Method for grinding a workpiece

Abstract

To provide a workpiece processing method which can inhibit variations in thickness in a workpiece even if creep feed grinding is performed to the workpiece.SOLUTION: In prior to performing grinding (creep feed grinding) to a workpiece, the holding surface side of a chuck table is ground so that a distribution of a predetermined height occurs on a holding surface of the chuck table. The process can inhibit variations in thickness in the workpiece even after creep feed grinding.SELECTED DRAWING: Figure 3

Description

[Technical field]

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

[0002] Chips of devices such as ICs (Integrated Circuits) and LSIs (Large Scale Integration) are essential components in various electronic devices such as mobile phones and personal computers. Such chips are manufactured, for example, by dividing a workpiece such as a wafer having a large number of devices formed on its surface into areas each including an individual device.

[0003] Furthermore, the workpiece is often thinned before being divided in order to reduce the size and weight of the chips. One method for thinning the workpiece is grinding using a grinding device. The grinding device includes, for example, a chuck table having a holding surface for holding the workpiece, and a grinding unit provided above the chuck table and having a spindle at the bottom end of which a grinding wheel having a plurality of grinding stones arranged in a circular ring shape is detachably attached.

[0004] In such a grinding device, the workpiece may be thinned by a grinding method also known as creep feed grinding (see, for example, Patent Document 1). In this grinding method, the front side of the workpiece is first held on the holding surface of the chuck table. Next, with the grinding unit positioned horizontally and spaced apart from the chuck table, the lower surface of each of the multiple grinding wheels is positioned at a height between the rear surface (upper surface) and the front surface (lower surface) of the workpiece.

[0005] Then, while rotating the grinding wheel, the chuck table and the grinding unit are moved relatively in the horizontal direction to grind the top surface (back surface) of the workpiece from one end to the other in the horizontal direction with the multiple grinding wheels. As a result, a portion of the top surface of the workpiece having a predetermined thickness is removed, and the workpiece is thinned. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2005-28550 A Summary of the Invention [Problem to be solved by the invention]

[0007] The shape of the workpiece used in the manufacture of chips is generally disk-shaped or rectangular. When the workpiece is thinned by creep feed grinding, the contact area between the multiple grinding wheels and the workpiece varies during grinding. For example, when creep feed grinding is performed on a disk-shaped workpiece using a grinding wheel with a diameter larger than that of the workpiece, the contact area between the multiple grinding wheels and the workpiece varies as follows.

[0008] First, the contact area between the lower surface of the grinding wheels (the former) and one end of the upper surface of the workpiece (the latter) in the horizontal direction (first horizontal direction) gradually increases until the former reaches one end and the other end of the latter in the direction perpendicular to the first horizontal direction (second horizontal direction).Then, the contact area between the grinding wheels gradually decreases until the former leaves one end and the other end of the latter in the second horizontal direction and reaches the other end of the latter in the first horizontal direction.

[0009] In addition, the resistance force (grinding load) that multiple grinding wheels experience during creep feed grinding varies depending on the contact area between the multiple grinding wheels and the workpiece. Specifically, the larger the contact area between the two, the larger the grinding load, and the smaller the contact area between the two, the smaller the grinding load.

[0010] When the grinding load is large, the amount of the workpiece removed by creep feed grinding is small, and when the grinding load is small, the amount of the workpiece removed by creep feed grinding is large. In other words, after creep feed grinding, the area of ​​the workpiece where the grinding load was large may be thicker than the area where the grinding load was small (thickness may vary within the workpiece).

[0011] In view of this, an object of the present invention is to provide a method for machining a workpiece that can suppress thickness variations within the workpiece even when creep feed grinding is performed on the workpiece. [Means for solving the problem]

[0012] According to the present invention, there is provided a method for grinding a workpiece held on a chuck table using a grinding device including a chuck table having a holding surface for holding the workpiece, a grinding unit having a spindle at its lower end to which a grinding wheel having a plurality of grinding wheels arranged discretely in an annular shape can be attached and detached, the grinding unit grinding the workpiece with the rotating grinding wheels, a horizontal movement mechanism for relatively moving the chuck table and the grinding unit along a horizontal direction, and a vertical movement mechanism for relatively moving the chuck table and the grinding unit along a vertical direction, the method comprising the steps of: moving the lower surfaces of each of the plurality of grinding wheels of the chuck table grinding wheel against the holding surface; thana first preparation step of positioning the workpiece at a height below the workpiece surface; a chuck table grinding step of grinding the holding surface side of the chuck table from one end to the other end in the horizontal direction with the plurality of grinding wheels while rotating the grinding wheel after the first preparation step, by relatively moving the chuck table and the grinding unit along the horizontal direction so as to generate a predetermined height distribution on the holding surface; and a workpiece grinding wheel attached to the lower end of the spindle after the chuck table grinding step. a second preparation step of positioning the lower surfaces of the plurality of grinding stones of the workpiece grinding wheel at a height between the upper and lower surfaces of the workpiece with the grinding unit having a grinding wheel mounted thereon positioned away from the chuck table in the horizontal direction; and a workpiece grinding step of grinding the upper surface of the workpiece from one end to the other end in the horizontal direction with the plurality of grinding stones after the second preparation step by relatively moving the chuck table and the grinding unit along the horizontal direction while rotating the grinding wheel. In the chuck table grinding step, the chuck table and the grinding unit are moved relatively along the horizontal direction, and the chuck table is ground while the chuck table and the grinding unit are moved relatively along the vertical direction. A method for grinding a workpiece is provided. Effect of the Invention

[0014] In the present invention, prior to grinding (creep feed grinding) the workpiece, the holding surface side of the chuck table is ground so as to produce a predetermined height distribution on the holding surface of the chuck table, thereby making it possible to suppress thickness variations within the workpiece even after creep feed grinding. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a partially sectional side view that illustrates an example of a grinding device. [Diagram 2] FIG. 2 is a perspective view that illustrates an example of a workpiece. [Diagram 3] FIG. 3 is a flow chart that illustrates a schematic example of a method for grinding a workpiece. [Figure 4]FIG. 4 is a partial cross-sectional side view that illustrates a schematic view of the chuck table and grinding unit positioned at predetermined positions in the first preparation step. [Diagram 5] FIG. 5 is a top view showing a schematic diagram of an area of ​​the upper surface of a workpiece that comes into contact with a plurality of grinding wheels when creep feed grinding is being performed on the workpiece. [Figure 6] FIG. 6 is a cross-sectional view that typically illustrates the chuck table ground in the chuck table grinding step. [Figure 7] FIG. 7 is a partial cross-sectional side view that illustrates a schematic view of the chuck table and grinding unit positioned at predetermined positions in the second preparation step. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] An embodiment of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a partially cross-sectional side view showing a schematic diagram of an example of a grinding device. Note that the X-axis direction (front-back direction, first horizontal direction) and the Y-axis direction (left-right direction, second horizontal direction) shown in Fig. 1 are directions perpendicular to each other on a horizontal plane, and the Z-axis direction (up-down direction) is a direction perpendicular to the X-axis direction and the Y-axis direction (vertical direction).

[0017] 1 includes a base 4 that supports or houses each of the components that make up the grinding device 2. A rectangular parallelepiped opening 4a is provided on the upper surface side of the base 4. A chuck table 6 is provided inside the opening 4a. The chuck table 6 is made of a metal such as stainless steel, glass, ceramics, resin, or the like, and has a cylindrical frame 8 with a step provided on the upper surface 8a side of its outer periphery.

[0018] A cylindrical recess is provided in the center of the upper surface 8a of the frame 8, and a disk-shaped holding member 10 made of porous ceramics or the like is fitted into this recess. Holes (flow paths) that communicate from the upper surface 10a to the lower surface are formed in the holding member 10. The upper surface 10a is connected to a suction source (not shown) such as an ejector via the holes formed in the holding member 10, flow paths (not shown) formed inside the frame 8, and valves (not shown).

[0019] When the valve is opened while the suction source is operating, the space near the upper surface 10a of the holding member 10 becomes negative pressure. Therefore, the chuck table 6 can suction-hold a workpiece placed on its upper surface (the upper surface 10a of the frame 8 and the upper surface 10a of the holding member 10). In other words, the upper surface of the chuck table 6 functions as a circular holding surface 6a that holds the workpiece.

[0020] Fig. 2 is a perspective view showing an example of a workpiece held by suction on the holding surface 6a of the chuck table 6. The workpiece 11 shown in Fig. 2 is, for example, a disk-shaped wafer having a circular front surface 11a and a back surface 11b, and made of a semiconductor material such as silicon (Si), silicon carbide (SiC) or gallium nitride (GaN). The front surface 11a side of the workpiece 11 is partitioned into a plurality of regions by a plurality of mutually intersecting division lines 13, and a device 15 such as an IC is formed in each region.

[0021] A film-like tape having a diameter approximately equal to that of the workpiece 11 may be attached to the front surface 11a of the workpiece 11. This tape is made of, for example, resin, and protects the device 15 by absorbing the impact applied to the front surface 11a when the back surface 11b of the workpiece 11 is ground.

[0022] 1, an X-axis movement mechanism (horizontal movement mechanism) 12 is provided inside the opening 4a. The X-axis movement mechanism 12 is connected to the chuck table 6 and moves the chuck table 6 along the X-axis direction. The X-axis movement mechanism 12 has a screw shaft 14 that extends along the X-axis direction.

[0023] A motor 16 for rotating the screw shaft 14 is connected to one end of the screw shaft 14. In addition, a nut portion (not shown) for accommodating balls that roll on the surface of the rotating screw shaft 14 is provided on the surface of the screw shaft 14 on which a spiral groove is formed, thereby forming a ball screw.

[0024] That is, when the screw shaft 14 rotates, the balls circulate inside the nut portion, causing the nut portion to move along the X-axis direction. This nut portion is also connected to the chuck table 6. Therefore, when the screw shaft 14 is rotated by the motor 16, the chuck table 6 moves along the X-axis direction together with the nut portion.

[0025] A rectangular parallelepiped support structure 18 is provided behind the chuck table 6 and the X-axis movement mechanism 12 (on the right side of the paper in FIG. 1). A Z-axis movement mechanism (vertical movement mechanism) 20 is provided on the surface (front surface) side of the support structure 18. The Z-axis movement mechanism 20 is connected to a grinding unit 32 (described later) and moves the grinding unit 32 along the Z-axis direction.

[0026] The Z-axis movement mechanism 20 is fixed to the front surface side of the support structure 18 and has a pair of guide rails 22 extending along the Z-axis direction. A moving plate 24 is connected to the front sides of the pair of guide rails 22 in a manner that allows it to slide along the pair of guide rails 22.

[0027] A screw shaft 26 extending along the Z-axis direction is disposed between the pair of guide rails 22. A motor 28 for rotating the screw shaft 26 is connected to one end of the screw shaft 26. In addition, a nut portion 30 for accommodating balls that roll on the surface of the rotating screw shaft 26 is provided on the surface of the screw shaft 26 on which a spiral groove is formed, thereby forming a ball screw.

[0028] That is, when the screw shaft 26 rotates, the balls circulate inside the nut portion 30, and the nut portion 30 moves along the Z-axis direction. The nut portion 30 is fixed to the back surface (rear surface) side of the moving plate 24. Therefore, when the screw shaft 26 is rotated by the motor 28, the moving plate 24 moves along the Z-axis direction together with the nut portion 30.

[0029] A grinding unit 32 is provided on the surface (front) side of the movable plate 24. The grinding unit 32 has a hollow, cylindrical support member 34 fixed to the surface side of the movable plate 24. A hollow, cylindrical housing 36 is accommodated in the support member 34. The housing 36 is fixed to the bottom wall of the support member 34 via a connecting member 38 provided on the lower surface thereof.

[0030] A cylindrical spindle 40 extending along the Z-axis direction is rotatably housed in the housing 36. The tip (lower end) of the spindle 40 is exposed from the housing 36 and protrudes downward from the bottom surface of the support member 34 through an opening provided in the bottom wall of the support member 34. In addition, a disk-shaped mount 42 made of metal or the like is fixed to the tip of the spindle 40.

[0031] The diameter of the mount 42 is greater than the diameter of the holding surface 6a of the chuck table 6. A circular grinding wheel 44 is attached to the lower surface of the mount 42 in a removable manner. The grinding wheel 44 is made of a metal such as aluminum or stainless steel. The grinding wheel 44 has a circular base 46, and the outer diameter of the base 46 is approximately equal to the diameter of the mount 42.

[0032] The upper surface side of the base 46 is fixed to the lower surface side of the mount 42 using fasteners such as bolts. A plurality of grinding wheels 48 arranged discretely in an annular shape are fixed to the lower surface side of the base 46. Each of the plurality of grinding wheels 48 has, for example, a rectangular parallelepiped shape, and is arranged at approximately equal intervals along the circumferential direction of the base 46.

[0033] The grinding wheel 48 is formed by fixing abrasive grains made of diamond, cBN (cubic boron nitride), or the like, with a bonding material (bond material) made of metal bond, resin bond, vitrified bond, or the like. However, there are no limitations on the material, shape, structure, size, etc., of the grinding wheel 48. In addition, the number of multiple grinding wheels 48 can be set arbitrarily.

[0034] A rotary drive source (not shown) such as a motor for rotating the spindle 40 is connected to the base end (upper end) of the spindle 40. When this rotary drive source rotates the spindle 40 about a rotation axis along the Z-axis direction, the mount 42 and the grinding wheel 44 (the base 46 and the multiple grinding stones 48) rotate together with the spindle 40.

[0035] Fig. 3 is a flow chart showing a schematic example of a method for grinding a workpiece 11 in the grinding device 2. In this method, first, the chuck table 6 and the grinding unit 32 are positioned at predetermined positions (first preparation step: S1). Fig. 4 is a partially sectional side view showing a schematic example of the chuck table 6 and the grinding unit 32 positioned at the predetermined positions in the first preparation step (S1).

[0036] In this first preparation step (S2), first, the X-axis moving mechanism 12 adjusts the position of the chuck table 6 in the X-axis direction so as to move the chuck table 6 away from the grinding unit 32. At this time, a chuck table grinding wheel 44a is attached to the tip (lower end) of the spindle 40 of the grinding unit 32.

[0037] That is, the upper surface side of the base 46a of the grinding wheel for the chuck table 44a is fixed to the lower surface side of the mount 42. Next, the Z-axis movement mechanism 20 adjusts the position of the grinding unit 32 so that the lower surfaces of the multiple grinding stones 48a of the grinding wheel for the chuck table 44a are positioned at a height that is a predetermined distance below the holding surface 6a of the chuck table 6 (see FIG. 4).

[0038] After the first preparation step (S1), the holding surface 6a of the chuck table 6 is ground so as to produce a predetermined height distribution on the holding surface 6a of the chuck table 6 (chuck table grinding step: S2). This height distribution is set according to the size of the contact area between the multiple grinding wheels 48 and the workpiece 11 when creep feed grinding the top surface (back surface 11b) side of the workpiece 11 (the size of the resistance force (grinding load) received by the multiple grinding wheels 48 during creep feed grinding).

[0039] This point will be described with reference to Fig. 5. Fig. 5 is a top view that typically shows the region of the upper surface of the workpiece 11 that comes into contact with the multiple grinding wheels 48 when creep feed grinding is being performed on the upper surface side of the workpiece 11. Specifically, the hatched region R1 shown in Fig. 5 indicates the region of the upper surface of the workpiece 11 that comes into contact with the multiple grinding wheels 48 at a relatively early timing t1 of the creep feed grinding. Moreover, the hatched region R2 shown in Fig. 5 indicates the region of the upper surface of the workpiece 11 that comes into contact with the multiple grinding wheels 48 at a timing t2 that is later than the timing t1.

[0040] That is, region R1 and region R2 respectively indicate the contact areas between the grinding wheels 48 and the workpiece 11 during creep feed grinding at timing t1 and timing t2. Region R2 includes one end and the other end in the Y-axis direction of the upper surface of the workpiece 11.

[0041] Here, region R2 is wider than region R1. In this case, the thickness of workpiece 11 removed by creep feed grinding is greater in region R1 than in region R2. That is, when creep feed grinding is performed on workpiece 11 having a uniform thickness, region R2 of workpiece 11 becomes thicker than region R1.

[0042] As a result, thickness variations occur in the workpiece 11. In consideration of this, in the chuck table grinding step (S2), the holding surface 6a side of the chuck table 6 is machined so as to generate a height distribution that offsets the thickness variations that occur in the workpiece 11 due to creep feed grinding.

[0043] Specifically, the chuck table 6 is ground in the same procedure as the creep feed grinding of the workpiece 11 (in short, creep feed grinding of the chuck table 6 is performed). That is, in the chuck table grinding step (S2), the X-axis moving mechanism 12 moves the chuck table 6 along the X-axis direction while rotating the chuck table grinding wheel 44a, thereby grinding the holding surface 6a side of the chuck table 6 from one end to the other end in the X-axis direction with the multiple grinding wheels 48a.

[0044] Here, since the holding surface 6a is circular like the top surface of the workpiece 11, the contact area between the multiple grinding wheels 48a and the chuck table 6 varies in the same way as the multiple grinding wheels 48 and the workpiece 11. That is, the grinding load when grinding the chuck table 6 varies in the same way as the grinding load when grinding the workpiece 11. Note that this grinding load can be evaluated based on, for example, the load current value that rotates the spindle 40 or the magnitude of the torque acting on the spindle 40.

[0045] In this case, this grinding causes the shape of the holding surface 6a side of the chuck table 6 to correspond to the shape of the upper surface side of the workpiece 11 after creep feed grinding. In other words, the holding surface 6a of the chuck table 6 comes to have a height distribution that corresponds to the variation in thickness within the workpiece 11 after creep feed grinding.

[0046] Therefore, when creep feed grinding is performed on the workpiece 11 while it is held by a holding surface 6a having such a height distribution, the thickness variation within the workpiece 11 after creep feed grinding can be reduced compared to when creep feed grinding is performed on the workpiece 11 while it is held by a flat holding surface 6a.

[0047] Furthermore, in the chuck table grinding step (S2), it is preferable that the X-axis moving mechanism 12 moves the chuck table 6 along the X-axis direction, and the Z-axis moving mechanism 20 moves the grinding unit 32 along the Z-axis direction. This point will be described below.

[0048] First, the workpiece 11 and the chuck table 6 are generally made of different materials, and the types of grinding wheels 48 used to grind them are also different. Furthermore, the upper surface of the workpiece 11 generally has a smaller diameter than the holding surface 6a of the chuck table 6, so the contact area between the multiple grinding wheels 48 and the workpiece 11 is smaller than the contact area between the multiple grinding wheels 48 and the chuck table 6.

[0049] Therefore, even if the chuck table 6 is ground using a procedure similar to that used for creep feed grinding of the workpiece 11, the shape of the holding surface 6a side of the chuck table 6 after grinding and the shape of the upper surface side of the workpiece 11 after creep feed grinding may not necessarily correspond sufficiently to each other.

[0050] In contrast, by performing the chuck table grinding step (S2) as described above, the shape of the holding surface 6a side of the chuck table 6 after grinding can be made closer to the shape of the upper surface side of the workpiece 11 after creep feed grinding. That is, by grinding the chuck table 6 while moving the grinding unit 32 along the Z-axis direction in the chuck table grinding step (S2), the shape of the holding surface 6a side of the chuck table 6 can be made into a more suitable shape.

[0051] 6 is a cross-sectional view that typically shows the chuck table 6 ground in the chuck table grinding step (S2). The holding surface 6a of the chuck table 6 after the chuck table grinding step (S2) has a curved shape such that an arc-shaped region including one end and the other end of the holding surface 6a in the Y-axis direction (a region slightly shifted to the left from the center of the holding surface 6a in the cross section shown in FIG. 6) is highest.

[0052] After the chuck table grinding step (S2), the chuck table 6 that holds the workpiece 11 and the grinding unit 32 are positioned at predetermined positions (second preparation step: S3). Fig. 7 is a partially sectional side view that shows the chuck table 6 and the grinding unit 32 positioned at predetermined positions in the second preparation step (S3). Note that here, the workpiece 11 is held on the holding surface 6a of the chuck table 6 with the back surface 11b facing upward.

[0053] In this second preparation step (S3), first, the X-axis moving mechanism 12 adjusts the position of the chuck table 6 in the X-axis direction so as to move the chuck table 6 away from the grinding unit 32. At this time, a workpiece grinding wheel 44b is attached to the tip (lower end) of the spindle 40 of the grinding unit 32.

[0054] That is, the upper surface side of the base 46b of the workpiece grinding wheel 44b is fixed to the lower surface side of the mount 42. Next, the Z-axis movement mechanism 20 adjusts the position of the grinding unit 32 so that the lower surfaces of the multiple grinding stones 48b of the workpiece grinding wheel 44b are positioned at a height between the upper surface (rear surface 11b) and the lower surface (front surface 11a) of the workpiece 11 (see FIG. 7).

[0055] After the second preparation step (S3), the upper surface side of the workpiece 11 is ground (creep feed grinding) (workpiece grinding step: S4). Specifically, while rotating the workpiece grinding wheel 44b, the X-axis moving mechanism 12 moves the chuck table 6 along the X-axis direction, so that the upper surface side of the workpiece 11 is ground from one end to the other end in the X-axis direction by the multiple grinding wheels 48b.

[0056] 3, prior to a workpiece grinding step (S4) in which the workpiece 11 is ground (creep feed grinding), a chuck table grinding step (S2) is performed in which the holding surface 6a side of the chuck table 6 is ground so as to produce a predetermined height distribution on the holding surface 6a of the chuck table 6. This makes it possible to suppress thickness variations in the workpiece 11 even after creep feed grinding.

[0057] The present invention is not limited to the above-mentioned method. For example, in the present invention, the moving directions of the chuck table 6 and the grinding unit 32 are not limited. Specifically, the chuck table 6 may be movable along the Y-axis direction and / or the Z-axis direction, and the grinding unit 32 may be movable along the X-axis direction and / or the Y-axis direction.

[0058] Furthermore, the workpiece in the present invention may be a rectangular parallelepiped package substrate such as a chip size package (CSP) substrate or a quad flat non-leaded package (QFN) substrate.

[0059] However, if the workpiece has a rectangular parallelepiped shape, it is necessary to change the structure of the chuck table that holds the workpiece. For example, the chuck table has a cylindrical frame with a rectangular parallelepiped recess in the center of the upper surface side, and a rectangular parallelepiped holding member fitted into the recess, and the upper surface of the chuck table is configured to function as a rectangular holding surface that holds the workpiece 11.

[0060] 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]

[0061] 2: Grinding equipment 4: Base (4a: opening) 6: Chuck table (6a: upper surface (holding surface)) 8: Frame body (8a: top surface) 10: Holding member (10a: upper surface) 11: Workpiece (11a: front side, 11b: back side) 12:X-axis movement mechanism (horizontal movement mechanism) 13: Planned division line 14: Screw shaft 15: Device 16: Motor 18:Support structure 20: Z-axis movement mechanism (vertical movement mechanism) 22: Guide rail 24: Moving plate 26: Screw shaft 28: Motor 30: Nut part 32: Grinding unit 34: Support member 36: Housing 38: Connection parts 40: Spindle 42: Mount 44: Grinding wheel (44a: Grinding wheel for chuck table, 44b: Grinding wheel for workpiece) 46: Base (46a, 46b: Base) 48: Grinding wheel (48a, 48b: Grinding wheel)

Claims

[Claim 1] a chuck table having a holding surface for holding a workpiece; a grinding unit having a grinding wheel on which a plurality of grinding stones are arranged in a circular ring shape and a detachable spindle at a lower end thereof, the grinding unit grinding the workpiece with the rotating grinding stones; a horizontal movement mechanism that moves the chuck table and the grinding unit relatively in a horizontal direction; a vertical movement mechanism for relatively moving the chuck table and the grinding unit along a vertical direction, the vertical movement mechanism being configured to grind the workpiece held on the chuck table, the method comprising: a first preparation step of positioning the lower surface of each of the plurality of grinding stones of the grinding wheel for the chuck table at a height lower than the holding surface while the grinding unit, having a grinding wheel for the chuck table attached to a lower end of the spindle, is positioned apart from the chuck table in the horizontal direction; a chuck table grinding step in which, after the first preparation step, the chuck table and the grinding unit are moved relatively along the horizontal direction while rotating the grinding wheel, thereby grinding the holding surface side of the chuck table from one end to the other end in the horizontal direction with the multiple grinding wheels so as to generate a predetermined height distribution on the holding surface; a second preparation step of holding the workpiece on the holding surface after the chuck table grinding step, and positioning the lower surface of each of the plurality of grinding stones of the workpiece grinding wheel at a height between the upper surface and the lower surface of the workpiece while the grinding unit, having a workpiece grinding wheel attached to a lower end of the spindle, is positioned away from the chuck table in the horizontal direction; a workpiece grinding step in which, after the second preparation step, the chuck table and the grinding unit are moved relatively along the horizontal direction while rotating the grinding wheel, thereby grinding an upper surface side of the workpiece from one end to the other end in the horizontal direction with the plurality of grinding wheels, A method for grinding a workpiece, in which, in the chuck table grinding step, the chuck table and the grinding unit are moved relatively along the horizontal direction while the chuck table and the grinding unit are moved relatively along the vertical direction to grind the chuck table.

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