Method for grinding hard wafers

Abstract

To grind a hard wafer to a uniform thickness.SOLUTION: A hard wafer grinding method includes: a first grinding step in which grinding wheels 341 are pressed on a hard wafer 100 held by a holding surface 210 by using a vertical moving mechanism 5 in a state that the holding surface 210 and a lower surface 345 of each grinding wheel 341 are arranged parallel to each other so as to grind the hard wafer 100 having a reverse conical shape by distortion in a grinding area of a radial portion; and a second grinding step in which the grinding wheels 341 are relatively moved in a horizontal direction from a center of the hard wafer 100 to an outer periphery by using a horizontal moving mechanism 5 while being moved in a vertical direction by using the vertical moving mechanism so that a load value measured by a load measuring device becomes a predetermined load value which is set in advance so as to grind the hard wafer 100 in a uniform thickness after the first grinding step.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a method for grinding hard wafers. [Background technology]

[0002] When grinding hard wafers such as GaN wafers and SiC wafers using an annular grinding wheel, grinding is performed with a high load by pressing the grinding wheel firmly against the grinding area of ​​the radius of the hard wafer (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2017-047520 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the grinding area where the grinding wheel and wafer come into contact, the holding surface of the chuck table that holds the wafer and the underside of the grinding wheel are parallel, but when the grinding wheel is pressed hard and grinding is performed while the abrasive grains are self-sharpening, the parallelism changes because the outer periphery of the chuck table is pressed down by the load perpendicular to the upper surface of the wafer.As a result, the ground hard wafer is formed into an inverted cone shape that is thin in the center and thick on the periphery.

[0005] On the other hand, when grinding is performed without pressing the grinding wheel hard, the abrasive grains do not self-sharpen and become dull, resulting in the problem of being unable to grind. For example, when a 2-inch GaN wafer is ground with a grinding wheel with a grit size of #8000, a load of 150N is applied. In this case, the GaN wafer has a thickness difference of 5μm between the center and the periphery. In contrast, when an 8-inch silicon wafer is ground with a grinding wheel with a grit size of #8000, a load of 50N is applied, but because the load value is small, the difference in thickness between the center and the periphery of the wafer is slight.

[0006] The present invention has been made in consideration of such problems, and has an object to grind a hard wafer to a uniform thickness by a series of grinding operations. [Means for solving the problem]

[0007] a grinding mechanism that rotates the center of an annular grinding wheel, which is disposed so that the radial portion of the holding surface is parallel to the bottom surface of the grinding wheel, around the center of the grinding wheel, to grind the hard wafer held on the holding surface; a vertical movement mechanism that moves the chuck table and the grinding wheel relatively in a direction perpendicular to the bottom surface of the grinding wheel; a horizontal movement mechanism that moves the grinding wheel and the chuck table relatively in a direction parallel to the bottom surface of the grinding wheel; and a load measuring device that measures the load value when the bottom surface of the grinding wheel is pressed against the top surface of the hard wafer in a direction perpendicular to the top surface of the hard wafer. a first grinding step of pressing the grinding wheel against the hard wafer held on the holding surface using the vertical movement mechanism while the holding surface and a lower surface of the grinding wheel are parallel in the grinding region, thereby grinding the hard wafer into an inverted cone-shaped hard wafer due to distortion of at least the chuck table or the grinding mechanism; and a second grinding step of, after the first grinding step, relatively moving the grinding wheel in the vertical direction using the vertical movement mechanism so that a load value measured by the load measuring device becomes a predetermined load value, while relatively moving the grinding wheel horizontally from the center of the hard wafer toward the periphery using the horizontal movement mechanism, thereby grinding the hard wafer to a uniform thickness. The first grinding step includes a setting step of setting a load value and a grinding time, and in the first grinding step, the load value set in the setting step is maintained and the wafer is ground for the grinding time set in the setting step. do. Also, The apparatus includes a chuck table that holds a hard wafer on a conical holding surface and rotates around the center of the holding surface as an axis; a grinding mechanism that rotates around the center of an annular grinding wheel that is arranged so that the radius of the holding surface and the bottom surface of the grinding wheel are parallel to each other, and grinds the hard wafer held on the holding surface; a vertical movement mechanism that moves the chuck table and the grinding wheel relatively in a direction perpendicular to the bottom surface of the grinding wheel; a horizontal movement mechanism that moves the grinding wheel and the chuck table relatively in a direction parallel to the bottom surface of the grinding wheel; and a horizontal movement mechanism that moves the grinding wheel and the chuck table relatively in a direction perpendicular to the top surface of the hard wafer. a load measuring device for measuring a load value when a lower surface of the grinding wheel is pressed against a radial portion of the hard wafer, the grinding device comprising: a grinding device for measuring a load value when a lower surface of the grinding wheel is pressed against the radial portion of the hard wafer; a first grinding step for grinding the hard wafer into an inverted cone-shaped hard wafer by using the vertical movement mechanism to press the grinding wheel against the hard wafer held on the holding surface in a state in which the holding surface and the lower surface of the grinding wheel are parallel to each other in the grinding area; a second grinding step in which, after the first grinding step, the grinding wheel is relatively moved in the vertical direction using the vertical movement mechanism while the grinding wheel is relatively moved horizontally from the center of the hard wafer toward the outer periphery using the horizontal movement mechanism so that the load value measured by the load measuring device becomes a predetermined load value set in advance, thereby grinding the hard wafer to a uniform thickness, wherein the first grinding step includes a setting step of setting a load value and a grinding time, and in the first grinding step, the load value set in the setting step is maintained and the wafer is ground for the grinding time set in the setting step, The second grinding step includes a load value setting step of setting a predetermined load value for each horizontal position of the grinding wheel relative to the hard wafer held on the holding surface in accordance with the horizontal position of the grinding wheel relative to the hard wafer held on the holding surface. The method may include a non-contact thickness measurement mechanism that measures the thickness of the hard wafer in the radial direction of the hard wafer held on the holding surface, and a thickness measurement step that measures the thickness of the hard wafer in the radial portion may be included between the first grinding step and the second grinding step. The hard wafer may be, for example, a SiC wafer, a GaN wafer, or a diamond wafer. [Effects of the Invention]

[0008] In the present invention, even in cases where it is difficult to form a uniform thickness of the hard wafer because it is necessary to apply a high load to the hard wafer during grinding, normal in-feed grinding is performed by applying a high load until the hard wafer reaches a predetermined thickness, and then, by controlling the load value to a preset value while moving the grinding wheel toward the outer periphery of the wafer, the distortion (mechanical deformation) caused by the load is restored, and the hard wafer can be ground flat. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a cross-sectional view schematically illustrating an example of a grinding device as viewed from the side. [Figure 2] FIG. 1 is a cross-sectional view schematically showing a state before a hard wafer is ground. [Figure 3] FIG. 10 is a plan view showing the grinding area of ​​the radius portion. [Figure 4] FIG. 4 is a cross-sectional view schematically showing a first grinding step. [Figure 5] 10A to 10C are cross-sectional views schematically illustrating a thickness measurement step. [Figure 6] FIG. 10 is a cross-sectional view schematically showing a second grinding step. [Figure 7] 10 is a graph showing the relationship between the grinding position of the hard wafer, the magnitude of the load, and the thickness of the hard wafer in the second grinding step. DETAILED DESCRIPTION OF THE INVENTION

[0010] 1. Grinding equipment configuration The grinding apparatus 1 shown in FIG. 1 includes a chuck table 2 that holds a wafer, and a grinding mechanism 3 that grinds the wafer held by the chuck table 2.

[0011] The chuck table 2 includes a suction unit 21 formed of a porous member and a frame 22 that supports the suction unit 21. A holding surface 210, which is the upper surface of the suction unit 21, and an upper surface 220 of the frame 22 are formed, for example, flush with each other. The suction unit 21 is connected to a suction source (not shown), and is capable of applying a suction force to the holding surface 210. The holding surface 210 is formed in a conical shape.

[0012] The lower surface of the frame body 22 is supported by a table support part 23. The table support part 23 is connected to a rotation drive part 6, and the chuck table 2 is driven by the rotation drive part 6 to be rotatable.

[0013] The lower part of the table support part 23 is supported at at least three points by at least three support shafts 24 (only two are shown in FIG. 1). The three support shafts 24 are arranged at 120-degree intervals in the circumferential direction. Of these, at least two support shafts 24 are each driven by an adjustment part 25 to be rotatable, and by rotating the support shafts 24, the table support part 23 can be raised and lowered, thereby adjusting the inclination of the holding surface 210.

[0014] The grinding mechanism 3 includes a spindle 30 having a rotation axis extending in the Z-axis direction, a spindle rotation mechanism 31 that rotates the spindle 30, a spindle housing 32 that rotatably supports the spindle 30, a mount 33 connected to the lower end of the spindle 30, and a grinding wheel 34 attached to the mount 33. When the spindle rotation mechanism 31 rotates the spindle 30, the grinding wheel 34 also rotates. The grinding wheel 34 is composed of a base 340 fixed to the mount 33 and multiple grinding stones 341 fixed in an annular shape to the underside of the base 340. The underside 345 of the grinding stone 341 is the grinding surface that comes into contact with the wafer to grind it. A grinding water jetting portion 342 that communicates with a water source (not shown) and opens at the bottom is formed inside the base 340.

[0015] The chuck table 2 is supported by a horizontal movement mechanism 4 so as to be movable in the Y-axis direction. The horizontal movement mechanism 4 includes a ball screw 40 having a rotation axis in the Y-axis direction, a motor 41 that rotates the ball screw 40, a pair of guide rails 42 arranged parallel to the ball screw 40, and a slide plate 43 whose bottom is in sliding contact with the guide rails 42 and has an internal nut portion 430 that threads onto the ball screw 40. An adjustment unit 25 is provided on the upper portion of the slide plate 43. When the ball screw 40 rotates, the slide plate 43 is guided by the guide rails 42 and moves in the Y-axis direction. The movement of the slide plate 43 in the Y-axis direction also moves the chuck table 2 in the Y-axis direction. This allows the grinding wheel 341 and the chuck table 2 to move relatively in a direction parallel to the lower surface 345 of the grinding wheel 341. The motor 41 is equipped with an encoder 44, and the position of the chuck table 2 in the Y-axis direction can be detected based on the encoder 44.

[0016] The grinding mechanism 3 is supported by a vertical movement mechanism 5 so as to be movable up and down in the Z-axis direction. The vertical movement mechanism 5 includes a ball screw 50 having a rotation axis in the Z-axis direction, a motor 51 for rotating the ball screw 50, a pair of guide rails 52 arranged parallel to the ball screw 50, a lift plate 53 whose sides are in sliding contact with the guide rails 52 and have a nut therein that screws onto the ball screw 50, and a holder 54 connected to the lift plate 53 and supporting the spindle housing 32. The holder 54 is composed of a lower plate 540 that supports the spindle housing 32 from below and upright side plates 541. A load measuring device 542 is disposed between the lower plate 540 and the side plates 541 to measure the load value when the lower surface 345 of the grinding wheel 341 is pressed against the wafer. The load measuring device 542 may be disposed at position 301 shown in FIG. 2 and configured to detect the air pressure of a thrust bearing (not shown) that supports the spindle 30. When the ball screw 50 rotates, the lifting plate 53 is guided by the guide rails 52 and moves in the Z-axis direction, and the grinding mechanism 3 also moves in the Z-axis direction. This allows the chuck table 2 and the grinding wheel 341 to move relatively in a direction perpendicular to the lower surface 345 of the grinding wheel 341. The position of the grinding mechanism 3 in the Z-axis direction can be recognized by the encoder 55.

[0017] A non-contact thickness gauge 7 is disposed above the movement path of the chuck table 2 in the Y-axis direction. The non-contact thickness gauge 7 includes a measurement unit 71 that projects measurement light downward and measures the thickness of the wafer based on the interference light between the light reflected on the upper surface of the wafer and the light reflected on the lower surface of the wafer, and a movement unit 72 that moves the measurement unit 71 in the Y-axis direction.

[0018] 2, the rotary drive unit 6 that rotates the chuck table 2 includes a rotary shaft 61 fixed to the underside of the table support unit 23 and a rotary joint 62 connected to the lower part of the rotary shaft 61. A driven pulley 63 is disposed around the rotary shaft 61, and a drive pulley 64 is disposed on the side of the driven pulley 63. The drive pulley 64 is driven by a motor 65. A belt 66 is wound around the drive pulley 64 and the driven pulley 63, and when the drive pulley 64 is driven by the motor 65 to rotate, the rotational force is transmitted to the driven pulley 63 by the belt 66, causing the rotary shaft 61 to rotate, and the chuck table 2 to rotate.

[0019] The rotation shaft 61 is rotatably supported by a rotation support part 67. A male screw 251 is formed at the tip of the support shaft 24, and a female screw 671 that screws into the male screw 251 is formed on the rotation support part 67. When the adjustment part 25 rotates the support shaft 24, the male screw 251 moves forward and backward relative to the female screw 671, thereby raising and lowering the rotation support part 67, and thereby the inclination of the holding surface 210 can be adjusted.

[0020] 2. Grinding method for hard wafers 2, in the grinding apparatus 1, the hard wafer 100 is suction-held on a holding surface 210 of the chuck table 2. A protective member 110 is attached to the lower surface 102 of the hard wafer 100, and the protective member 110 side is suction-held on the holding surface 210. Examples of the hard wafer 100 include a GaN wafer, a SiC wafer, and a diamond wafer.

[0021] As shown in Fig. 2, the holding surface 210 is formed in a conical surface shape, and therefore, as shown in Fig. 3, the rotational orbit 343 of the grinding wheel 341 passes through the rotation axis 200 of the hard wafer 100, and the grinding wheel 341 comes into contact with the upper surface 101 of the hard wafer 100 in a grinding region 344 in the radius portion of the holding surface 210 to perform grinding. In the grinding apparatus 1, before starting grinding of the hard wafer 100, the holding surface 210 and the lower surface 345 of the grinding wheel 341 are brought into a parallel state as shown in Fig. 2. This operation is performed by the adjustment unit 25 adjusting the height of the support shaft 24.

[0022] (1) First grinding process As shown in Fig. 2, the holding surface 210 and the lower surface 345 of the grinding wheel 341 are parallel to each other, and the hard wafer 100 is held on the holding surface 210 via the protective member 110. Then, the chuck table 2 is rotated about the rotation axis 200 passing through the center of the holding surface 210, and the annularly arranged grinding wheels 341 are rotated about their centers as axes, and the grinding mechanism 3 is lowered by the vertical movement mechanism 5. As a result, the lower surface 345 of the rotating grinding wheel 341 comes into contact with the upper surface 101 of the hard wafer 100, and grinding begins. The grinding wheel 341 comes into contact with the upper surface 101 of the hard wafer 100 in the grinding region 344 of the radius portion shown in Fig. 3.

[0023] When grinding the hard wafer 100, the grinding wheel 341 needs to be pressed firmly, and the measured value of the load measuring device 542 is higher than when grinding a silicon wafer or the like, causing distortion in the chuck table 2 or the grinding mechanism 3. For example, as shown in FIG. 4, when the grinding wheel 341 presses the hard wafer 100 on the +Y side in FIG. 4, the +Y side of the chuck table 2 also sinks, and the rotation axis 200 of the chuck table 2 tilts in the direction of arrow 205, which is a direction closer to being parallel to the rotation axis 300 of the grinding wheel 341. Furthermore, as the rotation axis 200 tilts in the direction of arrow 205, the rotation axis 300 of the grinding wheel 341 also tilts in the direction of arrow 305, which is the same direction as arrow 205, but the degree of tilt is smaller than that of the rotation axis 200. As a result, as shown in FIG. 4, the rotation axis 300 of the grinding wheel 341 is no longer perpendicular to the holding surface 210 in the grinding area 344 shown in FIG. 3, and the hard wafer 100 is formed into an inverted cone-shaped concave shape that is thin in the center and becomes thicker toward the outer periphery.

[0024] In this process, before starting grinding, a setting process is carried out in which a target load value to be measured by the load measuring device 542 during grinding and a grinding time are set in advance. These values ​​are set so that the degree of the central concavity at the end of this process, i.e., the difference in thickness between the central part and the peripheral part of the hard wafer 100, will be a target value, and the relationship between the load value, grinding time, and the degree of central concavity is determined in advance by experiment. Therefore, by setting a load value and grinding time determined in advance by experiment and performing grinding for the set time while controlling the vertical movement mechanism 5 so as to maintain that load value, it is possible to set the difference in thickness between the central part and the peripheral part of the hard wafer 100 to the target value.

[0025] (2) Thickness measurement process After the first grinding step, as shown in FIG. 5, the grinding wheel 341 is raised by the vertical movement mechanism 5 so that the grinding wheel 341 and the hard wafer 100 are not in contact with each other. The chuck table 2 is rotated about the rotation axis 200, and the measurement unit 71 of the non-contact thickness gauge 7 is moved in the radial direction of the hard wafer 100 to measure the thickness of the hard wafer 100, and it is determined whether the hard wafer 100 has the desired central concave shape. The measurement positions are, for example, three locations: the center, the middle part of the radius, and the outer periphery of the hard wafer 100. If the thickness measurement results show that the grinding is insufficient or that the desired central concave shape has not been achieved, the process returns to the first grinding step and continues grinding.

[0026] (2) Second grinding process After the thickness measurement step, the grinding wheel 341 is moved vertically using the vertical movement mechanism 5, and the rotating grinding wheel 341 is brought into contact with the upper surface 101 of the hard wafer 100 to start grinding.

[0027] At the start of grinding in this process, grinding is performed in the grinding region 344 of the radius portion shown in Fig. 3, as in the first grinding process, but as shown in Fig. 6, by changing the position of the chuck table 2 in the Y-axis direction using a horizontal movement mechanism, the orbit of the grinding wheel 341 is moved horizontally in the +Y direction from the orbit passing through the center of the hard wafer 100 toward the outer periphery. Since the hard wafer 100 is formed to be thin at the center and thick on the outer periphery, the orbit of the grinding wheel 341 moves toward the outer periphery of the hard wafer 100 and more of the outer periphery is ground, thereby making it possible to finally make the thickness of the hard wafer 100 uniform.

[0028] Here, in this process, before starting grinding, a load value setting process is carried out in which a predetermined load value is set for each horizontal position of the grinding wheel 341 relative to the hard wafer 100 held on the holding surface 210. These values ​​are set as target values ​​for making the thickness of the hard wafer 10 uniform at the end of this process, and the relationship between the horizontal relative position of the grinding wheel 341 relative to the hard wafer 100 and the load value is grasped in advance by experiment.

[0029] This relationship can be expressed, for example, as shown in the graph in Figure 7, where the horizontal axis represents the radial direction of the hard wafer 100 and the vertical axis represents the thickness of the hard wafer 100, the load during grinding, and the relative movement speed in the Y-axis direction between the chuck table 2 and the grinding wheel 341.At the end of the first grinding process, the thickness 82 of the hard wafer 100 becomes thicker as it moves toward the outer periphery, and in this process, the load 81 is reduced as the grinding position moves toward the outer periphery, thereby making it possible to make the thickness of the hard wafer 100 uniform. The relative movement speed 80 between the chuck table 2 and the grinding wheel 341 in the Y-axis direction is constant, and this speed is determined by experiment.

[0030] In this embodiment, the position of the grinding wheel 341 in the horizontal direction relative to the hard wafer 100 is determined by the position of the chuck table 2 in the Y-axis direction, and this position is recognized by the encoder 44 shown in Fig. 1. Therefore, by setting the position of the chuck table 2 in the Y-axis direction that has been determined through a prior experiment and a load value corresponding to that position, and controlling the vertical movement mechanism 5 so that the load measurement value of the load measuring device 542 changes to a predetermined value as the chuck table 2 moves in the +Y direction, the thickness of the hard wafer 100 can be made uniform. In this embodiment, the chuck table 2 is moved in the Y-axis direction as described above, but the grinding mechanism 3 may be configured to move in the Y-axis direction. Alternatively, a turntable may be provided with multiple chuck tables 2, and the grinding mechanism 3 may be moved in the Y-axis direction or the X-axis direction when the grinding wheel 341 is moved horizontally.

[0031] At the start of grinding in this process, the grinding position of the grinding wheel 341 relative to the hard wafer 100 is the same as in the first grinding process, so the rotation axis 200 of the chuck table 2 tilts in the direction of arrow 205 shown in FIG. 4. However, as the chuck table 2 moves in the -Y direction, the contact area between the grinding wheel 341 and the hard wafer 100 gradually decreases, causing springback to cause the rotation axis 200 to return in the direction of arrow 206 in FIG. 6. In other words, as the contact area gradually decreases, the load value should also gradually decrease. However, because the load value does not change due to springback, over-grinding occurs. Therefore, the load value is measured using the load measuring device 542, and the grinding wheel 341 is raised as it moves toward the outer periphery of the hard wafer 100 to prevent over-grinding due to springback. This makes it possible to uniform the in-plane thickness of the hard wafer 10.

[0032] Incidentally, one possible reason why the upper surface of the wafer after grinding is formed into an inverted cone shape (concave in the middle) is that the peripheral speed of the grinding wheel 341 varies depending on the position on the wafer. That is, the central part of the wafer is ground more because it comes into contact with the grinding wheel 341 more frequently, while the peripheral part is ground less because it comes into contact with the grinding wheel 341 less frequently. However, even if such a factor exists, the thickness of the hard wafer 100 can be made uniform according to the grinding method described above.

[0033] In the second grinding step, the tilt of the holding surface 210 is adjusted by the adjusting unit 25 shown in Fig. 1, and the grinding region 344 of the radius portion of the holding surface 210 shown in Fig. 3 and the lower surface 345 of the grinding wheel 341 are preferably kept parallel to each other. This allows the hard wafer 100 to have a more uniform thickness.

[0034] As described above, in this grinding method, normal infeed grinding is performed until the hard wafer 100 reaches a predetermined thickness, and then the grinding wheel 341 is rapidly moved backward toward the outer periphery of the hard wafer 100 while controlling the load to a preset value that gradually decreases, thereby restoring the distortion (mechanical deformation) caused by the load and making it possible to grind the hard wafer flat.

[0035] In the above embodiment, the vertical movement mechanism 5 is configured to move the grinding wheel 341 relative to the chuck table 2 in a direction perpendicular to the holding surface 210, but it may also be configured to move the chuck table 2 relative to the grinding wheel 341 in a direction perpendicular to the holding surface 210. Furthermore, although the horizontal movement mechanism 4 in the above embodiment is configured to move the chuck table 2 in a direction parallel to the lower surface 345 of the grinding wheel 342, it may also be configured to move the grinding wheel 341 in a direction parallel to the lower surface 345 of the chuck table 2. [Explanation of symbols]

[0036] 1: Grinding device 2: Chuck table 21: Suction part 210: Holding surface 22: Frame body 220: Top surface 23: Table support part 24: Support shaft 25: Adjustment part 251: Male screw 200: Rotation axis 3: Grinding mechanism 30: Spindle 31: Spindle rotation mechanism 32: Spindle housing 33: Mount 34: Grinding wheel 340: Base 341: Grinding wheel 342: Grinding water jet part 343: Rotation track 344: Grinding area 345: Bottom surface 300: Rotation axis 4: Horizontal movement mechanism 40: Ball screw 41: Motor 42: Guide rail 43: Slide plate 430: Nut part 44: Encoder 5:Vertical movement mechanism 50: Ball screw 51: Motor 52: Guide rail 53: Lifting plate 54: Holder 540: Lower plate 541: Side plate 542: Load measuring device 55: Encoder 6: Rotation drive unit 61: Rotating shaft 62: Rotary joint 63: Driven pulley 64: Driving pulley 65: Motor 66: Belt 67: Rotation support part 671: Female screw 7: Non-contact thickness measuring device 71: Measuring unit 72: Moving unit 80: Relative movement speed 81: Load 82: Thickness 100: Hard wafer 101: Upper surface 102: Lower surface 110: Protective material

Claims

1. a grinding mechanism that rotates the center of an annular grinding wheel, which is disposed so that the radius of the holding surface is parallel to the bottom surface of the grinding wheel, around the center of the grinding wheel, to grind the hard wafer held on the holding surface; a vertical movement mechanism that moves the chuck table and the grinding wheel relatively in a direction perpendicular to the bottom surface of the grinding wheel; a horizontal movement mechanism that moves the grinding wheel and the chuck table relatively in a direction parallel to the bottom surface of the grinding wheel; and a load measuring device that measures the load value when the bottom surface of the grinding wheel is pressed against the top surface of the hard wafer in a direction perpendicular to the bottom surface of the grinding wheel, A method for grinding a hard wafer, which grinds the hard wafer in a grinding region where the rotating grinding wheel contacts a radial portion of the hard wafer, comprising: a first grinding step in which, in the grinding region, the grinding wheel is pressed against the hard wafer held on the holding surface by using the vertical movement mechanism while the holding surface and a lower surface of the grinding wheel are parallel to each other, thereby grinding the hard wafer into an inverted cone-shaped wafer by distortion of at least the chuck table or the grinding mechanism; a second grinding step in which, after the first grinding step, the grinding wheel is relatively moved in a vertical direction using the vertical movement mechanism so that the load value measured by the load measuring device becomes a predetermined load value, while the grinding wheel is relatively moved horizontally using the horizontal movement mechanism from the center of the hard wafer toward the outer periphery, thereby grinding the hard wafer to a uniform thickness; Equipped with The first grinding step includes a setting step of setting a load value and a grinding time, In the first grinding step, the load value set in the setting step is maintained and the wafer is ground for the grinding time set in the setting step.

2. A grinding device comprising: a chuck table that holds a hard wafer on a conical holding surface and rotates around the center of the holding surface as an axis; a grinding mechanism that rotates around the center of an annular grinding wheel that is positioned so that the radius of the holding surface and the underside of the grinding wheel are parallel to each other, to grind the hard wafer held on the holding surface; a vertical movement mechanism that moves the chuck table and the grinding wheel relatively in a direction perpendicular to the underside of the grinding wheel; a horizontal movement mechanism that moves the grinding wheel and the chuck table relatively in a direction parallel to the underside of the grinding wheel; and a load measuring device that measures the load value when the underside of the grinding wheel is pressed vertically against the upper surface of the hard wafer, A method for grinding a hard wafer, which grinds the hard wafer in a grinding region where the rotating grinding wheel contacts a radial portion of the hard wafer, comprising: a first grinding step in which, in the grinding region, the grinding wheel is pressed against the hard wafer held on the holding surface by using the vertical movement mechanism while the holding surface and a lower surface of the grinding wheel are parallel to each other, thereby grinding the hard wafer into an inverted cone-shaped wafer by distortion of at least the chuck table or the grinding mechanism; a second grinding step in which, after the first grinding step, the grinding wheel is relatively moved in a vertical direction using the vertical movement mechanism so that the load value measured by the load measuring device becomes a predetermined load value, while the grinding wheel is relatively moved horizontally using the horizontal movement mechanism from the center of the hard wafer toward the outer periphery, thereby grinding the hard wafer to a uniform thickness; Equipped with The first grinding step includes a setting step of setting a load value and a grinding time, In the first grinding step, the load value set in the setting step is maintained and the wafer is ground for the grinding time set in the setting step; the second grinding step includes a load value setting step of setting a predetermined load value for each horizontal position of the grinding wheel relative to the hard wafer held on the holding surface, in accordance with the horizontal position of the grinding wheel relative to the hard wafer held on the holding surface; Method for grinding hard wafers.

3. a non-contact thickness measuring mechanism for measuring the thickness of the hard wafer in a radial direction of the hard wafer held on the holding surface; a thickness measuring step of measuring a thickness at a radius portion of the hard wafer between the first grinding step and the second grinding step; 3. The method for grinding a hard wafer according to claim 1 or 2.

4. The hard wafer is a SiC wafer, a GaN wafer, or a diamond wafer.

4. The method for grinding a hard wafer according to claim 1, 2 or 3.

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