SiC wafer grinding machine

Abstract

To provide a SiC wafer grinding apparatus which suppresses reduction in the sharpness of a grindstone part when grinding a SiC wafer and extends the life of the grindstone part.SOLUTION: A SiC wafer grinding apparatus 1 that grinds a surface of a SiC wafer includes: a workpiece holding part 2 which holds the SiC wafer as a workpiece W; a grindstone wheel 3 which has a grindstone part 32 containing a porous tissue; a grindstone wheel drive device 34 which axially rotates the grindstone wheel 3 to grind the workpiece W by the grindstone part 32; an ultrasonic exciter 4 that excites the grindstone part 32 in the axial direction by applying ultrasonic waves to the grindstone part 32; and a processing mode switching part 522 which switches between the cutting edge self-generation promotion mode that promotes cutting edge self-generation of abrasive grains by exciting the grindstone part 32 and the abrasion suppression mode that suppresses abrasion of the grindstone part 32 compared to the cutting edge self-generation promotion mode by stopping excitation of the grindstone part 32 or reducing excitation of the grindstone part 32 compared to the cutting edge self-generation promotion mode during grinding by controlling the operation of the ultrasonic exciter 4.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a SiC wafer grinding device.

Background Art

[0002] Since SiC wafers have higher hardness and brittleness compared to Si wafers and the like, when grinding SiC wafers, the abrasive grains located on the surface layer of the grinding wheel wear and flatten, resulting in a decrease in the sharpness of the grinding wheel and requiring a long time for grinding. Therefore, in the configurations disclosed in Patent Document 1 and Patent Document 2, ultrasonic waves are applied to the grinding wheel during grinding by an ultrasonic vibration device to vibrate the grinding wheel, causing minute pulverization at the tips of the abrasive grains due to minute collisions between the flattened abrasive grains on the surface layer of the grinding wheel and the surface of the workpiece (SiC wafer), and promoting the self-generation of cutting edges of the abrasive grains by finely shaving and retreating the bond between the abrasive grains on the surface layer of the grinding wheel. As a result, the decrease in the sharpness of the grinding wheel due to wear of the abrasive grains is suppressed, and the grinding time is shortened.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the configurations disclosed in Patent Document 1 and Patent Document 2, since the grinding wheel is continuously vibrated by ultrasonic waves during grinding, the wear of the grinding wheel itself is promoted together with the self-generation of cutting edges of the abrasive grains, and there is a risk that the life of the grinding wheel will be shortened. This is particularly prominent in the grinding of high-hardness SiC wafers.

[0005] This invention has been made in view of the above problems, and aims to provide a SiC wafer grinding apparatus that suppresses the deterioration of the cutting performance of the grinding wheel and extends the lifespan of the grinding wheel when grinding SiC wafers. [Means for solving the problem]

[0006] One aspect of the present invention is a SiC wafer grinding apparatus for grinding the surface of a SiC wafer, A workpiece holding section for holding the above-mentioned SiC wafer as a workpiece, A grinding wheel having a grinding section formed by bonding multiple abrasive grains together with a bond that forms a porous structure at the end of the base on the workpiece holding side, A grinding wheel drive device that rotates the grinding wheel around a grinding wheel spindle perpendicular to the end of the base, thereby grinding the surface of the workpiece held in the workpiece holder by the grinding wheel portion, An ultrasonic vibration device that applies ultrasonic waves to the grinding wheel and vibrates the grinding wheel in the axial direction of the grinding wheel spindle, The SiC wafer grinding apparatus includes a processing mode switching control unit that controls the operation of the ultrasonic vibration device described above, thereby switching between a self-sharpening promotion mode, which vibrates the grinding wheel to promote the self-sharpening of abrasive grains during the grinding process of the workpiece, and a wear suppression mode, which stops the vibration of the grinding wheel or reduces the vibration of the grinding wheel to a level lower than that of the self-sharpening promotion mode, thereby suppressing wear of the grinding wheel more effectively than that of the self-sharpening promotion mode. [Effects of the Invention]

[0007] According to one embodiment described above, in a configuration in which the grinding wheel is vibrated by an ultrasonic vibration device, the system is configured to switch between a self-sharpening promotion mode, in which the grinding wheel is vibrated during the grinding of a SiC wafer workpiece to promote the self-sharpening of abrasive grains, and a wear suppression mode, in which the vibration of the grinding wheel is stopped or reduced compared to the self-sharpening promotion mode, thereby suppressing wear of the grinding wheel more effectively than in the self-sharpening promotion mode. This promotes the self-sharpening of abrasive grains and suppresses a decrease in the sharpness of the grinding wheel, while also suppressing wear of the grinding wheel and extending its lifespan compared to a configuration in which the grinding wheel is continuously vibrated by ultrasound during the grinding of a SiC wafer workpiece.

[0008] As described above, according to one embodiment, it is possible to provide a SiC wafer grinding apparatus that suppresses the deterioration of the cutting performance of the grinding wheel and extends the lifespan of the grinding wheel when grinding a SiC wafer. [Brief explanation of the drawing]

[0009] [Figure 1] A conceptual diagram showing the configuration of the SiC wafer grinding apparatus in Embodiment 1. [Figure 2] A functional block diagram showing the general configuration of the SiC wafer grinding apparatus in Embodiment 1. [Figure 3] (a) Side view of the grinding wheel, (b) Bottom view of the grinding wheel in Embodiment 1. [Figure 4] Enlarged conceptual cross-sectional views of the grinding wheel surface in each of three states in Embodiment 1: (a) initial state, (b) wear occurrence state, and (c) self-sharpening state. [Figure 5] Enlarged cross-sectional view of the VV line position in Figure 3. [Figure 6] This figure shows the time change in the motor power value of the grinding wheel spindle in (a) the self-sharpening promotion mode and (b) the wear suppression mode, respectively, in Embodiment 1. [Figure 7] This figure shows the time change in the motor power value of the grinding wheel spindle when ultrasonic waves of (a) ultrasonic amplitude A1 and (b) ultrasonic amplitude A2 are applied in Embodiment 1. [Figure 8]Diagram showing the time charts of (a) the motor power value of the grinding wheel spindle, (b) the processing mode, (c) the application of ultrasonic waves, and (d) the amplitude of ultrasonic waves in the grinding process of Embodiment 1. [Figure 9] Diagram showing the time charts of (a) the motor power value of the grinding wheel spindle, (b) the processing mode, (c) the application of ultrasonic waves, and (d) the amplitude of ultrasonic waves in another grinding process of Embodiment 1. [Figure 10] Flow chart of the process for evaluating the grinding wheel state and optimizing the processing conditions in Embodiment 1. [Figure 11] Functional block diagram showing the schematic configuration of the SiC wafer grinding apparatus in Embodiment 2. [Figure 12] Conceptual diagram showing the configuration of the SiC wafer grinding apparatus in Embodiment 3. [Figure 13] Diagram showing an example of the acquired information of the grinding wheel information acquisition unit in Embodiment 3. [Figure 14] Diagram showing examples of (a) the abrasive grain area and (b) the number of abrasive grains as the analysis results by the grinding wheel state evaluation unit in Embodiment 3. [Figure 15] Diagram showing examples of the surface properties indicating (a) the self-generated cutting edge state of the abrasive grains and (b) the wear state of the abrasive grains as the analysis results by the grinding wheel state evaluation unit in Embodiment 3. [Figure 16] Conceptual diagrams of the states of (a) without ultrasonic vibration and (b) with ultrasonic vibration for explaining the entry angle of the abrasive grains in Embodiment 4. [Figure 17] Diagram showing the time change of the tip position of the abrasive grains in the depth of cut direction when ultrasonic waves of (a) ultrasonic amplitude A1 and (b) ultrasonic amplitude A2 are applied respectively in Embodiment 4.

Modes for Carrying Out the Invention

[0010] (Embodiment 1) 1. Configuration of the SiC Wafer Grinding Apparatus 1 The SiC wafer grinding apparatus 1 in Embodiment 1 will be described with reference to FIGS. 1 to 10. The SiC wafer grinding apparatus 1 grinds the surface of the flat portion of the SiC wafer as the workpiece W. As shown in FIG. 2, the SiC wafer grinding apparatus 1 in Embodiment 1 includes a chuck table 2, a grinding wheel 3, an ultrasonic vibration device 4, and a processing unit 5.

[0011] 2. Chuck table 2 (work holding part) As shown in FIG. 1, the chuck table 2 has chuck means 21 on which the workpiece W is mounted at the upper part, and functions as a work holding part for holding the workpiece W of the SiC wafer. The chuck means 21 is constituted by an adsorption type or other appropriate means, and the workpiece W is detachably mounted on its upper surface. The chuck table 2 is rotatable in the circumferential direction indicated by arrow A1 or the opposite circumferential direction indicated by arrow A2 substantially concentrically with the workpiece W mounted on the upper surface of the chuck means 21. The chuck table 2 is connected to a chuck table drive device 22 provided with a motor, and is rotationally driven by the chuck table drive device 22. The operation of the chuck table drive device 22 is controlled by a control device 52 described later.

[0012] 3. Grinding wheel 3 The grinding wheel 3 is located above the chuck table 2 and functions as a tool for grinding the upper surface of the workpiece W held by the chuck table 2. In Embodiment 1, a vertical surface grinding machine in which the chuck table 2 and the grinding wheel 3 rotate around the vertical axis is exemplified, but an inclined type in which the chuck table 2 or the like rotates around the inclined axis may also be used.

[0013] The grinding wheel 3 comprises a base 31, a grinding wheel section 32, and a grinding wheel spindle 33. The base 31 is provided at the lower end of the grinding wheel spindle 33. As shown in Figures 3(a) and 3(b), the base 31 is disc-shaped, with the end 31a on the chuck table 2 side being a substantially flat surface. The grinding wheel section 32 is provided at the end 31a of the base 31. Multiple grinding wheel sections 32 are provided and are arranged circumferentially along the outer edge of the end 31a as shown in Figure 3(b). The grinding wheel spindle 33 is provided perpendicular to the end 31a as shown in Figure 3(a), and as shown in Figure 1, it is connected to a grinding wheel drive device 34 equipped with a motor to rotate and constitute the rotation axis of the grinding wheel 3. The grinding wheel spindle 33 is supported by a spindle head (not shown).

[0014] The grinding wheel drive unit 34 rotates the grinding wheel 3 and is configured to move the headstock supporting the grinding spindle 33 in the X, Y, and Z directions. The operation of the grinding wheel drive unit 34 is controlled by a control device 52, which will be described later. In this embodiment 1, the grinding wheel drive unit 34 drives the grinding wheel 3 so that the axis of the grinding spindle 33 is positioned eccentrically with respect to the axis of the chuck table 2.

[0015] As shown in Figure 4(a), the grinding wheel portion 32 is a porous grinding wheel constructed by fixing multiple abrasive grains 321 with a bond that forms a porous structure 322. Superabrasive grains such as diamond or CBN are used for the abrasive grains 321. The bond can be vitrified (V), resinoid (B), rubber (R), silicate (S), shellac (E), metal (M), electroplated (P), magnesia cement (Mg), etc. The pores 323 in the porous structure 322 formed by the bond may include natural pores and pores formed by a pore-forming agent consisting of a foaming agent. The porosity of the grinding wheel portion 32 is not limited, but can be, for example, 10-90 volume%, 30-90 volume%, or 60-90 volume%. The grinding wheel portion 32 is elastically deformable due to the presence of pores 323. The elastic modulus of the grinding wheel portion 32 varies depending on the type of bond and porosity of the grinding wheel portion 32, and can be set as appropriate.

[0016] Although not shown in the diagram, the SiC wafer grinding apparatus 1 is equipped with a coolant system that supplies coolant from a coolant nozzle to the grinding point of the workpiece W by the grinding wheel 3. The coolant system cools the recovered coolant to a predetermined temperature and supplies it again to the grinding point. The coolant system allows for adjustment of the coolant flow rate and supply timing. Also, although not shown in the diagram, the SiC wafer grinding apparatus 1 may be equipped with a sizing device that detects the thickness of the workpiece W. The sizing device can acquire changes in the thickness of the workpiece W during processing. The configuration of the sizing device is not limited, and known configurations can be adopted.

[0017] 4. Ultrasonic Vibration Device 4 As shown in Figure 5, the grinding wheel section 32 is provided with an ultrasonic vibration device 4 that applies ultrasonic waves to the grinding wheel section 32 to excite it. The configuration of the ultrasonic vibration device 4 is not limited, but in this embodiment 1, it consists of a laminated piezoelectric actuator formed by stacking multiple piezoelectric elements 41 that expand and contract when voltage is applied. The ultrasonic vibration device 4 is connected to a high-frequency power supply 35, and is configured to vibrate ultrasonically in the stacking direction of the piezoelectric elements 41 when a high-frequency voltage is applied from the high-frequency power supply 35. In this embodiment 1, each grinding wheel section 32 is provided with a piezoelectric actuator consisting of a piezoelectric element 41 as shown in Figure 5 to vibrate each grinding wheel section 32 individually, but this is not limited to this configuration, and other configurations that can apply vibration to the grinding wheel section 32 are also possible. For example, a piezoelectric actuator may be provided on the grinding wheel spindle 33 to indirectly vibrate multiple grinding wheel sections 32 together via the base 31.

[0018] The ultrasonic vibration device 4 is housed in a recess 31b provided at the end 31a of the base 31, such that the stacking direction of the piezoelectric elements 41 coincides with the axial direction Z of the grinding wheel spindle 33 shown in Figure 1. The upper end of the grinding wheel portion 32 fits into the recess 31b, and an elastic support member 31c is interposed between the wall surface of the recess 31b and the upper end of the grinding wheel portion 32. As a result, ultrasonic waves are applied to the grinding wheel portion 32 by the ultrasonic vibration device 4, and the grinding wheel portion 32 is vibrated in the axial direction Z of the grinding wheel spindle 33.

[0019] The operation control of the ultrasonic vibration device 4, such as turning the ultrasonic output of the ultrasonic vibration device 4 on and off and adjusting the amplitude of the ultrasonic waves, can be performed by the control device 52 described later. Furthermore, the frequency of the ultrasonic waves applied to the grinding wheel section 32 by the ultrasonic vibration device 4 is selected to be a frequency suitable for applying excitation force to the grinding wheel section 32. This frequency can be determined according to the overall configuration of the device, including the grinding wheel 3.

[0020] 5. Processing Unit 5 The processing unit 5 is composed of a calculation unit and a memory device (not shown) and includes a processing unit 51 that performs processing described later, and a control device 52 that controls the chuck table drive unit 22, the grinding wheel drive unit 34, and the high-frequency power supply 35.

[0021] 5-1. Processing device 51 The processing unit 51 can function as a simulation device independent of the chuck table drive unit 22 and the grinding wheel drive unit 34, or it can function as a simulation device that operates in conjunction with the chuck table drive unit 22, the grinding wheel drive unit 34, and the high-frequency power supply 35. In the former case, the processing unit 51 can determine the optimal processing conditions without actually grinding the workpiece W. In the latter case, the processing unit 51 can adjust the processing conditions or operate in a way that affects various controls by processing in parallel with the grinding of the workpiece W by the chuck table drive unit 22, the grinding wheel drive unit 34, and the high-frequency power supply 35.

[0022] As shown in Figure 2, the processing apparatus 51 includes a grinding wheel information acquisition unit 511, a reference value storage unit 512, a grinding wheel condition evaluation unit 513, an evaluation result display unit 514, and a processing condition adjustment unit 515.

[0023] The grinding wheel information acquisition unit 511 acquires information regarding the grinding wheel 3. The information regarding the grinding wheel 3 is mechanical information related to the grinding wheel 3 that changes during grinding in the SiC wafer grinding apparatus 1, and in this embodiment 1, it is the motor power value of the grinding wheel drive device 34 that rotates the grinding wheel spindle 33 of the grinding wheel 3. The motor power value of the grinding wheel drive device 34 shows a positive linear relationship with the grinding resistance of the workpiece W on the grinding wheel 3 during grinding.

[0024] The reference value storage unit 512 stores a reference value for information related to the grinding wheel 3 that has been set in advance. This reference value is used in the grinding wheel condition evaluation unit 513, described later, when evaluating the cutting performance of the grinding wheel 32. In this embodiment 1, the motor power value of the grinding wheel drive device 34 when the cutting performance of the grinding wheel 32 changes from a good state to a bad state is acquired in advance, and this motor power value is stored in the reference value storage unit 512 as a reference value Pa. This reference value Pa can be changed according to the configuration and processing conditions of the grinding wheel 32, and multiple reference values ​​according to the configuration and processing conditions of the grinding wheel 32 may be stored.

[0025] The grinding wheel condition evaluation unit 513 evaluates the grinding wheel condition of the grinding wheel section 32 based on the information acquired by the grinding wheel information acquisition unit 511. The grinding wheel condition includes at least the cutting performance of the grinding wheel section 32, and may also include the progress of the self-sharpening of the abrasive grains 321 of the grinding wheel section 32. For example, as shown in Figure 6(a), the cutting performance of the grinding wheel section 32 is evaluated as good when the motor power value of the grinding wheel spindle 33 acquired by the grinding wheel information acquisition unit 511 does not exceed a reference value Pa. On the other hand, as shown in Figure 6(b), the cutting performance of the grinding wheel section 32 is evaluated as poor when the motor power value of the grinding wheel spindle 33 acquired by the grinding wheel information acquisition unit 511 exceeds a reference value Pa.

[0026] In Figures 6(a) and 6(b), the grinding wheel 3 starts rotating at time T0, and at this point the grinding wheel portion 32 is not in contact with the surface of the workpiece W. Subsequently, the grinding wheel 3 moves closer to the workpiece W, and at time T1, the grinding wheel portion 32 comes into contact with the surface of the workpiece W, and grinding of the surface of the workpiece W begins. Accordingly, the motor power value of the grinding wheel spindle 33 gradually increases, and in Figure 6(a), from time T2 onwards, the motor power value of the grinding wheel spindle 33 stabilizes, and the cutting performance of the grinding wheel portion 32 can be evaluated as good. On the other hand, in Figure 6(b), from time T3 onwards, the motor power value of the grinding wheel spindle 33 increases sharply, causing wear of the abrasive grains 321 to begin and increasing the grinding resistance of the grinding wheel portion 32. From time T4 onwards, the motor power value exceeds the reference value Pa, so the cutting performance of the grinding wheel portion 32 can be evaluated as poor.

[0027] The evaluation result display unit 514 can display the evaluation results from the grinding wheel condition evaluation unit 513. This allows the user to easily check the evaluation results from the grinding wheel condition evaluation unit 513.

[0028] The machining condition adjustment unit 515 adjusts the machining conditions of the workpiece W based on the evaluation results of the grinding wheel condition evaluation unit 513. For example, as shown in Figure 6(a), if the evaluation result indicates that the grinding wheel 32 has good cutting performance, the machining conditions can be adjusted to suppress wear of the grinding wheel 32 by reducing the amplitude and duration of the ultrasonic waves applied by the ultrasonic vibration device 4.

[0029] On the other hand, as shown in Figure 6(b), if the evaluation result indicates that the grinding wheel portion 32 has poor cutting performance, the processing conditions can be adjusted to restore the cutting performance of the grinding wheel portion 32 by increasing the amplitude and duration of the ultrasonic waves applied by the ultrasonic vibration device 4 to promote the spontaneous sharpening of the abrasive grains on the grinding wheel portion 32.

[0030] 5-2. Control device 52 The control device 52 includes a drive control unit 521 and a machining mode switching unit 522. The drive control unit 521 controls the grinding of the workpiece W by controlling the operation of the chuck table drive unit 22 and the grinding wheel drive unit 34 based on operation command data based on machining conditions created by the machining condition adjustment unit 515.

[0031] The machining mode switching unit 522 switches the machining mode of the workpiece W by controlling the operation of the high-frequency power supply 35. The machining modes include, for example, a self-sharpening promotion mode in which the grinding wheel 32 is vibrated by the application of ultrasonic waves to the grinding wheel 32 by the ultrasonic vibration device 4 to promote the self-sharpening of abrasive grains 321, and a wear suppression mode in which the vibration of the grinding wheel 32 is stopped or the vibration of the grinding wheel 32 is reduced compared to the self-sharpening promotion mode, thereby suppressing wear of the grinding wheel 32 more than in the self-sharpening promotion mode. The machining modes may further include other machining modes.

[0032] In the self-sharpening acceleration mode, as described above, ultrasonic waves are applied to the grinding wheel section 32 by the ultrasonic vibration device 4 during the grinding of the workpiece W. As a result, the grinding wheel section 32 is vibrated in the Z direction as shown in Figures 1 and 3(a). Consequently, minute collisions occur between the abrasive grains 321 located on the surface of the grinding wheel section 32 and the surface of the workpiece W. As the machining progresses, as shown in Figure 4(b), a load is placed on the worn and flattened abrasive grains 321, causing the surface abrasive grains 321 to fall off, as shown in Figure 4(c), and the embedded abrasive grains 321 are exposed on the surface, thereby accelerating self-sharpening. Furthermore, the porous structure 322, which consists of the bond between the abrasive grains 321 on the surface of the grinding wheel section 32, is finely shaved, causing the surface of the porous structure 322 to recede from the position indicated by reference numeral 322a to the position indicated by reference numeral 322b, resulting in the abrasive grains 321 protruding toward the workpiece W, and the protrusion height is maintained. This cycle is repeated during grinding. In addition, minute collisions between the abrasive grains 321 located on the surface of the grinding wheel 32 and the surface of the workpiece W can cause the tips of the abrasive grains 321 to be finely crushed and sharpened, which can also promote the self-sharpening of the flattened abrasive grains 321.

[0033] The amplitude of the ultrasonic wave applied to the grinding wheel portion 32 and the progress of the self-generated cutting edge of the abrasive grains 321 have a positive linear relationship. For example, as shown in FIGS. 7(a) and 7(b), in an example where the amplitude A of the ultrasonic wave is set to A1 and A2 (where A1 < A2), as shown in FIG. 7(a), when an ultrasonic wave with a small amplitude A1 is applied, the motor power value of the grinding wheel spindle 33 exceeds the reference value Pa at time T5, and it can be evaluated that the wear of the abrasive grains 321 progresses and the self-generated cutting edge is not sufficiently performed. On the other hand, as shown in FIG. 7(b), when an ultrasonic wave with a large amplitude A2 is applied, the motor power value of the grinding wheel spindle 33 does not reach the reference value Pa even at time T5, and thereafter, it becomes a stable value, and it can be evaluated that the wear of the abrasive grains 321 is suppressed and the self-generated cutting edge is promoted. Note that the degree of influence of the magnitude of the amplitude A of the ultrasonic wave applied to the grinding wheel portion 32 on the progress of the self-generated cutting edge of the abrasive grains 321 varies depending on the configuration of the grinding wheel portion 32 (such as the material of the abrasive grains 321 and the porous structure 322, the porosity of the porous structure 322, etc.).

[0034] Also, since the application time of the ultrasonic wave applied to the grinding wheel portion 32 and the progress of the self-generated cutting edge of the abrasive grains 321 have a positive linear relationship, when the application time of the ultrasonic wave becomes longer, the progress of the self-generated cutting edge of the abrasive grains 321 also becomes higher. On the other hand, when the application time of the ultrasonic wave applied to the grinding wheel portion 32 becomes longer, the detachment of the abrasive grains 321 and the recession of the porous structure 322 in the grinding wheel portion 32 are promoted, and the wear of the grinding wheel portion 32 itself also tends to progress. Therefore, by stopping the application of the ultrasonic wave to the grinding wheel portion 32, the wear of the grinding wheel portion 32 can be suppressed. Also, instead of stopping the application of the ultrasonic wave to the grinding wheel portion 32, by reducing the amplitude A of the ultrasonic wave applied to the grinding wheel portion 32, the wear of the grinding wheel portion 3 can also be suppressed.

[0035] Therefore, in the wear suppression mode, by stopping the application of the ultrasonic wave to the grinding wheel portion 32 or reducing the vibration of the grinding wheel portion 32 more than in the self-generated cutting edge promotion mode, the progress of the wear of the grinding wheel portion 32 itself can be suppressed more than in the self-generated cutting edge promotion mode. Note that in the wear suppression mode, the self-generated cutting edge of the abrasive grains 321 is suppressed more than in the self-generated cutting edge promotion mode.

[0036] In this embodiment 1, the processing mode switching unit 522 can switch processing modes based on the evaluation results of the grinding wheel condition evaluation unit 513. For example, as shown in Figures 8(a) to 8(d), when grinding starts, the application of ultrasonic waves is stopped to set the wear suppression mode Ma. When the grinding wheel condition evaluation unit 513 determines that the motor power value of the grinding wheel spindle 33 has reached a reference value Pa during grinding, the application of ultrasonic waves is started to set the self-sharpening promotion mode Mb. After that, the self-sharpening promotion mode Mb is maintained for a predetermined time, then the application of ultrasonic waves is stopped to return to the wear suppression mode Ma, and this cycle is repeated. This makes it possible to promote the self-sharpening of abrasive grains 321 in the self-sharpening promotion mode Mb, and by switching to the wear suppression mode Ma, wear of the grinding wheel 32 can be suppressed compared to when the self-sharpening promotion mode Mb is maintained, thereby extending the lifespan of the grinding wheel 32.

[0037] In the examples shown in Figures 8(a) to 8(d), ultrasonic waves are stopped from being applied to the grinding wheel 32 in wear suppression mode Ma, and are applied to the grinding wheel 32 in self-sharpening promotion mode Mb. However, instead, as shown in the examples in Figures 9(a) to 9(d), the wear suppression mode Ma and the self-sharpening promotion mode Mb may be switched by changing the amplitude A of the ultrasonic waves applied to the grinding wheel 32. In the examples shown in Figures 9(a) to 9(d), ultrasonic waves are applied to the grinding wheel 32 at all times during grinding, with the amplitude A of the ultrasonic waves in wear suppression mode Ma set to A1, and the amplitude A of the ultrasonic waves in self-sharpening promotion mode Mb set to A2, which is greater than A1.

[0038] 6. Grinding wheel condition evaluation and machining condition optimization process Next, the process of evaluating the grinding wheel condition and optimizing the processing conditions in the SiC wafer grinding apparatus 1 of this embodiment 1 will be explained with reference to the flowchart in Figure 10. First, in this flowchart, in step S1, as a preparation step, the workpiece W made of a SiC wafer is mounted on the chuck table 2. Then, in the control device 52, the processing mode switching unit 522 sets the processing mode to wear suppression mode Ma, which does not apply ultrasonic waves, based on the initial processing conditions, and stops the output of the high-frequency power supply 35.

[0039] Subsequently, in step S2, the drive control unit 521 drives the grinding wheel drive unit 34 and the chuck table drive unit 22 to start grinding the workpiece W mounted on the chuck table 2. Then, in step S3, the grinding wheel information acquisition unit 511 acquires the motor power value P of the grinding wheel spindle 33.

[0040] Next, in step S4, the grinding wheel condition evaluation unit 513 compares the motor power value P of the grinding wheel spindle 33 with the reference value Pa stored in the reference value storage unit 512 to determine whether P > Pa. If it is determined in step S4 that P > Pa is not true, the process proceeds to step S4 No., and in step S5, the grinding wheel condition evaluation unit 513 evaluates that the grinding wheel 32 has good cutting performance and that the progress of self-sharpening of the abrasive grains 321 is high, and displays the evaluation result on the evaluation result display unit 514.

[0041] Subsequently, in step S6, it is determined whether or not the grinding completion time has arrived. If it is determined in step S6 that the grinding completion time has not arrived, the process proceeds to step S6 No., and steps S2 onwards are performed again. If it is determined in step S6 that the grinding completion time has arrived, the flow is terminated.

[0042] On the other hand, if it is determined in step S4 that P > Pa, the process proceeds to Yes in step S4, and in step S7, the grinding wheel condition evaluation unit 513 determines that the cutting performance of the grinding wheel 32 is poor and that the progress of the self-sharpening of the abrasive grains 321 is low, and the process proceeds to step S8. In step S8, the processing condition adjustment unit 515 adjusts the processing conditions to improve the cutting performance of the grinding wheel 32 and to promote the progress of the self-sharpening of the abrasive grains 321. In this embodiment 1, as shown in Figures 8(a) to 8(d), the processing conditions are adjusted to switch between processing modes by switching the application of ultrasonic waves to the grinding wheel 32 on and off.

[0043] Subsequently, in step S9, the processing mode switching unit 522 switches the processing mode from wear suppression mode Ma to self-sharpening promotion mode Mb according to the processing conditions. In step S10, the output of the high-frequency power supply 35 is started, and ultrasonic vibration is applied to the grinding wheel section 32 by the ultrasonic vibration device 4 to perform vibration. Then, the process proceeds to step S6. If it is determined that the grinding completion time has not yet arrived, the process proceeds to step S6 No., and steps S2 onwards are repeated. If it is determined in step S6 that the grinding completion time has arrived, the process ends.

[0044] The flow chart shown in Figure 10 allows for the evaluation of the grinding wheel condition of the grinding wheel section 32, and enables the adjustment of processing conditions to achieve a state where the grinding wheel section 32 has good cutting performance and the self-sharpening of abrasive grains 321 is advanced, thereby optimizing the processing conditions. Furthermore, by switching between the self-sharpening acceleration mode Mb and the wear suppression mode Ma, wear of the grinding wheel section 32 is suppressed compared to continuously using the self-sharpening acceleration mode Mb, thereby extending the lifespan of the grinding wheel section 32.

[0045] In the above flow, the machining mode was switched by switching the application of ultrasonic waves to the grinding wheel 32 on and off, as shown in Figures 8(a) to 8(d). Alternatively, the machining mode may be switched by changing the amplitude A of the ultrasonic waves applied to the grinding wheel 32, as shown in Figures 9(a) to 9(d).

[0046] 7. Effects The effects of the SiC wafer grinding apparatus 1 in this embodiment 1 are described below. In the SiC wafer grinding apparatus 1 in this embodiment 1, the grinding wheel section 32 is vibrated by an ultrasonic vibrator 4. The apparatus is configured to switch between a self-sharpening promotion mode Mb, which vibrates the grinding wheel section 32 to promote the self-sharpening of abrasive grains 321 during the grinding of the SiC wafer workpiece W, and a wear suppression mode Ma, which stops the vibration of the grinding wheel section 32 or reduces the vibration of the grinding wheel section 32 compared to the self-sharpening promotion mode Mb, thereby suppressing wear of the grinding wheel section 32 more effectively than the self-sharpening promotion mode Mb. This promotes the self-sharpening of abrasive grains 321 and suppresses a decrease in the sharpness of the grinding wheel section 32. Compared to a configuration in which the grinding wheel section 32 is continuously vibrated by ultrasound during the grinding of the SiC wafer workpiece W, wear of the grinding wheel section 32 is suppressed, thereby extending the lifespan of the grinding wheel section 32.

[0047] Furthermore, in the grinding process shown in Figure 8 of this embodiment 1, in wear suppression mode Ma, the vibration of the grinding wheel 32 is stopped by stopping the application of ultrasonic waves to the grinding wheel 32 by the ultrasonic vibration device 4. As a result, in wear suppression mode Ma, the vibration of the grinding wheel 32 is stopped, which further suppresses wear of the grinding wheel 32.

[0048] Furthermore, in the other grinding operations shown in Figure 9 of this embodiment 1, in wear suppression mode Ma, the amplitude A of the ultrasonic waves applied to the grinding wheel 32 by the ultrasonic vibration device 4 is made smaller than the amplitude A of the ultrasonic waves applied to the grinding wheel 32 by the ultrasonic vibration device 4 in self-sharpening promotion mode Mb, thereby reducing the vibration of the grinding wheel 32 compared to self-sharpening promotion mode Mb. As a result, the wear suppression mode Ma and the self-sharpening promotion mode Mb can be switched by changing the amplitude of the ultrasonic waves without stopping the ultrasonic waves from the ultrasonic vibration device 4, making it easier to control the switching of processing modes.

[0049] In this embodiment 1, a SiC wafer is used as the workpiece W. SiC wafers have high hardness and brittleness, and in conventional configurations, grinding is difficult because abrasive grain wear occurs, requiring a long time for grinding or causing the grinding wheel to wear out prematurely. However, as described above, the SiC wafer grinding apparatus 1 of this embodiment 1 achieves both the promotion of self-sharpening of abrasive grains 321 and the suppression of wear of the grinding wheel 32, thereby enabling good grinding of SiC wafers.

[0050] In this embodiment 1, the reference value storage unit 512 stores the motor power value of the grinding wheel spindle 33 in the grinding wheel drive device 34 as a reference value Pa when the cutting performance of the grinding wheel unit 32 changes from a good state to a bad state. However, the reference value storage unit 512 may also store the upper and lower limit waveforms of the motor power value of the grinding wheel spindle 33 along with the reference value Pa, and the machining condition adjustment unit 515 may adjust the machining conditions so that the motor power value of the grinding wheel spindle 33 falls within the range of the upper and lower limit waveforms.

[0051] Furthermore, the reference value storage unit 512 stores a predetermined time as a reference value during which the differential value of the motor power value of the grinding wheel spindle 33 is continuously positive (or greater than or equal to a predetermined positive value). The grinding wheel condition evaluation unit 513 compares the time change of the differential value of the motor power value of the grinding wheel spindle 33 acquired by the grinding wheel information acquisition unit 511 with the reference value, and when the differential value is continuously positive (or greater than or equal to a predetermined positive value) for a period of time exceeding the reference value, it may determine that the motor power value of the grinding wheel spindle 33 is tending to rise continuously, and evaluate that the cutting performance of the grinding wheel section 32 is deteriorating. The machining condition adjustment unit 515 may then adjust the machining conditions so that the differential value of the motor power value of the grinding wheel spindle 33 does not continuously rise for a period of time exceeding the reference value when it is evaluated that the cutting performance of the grinding wheel section 32 is deteriorating.

[0052] As described above, according to this embodiment 1, it is possible to provide a SiC wafer grinding apparatus 1 that suppresses the decrease in the cutting performance of the grinding wheel 32 when grinding a SiC wafer and extends the lifespan of the grinding wheel 32.

[0053] (Embodiment 2) The SiC wafer grinding apparatus 1 of this second embodiment, compared to the first embodiment shown in Figure 2, includes a learning processing apparatus 53 as shown in Figure 11, and replaces the reference value storage unit 512 of the first embodiment with a learned model storage unit 516. The other configurations in the second embodiment are the same as those in the first embodiment, and their description is omitted.

[0054] 8. Configuration of the learning processing device 53 The learning processing device 53 shown in Figure 11 creates a trained model using information about the grinding wheel unit 32 as explanatory variables and the grinding wheel state of the grinding wheel unit 32 as the target variable. The learning processing device 53 includes a training data acquisition unit 531, a grinding wheel state acquisition unit 532, a feature calculation unit 533, and a model creation unit 534.

[0055] The training data acquisition unit 531 acquires information about the grinding wheel unit 32 as training data for creating a trained model. This information is the same as the information about the grinding wheel unit 32 described above in Embodiment 1, and in Embodiment 2, the training data acquisition unit 531 acquires the motor power value of the grinding wheel spindle 33 in the grinding wheel drive device 34.

[0056] In this second embodiment, the training data acquisition unit 531 acquires training data for grinding wheels 3 whose grinding wheel state during grinding is known. The grinding wheel state acquisition unit 532 then acquires the grinding wheel state associated with the training data. This grinding wheel state is equivalent to the grinding wheel state of the grinding wheel section 32 described above in the first embodiment, and in this second embodiment, the grinding wheel state includes the sharpness of the grinding wheel section 32 and the progress of the self-sharpening of the abrasive grains 321. In the learning processing device 53, the grinding wheel state can be a value obtained by actually measuring the grinding wheel 3 used in grinding. The feature calculation unit 533 calculates feature quantities related to the grinding wheel state from the training data. These are composed of a predetermined calculation device (not shown).

[0057] Then, the model creation unit 534 creates a trained model based on the features and the grinding wheel state. The model creation unit 534 is also composed of a predetermined computing device (not shown). The trained model created by the model creation unit 534 is stored in the trained model storage unit 516. The form of the trained model is not limited and may be created by machine learning based on training data, and may constitute a neural network.

[0058] The grinding wheel condition evaluation unit 513 then inputs the information about the grinding wheel unit 32 acquired by the grinding wheel information acquisition unit 511 into the trained model stored in the trained model storage unit 516, and uses the output grinding wheel condition as the evaluation result.

[0059] According to the SiC wafer grinding apparatus 1 of this second embodiment, the grinding wheel condition can be evaluated with higher accuracy by using a pre-trained model. Furthermore, this second embodiment achieves the same effects and advantages as the first embodiment.

[0060] (Embodiment 3) In the above-described embodiment 1, the grinding wheel information acquisition unit 511 acquired the motor power value of the grinding wheel spindle 33 as information about the grinding wheel 32. However, in this embodiment 3, instead, the grinding wheel information acquisition unit 511 acquires image data of the grinding wheel 32 as information about the grinding wheel 32. The grinding wheel information acquisition unit 511 is configured as an image capture device, as shown in Figure 12. The grinding wheel information acquisition unit 511 acquires image data of the surface of the grinding wheel 32, for example, as shown in Figure 13. As shown in Figure 13, it can be confirmed in the image data that abrasive grains 321 are exposed on the surface of the grinding wheel 32.

[0061] In this third embodiment, the grinding wheel condition evaluation unit 513 evaluates the grinding wheel condition based on the analysis results obtained by analyzing the image data acquired by the grinding wheel information acquisition unit 511. In this third embodiment, as an analysis result of the image data, it is possible to obtain the abrasive grain area, which is the total area of ​​multiple abrasive grains 321 in the image data, as shown in Figure 14(a), or the number of abrasive grains, which is the total number of abrasive grains 321 in the image data, as shown in Figure 14(b). In addition, as shown in Figures 14(a) and 14(b), the reference value storage unit 512 stores reference values ​​Pb and Pc corresponding to the above analysis results.

[0062] Furthermore, as shown in Figure 14(a), the grinding wheel condition evaluation unit 513 can evaluate that the grinding wheel part 32 has good cutting performance and that the progress of self-sharpening of the abrasive grains 321 is high when the abrasive grain area as an analysis result does not exceed the reference value Pb from time T1 to T4. After time T4, if the abrasive grain area exceeds the reference value Pb, the grinding wheel part 32 has poor cutting performance and that the progress of self-sharpening of the abrasive grains 321 is low.

[0063] Furthermore, as shown in Figure 14(b), the grinding wheel condition evaluation unit 513 can evaluate that the grinding wheel section 32 has good cutting performance and that the progress of self-sharpening of the abrasive grains 321 is high when the number of abrasive grains as an analysis result does not exceed the reference value Pc from time T1 to T4. After time T4, if the number of abrasive grains exceeds the reference value Pc, the grinding wheel section 32 has poor cutting performance and that the progress of self-sharpening of the abrasive grains 321 is low.

[0064] Furthermore, as a result of analyzing the image data, the surface properties of the grinding wheel 32 can be obtained instead of the abrasive grain area or the number of abrasive grains. For example, as shown in Figures 15(a) and 15(b), the position (depth) in the thickness direction at each surface direction position on the surface of the grinding wheel 32 is obtained from the image data as the surface properties of the grinding wheel 32. Then, a reference value Pd is set for the position where the region in which the position in the thickness direction is within a predetermined range D is continuous over a predetermined range, and it is determined that the abrasive grains 321 are worn down and flattened at the position where the position in the thickness direction within the predetermined range D is continuous in the surface direction beyond the reference value Pd, and the progress of the self-sharpening of the abrasive grains 321 can be evaluated. In this case, the reference value Pd is stored in the reference value storage unit 512.

[0065] In the example shown in Figure 15(a), since no continuous region is detected where the position in the thickness direction within the predetermined range D exceeds the reference value Pd, it is determined that the abrasive grains 321 are not worn down, and the degree of self-sharpening of the abrasive grains 321 is evaluated as high, and the sharpness of the grinding wheel 32 can be evaluated as good. On the other hand, in the example shown in Figure 15(b), since a continuous region WA is detected where the position in the thickness direction within the predetermined range D exceeds the reference value Pd, it is determined that the abrasive grains 321 are worn down in that region WA, and the degree of self-sharpening of the abrasive grains 321 is evaluated as low, and the sharpness of the grinding wheel 32 can be evaluated as poor.

[0066] As described above, in Embodiment 3, the grinding wheel information acquisition unit 511 acquires image data of the grinding wheel 32 as information related to the grinding wheel 32, and the grinding wheel condition evaluation unit 513 evaluates the grinding wheel condition based on at least one of the number of abrasive grains 321, the area of ​​the abrasive grains 321, and the surface properties of the grinding wheel 32, which are obtained by analyzing the image data. This also produces the same effects as in Embodiment 1.

[0067] (Embodiment 4) In the above-described embodiment 1, the machining condition adjustment unit 515 adjusts the machining conditions of the workpiece W by increasing or decreasing the amplitude and duration of the ultrasonic waves applied by the ultrasonic vibration device 4 based on the evaluation results of the grinding wheel condition evaluation unit 513. However, in this embodiment 4, instead, an example is shown in which the machining conditions are adjusted by increasing or decreasing the entry angle θ of the abrasive grains 321 in the grinding wheel section 32 with respect to the workpiece W based on the evaluation results of the grinding wheel condition evaluation unit 513.

[0068] First, the entry angle of the abrasive grains 321 into the workpiece W in the grinding wheel section 32 can be calculated based on the cutting speed of the grinding wheel section 32, which is set as a processing condition, when the grinding wheel section 32 is not vibrated by the ultrasonic vibration device 4. Then, when the grinding wheel section 32 is vibrated by the ultrasonic vibration device 4, the grinding wheel section 32 moves up and down periodically in the Z direction (see Figure 1) according to the frequency of the ultrasonic waves applied to the grinding wheel section 32, and the entry angle of the abrasive grains 321 into the workpiece W also increases or decreases periodically accordingly.

[0069] As shown in Figure 16(a), the entry angle θ of the abrasive grain 321 can be expressed as the angle between the relative rotation direction R with respect to a predetermined reference point 0 and the tip position 321a in the cutting depth direction C of the abrasive grain 321 at the cutting speed based on the processing conditions, when the grinding wheel section 32 is not being vibrated by the ultrasonic vibrator 4. As shown by the dashed line C0 in Figure 17(a), the tip position 321a of the abrasive grain 321 in the cutting depth direction C becomes deeper as the grinding process progresses. The entry angle θ of the abrasive grain 321 when the grinding wheel section 32 is not being vibrated by the ultrasonic vibrator 4 is shown in Figure 17(a) as the slope of the dashed line C0.

[0070] Furthermore, when the grinding wheel section 32 is being vibrated by the ultrasonic vibration device 4, the entry angle θ of the abrasive grains 321 periodically changes between θmin and θmax with an excitation period corresponding to the frequency of the ultrasonic waves from the ultrasonic vibration device 4, as shown in Figure 16(b). The tip position 321a of the abrasive grains 321 in the cutting depth direction C periodically changes between the tip position 321b corresponding to θmin and the tip position 321c corresponding to θmax. More specifically, as shown by the solid line Cv in Figure 17(a), the tip position 321a of the abrasive grains 321 in the cutting depth direction C deepens while periodically changing with an excitation period Vp corresponding to the frequency of the ultrasonic waves from the ultrasonic vibration device 4 as the grinding progresses. Furthermore, the entry angle θ of the abrasive grains 321 when the grinding wheel section 32 is being vibrated by the ultrasonic vibration device 4 is shown in Figure 17(a) as the slope of the solid line Cv from the tip position 321b corresponding to θmin to the tip position 321c corresponding to θmax.

[0071] Furthermore, the amplitude A of the ultrasonic waves applied to the grinding wheel section 32 by the ultrasonic vibration device 4 changes the tip positions 321b corresponding to θmin and 321c corresponding to θmax in the abrasive grains 321. For example, compared to the case where ultrasonic waves with a small amplitude A1 are applied as shown in Figure 17(a), the entry angle θ of the abrasive grains 321 (the slope of the solid line Cv from the tip position 321b corresponding to θmin to the tip position 321c corresponding to θmax) becomes larger when ultrasonic waves with a large amplitude A2 are applied as shown in Figure 17(b).

[0072] Therefore, the amplitude A of the ultrasonic waves applied to the grinding wheel section 32 by the ultrasonic vibration device 4 and the entry angle θ of the abrasive grains 321 have a positive linear relationship with each other. The entry angle θ of the abrasive grains 321 can be calculated based on the cutting speed of the grinding wheel 3 and the amplitude A of the ultrasonic waves from the ultrasonic vibration device 4. In this embodiment 4, similar to how the processing conditions were adjusted in embodiment 1 to change the amplitude of the ultrasonic waves applied by the ultrasonic vibration device 4 based on the evaluation results of the grinding wheel condition evaluation unit 513, the processing conditions are adjusted to change the entry angle θ of the abrasive grains 321 based on the evaluation results of the grinding wheel condition evaluation unit 513.

[0073] In other words, in this embodiment 4, if the grinding wheel condition evaluation unit 513 evaluates that the grinding wheel 32 has good cutting performance, the processing conditions can be adjusted by changing the processing mode to wear suppression mode Ma so that the entry angle θ of the abrasive grains 321 into the workpiece W becomes smaller. On the other hand, if the grinding wheel condition evaluation unit 513 evaluates that the grinding wheel 32 has poor cutting performance, the processing conditions can be adjusted by changing the processing mode to self-sharpening promotion mode Mb so that the entry angle θ of the abrasive grains 321 into the workpiece W becomes larger. Then, the processing conditions can be optimized by adjusting the processing conditions based on the entry angle θ of the abrasive grains 321 into the workpiece W using the processing condition adjustment unit 515.

[0074] As described above, in this embodiment 4, the machining condition adjustment unit 515 is configured to optimize the machining conditions of the workpiece W by changing the entry angle θ, which is the angle in the direction in which the abrasive grains 321 enter the workpiece W with respect to the surface of the workpiece W. This makes it possible to easily optimize the machining conditions.

[0075] The present invention is not limited to the embodiments described above, and can be applied to various embodiments without departing from its spirit. For example, the grinding wheel state evaluation unit 513 may evaluate the grinding wheel state based on both the motor power value of the grinding wheel spindle 33 in Embodiment 1 and the image analysis results in Embodiment 3. Alternatively, the trained model in Embodiment 2 may be used with the image analysis results in Embodiment 3 as explanatory variables. Furthermore, in Embodiments 1 to 3, the machining condition adjustment unit 515 may adjust the machining conditions by changing the entry angle θ, which is the angle in the direction in which the abrasive grains 321 enter the workpiece W, as in Embodiment 4. In this way, configurations can be arbitrarily combined from the configurations in Embodiments 1 to 4. [Explanation of Symbols]

[0076] 1 SiC wafer grinding machine 2. Chuck table (workpiece holding section) 22 Chuck table drive device 3. Grinding Wheel 31 base 31a End 32. Grinding Wheel Section 321 abrasive grains 321a~c Tip position 322 Porous tissue 323 Stomata 33 Grinding wheel spindle 34. Grinding wheel drive system 35 High frequency power supply 4. Ultrasonic Vibration Device 41 Piezoelectric element 511 Grinding Wheel Information Acquisition Unit 512 Reference Value Storage Unit 513 Grinding Wheel Condition Evaluation Unit 515 Machining condition adjustment section 516 Pre-trained model memory 521 Drive Unit Control Unit 522 Processing mode switching section

Claims

1. A SiC wafer grinding apparatus for grinding the surface of a SiC wafer, A workpiece holding section for holding the workpiece as a SiC wafer, A grinding wheel having a grinding section formed by bonding multiple abrasive grains together with a bond having a porous structure at the end of the base, A grinding wheel drive device that rotates the grinding wheel around a grinding wheel spindle perpendicular to the end of the base, thereby grinding the surface of the workpiece held in the workpiece holder by the grinding wheel portion, An ultrasonic vibration device that applies ultrasonic waves to the grinding wheel and vibrates the grinding wheel in the axial direction of the grinding wheel spindle, A SiC wafer grinding apparatus comprising a processing mode switching unit that controls the operation of the ultrasonic vibration device described above, thereby switching between a self-sharpening promotion mode, in which the grinding wheel is vibrated to promote the self-sharpening of the abrasive grains during the grinding process of the workpiece, and a wear suppression mode, in which the vibration of the grinding wheel is stopped or reduced compared to the self-sharpening promotion mode, thereby suppressing wear of the grinding wheel more effectively than in the self-sharpening promotion mode.

2. In the above wear suppression mode, the vibration of the grinding wheel is stopped by stopping the application of ultrasonic waves to the grinding wheel by the ultrasonic vibration device, as described in claim 1.

3. In the wear suppression mode, the amplitude of the ultrasonic waves applied to the grinding wheel by the ultrasonic vibration device is made smaller than the amplitude of the ultrasonic waves applied to the grinding wheel by the ultrasonic vibration device in the self-sharpening promotion mode, thereby reducing the vibration of the grinding wheel compared to the self-sharpening promotion mode, as described in claim 1.

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