shown) such as a servo motor.

The table base 18 is supported by the tilt adjustment unit 20. The tilt adjustment unit 20 is supported by the moving plate 8. The tilt adjustment unit 20 has one fixed support part 20a and two movable support parts 20b arranged at approximately equal intervals along the circumferential direction of the table base 18. One movable support part 20b is shown in FIG. 2.

The inclination of the table base 18 is adjusted by adjusting the height position of the upper end of the movable support part 20b in the Z-axis direction. The inclination of the table base 18 is adjusted, for example, so that a part of the first holding surface 16a is approximately parallel to the grinding surface of the first grinding wheel 46 described below.

When the tilt of the table base 18 is adjusted, the rotation axis 16b also tilts accordingly. However, the angle of tilt is very small. The first chuck table 16 can rotate around the rotation axis 16b at a predetermined speed while the rotation axis 16b is tilted.

In the X-axis direction, bellows-shaped cover members 22 that can expand and contract along the X-axis direction are provided on both sides of the first chuck table 16. The cover members 22 prevent contamination of the moving mechanism 6 by grinding debris, grinding water, etc. generated during grinding.

A rectangular parallelepiped support structure 4b is provided integrally with the base 4 in an upwardly protruding manner on the rear side (one side in the X-axis direction) of the first grinding device 2. A ball screw type grinding feed mechanism 24 is provided on the front side (the other side in the X-axis direction) of the support structure 4b.

The grinding feed mechanism 24 includes a pair of guide rails 26 arranged along the Z-axis direction. The pair of guide rails 26 are fixed to the front side of the support structure 4b. A rectangular moving plate 28 is fixed to the pair of guide rails 26 so as to be slidable in the Z-axis direction.

A nut portion 30 is provided on the rear side of the moving plate 28, and a screw shaft 32 is rotatably connected to the nut portion 30 via a number of balls (not shown). The screw shaft 32 is disposed along the Z-axis direction between the pair of guide rails 26.

A motor 34, such as a stepping motor or pulse motor, is connected to the upper end of the screw shaft 32 to rotate the screw shaft 32. When the motor 34 rotates the screw shaft 32, the moving plate 28 moves along the Z-axis direction.

A holding member 38 for holding the first grinding unit 36 is fixed to the front side of the moving plate 28. The first grinding unit 36 has a cylindrical spindle housing 40 disposed in the hollow portion of the holding member 38.

A part of a cylindrical spindle 42, whose longitudinal direction is arranged along the Z-axis direction, is rotatably housed in the spindle housing 40. A rotation drive source (not shown), such as a servo motor, is provided near the upper end of the spindle 42.

The lower end of the spindle 42 protrudes downward from the lower end of the holding member 38 through a through hole formed in the lower surface of the holding member 38. A disk-shaped mount 44 is fixed to the lower end of the spindle 42.

A circular first grinding wheel 46 is attached to the underside of the mount 44 by a bolt (not shown). The first grinding wheel 46 includes a circular first wheel base 46a having an outer diameter approximately the same as that of the mount 44.

The first wheel base 46a is made of a metal such as an aluminum alloy. A plurality of first grinding wheels 46b are fixed to the lower surface _46a1 side of the first wheel base 46a at approximately equal intervals along the circumferential direction of the first wheel base 46a. In other words, the plurality of first grinding wheels 46b are arranged in a ring shape.

Each first grinding wheel 46b has abrasive grains made of diamond, cBN (cubic boron nitride), etc., and a bonding material (bond material) made of resin, metal, vitrified, etc., that fixes the abrasive grains.

The first grinding wheel 46b has an average grain size larger than the average grain size of the abrasive grains of the second grinding wheel 56b described below. For example, when the size of a single grain is expressed as a predetermined grain size (i.e., length), the average grain size is determined based on the frequency distribution of a group of grains expressed using this grain size. There are known methods for expressing grain size, such as geometric diameter and equivalent diameter.

Geometric diameters include Feret diameter, maximum diameter in a certain direction (i.e., Krummbein diameter), Martin diameter, sieve diameter, etc., and equivalent diameters include projected area circle equivalent diameter (i.e., Heywood diameter), equal surface area sphere equivalent diameter, equal volume sphere equivalent diameter, Stokes diameter, light scattering diameter, etc. For a particle group, when a frequency distribution is created with particle diameter (μm) on the horizontal axis and frequency on the vertical axis, the average particle diameter, for example, in the weight-based distribution or volume-based distribution is the average particle size.

The first grinding wheel 46b in this embodiment is a rough grinding wheel, and has abrasive grains with a grain size of, for example, #240 to #1200. The grain size is described in JIS R6001-2:2017 (Grain size of abrasives for grinding wheels - Part 2: Fine powder) of the JIS standard established by the Japanese Industrial Standards Committee.

When the spindle 42 is rotated, the first grinding wheel 46 rotates around the spindle 42. In other words, the spindle 42 becomes the axis of rotation of the first grinding wheel 46. When the first grinding wheel 46 rotates, a circular grinding surface is formed by the trajectory of the bottom surfaces of the multiple first grinding stones 46b. In this embodiment, the grinding surface is disposed approximately parallel to the XY plane.

A grinding water supply nozzle (not shown) is provided directly below the first grinding wheel 46. The grinding water supply nozzle supplies grinding liquid (typically pure water) to the contact area between the first grinding wheel 46b and the workpiece 11 when grinding the workpiece 11. During grinding, this liquid is used to remove heat and grinding debris generated in the processing area.

When grinding the workpiece 11, first, the first chuck table 16 is placed in the loading/unloading area A1 located in front of the first grinding device 2, and the surface 11a side is suction-held by the first chuck table 16 via the protective member 13.

Then, the first chuck table 16 is placed at the grinding position A2 directly below the first grinding unit 36. At this time, the first grinding wheel 46 and the first chuck table 16 are positioned so that the grinding surface (i.e., the trajectories of the multiple first grinding wheels 46b) overlaps with the center 16c of the first holding surface 16a in the Z-axis direction.

Then, while rotating the spindle 42 and the first chuck table 16 in a predetermined direction, the first grinding unit 36 is moved downward at a predetermined speed (i.e., grinding feed). In this embodiment, the spindle 42 is arranged along the Z-axis direction.

When the first grinding unit 36 is fed for grinding, the first grinding wheel 46 moves along the Z-axis direction (the direction of the rotation axis of the first grinding wheel 46) relative to the first chuck table 16. When the grinding surface comes into contact with the back surface 11b of the workpiece 11, the workpiece 11 is ground.

Next, with reference to Figures 3(A) to 5(B), the first grinding step S10 in which the workpiece 11 is ground using the first grinding device 2 will be described.

The first grinding step S10 includes a top-side grinding step S11 (see Figs. 3(A) and 3(B)) in which the top side (i.e., the back side 11b side) of the workpiece 11 is uniformly ground. Fig. 3(A) is a partially cross-sectional side view showing the top-side grinding step S11, and Fig. 3(B) is a perspective view showing the top-side grinding step S11.

In the top surface grinding step S11, as shown in FIG. 3(A) and FIG. 3(B), the top surface side (i.e., the back surface 11b side) of the workpiece 11 is ground while the first grinding wheel 46 and the first chuck table 16 are both rotating. This allows the back surface 11b side to be ground uniformly.

In the top side grinding step S11, the rotation speed of the first chuck table 16 is set to 100 rpm or more and 600 rpm or less (e.g., 300 rpm), the rotation speed of the first grinding wheel 46 is set to 1000 rpm or more and 7000 rpm or less (e.g., 4500 rpm), and the grinding feed rate is set to 0.8 μm/s or more and 10 μm/s or less (e.g., 6.0 μm/s).

After the top-side grinding step S11, a groove forming step S12 is performed to form multiple grooves on the back surface 11b side of the workpiece 11. By performing the top-side grinding step S11 first, the travel distance of the first grinding unit 36 in the Z-axis direction can be shortened compared to when the groove forming step S12 is performed first, and therefore the grinding time can be shortened.

The groove forming step S12 in this embodiment includes a first groove forming step S13 to a fourth groove forming step S16. In the first groove forming step S13, as shown in Fig. 4(A), the first grinding wheel 46 is rotated and the workpiece 11 is ground while the first chuck table 16 is stationary (i.e., not rotated) to form an arc-shaped first groove _11c1 having a first depth _11d1 (see Fig. 5(B)) in the workpiece 11.

Figure 4 (A) is a top view showing the first groove formation step S13. The rotation axis 16b of the first chuck table 16 is inclined with respect to the Z-axis direction, and the arc-shaped region 11e of the workpiece 11 held by suction on the first holding surface 16a, indicated by the double arrow in Figure 4 (A), is disposed approximately parallel to the XY plane.

When the first grinding unit 36 is fed for grinding, the arc-shaped region 11e is ground first. When the grinding is further advanced, the overlapping region between the grinding surface and the back surface 11b other than the arc-shaped region 11e is gradually ground, and the first groove _11c1 is formed.

4B is a top view of the workpiece 11 in which the first groove _11c1 is formed. The first groove _11c1 has a flat portion _11c1A having a substantially uniform depth and a substantially flat bottom in a region corresponding to the above-mentioned arc-shaped region 11e. In contrast, in a region other than the region corresponding to the arc-shaped region 11e, the first groove _11c1 has an inclined portion _11c1B whose depth gradually becomes shallower from the center in the radial direction of the back surface 11b toward the outer circumferential edge.

After the first groove forming step S13, the first grinding unit 36 is temporarily raised so as not to come into contact with the back surface 11b of the workpiece 11. Next, the first chuck table 16 is rotated approximately 90 degrees, and then a second arc-shaped groove _11c2 (see FIG. 5A) is formed (second groove forming step S14).

In the second groove forming step S14, the first grinding wheel 46 is rotated, and the first grinding unit 36 is fed to grind the workpiece 11 without rotating the first chuck table 16. In this way, the second groove _11c2 is formed.

The second groove _11c2 overlaps with the first groove _11c1 in the vicinity of the region corresponding to the center 16c of the first holding surface 16a, but does not overlap with the first groove _11c1 in other regions. That is, in the second groove forming step S14, a region at least partially different from the first groove _11c1 is ground.

5B, the second groove _11c2 of this embodiment also has a flat portion _11c2A and an inclined portion _11c2B . The flat portion _11c2A has a second depth _11d2 . The second depth _11d2 is different from the first depth _11d1 .

In this embodiment, the second depth _11d2 is deeper than the first depth _11d1 . However, the inclined portion _11c2B gradually becomes shallower from the center toward the outer circumferential edge in the radial direction of the back surface 11b.

After the second groove forming step S14, the first grinding unit 36 is raised again to an extent that it does not come into contact with the back surface 11b of the workpiece 11. Next, the first chuck table 16 is rotated approximately 90 degrees, and then a third groove _11c3 (see FIG. 5A) having an arc shape is formed (third groove forming step S15).

In the third groove forming step S15, the first grinding wheel 46 is rotated, and the first grinding unit 36 is fed to grind the workpiece 11 without rotating the first chuck table 16.

As a result, a region at least partially different from the first groove _11c1 and the second groove _11c2 is ground to form a third groove _11c3 . The third groove _11c3 also overlaps with the first groove _11c1 and the second groove _11c2 in the vicinity of a region corresponding to the center 16c of the first holding surface 16a.

5B, the third groove _11c3 of this embodiment also has a flat portion _11c3A and an inclined portion _11c3B . The flat portion _11c3A has a third depth _11d3 . The third depth _11d3 is different from the first depth _11d1 and the second depth _11d2 .

In this embodiment, the third depth _11d3 is deeper than the second depth _11d2 . However, the inclined portion _11c3B gradually becomes shallower from the center toward the outer circumferential edge in the radial direction of the back surface 11b.

After the third groove forming step S15, the first grinding unit 36 is raised again to a position where it does not come into contact with the back surface 11b of the workpiece 11. Next, the first chuck table 16 is rotated approximately 90 degrees, and then a fourth arc-shaped groove _11c4 (see FIG. 5A) is formed (fourth groove forming step S16).

In the fourth groove forming step S16, the first grinding wheel 46 is rotated, and the first grinding unit 36 is fed to grind the workpiece 11 without rotating the first chuck table 16.

As a result, at least a portion of an area different from the first groove _11c1 , the second groove _11c2 , and the third groove _11c3 is ground to form the fourth groove _11c4 . The fourth groove _11c4 also overlaps with the first groove _11c1 , the second groove _11c2 , and the third groove _11c3 in the vicinity of the area corresponding to the center 16c of the first holding surface 16a.

5B, the fourth groove _11c4 of this embodiment also has a flat portion _11c4A and an inclined portion _11c4B . The flat portion _11c4A has a fourth depth _11d4 . The fourth depth _11d4 is different from the first depth _11d1 , the second depth _11d2 , and the third depth _11d3 .

In this embodiment, the fourth depth 11d ₄ is deeper than the third depth 11d _3. The thickness from the bottom of the deepest flat portion 11c _4A to the front surface 11a is shallower than the final finished thickness of the workpiece 11 by a predetermined value (e.g., 15 μm to 20 μm). The inclined portion 11c _4B becomes gradually shallower from the radial center of the back surface 11b toward the outer circumferential edge.

In the groove forming step S12, the rotation speed of the first grinding wheel 46 is set to 1000 rpm or more and 7000 rpm or less (e.g., 4500 rpm), and the grinding feed rate is set to 0.8 μm/s or more and 10 μm/s or less (e.g., 6.0 μm/s).

FIG. 5(A) is a top view of the workpiece 11 after the groove forming step S12, and FIG. 5(B) is a graph showing an example of an outline of the depth of each groove (first groove _11c1 to fourth groove _11c4 ) in the workpiece 11 after the groove forming step S12 and before the second grinding step S20.

The horizontal axis in FIG. 5(B) is the distance from center 16c (i.e., the center of back surface 11b). The vertical axis in FIG. 5(B) is the thickness of workpiece 11. Note that zero on the vertical axis corresponds to front surface 11a, and thickness T corresponds to the thickness of workpiece 11 after top surface grinding step S11 and before groove formation step S12 (i.e., the distance from front surface 11a to back surface 11b).

After the first grinding step S10, the workpiece 11 is transported from the first grinding device 2 to the second grinding device 50 (see FIG. 6(A)), where the second grinding step S20 is performed. The second grinding device 50 is substantially the same as the first grinding device 2. Therefore, unless components different from the first grinding device 2 are clearly indicated, the second grinding device 50 has the same components as the first grinding device 2 shown in FIG. 2.

As shown in FIG. 6(A), the second grinding device 50 has a second chuck table 52 having substantially the same structure and size as the first chuck table 16. The second chuck table 52 is capable of rotating around a predetermined rotation axis 52b similar to the rotation axis 16b while suction-holding the workpiece 11 after the first grinding step S10 on the second holding surface 52a.

A second grinding unit 54 is disposed above the second chuck table 52. The second grinding unit 54 has substantially the same structure and size as the first grinding unit 36. A second grinding wheel 56 is attached to the lower end of the spindle 42 of the second grinding unit 54 via a mount 44.

The second grinding wheel 56 includes a second wheel base 56a that is annular and has an outer diameter that is approximately the same as that of the mount 44. The second wheel base 56a is made of a metal such as an aluminum alloy.

A plurality of second grinding wheels 56b are fixed to a lower surface _56a1 (see FIG. 6B) of the second wheel base 56a at approximately equal intervals along the circumferential direction of the second wheel base 56a. In other words, the plurality of second grinding wheels 56b are arranged in an annular shape along the circumferential direction of the second wheel base 56a.

Each second grinding wheel 56b also has abrasive grains made of diamond, cBN (cubic boron nitride), etc., and a bonding material (bond material) made of resin, metal, vitrified, etc., that fixes the abrasive grains.

However, the second grinding wheel 56b is a so-called finishing grinding wheel, and has abrasive grains whose average grain size is smaller than that of the first grinding wheels 46b. The grain size of the abrasive grains of the second grinding wheel 56b is, for example, #2000 to #10000. Note that for grain sizes not specified in JIS R6001-2:2017, the notation used in the industry that manufactures and sells grinding wheels shall be followed or equivalent.

Fig. 6(A) is a top view showing the second grinding step S20, and Fig. 6(B) is a partially sectional side view of the second grinding unit 54 and the second chuck table 52 in the second grinding device 50. Although omitted in Fig. 6(B), the workpiece 11 has the above-mentioned first groove _11c1 to fourth groove _11c4 formed therein.

In the second grinding step S20, the second grinding wheel 56 and the second chuck table 52 are positioned so that the grinding surface (i.e., the trajectory of the multiple second grinding wheels 56b) overlaps with the center 52c of the second holding surface 52a in the Z-axis direction, and the second grinding wheel 56 is moved along the Z-axis direction relative to the second chuck table 52.

In the second grinding step S20, the rotation axis direction of the second grinding wheel 56 corresponds to the Z-axis direction. When the second grinding wheel 56 is fed for grinding, the first groove _11c1 , the second groove _11c2 , the third groove _11c3 , and the fourth groove _11c4 are gradually removed as the back surface 11b side is ground.

Upon completion of the second grinding step S20, the workpiece 11 is ground to a position that is a predetermined value (e.g., 15 μm or more and 20 μm or less) deeper than the fourth depth _11d4 , thereby exposing the back surface 11b, the entire surface of which has been ground by the second grinding wheel 56.

In this embodiment, the second grinding wheel 56b can be dressed in stages using the first groove _11c1 to the fourth groove _11c4 . Specifically, the lower surface of the second grinding wheel 56b collides with the inner wall of each groove, which makes the binder of the second grinding wheel 56b more likely to wear. As a result, self-sharpening is promoted, and deterioration of the condition of the second grinding wheel 56b can be reduced.

In particular, the first groove _11c1 to the fourth groove _11c4 in this embodiment have different depths. Therefore, at the beginning of the second grinding step S20, the second grinding wheel 56b can be dressed using all of the first groove _11c1 to the fourth groove _11c4 . This can promote the wear of the binder.

In contrast, as the grinding feed advances, the number of grooves that can be dressed on the second grinding wheel 56b gradually decreases. Therefore, at the end of the second grinding step S20, wear of the binder is suppressed compared to the beginning of the second grinding step S20. In other words, at the end of the second grinding step S20, wear of the second grinding wheel 56b can be reduced.

In this manner, by utilizing the first groove _11c1 to the fourth groove _11c4 , each having a different depth, in the second grinding step S20, it is possible to simultaneously reduce deterioration of the second grinding wheel 56b and suppress excessive wear of the second grinding wheel 56b.

(First modified example) Figure 7 is a graph showing an outline of another example of the depth of each groove formed in the groove forming step S12. The horizontal axis of Figure 7 is the same as the horizontal axis of the graph shown in Figure 5 (B), and the vertical axis of Figure 7 is the same as the vertical axis of the graph shown in Figure 5 (B).

In the first modified example, the shallowest region of the inclined portion _11c4B of the fourth groove _11c4 is shallower than the depth of the flat portion _11c1A of the first groove _11c1 in the thickness direction of the workpiece 11. However, the situation in which the flat portion _11c1A has the deepest depth and _{the flat portion 11c4A has} the deepest depth among the flat portions 11c1A and _11c4A is the same as the example of FIG.

The first modified example can also achieve the same effect as the above-mentioned embodiment. Since the effect of dressing in each groove is considered to be greater in the flat portion than in the inclined portion, when adjusting the depth of each groove, the depth of the flat portion can be adjusted in stages.

8 is a top view of the workpiece 11 after the groove forming step S12 according to the second modified example. In the groove forming step S12 of the second modified example, the first groove forming step S13 and the second groove forming step S14 are alternately repeated to form two first grooves _11c1 and two second grooves _11c2 .

More specifically, the first groove forming step S13 is performed to form the first first groove _11c1 , and then the first chuck table 16 is rotated approximately 90 degrees. Next, the second groove forming step S14 is performed to form the first second groove _11c2 , and then the first chuck table 16 is rotated approximately 90 degrees in the same manner.

Furthermore, a first groove forming step S13 is performed to form the second first groove _11c1 , and then the first chuck table 16 is rotated approximately 90 degrees. Next, a second groove forming step S14 is performed to form the second second groove _11c2 .

As a result, in the circumferential direction of the workpiece 11, the first flat portion 11c _1A , the first flat portion 11c _2A , the second flat portion 11c _1A , and the second flat portion 11c _2A are arranged in this order at approximately equal intervals.

By arranging multiple flat portions, each having a different depth, alternately along the circumferential direction of the workpiece 11, the effect of dressing the multiple second grinding wheels 56b in the second grinding step S20 can be more evenly exerted within the back surface 11b of the workpiece 11.

In addition, by repeatedly forming the first groove _11c1 to the third groove _11c3 in this order, the first flat portion _11c1A , the first flat portion _11c2A , the first flat portion _11c3A , the second flat portion _11c1A , the second flat portion _11c2A , and the second flat portion _11c3A may be formed in this order at approximately equal intervals in the circumferential direction of the workpiece 11.

By periodically arranging multiple flat portions, each having a different depth, along the circumferential direction of the workpiece 11, the effect of dressing the multiple second grinding wheels 56b in the second grinding step S20 can be more evenly exerted within the back surface 11b of the workpiece 11.

(Third Modification) In the above-mentioned embodiment and modification, the case where two manual grinders (first grinding device 2 and second grinding device 50) are used has been described. However, the first grinding step S10 and the second grinding step S20 may be performed using a so-called automatic grinding device (not shown) equipped with a first grinding unit 36 and a second grinding unit 54.

An automated grinding device has one disk-shaped turntable. For example, three chuck tables are provided on the turntable. These three chuck tables are arranged at approximately equal intervals along the circumferential direction of the turntable.

By rotating the turntable clockwise or counterclockwise at a predetermined timing, the workpiece 11 held by suction on one chuck table moves in the following order: the loading/unloading position, the position directly below the first grinding unit 36, the position directly below the second grinding unit 54, and then the loading/unloading position.

For example, when one chuck table is positioned at the loading/unloading position, another chuck table is positioned directly below the first grinding unit 36, and yet another chuck table is positioned directly below the second grinding unit 54.

In an automated grinding device, one chuck table functions as the first chuck table 16 and the second chuck table 52 described above. In other words, in an automated grinding device, the first chuck table 16 and the second chuck table 52 described above are the same.

When performing the first grinding step S10 in an automated grinding device, first, one chuck table holding the workpiece 11 by suction is placed directly below the first grinding unit 36, and the top surface grinding step S11 is performed.

Next, by adjusting the rotation angle of the chuck table in approximately 90 degree increments, the first groove _11c1 , the second groove _11c2 , etc. are formed in a groove forming step S12, as shown in Figures 4(A) and 5(A). After the groove forming step S12, the turntable is rotated, and the workpiece 11 is placed directly below the second grinding unit 54, and a second grinding step S20 is performed.

The structures, methods, etc. according to the above-described embodiments can be modified as appropriate without departing from the scope of the present invention. For example, the groove formation step S12 may be performed first, and then the top surface grinding step S11 may be performed, although this will reduce the effect of shortening the grinding time.

When the groove forming step S12 is performed prior to the top surface grinding step S11, the depths of the first groove _11c1 , second groove _11c2 , etc. are appropriately adjusted so that they are not completely removed in the top surface grinding step S11.

The number of grooves formed in the groove forming step S12 is not limited to four. In the groove forming step S12, two or more grooves (e.g., three, five, six, etc.) having different depths may be formed.

2: First grinding device, 4: Base, 4a: Recess, 4b: Support structure, 6: Moving mechanism, 8: Moving plate, 10: Nut portion, 11: Workpiece, 11a: Front surface, 11b: Back surface, 11c ₁ : First groove, 11c _1A : Flat portion, 11c _1B : Inclined portion, 11c ₂ : Second groove, 11c _2A : Flat portion, 11c _2B : Inclined portion, 11c ₃ : Third groove, 11c _3A : Flat portion, 11c _3B : Inclined portion, 11c ₄ : Fourth groove, 11c _4A : Flat portion, 11c _4B : Inclined portion, 11d ₁ : First depth, 11d ₂ : Second depth, 11d ₃ : Third depth, 11d ₄ : Fourth depth 11e: Arc-shaped region, 13: Protective member 12: Screw shaft, 14: Motor 16: First chuck table, 16a: First holding surface, 16b: Rotation shaft, 16c: Center 18: Table base 20: Tilt adjustment unit, 20a: Fixed support part, 20b: Movable support part 22: Cover member, 24: Grinding feed mechanism, 26: Guide rail, 28: Moving plate 30: Nut part, 32: Screw shaft, 34: Motor 36: First grinding unit, 38: Holding member, 40: Spindle housing 42: Spindle, 44: Mount 46: First grinding wheel, 46a: First wheel base, 46a ₁ : Lower surface 46b: First grinding wheel 50: Second grinding device 52: Second chuck table, 52a: Second holding surface, 52b: Rotary shaft, 52c: Center 54: Second grinding unit, 56: Second grinding wheel, 56a: Second wheel base _56a1 : Lower surface, 56b: Second grinding wheel A1: Loading/unloading area, A2: Grinding position, T: Thickness S10: First grinding step, S11: Upper surface grinding step, S12: Groove forming step S13: First groove forming step, S14: Second groove forming step S15: Third groove forming step, S16: Fourth groove forming step S20: Second grinding step

Claims (1)

A method for grinding a workpiece, comprising the steps of:
a first grinding step in which a first grinding wheel having a plurality of first grinding stones arranged in an annular shape on the underside of a first wheel base and a disk-shaped first chuck table having a circular first holding surface are moved relatively along a rotation axis direction of the first grinding wheel to grind the workpiece;
a second grinding step in which, after the first grinding step, a second grinding wheel in which a plurality of second grinding wheels each having a smaller average grain size than the average grain size of the abrasive grains of each of the first grinding wheels are annularly arranged on the lower surface side of a second wheel base and a disk-shaped second chuck table having a circular second holding surface are moved relatively along the rotation axis direction of the second grinding wheel to grind the workpiece;
Equipped with
The first grinding step includes:
an upper surface side grinding step of grinding an upper surface side of the workpiece while rotating the first grinding wheel and the first chuck table;
a first groove forming step of grinding the workpiece while rotating the first grinding wheel and not rotating the first chuck table, thereby forming a first arc-shaped groove having a first depth in the workpiece; and a second groove forming step of rotating the first grinding wheel after the first groove forming step, grinding the workpiece while rotating the first grinding wheel and not rotating the first chuck table so as to grind at least a portion of a region different from the first groove, thereby forming a second arc-shaped groove having a second depth different from the first depth in the workpiece;
having
In the second grinding step,
grinding the workpiece with the second grinding wheel to remove the first groove and the second groove.

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