Method for grinding hard wafers

Abstract

To enable a grinding stone causing blinding to be subjected to dressing, so that a hard wafer can be ground into a predetermined thickness.SOLUTION: In a finish grinding step, areas of an annular area to be ground of an outer peripheral part of a hard wafer 100 are increased towards a center, while making the outer peripheral part of the hard wafer 100 subject a lower surface of a grinding stone 307 to dressing, to set the whole surface of the wafer 100 as the area to be ground, and further the wafer 100 is subjected to finish-grinding so that the wafer has a predetermined thickness T1. Therefore, the outer peripheral part of the hard wafer 100 can subject the finish-grinding stone 307 to dressing excellently, even if the finish-grinding stone 307 causes blinding, which can eliminate the blinding. This enables the wafer 100 to be easily ground into the predetermined thickness.SELECTED DRAWING: Figure 5

Description

[Technical Field]

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

[0002] When a sapphire wafer is ground with a grinding wheel, the sapphire wafer is hard, and the grinding wheel may be glared, making it difficult to grind the sapphire wafer to a predetermined thickness.

[0003] This glazing does not occur during rough grinding with a rough grinding wheel, but occurs during finish grinding with a finish grinding wheel. This glazing is thought to occur during the escape cut, which separates the finish grinding wheel, which has been ground to a predetermined thickness, from the sapphire wafer.

[0004] Therefore, Patent Documents 1 to 3 disclose techniques for dressing the grinding wheel during grinding. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2015-020250 [Patent Document 2] Patent Publication No. 2014-180739 [Patent Document 3] Patent Publication No. 2015-160251 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the techniques of Patent Documents 1 to 3 result in a large amount of wear of the grinding wheel. Therefore, an object of the present invention is to enable dressing of a worn grinding wheel while suppressing wear of the grinding wheel when grinding a hard wafer such as a sapphire wafer or a SiC wafer, and to grind the hard wafer to a predetermined thickness. [Means for solving the problem]

[0007] The first hard wafer grinding method (first grinding method) of the present invention is a method for grinding a radius portion of a hard wafer from the center to the periphery held on a holding surface of a chuck table with the underside of an annular grinding wheel having a diameter larger than the radius of the hard wafer, the method comprising: a rough grinding step of rotating the chuck table holding the hard wafer by the holding surface, bringing an annular rough grinding wheel into contact with the radius portion of the hard wafer, and roughly grinding the hard wafer so that the center is thinner than the periphery, thereby giving the cross section of the diameter a concave shape; and rotating the chuck table holding the roughly ground hard wafer with the holding surface, and bringing an annular finish grinding wheel that can come into contact with the radius portion of the hard wafer toward the hard wafer from above the holding surface in a direction perpendicular to the holding surface, thereby grinding the radius portion of the hard wafer with the finish grinding wheel at the periphery of the hard wafer. My eyes are blinded and a finish grinding step in which, while dressing the lower surface, the area of ​​the annular grinding area on the outer periphery of the hard wafer is expanded toward the center until the entire surface of the hard wafer becomes the grinding area, and then the hard wafer is finish-ground to have a predetermined thickness. The second hard wafer grinding method (second grinding method) of the present invention is a method for grinding a radius portion of a hard wafer from the center to the periphery held on the holding surface of a chuck table with the underside of an annular grinding wheel having a diameter larger than the radius of the hard wafer, the method comprising: a rough grinding step of rotating the chuck table holding the hard wafer by the holding surface, bringing an annular rough grinding wheel into contact with the radius portion of the hard wafer, and roughly grinding the hard wafer so that the periphery portion is thinner than the center, thereby giving the cross section of the diameter a convex shape; and a rough grinding step of rotating the chuck table holding the roughly ground hard wafer with the holding surface, bringing an annular finish grinding wheel that can contact the radius portion of the hard wafer toward the hard wafer from above the holding surface in a direction perpendicular to the holding surface, thereby grinding the radius portion of the hard wafer with the finish grinding wheel at the center portion of the hard wafer. My eyes are blinded and a finish grinding step in which, while dressing the lower surface, the area of ​​the area to be ground in the center of the hard wafer is expanded toward the periphery until the entire surface of the hard wafer becomes the area to be ground, and then the hard wafer is finish-ground to have a predetermined thickness. The third grinding method for hard wafers (third grinding method) of the present invention is a method for grinding hard wafers, in which a radial portion from the center to the outer periphery of a hard wafer held on a holding surface of a chuck table is ground with the underside of an annular grinding wheel having a diameter larger than the radius of the hard wafer, and includes a rough grinding step of rotating the chuck table holding the hard wafer by the holding surface, bringing an annular rough grinding wheel into contact with the radial portion of the hard wafer, and roughly grinding the hard wafer so that the central portion of the radius is thinnest, thereby forming a W-shaped cross section of the diameter; and a rough grinding step of rotating the chuck table holding the roughly ground W-shaped hard wafer by the holding surface, and bringing an annular finish grinding wheel that can contact the radial portion of the hard wafer toward the hard wafer from above the holding surface in a direction perpendicular to the holding surface, thereby grinding the hard wafer at the central and outer periphery of the hard wafer with the finish grinding wheel. My eyes are blindedand a finish grinding step in which, while dressing the lower surface, the area of ​​the area to be ground in the central part of the hard wafer is expanded toward the periphery, and the area of ​​the area to be ground in the peripheral part of the hard wafer is expanded toward the center, until the entire surface of the hard wafer becomes the area to be ground, and further the hard wafer is finish-ground to have a predetermined thickness. In the first grinding method, the second grinding method, and the third grinding method, a grinding wheel having a grit size of #1000 to #1400 may be used as the rough grinding wheel, and a grinding wheel having a grit size of #1800 to #2400 may be used as the finish grinding wheel. [Effects of the Invention]

[0008] In the first, second, and third grinding methods, the finish grinding step involves dressing the underside of the finish grinding wheel at the outer periphery, the center, or both the outer periphery, and the center of the hard wafer, while expanding the area of ​​the hard wafer to be ground, so that the entire hard wafer is ground. Therefore, even if the finish grinding wheel is glazing, the finish grinding wheel can be well dressed at the outer periphery and / or the center of the hard wafer at the beginning of grinding the hard wafer, thereby eliminating the glazing. This makes it easy to grind the hard wafer to the specified thickness.

[0009] Furthermore, when grinding hard wafers, there is no need to perform separate dressing on the finish grinding wheel, which reduces unnecessary wear on the finish grinding wheel.Furthermore, since there is no need to use a dressing device, the cost of grinding hard wafers can be reduced. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 2 is a perspective view showing the configuration of a grinding device. [Figure 2] FIG. 2 is an explanatory diagram showing the configuration of a chuck table and its vicinity. [Figure 3]10 is an explanatory diagram showing the inclination of the chuck table when forming a wafer with a concave central shape. FIG. [Figure 4] FIG. 10 is an explanatory diagram showing a wafer having a concave shape. [Figure 5] 10 is an explanatory diagram showing a finish grinding process for a wafer having a concave central shape. FIG. [Figure 6] 10 is an explanatory diagram showing a finish grinding process for a wafer having a concave central shape. FIG. [Figure 7] FIG. 2 is an explanatory diagram showing the wafer after finish grinding. [Figure 8] FIG. 10 is an explanatory diagram showing a wafer having a concave shape. [Figure 9] FIG. 10 is an explanatory diagram showing a wafer having a concave shape. [Figure 10] 10 is an explanatory diagram showing the inclination of the chuck table when forming a wafer with a convex center. FIG. [Figure 11] FIG. 10 is an explanatory diagram showing a wafer having a convex shape in the middle. [Figure 12] FIG. 10 is an explanatory diagram showing a finish grinding process for a wafer having a convex central shape. [Figure 13] FIG. 10 is an explanatory diagram showing a finish grinding process for a wafer having a convex central shape. [Figure 14] FIG. 10 is an explanatory diagram showing the inclination of the chuck table when forming a W-shaped wafer. [Figure 15] FIG. 1 is an explanatory diagram showing a diameter cross section of a wafer. [Figure 16] FIG. 10 is an explanatory diagram showing a finish grinding process for a W-shaped wafer. DETAILED DESCRIPTION OF THE INVENTION

[0011] The grinding apparatus 1 shown in FIG. 1 includes a rough grinding mechanism 30 and a finish grinding mechanism 31, and grinds a wafer 100 held on a chuck table 5 by means of the rough grinding mechanism 30 and the finish grinding mechanism 31.

[0012] The wafer 100 shown in Fig. 1 is a hard wafer, such as a circular sapphire wafer or SiC wafer. A device (not shown) is formed on a front surface 101 of the wafer 100. The front surface 101 of the wafer 100 faces downward in Fig. 1 and is protected by a protective tape (not shown) attached thereto. The back surface 103 of the wafer 100 is the processing surface that is subjected to the grinding process.

[0013] The grinding apparatus 1 has a first apparatus base 10 and a second apparatus base 11 disposed behind (on the +Y direction side of) the first apparatus base 10. The area above the first apparatus base 10 is a loading / unloading area 17 where the wafer 100 is loaded and unloaded. The area above the second apparatus base 11 is a processing area 18. In this processing area 18, the wafer 100 held on the chuck table 5 is processed by a rough grinding mechanism 30 and a finish grinding mechanism 31.

[0014] A first cassette stage 160 and a second cassette stage 162 are provided on the front side (-Y direction side) of the first equipment base 10. A first cassette 161 that stores unprocessed wafers 100 is placed on the first cassette stage 160. A second cassette 163 that stores processed wafers 100 is placed on the second cassette stage 162.

[0015] The first cassette 161 and the second cassette 163 each have a plurality of shelves therein, and each shelf accommodates one wafer 100. That is, the first cassette 161 and the second cassette 163 accommodate a plurality of wafers 100 in a shelf-like manner.

[0016] The openings (not shown) of the first cassette 161 and the second cassette 163 face the +Y direction side. A robot 155 is disposed on the +Y direction side of these openings. The robot 155 has a holding surface for holding the wafer 100. The robot 155 carries (stores) the processed wafer 100 into the second cassette 163. The robot 155 also removes the unprocessed wafer 100 from the first cassette 161 and places it on the temporary placement table 154 of the temporary placement mechanism 152.

[0017] The temporary placement mechanism 152 is used to temporarily place the wafer 100 removed from the first cassette 161, and is provided at a position adjacent to the robot 155. The temporary placement mechanism 152 has a temporary placement table 154 and an alignment member 153. The alignment member 153 has a plurality of alignment pins arranged on the outside so as to surround the temporary placement table 154, and a slider that moves the alignment pins in the radial direction of the temporary placement table 154. In the alignment member 153, the alignment pins are moved toward the center in the radial direction of the temporary placement table 154, thereby reducing the diameter of a circle connecting the plurality of alignment pins. As a result, the wafer 100 placed on the temporary placement table 154 with the back surface 103 facing up is aligned (centered) at a predetermined position.

[0018] A carry-in mechanism 170 is provided at a position adjacent to the temporary placement mechanism 152. The carry-in mechanism 170 carries the wafer 100, which is temporarily placed on the temporary placement mechanism 152, into the chuck table 5. The carry-in mechanism 170 is equipped with a transport pad 171 having a suction surface that suction-holds the back surface 103 of the wafer 100. The carry-in mechanism 170 suction-holds the wafer 100, which is temporarily placed on the temporary placement table 154, with the transport pad 171, transports the wafer 100 to the chuck table 5 located near the temporary placement mechanism 152 in the processing area 18, and places the wafer on the holding surface 50.

[0019] The chuck table 5 is an example of a holding member that holds the wafer 100, and includes a holding surface 50 that holds the wafer 100 by suction. The holding surface 50 is connected to a suction source (not shown) and is capable of holding the wafer 100 by suction via a protective tape. With the wafer 100 held by the holding surface 50 by suction, the chuck table 5 is rotatable about a table rotation axis 501 (see FIG. 2 ), which is a central axis that passes through the center of the holding surface 50 and extends in the Z-axis direction.

[0020] In this embodiment, three chuck tables 5 are arranged at equal intervals on the upper surface of a turntable 6 arranged on the second device base 11 on a circle centered at the center of the turntable 6. A rotation shaft (not shown) for rotating the turntable 6 is arranged at the center of the turntable 6. This rotation shaft allows the turntable 6 to rotate about an axis extending in the Z-axis direction. The rotation of the turntable 6 causes the three chuck tables 5 to revolve. This allows the chuck tables 5 to be positioned sequentially near the temporary placement mechanism 152, below the rough grinding mechanism 30, and below the finish grinding mechanism 31.

[0021] A first column 12 is erected at the rear (+Y direction side) of the second device base 11. A rough grinding mechanism 30 that rough grinds the wafer 100 and a rough grinding feed mechanism 20 that feeds the rough grinding mechanism 30 for grinding are disposed in front of the first column 12.

[0022] The rough grinding feed mechanism 20 includes a pair of guide rails 201 parallel to the Z-axis direction, a lifting table 203 that slides on the guide rails 201, a ball screw 200 parallel to the guide rails 201, a motor 202 that rotates the ball screw 200, and a holder 204 attached to the lifting table 203. The holder 204 holds the rough grinding mechanism 30.

[0023] The lift table 203 is slidably installed on the guide rail 201. A nut portion (not shown) is fixed to the lift table 203. A ball screw 200 is threadedly engaged with this nut portion. The motor 202 is connected to one end of the ball screw 200.

[0024] In the rough grinding feed mechanism 20, the motor 202 rotates the ball screw 200, causing the lifting table 203 to move in the Z-axis direction along the guide rail 201. As a result, the holder 204 attached to the lifting table 203 and the rough grinding mechanism 30 held by the holder 204 also move in the Z-axis direction together with the lifting table 203. In this way, the rough grinding feed mechanism 20 grinds and feeds the rough grinding mechanism 30 along the Z-axis direction.

[0025] The rough grinding mechanism 30 includes a spindle housing 301 fixed to the holder 204, a spindle 300 rotatably held in the spindle housing 301, a motor 302 that rotates the spindle 300, a wheel mount 303 attached to the lower end of the spindle 300, and a grinding wheel 304 detachably connected to the lower surface of the wheel mount 303.

[0026] The spindle housing 301 is held by the holder 204 so as to extend in the Z-axis direction. The spindle 300 extends in the Z-axis direction so as to be perpendicular to the holding surface 50 of the chuck table 5, and is rotatably supported by the spindle housing 301.

[0027] The motor 302 is connected to the upper end side of the spindle 300. The motor 302 rotates the spindle 300 around a spindle rotation axis 505 (see FIG. 2) that extends in the Z-axis direction.

[0028] The wheel mount 303 is formed in a disk shape, is fixed to the lower end of the spindle 300, and rotates in accordance with the rotation of the spindle 300. The wheel mount 303 supports a grinding wheel 304.

[0029] The grinding wheel 304 is formed so that its outer diameter is approximately the same as the outer diameter of the wheel mount 303. The grinding wheel 304 includes an annular wheel base (annular base) 305 made of a metal material such as an aluminum alloy. A rough grinding stone 306 is fixed to the underside of the wheel base 305 around the entire circumference. The rough grinding stone 306 is an annular grinding stone having a diameter larger than the radius of the wafer 100, and is capable of contacting the radial portion of the wafer 100 held on the holding surface 50 of the chuck table 5.

[0030] The rough grinding wheel 306 is rotated by the motor 302 via the spindle 300, wheel mount 303, and wheel base 305 about a spindle rotation axis 505 (see FIG. 2) that passes through the center of the rough grinding wheel 306 and extends in the Z-axis direction, so as to pass through the center of the holding surface 50 of the chuck table 5 (i.e., the center of the wafer 100 held on the holding surface 50), and its lower surface grinds the radial portion from the center to the outer periphery of the wafer 100 held on the chuck table 5. The rough grinding wheel 306 is a grinding wheel containing relatively large abrasive grains, for example, a grinding wheel with a grit size of #1000 to #1400.

[0031] A grinding water flow path extending in the Z-axis direction is formed inside the spindle 300, and this grinding water flow path is connected to a grinding water supply mechanism (not shown) (both not shown). The grinding water supplied to the spindle 300 from the grinding water supply mechanism is sprayed downward from an opening at the lower end of the grinding water flow path toward the rough grinding wheel 306, and reaches the contact point between the rough grinding wheel 306 and the wafer 100.

[0032] A first height gauge 81 is disposed adjacent to the chuck table 5 disposed below the rough grinding mechanism 30. The first height gauge 81 measures the thickness of the wafer 100 in a contact or non-contact manner, for example, during rough grinding.

[0033] Furthermore, a second column 13 is erected at the rear of the second apparatus base 11 so as to be adjacent to the first column 12 along the X-axis direction. A finish grinding mechanism 31 that finish-grinds the wafers 100, and a finish grinding feed mechanism 21 that feeds the finish grinding mechanism 31 for grinding are disposed in front of the second column 13.

[0034] The finish grinding feed mechanism 21 has a configuration similar to that of the rough grinding feed mechanism 20, and can feed the finish grinding mechanism 31 for grinding along the Z-axis direction. The finish grinding mechanism 31 has a configuration similar to that of the rough grinding mechanism 30, except that it is equipped with a finish grinding wheel 307 instead of the rough grinding wheel 306. Like the rough grinding wheel 306, the finish grinding wheel 307 is an annular grinding wheel having a diameter larger than the radius of the wafer 100, and is capable of contacting the radial portion of the wafer 100 held on the holding surface 50 of the chuck table 5.

[0035] The finish grinding wheel 307 is also rotated by the motor 302 via the spindle 300, wheel mount 303, and wheel base 305 about a spindle rotation axis 505 (see FIG. 2) that passes through the center of the finish grinding wheel 307 and extends in the Z-axis direction, so as to pass through the center of the holding surface 50 of the chuck table 5, and its underside grinds the radial portion of the wafer 100 held on the chuck table 5. The finish grinding wheel 307 is a grinding wheel containing relatively small abrasive grains, for example, a grinding wheel with a grit size of #1800 to #2400.

[0036] A second height gauge 82 is disposed adjacent to the chuck table 5 disposed below the finish grinding mechanism 31. The second height gauge 82 measures the thickness of the wafer 100 in a contact or non-contact manner, for example, during finish grinding.

[0037] After the finish grinding, the wafer 100 is carried out by the carrying-out mechanism 172. The carrying-out mechanism 172 transports the wafer 100 held on the chuck table 5 to the spinner cleaning mechanism 156.

[0038] The carry-out mechanism 172 includes a transfer pad 173 having a suction surface that suction-holds the back surface 103 of the wafer 100. The carry-out mechanism 172 suction-holds the back surface 103 of the finish-ground wafer 100 placed on the chuck table 5 using the transfer pad 173. Thereafter, the carry-out mechanism 172 carries the wafer 100 out of the chuck table 5 and transfers it to a spinner table 157 of a single-wafer spinner cleaning mechanism 156.

[0039] The spinner cleaning mechanism 156 is a spinner cleaning unit that cleans the wafer 100. The spinner cleaning mechanism 156 includes a spinner table 157 that holds the wafer 100, and a nozzle 158 that sprays cleaning water and dry air toward the spinner table 157.

[0040] In the spinner cleaning mechanism 156, a spinner table 157 holding the wafer 100 rotates, and cleaning water is sprayed toward the back surface 103 of the wafer 100, thereby spinner-cleaning the back surface 103. Dry air is then blown onto the wafer 100, thereby drying the wafer 100.

[0041] The wafer 100 cleaned by the spinner cleaning mechanism 156 is carried into a second cassette 163 on a second cassette stage 162 by the robot 155 .

[0042] The grinding device 1 also includes a housing 15 that covers the first device base 10 and the second device base 11. A touch panel 60 is provided on the side of the housing 15.

[0043] The touch panel 60 displays various types of information such as device data (processing conditions) related to the grinding device 1. The touch panel 60 is also used to input various types of information such as device data. In this way, the touch panel 60 functions as a display member for displaying information and also as an input member for inputting information.

[0044] The grinding apparatus 1 also has a control unit 7 therein for controlling the grinding apparatus 1. The control unit 7 includes a CPU that performs calculations according to a control program, and a storage medium such as a memory. The control unit 7 executes various processes and controls each component of the grinding apparatus 1.

[0045] Here, the configuration of the chuck table 5 and its vicinity will be described in detail. As shown in FIG. 2, the chuck table 5 is a substantially disk-shaped table for holding the wafer 100, and includes a substantially disk-shaped porous member 51 and a frame 52 that supports the porous member 51.

[0046] The upper surface of the porous member 51 serves as the aforementioned holding surface 50 for holding the wafer 100. The holding surface 50 is formed as a conical surface with its apex at the center. When a suction force from a suction source (not shown) is transmitted to the holding surface 50, the chuck table 5 can suction-hold the wafer 100 by means of the holding surface 50.

[0047] The chuck table 5 is rotatable by a table rotation mechanism 53. That is, a cylindrical table base 55 that supports the chuck table 5 is provided below the chuck table 5. The table rotation mechanism 53 that rotatably supports the table base 55 is disposed below the table base 55.

[0048] The table rotation mechanism 53 is, for example, a pulley mechanism, and includes a motor 521 serving as a drive source, a drive pulley 522 attached to the shaft of the motor 521, a driven pulley 524 connected to the drive pulley 522 via an endless belt 523, a rotor 520 supporting the driven pulley 524, and a rotary joint 525 disposed below the rotor 520. The rotary joint 525 is used to connect the suction source and the holding surface 50. The rotor 520 is connected to the underside of the table base 55 directly below the center of the holding surface 50, and extends perpendicular to the underside of the table base 55.

[0049] In the table rotation mechanism 53, a motor 521 rotates a drive pulley 522, which rotates an endless belt 523 in accordance with the rotation of the drive pulley 522. The rotation of the endless belt 523 rotates a driven pulley 524 and a rotating body 520. As a result, the table base 55 and the chuck table 5 rotate as shown by an arrow 502 around a table rotation axis 501, which is the central axis of the holding surface 50.

[0050] In addition, a tilt adjustment mechanism 40 is provided around the periphery of the table base 55 to adjust the relative tilt between the lower surface of the rough grinding wheel 306 or the finish grinding wheel 307 and the holding surface 50. In this embodiment, the tilt adjustment mechanism 40 is configured to adjust the tilt of the chuck table 5, thereby adjusting the tilt of the holding surface 50 with respect to the lower surface of the rough grinding wheel 306 or the finish grinding wheel 307. The tilt adjustment mechanism 40 includes an internal base 41 that is positioned below the chuck table 5 and has an opening 412 that surrounds the table rotation mechanism 53, an inclination adjustment shaft 42 that passes through the internal base 41, a fixed shaft 43 that is fixed to the internal base 41, and an annular member 45.

[0051] The annular member 45 rotatably supports the table base 55 so as to surround the table base 55 via a connecting portion 46 including a bearing.

[0052] The fixed shaft 43 has its upper end fixed to the lower surface of the annular member 45 and its lower end fixed to the upper surface of the internal base 41 .

[0053] The inclination adjustment shaft 42 is provided to pass through a through-hole 411 extending in the Z-axis direction formed in the internal base 41. In addition, a male screw 421 is formed on the upper end side of the inclination adjustment shaft 42.

[0054] Furthermore, a through-hole 450 is formed in the portion of the annular member 45 that corresponds to the inclination adjustment shaft 42. The through-hole 450 is formed with a female screw 451 that has a shape that corresponds to the male screw 421 of the inclination adjustment shaft 42. The tilt adjustment shaft 42 is inserted into this through-hole 450 and supports the annular member 45 with its male thread 421 threadedly engaged with the female thread 451 of the annular member 45 .

[0055] The tilt adjustment mechanism 40 further includes a drive unit 48 that rotationally drives the tilt adjustment shaft 42, and a fixing member 47 that fixes the drive unit 48 to the lower surface 413 of the internal base 41. When the drive unit 48 rotationally drives the tilt adjustment shaft 42, the portion of the annular member 45 where the through hole 450 into which the tilt adjustment shaft 42 is inserted (the +Y direction side in FIG. 2) moves up and down along the Z axis direction. As a result, the table base 55 supported by the annular member 45 and the +Y direction side of the chuck table 5 supported by the table base 55 also move up and down along the Z axis direction. This adjusts the tilt of the holding surface 50 of the chuck table 5.

[0056] In this embodiment, the tilt adjustment mechanism 40 is provided with two tilt adjustment shafts 42 (one of which is not shown), and one or both of the tilt adjustment shafts 42 are rotationally driven to adjust the tilt of the holding surface 50 of the chuck table 5. The two tilt adjustment shafts 42 and the fixed shaft 43 are provided on the internal base 41, for example, at intervals of 120 degrees around the center of the holding surface 50.

[0057] As described above, in this embodiment, the tilt of the chuck table 5 is adjusted by the tilt adjustment mechanism 40, and the chuck table 5 is rotated around the table rotation axis 501 by the table rotation mechanism 53. The radial portion of the wafer 100 held on the holding surface 50 of the chuck table 5 is ground by the rough grinding wheel 306 or the finish grinding wheel 307, which is arranged so as to pass through the center of the wafer 100 and rotates around the spindle rotation axis 505 as indicated by the arrow 506.

[0058] Next, a more detailed description will be given of a method for grinding wafers in the grinding apparatus 1 under the control of the control unit 7. This grinding method is a method for grinding hard wafers, in which the radial portion of the wafer 100, which is a hard wafer held on the holding surface 50 of the chuck table 5, is ground with the lower surfaces of annular rough grinding wheel 306 and finish grinding wheel 307, each having a diameter larger than the radius of the wafer 100.

[0059] (1) Holding process First, the control unit 7 controls the robot 155 shown in FIG. 1 to remove the unprocessed wafer 100 from the first cassette 161 and place it on the temporary placement table 154 of the temporary placement mechanism 152, and align the wafer 100. Furthermore, the control unit 7 controls the carry-in mechanism 170 to hold the wafer 100 on the temporary placement table 154 and place the wafer 100 with its back surface 103 facing up on the holding surface 50 of the chuck table 5 arranged near the temporary placement mechanism 152. Thereafter, the control unit 7 connects the holding surface 50 to a suction source (not shown). As a result, the holding surface 50 suction-holds the wafer 100, as shown in FIG. 2. In this manner, the chuck table 5 holds the wafer 100 on the holding surface 50.

[0060] (2) Rough grinding process In this process, the chuck table 5 holding the wafer 100 by the holding surface 50 is rotated, and the rough grinding wheel 306 is brought into contact with the radial portion of the wafer 100, and the wafer 100 is roughly ground so that the center is thinner than the outer periphery, giving the cross section of the diameter a concave shape.

[0061] Specifically, after the holding step, the control unit 7 rotates the turntable 6 shown in FIG. 1 so that the chuck table 5 holding the wafer 100 is positioned below the rough grinding mechanism 30.

[0062] At this time, the control unit 7 controls the tilt adjustment mechanism 40 to adjust the tilt of the chuck table 5, thereby adjusting the tilt of the holding surface 50 relative to the underside of the rough grinding wheel 306 so that the center side of the wafer 100 comes into contact with the rough grinding wheel 306 before the outer periphery side, as shown in Figure 3, for example.

[0063] Next, the control unit 7 uses the motor 302 (see FIG. 1) of the rough grinding mechanism 30 to drive the spindle 300 to rotate about the spindle rotation axis 505, as shown by arrow 506. This rotates the rough grinding wheel 306 attached to the lower end of the spindle 300. In this state, the control unit 7 causes the rough grinding mechanism 30 to descend along the Z-axis direction using the rough grinding feed mechanism 20. Furthermore, the control unit 7 causes the table rotation mechanism 53 (see FIG. 2) to rotate the chuck table 5 about the table rotation axis 501, as shown by arrow 502. As a result, the rotating rough grinding wheel 306 comes into contact with the back surface 103 of the wafer 100 held on the rotating chuck table 5, and roughly grinds the back surface 103.

[0064] In this grinding, as shown in Fig. 3, the center side of the wafer 100 comes into contact with the rough grinding wheel 306 before the outer periphery side. Therefore, grinding starts from the center, and the back surface 103 of the wafer 100 is ground so that the grinding area gradually spreads toward the outer periphery. As a result, as shown in Fig. 4, the wafer 100 is ground so that the center of the back surface 103, which is the grinding surface, is recessed and the cross section of the diameter has a central recess shape, resulting in the wafer 100 having a central recess shape.

[0065] During the rough grinding process, the control unit 7 measures the thickness of the center of the wafer 100 using the first height gauge 81, for example, and carries out rough grinding until this thickness reaches a predetermined thickness. It is preferable that the measurement position of the first height gauge 81 is set so as to measure the thinnest part of the wafer 100.

[0066] (3) Finish grinding process In this step, the control unit 7 first rotates the turntable 6 shown in Fig. 1 on its axis, thereby positioning the chuck table 5, which holds the roughly ground wafer 100 having a concave shape on its holding surface 50, below the finish grinding mechanism 31. As a result, the wafer 100 having a concave shape is positioned below the finish grinding wheel 307 in the finish grinding mechanism 31, as shown in Fig. 5.

[0067] Next, the control unit 7 drives the motor 302 (see FIG. 1) of the finish grinding mechanism 31 to rotate the spindle 300 around the spindle rotation axis 505 as shown by arrow 506. This rotates the finish grinding wheel 307 attached to the lower end of the spindle 300. Furthermore, the control unit 7 rotates the chuck table 5 using the table rotation mechanism 53 (see FIG. 2). This causes the wafer 100 to rotate around the table rotation axis 501 as shown by arrow 502, as shown in FIG.

[0068] In this state, the control unit 7 causes the finish grinding mechanism 31 to move down along the Z-axis direction using the finish grinding feed mechanism 21. In this way, the control unit 7 causes the rotating finish grinding wheel 307 to move down from above the holding surface 50 in a direction perpendicular to the holding surface 50, bringing it close to the wafer 100. Then, the control unit 7 brings the finish grinding wheel 307 into contact with the back surface 103 of the wafer 100 held on the rotating chuck table 5, thereby finish-grinding the back surface 103. FIG. 5 shows a finished thickness T1, which is the thickness of the wafer 100 after the finish grinding process.

[0069] In this grinding, since the wafer 100 has a concave shape, as shown in Fig. 5, the finish grinding wheel 307 first comes into contact with the outer periphery of the wafer 100 and grinds the outer periphery of the wafer 100. As a result, the outer periphery of the wafer 100 dresses the lower surface of the finish grinding wheel 307.

[0070] Thereafter, as the finish grinding mechanism 31 is lowered by the finish grinding feed mechanism 21, the area of ​​the annular area to be ground on the outer periphery of the wafer 100 expands toward the center, as shown in Fig. 6. In this way, the entire surface of the wafer 100 becomes the area to be ground.

[0071] Furthermore, during finish grinding, the control unit 7 measures the thickness of the wafer 100 using the second height gauge 82. The control unit 7 carries out the finish grinding until the thickness of the wafer 100 reaches a predetermined finish thickness T1. As a result, as shown in FIG. 7, a wafer 100 having a uniform finish thickness T1 is obtained.

[0072] As described above, in this embodiment, in the finish grinding step, the area of ​​the annular area to be ground on the outer periphery of the wafer 100 is expanded toward the center while the lower surface of the finish grinding wheel 307 is dressed on the outer periphery of the wafer 100. Then, the entire surface of the wafer 100 is treated as the area to be ground, and the wafer 100 is finish ground to have a predetermined finishing thickness T1.

[0073] Therefore, in this embodiment, when finish-grinding the wafer 100, which is a hard wafer such as a sapphire wafer or a SiC wafer, even if the finish grinding wheel 307 is glazing, the finish grinding wheel 307 can be well dressed at the outer periphery of the hard wafer 100 at the beginning of grinding the wafer 100, thereby eliminating the glazing. This makes it easy to grind the wafer 100 to a predetermined thickness.

[0074] Furthermore, when grinding the wafer 100, which is a hard wafer, there is no need to perform separate dressing on the finish grinding wheel 307, which can prevent unnecessary wear on the finish grinding wheel 307. Furthermore, there is no need to use a dressing device, which can reduce the cost of grinding the wafer 100.

[0075] In this embodiment, in the finish grinding step, the wafer 100 having a concave shape as shown in Fig. 4 and Fig. 8 is finish ground to have a predetermined finish thickness T1. In this case, as shown in Fig. 8, until the area to be ground of the wafer 100 reaches the center, that is, until the thickness to be ground of the wafer 100 reaches thickness T2, the finish grinding wheel 307 is dressed by the hard outer peripheral portion of the wafer 100, and therefore a high dressing effect can be obtained for the finish grinding wheel 307.

[0076] On the other hand, from the time when the grinding area of ​​the wafer 100 reaches the center until the thickness of the wafer 100 reaches the finishing thickness T1, that is, from the time when the grinding area reaches the center until the grinding thickness reaches the thickness T3, the entire surface of the wafer 100 becomes the grinding area, and therefore the sharpening effect of the finish grinding wheel 307 becomes small.

[0077] In addition, in the above-mentioned rough grinding process, the control unit 7 forms the wafer 100 with a concave shape, as shown in Figures 4 and 8, in which the back surface 103 of the wafer 100 has a substantially uniform slope from the outer periphery to the center.

[0078] In this regard, the control unit 7 may adjust the inclination of the chuck table 5 using the inclination adjustment mechanism 40 during the rough grinding process to form a wafer 100 with a concave shape, as shown in Figure 9, in which the back surface 103 of the wafer 100 has a downward convex slope from the outer periphery to the center. Even in this case, a high dressing effect can be obtained with the finish grinding wheel 307 until the grinding area of ​​the wafer 100 reaches the center (until the grinding thickness reaches thickness T2). On the other hand, the dressing effect of the finish grinding wheel 307 decreases from the time the grinding area reaches the center until the thickness of the wafer 100 reaches the finishing thickness T1 (until the grinding thickness reaches thickness T3).

[0079] In addition, in the rough grinding process, the control unit 7 may rotate the chuck table 5 holding the wafer 100 by the holding surface 50, bring the rough grinding wheel 306 into contact with the radial portion of the wafer 100, and rough grind the wafer 100 so that the outer periphery is thinner than the center, thereby making the cross section of the diameter into a convex shape.

[0080] Specifically, after the holding process, when the control unit 7 positions the chuck table 5 holding the wafer 100 below the rough grinding mechanism 30, it controls the tilt adjustment mechanism 40 to adjust the tilt of the chuck table 5, thereby adjusting the tilt of the holding surface 50 relative to the underside of the rough grinding wheel 306 so that the outer periphery of the wafer 100 comes into contact with the rough grinding wheel 306 before the center, as shown in Figure 10.

[0081] Next, the control unit 7 uses the motor 302 (see FIG. 1) of the rough grinding mechanism 30 to drive the spindle 300 to rotate about the spindle rotation axis 505, as shown by arrow 506. This rotates the rough grinding wheel 306 attached to the lower end of the spindle 300. In this state, the control unit 7 causes the rough grinding mechanism 30 to descend along the Z-axis direction using the rough grinding feed mechanism 20. Furthermore, the control unit 7 causes the table rotation mechanism 53 (see FIG. 2) to rotate the chuck table 5 about the table rotation axis 501, as shown by arrow 502. As a result, the rotating rough grinding wheel 306 comes into contact with the back surface 103 of the wafer 100 held on the rotating chuck table 5, and roughly grinds the back surface 103.

[0082] In this grinding, as shown in Fig. 10, the outer periphery of the wafer 100 comes into contact with the rough grinding wheel 306 before the center. Therefore, grinding starts from the outer periphery, and the back surface 103 of the wafer 100 is ground so that the grinding area gradually spreads toward the center. As a result, as shown in Fig. 11, the center of the back surface 103, which is the grinding surface, is higher, and the wafer 100 is ground so that the cross section of the diameter has a convex shape, resulting in a convex-shaped wafer 100.

[0083] During the rough grinding process, the control unit 7 measures, for example, the thickness of the outer periphery of the wafer 100 using the first height gauge 81, and carries out rough grinding until this thickness reaches a predetermined thickness. It is preferable that the measurement position of the first height gauge 81 is set so as to measure the thinnest part of the wafer 100.

[0084] In the finish grinding process for the wafer 100 having a convex center, the control unit 7 first rotates the turntable 6 shown in Fig. 1 on its axis, thereby disposing the chuck table 5, which holds the roughly ground wafer 100 having a convex center by its holding surface 50, below the finish grinding mechanism 31. As a result, the wafer 100 having a convex center is disposed below the finish grinding wheel 307 in the finish grinding mechanism 31, as shown in Fig. 12.

[0085] Next, the control unit 7 drives the motor 302 (see FIG. 1) of the finish grinding mechanism 31 to rotate the spindle 300 around the spindle rotation axis 505 as shown by arrow 506. This rotates the finish grinding wheel 307 attached to the lower end of the spindle 300. Furthermore, the control unit 7 rotates the chuck table 5 using the table rotation mechanism 53 (see FIG. 2). This causes the wafer 100 to rotate around the table rotation axis 501 as shown by arrow 502 as shown in FIG. 12.

[0086] In this state, the control unit 7 causes the finish grinding mechanism 31 to move down along the Z-axis direction using the finish grinding feed mechanism 21. In this way, the control unit 7 causes the rotating finish grinding wheel 307 to move down from above the holding surface 50 in a direction perpendicular to the holding surface 50, bringing it close to the wafer 100. Then, the control unit 7 brings the finish grinding wheel 307 into contact with the back surface 103 of the wafer 100 held on the rotating chuck table 5, thereby finish-grinding the back surface 103. FIG. 12 also shows the finished thickness T1, which is the thickness of the wafer 100 after the finish grinding process.

[0087] In this grinding, since the wafer 100 has a convex shape, as shown in Fig. 12, the finish grinding wheel 307 first comes into contact with the center portion of the wafer 100 and grinds the center portion of the wafer 100. As a result, the lower surface of the finish grinding wheel 307 is dressed by the center portion of the wafer 100.

[0088] Thereafter, as the finish grinding mechanism 31 is lowered by the finish grinding feed mechanism 21, the area of ​​the area to be ground in the center of the wafer 100 expands toward the periphery, as shown in Fig. 13. In this way, the entire surface of the wafer 100 becomes the area to be ground.

[0089] The control unit 7 also measures the thickness of the wafer 100 using the second height gauge 82. The control unit 7 performs finish grinding until the thickness of the wafer 100 reaches a predetermined finish thickness T1. As a result, a wafer 100 having a uniform finish thickness T1 is obtained, as shown in FIG.

[0090] As described above, in the finish grinding process for the wafer 100 having a convex center, the area of ​​the center of the wafer 100 to be ground is expanded toward the periphery while the lower surface of the finish grinding wheel 307 is dressed at the center of the wafer 100. Then, the entire surface of the wafer 100 is treated as the area to be ground, and the wafer 100 is finish ground to have a predetermined finished thickness T1.

[0091] Therefore, even if the finish grinding wheel 307 is bald, the finish grinding wheel 307 can be well dressed at the center of the hard wafer 100 at the beginning of grinding the wafer 100, thereby eliminating the baldness. This makes it easy to grind the wafer 100 to a predetermined thickness. Furthermore, since there is no need to perform separate dressing on the finish grinding wheel 307, unnecessary wear of the finish grinding wheel 307 can be suppressed and grinding costs can be reduced.

[0092] 5, 6, 12 and 13, the wafer 100 placed on the conical holding surface 50 of the chuck table 5 is omitted.

[0093] Furthermore, the angle of the chuck table 5 in the finish grinding process is, for example, an angle such that the lower surface of the finish grinding wheel 307 and the portion of the conical holding surface 50 located below the finish grinding wheel 307 are parallel to each other (see Figure 2). Furthermore, the direction perpendicular to the holding surface 50, which is the descending direction of the finish grinding wheel 307 in the finish grinding process, is, for example, a direction perpendicular to the portion of the conical holding surface 50 located below the finish grinding wheel 307 (the portion parallel to the lower surface of the finish grinding wheel 307).

[0094] However, the angle of the chuck table 5 in the finish grinding step is not limited to the above-mentioned angle, and may be the same as or different from the angle of the chuck table 5 in the rough grinding step.

[0095] Furthermore, in the rough grinding step, the control unit 7 may rotate the chuck table 5 holding the wafer 100 by the holding surface 50, bring the rough grinding wheel 306 into contact with the radial portion of the wafer 100, and rough grind the wafer 100 so that the central portion of the radius is the thinnest, thereby forming a W-shaped cross section of the diameter of the wafer 100, i.e., a shape in which the central portion of the radius is thinner than the central and outer peripheral portions of the wafer 100. Note that the central portion of the radius of the wafer 100 is the portion midway between the central and outer peripheral portions of the wafer 100.

[0096] Specifically, after the holding process, when the control unit 7 positions the chuck table 5 holding the wafer 100 below the rough grinding mechanism 30, it controls the tilt adjustment mechanism 40 to adjust the tilt of the chuck table 5, thereby adjusting the tilt of the holding surface 50 relative to the underside of the rough grinding wheel 306 so that the central part of the radius of the wafer 100 comes into contact with the rough grinding wheel 306 first, as shown in Figure 14.

[0097] Next, the control unit 7 uses the motor 302 (see FIG. 1) of the rough grinding mechanism 30 to drive the spindle 300 to rotate about the spindle rotation axis 505, as shown by arrow 506. This rotates the rough grinding wheel 306 attached to the lower end of the spindle 300. In this state, the control unit 7 causes the rough grinding mechanism 30 to descend along the Z-axis direction using the rough grinding feed mechanism 20. Furthermore, the control unit 7 causes the table rotation mechanism 53 (see FIG. 2) to rotate the chuck table 5 about the table rotation axis 501, as shown by arrow 502. As a result, the rotating rough grinding wheel 306 comes into contact with the back surface 103 of the wafer 100 held on the rotating chuck table 5, and roughly grinds the back surface 103.

[0098] In this grinding, as shown in Fig. 14, the central portion of the radius of the wafer 100 comes into contact with the rough grinding wheel 306 first, that is, before the central and outer periphery sides of the wafer 100. For this reason, grinding starts from the central portion of the radius, and the back surface 103 of the wafer 100 is ground so that the grinding area gradually spreads toward the central and outer periphery sides of the wafer 100. As a result, as shown in Fig. 15, the wafer 100 is ground so that the central portion of the radius of the back surface 103, which is the grinding surface, is thinner than the central and outer periphery parts of the wafer 100, and the wafer 100 has a W-shaped cross section in diameter, resulting in a W-shaped wafer 100.

[0099] During the rough grinding process, the control unit 7 uses the first height gauge 81 to measure the thickness of the central part of the radius of the wafer 100, for example, and carries out rough grinding until this thickness reaches a predetermined thickness. It is preferable that the measurement position of the first height gauge 81 is set so as to measure the thinnest part of the wafer 100.

[0100] In the finish grinding process for the W-shaped wafer 100, the control unit 7 first rotates the turntable 6 shown in Fig. 1 so that the chuck table 5, which holds the roughly ground W-shaped wafer 100 by the holding surface 50, is positioned below the finish grinding mechanism 31. As a result, the W-shaped wafer 100 is positioned below the finish grinding stone 307 in the finish grinding mechanism 31, as shown in Fig. 16.

[0101] Next, the control unit 7 drives the motor 302 (see FIG. 1) of the finish grinding mechanism 31 to rotate the spindle 300 around the spindle rotation axis 505 as shown by arrow 506. This rotates the finish grinding wheel 307 attached to the lower end of the spindle 300. Furthermore, the control unit 7 rotates the chuck table 5 using the table rotation mechanism 53 (see FIG. 2). This causes the wafer 100 to rotate around the table rotation axis 501 as shown by arrow 502, as shown in FIG.

[0102] In this state, the control unit 7 causes the finish grinding mechanism 31 to move down along the Z-axis direction using the finish grinding feed mechanism 21. In this way, the control unit 7 causes the rotating finish grinding wheel 307 to move down from above the holding surface 50 in a direction perpendicular to the holding surface 50, bringing it close to the wafer 100. Then, the control unit 7 brings the finish grinding wheel 307 into contact with the back surface 103 of the wafer 100 held on the rotating chuck table 5, thereby finish-grinding the back surface 103.

[0103] 16, since the wafer 100 has a W-shape, the finish grinding wheel 307 first comes into contact with the central and peripheral portions of the wafer 100 and grinds the central and peripheral portions of the wafer 100. As a result, the central and peripheral portions of the wafer 100 dress the lower surface of the finish grinding wheel 307.

[0104] Thereafter, as the finish grinding mechanism 31 is lowered by the finish grinding feed mechanism 21, the area of ​​the area to be ground in the central part of the wafer 100 expands toward the periphery, and the area of ​​the area to be ground in the peripheral part of the wafer 100 expands toward the center. In this way, the entire surface of the wafer 100 becomes the area to be ground.

[0105] The control unit 7 also measures the thickness of the wafer 100 using the second height gauge 82. The control unit 7 performs finish grinding until the thickness of the wafer 100 reaches a predetermined finish thickness T1 (see FIG. 7). As a result, a wafer 100 having a uniform finish thickness T1 is obtained, as shown in FIG.

[0106] As described above, in the finish grinding process for the W-shaped wafer 100, the underside of the finish grinding wheel 307 is dressed at the center and outer periphery of the wafer 100, while the area of ​​the area to be ground at the center of the wafer 100 is expanded toward the periphery and the area of ​​the area to be ground at the outer periphery of the wafer 100 is expanded toward the center. Then, the entire surface of the wafer 100 is treated as the area to be ground, and the wafer 100 is finish ground to have a predetermined finished thickness T1.

[0107] Therefore, even if the finish grinding wheel 307 is bald, the finish grinding wheel 307 can be well dressed at the center and outer periphery of the hard wafer 100 at the beginning of grinding the wafer 100, thereby eliminating the baldness. This makes it easy to grind the wafer 100 to a predetermined thickness. Furthermore, since there is no need to perform separate dressing on the finish grinding wheel 307, unnecessary wear of the finish grinding wheel 307 can be suppressed and grinding costs can be reduced.

[0108] 14 and 16 show the chuck table 5, the rough grinding mechanism 30, and the finish grinding mechanism 31 from a different direction than in FIGS. 10 and 12. In the rough grinding step shown in FIG. 14 and the finish grinding step shown in FIG. 16, the rough grinding wheel 306 and the finish grinding wheel 307 are also arranged to pass through the center of the wafer 100.

[0109] In addition, in this embodiment, when grinding the wafer 100 into a concave, convex, or W-shaped cross section in the rough grinding process, the tilt of the holding surface 50 relative to the lower surface of the rough grinding wheel 306 is adjusted by adjusting the tilt of the chuck table 5 using the tilt adjustment mechanism 40 (see Figure 2). In this regard, in the rough grinding process, when grinding the wafer 100 into a concave, convex, or W-shaped cross section, instead of or in addition to adjusting the inclination of the chuck table 5, the inclination of the lower surface of the rough grinding wheel 306 relative to the holding surface 50 of the chuck table 5 may be adjusted by adjusting the inclination of the spindle 300 in the rough grinding mechanism 30 using an inclination adjustment mechanism (not shown) provided in the rough grinding mechanism 30. [Explanation of symbols]

[0110] 1: grinding device, 6: turntable, 7: control unit, 10: first device base, 11: second device base, 12: first column, 13: second column, 15: housing, 17: Loading / unloading area, 18: Processing area, 20: Rough grinding feed mechanism, 21: Finish grinding feed mechanism, 200: ball screw, 201: guide rail, 202: motor, 203: Lift table, 204: Holder, 30: rough grinding mechanism, 31: finish grinding mechanism, 300: spindle, 301: spindle housing, 302: motor, 303: Wheel mount, 304: Grinding wheel, 305: Wheel base, 306: Rough grinding wheel, 307: Finish grinding wheel, 40: tilt adjustment mechanism, 41: internal base, 42: tilt adjustment shaft, 43: fixed shaft, 45: annular member, 46: connecting portion, 47: fixed member, 48: driving portion, 411: Through hole, 412: Opening, 413: Bottom surface, 421: male screw, 450: through hole, 451: female screw, 5: chuck table, 50: holding surface, 51: porous member, 52: frame body, 55: Table base, 53: table rotation mechanism, 520: rotating body, 521: motor, 522: driving pulley, 523: endless belt, 524: driven pulley, 81: First height gauge, 82: Second height gauge, 100: wafer, 101: front surface, 103: back surface, 152: temporary placement mechanism, 153: alignment member, 154: temporary placement table, 155: Robot, 156: Spinner cleaning mechanism, 157: Spinner table, 158: Nozzle, 160: first cassette stage, 161: first cassette, 162: second cassette stage, 163: second cassette, 170: Loading mechanism, 171: Transport pad, 172: Unloading mechanism, 173: Transport pad

Claims

1. A method for grinding a hard wafer, comprising grinding a radial portion from the center to the outer periphery of a hard wafer held on a holding surface of a chuck table with a lower surface of an annular grinding wheel having a diameter larger than the radius of the hard wafer, a rough grinding step of rotating the chuck table holding the hard wafer by the holding surface, bringing an annular rough grinding wheel into contact with the radial portion of the hard wafer, and rough grinding the hard wafer so that the center is thinner than the outer periphery, thereby forming a concave shape in the cross section of the diameter; a finish grinding step of rotating the chuck table holding the roughly ground hard wafer having a concave shape by means of the holding surface, and bringing an annular finish grinding stone capable of contacting the radial portion of the hard wafer from above the holding surface toward the hard wafer in a direction perpendicular to the holding surface, thereby dressing the blemished lower surface of the finish grinding stone with the outer periphery of the hard wafer and expanding the area of ​​the annular grinding area of ​​the outer periphery of the hard wafer toward the center until the entire surface of the hard wafer becomes the grinding area, and further finish grinding the hard wafer to a predetermined thickness. Method for grinding hard wafers.

2. A method for grinding a hard wafer, comprising grinding a radial portion from the center to the outer periphery of a hard wafer held on a holding surface of a chuck table with a lower surface of an annular grinding wheel having a diameter larger than the radius of the hard wafer, a rough grinding step of rotating the chuck table holding the hard wafer by the holding surface, bringing an annular rough grinding wheel into contact with the radius portion of the hard wafer, and rough grinding the hard wafer so that the outer periphery becomes thinner than the center, thereby forming a cross section of the diameter into a convex shape; a finish grinding step of rotating the chuck table holding the roughly ground hard wafer of convex shape by the holding surface, and bringing an annular finish grinding stone capable of contacting the radial portion of the hard wafer from above the holding surface toward the hard wafer in a direction perpendicular to the holding surface, thereby dressing the blemished lower surface of the finish grinding stone at the center of the hard wafer while expanding the area of ​​the grinding area at the center of the hard wafer toward the periphery, until the entire surface of the hard wafer becomes the grinding area, and further finish grinding the hard wafer to a predetermined thickness. Method for grinding hard wafers.

3. A method for grinding a hard wafer, comprising grinding a radial portion from the center to the outer periphery of a hard wafer held on a holding surface of a chuck table with a lower surface of an annular grinding wheel having a diameter larger than the radius of the hard wafer, a rough grinding step of rotating the chuck table holding the hard wafer by the holding surface, bringing an annular rough grinding wheel into contact with the radius portion of the hard wafer, and rough grinding the hard wafer so that the central portion of the radius is the thinnest, thereby forming a W-shaped cross section of the diameter; and a finish grinding step of rotating the chuck table holding the roughly ground W-shaped hard wafer by the holding surface, and bringing an annular finish grinding stone capable of contacting the radius portion of the hard wafer from above the holding surface toward the hard wafer in a direction perpendicular to the holding surface, thereby dressing the dulled lower surface of the finish grinding stone with the central and peripheral portions of the hard wafer, while expanding the area of ​​the grinding area in the central portion of the hard wafer toward the periphery and expanding the area of ​​the grinding area in the peripheral portion of the hard wafer toward the center, until the entire surface of the hard wafer becomes the grinding area, and further finish-grinding the hard wafer to a predetermined thickness. Method for grinding hard wafers.

4. As the rough grinding stone, a grinding stone having a grain size of #1000 to #1400 is used, As the finishing grinding wheel, a grinding wheel having a grain size of #1800 to #2400 is used.

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

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