JP2023036121A - Grinding method for workpiece - Google Patents

Abstract

To provide a grinding method for a workpiece capable of suppressing to a minimum reduction of productivity with setting of a grinding stone.SOLUTION: The present invention relates to a grinding method for a workpiece including: a grinding step of grinding a front face side of the workpiece, of which the modified layer is exposed on a front face, by selectively using an annular first grinding wheel comprising a first grinding stone in which abrasive grains are dispersed and an annular second grinding wheel comprising a second grinding stone in which abrasive grains having an average grain size smaller than that of the abrasive grains of the first grinding stone are dispersed; and a determination step of determining whether or not setting for aligning the second grinding stone into a state suitable for grinding is required before the grinding step. In the grinding step, in a case where it is determined in the determination step that the setting is required, the front face side of the workpiece is ground using the second grinding wheel without grinding the front face side of the workpiece using the first grinding wheel, thereby grinding the front face side of the workpiece while performing the setting of the second grinding stone in accordance with front face ruggedness caused by the modified layer.SELECTED DRAWING: Figure 4

Description

TECHNICAL FIELD The present invention relates to a method of grinding a plate-shaped workpiece having a modified layer exposed on the surface thereof.

A disk-shaped semiconductor wafer made of a semiconductor material such as single-crystal silicon carbide (SiC), for example, is used to produce device chips to be incorporated in various electronic devices. This semiconductor wafer is obtained, for example, by slicing a cylindrical semiconductor ingot with a wire saw to form a disk-shaped as-sliced wafer, and improving the flatness of the front and back surfaces by lapping or the like.

On the other hand, silicon carbide is very hard and cannot necessarily be easily cut by the method using a wire saw as described above. Therefore, manufacturing a semiconductor wafer made of silicon carbide requires a great deal of cost. To solve this problem, in recent years, a region of a predetermined depth from the surface of a semiconductor ingot is modified with a laser beam, and this modified region (hereinafter referred to as a modified layer) is used as a boundary to separate the semiconductor ingot from the semiconductor wafer. has been proposed (see, for example, Patent Document 1).

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

JP 2016-111143 A

However, as described above, since silicon carbide is very hard, when a grinding wheel in which abrasive grains having a small grain size are dispersed is used for grinding, the grinding wheel may be damaged by the wear of the abrasive grains. performance tends to deteriorate. When the performance of the grinding wheel deteriorates, a dedicated dressing board is used to adjust the condition of the grinding wheel. At that time, the grinding machine is stopped to install the dressing board. It will be. Therefore, when the frequency of sharpening becomes high, there is a problem that the productivity is lowered.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a method of grinding a workpiece that can minimize a decrease in productivity associated with dressing of a grinding wheel.

According to one aspect of the present invention, there is provided a method for grinding a plate-shaped workpiece having a modified layer modified by a laser beam exposed on the surface thereof, comprising: An annular first grinding wheel having a first grinding wheel with dispersed abrasive grains, and an annular second grinding wheel having a second grinding wheel with dispersed abrasive grains having an average grain size smaller than that of the abrasive grains of the first grinding wheel. A grinding step of selectively grinding the surface side of the workpiece using 2 grinding wheels, and prior to the grinding step, a dressing is required to prepare the second grinding wheel to a state suitable for grinding. and, in the grinding step, if it is determined in the determination step that the dressing of the second grinding wheel is unnecessary, the first grinding wheel is used to grind the workpiece. After grinding the surface side of the workpiece, grinding the surface side of the workpiece using the second grinding wheel, and if it is determined in the determining step that the dressing is required, the first grinding wheel is ground. By 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, the modified layer causes There is provided a method of grinding a workpiece for grinding the surface side of the workpiece while performing the dressing of the second grinding wheel using the unevenness of the surface.

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

In the method for grinding a workpiece according to one aspect of the present invention, when it is determined that dressing of the second grinding wheel in which abrasive grains having an average particle diameter smaller than that of the first grinding wheel are dispersed is necessary, By grinding the surface side of the workpiece on which the modified layer remains using the second grinding wheel, the surface of the workpiece is ground while the second grinding wheel is dressed by the unevenness of the surface caused by the modified layer. Since the side is ground, there is no need to use a dedicated dressing board for dressing the second grinding wheel.

In other words, since it is not necessary to stop the grinding device to install the dressing board, productivity is less likely to decrease even if the frequency of dressing increases. As described above, according to the method for grinding a workpiece according to one aspect of the present invention, it is possible to minimize a decrease in productivity due to dressing of the grinding wheel.

FIG. 1 is a perspective view schematically showing a grinding device. FIG. 2 is a cross-sectional view schematically showing how a workpiece is ground by the first grinding wheel of the first grinding wheel. FIG. 3 is a cross-sectional view schematically showing how the workpiece is ground by the second grinding wheel of the second grinding wheel. FIG. 4 is a flow chart showing a method of grinding a workpiece. FIG. 5 is a cross-sectional view schematically showing how the second grinding wheel is dressed.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. First, an example of a grinding apparatus used in the method for grinding a workpiece according to this embodiment will be described. FIG. 1 is a perspective view schematically showing a grinding device 2, and FIGS. 2 and 3 are cross-sectional views schematically showing how a workpiece 11 is ground. In addition, in FIG. 1, some elements constituting the grinding apparatus 2 are represented by functional blocks. Also, the X-axis direction (front-rear direction), the Y-axis direction (left-right direction), and the Z-axis direction (vertical direction) used in the following description are perpendicular to each other.

As shown in FIG. 1 , the grinding machine 2 has a base 4 that supports various elements that make up the grinding machine 2 . On the front end side of the upper surface of the base 4, a recessed accommodating portion 4a with an open upper end is provided. 6 are accommodated. The first transport mechanism 6 is typically a robot arm having a plurality of joints, and can not only transport the workpiece 11 but also turn 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 to the front surface 11a. As shown in FIG. 2, on the surface 11a side of the workpiece 11, there remains a modified layer 11c which was the starting point of separation when the workpiece 11 was separated from the semiconductor ingot.

The modified layer 11c is formed by, for example, condensing a laser beam having a wavelength that is difficult to be absorbed by the semiconductor ingot (a wavelength that is easily transmitted) to a region at a predetermined depth from the surface of the semiconductor ingot to cause multiphoton absorption. It is formed. The modified layer 11c is more fragile than other regions of the semiconductor ingot, and cracks occur in the vicinity thereof as the modified layer 11c is formed. Therefore, the semiconductor wafer can be easily separated from the semiconductor ingot with a small force using the modified layer 11c as a separation starting point.

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

In this embodiment, a disk-shaped semiconductor wafer made of a semiconductor material such as single-crystal silicon carbide is used as the workpiece 11, but the material, shape, structure, size, etc. of the workpiece 11 are not limited. do not have. For example, a diamond wafer or the like made of diamond can be used as the workpiece 11 . Moreover, the modified layer 11c does not necessarily have to remain on the surface 11a side of the workpiece 11 . However, it is necessary to form unevenness of a certain size on the surface 11a of the workpiece 11 in order to implement the dressing described later.

As shown in FIG. 1, cassette tables 10a and 10b on which cassettes 8a and 8b capable of accommodating a plurality of workpieces 11 are mounted are provided in front of the accommodating portion 4a. A position adjusting mechanism 12 for adjusting the position of the workpiece 11 is provided obliquely behind the accommodating portion 4a. The position adjustment mechanism 12 includes a disk-shaped position adjustment table and a plurality of pins arranged around the position adjustment table.

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

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

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 generally parallel to the Z-axis direction. Three chuck tables 18 used to hold the workpiece 11 are provided on the upper surface of the turntable 16 at approximately equal angular intervals. The number of chuck tables 18 provided on the turntable 16 is not limited.

The turntable 16 rotates in the direction of the arrow in FIG. The grinding area B and the finish grinding area C on the side of the rough grinding area B are moved in this order. 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 the loading/unloading area A. FIG.

As shown in FIGS. 2 and 3, each chuck table 18 includes a disk-shaped frame 20 made of, for example, ceramics. A concave portion 20 a having a circular opening at the upper end is formed on the upper surface side of the frame 20 . A retainer plate 22 made of ceramics or the like and formed into a porous disc shape is fixed to the recess 20 a of the frame 20 .

When the workpiece 11 is held by the chuck table 18 , the upper surface 22 a of the holding plate 22 is brought into contact with the lower surface of the workpiece 11 (back surface 11 b in this embodiment). 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 22 a of the holding plate 22 .

The lower surface side 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, a valve (not shown), and the like. Therefore, by bringing the lower surface of the workpiece 11 into contact with the upper surface 22a of the holding plate 22, opening the valve, and applying the negative pressure of the suction source, the workpiece 11 is moved by the suction force caused by the negative pressure. It is held on the chuck table 18 .

A rotary drive source (not shown) such as a motor is connected to the lower portion of the frame 20 . The chuck table 18 rotates along a rotation axis parallel to the Z-axis direction or slightly inclined relative to the Z-axis direction so that the center of the upper surface 22a becomes the center of rotation by the force generated by this rotation drive source. Rotate around an axis.

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

A nut (not shown) constituting a ball screw is fixed to the rear surface side (rear side) of each moving plate 30, and a screw shaft 32 substantially parallel to the guide rail 28 can rotate on this nut. connected in a manner. A motor 34 is connected to one end of the screw shaft 32 . By rotating the screw shaft 32 with the motor 34, the moving plate 30 moves along the guide rail 28 (Z-axis direction). A fixture 36 is provided on the front surface (surface) of each moving plate 30 .

Each fixture 36 carries a grinding unit 38 capable of grinding the workpiece 11 . Each grinding unit 38 includes a spindle housing 40 secured to fixture 36 . Each spindle housing 40 rotatably accommodates a spindle 42 having a rotation axis parallel to the Z-axis direction or a rotation axis slightly inclined with respect 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 the lower end. A plurality of holes (not shown) passing through the mount 44 in the thickness direction are provided in the outer peripheral portion of the mount 44, and a bolt 46 or the like is inserted into each hole.

A first grinding wheel 48 a for rough grinding is attached with bolts 46 to the lower surface 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 accommodated 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 along with the spindle 42 .

As shown in FIG. 2, the first grinding wheel 48a includes an annular first wheel base 50a made of metal such as stainless steel or aluminum. On the lower surface of the first wheel base 50a, a plurality of first grinding wheels 52a in which abrasive grains such as diamond are dispersed in a binder such as vitrified or resinoid are arranged along the circumferential direction of the first wheel base 50a. Fixed.

Next to the first grinding wheel 48a, there is a liquid supply nozzle (not shown) capable of supplying a liquid (processing liquid) such as water to a portion (processing point) where the workpiece 11 and the first grinding wheel 52a contact each other. is provided. However, instead of or together with this liquid supply nozzle, a liquid supply port used for supplying liquid may be provided in the first grinding wheel 48a or the like.

On the other hand, a second grinding wheel 48b for finish grinding is attached with bolts 46 to the lower surface 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 accommodated in the spindle housing 40 of the grinding unit 38 on the finish grinding area C side. The power of this motor rotates the second grinding wheel 48b along with the spindle 42 .

As shown in FIG. 3, the second grinding wheel 48b includes an annular second wheel base 50b made of metal such as stainless steel or aluminum. On the lower surface of the second wheel base 50b, a plurality of second grinding wheels 52b in which abrasive grains such as diamond are dispersed in a binder such as vitrified or resinoid are arranged along the circumferential direction of the second wheel base 50b. Fixed.

Next to the second grinding wheel 48b, there is a liquid supply nozzle (not shown) capable of supplying a liquid (processing liquid) such as water to a portion (processing point) where the workpiece 11 and the second grinding wheel 52b contact each other. is provided. However, instead of or together with this liquid supply nozzle, a liquid supply port used for supplying liquid may be provided on the second grinding wheel 48b or the like.

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 the first grinding wheel 48a suitable for rough grinding and the second grinding wheel 48b suitable for finish grinding.

Although there is no specific limitation on the size of the abrasive grains, for example, by setting the average grain size of the abrasive grains contained in the second grinding wheel 52b to 1 μm or less, the finish grinding using this second grinding wheel 52b The flatness of the workpiece 11 can be sufficiently enhanced. In this case, the average grain size of the abrasive grains contained in the first grinding wheel 52a is larger 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 upper surface of the workpiece 11 held on the chuck table 18 in the rough grinding area B is ground by the grinding unit 38 on the rough grinding area B side. The top surface of the workpiece 11 held on the chuck table 18 in the finish grinding area C is ground by the grinding unit 38 on the finish grinding area C side.

Therefore, by moving the chuck table 18 holding the workpiece 11 in order of the carry-in/carry-out area A, the rough grinding area B, and the finish grinding area C, rough grinding of the workpiece 11 and post-rough grinding Finish grinding can be performed continuously. The chuck table 18 in the finish grinding area C is again positioned in the loading/unloading area A after finishing the finish grinding of the workpiece 11 .

As shown in FIG. 1, in front of the loading/unloading area A and at the side of the second transporting mechanism 14, there is a third transporting mechanism 54 that holds and forwards the workpiece 11 after grinding. is provided. The third transport mechanism 54 includes a holding pad that sucks and holds the upper surface of the workpiece 11, and an arm connected to the holding pad. The workpiece 11 is transported forward from the chuck table 18 in the loading/unloading area A.

A cleaning unit 56 for cleaning the workpiece 11 carried out by the third transport mechanism 54 is provided on the side of the third transport mechanism 54 . The cleaning unit 56 includes, for example, a spinner table that rotates while holding the lower surface of the workpiece 11, and a cleaning nozzle that injects a cleaning fluid onto the upper surface of the workpiece 11 held by the spinner table. ,including.

The cleaning fluid used in this cleaning unit 56 is typically a mixed fluid (two fluids) in which air and water are mixed. Of course, water or the like that is not mixed with air may be used as the cleaning fluid. The workpiece 11 cleaned by the cleaning unit 56 is transported by the first transport mechanism 6 and stored in, for example, a cassette 8b.

A control unit 58 is connected to each element of the grinding device 2 . This control unit 58 is composed of, for example, 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. etc.

The processing device is typically a CPU (Central Processing Unit), and performs various processes necessary to control the elements described above. 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 and a flash memory.

The input device is, for example, a touch panel, and also serves as an output device (display device). Note that a keyboard, mouse, or the like may be employed as an input device. The functions of the control unit 58 are implemented by the processing device operating according to software stored in the storage device, for example.

FIG. 4 is a flow chart showing a method of 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 particle diameter, the exposed Phenomena such as crushed eyes tend to occur in which the abrasive grains that are present are lost due to wear. Therefore, in the present embodiment, first, it is determined whether or not the second grinding wheel 52b needs to be dressed so as to be suitable for grinding (determination step ST1).

Specifically, whether or not the second grinding wheel 52b is in a state suitable for grinding is determined based on arbitrary criteria. For example, if the performance of the second grinding wheel 52b is deteriorated due to the above-mentioned crushed eyes or the like, the workpiece 11 will not be properly ground, and the load accompanying the rotation of the second grinding wheel 48b will increase. Therefore, by using this phenomenon, it is possible to determine whether or not the second grinding wheel 52b is in a state suitable for grinding.

For example, when the load current value of the motor that rotates the second grinding wheel 48b (hereinafter referred to as the previous load current value) measured in 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 that sharpening is required (YES in determination 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 that dressing is unnecessary (NO in determination step ST1).

Instead of the load current value of the motor, it is determined whether the second grinding wheel 48b (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). You can judge.

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

By the way, in the new second grinding wheel 48b immediately after being replaced, the abrasive grains are not properly exposed on the surface of the second grinding wheel 52b, and the performance of the second grinding wheel 52b is not sufficient. Therefore, even if the second grinding wheel 48b has been replaced immediately before, it is determined that the second grinding wheel 52b is not in a state suitable for grinding and that dressing is necessary (YES in determination step ST1).

These determinations are made by the control unit 58 of the grinding device 2, for example. However, an operator or the like of the grinding device 2 may make these determinations. After determining whether or not the second grinding wheel 52b needs to be dressed, 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, when it is determined that dressing of the second grinding wheel 52b is unnecessary (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. After being moved, the first grinding wheel 48a (first grinding wheel 52a) is used to roughly grind the workpiece 11 (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 supplying the liquid from the liquid supply nozzle. . Thereby, the first grinding wheel 52a is brought into contact with the surface 11a of the workpiece 11, and the surface 11a side of the workpiece 11 can 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 ends.

When the first grinding wheel 52a finishes grinding the workpiece 11, 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 moves the second grinding wheel 52a. The grinding wheel 48b (second grinding wheel 52b) is used to finish grind the workpiece 11 (finish grinding step ST3).

Specifically, as shown in FIG. 3, both the chuck table 18 and the second grinding wheel 48b are rotated, and the second grinding wheel 48b is gradually lowered while supplying the liquid from the liquid supply nozzle. . Thereby, the second grinding wheel 52b is brought 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 accuracy. For example, when the flatness of the surface 11d is increased to a certain extent, 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 dressed (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. , the workpiece 11 is ground using the second grinding wheel 48b. That is, the workpiece 11 is ground using the second grinding wheel 48b without grinding the workpiece 11 using the first grinding wheel 48a (dressing grinding step ST4).

As described above, the modified layer 11c remains on the surface 11a side of the workpiece 11, and unevenness due to the modified layer 11c exists on the surface 11a. Therefore, when the second grinding wheel 48b is used to grind the surface 11a side of the workpiece 11 on which the modified layer 11c remains, the second grinding wheel 52b is sufficiently consumed to expose the abrasive grains to the surface. be able to. That is, the second grinding wheel 52b can be dressed. FIG. 5 is a cross-sectional view schematically showing how the second grinding wheel 52b is dressed.

Specifically, as shown in FIG. 5, both the chuck table 18 and the second grinding wheel 48b are rotated, and the second grinding wheel 48b is gradually lowered while supplying the liquid from the liquid supply nozzle. . As a result, the second grinding wheel 52b is brought into contact with the surface 11a of the workpiece 11 on which the modified layer 11c remains, and the unevenness of the surface 11a caused by the modified layer 11c sets the second grinding wheel 52b. The surface 11a side of the workpiece 11 can be ground while performing the grinding.

The conditions for this grinding (the number of rotations of the chuck table 18, the number of rotations of the spindle 42, the lowering 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 dressing the second grinding wheel 52b can also be applied.

In addition, the average value of the height difference of the unevenness on the surface of the workpiece 11 is typically 10 μm or more, preferably 20 μm or more and 30 μm or less. The unevenness of the surface 11a having such a height difference enables appropriate dressing of the second grinding wheel 52b. For example, when the surface 11a side of the workpiece 11 is ground to some extent, the grinding of the workpiece 11 accompanied by the dressing of the second grinding wheel 52b is completed. It is not necessary to completely remove the modified layer 11c from the workpiece 11 in this grinding.

After finishing the grinding of the workpiece 11 accompanied by the setting of the second grinding wheel 52b, the first grinding wheel 48a (the first grinding wheel 52a) is used to roughly grind the workpiece 11 (rough grinding). In step ST2), the second grinding wheel 48b (second grinding wheel 52b) is used to finish grind the workpiece 11 (finish grinding step ST3).

Thereby, the modified layer 11c remaining on the workpiece 11 can be removed, and the flatness of the workpiece 11 can be improved. If the modified layer 11c is sufficiently thin and can be removed in a short period of time by grinding the workpiece 11 with the second grinding wheel 52b, the subsequent rough grinding and finish grinding can be performed. You can omit it.

As described above, in the method for grinding a workpiece according to the present embodiment, it is determined that dressing is necessary for the second grinding wheel 52b in which abrasive grains having a smaller average particle diameter than the abrasive grains of the first grinding wheel 52a are dispersed. In this case, the second grinding wheel 48b is used to grind the surface 11a side of the workpiece 11 on which the modified layer 11c remains. Since the surface 11a side of the workpiece 11 is ground while dressing 52b, there is no need to use a dedicated dressing board for dressing the second grinding wheel 52b.

In other words, since it is not necessary to stop the grinding device 2 in order to install the dressing board, even if the frequency of dressing increases, the productivity does not easily decrease. As described above, according to the method for grinding a workpiece according to the present embodiment, it is possible to minimize the decrease in productivity due to the dressing of the grinding wheel.

It should be noted that the present invention is not limited to the description of the above-described embodiment and can be implemented with various modifications. For example, in the above-described embodiment, the case where the workpiece 11 is ground using two types of grinding wheels has been described as an example, but the present invention uses three or more types of grinding wheels to grind the workpiece. 11 can also be applied. Typically, prior to rough grinding, coarser grinding can be performed using a grinding wheel (grinding wheel) containing abrasive grains having a larger average grain size than the abrasive grains of the first grinding wheel 52a.

In addition, the structures, methods, and the like according to the above-described embodiments and modifications can be modified as appropriate without departing from the scope of the present invention.

REFERENCE SIGNS LIST 11: Workpiece 11a: Front surface 11b: Back surface 11c: Modified layer 11d: Surface ST1: Judgment step ST2: Rough grinding step ST3: Finish grinding step ST4: Dressing grinding step 2: Grinding device 4: Base 4a: Receiving part 6: First transport mechanism 8a: Cassette 8b: Cassette 10a: Cassette table 10b: Cassette table 12: Position adjustment mechanism 14: Second transport mechanism 16: Turntable 18: Chuck table 20: Frame 20a: Concave portion 20b: Flow path 22: Holding plate 22a: Upper surface 24: Support structure 26: Z-axis movement mechanism 28: Guide rail 30: Movement 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 conveying mechanism 56: cleaning Unit 58: control unit

Claims (3)

A method for grinding a plate-shaped workpiece having a modified layer modified by a laser beam exposed on the surface thereof, the grinding method comprising:
An annular first grinding wheel having a first grinding wheel with dispersed abrasive grains, and an annular second grinding wheel having a second grinding wheel with dispersed abrasive grains having an average grain size smaller than that of the abrasive grains of the first grinding wheel. a grinding step of selectively grinding the surface side of the workpiece using 2 grinding wheels;
determining whether or not the second grinding wheel needs to be dressed before the grinding step;
In the grinding step,
When it is determined in the determination step that the dressing 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 ground. Grinding the surface side of the workpiece using
If it is determined in the determining step that the dressing is necessary, the workpiece is ground using the second grinding wheel without grinding the surface side of the workpiece using the first grinding wheel. Grinding of the work piece by grinding the surface side of the work piece while performing the dressing of the second grinding wheel by the unevenness of the surface caused by the modified layer. Method. In the grinding step,
If it is determined that the dressing is necessary in the determination step, grinding the surface side of the workpiece while performing the dressing of the second grinding wheel by the unevenness of the surface caused by the modified layer, 2. The method of claim 1, wherein thereafter, 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. A method of grinding a workpiece. 3. The method of grinding a workpiece according to claim 1, wherein the workpiece is a semiconductor wafer separated from a semiconductor ingot using the modified layer as a separation starting point.

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