Grinding method for workpieces

Abstract

To provide a work-piece grinding method that can correctly make a work-piece to a finished thickness.SOLUTION: A distance between a chuck table and a grinding wheel, which approach each other in association with spring back during spark-out (fourth grinding step) is grasped prior to spark-out. By this, the spark-out is started when a thickness of a work-piece reaches a finished thickness plus the distance, whereby the work-piece can be correctly made to the finished thickness.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a method for grinding a workpiece, in which both a chuck table for holding the workpiece and a grinding wheel are rotated, and the chuck table and the grinding wheel are approximated by a moving mechanism capable of adjusting the distance between the chuck table and the grinding wheel until a finish thickness is reached, and the workpiece is 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 dividing a workpiece including a wafer or the like on which a plurality of devices are formed on the surface side into regions each including an individual device.

[0003] This workpiece may be thinned prior to its division for the purpose of miniaturizing the chips to be manufactured. As a method for thinning the workpiece, grinding can be mentioned. Grinding is generally performed while measuring the thickness of the workpiece until the thickness of the workpiece reaches a desired thickness (see, for example, Patent Document 1).

[0004] Specifically, grinding is performed by rotating both a chuck table for holding the workpiece and a grinding wheel, and approaching the two by a moving mechanism capable of adjusting the distance between the chuck table and the grinding wheel. That is, this grinding is performed by pressing the two against each other while both the chuck table for holding the workpiece and the grinding wheel are rotating.

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

[0006] Specifically, spark-out is achieved by rotating both the chuck table that holds the workpiece and the grinding wheel, while stopping the movement of the moving mechanism when the workpiece and the grinding wheel are in contact.

[0007] In this case, a so-called springback occurs, where the force pressing the chuck table and grinding wheel against each other via the workpiece decreases, and the distance between them shrinks. 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. 2000-6018 [Patent Document 2] Japanese Patent Publication No. 2003-236736 [Overview of the project] [Problems that the invention aims to solve]

[0009] When spark-out occurs, the thickness of the workpiece becomes smaller than the thickness at the time the movement mechanism stops. In this case, it may become difficult to grind the workpiece to the desired finish thickness. In view of this, the object of the present invention is to provide a workpiece grinding method that can accurately finish the workpiece to the desired thickness. [Means for solving the problem]

[0010] According to the present invention, a method for grinding a workpiece is provided, wherein the chuck table that holds the workpiece and the grinding wheel are rotated together, and the distance between the chuck table and the grinding wheel is adjusted by a moving mechanism, and the workpiece is ground until the finished thickness is achieved, comprising a holding step of holding the workpiece with the chuck table, and after the holding step, the chuck table is rotated at a first rotational speed and the grinding wheel is rotated at a second rotational speed, while the chuck table and the grinding wheel are moved closer together A first grinding step involves operating the moving mechanism to bring the chuck table and the grinding wheel closer together at a predetermined moving speed, thereby grinding the workpiece until it reaches a predetermined thickness greater than the finished thickness, with the chuck table and the grinding wheel pressed against each other via the workpiece. After the first grinding step, the chuck table is rotated at a first rotational speed and the grinding wheel is rotated at a second rotational speed, and the operation of the moving mechanism is stopped while the workpiece and the grinding wheel are in contact, thereby allowing the chuck table and the grinding wheel to move together via the workpiece. A second grinding step in which the workpiece is ground for a predetermined period of time while reducing the force with which the chuck table and grinding wheel press against each other; a measuring step in which the thickness of the workpiece is measured after the second grinding step; a calculation step in which the distance between the chuck table and the grinding wheel in the second grinding step is calculated by subtracting the thickness of the workpiece measured in the measuring step from the predetermined thickness; and a final calculation step in which the chuck table is rotated at the first rotational speed and the grinding wheel is rotated at the second rotational speed. A third grinding step in which the chuck table and the grinding wheel are brought closer together at a predetermined speed, and the chuck table and the grinding wheel are pressed against each other through the workpiece, and the workpiece is ground until it reaches a thickness equal to the finished thickness plus the distance, and after the third grinding step, the chuck table is rotated at the first rotational speed and the grinding wheel is rotated at the second rotational speed, and the operation of the moving mechanism is stopped while the workpiece and the grinding wheel are in contact,A method for grinding a workpiece is provided, comprising: a fourth grinding step of grinding the workpiece for a predetermined period of time while reducing the force with which the chuck table and the grinding wheel press against each other through the workpiece. [Effects of the Invention]

[0011] In this invention, the distance between the chuck table and the grinding wheel, which approaches each other due to springback during the spark-out (fourth grinding step), is determined prior to the spark-out. As a result, in this invention, by starting the spark-out when the thickness of the workpiece reaches the finished thickness plus the distance, it is possible to accurately finish the workpiece to its final thickness. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a schematic perspective view showing an example of a grinding apparatus. [Figure 2] Figure 2 is a schematic cross-sectional view showing an example of a grinding apparatus. [Figure 3] Figure 3 is a schematic functional block diagram showing an example of a control unit built into a grinding machine. [Figure 4] Figure 4 is a flowchart schematically showing an example of a workpiece grinding method. [Modes for carrying out the invention]

[0013] 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 cross-sectional view showing an example of the grinding apparatus shown in Figure 1. Note that the X-axis direction (front-back direction) and Y-axis direction (left-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 a direction perpendicular to the X-axis direction and the Y-axis direction (vertical direction).

[0014] 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.

[0015] This X-axis movement mechanism 6 has a pair of guide rails 8, each extending along the X-axis direction. A rectangular parallelepiped X-axis movement plate 10 is attached to the upper side of the pair of guide rails 8 in a manner that allows it to slide along the X-axis direction. A screw shaft 12 extending along the X-axis direction is positioned between the pair of guide rails 8.

[0016] A pulse motor 14 for rotating the screw shaft 12 is connected to the rear end of the screw shaft 12. A nut 16 for housing a number of balls that circulate in accordance with the rotation of the screw shaft 12 is provided on the outer surface of the screw shaft 12 where the screw threads are formed, thus forming a ball screw.

[0017] Furthermore, the nut 16 is fixed to the lower side of the X-axis moving plate 10. Therefore, when the screw shaft 12 is rotated by the pulse motor 14, the X-axis moving plate 10 moves along the X-axis direction together with the nut 16. On top of the X-axis moving plate 10, there is a rotating body to which a driven pulley 18 is connected at its lower end, and a rotational drive source (not shown), such as a motor, is connected to a driving pulley (not shown).

[0018] Furthermore, an endless belt (not shown) is stretched between the driven pulley 18 and the driving pulley. In addition, a tilt adjustment mechanism is provided on the X-axis moving plate 10, which has one fixed shaft (not shown) and two movable shafts 20 whose lengths are variable along their respective Z-axis directions. The fixed shaft and the two movable shafts 20 are connected to the lower side of the table base 22, supporting the table base 22.

[0019] A through hole (not shown) is formed in the center of the table base 22, and a rotating body having a driven pulley 18 connected to its lower end is passed through the through hole. And the upper end of this rotating body is connected to the lower surface side of the disk-shaped chuck table 24. Therefore, when an operation is performed on a rotational drive source connected to a driving pulley so as to rotate an endless belt stretched over the driven pulley 18, the chuck table 24 rotates along the circumferential direction of the chuck table 24.

[0020] Also, the chuck table 24 is supported by the table base 22 via a bearing (not shown). Therefore, even if the chuck table 24 is rotated as described above, the table base 22 does not rotate. On the other hand, when the lengths of the respective two movable shafts 20 in the Z-axis direction are adjusted in the tilt adjustment mechanism, not only the table base 22 but also the tilt of the chuck table 24 is adjusted.

[0021] The chuck table 24 has a disk-shaped frame body 26 made of ceramics or the like. This frame body 26 has a disk-shaped bottom wall and a cylindrical side wall standing from this bottom wall. That is, on the upper surface side of the frame body 26, a disk-shaped recess defined by the bottom wall and the side wall is formed.

[0022] Note that the inner diameter of the side wall of the frame body 26 is slightly shorter than the diameter of the workpiece 11 described later, and its outer diameter is slightly longer than the diameter of the workpiece 11. Further, a flow path (not shown) that opens on the bottom surface of the recess is formed in the bottom wall of the frame body 26, and this flow path communicates with a suction source (not shown) such as an ejector.

[0023] Furthermore, a disk-shaped porous plate 28 having a diameter approximately equal to the diameter of the recess formed on the upper surface side of the frame body 26 is fixed to the recess. This porous plate 28 is made of, for example, porous ceramics. Also, the upper surface of the porous plate 28 and the upper surface of the side wall of the frame body 26 have a shape corresponding to the side surface of a cone (a shape in which the center protrudes more than the outer circumference).

[0024] 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).

[0025] 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, for example, made of a semiconductor material such as silicon and has a wafer 13 on its surface 13a side with multiple devices formed thereon.

[0026] 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.

[0027] 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. In addition, a dustproof and splashproof cover 32 that can be extended and retracted along the X-axis is provided on the front and rear of the table cover 30.

[0028] Furthermore, a rectangular prism-shaped support structure 34 is provided in the area of ​​the upper surface of the base 4 located behind the groove 4a. A Z-axis direction movement mechanism 36 is provided on the front of this support structure 34. This Z-axis direction movement mechanism 36 has a pair of guide rails 38, each extending along the Z-axis direction. 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).

[0029] Furthermore, the front end of the slider 40 is fixed to the rear side of the rectangular parallelepiped Z-axis moving plate 42. In addition, a screw shaft 44 extending along the Z-axis direction is positioned between a pair of guide rails 38. A pulse motor 46 for rotating the screw shaft 44 is connected to the upper end of the screw shaft 44.

[0030] Furthermore, a nut 48 is provided on the outer surface of the screw shaft 44 where the screw threads are formed, housing a number of balls that circulate in accordance with the rotation of the screw shaft 44, thus forming a ball screw. 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.

[0031] 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.

[0032] 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 is connected to a rotational drive source 58 such as a motor.

[0033] Furthermore, the lower end of the spindle 56 is exposed from the spindle housing 54 and fixed to 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 lower surface of the wheel mount 60 using fixing members (not shown), such as bolts.

[0034] 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.

[0035] The multiple grinding wheels 62a each contain abrasive grains such as diamond or cBN dispersed in a binder such as a vitrified bond or resin bond. The wheel base 62b is made of a metal material such as stainless steel or aluminum.

[0036] 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.

[0037] 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.

[0038] The measuring probe of the height gauge 64a can be positioned to contact 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 can be positioned to contact the holding surface 24a of the chuck table 24 (specifically, the upper surface of the side wall of the frame 26).

[0039] Therefore, by arranging the measuring probes of each height gauge 64a, 64b in this manner prior to or during grinding of the back surface 13b side of the wafer 13, the thickness of the workpiece 11 can be measured in the measuring unit 64.

[0040] Furthermore, the grinding device 2 incorporates a control unit that controls the components described above. Figure 3 is a schematic functional block diagram showing an example of a control unit incorporated in the grinding device 2. The control unit 66 shown in Figure 3 has a processing unit 68 and a storage unit 70.

[0041] The processing unit 68 is composed of a processor such as a CPU (Central Processing Unit). The storage unit 70 is composed of volatile memory such as DRAM (Dynamic Random Access Memory) or SRAM (Static Random Access Memory) and non-volatile memory such as an SSD (Solid State Drive) (NAND flash memory) or an HDD (Hard Disk Drive) (magnetic storage device).

[0042] The memory unit 70 stores various types of information (data, programs, etc.) used in the processing unit 68. For example, the memory unit 70 stores the initial thickness (T1) of the workpiece 11 before grinding and the finished thickness (T2) of the workpiece 11.

[0043] Furthermore, the processing unit 68 reads and executes various programs stored in the storage unit 70 to control the components of the grinding device 2. This processing unit 68 includes, for example, a drive unit 72 and a calculation unit 74.

[0044] The drive unit 72 controls the movement or rotation of the components of the grinding device 2. Specifically, the drive unit 72 controls the X-axis movement mechanism 6 (specifically, the pulse motor 14), the Z-axis movement mechanism 36 (specifically, the pulse motor 46), the tilt adjustment mechanism (specifically, the movable shaft 20), the rotational drive source that rotates the chuck table 24, and the rotational drive source 58 that rotates the grinding wheel 62.

[0045] The calculation unit 74 calculates the distance between the chuck table 24 and the grinding wheel 62 as they approach each other due to the springback during spark-out. The specific method for calculating this distance will be described later.

[0046] Figure 4 is a schematic flowchart illustrating an example of a workpiece grinding method in which the workpiece 11 is ground in the grinding apparatus 2 from its initial thickness (T1) to its finished thickness (T2).

[0047] In this method, first, the workpiece 11 is held by the chuck table 24 (holding step: S1). Specifically, the workpiece 11 is brought onto the holding surface 24a of the chuck table 24 so that the protective tape 15 is facing downwards, and then the suction source communicating with the porous plate 28 of the chuck table 24 is activated.

[0048] Next, the workpiece 11 is ground while the chuck table 24 and the grinding wheel 62 are pressed against each other via the workpiece 11 (first grinding step: S2). Specifically, first, the tilt adjustment mechanism (specifically, the movable axis 20) is operated so that the line segment connecting the highest point on the outer circumference of the holding surface of the chuck table 24 and the center of the holding surface is perpendicular to the Z-axis direction.

[0049] Next, in a plan view, the X-axis movement mechanism is operated so that the trajectories of the multiple grinding wheels 62a when the grinding wheel 62 is rotated coincide with one end and the other end of the line segment described above. Then, the rotational drive source connected to the above-mentioned drive pulley is operated so that the chuck table 24 rotates at a first rotational speed (for example, 100 rpm to 700 rpm, typically 300 rpm), and the rotational drive source 58 connected to the upper end of the spindle 56 is operated so that the grinding wheel 62 rotates at a second rotational speed (for example, 1000 rpm to 7000 rpm, typically 4000 rpm).

[0050] Next, without changing the rotational speed of each, the Z-axis movement mechanism 36 is operated to move the chuck table 24 and the grinding wheel 62 closer together at a predetermined movement speed (for example, 0.1 μm / s to 0.6 μm / s, typically 0.3 μm / s) while both the chuck table 24 and the grinding wheel 62 are rotating.

[0051] As a result, the lower surfaces of the multiple rotating grinding wheels 62a come into contact with the back surface 13b of the rotating wafer 13, and the chuck table 24 and the grinding wheel 62 are pressed against each other via the workpiece 11. Consequently, the back surface 13b of the wafer 13 is ground by the multiple grinding wheels 62a.

[0052] Furthermore, prior to or during grinding the back surface 13b of the wafer 13, the measuring probes of the height gauge 64a and height gauge 64b are brought into contact with the back surface 13b of the wafer 13 and the upper surface of the side wall of the frame 26, respectively, so that the thickness of the workpiece 11 can be measured by the measuring unit 64.

[0053] Then, if the thickness of the workpiece 11 measured by the measuring unit 64 is greater than a predetermined thickness (T3) (step (S3): NO), grinding of the back surface 13b of the wafer 13 is continued. In this first grinding step (S2), for example, the workpiece 11 is ground so that at least 1 / 3 of the amount of grinding of the workpiece 11 (thickness obtained by subtracting the finish thickness (T2) from the initial thickness (T1)) remains.

[0054] In other words, this predetermined thickness (T3) is, for example, smaller than the initial thickness (T1) and greater than the sum of the initial thickness (T1) and twice the finished thickness (T2) multiplied by 1 / 3 (T1>T3>(T1+2×T2) / 3). This predetermined thickness is stored in the memory unit 70 of the control unit 66.

[0055] Then, when the thickness of the workpiece 11 measured by the measuring unit 64 reaches a predetermined thickness (T3) (step (S3): YES), the workpiece 11 is ground for a predetermined period of time while reducing the force with which the chuck table 24 and the grinding wheel 62 press against each other through the workpiece 11 (second grinding step: S4).

[0056] Specifically, without changing their respective rotational speeds, the chuck table 24 and the grinding wheel 62 are kept rotating, and the Z-axis movement mechanism 36 is stopped while the workpiece 11 and the grinding wheel 62 are in contact. In other words, when the thickness of the workpiece 11 measured by the measuring unit 64 reaches a predetermined thickness (T3), the spark-out process, which is performed at the end of grinding the workpiece 11, is executed.

[0057] In this second grinding step (S4), a so-called springback occurs, in which the force pressing the chuck table 24 and the grinding wheel 62 against each other via the workpiece 11 decreases, and the distance between them becomes smaller. When springback occurs, the back surface 13b of the wafer 13 is ground, and when the springback is substantially complete, the back surface 13b of the wafer 13 is substantially no longer ground.

[0058] Furthermore, the second grinding step (S4) is carried out until the springback is substantially completed, that is, until the back surface 13b of the wafer 13 is substantially no longer ground. In other words, the predetermined period mentioned above is the period until the springback is substantially completed, that is, the period until the back surface 13b of the wafer 13 is substantially no longer ground.

[0059] In the second grinding step (S4), the measuring probe of the height gauge 64a may be separated from the back surface 13b of the wafer 13, or it may remain in contact with it. Separating the measuring probe is preferable because it prevents contact marks from remaining on the back surface 13b of the wafer 13 after the second grinding step (S4). On the other hand, remaining in contact is preferable because it simplifies the operation of the grinding apparatus 2.

[0060] Next, the thickness of the workpiece 11 is measured (measurement step: S5). Specifically, prior to or after the second grinding step (S4), the measuring probes of the height gauge 64a and 64b are brought into contact with the back surface 13b of the wafer 13 and the upper surface of the side wall of the frame 26, respectively. As a result, the thickness (T4) of the workpiece 11 after the second grinding step (S4) is measured by the measuring unit 64.

[0061] Next, in the second grinding step (S4), the distance (D) between the approaching chuck table 24 and the grinding wheel 62 is calculated (calculation step: S6). Specifically, this distance (D) is calculated by subtracting the thickness (T4) of the workpiece 11 measured in the measurement step (S5) from the predetermined thickness (T3) (D = T3 - T4). Furthermore, this distance (D) can be described as the distance between the approaching chuck table 24 and the grinding wheel 62 due to the springback during spark-out.

[0062] The measurement step (S5) and the calculation step (S6) may be performed with both the chuck table 24 and the grinding wheel 62 rotating, or with both rotations stopped. Furthermore, the measurement step (S5) and the calculation step (S6) may be performed with the workpiece 11 and the grinding wheel 62 in close proximity, or after operating the Z-axis movement mechanism 36 to move them apart.

[0063] Next, the workpiece 11 is ground while the chuck table 24 and the grinding wheel 62 are pressed against each other via the workpiece 11 (third grinding step: S7). Specifically, similar to the first grinding step (S2) described above, the Z-axis movement mechanism 36 is operated so that the chuck table 24 and the grinding wheel 62 are brought closer together at a predetermined moving speed while the chuck table 24 is rotated at a first rotational speed and the grinding wheel 62 is rotated at a second rotational speed.

[0064] Furthermore, prior to or during the third grinding step (S7), the measuring probes of the height gauge 64a and 64b are brought into contact with the back surface 13b of the wafer 13 and the upper surface of the side wall of the frame 26, respectively, so that the thickness of the workpiece 11 is measured by the measuring unit 64.

[0065] Then, if the thickness of the workpiece 11 measured by the measuring unit 64 is greater than the thickness obtained by adding the above distance (D) to the finished thickness (T2) (T2+D) (step (S8): NO), grinding of the back surface 13b of the wafer 13 is continued.

[0066] On the other hand, when the thickness of the workpiece 11 measured by the measuring unit 64 reaches the specified thickness (T2+D) (step (S8): YES), the workpiece 11 is ground while reducing the force with which the chuck table 24 and the grinding wheel 62 press against each other via the workpiece 11 until a predetermined period of time has elapsed (fourth grinding step: S9).

[0067] Specifically, similar to the second grinding step (S4) described above, the operation of the Z-axis movement mechanism 36 is stopped while the chuck table 24 and the grinding wheel 62 are rotating without changing their respective rotational speeds, and the workpiece 11 and the grinding wheel 62 are in contact. In other words, spark-out is performed when the thickness of the workpiece 11 measured by the measuring unit 64 reaches the specified thickness (T2 + D).

[0068] Furthermore, it is preferable that the measuring probe of the height gauge 64a is separated from the back surface 13b of the wafer 13 during the fourth grinding step (S4). This prevents contact marks from the measuring probe from remaining on the back surface 13b of the wafer 13 after the fourth grinding step (S4).

[0069] Furthermore, the above distance (D) is the distance between the chuck table 24 and the grinding wheel 62 that approaches each other due to the springback during spark-out, as described above. Therefore, the thickness of the workpiece 11 after the fourth grinding step (S9) becomes the finished thickness (T2).

[0070] In the method shown in Figure 4, the distance (D) between the chuck table 24 and the grinding wheel 62, which approaches each other due to springback during the spark-out (fourth grinding step (S4)), is determined prior to the spark-out. This makes it possible to accurately finish the workpiece 11 to the final thickness (T2) by starting the spark-out when the thickness of the workpiece 11 reaches the final thickness (T2) plus the distance (D).

[0071] 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, in the present invention, there are no limitations on the movement mechanism for relatively moving the chuck table 24 and the grinding wheel 62. For example, in the present invention, instead of the X-axis movement mechanism 6 and the Z-axis movement mechanism 36, a Z-axis movement mechanism for moving the chuck table 24 in the Z-axis direction and an X-axis movement mechanism for moving the grinding wheel 62 in the X-axis direction may be provided.

[0072] Furthermore, in the present invention, there are no limitations on the measuring unit for measuring the thickness of the workpiece 11. For example, in the grinding apparatus of the present invention, a measuring unit for measuring the thickness of the workpiece 11 in a non-contact manner may be provided instead of the measuring unit 64.

[0073] 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]

[0074] 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) 66: Control Unit 68: Processing Unit 70: Storage section 72: Drive unit 74: Calculation Section

Claims

[Claim 1] A method for grinding a workpiece, comprising rotating both the chuck table that holds the workpiece and the grinding wheel, and using a moving mechanism that can adjust the distance between the chuck table and the grinding wheel to bring the chuck table and the grinding wheel closer together, thereby grinding the workpiece until the desired thickness is achieved, A holding step of holding the workpiece with the chuck table, A first grinding step is performed in which, after the holding step, the chuck table is rotated at a first rotational speed and the grinding wheel is rotated at a second rotational speed, and the moving mechanism is operated to bring the chuck table and the grinding wheel closer together at a predetermined moving speed, thereby grinding the workpiece until it reaches a predetermined thickness greater than the finished thickness, with the chuck table and the grinding wheel pressed against each other through the workpiece. A second grinding step is performed after the first grinding step, in which the chuck table is rotated at the first rotational speed and the grinding wheel is rotated at the second rotational speed, and the operation of the moving mechanism is stopped while the workpiece and the grinding wheel are in contact, thereby reducing the force pressing the chuck table and the grinding wheel against each other through the workpiece, and grinding the workpiece until a predetermined period of time has elapsed. Following the second grinding step, a measuring step is performed to measure the thickness of the workpiece. A calculation step is performed to calculate the distance between the chuck table and the grinding wheel approaching in the second grinding step by subtracting the thickness of the workpiece measured in the measurement step from the predetermined thickness. A third grinding step is performed in which, after the calculation step, the chuck table is rotated at the first rotational speed and the grinding wheel is rotated at the second rotational speed, and the moving mechanism is operated to bring the chuck table and the grinding wheel closer together at the predetermined moving speed, thereby grinding the workpiece until the thickness is the finished thickness plus the distance, with the chuck table and the grinding wheel pressed against each other through the workpiece. A fourth grinding step is performed after the third grinding step, in which the chuck table is rotated at the first rotational speed and the grinding wheel is rotated at the second rotational speed, and the operation of the moving mechanism is stopped while the workpiece and the grinding wheel are in contact, thereby reducing the force with which the chuck table and the grinding wheel press against each other through the workpiece, and grinding the workpiece until the predetermined period of time has elapsed. A method for grinding a workpiece, comprising the following components.

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