Grinding method for workpieces

Abstract

To provide a workpiece grinding method capable of suppressing prolonging of time necessary for grinding a workpiece.SOLUTION: Prior to a stop step of sparking-out, a separation step of separating a chuck table and a grinding wheel by operating a moving mechanism while maintaining a contact state between a plurality of grindstones and a workpiece is executed. In the separation step, a grinding load is reduced. Thus, time necessary for completing the sparking-out is reduced as compared with a case where the separation step is not executed, and prolonging of time necessary for grinding the workpiece can be suppressed.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a method for grinding a workpiece to be ground.

Background Art

[0002] Chips of devices such as ICs (Integrated Circuits) are essential components in various electronic devices such as mobile phones and personal computers. Such chips are manufactured, for example, by thinning a workpiece such as a wafer having a large number of devices formed on its surface and then dividing the workpiece for each region including individual devices.

[0003] As a method for thinning a workpiece, for example, grinding on the back side of the workpiece in a grinding apparatus can be mentioned. This grinding apparatus generally includes a chuck table rotatable about a straight line passing through the center of the holding surface as a rotation axis, and a spindle having an annular grinding wheel with a plurality of grinding wheels discretely arranged in an annular shape mounted at its tip.

[0004] In the grinding apparatus, while rotating both the chuck table holding the workpiece on the holding surface and the spindle, the workpiece is ground by bringing them into contact with each other by a moving mechanism capable of adjusting the distance between the chuck table and the grinding wheel. That is, this grinding is performed in a state where both the chuck table and the grinding wheel are rotating and are pressing against each other through the workpiece.

[0005] When the workpiece is ground in this way, periodic unevenness (grinding marks) may be formed on the surface of the workpiece to be ground. Therefore, when grinding the workpiece, grinding for removing the grinding marks and flattening the surface of the workpiece to be ground, so-called spark out, may be performed last (see, for example, Patent Documents 1 and 2).

[0006] Specifically, spark-out is achieved by rotating both the chuck table and the spindle that hold the workpiece on the holding surface, while stopping the movement of the moving mechanism while the workpiece is in contact with multiple grinding wheels.

[0007] During spark-out, the chuck table and grinding wheel push against each other through the workpiece, causing a decrease in the load (grinding load) on both and reducing the distance between them, a phenomenon known as springback. When springback occurs, the workpiece is ground, and when the springback is substantially complete, the workpiece is no longer substantially ground. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2003-236736 [Patent Document 2] Japanese Patent Publication No. 2009-12134 [Overview of the project] [Problems that the invention aims to solve]

[0009] To grind workpieces made of hard materials such as silicon carbide (SiC), gallium nitride (GaN), or sapphire (Al2O3), a high grinding load is necessary. However, a high grinding load also increases the time required to complete the spark-out process.

[0010] Therefore, in this case, the throughput when grinding the workpiece in the grinding device may decrease. In view of this, the object of the present invention is to provide a method for grinding a workpiece that can suppress the prolongation of the time required to grind the workpiece. [Means for solving the problem]

[0011] According to the present invention, a grinding apparatus comprising a chuck table rotatable about a straight line passing through the center of the holding surface as the axis of rotation, a spindle with an annular grinding wheel having a plurality of grinding wheels arranged in a circular dispersion at its tip, and a moving mechanism capable of adjusting the distance between the chuck table and the grinding wheel, wherein a method for grinding a workpiece comprises a holding step of holding the workpiece on the holding surface of the chuck table, and a grinding step after the holding step of operating the moving mechanism to bring the plurality of grinding wheels into contact with the workpiece while rotating both the chuck table and the spindle, thereby grinding the workpiece. The grinding step includes: an approach step, which involves operating the moving mechanism to bring the chuck table and the grinding wheel closer together so that the workpiece is ground while the chuck table and the grinding wheel are pressing against each other through the workpiece; a separation step, which involves operating the moving mechanism to separate the chuck table and the grinding wheel after the approach step so as to reduce the grinding load applied to the chuck table and the grinding wheel while maintaining contact between the multiple grinding wheels and the workpiece; and a stop step, which involves stopping the operation of the moving mechanism after the separation step so that the workpiece is ground while reducing the grinding load. The timing for ending the separation step and the timing for ending the stopping step are determined according to the current supplied to the rotational drive source for rotating the spindle or the grinding load. A method for grinding a workpiece is provided. In this workpiece grinding method, the grinding load at the time the approach step is completed is a first value, the separation step may be completed when the grinding load decreases to a second value less than 1 / 3 of the first value, and the stopping step may be completed when the grinding load decreases to a third value less than 1 / 5 of the second value. [Effects of the Invention]

[0012] In the present invention, prior to the stopping step in which spark-out occurs, a separation step is performed in which the moving mechanism is operated to separate the chuck table and the grinding wheel while maintaining a state in which multiple grinding wheels and the workpiece are in contact.

[0013] Furthermore, during the separation step, the grinding load applied to the chuck table and grinding wheel is reduced. Therefore, in this invention, the time required to complete the spark-out is shortened compared to when the separation step is not performed, and it is possible to suppress the prolongation of the time required to grind the workpiece. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 is a schematic perspective view showing an example of a grinding apparatus. [Figure 2] Figure 2 is a schematic partial cross-sectional side view showing an example of a grinding apparatus. [Figure 3] Figure 3 is a schematic flowchart illustrating an example of a workpiece grinding method used in a grinding machine. [Figure 4] Figure 4 is a flowchart that schematically shows an example of the operation when grinding a workpiece. [Figure 5] Figure 5 is a schematic graph showing the change over time of the grinding load applied to the chuck table and grinding wheel via the workpiece during grinding. [Modes for carrying out the invention]

[0015] Embodiments of the present invention will be described with reference to the attached drawings. Figure 1 is a schematic perspective view showing an example of a grinding apparatus, and Figure 2 is a schematic partial cross-sectional side view showing an example of the grinding apparatus shown in Figure 1.

[0016] Note that the X-axis direction (front-to-back direction) and Y-axis direction (left-to-right direction) shown in Figures 1 and 2 are mutually orthogonal directions on the horizontal plane, and the Z-axis direction (up-down direction) is perpendicular to the X-axis and Y-axis directions (vertical direction).

[0017] The grinding apparatus 2 shown in Figures 1 and 2 has a base 4 that supports each component. A rectangular parallelepiped groove 4a extending along the X-axis is formed on the upper surface of the base 4. An X-axis movement mechanism 6 for moving the chuck table 24, which will be described later, along the X-axis is provided on the bottom surface of the groove 4a.

[0018] This X-axis direction movement mechanism 6 has a pair of guide rails 8 each extending along the X-axis direction. Above the pair of guide rails 8, a rectangular parallelepiped-shaped X-axis movement plate 10 is attached in a slidable manner along the X-axis direction. Also, between the pair of guide rails 8, a screw shaft 12 extending along the X-axis direction is arranged.

[0019] And at the rear end portion of the screw shaft 12, a pulse motor 14 for rotating the screw shaft 12 is connected. Also, on the outer peripheral surface where the screw thread of the screw shaft 12 is formed, a nut 16 for accommodating a large number of balls that circulate in response to the rotation of the screw shaft 12 is provided, and a ball screw is constituted.

[0020] Also, the nut 16 is fixed to the lower surface side of the X-axis movement plate 10. Therefore, if the screw shaft 12 is rotated by the pulse motor 14, the X-axis movement plate 10 together with the nut 16 moves along the X-axis direction.

[0021] On the X-axis movement plate 10, a rotating body having a driven pulley 18 connected to the lower end portion and a rotational drive source such as a motor (not shown) connected to a driving pulley (not shown) are provided. Also, an endless belt (not shown) is stretched between the driven pulley 18 and the driving pulley.

[0022] Furthermore, on the X-axis movement plate 10, an inclination adjustment mechanism having one fixed shaft (not shown) and two movable shafts 20 with variable lengths along their respective Z-axis directions is provided. Also, the fixed shaft and the two movable shafts 20 are connected to the lower surface side of the table base 22 and support the table base 22.

[0023] A through hole (not shown) is formed at the center of this table base 22, and a rotating body having a driven pulley 18 connected to the lower end portion is passed through this through hole. And the upper end portion of this rotating body is connected to the lower surface side of a disk-shaped chuck table 24.

[0024] Therefore, when the rotational drive source connected to the drive pulley is operated to rotate the endless belt stretched over the driven pulley 18, the chuck table 24 rotates along the circumferential direction of the chuck table 24.

[0025] Furthermore, the chuck table 24 is supported by the table base 22 via bearings (not shown). Therefore, as described above, even if the chuck table 24 is rotated, the table base 22 will not rotate.

[0026] On the other hand, when the tilt adjustment mechanism provided on the X-axis moving plate 10 is operated, that is, when the length along the Z-axis direction of at least one of the two movable axes 20 is adjusted, the tilt of not only the table base 22 but also the chuck table 24 is adjusted.

[0027] The chuck table 24 has a disc-shaped frame 26 made of ceramics or the like. This frame 26 has a disc-shaped bottom wall and cylindrical side walls that rise from this bottom wall. That is, a disc-shaped recess is formed on the upper surface of the frame 26, defined by the bottom wall and the side walls.

[0028] The inner diameter of the side wall of the frame 26 is slightly shorter than the diameter of the workpiece 11, which will be described later, and its outer diameter is slightly longer than the diameter of the workpiece 11. In addition, a flow channel (not shown) is formed in the bottom wall of the frame 26, which opens at the bottom surface of the recess, and this flow channel communicates with a suction source (not shown), such as an ejector.

[0029] Furthermore, a disc-shaped porous plate 28 having a diameter approximately equal to the diameter of the recess is fixed to a recess formed on the upper side of the frame 26. This porous plate 28 is made of, for example, porous ceramics. The upper surface of the porous plate 28 and the upper surface of the side wall of the frame 26 have a shape corresponding to the side surface of a cone (a shape in which the center protrudes beyond the outer circumference).

[0030] When the suction source, which communicates with the flow path formed inside the frame 26, is activated, a suction force acts on the space near the upper surface of the porous plate 28. As a result, the upper surface of the porous plate 28 and the upper surface of the side wall of the frame 26 function as the holding surface 24a of the chuck table 24 (see Figure 1).

[0031] For example, the workpiece 11 is held in place by the chuck table 24 by operating the suction source while the workpiece 11 is placed on the holding surface 24a of the chuck table 24. The workpiece 11 is made of, for example, silicon carbide, gallium nitride, or sapphire, and has a wafer 13 on which multiple devices are formed on its surface 13a.

[0032] Furthermore, a protective tape 15, made of, for example, resin, is attached to the surface 13a of the wafer 13 to prevent damage to the device when grinding the back surface 13b of the wafer 13. The workpiece 11 is held on the chuck table 24 so that the wafer 13 is held via the protective tape 15, that is, so that the back surface 13b of the wafer 13 is exposed.

[0033] Furthermore, a rectangular parallelepiped table cover 30 is provided around the chuck table 24, surrounding it so that its holding surface 24a is exposed. The width (length along the Y-axis) of this table cover 30 is approximately equal to the width of the groove 4a formed on the upper surface of the base 4.

[0034] Furthermore, the table cover 30 is provided with dustproof and splashproof covers 32 that can be extended and retracted along the X-axis direction on both the front and rear sides. In addition, a rectangular prism-shaped support structure 34 is provided on the upper surface of the base 4 in the area located behind the groove 4a.

[0035] The front of this support structure 34 is provided with a Z-axis movement mechanism 36 that can adjust the distance between the chuck table 24 and the grinding wheel 62, which will be described later. This Z-axis movement mechanism 36 has a pair of guide rails 38, each extending along the Z-axis direction.

[0036] A slider 40 is provided on the front side of each of the pair of guide rails 38 in a manner that allows it to slide along the Z-axis direction (see Figure 2). The front end of the slider 40 is fixed to the rear side of the rectangular parallelepiped Z-axis moving plate 42. Furthermore, a screw shaft 44 extending along the Z-axis direction is positioned between the pair of guide rails 38.

[0037] A pulse motor 46 for rotating the screw shaft 44 is connected to the upper end of the screw shaft 44. A nut 48 for housing a number of balls that circulate in accordance with the rotation of the screw shaft 44 is provided on the outer surface of the screw shaft 44 where the screw threads are formed, thus forming a ball screw.

[0038] Furthermore, the nut 48 is fixed to the rear side of the Z-axis moving plate 42. Therefore, when the screw shaft 44 is rotated by the pulse motor 46, the Z-axis moving plate 42 moves along the Z-axis direction together with the nut 48.

[0039] A grinding unit 50 is provided on the front side of the Z-axis moving plate 42. This grinding unit 50 has a cylindrical holding member 52 fixed to the front surface of the Z-axis moving plate 42. Inside the holding member 52, a cylindrical spindle housing 54 is provided that extends along the Z-axis direction.

[0040] Furthermore, a cylindrical spindle 56 extending along the Z-axis direction is provided inside the spindle housing 54 (see Figure 2). This spindle 56 is supported by the spindle housing 54 in a rotatable manner, and its upper end (base end) is connected to a rotational drive source 58 such as a motor.

[0041] Furthermore, the lower end (tip) of the spindle 56 is exposed from the spindle housing 54 and forms a disc-shaped wheel mount 60. An annular grinding wheel 62, having an outer diameter approximately equal to the diameter of the wheel mount 60, is attached to the underside of the wheel mount 60 using fixing members (not shown), such as bolts.

[0042] The grinding wheel 62 has a plurality of grinding wheels 62a and a wheel base 62b having a lower surface on which the plurality of grinding wheels 62a are arranged in a circular, discrete manner. When the rotation drive source 58 is operated, the wheel mount 60 and the grinding wheel 62 rotate together with the spindle 56, with the rotation axis being a straight line along the Z-axis.

[0043] The multiple grinding wheels 62a each contain abrasive grains such as diamond or cBN dispersed in a bonding material such as a vitrified bond or resin bond. The wheel base 62b is made of a metal material such as stainless steel or aluminum.

[0044] Furthermore, a grinding water supply nozzle is provided near the grinding wheel 62. This grinding water supply nozzle supplies a liquid (grinding water) such as pure water to the processing point at a predetermined flow rate when grinding the workpiece 11 with multiple grinding wheels 62a.

[0045] Furthermore, a measuring unit 64 is provided on the upper surface of the base 4, in an area located to the side of the groove 4a and close to the grinding unit 50. This measuring unit 64 has, for example, a pair of height gauges 64a and 64b that measure the height of the position where each measuring probe makes contact.

[0046] The measuring probe of the height gauge 64a is positioned to contact, for example, the back surface 13b of the wafer 13 included in the workpiece 11 held in the chuck table 24. Alternatively, the measuring probe of the height gauge 64b is positioned to contact, for example, the holding surface 24a of the chuck table 24 (specifically, the upper surface of the side wall of the frame 26).

[0047] Then, prior to or during grinding the back surface 13b of the wafer 13, the thickness of the workpiece 11 can be measured in the measuring unit 64 by arranging the measuring probes of each height gauge 64a, 64b in this manner.

[0048] Figure 3 is a schematic flowchart illustrating an example of a workpiece grinding method for grinding a workpiece 11 in the grinding apparatus 2. In this method, first, the workpiece 11 is held on the holding surface 24a of the chuck table 24 (holding step: S1).

[0049] Specifically, the workpiece 11 is placed into the chuck table 24 so that the protective tape 15 is facing downwards and the center of the lower surface of the workpiece 11 (the lower surface of the protective tape 15) aligns with the center of the holding surface 24a of the chuck table 24. Then, a suction force is applied to the workpiece 11 by operating a suction source that communicates with a flow path formed in the bottom wall of the frame 26 of the chuck table 24.

[0050] As a result, the workpiece 11 elastically deforms to conform to the holding surface 24a of the chuck table 24. That is, the workpiece 11 deforms to correspond to the side surface of a cone, and the holding surface 24a of the chuck table 24 is covered by the workpiece 11. Consequently, the workpiece 11 is held on the holding surface 24a of the chuck table 24.

[0051] After this holding step (S1), the workpiece 11 is ground by operating the Z-axis movement mechanism 36 so that multiple grinding wheels 62a come into contact with the workpiece 11 while rotating both the chuck table 24 and the spindle 56 (grinding step: S2).

[0052] In this grinding step (S2), first, the X-axis movement mechanism 6 (specifically, the pulse motor 14) is operated to adjust the position of the chuck table 24 so that the trajectories of the multiple grinding wheels 62a when the spindle 56 is rotated overlap with the workpiece 11 in the Z-axis direction.

[0053] In this adjustment, for example, the center and outer circumference of the holding surface 24a of the chuck table 24 are connected by the shortest distance, and the line segment perpendicular to the Z-axis direction is superimposed in the Z-axis direction with the trajectories of the multiple rotating grinding wheels 62a.

[0054] In other words, the coordinates of the line segment and the coordinates of the trajectory are superimposed on a coordinate plane (XY coordinate plane) perpendicular to the Z-axis direction. Therefore, if necessary, the tilt adjustment mechanism may be operated to adjust the tilt of the chuck table 24 prior to this adjustment.

[0055] Next, the measuring probe of the height gauge 64a is positioned to contact the upper surface of the workpiece 11 (the back surface 13b of the wafer 13), and the measuring probe of the height gauge 64b is positioned to contact the upper surface of the side wall of the frame 26 of the chuck table 24.

[0056] At this time, the measuring unit 64 measures the thickness of the workpiece 11 at the start of the grinding step (S2). Furthermore, the measurement of the thickness of the workpiece 11 by the measuring unit 64 is continued throughout the grinding step (S2).

[0057] Next, while rotating both the chuck table 24 and the spindle 56, the Z-axis movement mechanism 36 (specifically, the pulse motor 14) is operated to bring the upper surface of the workpiece 11 into contact with the lower surfaces of the multiple grinding wheels 62a, thereby bringing the chuck table 24 and the grinding wheel 62 closer together, that is, lowering the grinding wheel 62.

[0058] Furthermore, when the lower surfaces of multiple grinding wheels 62a come into contact with the upper surface of the workpiece 11, the current supplied to the rotational drive source 58 for rotating the spindle 56 increases, and the grinding load applied to the chuck table 24 and grinding wheel 62 also increases. Therefore, by detecting this current or grinding load, the timing of contact between the lower surfaces of the multiple grinding wheels 62a and the upper surface of the workpiece 11 can be determined.

[0059] Furthermore, grinding water is supplied to the contact interface between the lower surfaces of the multiple grinding wheels 62a and the upper surface of the workpiece 11 from a grinding water supply nozzle located near the grinding wheel 62. When the lower surfaces of the multiple grinding wheels 62a come into contact with the upper surface of the workpiece 11, grinding of the workpiece 11 begins.

[0060] Figure 4 is a schematic flowchart illustrating an example of the operation when grinding the workpiece 11. Figure 5 is a schematic graph illustrating the change over time of the grinding load applied to the chuck table 24 and grinding wheel 62 via the workpiece 11 when grinding the workpiece 11.

[0061] When grinding the workpiece 11, first, the chuck table 24 and the grinding wheel 62 are brought closer together (approach step: S21). Specifically, the Z-axis movement mechanism 36 is operated to lower the grinding wheel 62 at a predetermined grinding feed rate (for example, 0.1 μm / s to 0.5 μm / s, typically 0.3 μm / s).

[0062] Here, in the initial stages of the approach step (S21) (T0-T1 shown in Figure 5), the grinding feed rate is greater than the rate at which the thickness of the workpiece 11 removed by grinding decreases. In this case, the grinding load also increases over time. On the other hand, as the grinding load increases, this rate of decrease also increases.

[0063] Then, when the grinding load reaches L1, which is the grinding load at which this rate of decrease equals the grinding feed rate, the grinding load hardly changes from L1. The approach step (S21) ends, for example, when the thickness of the workpiece 11 measured by the measuring unit 64 reaches a predetermined thickness (T2 shown in Figure 5).

[0064] After the approach step (S21), the chuck table 24 and the grinding wheel 62 are separated while maintaining contact between the multiple grinding wheels 62a and the workpiece 11 (separation step: S22).

[0065] Specifically, the Z-axis movement mechanism 36 is operated to slightly raise the grinding wheel 62 at a predetermined retraction speed (for example, 0.5 μm / s to 1.5 μm / s, typically 1.0 μm / s) within the range in which the workpiece 11 rises following the multiple grinding wheels 62a due to springback.

[0066] In the separation step (S22), the grinding load decreases over time. The separation step (S22) ends, for example, when the grinding load decreases to L2, which is less than 1 / 3 of L1 (T3 shown in Figure 5).

[0067] After the separation step (S22), the movement of the Z-axis movement mechanism 36 is stopped (stop step: S23). This causes a spark-out process to occur, in which the workpiece 11 is ground while reducing the grinding load.

[0068] The stopping step (S23) then ends, for example, when the grinding load decreases to less than 1 / 5 of L2 or when a predetermined period of time has elapsed (T4 shown in Figure 5). With this, the grinding of the workpiece 11 in the grinding device 2 is completed.

[0069] Once grinding of the workpiece 11 is complete, the rotation of both the chuck table 24 and the spindle 56, as well as the supply of grinding water from the grinding water supply nozzle, are stopped, and the Z-axis movement mechanism 36 is operated to separate the chuck table 24 from the grinding wheel 62, that is, to raise the grinding wheel 62.

[0070] Next, the measuring probe of the height gauge 64a is moved away from the upper surface of the workpiece 11, and the operation of the suction source, which communicates with the flow path formed in the bottom wall of the frame 26 of the chuck table 24, is stopped. Then, the ground workpiece 11 is removed from the chuck table 24.

[0071] In the workpiece grinding method described above, prior to the stop step (S23) in which spark-out occurs, a separation step (S22) is performed in which the Z-axis movement mechanism 36 is operated to separate the chuck table 24 and the grinding wheel 62 while maintaining contact between the multiple grinding wheels 62a and the workpiece 11.

[0072] Furthermore, in the separation step (S22), the grinding load applied to the chuck table 24 and the grinding wheel 62 is reduced. Therefore, in this method, the time required to complete the spark-out is shortened compared to when the separation step (S22) is not performed, and it is possible to suppress the prolongation of the time required to grind the workpiece 11.

[0073] It should be noted that the above description represents only one aspect of the present invention, and the present invention is not limited to the above description. For example, the structure of the grinding apparatus used in the present invention is not limited to the structure of the grinding apparatus 2 described above. Specifically, the grinding apparatus of the present invention may be provided with a Z-axis movement mechanism for moving the chuck table 24 along the Z-axis direction, and an X-axis movement mechanism for moving the grinding unit 50 along the X-axis direction.

[0074] Furthermore, the structures and methods of the embodiments described above can be modified as appropriate without departing from the scope of the present invention. [Explanation of Symbols]

[0075] 2: Grinding equipment 4: Base (4a: Groove) 6:X-axis direction movement mechanism 8: Guide rail 10: X-axis movement plate 11: Workpiece 12: Screw shaft 13: Wafer (13a: Front side, 13b: Back side) 14: Pulse motor 15: Protective tape 16: Nut 18: Driven pulley 20: Movable axis 22: Table base 24: Chuck table (24a: Holding surface) 26: Frame 28: Porous plate 30: Table cover 32: Dustproof and splashproof cover 34: Support structure 36: Z-axis direction movement mechanism 38: Guide rail 40: Slider 42: Z-axis movement plate 44: Screw shaft 46: Pulse motor 48: Nut 50: Grinding Unit 52: Retaining member 54: Spindle Housing 56: Spindle 58: Rotary drive source 60: Wheel Mount 62: Grinding wheel (62a: Grinding wheel, 62b: Wheel base) 64: Measuring unit (64a, 64b: Height gauge)

Claims

1. A grinding apparatus comprising a chuck table rotatable about a straight line passing through the center of the holding surface as the axis of rotation, a spindle with an annular grinding wheel having multiple grinding wheels arranged in a circular pattern attached to its tip, and a moving mechanism capable of adjusting the distance between the chuck table and the grinding wheel, wherein a method for grinding a workpiece is provided for grinding the workpiece, A holding step of holding the workpiece on the holding surface of the chuck table, The apparatus further comprises a grinding step, in which, after the holding step, the moving mechanism is operated to bring the workpiece into contact with the plurality of grinding wheels while rotating both the chuck table and the spindle, thereby grinding the workpiece. The grinding step is, An approach step in which the moving mechanism is operated to bring the chuck table and the grinding wheel closer together so that the workpiece is ground while the chuck table and the grinding wheel are pressing against each other through the workpiece, Following the approach step, a separation step is performed to move the moving mechanism to separate the chuck table and the grinding wheel, while maintaining contact between the multiple grinding wheels and the workpiece, thereby reducing the grinding load applied to the chuck table and the grinding wheel. The process includes, after the separation step, a stopping step which stops the movement of the moving mechanism so that the workpiece is ground while reducing the grinding load, A method for grinding a workpiece, wherein the timing for ending the separation step and the timing for ending the stopping step are determined according to the current supplied to a rotational drive source for rotating the spindle or the grinding load.

2. The grinding load at the time the approach step is completed is a first value, The separation step is terminated when the grinding load decreases to a second value less than 1 / 3 of the first value. The method for grinding a workpiece according to claim 1, wherein the stopping step is terminated when the grinding load decreases to a third value less than 1 / 5 of the second value.

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