Chuck table, grinding device and work-piece grinding method

Abstract

To reduce not only variation in thickness occurring due to increase / decrease of a grinding area, but also variation in thickness occurring due to difference in grinding frequency when grinding a flat plate-like work-piece such as a package substrate having four or more corners in a plan view.SOLUTION: A chuck table, which is used when a flat plate-like work-piece having four or more corners in a plan view, includes a holding surface that is divided into a circular first area, and a polygonal second area which surrounds the first area and of which an outer periphery has four or more corners in a plan view. The holding surface has such a shape that a center of the first area is lowest and becomes higher as further away from the center, and an angle between a reference tangential plane of the holding surface at the center of the first area and a first tangential plane of the holding surface at points included in the first area other than the center is smaller than angle between the reference tangential plane and a second tangential plane of the holding surface at points included in the second area.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a chuck table used when grinding a flat workpiece having four or more corners in a planar view, a grinding device equipped with this chuck table, and a grinding method for grinding a workpiece using this grinding device. [Background technology]

[0002] Device chips such as integrated circuits (ICs) are essential components in various electronic devices such as mobile phones and personal computers. These chips are manufactured, for example, by grinding the backside of a package substrate having a plurality of devices arranged in a matrix on its front side, and then dividing the package substrate along the boundaries of the plurality of devices.

[0003] A grinding device for grinding the back side of a package substrate generally comprises a chuck table that can rotate around a rotation axis that is a straight line passing through the center of the surface (holding surface) on which the package substrate is held, and a spindle at the tip of which is mounted a grinding wheel having multiple grinding stones arranged discretely in a ring shape.

[0004] In addition, a package substrate is generally square or rectangular in plan view. Therefore, the holding surface of the chuck table that holds the package substrate is also generally square or rectangular in plan view. Furthermore, the outer diameter of the trajectory of the multiple grinding wheels when the spindle is rotated is larger than the distance between the center of the holding surface of the chuck table and each corner.

[0005] Grinding of the backside of the package substrate in this grinding device is performed, for example, in the following order: First, the front side of the package substrate is held on the holding surface of the chuck table, and then the chuck table and the spindle are moved relative to each other so that the center of the backside of the package substrate and the above-mentioned trajectory overlap in a predetermined direction (for example, the vertical direction).

[0006] Next, while both the chuck table and the spindle are rotated, the chuck table and the spindle are moved closer to each other in the predetermined direction so that the backside of the package substrate comes into contact with the grinding wheels, thereby grinding the portions of the backside of the package substrate that come into contact with the grinding wheels.

[0007] This grinding is performed while increasing or decreasing the contact area (grinding area) between the backside of the package substrate and the multiple grinding wheels. For example, the grinding area when grinding the area between the center and each corner of the backside of the package substrate is larger than the grinding area when grinding other areas (for example, the area between the center and the middle of a pair of adjacent corners).

[0008] When the grinding area increases or decreases in this way, the load (grinding load) generated on the chuck table and spindle during grinding also increases or decreases. In this case, the force (grinding force) applied to the workpiece when grinding the backside of the package substrate repeatedly disperses and concentrates.

[0009] Specifically, when grinding the area between the center and each corner on the back side of the package substrate, the grinding force is dispersed, and when grinding the area between the center and the middle of a pair of adjacent corners, the grinding force is concentrated. As a result, when grinding the back side of the package substrate, the areas near the corners are not sufficiently removed, and the finished thickness tends to be thicker than the other areas.

[0010] In light of this, a method for grinding the holding surface of a chuck table has been proposed to reduce variations in thickness that occur when the package substrate is ground (see, for example, Patent Document 1). Specifically, this method proposes grinding the holding surface of the chuck table so as to form a curvature on the holding surface that is similar to the curvature formed on the back surface of the package substrate due to an increase or decrease in the grinding area when the package substrate is ground. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Application Publication No. 2020-55080 Summary of the Invention [Problem to be solved by the invention]

[0012] The factors that affect the thickness variations that occur during grinding of the package substrate mentioned above are not limited to the increase or decrease in the grinding area. Another example of this factor is the number of times that one of the multiple grinding wheels comes into contact with each part of the back side of the package substrate (grinding frequency).

[0013] Specifically, when grinding a package substrate as described above, the trajectories of the multiple grinding wheels as the spindle is rotated always overlap with the area near the center of the back side of the package substrate, but only intermittently overlap with the area near the periphery (for example, the area near each corner or the area near the middle between a pair of adjacent corners).

[0014] In this case, the portion near the center of the back surface of the package substrate is ground more frequently than the portion near the periphery, and therefore, the portion near the periphery is not sufficiently removed, and the finished thickness tends to be thicker than the portion near the center.

[0015] In view of this, an object of the present invention is to reduce not only thickness variations caused by increases or decreases in the grinding area but also thickness variations caused by differences in grinding frequency when grinding a flat workpiece having four or more corners in a planar view, such as a package substrate. [Means for solving the problem]

[0016] According to one aspect of the present invention, there is provided a chuck table used when grinding a flat workpiece having four or more corners in a planar view, the chuck table including a holding surface which is divided into a circular first region in a planar view and a polygonal second region surrounding the first region and having four or more corners on its outer periphery, the holding surface having a shape that is lowest at the center of the first region and becomes higher the further away from the center, and the angle formed by a reference tangent plane of the holding surface at the center of the first region and a first tangent plane of the holding surface at a point other than the center included in the first region is smaller than the angle formed by the reference tangent plane and a second tangent plane of the holding surface at a point included in the second region.

[0017] According to another aspect of the present invention, there is provided a grinding device for grinding a flat workpiece having four or more corners in a plan view, the grinding device comprising: a chuck table including a holding surface which is divided into a circular first region in a plan view and a polygonal second region surrounding the first region and having four or more corners on its outer periphery; the chuck table being rotatable about a straight line passing through the center of the first region; and a spindle having a grinding wheel attached to its tip end, the grinding wheel having a plurality of grinding stones arranged discretely in an annular shape; and a grinding wheel for rotating the spindle. The grinding device provides a grinding device in which the outer diameter of the trajectory of the plurality of grinding wheels when rotated is larger than the distance between the center of the first region of the holding surface and each of the four or more corners, the holding surface has a shape that is lowest at the center of the first region and becomes higher the farther away from the center, and the angle formed by the reference tangent plane of the holding surface at the center of the first region and a first tangent plane of the holding surface at a point other than the center included in the first region is smaller than the angle formed by the reference tangent plane and a second tangent plane of the holding surface at a point included in the second region.

[0018] According to yet another aspect of the present invention, there is provided a method for grinding a flat workpiece having four or more corners in a plan view using a grinding apparatus including: a chuck table that includes, in a plan view, a holding surface that is divided into a circular first region and a polygonal second region that surrounds the first region and has four or more corners on its outer periphery, the polygonal second region surrounding the first region and having four or more corners; and a spindle having a grinding wheel attached to its tip end, the grinding wheel having a plurality of grinding wheels that are discretely arranged in an annular shape, wherein the outer diameter of the trajectory of the plurality of grinding wheels when the spindle is rotated is greater than the distance between the center of the first region of the holding surface and each of the four or more corners, the method comprising: a holding step of holding the front side of the workpiece in a predetermined direction; an arrangement step of moving the chuck table and the spindle relatively after the holding step so that the center of the first region and the locus overlap in a predetermined direction; and a grinding step of bringing the chuck table and the spindle closer together along the predetermined direction while rotating both the chuck table and the spindle after the arrangement step so that the back side of the workpiece comes into contact with the plurality of grinding wheels, wherein the holding surface has a shape that is lowest at the center of the first region and becomes higher as it goes away from the center, and an angle formed by a reference tangent plane of the holding surface at the center of the first region and a first tangent plane of the holding surface at a point other than the center that is included in the first region is smaller than an angle formed by the reference tangent plane and a second tangent plane of the holding surface at a point that is included in the second region. [Effects of the Invention]

[0019] In the chuck table of the present invention, the holding surface has a shape in which the center of the circular first region is lowest and the height increases with increasing distance from the center. When a workpiece is ground using this chuck table, the portion near the periphery of the workpiece that overlaps the center of the first region is more easily removed than the portion near the center. Therefore, in this case, thickness variations caused by differences in grinding frequency can be reduced.

[0020] Furthermore, in the chuck table of the present invention, the angle between the reference tangent plane and the first tangent plane is smaller than the angle between the reference tangent plane and the second tangent plane. When this chuck table is used to grind a workpiece, the portions of the workpiece near each corner that overlap with the second region are more easily removed than other portions. Therefore, in this case, thickness variations caused by increases or decreases in the grinding area can be reduced. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1A is a plan view that schematically shows an example of a chuck table, and FIG. 1B is a vertical cross-sectional view of the chuck table shown in FIG. 1A. [Figure 2] FIG. 2 is a partial cross-sectional side view that schematically shows a grinding device that can grind a workpiece while the workpiece is held on the holding surface of a chuck table. [Figure 3] FIG. 3 is a flow chart that schematically shows an example of a method for grinding a workpiece in a grinding device. [Figure 4] FIG. 4 is a plan view that schematically shows an example of a chuck table that is suitable for use when grinding a workpiece that is rectangular in plan view. [Figure 5] FIG. 5 is a plan view that schematically shows an example of a chuck table that is suitable for use when grinding a workpiece that has a regular pentagonal shape in plan view. [Figure 6]FIG. 6 is a plan view that schematically shows an example of a chuck table that is suitable for use when grinding a workpiece that has an isosceles trapezoidal shape in a plan view. [Figure 7] FIG. 7(A) is a plan view schematically showing an example of a chuck table having components that can be separated from each other, and FIG. 7(B) is a vertical cross-sectional view of the chuck table shown in FIG. 7(A). [Figure 8] FIG. 8(A) is a plan view schematically showing a first member provided on the chuck table shown in FIGS. 7(A) and 7(B), and FIG. 8(B) is a vertical cross-sectional view of the first member shown in FIG. 8(A). [Figure 9] FIG. 9(A) is a plan view schematically showing an example of a chuck table that does not include a porous plate, and FIG. 9(B) is a vertical cross-sectional view of the chuck table shown in FIG. 9(A). DETAILED DESCRIPTION OF THE INVENTION

[0022] Embodiments of the present invention will be described with reference to the accompanying drawings. Note that the accompanying drawings are intended to facilitate understanding of the present invention and do not necessarily accurately reflect the products and / or methods embodying the present invention. Fig. 1(A) is a plan view schematically showing an example of a chuck table, and Fig. 1(B) is a vertical cross-sectional view of the chuck table shown in Fig. 1(A).

[0023] 1(A) and 1(B) has a frame 4 made of, for example, stainless steel (SUS). In plan view, the frame 4 has an upper surface 4a whose outer periphery is square, and a circular recess is formed on the upper surface 4a side. In other words, the frame 4 has an upper surface 4a shaped like a square with a circular portion cut out at the center thereof in plan view.

[0024] A circular porous plate 6 made of, for example, ceramic is fixed in this recess. Therefore, in a plan view, the chuck table 2 is divided into an upper surface 6a (first region) of the circular porous plate 6 and an upper surface 4a (second region) of the frame 4 that surrounds the upper surface 6a of the porous plate 6 and has a square outer periphery.

[0025] The upper surface of the chuck table 2 (the upper surface 4a of the frame 4 and the upper surface 6a of the porous plate 6) has a shape that is lowest at the center C of the upper surface 6a of the porous plate 6 and becomes higher as it moves away from the center C. Specifically, the upper surface 6a of the porous plate 6 has a shape that corresponds to the side of an inverted cone with the center C as its apex. Furthermore, the upper surface 4a of the frame 4 has a shape in which the regions near each corner are higher than the region located midway between a pair of adjacent corners.

[0026] Furthermore, the upper surface 6a of the porous plate 6 has a smaller inclination than the upper surface 4a of the frame 4. In other words, the angle formed by the tangent plane (reference tangent plane) of the upper surface 6a of the porous plate 6 at the center C of the upper surface 6a and the tangent plane (first tangent plane) of the upper surface 6a at a point other than the center C included in the upper surface 6a is smaller than the angle formed by the reference tangent plane and the tangent plane (second tangent plane) of the upper surface 4a at a point included in the upper surface 4a of the frame 4.

[0027] A groove 8 is formed on the upper surface 4a of the frame 4. In plan view, this groove 8 includes a circular ring portion 8a whose inner and outer peripheries extend concentrically with the outer periphery of the upper surface 6a of the porous plate 6, and a square ring portion 8b that extends so that the inner periphery of the circular ring portion 8a is inscribed at the center of each side included in the inner periphery of a square, and the outer periphery of the circular ring portion 8a is inscribed at the center of each side included in the outer periphery of the square.

[0028] The groove 8 also includes two arcuate portions 8c, 8d located in each of four regions defined by the annular portion 8a and the angular annular portion 8b in plan view. Both ends of each of the arcuate portions 8c, 8d are connected to the angular annular portion 8b, and the inner and outer peripheries of each arcuate portion 8c, 8d extend so as to overlap with parts of the concentric circles of the outer periphery of the upper surface 6a of the porous plate 6.

[0029] A communication path 10 is formed inside the frame body 4. This communication path 10 includes a main path 10a that opens at the bottom surface of a recess formed on the upper surface 4a side of the frame body 4 and penetrates the frame body 4 in its thickness direction, and a plurality of intermediate paths 10b, 10c that have one end connected to the main path 10a and extend perpendicular to the main path 10a.

[0030] The communication path 10 also includes a plurality of sub-paths 10d, 10e, 10f, and 10g, each of which has one end connected to one of the plurality of intermediate paths 10b and 10c and extends parallel to the main path 10a. The other end of the sub-path 10d, the other end of the sub-path 10e, the other end of the sub-path 10f, and the other end of the sub-path 10g are connected to the annular portion 8a, the angular annular portion 8b, the arc portion 8c, and the arc portion 8d of the groove 8, respectively.

[0031] Furthermore, the communication passage 10 (specifically, the main passage 10a) can be connected to a suction source such as an ejector provided in the grinding machine. When the suction source is operated with the communication passage 10 connected to the suction source, a suction force acts on the space near the upper surface of the chuck table 2.

[0032] Specifically, in this case, suction force acts on the space near the upper surface 6a via the main path 10a and the porous plate 6, and suction force acts on the space near the upper surface 4a of the frame body 4 via the main path 10a, the multiple intermediate paths 10b, 10c, the multiple sub-paths 10d, 10e, 10f, 10g and the groove 8.

[0033] Therefore, the chuck table 2 can use its upper surface (upper surface 4a of the frame body 4 and upper surface 6a of the porous plate 6) as a holding surface to hold a workpiece having a shape such that, in a planar view, its outer periphery is located inside the outer periphery of the frame body 4 and outside the angular ring portion 8b of the groove 8.

[0034] Fig. 2 is a partial cross-sectional side view that schematically shows a grinding device that can grind a workpiece while the workpiece is held on the holding surface of a chuck table 2. Note that the direction indicated by arrow X (X direction) and the direction indicated by arrow Y (Y direction) shown in Fig. 2 are directions that are perpendicular to each other on a horizontal plane, and the direction indicated by arrow Z (Z direction) is a direction (vertical direction) that is perpendicular to the X direction and the Y direction.

[0035] 2, the holding surface (top surface) of the chuck table 2 is depicted as being generally flat in order to more accurately reflect the scale of the actual thickness, width, etc. of the chuck table 2. That is, in FIG. 1(B), differences in thickness among portions included in the chuck table 2 and differences in inclination among regions included in the holding surface are depicted with emphasis so that the shape of the holding surface of the chuck table 2 can be easily understood.

[0036] The grinding apparatus 12 shown in Fig. 2 has a base 14 that supports each of the components. An X-direction movement mechanism 16 is provided on the upper surface of this base 14. The X-direction movement mechanism 16 has a pair of guide rails 18 that each extend along the X direction. A rectangular parallelepiped X-direction movement plate 20 is attached to the pair of guide rails 18 in a manner that allows it to slide along the X direction.

[0037] A screw shaft 22 extending along the X direction is disposed between the pair of guide rails 18. A stepping motor 24 for rotating the screw shaft 22 is connected to one end of the screw shaft 22. A nut 26 that houses a large number of balls that circulate in response to the rotation of the screw shaft 22 is provided on the outer circumferential surface of the screw shaft 22 on which the threads are formed, thereby constituting a ball screw.

[0038] The nut 26 is fixed to the underside of the X-direction moving plate 20. Therefore, when the screw shaft 22 is rotated by the stepping motor 24, the X-direction moving plate 20 moves in the X direction together with the nut 26. The chuck table 2 is connected to the top of the X-direction moving plate 20 in a manner that allows it to move in the X direction together with the X-direction moving plate 20.

[0039] Specifically, when the stepping motor 24 of the X-direction movement mechanism 16 is operated, the chuck table 2 moves between a loading / unloading position and a grinding position. This loading / unloading position is a position suitable for loading and unloading a workpiece onto and from the chuck table 2, and is, for example, a position that does not overlap with a grinding wheel 56 (described later) in the Z direction.

[0040] The grinding position is a position suitable for grinding the workpiece held on the holding surface of the chuck table 2, for example, a position where the trajectory of the multiple grinding stones 56b included in the grinding wheel 56 when the spindle 54 described later is rotated in the Z direction overlaps with the center of the holding surface of the chuck table 2 (center C of the upper surface 6a of the porous plate 6).

[0041] Furthermore, below the chuck table 2, there are provided the above-mentioned suction source and a rotation mechanism (not shown) for rotating the chuck table 2. This rotation mechanism includes, for example, a pulley and a servo motor. When this rotation mechanism is operated, the chuck table 2 rotates around a rotation axis that is a straight line passing through the center of the holding surface.

[0042] In addition, a cylindrical bearing 28 and a cylindrical table base 30 are provided below the chuck table 2 to support the chuck table 2 in a rotatable manner. The chuck table 2 is supported by an inclination adjustment mechanism 32 via the bearing 28 and the table base 30.

[0043] The tilt adjustment mechanism 32 has two movable shafts 32a, 32b and one fixed shaft 32c that are arranged at approximately equal angular intervals along the circumferential direction of the chuck table 2 and have their lower ends fixed to the upper surface side of the X-direction moving plate 20. When at least one of the two movable shafts 32a, 32b partially raises or lowers the chuck table 2, the tilt of the rotation axis of the chuck table 2 is adjusted.

[0044] A support structure 34 extending along the Z direction is provided on an end of the base 14. A Z-direction movement mechanism 36 is provided on the surface of this support structure 34 facing the chuck table 2. This Z-direction movement mechanism 36 has a pair of guide rails 38 each extending along the Z direction. A rectangular parallelepiped Z-direction movement plate 40 is attached to the surface of the pair of guide rails 38 in a manner that allows it to slide along the Z direction.

[0045] A screw shaft 42 extending along the Z direction is disposed between the pair of guide rails 38. A stepping motor 44 for rotating the screw shaft 42 is connected to one end (upper end) of the screw shaft 42. A nut 46 that houses a large number of balls that circulate in response to the rotation of the screw shaft 42 is provided on the outer circumferential surface of the screw shaft 42 on which the threads are formed, thereby constituting a ball screw.

[0046] The nut 46 is fixed to the back surface of the Z-direction moving plate 40. Therefore, when the stepping motor 44 rotates the screw shaft 42, the Z-direction moving plate 40 moves in the Z direction together with the nut 46. A cylindrical cover 48 with a bottom is fixed to the front surface of the Z-direction moving plate 40. A through hole 48a is formed in the center of the bottom of this cover 48.

[0047] A housing 50 is provided inside the cover 48. The housing 50 is supported on the bottom of the cover 48 via two spacers 52a and 52b, and a part of a spindle 54 extending along the Z direction is rotatably housed in the housing 50.

[0048] The housing 50 also accommodates a servo motor (not shown) connected to the base end (upper end) of the spindle 54. The spindle 54 protrudes downward through a through-hole 48a formed in the bottom of the cover 48. The tip end (lower end) 54a of the spindle 54 has a disk-like shape and functions as a wheel mount.

[0049] A plurality of through holes are formed at approximately equal angular intervals along the circumferential direction of the tip 54a of the spindle 54. A grinding wheel 56 is attached to the tip 54a of the spindle 54 using fasteners (not shown), such as bolts, that are inserted into the respective through holes.

[0050] The grinding wheel 56 includes an annular wheel base 56a made of a metal material such as stainless steel. A plurality of grinding stones 56b are arranged in a circular pattern on the underside of the wheel base 56a. Each of the grinding stones 56b includes a binder such as vitrified or resinoid and abrasive grains such as diamond dispersed in the binder.

[0051] When the servo motor connected to the base end of the spindle 54 is operated, the grinding wheel 56 rotates together with the spindle 54. The outer diameter of the trajectory of the multiple grinding stones 56b when the spindle 54 is rotated is larger than the distance between the center of the holding surface of the chuck table 2 (the center C of the upper surface 6a of the porous plate 6) and each of the four corners.

[0052] 3 is a flowchart schematically illustrating an example of a method for grinding a workpiece in the grinding device 12. The workpiece may be, for example, a package substrate having a plurality of devices on its surface side and having a shape in which the outer periphery is located inside the outer periphery of the frame 4 and outside the corner ring portion 8b of the groove 8 in a plan view.

[0053] In this method, first, the front side of the workpiece is held on the holding surface of the chuck table 2 (holding step S1). Specifically, in holding step S1, the workpiece is placed on the holding surface of the chuck table 2 positioned at the loading / unloading position with its back side facing upward and covering the porous plate 6 and groove 8, and then the suction source communicating with the communication passage 10 is operated.

[0054] After the holding step S1, the chuck table 2 is moved (placement step S2) so that the center of the holding surface of the chuck table 2 is positioned directly below the trajectories of the multiple grinding wheels 56b when the spindle 54 is rotated. Specifically, in the placement step S2, the stepping motor 24 of the X-direction movement mechanism 16 is operated so as to position the chuck table 2 at the grinding position.

[0055] After the placement step S2, while both the chuck table 2 and the spindle 54 are rotated, the spindle 54 is lowered so that the back side of the workpiece comes into contact with the plurality of grinding wheels 56b (grinding step S3). Specifically, in the grinding step S3, the stepping motor 44 of the Z-direction movement mechanism 36 is operated while both the servo motor included in the rotation mechanism provided below the chuck table 2 and the servo motor housed in the housing 50 are operated. Then, when the back side of the workpiece comes into contact with the plurality of grinding wheels 56b, the back side of the workpiece is ground.

[0056] In the chuck table 2, the holding surface is lowest at the center C of the upper surface 6a (first region) of the circular porous plate 6, and has a shape that increases in height as it moves away from this center C. When a workpiece is ground using this chuck table 2, the portion near the periphery of the workpiece that overlaps with the center C of the first region is more easily removed than the portion near the center C. Therefore, in this case, it is possible to reduce variations in thickness that arise due to differences in grinding frequency.

[0057] Furthermore, in the chuck table 2, the angle formed by the tangent plane (reference tangent plane) of the upper surface 6a of the porous plate 6 at the center C of the upper surface 6a and the tangent plane (first tangent plane) of the upper surface 6a at a point other than the center C included in the upper surface 6a is smaller than the angle formed by the reference tangent plane and the tangent plane (second tangent plane) of the upper surface 4a of the frame 4 at a point included in the upper surface 4a of the frame 4. When the chuck table 2 is used to grind a workpiece, the portions of the workpiece near each corner that surround the upper surface 6a of the porous plate 6 and whose outer periphery overlaps with the square-shaped upper surface 4a (second region) of the frame 4 are more easily removed than other portions. Therefore, in this case, it is possible to reduce variations in thickness resulting from increases or decreases in the grinding area.

[0058] The above-described content is one aspect of the present invention, and the present invention is not limited to the above-described content. For example, the chuck table of the present invention may have a holding surface shaped such that its vertical cross section is curved. Specifically, the chuck table of the present invention may have an upper surface such that the angle formed between a tangent plane (reference tangent plane) of the holding surface at the center and a tangent plane of the holding surface at a point other than the center increases as the point moves away from the center.

[0059] Furthermore, the chuck table of the present invention may have a holding surface that has a polygonal shape other than a triangle or a square when viewed from above. In other words, the chuck table of the present invention can be appropriately modified into a shape suitable for use in grinding a flat workpiece having four or more corners.

[0060] Fig. 4 is a plan view schematically illustrating an example of a chuck table having a shape suitable for use in grinding a workpiece that is rectangular in plan view. The chuck table 58 shown in Fig. 4 has a frame 60 made of, for example, stainless steel (SUS). This frame 60 has an upper surface 60a whose outer periphery is rectangular in plan view, and a circular recess is formed on the upper surface 60a side. In other words, the frame 60 has an upper surface 60a shaped like a rectangle with a circular portion cut out at the center in plan view.

[0061] A circular porous plate 62 made of, for example, ceramic is fixed in this recess. Therefore, the holding surface of the chuck table 58 is divided, in a plan view, into an upper surface 62a (first region) of the circular porous plate 62 and an upper surface 60a (second region) of a frame 60 that surrounds the upper surface 62a of the porous plate 62 and has a rectangular outer periphery.

[0062] A groove 64 is formed on the upper surface 60a of the frame 60. In a plan view, the groove 64 includes a circular ring portion 64a whose inner and outer peripheries extend concentrically with the outer periphery of the upper surface 62a of the porous plate 62, and a rectangular ring portion 64b that extends such that the inner periphery of the circular ring portion 64a is inscribed at the center of each long side included in the inner periphery of a rectangle, and the outer periphery of the circular ring portion 64a is inscribed at the center of each long side included in the outer periphery of a rectangle.

[0063] The groove 64 also includes two arc-shaped portions 64c, 64d located in each of two regions defined by the circular ring portion 64a and the angular ring portion 64b in a plan view. Both ends of each of the arc-shaped portions 64c, 64d are connected to the angular ring portion 64b, and the inner and outer peripheries of each arc-shaped portion 64c, 64d extend so as to overlap with parts of the concentric circle of the outer periphery of the upper surface 62a of the porous plate 62. The inner periphery of the arc-shaped portion 64d is inscribed in the center of the short side included in the inner periphery of the angular ring portion 64b, and the outer periphery of each arc-shaped portion 64d extends so as to inscribe in the center of the short side included in the outer periphery of the angular ring portion 64b.

[0064] The groove 64 also includes arc portions 64e located in four regions defined by the angular ring portions 64b and the arc portions 64d in a plan view. The arc portions 64e are connected at both ends to the angular ring portions 64b, and extend such that their inner and outer peripheries overlap with parts of the concentric circles of the outer periphery of the upper surface 62a of the porous plate 62.

[0065] The chuck table 58 is used, for example, when grinding a workpiece having a shape such that its outer periphery is located inside the outer periphery of the upper surface 60a of the frame body 60 and outside the angular ring portion 64b of the groove 64 when viewed in a plane.

[0066] Fig. 5 is a plan view schematically illustrating an example of a chuck table having a shape suitable for use in grinding a workpiece having a regular pentagonal shape in plan view. The chuck table 66 shown in Fig. 5 has a frame 68 made of, for example, stainless steel (SUS). In plan view, this frame 68 has an upper surface 68a whose outer periphery is a regular pentagon, and a circular recess is formed on the side of this upper surface 68a. In other words, the frame 68 has an upper surface 68a shaped like a regular pentagon with a circular portion located in the center cut out in plan view.

[0067] A circular porous plate 70 made of, for example, ceramic is fixed in this recess. Therefore, the holding surface of the chuck table 66 is divided into an upper surface 70a (first region) of the circular porous plate 70 and an upper surface 68a (second region) of a frame 68 that surrounds the upper surface 70a of the porous plate 70 and has a regular pentagonal outer periphery.

[0068] A groove 72 is formed on the upper surface 68a of the frame 68. In a plan view, the groove 72 includes a circular ring portion 72a whose inner and outer peripheries extend concentrically with the outer periphery of the upper surface 70a of the porous plate 70, and a square ring portion 72b that extends such that the inner periphery of the circular ring portion 72a is inscribed at the center of each side included in the inner periphery of a regular pentagon and the outer periphery of the circular ring portion 72a is inscribed at the center of each side included in the outer periphery of the regular pentagon.

[0069] The groove 72 also includes arc portions 72c located in five regions defined by the annular portion 72a and the angular ring portion 72b in a plan view. The arc portions 72c are connected at both ends to the angular ring portions 72b, and extend such that their inner and outer peripheries overlap with parts of the concentric circles of the outer periphery of the upper surface 70a of the porous plate 70.

[0070] The chuck table 66 is used, for example, when grinding a workpiece having a shape such that its outer periphery is located inside the outer periphery of the upper surface 68a of the frame body 68 and outside the angular ring portion 72b of the groove 72 when viewed in a plane.

[0071] Fig. 6 is a plan view schematically illustrating an example of a chuck table having a shape suitable for use in grinding a workpiece having an isosceles trapezoidal shape in plan view. The chuck table 74 shown in Fig. 6 has a frame 76 made of, for example, stainless steel (SUS). In plan view, this frame 76 has an upper surface 76a whose outer periphery has an isosceles trapezoidal shape, and a circular recess is formed on the upper surface 76a side. In other words, the frame 76 has an upper surface 76a shaped like an isosceles trapezoid with a circular portion located in the center cut out in plan view.

[0072] A circular porous plate 78 made of, for example, ceramic is fixed in this recess. Therefore, the holding surface of the chuck table 74 is divided, in a plan view, into an upper surface 78a (first region) of the circular porous plate 78 and an upper surface 76a (second region) of a frame 76 that surrounds the upper surface 78a of the porous plate 78 and has an isosceles trapezoidal outer periphery.

[0073] A groove 80 is formed on the upper surface 76a of the frame 76. In a plan view, the groove 80 includes a circular ring portion 80a whose inner and outer peripheries extend concentrically with the outer periphery of the upper surface 78a of the porous plate 78, and a square ring portion 80b that extends such that the inner periphery of the circular ring portion 80a is inscribed at the center of each of the short and long bases included in the inner periphery of an isosceles trapezoid, and the outer periphery of the circular ring portion 80a is inscribed at the center of each of the short and long bases included in the outer periphery of the isosceles trapezoid.

[0074] The groove 80 also includes two arc-shaped portions 80c and 80d located in two regions defined by the circular ring portion 80a and the angular ring portion 80b in a plan view. Both ends of each of the arc-shaped portions 80c and 80d are connected to the angular ring portion 80b, and the inner and outer peripheries of each arc-shaped portion 80c and 80d extend so as to overlap with parts of the concentric circles of the outer periphery of the upper surface 78a of the porous plate 78. The inner periphery of the arc-shaped portion 80d is inscribed in a side of the inner periphery of the angular ring portion 80b other than the base, and the outer periphery of the arc-shaped portion 80d is inscribed in a side of the outer periphery of the angular ring portion 80b other than the base.

[0075] The groove 80 also includes arc portions 80e located in two regions defined by the short base side of the ring portion 80b and the arc portion 80d in a plan view. The arc portions 80e are connected at both ends to the ring portion 80b, and extend so that their inner and outer peripheries overlap with parts of the concentric circle of the outer periphery of the upper surface 78a of the porous plate 78.

[0076] The groove 80 also includes three arc portions 80f, 80g, and 80h located in two regions defined by the long base side of the ring portion 80b and the arc portion 80d in a plan view. Both ends of each of the arc portions 80f, 80g, and 80h are connected to the ring portion 80b, and the inner and outer peripheries of each arc portion 80f, 80g, and 80h extend so as to overlap with parts of the concentric circles of the outer periphery of the upper surface 78a of the porous plate 78.

[0077] The chuck table 74 is used, for example, when grinding a workpiece having a shape such that its outer periphery is located inside the outer periphery of the upper surface 76a of the frame body 76 and outside the angular ring portion 80b of the groove 80 in a planar view.

[0078] The chuck table of the present invention may also include components that are separable from one another. Figure 7(A) is a plan view schematically showing an example of such a chuck table, and Figure 7(B) is a vertical cross-sectional view of the chuck table shown in Figure 7(A).

[0079] 7(A) and 7(B) includes a first member 84. The first member 84 has a disk-shaped dense frame body 86 made of, for example, ceramics. The frame body 86 includes a cylindrical protrusion 88 on its side. A circular recess is formed on an upper surface 88a of the protrusion 88 in a plan view.

[0080] In other words, the protrusion 88 of the frame 86 has an upper surface 88a shaped like a recess in the center of a circle in a plan view. A circular porous plate 90 made of, for example, ceramics is fixed to the recess formed in the upper surface 88a of the protrusion 88.

[0081] A ring-shaped, dense second member 92 made of a metal such as stainless steel or aluminum, or ceramics, is provided on a lower surface 88b of the protrusion 88 that surrounds the upper surface 88a in plan view. In plan view, the second member 92 has a circular inner periphery and a square outer periphery. In other words, the second member 92 is a plate-like structure that resembles a square with a circular portion cut out in the center in plan view.

[0082] The inner diameter of the second member 92 in plan view is equal to or slightly larger than the diameter of the upper surface 88a of the convex portion 88. Therefore, the upper surface (holding surface) of the chuck table 82 is partitioned in plan view into a circular region (the upper surface 88a of the convex portion 88 and the upper surface 90a of the porous plate 90) (first region) and a region (the upper surface 92a of the second member 92) (second region) that surrounds the first region and has a square outer periphery.

[0083] Furthermore, the holding surfaces of the chuck table 82 (the upper surface 88a of the convex portion 88, the upper surface 90a of the porous plate 90, and the upper surface 92a of the second member 92) have a shape that is lowest at the center of the upper surface 90a of the porous plate 90 and becomes higher as it moves away from this center. Specifically, the upper surface 88a of the convex portion 88 and the upper surface 90a of the porous plate 90 have a shape that corresponds to the side of an inverted cone with its apex at the center of the upper surface 90a of the porous plate 90. Furthermore, the upper surface 92a of the second member 92 has a shape in which the areas near each corner are higher than the area located midway between a pair of adjacent corners.

[0084] Furthermore, the upper step surface 88a of the convex portion 88 and the upper surface 90a of the porous plate 90 have a smaller inclination than the upper surface 92a of the second member 92. In other words, the angle formed by the tangent plane (reference tangent plane) of the upper surface 90a at the center of the upper surface 90a of the porous plate 90 and the tangent plane (first tangent plane) of the upper step surface 88a of the convex portion 88 and the upper surface 90a of the porous plate 90 at a point other than the center that is included in the upper step surface 88a of the convex portion 88 and the upper surface 90a of the porous plate 90 is smaller than the angle formed by the reference tangent plane and the tangent plane (second tangent plane) of the upper surface 92a at a point that is included in the upper surface 92a of the second member 92.

[0085] Four grooves 94 are formed on the upper surface 92a side of the second member 92. Each groove 94 includes a bracket portion 94a that extends in an L-shape in plan view, and an arc portion 94b whose inner and outer peripheries overlap with parts of the concentric circle of the outer periphery of the upper surface 90a of the porous plate 90 and whose opposite ends are connected to the bracket portion 94a.

[0086] Furthermore, each groove 94 includes, in a plan view, two arc portions 94c, 94d and a straight portion 94e located in the area defined by the bracket portion 94a and the arc portion 94b. The inner and outer peripheries of each arc portion 94c, 94d overlap with parts of the concentric circles of the outer periphery of the upper surface 90a of the porous plate 90, and each arc portion 94c, 94d extends so that both ends are connected to the bracket portion 94a.

[0087] The straight portion 94e extends radially on the upper surface 90a of the porous plate 90 so that its outer end is connected to the center of the bracket portion 94a and its inner end is connected to the center of the arc portion 94b. That is, the straight portion 94e extends so as to penetrate through the centers of the two arc portions 94c and 94d.

[0088] A plurality of through passages 96 are formed inside the second member 92, each penetrating the second member 92 in the thickness direction. Each of the plurality of through passages 96 opens at the bottom surface of a linear portion 94e of the groove 94. In other words, the plurality of through passages 96 are aligned along the radial direction of the upper surface 90a of the porous plate 90.

[0089] The outermost of the multiple through passages 96 opens at the center of the bracket portion 94a of the groove 94, i.e., at the point where the bracket portion 94a and the straight portion 94e connect. The innermost of the multiple through passages 96 opens at the point where the arc portion 94c of the groove 94 connects with the straight portion 94e.

[0090] A first communication passage 98 is formed inside the frame body 86 of the first member 84. This first communication passage 98 includes a main passage 98a that opens at the bottom surface of a recess formed on the upper surface 88a side of the convex portion 88 and that penetrates the frame body 86 in its thickness direction, and a plurality of intermediate passages 98b, 98c that have one ends connected to the main passage 98a and extend perpendicular to the main passage 98a.

[0091] Furthermore, the first communication passage 98 includes a plurality of sub-passages 98d, each of which has one end connected to one of the plurality of intermediate passages 98b, 98c and extends parallel to the main passage 98a. Each of the plurality of sub-passages 98d opens at the lower surface 88b of the protrusion 88 and is formed so as to overlap in the vertical direction with the plurality of through passages 96 formed inside the second member 92.

[0092] The first member 84 and the second member 92 can be separated on the chuck table 82. Fig. 8(A) is a plan view that schematically shows the first member 84 in a state in which the second member 92 has been separated, and Fig. 8(B) is a vertical cross-sectional view of the first member 84 shown in Fig. 8(A).

[0093] A second communication passage 100 is further formed inside the frame body 86 of the first member 84. This second communication passage 100 includes a main passage 100a extending along the thickness direction of the frame body 86, and an intermediate passage 100b connected to the main passage 100a and extending in an annular shape so as to surround the recess.

[0094] The second communication passage 100 also includes a plurality of sub-paths 100c, each of which has one end connected to the intermediate path 100b and extends parallel to the main path 100a. Each sub-path 100c opens at the lower surface 88b of the convex portion 88 and is formed so as to overlap with a region of the second member 92 that is defined in plan view by the bracket portion 94a, the two arc portions 94b, 94c, and the straight portion 94e.

[0095] The first communication passage 98 (specifically, its main path 98a) and the second communication passage 100 (specifically, its main path 100a) can be connected to a suction source such as an ejector provided in the grinding machine. Specifically, the first communication passage 98 is connected to the suction source via a first valve, and the second communication passage 100 is connected to the suction source via a second valve different from the first valve.

[0096] When the first valve is closed, the second valve is opened, and the suction source is operated, a suction force acts on the space near the lower surface 88b of the convex portion 88 of the first member 84. Specifically, in this case, the suction force acts on the space near the lower surface 88b of the convex portion 88 via the main path 100a, the intermediate path 100b, and the multiple sub-paths 100c of the second communication passage 100 formed in the first member 84.

[0097] 7(A) and 7(B), by applying suction force in this manner with the second member 92 placed on the first member 84, it is possible to hold the second member 92 on the lower surface 88b of the convex portion 88 of the first member 84. Furthermore, when the first valve is opened and the second valve is closed while the suction source is operating, a suction force acts on the space near the upper surface 90a of the porous plate 90 and the upper surface 92a of the second member 92.

[0098] Specifically, in this case, suction force acts on the space near the upper surface 90a of the porous plate 90 via the main path 98a of the first communication passage 98 formed in the first member 84 and the porous plate 90, and suction force acts on the space near the upper surface 92a of the second member 92 via the main path 98a, multiple intermediate paths 98b, 98c and multiple sub-paths 98d of the first communication passage 98 formed in the first member 84, and the multiple through paths 96 and four grooves 94 formed in the second member 92.

[0099] Therefore, the chuck table 82 can hold a workpiece having a shape such that, in a planar view, its outer periphery is located inside the outer periphery of the second member 92 and outside the bracket portions 94a of each groove 94, using the upper surface 88a of the convex portion 88 of the first member 84, the upper surface 90a of the porous plate 90, and the upper surface 92a of the second member 92 as holding surfaces.

[0100] Furthermore, the chuck table of the present invention does not necessarily have to include a porous plate. Figure 9(A) is a plan view schematically showing an example of such a chuck table, and Figure 9(B) is a vertical cross-sectional view of the chuck table shown in Figure 9(A).

[0101] 9(A) and 9(B) has the same structure as the chuck table 82 shown in Figures 7(A) and 7(B), except that the first member 84 is replaced with a first member 104. This first member 104 is a disk-shaped dense structure made of, for example, a metal such as aluminum or ceramics, and its side surface includes a cylindrical protrusion 106.

[0102] The convex portion 106 has a circular upper surface 106a in a plan view. The second member 92 described above is provided on a lower surface 106b of the convex portion 106 that surrounds the upper surface 106a in a plan view. The diameter of the convex portion 106 in a plan view is equal to or slightly smaller than the inner diameter of the second member 92 in a plan view.

[0103] Therefore, when viewed in a plane, the upper surface (holding surface) of the chuck table 102 is divided into a circular area (upper surface 106a of the convex portion 106) (first area) and an area (upper surface 92a of the second member 92) (second area) that surrounds the first area and has a square-shaped outer periphery.

[0104] Furthermore, the holding surfaces of the chuck table 102 (the upper surface 106a of the convex portion 106 and the upper surface 92a of the second member 92) are shaped so that the center of the upper surface 106a of the convex portion 106 is lowest and the surface becomes higher as it moves away from the center. Specifically, the upper surface 106a of the convex portion 106 has a shape corresponding to the side of an inverted cone with its apex at the center. Furthermore, the upper surface 92a of the second member 92 has a shape such that the areas near each corner are higher than the area located midway between a pair of adjacent corners.

[0105] Furthermore, the upper step surface 106a of the convex portion 106 has a smaller inclination than the upper surface 92a of the second member 92. In other words, the angle formed by the tangent plane (reference tangent plane) of the upper step surface 106a of the convex portion 106 at the center of the upper step surface 106a of the convex portion 106 and the tangent plane (first tangent plane) of the upper step surface 106a of the convex portion 106 at a point other than the center that is included on the upper step surface 106a of the convex portion 106 is smaller than the angle formed by the reference tangent plane and the tangent plane (second tangent plane) of the upper surface 92a at a point that is included on the upper surface 92a of the second member 92.

[0106] Grooves 108 are formed on the upper surface 106a side of the protrusion 106 of the first member 104. The grooves 108 include a plurality of annular portions 108a whose inner and outer peripheries extend concentrically with the outer periphery of the upper surface 106a, and two main straight line portions 108b whose both ends are connected to the annular portions 108a, which pass through the center of the upper surface 106a, and which extend perpendicular to each other.

[0107] Furthermore, groove 108 includes a minor linear portion 108c in each of four regions defined by the outermost of the multiple annular portions 108a and the two main linear portions 108b. This minor linear portion 108c extends so that its outer end is connected to the outermost of the multiple annular portions 108a and its inner end is connected to the innermost of the multiple annular portions 108a. Furthermore, this minor linear portion 108c extends in a direction that forms a 45° angle with the extension directions of each of the two main linear portions 108b.

[0108] A first communication passage 110 and a second communication passage (not shown) similar to the second communication passage 100 shown in Figures 8(A) and 8(B) are formed inside the first member 104. This first communication passage 110 includes a main passage 110a extending along the thickness direction of the first member 104, and a plurality of intermediate passages 110b, 110c each having one end connected to the main passage 110a and extending perpendicular to the main passage 110a.

[0109] Furthermore, the first communication passage 110 includes a plurality of inner sub-paths 110d and a plurality of outer sub-paths 110e, each of which has one end connected to one of the plurality of intermediate paths 110b, 110c and extends parallel to the main path 98a.

[0110] The multiple inner sub-passages 110d each open at the bottom surface of a groove 108 formed in the upper surface 106a of the convex portion 106. The multiple outer sub-passages 110e each open at the lower surface 106b of the convex portion 106, and are formed so as to overlap in the vertical direction with the multiple through passages 96 formed inside the second member 92.

[0111] The first communication passage 110 (specifically, its main path 98a) and the second communication passage can be connected to a suction source such as an ejector provided in the grinding machine. Specifically, the first communication passage 110 is connected to the suction source via a first valve, and the second communication passage is connected to the suction source via a second valve different from the first valve.

[0112] Then, when the first valve is closed, the second valve is opened, and the suction source is operated, a suction force acts on the space near the lower surface 106b of the convex portion 106 of the first member 104. Specifically, in this case, the suction force acts on the space near the lower surface 106b of the convex portion 106 via the second communication passage formed in the first member 104.

[0113] 9(A) and 9(B), by applying suction force in this manner with the second member 92 placed on the first member 104, it is possible to hold the second member 92 on the lower surface 106b of the convex portion 106 of the first member 104. Furthermore, when the first valve is opened and the second valve is closed while the suction source is operating, suction force acts on the space near the upper surface 106a of the convex portion 106 and the space near the upper surface 92a of the second member 92.

[0114] Specifically, in this case, suction force acts on the space near the upper surface 90a of the porous plate 90 via the main path 110a, the multiple intermediate paths 110b, 110c, and the multiple inner sub-paths 110d of the first communication passage 110 formed in the first member 104, and suction force acts on the space near the upper surface 92a of the second member 92 via the main path 110a, the multiple intermediate paths 110b, 110c, and the multiple outer sub-paths 110e of the first communication passage 110 formed in the first member 104, and the multiple through paths 96 and four grooves 94 formed in the second member 92.

[0115] Therefore, the chuck table 102 can hold a workpiece having a shape such that, in a planar view, its outer periphery is located inside the outer periphery of the second member 92 and outside the bracket portions 94a of each groove 94, using the upper surface 106a of the convex portion 106 of the first member 104 and the upper surface 92a of the second member 92 as holding surfaces.

[0116] In addition, the structures and methods according to the above-described embodiments can be modified as appropriate without departing from the scope of the present invention. [Explanation of symbols]

[0117] 2: Chuck table 4: Frame (4a: top surface) 6: Porous plate (6a: top surface) 8: Groove (8a: ring portion, 8b: angular ring portion, 8c, 8d: arc portion) 10: Communication path (10a: main path, 10b, 10c: intermediate paths) (10d, 10e, 10f, 10g: Alternative pathway) 12: Grinding device 14: Base 16:X direction movement mechanism 18: Guide rail 20: X-direction moving plate 22: Screw shaft 24: Stepping motor 26: Nut 28: Bearing 30: Table base 32: Tilt adjustment mechanism (32a, 32b: movable axis, 32c: fixed axis) 34: Support structure 36:Z direction movement mechanism 38: Guide rail 40: Z-direction moving plate 42: Screw shaft 44: Stepping motor 46: Nut 48: Cover (48a: Through hole) 50: Housing 52a, 52b: Spacers 54: Spindle (54a: Tip (lower end)) 56: Grinding wheel (56a: wheel base, 56b: grinding stone) 58: Chuck table 60: Frame (60a: Top surface) 62: Porous plate (62a: top surface) 64: Groove (64a: Circular ring portion, 64b: Square ring portion, 64c, 64d, 64e: Arc portion) 66: Chuck table 68: Frame (68a: Top surface) 70: Porous plate (70a: top surface) 72: Groove (72a: Circular ring portion, 72b: Square ring portion, 72c: Arc portion) 74: Chuck table 76: Frame (76a: Top surface) 78: Porous plate (78a: top surface) 80: Groove (80a: Circular ring portion, 80b: Square ring portion) (80c, 80d, 80e, 80f, 80g, 80h: arc section) 82: Chuck table 84: First member 86: Frame 88: Convex portion (88a: upper surface, 88b: lower surface) 90: Porous plate (90a: top surface) 92: Second member (92a: upper surface 94: Groove (94a: bracket portion, 94b, 94c, 94d: arc portion, 94e: straight portion) 96: Passage 98: First communication path (98a: Main path, 98b, 98c: Intermediate paths, 98d: Sub-path) 100: Second communication path (100a: Main path, 100b: Intermediate path, 100c: Sub-path) 102: Chuck table 104: First member 106: Convex portion (106a: upper surface, 106b: lower surface) 108: Groove (108a: Annular portion, 108b: Main straight portion, 108c: Sub-straight portion) 110: First communication path (110a: Main path, 110b, 110c: Intermediate paths) (110d: medial accessory pathway, 110e: lateral accessory pathway)

Claims

1. A chuck table used when grinding a flat workpiece having four or more corners in a plan view, The holding surface is partitioned into a circular first region and a polygonal second region surrounding the first region and having an outer periphery with four or more corners in a plan view, the holding surface has a shape that is lowest at the center of the first region and becomes higher as it moves away from the center, a chuck table, wherein an angle formed by a reference tangent plane of the holding surface at the center of the first region and a first tangent plane of the holding surface at a point other than the center included in the first region is smaller than an angle formed by the reference tangent plane and a second tangent plane of the holding surface at a point included in the second region.

2. A grinding device for grinding a flat workpiece having four or more corners in a plan view, a chuck table including a holding surface that is partitioned into a circular first region and a polygonal second region that surrounds the first region and has an outer periphery with four or more corners, in a plan view, and that is rotatable about a straight line that passes through the center of the first region as a rotation axis; a spindle having a grinding wheel attached to a tip end thereof, the grinding wheel having a plurality of grinding stones arranged discretely in an annular shape; an outer diameter of a path of the grinding wheels when the spindle is rotated is larger than a distance between the center of the first region of the holding surface and each of the four or more corners; the holding surface has a shape that is lowest at the center of the first region and becomes higher as it moves away from the center, a grinding device, wherein an angle formed by a reference tangent plane of the holding surface at the center of the first region and a first tangent plane of the holding surface at a point other than the center included in the first region is smaller than an angle formed by the reference tangent plane and a second tangent plane of the holding surface at a point included in the second region.

3. a chuck table that includes a holding surface that is divided into a circular first region in a plan view and a polygonal second region that surrounds the first region and has four or more corners on its outer periphery, the chuck table being rotatable about a rotation axis that is a straight line passing through the center of the first region; and a spindle that has a grinding wheel attached to its tip end, the grinding wheel having a plurality of grinding wheels that are discretely arranged in an annular shape, wherein the outer diameter of the trajectory of the plurality of grinding wheels when the spindle is rotated is greater than the distance between the center of the first region of the holding surface and each of the four or more corners, the method comprising: a holding step of holding a front surface side of the workpiece on the holding surface of the chuck table in a state where each of four or more corners of the workpiece is positioned in the same direction as any of four or more corners of the second area when viewed from the center of the first area; a positioning step of relatively moving the chuck table and the spindle after the holding step so that the center of the first region and the locus overlap in a predetermined direction; a grinding step in which, after the placing step, the chuck table and the spindle are brought closer to each other along the predetermined direction while rotating both the chuck table and the spindle so that the back side of the workpiece comes into contact with the plurality of grinding wheels, the holding surface has a shape that is lowest at the center of the first region and becomes higher as it moves away from the center, a grinding method for a workpiece, wherein an angle formed by a reference tangent plane of the holding surface at the center of the first region and a first tangent plane of the holding surface at a point other than the center included in the first region is smaller than an angle formed by the reference tangent plane and a second tangent plane of the holding surface at a point included in the second region.

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