JP7708620B2 - Method for grinding a workpiece - Google Patents

Description

The present invention relates to a method for grinding a workpiece that is used when grinding a plate-shaped workpiece having a modified layer exposed on its surface.

For example, disk-shaped semiconductor wafers made of semiconductor materials such as single crystal silicon carbide (SiC) are used to produce device chips that are incorporated into various electronic devices. These semiconductor wafers are obtained, for example, by cutting a cylindrical semiconductor ingot with a wire saw to form disk-shaped as-sliced wafers, and then increasing the flatness of the front and back surfaces by lapping or other processes.

On the other hand, silicon carbide is very hard and cannot necessarily be cut easily using the above-mentioned wire saw method. For this reason, the production of semiconductor wafers made of silicon carbide requires a great deal of cost. In response to this problem, a technology has been proposed in recent years in which a region at a certain depth from the surface of a semiconductor ingot is modified with a laser beam, and the semiconductor wafer is separated from the semiconductor ingot at the boundary of this modified region (hereinafter, modified layer) (see, for example, Patent Document 1).

The modified layer formed by irradiation with a laser beam is more fragile than other regions, and cracks occur in the vicinity of the modified layer as it is formed. Therefore, by using this technology, the semiconductor wafer can be easily separated from the semiconductor ingot. The modified layer remaining on the surface of the resulting semiconductor wafer is later removed by a method such as grinding using a grinding wheel with dispersed abrasive grains.

JP 2016-111143 A

However, as mentioned above, silicon carbide is very hard, so when a grinding wheel containing dispersed small grains is used for grinding, the performance of the grinding wheel is likely to deteriorate due to wear and tear of the grains. When the performance of the grinding wheel deteriorates, a dedicated dressing board is used to sharpen the wheel to restore its condition, but in this case, the grinding device must be stopped to install the dressing board. This causes the problem that productivity decreases when sharpening is performed frequently.

Therefore, the object of the present invention is to provide a method for grinding a workpiece that can minimize the loss of productivity associated with sharpening a grinding wheel.

According to one aspect of the present invention, a method for grinding a workpiece used when grinding a plate-shaped workpiece having an exposed modified layer modified by a laser beam on its surface includes a grinding step of selectively using a first annular grinding wheel having a first grinding stone with dispersed abrasive grains and a second annular grinding stone having a second grinding stone with dispersed abrasive grains having an average grain size smaller than that of the first grinding stone to grind the surface side of the workpiece, and a determination step of determining whether or not the second grinding stone needs to be sharpened to prepare it in a state suitable for grinding before the grinding step. In the grinding step, If it is determined in the determination step that the sharpening of the second grinding wheel is not necessary, the surface side of the workpiece is ground using the first grinding wheel, and then the surface side of the workpiece is ground using the second grinding wheel. If it is determined in the determination step that the sharpening is necessary, the surface side of the workpiece is ground using the second grinding wheel without grinding the surface side of the workpiece using the first grinding wheel, thereby providing a method for grinding the surface side of the workpiece while sharpening the second grinding wheel due to the unevenness of the surface caused by the modified layer.

Preferably, in the grinding step, if it is determined in the determination step that the sharpening is necessary, the surface side of the workpiece is ground while sharpening the second grinding wheel due to the unevenness of the surface caused by the modified layer, and then the surface side of the workpiece is ground using the first grinding wheel, and then the surface side of the workpiece is ground using the second grinding wheel. Also, preferably, the workpiece is a semiconductor wafer separated from a semiconductor ingot using the modified layer as the starting point of separation.

In one aspect of the present invention, in a method for grinding a workpiece, when it is determined that a second grinding wheel in which abrasive grains having a smaller average grain size than the abrasive grains of the first grinding wheel need to be sharpened, the second grinding wheel is used to grind the surface side of the workpiece on which the modified layer remains, and the surface side of the workpiece is ground while sharpening the second grinding wheel due to the surface irregularities caused by the modified layer, so there is no need to use a dedicated dressing board to sharpen the second grinding wheel.

In other words, since there is no need to stop the grinding device to install the dressing board, productivity is less likely to decrease even if the frequency of sharpening increases. In this way, according to the method for grinding a workpiece according to one aspect of the present invention, it is possible to minimize the decrease in productivity that accompanies sharpening of the grinding wheel.

FIG. 1 is a perspective view showing a schematic diagram of a grinding apparatus. FIG. 2 is a cross-sectional view that typically shows how a workpiece is ground by a first grinding stone of a first grinding wheel. FIG. 3 is a cross-sectional view that typically shows how a workpiece is ground by the second grinding stone of the second grinding wheel. FIG. 4 is a flow chart showing a method for grinding a workpiece. FIG. 5 is a cross-sectional view showing a schematic view of how the second grinding wheel is dressed.

Below, an embodiment of the present invention will be described with reference to the attached drawings. First, an example of a grinding device used in the grinding method of the workpiece according to this embodiment will be described. FIG. 1 is a perspective view showing a grinding device 2, and FIGS. 2 and 3 are cross-sectional views showing a state in which a workpiece 11 is ground. Note that in FIG. 1, some of the elements constituting the grinding device 2 are expressed as functional blocks. Also, the X-axis direction (front-back direction), Y-axis direction (left-right direction), and Z-axis direction (vertical direction) used in the following description are perpendicular to each other.

As shown in FIG. 1, the grinding device 2 is equipped with a base 4 that supports various elements that make up the grinding device 2. A concave storage section 4a with an open top is provided on the front end side of the upper surface of the base 4, and a first transport mechanism 6 used to transport a plate-shaped workpiece 11 is housed within this storage section 4a. The first transport mechanism 6 is typically a robot arm with multiple joints, and is capable of not only transporting the workpiece 11, but also of flipping the workpiece 11 upside down.

The workpiece 11 is, for example, a disk-shaped semiconductor wafer separated from a cylindrical semiconductor ingot made of a semiconductor material such as single crystal silicon carbide (SiC). That is, the workpiece 11 has a circular front surface 11a and a circular back surface 11b opposite the front surface 11a. As shown in FIG. 2, a modified layer 11c remains on the front surface 11a side of the workpiece 11, which was the starting point of separation when the workpiece 11 was separated from the semiconductor ingot.

The modified layer 11c is formed, for example, by focusing a laser beam of a wavelength that is not easily absorbed by the semiconductor ingot (a wavelength that is easily transmitted) on a region at a predetermined depth from the surface of the semiconductor ingot to cause multiphoton absorption. The modified layer 11c is more fragile than other regions of the semiconductor ingot, and cracks occur in the vicinity of the modified layer 11c as it is formed. Therefore, the semiconductor wafer can be easily separated from the semiconductor ingot with little force, using the modified layer 11c as the starting point for separation.

As described above, the modified layer 11c remains on the surface 11a of the workpiece 11 obtained in this manner, and the surface 11a has irregularities caused by separation from the semiconductor ingot. In other words, the surface 11a of the workpiece 11 has irregularities caused by the modified layer 11c. In the method for grinding the workpiece according to this embodiment, the surface 11a of the workpiece 11 is ground with the grinding device 2, thereby removing the modified layer 11c from the workpiece 11 along with the irregularities.

In this embodiment, the workpiece 11 is a disk-shaped semiconductor wafer made of a semiconductor material such as single crystal silicon carbide, but there are no limitations on the material, shape, structure, size, etc. of the workpiece 11. For example, a diamond wafer made of diamond can also be used as the workpiece 11. In addition, the modified layer 11c does not necessarily have to remain on the surface 11a side of the workpiece 11. However, in order to perform the sharpening described below, it is necessary that a certain amount of unevenness is formed on the surface 11a of the workpiece 11.

As shown in FIG. 1, in front of the storage section 4a, cassette tables 10a and 10b are provided on which cassettes 8a and 8b capable of storing multiple workpieces 11 can be placed. Diagonally behind the storage section 4a, a position adjustment mechanism 12 is provided for adjusting the position of the workpieces 11. The position adjustment mechanism 12 includes a disk-shaped position adjustment table and multiple pins arranged around the position adjustment table.

By moving multiple pins along the radial direction of the position adjustment table, for example, the center of the workpiece 11, which is carried out from the cassette 8a by the first transport mechanism 6 and placed on the position adjustment table, is aligned to a predetermined position in the X-axis direction and the Y-axis direction. The workpiece 11 is placed on the position adjustment table so that its grinding surface (surface 11a in this embodiment) is exposed upward.

A second transport mechanism 14 is provided to the side of the position adjustment mechanism 12, which holds the workpiece 11 and transports it backward. The second transport mechanism 14 includes, for example, an arm and a holding pad connected to the tip of the arm that can hold the top surface (surface to be ground) of the workpiece 11 by suction, and transports the workpiece 11, whose position has been adjusted by the position adjustment mechanism 12, backward by rotating the holding pad with the arm.

A turntable 16 is provided behind the second transport mechanism 14. The turntable 16 is connected to a rotary drive source (not shown) such as a motor, and rotates around a rotation axis that is generally parallel to the Z-axis direction. On the upper surface of the turntable 16, three chuck tables 18 used to hold the workpiece 11 are provided at approximately equal angular intervals. There is no limit to the number of chuck tables 18 provided on the turntable 16.

The turntable 16 rotates in the direction of the arrow in FIG. 1 and in the direction opposite to the arrow, moving each chuck table 18 in the order of load/unload area A adjacent to the second transport mechanism 14, rough grinding area B behind load/unload area A, and finish grinding area C to the side of rough grinding area B. The second transport mechanism 14 transports the workpiece 11 held by the holding pad from the position adjustment table of the position adjustment mechanism 12 to the chuck table 18 arranged in load/unload area A.

As shown in Figures 2 and 3, each chuck table 18 includes a disk-shaped frame 20 made of, for example, ceramics. A recess 20a with a circular opening at the top end is formed on the upper surface side of the frame 20. A retaining plate 22 made of, for example, ceramics and having a porous disk shape is fixed to the recess 20a of the frame 20.

When the workpiece 11 is held by the chuck table 18, the lower surface (back surface 11b in this embodiment) of the workpiece 11 comes into contact with the upper surface 22a of the holding plate 22. A protective member made of resin or the like may be attached in advance to the lower surface of the workpiece 11. In that case, the protective member comes into contact with the upper surface 22a of the holding plate 22.

The lower surface of the holding plate 22 is connected to a suction source (not shown) such as an ejector via a flow path 20b provided inside the frame 20 and a valve (not shown). Therefore, by contacting the lower surface of the workpiece 11 with the upper surface 22a of the holding plate 22, opening the valve, and applying negative pressure from the suction source, the workpiece 11 is held on the chuck table 18 by the suction force caused by the negative pressure.

A rotational drive source (not shown) such as a motor is connected to the bottom of the frame 20. The force generated by this rotational drive source causes the chuck table 18 to rotate around an axis of rotation parallel to the Z-axis direction or slightly tilted relative to the Z-axis direction, with the center of the upper surface 22a being the center of rotation.

As shown in FIG. 1, a columnar support structure 24 is provided behind the rough grinding area B and the finish grinding area C (behind the turntable 16). A Z-axis movement mechanism 26 is provided on the front side of each support structure 24. Each Z-axis movement mechanism 26 has a pair of guide rails 28 that are generally parallel to the Z-axis direction, and a moving plate 30 is attached to the guide rails 28 in a manner that allows it to slide.

A nut (not shown) constituting a ball screw is fixed to the rear side (back side) of each moving plate 30, and a screw shaft 32 that is roughly parallel to the guide rail 28 is rotatably connected to this nut. A motor 34 is connected to one end of the screw shaft 32. By rotating the screw shaft 32 by the motor 34, the moving plate 30 moves along the guide rail 28 (Z-axis direction). A fixing device 36 is provided on the front side (surface) of each moving plate 30.

Each fixture 36 supports a grinding unit 38 capable of grinding the workpiece 11. Each grinding unit 38 has a spindle housing 40 fixed to the fixture 36. Each spindle housing 40 accommodates a spindle 42 in a rotatable manner, the spindle 42 having a rotation axis parallel to the Z-axis direction or a rotation axis slightly tilted relative to the Z-axis direction.

The lower end of each spindle 42 is exposed from the lower end surface of the spindle housing 40, and a disk-shaped mount 44 is fixed to this lower end. The outer periphery of the mount 44 is provided with multiple holes (not shown) that penetrate the mount 44 in the thickness direction, and a bolt 46 or the like is inserted into each hole.

A first grinding wheel 48a for rough grinding is attached with bolts 46 to the underside of the mount 44 of the grinding unit 38 on the rough grinding area B side. A motor (not shown) connected to the upper end side of the spindle 42 is housed in the spindle housing 40 of the grinding unit 38 on the rough grinding area B side. The power of this motor rotates the first grinding wheel 48a together with the spindle 42.

As shown in FIG. 2, the first grinding wheel 48a includes an annular first wheel base 50a formed of a metal such as stainless steel or aluminum. A plurality of first grinding stones 52a, which are made of abrasive grains such as diamond dispersed in a binder such as vitrified or resinoid, are fixed to the underside of the first wheel base 50a along the circumferential direction of the first wheel base 50a.

A liquid supply nozzle (not shown) is provided next to the first grinding wheel 48a, which can supply a liquid (processing liquid) such as water to the portion (processing point) where the workpiece 11 and the first grinding wheel 52a come into contact. However, instead of or together with this liquid supply nozzle, a liquid supply port used to supply liquid may be provided on the first grinding wheel 48a, etc.

On the other hand, a second grinding wheel 48b for finish grinding is attached with bolts 46 to the underside of the mount 44 of the grinding unit 38 on the finish grinding area C side. A motor (not shown) connected to the upper end side of the spindle 42 is housed in the spindle housing 40 of the grinding unit 38 on the finish grinding area C side. The second grinding wheel 48b rotates together with the spindle 42 due to the power of this motor.

As shown in FIG. 3, the second grinding wheel 48b includes an annular second wheel base 50b made of a metal such as stainless steel or aluminum. A plurality of second grinding stones 52b, which are made of abrasive grains such as diamond dispersed in a binder such as vitrified or resinoid, are fixed to the underside of the second wheel base 50b along the circumferential direction of the second wheel base 50b.

A liquid supply nozzle (not shown) is provided next to the second grinding wheel 48b, which can supply a liquid (processing liquid) such as water to the portion (processing point) where the workpiece 11 and the second grinding wheel 52b come into contact. However, instead of or together with this liquid supply nozzle, a liquid supply port used to supply liquid may be provided on the second grinding wheel 48b, etc.

The average grain size of the abrasive grains contained in the second grinding wheel 52b for finish grinding is smaller than the average grain size of the abrasive grains contained in the first grinding wheel 52a for rough grinding. In other words, the average grain size of the abrasive grains contained in the first grinding wheel 52a for rough grinding is larger than the average grain size of the abrasive grains contained in the second grinding wheel 52b for finish grinding. This realizes a first grinding wheel 48a suitable for rough grinding and a second grinding wheel 48b suitable for finish grinding.

There is no limit to the specific size of the abrasive grains, but for example, by making the average grain size of the abrasive grains contained in the second grinding wheel 52b 1 μm or less, the flatness of the workpiece 11 can be sufficiently improved by finish grinding using this second grinding wheel 52b. In this case, the average grain size of the abrasive grains contained in the first grinding wheel 52a is greater than 1 μm. For example, by making the average grain size of the abrasive grains contained in the first grinding wheel 52a greater than 3 μm, the workpiece 11 can be efficiently processed by rough grinding using the first grinding wheel 52a.

The workpiece 11 held on the chuck table 18 in the rough grinding area B has its upper surface ground by the grinding unit 38 on the rough grinding area B side described above. Also, the workpiece 11 held on the chuck table 18 in the finish grinding area C has its upper surface ground by the grinding unit 38 on the finish grinding area C side described above.

Therefore, by moving the chuck table 18 holding the workpiece 11 through the loading/unloading area A, the rough grinding area B, and the finish grinding area C in that order, it is possible to continuously perform rough grinding of the workpiece 11 and the finish grinding after the rough grinding. When the finish grinding of the workpiece 11 is completed, the chuck table 18 in the finish grinding area C is again positioned in the loading/unloading area A.

As shown in FIG. 1, a third transport mechanism 54 that holds the ground workpiece 11 and transports it forward is provided in front of the loading/unloading area A and to the side of the second transport mechanism 14. The third transport mechanism 54 includes a holding pad that holds the top side of the workpiece 11 by suction and an arm connected to the holding pad, and transports the ground workpiece 11 forward from the chuck table 18 in the loading/unloading area A by rotating the holding pad with the arm.

A cleaning unit 56 is provided to the side of the third transport mechanism 54 to clean the workpiece 11 carried out by the third transport mechanism 54. The cleaning unit 56 includes, for example, a spinner table that rotates while holding the underside of the workpiece 11, and a cleaning nozzle that sprays a cleaning fluid onto the top side of the workpiece 11 held by the spinner table.

The cleaning fluid used in this cleaning unit 56 is typically a mixed fluid (two fluids) of air and water. Of course, water without air mixed therein may also be used as the cleaning fluid. The workpiece 11 cleaned in the cleaning unit 56 is transported by the first transport mechanism 6 and is stored, for example, in a cassette 8b.

A control unit 58 is connected to each element of the grinding device 2. This control unit 58 is configured, for example, by a computer including a processing device, a storage device, and an input device, and controls the operation of each element of the grinding device 2 described above so that the workpiece 11 is appropriately ground.

The processing device is typically a CPU (Central Processing Unit) that performs various processes necessary to control the above-mentioned elements. The storage device includes, for example, a main storage device such as a DRAM (Dynamic Random Access Memory) and an auxiliary storage device such as a hard disk drive or flash memory.

The input device is, for example, a touch panel, which also serves as an output device (display device). Note that a keyboard, mouse, etc. may also be used as an input device. The function of this control unit 58 is realized, for example, by the processing device operating in accordance with software stored in the storage device.

Figure 4 is a flow chart showing a method for grinding a workpiece. For example, when a hard workpiece 11 such as a semiconductor wafer made of a semiconductor material such as silicon carbide (SiC) is ground using the second grinding wheel 52b containing abrasive grains with a small average grain size, a phenomenon such as blunting, in which exposed abrasive grains are worn away, is likely to occur. Therefore, in this embodiment, first, it is determined whether or not the second grinding wheel 52b needs to be sharpened to a state suitable for grinding (determination step ST1).

Specifically, whether the second grinding wheel 52b is in a suitable state for grinding is judged based on an arbitrary criterion. For example, if the performance of the second grinding wheel 52b is degraded due to the above-mentioned damage, the workpiece 11 will not be ground properly and the load associated with the rotation of the second grinding wheel 48b will increase. Therefore, by utilizing this phenomenon, it is possible to judge whether the second grinding wheel 52b is in a suitable state for grinding.

For example, if the load current value of the motor rotating the second grinding wheel 48b measured during the previous finish grinding of the workpiece 11 (hereinafter, the previous load current value) exceeds a predetermined threshold value, it is determined that the second grinding wheel 52b is not in a state suitable for grinding and sharpening is required (YES in judgment step ST1). On the other hand, if the previous load current value did not exceed the predetermined threshold value, it is determined that the second grinding wheel 52b is in a state suitable for grinding and sharpening is not required (NO in judgment step ST1).

Instead of the load current value of the motor, it may be possible to determine whether the second grinding wheel 52b is in a state suitable for grinding based on the load applied to the workpiece 11 from the second grinding wheel 48b (second grinding wheel 52b).

In this case, for example, if the load measured during the previous finish grinding of the workpiece 11 exceeds a predetermined threshold, it is determined that the second grinding wheel 52b is not in a state suitable for grinding and sharpening is required (YES in judgment step ST1), and if the previous load did not exceed the predetermined threshold, it is determined that the second grinding wheel 52b is in a state suitable for grinding and sharpening is not required (NO in judgment step ST1).

However, immediately after replacement, the abrasive grains of the new second grinding wheel 48b are not properly exposed on the surface of the second grinding wheel 52b, and the performance of the second grinding wheel 52b is insufficient. Therefore, even if the second grinding wheel 48b has just been replaced, it is determined that the second grinding wheel 52b is not in a condition suitable for grinding and requires sharpening (YES in determination step ST1).

These determinations are made, for example, by the control unit 58 of the grinding device 2. However, these determinations may also be made by an operator of the grinding device 2. After determining whether or not sharpening of the second grinding wheel 52b is necessary, the first grinding wheel 48a and the second grinding wheel 48b are selectively used to grind the surface 11a side of the workpiece 11 (grinding step).

For example, if it is determined that sharpening of the second grinding wheel 52b is not necessary (NO in determination step ST1), the control unit 58 moves the chuck table 18 holding the workpiece 11 from the loading/unloading area A to the rough grinding area B, and then roughly grinds the workpiece 11 using the first grinding wheel 48a (first grinding wheel 52a) (rough grinding step ST2).

Specifically, as shown in FIG. 2, the chuck table 18 and the first grinding wheel 48a are rotated together, and the first grinding wheel 48a is gradually lowered while liquid is supplied from the liquid supply nozzle. This allows the first grinding wheel 52a to come into contact with the surface 11a of the workpiece 11, and the surface 11a side of the workpiece 11 to be ground with high efficiency. For example, when the modified layer 11c on the surface 11a side is completely removed, rough grinding of the workpiece 11 using the first grinding wheel 48a is completed.

When grinding of the workpiece 11 by the first grinding wheel 52a is completed, the control unit 58 moves the chuck table 18 holding the workpiece 11 from the rough grinding area B to the finish grinding area C, and then finish-grinds the workpiece 11 using the second grinding wheel 48b (second grinding wheel 52b) (finish grinding step ST3).

Specifically, as shown in FIG. 3, the chuck table 18 and the second grinding wheel 48b are rotated together, and the second grinding wheel 48b is gradually lowered while liquid is supplied from the liquid supply nozzle. This allows the second grinding wheel 52b to come into contact with the new surface 11d of the workpiece 11 from which the modified layer 11c has been removed, and the surface 11d side of the workpiece 11 can be ground with high precision. For example, when the flatness of the surface 11d side is increased to a certain level, the finish grinding of the workpiece 11 using the second grinding wheel 48b is completed.

On the other hand, if it is determined that the second grinding wheel 52b needs to be sharpened (YES in determination step ST1), the control unit 58 moves the chuck table 18 holding the workpiece 11 from the loading/unloading area A to the finish grinding area C, and grinds the workpiece 11 using the second grinding wheel 48b. In other words, the workpiece 11 is ground using the second grinding wheel 48b without grinding the workpiece 11 using the first grinding wheel 48a (sharpening grinding step ST4).

As described above, the modified layer 11c remains on the surface 11a of the workpiece 11, and the surface 11a has irregularities caused by the modified layer 11c. Therefore, when the second grinding wheel 48b is used to grind the surface 11a of the workpiece 11 on which the modified layer 11c remains, the second grinding wheel 52b can be sufficiently worn down to expose the abrasive grains on the surface. In other words, the second grinding wheel 52b can be sharpened. Figure 5 is a cross-sectional view that shows a schematic view of the sharpening of the second grinding wheel 52b.

Specifically, as shown in FIG. 5, the chuck table 18 and the second grinding wheel 48b are rotated together, and the second grinding wheel 48b is gradually lowered while liquid is supplied from the liquid supply nozzle. This brings the second grinding wheel 52b into contact with the surface 11a of the workpiece 11 on which the modified layer 11c remains, and the second grinding wheel 52b can be sharpened by the unevenness of the surface 11a caused by the modified layer 11c while grinding the surface 11a side of the workpiece 11.

The grinding conditions (rotation speed of the chuck table 18, rotation speed of the spindle 42, descent speed of the second grinding wheel 48b, etc.) may be the same as the conditions for finish grinding using the second grinding wheel 48b. Of course, other conditions suitable for sharpening the second grinding wheel 52b can also be applied.

The average height difference of the unevenness of the surface of the workpiece 11 is typically 10 μm or more, and preferably 20 μm or more and 30 μm or less. The unevenness of the surface 11a with such height difference allows the second grinding wheel 52b to be properly sharpened. For example, when the surface 11a side of the workpiece 11 is ground to a certain extent, the grinding of the workpiece 11 including the sharpening of the second grinding wheel 52b is completed. In this grinding, it is not necessary to completely remove the modified layer 11c from the workpiece 11.

After grinding of the workpiece 11, including sharpening of the second grinding wheel 52b, is completed, the first grinding wheel 48a (first grinding wheel 52a) is used to roughly grind the workpiece 11 (rough grinding step ST2), and then the second grinding wheel 48b (second grinding wheel 52b) is used to finish grind the workpiece 11 (finish grinding step ST3).

This allows the modified layer 11c remaining on the workpiece 11 to be removed, improving the flatness of the workpiece 11. If the modified layer 11c is sufficiently thin and can be removed in a short time by grinding the workpiece 11 while sharpening the second grinding wheel 52b, the subsequent rough grinding and finish grinding may be omitted.

As described above, in the method for grinding a workpiece according to this embodiment, when it is determined that the second grinding wheel 52b, in which abrasive grains having an average grain size smaller than that of the first grinding wheel 52a are dispersed, needs to be sharpened, the second grinding wheel 48b is used to grind the surface 11a side of the workpiece 11 on which the modified layer 11c remains, and the surface 11a side of the workpiece 11 is ground while sharpening the second grinding wheel 52b due to the surface irregularities caused by the modified layer 11c. Therefore, there is no need to use a dedicated dressing board to sharpen the second grinding wheel 52b.

In other words, since there is no need to stop the grinding device 2 to install the dressing board, productivity is less likely to decrease even if the sharpening frequency increases. In this way, according to the method for grinding a workpiece of this embodiment, the decrease in productivity associated with sharpening the grinding wheel can be kept to a minimum.

The present invention is not limited to the above-described embodiment, and can be modified in various ways. For example, the above-described embodiment has been described with reference to an example in which the workpiece 11 is ground using two types of grinding wheels, but the present invention can also be applied to a case in which the workpiece 11 is ground using three or more types of grinding wheels. Typically, before rough grinding, a coarser grinding can be performed using a grinding wheel (grinding wheel) containing abrasive grains with a larger average grain size than the abrasive grains of the first grinding wheel 52a.

In addition, the structures, methods, etc. of the above-mentioned embodiments and variations can be modified as appropriate without departing from the scope of the present invention.

DESCRIPTION OF SYMBOLS 11: Workpiece 11a: Front surface 11b: Back surface 11c: Modified layer 11d: Front surface ST1: Judgment step ST2: Rough grinding step ST3: Finish grinding step ST4: Dressing grinding step 2: Grinding device 4: Base 4a: Storage section 6: First conveying mechanism 8a: Cassette 8b: Cassette 10a: Cassette table 10b: Cassette table 12: Position adjustment mechanism 14: Second conveying mechanism 16: Turntable 18: Chuck table 20: Frame 20a: Recess 20b: Flow path 22: Holding plate 22a: Upper surface 24: Support structure 26: Z-axis moving mechanism 28: Guide rail 30: Moving plate 32: Screw shaft 34: Motor 36: Fixture 38: Grinding unit 40: Spindle housing 42: Spindle 44: Mount 46: Bolt 48a: First grinding wheel 48b: Second grinding wheel 50a: First wheel base 50b: Second wheel base 52a: First grinding wheel 52b: Second grinding wheel 54: Third transport mechanism 56: Cleaning unit 58: Control unit

Claims (3)

A method for grinding a workpiece used for grinding a plate-shaped workpiece having a modified layer exposed on a surface thereof, the method comprising the steps of:
a grinding step of selectively using an annular first grinding wheel having a first grinding stone with abrasive grains dispersed therein and an annular second grinding wheel having a second grinding stone with abrasive grains dispersed therein having an average grain size smaller than that of the abrasive grains of the first grinding stone to grind the front surface side of the workpiece;
and a determining step of determining whether or not the second grinding wheel needs to be dressed to prepare it for grinding before the grinding step,
In the grinding step,
When it is determined in the determination step that the sharpening of the second grinding wheel is unnecessary, the first grinding wheel is used to grind the surface side of the workpiece, and then the second grinding wheel is used to grind the surface side of the workpiece;
When it is determined in the judgment step that sharpening is necessary, the method for grinding a workpiece includes grinding the surface side of the workpiece using the second grinding wheel without grinding the surface side of the workpiece using the first grinding wheel, thereby grinding the surface side of the workpiece while sharpening the second grinding wheel due to the unevenness of the surface caused by the modified layer. In the grinding step,
2. A method for grinding a workpiece as described in claim 1, wherein, when it is determined in the judgment step that the sharpening is necessary, the surface side of the workpiece is ground while sharpening the second grinding wheel due to the unevenness of the surface caused by the modified layer, and then the surface side of the workpiece is ground using the first grinding wheel, and then the surface side of the workpiece is ground using the second grinding wheel. The method for grinding a workpiece according to claim 1 or 2, wherein the workpiece is a semiconductor wafer separated from a semiconductor ingot using the modified layer as the starting point for separation.