JP2024074422A - Grinding method of workpiece - Google Patents

Abstract

To reduce deterioration in the condition of a second grinding stone.SOLUTION: A grinding method of workpiece includes a first grinding step of grinding workpiece by a first grinding wheel having a plurality of first grinding stones, and a second grinding step of grinding the workpiece by a second grinding wheel having a plurality of second grinding stones having abrasive grains having the average particle diameter smaller than the average particle diameter of abrasive grains of the respective first grinding stones, wherein the first grinding step includes an upper face side grinding step of grinding the upper face side of the workpiece in a state in which the loci of the plurality of first grinding stones overlap the center of a first holding surface in a rotation axis direction of the first grinding wheel, and a projection formation step of grinding an annular region on the upper face side of the workpiece in a state where the loci of the plurality of first grinding stones do not overlap the center of the first holding surface in the rotation axis direction of the first grinding wheel, and thereby forming a disk-like projection in the central part of the workpiece, wherein the second grinding step sequentially grinds the projection and the annular region by the second grinding wheel.SELECTED DRAWING: 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.

One aspect of the present invention is a method for grinding a workpiece, comprising: 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, the first grinding step being performed by moving the first grinding wheel along a trajectory formed by the rotation of the plurality of first grinding wheels. The method includes an upper surface grinding step of grinding the upper surface side of the workpiece with the first grinding wheel and the first chuck table arranged so that the tracks formed by the rotation of the first grinding wheels overlap the center of the first holding surface in the direction of the rotation axis of the first grinding wheel, and a convexity forming step of grinding an annular region on the upper surface side of the workpiece from the edge to an inner periphery located a predetermined distance inward from the edge to form a disk-shaped convexity protruding from the annular region in the center of the workpiece, with the first grinding wheel and the first chuck table arranged so that the tracks formed by the rotation of the first grinding wheels do not overlap the center of the first holding surface in the direction of the rotation axis of the first grinding wheel, and in the second grinding step, the convexity and the annular region are sequentially ground with the second grinding wheel in the thickness direction of the workpiece.

In the second grinding step of the grinding method according to one aspect of the present invention, the convex portion formed in the center of the workpiece in the first grinding step and the annular region located around the convex portion are sequentially ground with a second grinding wheel.

In particular, in the second grinding step, the rough grinding areas formed in the convex portion and the annular area in the first grinding step are sequentially ground with the second grinding wheel, so that the rough grinding areas of the workpiece can be used to gradually dress the second grinding wheel. This reduces 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 first 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 partial cross-sectional side view showing the protrusion forming step, and FIG. 4B is a perspective view showing the protrusion forming step. FIG. 5A is a top view showing the convex portion forming step, and FIG. 5B is a side view of a part of the workpiece after the convex portion forming step. FIG. 6A is a partial cross-sectional side view showing the first half of the second grinding step, and FIG. 6B is a partial cross-sectional side view showing the second half of the second grinding step. 13 is a top view showing a modified example of the convex portion forming step. FIG.

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 becomes approximately parallel to a grinding surface _46b1 of a first grinding wheel 46 (see FIG. 5A) described later.

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 serves as the rotation axis of the first grinding wheel 46. When the first grinding wheel 46 rotates, an annular grinding surface _46b1 is formed by the trajectory of the bottom surfaces of the multiple first grinding stones 46b. In this embodiment, the grinding surface _46b1 is disposed substantially 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. 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, and 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 _46b1 comes into contact with the back surface 11b of the workpiece 11, the workpiece 11 is ground. Next, a first grinding step S10 in which the workpiece 11 is ground using the first grinding device 2 will be described with reference to Figs. 3(A) to 5(B).

The first grinding step S10 includes a top-side grinding step S12 (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 S12, and Fig. 3(B) is a perspective view showing the top-side grinding step S12.

In the upper surface grinding step S12, as shown in Figures 3(A) and 3(B), the first grinding wheel 46 and the first chuck table 16 are positioned so that the grinding surface _46b1 (i.e., the trajectory of the multiple first grinding wheels 46b) overlaps with the center 16c of the first holding surface 16a in the Z-axis direction, and a predetermined amount of the workpiece 11 is ground.

As a result, the back surface 11b side is ground uniformly, forming a roughly ground region 11c (see FIG. 5B). The roughly ground region 11c is an area that has been ground with the first grinding wheel 46, but has not been ground or polished with other grinding wheels having an average grain size smaller than that of the first grinding wheel 46b.

In the top side grinding step S12, 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 grinding step S12, an annular region 11f (see FIG. 4A) is ground on the top side (i.e., the back side 11b) of the workpiece 11 from the edge 11d to the inner periphery 11e located a predetermined distance inward, forming a disk-shaped protrusion 11g (see FIG. 4B) that protrudes compared to the annular region 11f in the center of the workpiece 11 (protrusion forming step S14).

Fig. 4(A) is a partially sectional side view showing the convex portion forming step S14, and Fig. 4(B) is a perspective view showing the convex portion forming step S14. Fig. 5(A) is a top view showing the convex portion forming step S14. In Fig. 5(A), the grinding surface _46b1 of the first grinding wheel 46 is shown by a hollow ring.

In the convex portion forming step S14 after the top surface grinding step S12, the first grinding unit 36 is raised to a position where the first grinding wheel 46 does not come into contact with the workpiece 11 while maintaining the rotation of the first grinding wheel 46 and the first chuck table 16. Then, the first chuck table 16 is moved in the X-axis direction.

As a result, the first grinding wheel 46 and the first chuck table 16 are positioned so that the grinding surface _46b1 does not overlap the center 16c of the first holding surface 16a in the Z-axis direction. In this state, the first grinding unit 36 is fed for grinding to grind the back surface 11b side of the workpiece 11.

In the protrusion forming step S14, 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).

In this way, the annular region 11f is ground by a predetermined amount to form an annular region 11f in which the roughly ground region 11c is exposed on the upper surface and the cylindrical side surface, and a convex portion 11g in which the roughly ground region 11c is exposed on the upper surface. Figure 5 (B) is a side view of a portion of the workpiece 11 after the convex portion forming step S14.

The amount of grinding in the first grinding step S10 is adjusted so that the annular region 11f is thicker than the thickness of the workpiece 11 at the completion of the second grinding step S20 by a predetermined value (e.g., 15 μm or more and 20 μm or less).

Since the grinding feed speed of the first grinding unit 36 is constant during grinding of the workpiece 11, the movement distance in the Z-axis direction of the first grinding unit 36 can be made shorter by performing the convex portion forming step S14 after the top surface grinding step S12, as in this embodiment, compared to performing the top surface grinding step S12 after the convex portion forming step S14.

In other words, performing the convex portion forming step S14 after the top surface grinding step S12 has the advantage that the grinding time required for the top surface grinding step S12 and the convex portion forming step S14 can be shortened compared to performing the top surface grinding step S12 after the convex portion forming step S14.

After the convex portion forming step S14, 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 otherwise specified, 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 that has substantially the same structure and size as the first chuck table 16.

The second chuck table 52 can rotate around the rotation axis 52b 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 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 a ring 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.

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 disk-shaped protrusion 11g is first ground by the second grinding wheel 56.

Figure 6 (A) is a partial cross-sectional side view showing the first half of the second grinding step S20. In the first half of the second grinding step S20, the convex portion 11g is ground with the second grinding wheel 56.

As described above, the rough grinding area 11c is formed on the upper surface and side surface of the protrusion 11g, so that the rough grinding area 11c of the protrusion 11g can be used to perform dressing on the second grinding wheel 56b.

Figure 6 (B) is a partial cross-sectional side view showing the latter half of the second grinding step S20, which is performed after the protrusion 11g is removed. In the latter half of the second grinding step S20, the entire back surface 11b is uniformly ground with the second grinding wheel 56.

As described above, the rough grinding area 11c is formed on the upper surface of the annular area 11f, so in addition to grinding the back surface 11b side, the rough grinding area 11c can be used to dress the second grinding wheel 56b.

In this way, by sequentially grinding the convex portion 11g and the annular region 11f with the second grinding wheel 56 in the thickness direction of the workpiece 11 (i.e., the direction from the back surface 11b to the front surface 11a), the second grinding wheel 56b can be dressed in stages using the rough grinding region 11c. This reduces deterioration of the condition of the second grinding wheel 56b.

(First Modification) Fig. 7 is a top view showing a modification of the convex portion forming step S14 in the first grinding step S10. For convenience of explanation, the grinding surface _46b1 of the first grinding wheel 46 is shown as a hollow ring in Fig. 7.

7, the first grinding wheel 46 and the first chuck table 16 are arranged so that the grinding surface _46b1 does not overlap the center 16c of the first holding surface 16a in the Z-axis direction. In this state, the first grinding unit 36 is fed for grinding to grind the back surface 11b side of the workpiece 11.

This grinds the annular region 11f on the top surface of the workpiece 11 from the edge 11d to the inner circumference 11e, which is located a predetermined distance inward, forming a disk-shaped protrusion 11g in the center of the workpiece 11.

(Second Modification) In the above 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 S12 is performed.

Then, by adjusting the rotation angle of the turntable, the positions of the chuck table and the first grinding wheel 46 are adjusted as shown in FIG. 5(A) or FIG. 7, and the protrusion forming step S14 is performed. In this way, the protrusion 11g and the annular region 11f can be formed on the workpiece 11.

In addition, the structures, methods, etc. according to the above-described embodiments can be modified as appropriate without departing from the scope of the present invention. In the first grinding step S10, in the side view shown in FIG. 5(B), the annular region 11f and the protruding portion 11g may form one step, or two or more steps.

By forming two or more steps, more timing can be set for restoring the condition of the second grinding wheel 56b in the second grinding step S20, further reducing deterioration of the condition of the second grinding wheel 56b.

Although the effect of shortening the grinding time will be less, the convex portion forming step S14 may be performed first, and then the top surface grinding step S12 may be performed to grind the top surface of the convex portion 11g.

2: First grinding device 4: Base, 4a: Recess, 4b: Support structure 6: Moving mechanism, 8: Moving plate, 10: Nut, 12: Screw shaft, 14: Motor 11: Workpiece, 11a: Front surface, 11b: Back surface 11c: Rough grinding area, 11d: Edge, 11e: Inner circumference, 11f: Annular area, 11g: Convex 13: Protective member 16: First chuck table, 16a: First holding surface, 16b: Rotating shaft, 16c: Center 18: Te Cable base 20: inclination adjustment unit, 20a: fixed support portion, 20b: movable support portion, 22: cover member 24: grinding feed mechanism, 26: guide rail, 28: moving plate 30: nut portion, 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, _46b1 : Grinding surface 50: Second grinding device 52: Second chuck table, 52a: Second holding surface, 52b: Rotating 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 S10: First grinding step, S12: Upper surface grinding step, S14: Convex portion 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 in a state in which the first grinding wheel and the first chuck table are disposed so that a track formed by rotation of the plurality of first grinding wheels overlaps with a center of the first holding surface in a direction of a rotation axis of the first grinding wheel;
a convexity forming step of grinding an annular region on the upper surface side of the workpiece from an edge portion to an inner peripheral portion located a predetermined distance inward, in a state in which the first grinding wheel and the first chuck table are positioned so that a track formed by the rotation of the plurality of first grinding wheels does not overlap the center of the first holding surface in the rotation axis direction of the first grinding wheel, thereby forming a disk-shaped convexity in the center of the workpiece that protrudes compared to the annular region,
In the second grinding step,
a second grinding wheel for grinding the protrusion and the annular region in the thickness direction of the workpiece, the second grinding wheel being disposed adjacent the protrusion and the annular region in the thickness direction of the workpiece.

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