Wafer grinding methods and grinding equipment

Abstract

[Problem] In the case of grinding a wafer whose outer periphery tends to lift, the ground wafer is finished to a uniform thickness. [Solution] In the first grinding step, while the outer periphery is supported by the elastic member 217, the wafer 10 is ground to reduce the force causing the wafer 10 to lift. In the subsequent second holding step, the lower surface 101 of the wafer 10 is held in place. Then, in the second grinding step, since grinding is performed while the lower surface 101 of the wafer 10 is held in place, the entire surface of the wafer 10, including the outer periphery, can be finished to be flat. Therefore, the risk of defects in the components 12 formed near the outer periphery of the wafer 10 is reduced.

Description

[Technical Field]

[0001] This invention relates to a method and apparatus for grinding a warped wafer. [Previous Technology]

[0002] A chuck stage for holding a wafer whose outer periphery has a greater warping element than its center may have a structure comprising an attraction surface and an annular elastic member (sponge, rubber sheet, rubber tube, etc.). The attraction surface attracts the lower surface of the central portion of the wafer, and the annular elastic member contacts the lower surface of the outer periphery of the wafer. If the wafer held in this chuck stage is ground with a grinding stone, the elastic member will be flattened by the grinding load, thus preventing leakage of the attraction force and reliably attracting and holding the wafer (for example, see Patent Documents 1 and 2). [Conventional Art Documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2016-031979 [Patent Document 2] Japanese Patent Application Publication No. 2018-207033 [Summary of the Invention]

[0004] [Problem to be solved by the invention] However, because the elastic member is flattened during the grinding process, the part of the wafer supported by the elastic member is formed to be thicker, thus there is a problem that the thick part is formed in a ring while the outer periphery is formed to be thinner.

[0005] The present invention was made in view of such problems, and its object is to finish a wafer with a uniform thickness when grinding a wafer whose outer peripheral side is raised.

[0006] [Technical Means for Solving the Problem] The present invention relates to a wafer grinding method, which involves attracting and holding a wafer with raised outer periphery along the attraction surface of a chuck stage, and grinding the wafer using a grinding stone. The wafer grinding method comprises the following steps: a first holding step, in which the wafer is attracted and held on the first attraction surface of a first chuck stage composed of an annular elastic member and an attraction member, the annular elastic member contacting the lower surface of the outer periphery of the wafer, and the attraction member having the first attraction surface on the inner side of the elastic member to attract the lower surface of the wafer; a first grinding step, in which the wafer is ground by a first grinding stone... The wafer is ground to a thickness below the finished thickness using a grinding stone, reducing wafer warpage. A conveying step transfers the wafer to a second suction surface of a second chuck stage equipped with a porous component that attracts the entire lower surface of the wafer. A second holding step holds the wafer ground to the second suction surface. A second grinding step uses a second grinding stone to grind the wafer to the finished thickness. In this wafer grinding method, a coarse grinding stone can be used in the first grinding step, and a fine grinding stone can be used in the second grinding step. Furthermore, the present invention is a grinding apparatus that grinds a wafer whose outer peripheral portion has warped by means of a grinding stone, and comprises: a first chuck stage, which is composed of an annular elastic member and a suction member, the annular elastic member contacting the lower surface of the outer peripheral portion of the warped wafer, the suction member having a first suction surface on the inner side of the elastic member for attracting the lower surface of the wafer; a first grinding mechanism that grinds the wafer held on the first suction surface by means of a first grinding stone; a second chuck stage, which comprises a porous member having a second suction surface for attracting the entire lower surface of the wafer; a second grinding mechanism that grinds the wafer held on the second suction surface by means of a second grinding stone; and a conveying mechanism that conveys the wafer from the first suction surface to the second suction surface.

[0007] [Effect of the Invention] In the wafer grinding method of the present invention, in the first grinding step, since the wafer is ground while the outer peripheral portion is supported by an elastic member, the force that would cause the wafer to lift is weakened, thus enabling the lower surface of the wafer to be held in the subsequent second holding step. Then, in the second grinding step, since grinding is performed while the lower surface of the wafer 10 is held in a state of being held in a state of being held in a state of being held in a state of being held in a state of being held in a state of being held in a state of being held in a state of being held in a state of being held in a state of being held in a state of being held in a state of being held in a state of being held in a state of being flattened, the entire surface of the wafer including the outer peripheral portion can be finished into a flat surface. Therefore, the risk of components formed near the outer periphery of the wafer becoming defective is reduced. Furthermore, the grinding apparatus of the present invention has an annular elastic member on the lower surface of the outer periphery of the wafer and a first suction surface on the inner side of the elastic member to attract the lower surface of the wafer, and a second suction surface on the second chuck to attract the entire lower surface of the wafer. It also has a conveying mechanism for transporting the wafer from the first suction surface to the second suction surface. Therefore, it is suitable for implementing the above-mentioned wafer grinding method and can automate a series of steps until the entire surface of the wafer is finished to be flat.

Implementation Method

[0009] The grinding apparatus 1 shown in FIG1 includes: a first chuck stage 21 and a second chuck stage 22, which attract and hold the wafer 10; a first grinding mechanism 3, which grinds the wafer 10 held on the first chuck stage 21; and a second grinding mechanism 4, which grinds the wafer 10 held on the second chuck stage 22.

[0010] The front part of the grinding apparatus 1 is provided with cassette mounting areas 61 and 62, which hold cassettes 610 and 620 for accommodating wafers 10. For example, cassette 610 holds wafers 10 before grinding, and cassette 620 holds wafers 10 after grinding.

[0011] A robot 63 is provided behind (on the +Y side) the cartridge loading areas 61 and 62 for moving the wafer 10 into and out of the cartridges 610 and 620. The robot 63 includes: a hand 631 that attracts and holds the wafer 10; a reversing drive unit 632 that reverses the front and back of the hand 631; and an arm 633 that is connected to the reversing drive unit 632 and causes the hand 631 to rotate and move up and down.

[0012] A temporary placement mechanism 64 for temporarily placing the wafer 10 before grinding is provided in the movable area of ​​the hand 631. The temporary placement mechanism 64 includes: a stage 641 on which the wafer 10 is placed; and a plurality of positioning pins 642, which are arranged in an arc shape and can move radially toward the center of the stage 641. By moving the plurality of positioning pins 642 toward each other while the wafer 10 is placed on the stage 641, the wafer 10 can be positioned at a predetermined position.

[0013] In the movable area of ​​the hand 631, a cleaning mechanism 65 for cleaning the milled wafer 10 is provided at a position aligned with the temporary holding mechanism 64 in the X-axis direction. The cleaning mechanism 65 includes: a rotating stage 651 that attracts and holds the milled wafer 10; and a nozzle 652 that sprays cleaning fluid onto the wafer 10 held on the rotating stage 651.

[0014] The first chuck stage 21 and the second chuck stage 22 are driven by a horizontal moving mechanism (not shown) to become movable in the Y-axis direction. A conveying mechanism 7 for transporting the wafer 10 is provided between the moving path of the first chuck stage 21 in the Y-axis direction and the moving path of the second chuck stage 22. This conveying mechanism 7 is located at position 70 in Figure 1.

[0015] The conveying mechanism 7 includes: a gate-shaped wall portion 71; a ball screw 72 disposed on one side of the surface of the wall portion 71 and having an axis in the Y-axis direction; a pair of guide rails 73 disposed parallel to the ball screw 72; a motor 74 connected to one end of the ball screw 72 and causing the ball screw 72 to rotate; and a sliding portion 75 having a nut internally engaged with the ball screw 72 and its side slidably connected to the guide rails 73. When the motor 74 causes the ball screw 72 to rotate, the sliding portion 75 is guided by the guide rails 73 to move in the Y-axis direction.

[0016] A lifting mechanism 8 is provided on the side of the sliding portion 75, which raises and lowers the attraction holding portion 89 of the upper surface 100 of the attraction holding wafer 10. The lifting mechanism 8 includes: a ball screw 81 having an axis in the Z-axis direction; a guide rail 82 arranged parallel to the ball screw 81; a motor 83 connected to one end of the ball screw 81 and causing the ball screw 81 to rotate; and a lifting member 84 having a nut internally screwed into the ball screw 81 and its side slidably connected to the guide rail 82. When the motor 83 causes the ball screw 81 to rotate, the lifting member 84 is guided by the guide rail 82 to rise and fall in the Z-axis direction.

[0017] The lifting member 84 supports the rotary mechanism 85. The rotary mechanism 85 includes: a shaft 86 hanging down from the lifting member 84; a motor 87 connected to the upper end of the shaft 86; and an arm 88 connected to the lower end of the shaft 86, and a suction holding part 89 connected to the front end of the arm 88. When the motor 87 rotates the shaft 86, the arm 88 rotates and the suction holding part 89 rotates about the shaft 86. By rotating, the suction holding part 89 passes under the wall 71 and can move between the front side (+X direction side) and the back side (-X direction side) of the wall 71, and can move from the movement path of the first chuck table 21 to the movement path of the second chuck table 22. Furthermore, the motor 74 rotates the ball screw 72 and the sliding part 75 is guided by the guide rail 73 to move in the Y-axis direction, and the suction holding part 89 also moves in the Y-axis direction. Furthermore, if the motor 83 rotates the ball screw 81, causing the lifting member 84 to rise and fall in the Z-axis direction, the suction holding part 89 will also rise and fall in the Z-axis direction. The lower part of the suction holding part 89 has a suction pad that connects to a suction source (not shown).

[0018] The first grinding mechanism 3 includes: a spindle 30 having a rotating shaft 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 mounting member 33 connected to the lower end of the spindle 30; and a grinding wheel 34 mounted on the mounting member 33. If 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 an annular mounting member 33 with a central opening; and a plurality of first grinding stones 341, which are fixed in a ring shape on the lower surface of the base 340. The first grinding stones 341 are, for example, coarse grinding stones with a larger abrasive grain size.

[0019] The second grinding mechanism 4, except for the second grinding stone 342, is configured the same as the first grinding mechanism 3. The second grinding stone 342 is a fine grinding stone whose abrasive grain size is smaller than that of the first grinding stone 341 of the first grinding mechanism 3. For parts other than the second grinding stone 342, the same symbols as those in the first grinding mechanism 3 are used, and the description is omitted.

[0020] The first grinding mechanism 3 and the second grinding mechanism 4 are supported vertically by a grinding feed mechanism 5, which is constructed with the same structure. The grinding feed mechanism 5 includes: a ball screw 50 having a rotation axis in the Z-axis direction; a motor 51 that rotates the ball screw 50; a pair of guide rails 52 arranged parallel to the ball screw 50; a lifting plate 53 whose side is slidably connected to the guide rails 52 and has a nut (not shown) that is screwed into the ball screw 50 inside; and a retaining seat 54 connected to the lifting plate 53 and supporting the spindle housing 32. When the ball screw 50 rotates, the lifting plate 53 is guided by the guide rails 52 to move in the Z-axis direction, and the first grinding mechanism 3 also moves in the Z-axis direction.

[0021] As shown in FIG. 2, the first chuck stage 21 is composed of the following components: an attraction member 211, which is made of porous material; and a frame 212, which supports the attraction member 211 from the outer periphery and below. The surface of the attraction member 211, i.e., the first attraction surface 213, attracts the lower surface 101 of the warped wafer 10. The first attraction surface 213 is formed with a diameter smaller than that of the warped wafer 10. Furthermore, the first attraction surface 213 is formed to be on the same plane as the upper surface 214 of the frame 212. An annular recess 215 is formed on the outer periphery of the first attraction surface 213, i.e., the outer periphery of the upper surface 214 of the frame 212. A space 216 is formed in the recess 215, which extends from the lower part of the space of the recess 215 toward the center side of the first chuck stage 21. An elastic member 217 is accommodated in the recess 215. One end of the elastic member 217 is fixed to the space 216, and the other end protrudes upward beyond the upper surface 214. The elastic member 217 is formed into a ring shape, for example, using a sponge or rubber sheet, and has a bent portion 218 that bends upward from the portion accommodated in the space 216. If a warped wafer 10 is attracted and held on the first attraction surface 213, the bent portion 218 will fall down, and the elastic member 217 will contact the outer periphery of the lower surface 101 of the wafer 10. Furthermore, the outer periphery of the wafer 10 contacts the upper surface 214 of the frame 212. Then, the upper surface of the recess 215 becomes blocked by the lower surface 101 of the wafer 10.

[0022] The lower part of the frame 212 is connected to the upper end of the rotating shaft 231. The lower end of the rotating shaft 231 is rotatably supported by the support part 232. A driven pulley 233 is arranged around the rotating shaft 231, and a drive pulley 234 is arranged on the side of the driven pulley 233. The drive pulley 234 is driven by the motor 235. A belt 236 is wound around the drive pulley 234 and the driven pulley 233. When the drive pulley 234 is driven by the motor 235 to rotate, its rotational force is transmitted to the driven pulley 233 through the belt 236, the rotating shaft 231 will rotate, and the first chuck table 21 will rotate.

[0023] A flow path 241 for fluid passage is formed through the frame 212, the rotating shaft 231, and the support 232. One end of the flow path 241 is connected to an opening on the upper surface of the frame 212 and communicates with the suction member 211. The other end of the flow path 241 branches into three paths, each of which is connected to the suction source 245, the air supply source 246, and the water supply source 247 through valves 242, 243, and 244. A pressure gauge 248 for measuring the pressure within the flow path 241 is connected to the flow path 241.

[0024] As shown in FIG1, the second chuck stage 22 includes: a porous member 221; and a frame 222 supporting the porous member 221. The surface of the porous member 221, namely the second attraction surface 223, attracts the entire lower surface of the wafer 10. The second attraction surface 223 is formed to be on the same plane as the upper surface 224 of the frame 222. The second chuck stage 22 is rotatable, for example, by a rotary drive mechanism (not shown) similar to that of the first chuck stage 21 shown in FIG2. Furthermore, the frame 222 and the area below the second chuck stage 22 are provided with a flow path 241, similar to that of the first chuck stage 21 and as shown in FIG2. The flow path 241 is connected to the attraction source 245, the air supply source 246, and the water supply source 247 through valves 242, 243, and 244.

[0025] A thickness measuring device 25 is disposed on the side of the movement path of the first chuck stage 21. The thickness measuring device 25 measures the thickness of the wafer 10 held on the first chuck stage 21. The thickness measuring device 25 includes: a first measuring part 251, which measures the height of the upper surface 214 of the frame 212; and a second measuring part 252, which measures the height of the upper surface 100 of the wafer 10 attracted and held on the first attraction surface 213. The thickness measuring device 25 calculates the thickness of the wafer 10 based on the difference between the measurement value of the first measuring part 251 and the measurement value of the second measuring part 252.

[0026] A thickness measuring device 26 is disposed on the side of the movement path of the second chuck stage 22. The thickness measuring device 26 measures the thickness of the wafer 10 held on the second chuck stage 22. The thickness measuring device 26 includes: a first measuring part 261, which measures the height of the upper surface 224 of the frame 222; and a second measuring part 262, which measures the height of the upper surface 100 of the wafer 10 attracted and held on the second attraction surface 223. The thickness measuring device 26 calculates the thickness of the wafer 10 based on the difference between the measurement value of the first measuring part 261 and the measurement value of the second measuring part 262.

[0027] Next, the operation of the grinding apparatus 1 when grinding the warped wafer 10 shown in FIG2 will be described. This wafer 10 has elements 12 formed on a substrate 11, and the elements 12 are sealed with resin 13 and have elements that can warp due to the shrinkage of the resin 13.

[0028] Multiple wafers 10 are housed inside the cassette 610 shown in FIG. 1. Then, by rotating and lifting the arm 633, the hand 631 of the robot 63 enters the interior of the cassette 610 and attracts and holds one wafer 10. Afterward, the hand 631 withdraws from the cassette 610 and places the wafer 10 on the mounting stage 641 of the temporary holding mechanism 64. Then, the positioning pin 642 moves in a direction that brings them closer together, and the wafer 10 is aligned in a predetermined position.

[0029] (1) First holding step Next, the attraction holding part 89 is moved in the -Y direction by the conveying mechanism 7 and the rotation mechanism 85 rotates the attraction holding part 89, thereby moving the attraction holding part 89 above the wafer 10 placed on the mounting stage 641. Then, the lifting mechanism 8 further lowers the attraction holding part 89 to attract and hold the upper surface 100 of the wafer 10.

[0030] Next, the lifting mechanism 8 raises the attraction holding part 89, the conveying mechanism 7 moves the attraction holding part 89 in the +Y direction, and the rotating mechanism 85 rotates the attraction holding part 89, moving the attraction holding part 89 of the attraction holding wafer 10 above the first chuck stage 21. The lifting mechanism 8 then lowers the attraction holding part 89 and places the lower surface 101 of the wafer 10 on the first chuck stage 21. Then, the valve 242 shown in FIG. 2 is opened, connecting the attraction member 211 of the first chuck stage 21 to the attraction source 245, thereby causing the attraction force to act on the first attraction surface 213 to attract and hold the lower surface 101 of the wafer 10. At this time, by placing the wafer 10 at a predetermined position in the temporary holding mechanism 64, the center of the first attraction surface 213 coincides with the center of the wafer 10. Afterwards, the attraction force of the attraction holding part 89 is released, and the lifting mechanism 8 raises the attraction holding part 89.

[0031] Thus, with the center of the first attraction surface 213 aligned with the center of the wafer 10, the lower surface 101 of the warped wafer 10 is attracted and held along the first attraction surface 213. Because the outer periphery of the wafer 10 is warped, and the first attraction surface 213 is formed with a diameter smaller than that of the wafer 10, the warped outer periphery of the wafer 10 is not attracted and held. That is, the lower surface 101 of the wafer 10 is attracted and held on the inner periphery side of the elastic member 217.

[0032] (2) First Grinding Step Next, the first chuck stage 21 is moved in the +Y direction, so that the wafer 10 is located below the first grinding mechanism 3. Then, as shown in FIG3, the first chuck stage 21 is driven by the motor 235 to rotate, and the spindle rotation mechanism 31 rotates the spindle 30 and the first grinding stone 341 rotates. Furthermore, the grinding feed mechanism 5 shown in FIG1 lowers the first grinding mechanism 3, thereby causing the rotating first grinding stone 341 to contact the upper surface 100 of the wafer 10. In this way, the raised part of the wafer 10 is pressed down and the lower surface 101 contacts the elastic member 217. As shown in the enlarged view in FIG3, the elastic member 217 is pressed down by the outer periphery of the lower surface 101, and the attraction force becomes non-leaking.

[0033] Then, the grinding feed mechanism 5 further lowers the first grinding mechanism 3 to perform rough grinding on the upper surface 100 of the wafer 10. During grinding, the front end of the first measuring part 251 of the thickness measuring device 25 contacts the upper surface 214 of the frame 212, and the front end of the second measuring part 252 of the thickness measuring device 25 contacts the upper surface 100 of the wafer 10. The thickness of the wafer 10 is calculated by the difference between the measurement value of the first measuring part 251 and the measurement value of the second measuring part 252. Then, if the calculated value is the predetermined thickness value, the grinding feed mechanism 5 raises the first grinding mechanism 3 to end the grinding. Here, the predetermined thickness is the value of the unfinished thickness.

[0034] Because the resin 13 becomes thinner by the grinding of the wafer 10 in the first grinding step, the warping factor of the wafer 10 is reduced. Furthermore, in the first grinding step, since the grinding is performed with the outer periphery of the lower surface 101 of the wafer 10 supported by the elastic member 217, during the grinding process, as shown in the enlarged view of FIG3, the elastic member 217 will sink slightly due to the grinding load of the first grinding stone 341 being pushed onto the wafer 10. The portion of the wafer 10 supported by the elastic member 217 will be slightly inserted into the recess 215. Therefore, the portion supported by the elastic member will be formed to be thicker, and its outer periphery will be formed to be thinner.

[0035] (3) Transfer Step Next, the lifting mechanism 8 lowers the suction holding part 89 to hold the upper surface 100 of the rough-ground wafer 10. Then, the valve 242 is closed to release the suction force acting on the first suction surface 213 of the first chuck stage 21, and the valve 243 is opened to spray air from the first suction surface 213. At this time, the valve 244 can also be opened to spray water and air together from the first suction surface 213. In this way, with only air or air and water sprayed from the first suction surface 213, the lifting mechanism 8 raises the suction holding part 89, thereby separating the wafer 10 from the first chuck stage 21.

[0036] With the attraction holding part 89 raised, the rotation mechanism 85 rotates the attraction holding part 89 and positions it further to the +X side than the wall part 74. Then, the wafer 10 is positioned above the second chuck stage 22, and the lifting mechanism 8 lowers the attraction holding part 89, placing the lower surface 101 of the rough-ground wafer 10 onto the second chuck stage 22.

[0037] (4) Second Holding Step Next, the valve 242 shown in FIG4 is opened to connect the attraction source 245 with the second attraction surface 223, so that the attraction force acts on the second attraction surface 223. Afterwards, if the attraction force of the attraction holding part 89 is released and the lifting mechanism 8 raises the attraction holding part 89, the attraction holding part 89 is separated from the upper surface 100 of the wafer 10. In this way, the entire lower surface 101 of the wafer 10, which is formed to a thickness that does not reach the finished thickness by grinding in the first grinding step, is attracted and held by the second attraction surface 223 of the second chuck stage 22. Since the warpage of the wafer 10 is reduced in the first grinding step, the entire lower surface 101 of the wafer 10 can be attracted and held by the second attraction surface 223. Furthermore, in the first grinding step, the outer periphery of the lower surface 101 of the wafer 10 is supported by the elastic member 217 and ground, thereby forming a convex portion 102 in an annular shape on the wafer 10, wherein the convex portion 102 is locally formed to be thicker.

[0038] (5) Second Grinding Step Next, the rough-ground wafer 10 held on the second chuck stage 22 is positioned below the second grinding mechanism 4. Then, as shown in FIG4, the second chuck stage 22 is driven to rotate by the motor 235, and the spindle rotation mechanism 31 rotates the spindle 30 and the second grinding stone 342. Furthermore, the grinding feed mechanism 5 shown in FIG1 lowers the second grinding mechanism 4, thereby causing the rotating second grinding stone 342 to contact the rough-ground upper surface 100. Then, the grinding feed mechanism 5 further lowers the second grinding mechanism 4 to perform fine grinding on the rough-ground upper surface 100 that is attracted and held on the second attraction surface 223. During grinding, the front end of the first measuring part 261 of the thickness measuring device 26 contacts the upper surface 224 of the frame 222, and the front end of the second measuring part 262 of the thickness measuring device 26 contacts the upper surface 100 of the wafer 10. The thickness of the wafer 10 is calculated by the difference between the measurement value of the first measuring part 261 and the measurement value of the second measuring part 262. Then, if the calculated value is the predetermined finished thickness value, the grinding feed mechanism 5 raises the second grinding mechanism 4 and ends the grinding process.

[0039] In the second grinding step, since grinding is performed on the entire lower surface 101 of the wafer 10 while it is held in place by suction, the protrusion 102 can be removed, and the entire surface can be finished flat. Therefore, the risk of defects in components 12 formed near the outer periphery of the wafer 10 is reduced. Furthermore, the first grinding stone 341 and the second grinding stone 342 can be of the same type or different types. [Simplified Explanation of the Diagram]

[0008] Figure 1 is a perspective view showing an example of a grinding apparatus. Figure 2 is a schematic cross-sectional view showing a chuck stage and a warped wafer. Figure 3 is a schematic cross-sectional view showing the first grinding step. Figure 4 is a schematic cross-sectional view showing the second grinding step.

Claims

1. A wafer grinding method comprising holding a wafer with its outer periphery raised along the attraction surface of a chuck stage and grinding the wafer by means of a grinding stone, the wafer grinding method comprising the following steps: a first holding step wherein, with an elastic member in contact with the lower surface of the raised outer periphery of the wafer, the wafer is held at the first attraction surface of a first chuck stage, the first chuck stage being composed of an attraction member and a frame, the attraction member having the first attraction surface for attracting the lower surface of the wafer, the frame supporting the attraction member from the outer periphery and below, an annular recess being formed on the upper surface of the frame, the elastic member being accommodated in the recess, the elastic member being formed into an annular shape by means of a rubber plate protruding upward above the upper surface of the frame; In the first grinding step, a first grinding stone is brought into contact with the upper surface of the wafer that has been attracted and held on the first attraction surface. As the first grinding stone pushes the wafer under the grinding load, the elastic member sinks into the recess. At the same time, the first grinding stone grinds the wafer with its lower surface inside the recess to a thickness that does not reach the finished thickness. A thicker portion is formed in a ring shape on the outer periphery of the wafer to reduce the force that will cause the wafer to lift. In the transfer step, the wafer that has been attracted and held on the first attraction surface is transferred to the second attraction surface of the second chuck stage with a porous member. The porous member has a second attraction surface that attracts the entire lower surface of the wafer. The second holding step attracts and holds the wafer, which has been ground to a thickness below the final thickness, on the second attraction surface; and the second grinding step removes the thicker portion of the wafer, which has been attracted and held on the second attraction surface, from the outer periphery of the wafer by means of a second grinding stone, while grinding it to the final thickness.

2. The wafer grinding method as described in claim 1, wherein, A coarse grinding stone is used in the first grinding step, and a fine grinding stone is used in the second grinding step.

3. A grinding apparatus for grinding a wafer whose outer peripheral portion has been raised by means of a grinding stone, and comprising: a first chuck stage, which is composed of an attraction member and a frame, the attraction member having a first attraction surface for attracting the lower surface of the wafer, the frame supporting the attraction member from the outer peripheral side and below, an annular recess being formed on the upper surface of the frame, an elastic member being accommodated in the recess, the elastic member being formed into an annular shape by means of a rubber plate protruding upward above the upper surface of the frame, the first chuck stage attracting and holding the wafer on the first attraction surface when the elastic member contacts the lower surface of the raised outer peripheral portion of the wafer; A first grinding mechanism contacts the upper surface of the wafer held on the first attraction surface with a first grinding stone. As the first grinding stone pushes the wafer under grinding load, causing the elastic member to sink into the recess, the wafer with its lower surface inside the recess is ground down to a thickness below the finished thickness. A thicker portion is formed in a ring shape on the outer periphery of the wafer, reducing the force that would cause the wafer to lift. A second chuck stage has a porous component with a second attraction surface that attracts the entire lower surface of the wafer. A conveying mechanism transports the wafer, held on the first attraction surface and with a thicker portion formed in a ring shape on its outer periphery, from the first attraction surface to the second attraction surface. A second grinding mechanism removes the thicker portion formed in a ring shape on the outer periphery of the wafer held on the second attraction surface using a second grinding stone, while simultaneously grinding it to the finished thickness.

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