Grinding method of workpiece

Abstract

To provide a grinding method of a workpiece, capable of grinding a surface of a workpiece having a transparent member on its upper surface side while measuring an upper surface height of the workpiece by optically non-contact manner.SOLUTION: A grinding method of grinding an upper surface of a workpiece W having a SiO2 layer (transparent member) F on its upper surface side includes: a holding step of holding the workpiece W on a chuck table 10 while directing the SiO2 layer F upward; a damaging step of damaging the upper surface by bringing a damaging whetstone 25b1 into contact with the upper surface of the workpiece W and rotating; after the damaging step, a grinding step of removing the scratches formed on the upper surface of the workpiece W by grinding the upper surface of the workpiece W until the upper surface becomes a prescribed height by using a grinding whetstone 25b2 while measuring the upper surface height of the workpiece W by projecting measurement light L1 to the SiO2 layer F from above the workpiece W using a non-contact height measuring apparatus 50 and receiving reflected light L2 reflected from the upper surface of the workpiece W.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a method for grinding a workpiece, which grinds the top surface of a workpiece having a transparent member on its top surface side or a workpiece entirely made of a transparent member. [Background technology]

[0002] In recent years, bonded wafers (stacked wafers or composite wafers) such as SOI (Silicon On Insulator) substrates that can realize high integration, low power consumption, high speed, high reliability, etc. of semiconductor devices have been put to practical use (see, for example, Patent Documents 1 and 2). For example, an SOI substrate is made by bonding two silicon wafers together with a SiO2 layer interposed between them as an insulating layer.

[0003] Specifically, an SOI substrate is obtained by forming a SiO2 layer on the top surface of one wafer by a method such as plasma CVD, grinding and polishing the surface of the SiO2 layer, placing another wafer on the surface of the SiO2 layer and bonding the two together by a method such as fusion bonding, and finally grinding both wafers to a specified thickness.

[0004] Here, when grinding the SiO2 layer formed on the upper surface of the support wafer before bonding the support wafer and the wafer to be ground with the SiO2 layer interposed therebetween, the probes of a contact type thickness measuring device (height gauge) are brought into contact with the upper surface of the SiO2 layer of the support wafer held on the chuck table and the holding surface of the chuck table, respectively, and the thickness of the support wafer including the SiO2 layer is calculated from the difference between the upper surface height of the SiO2 layer measured by these probes and the height of the holding surface of the chuck table, and the upper surface of the SiO2 layer is ground until this thickness reaches a predetermined thickness. However, if the probe is brought into contact with the upper surface of the SiO2 layer to measure the height on the upper surface, contact marks remain on the upper surface of the SiO2 layer, which may lead to a decrease in performance of the SOI substrate. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2018-056459 A [Patent Document 2] JP 2023-083605 A Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, when grinding the top surface of the SiO2 layer, it is possible to optically measure the top surface height of the SiO2 layer without contact, but this poses the problem that the top surface height of the SiO2 layer cannot be measured because the measurement light is not reflected by the transparent top surface of the SiO2 layer.

[0007] The present invention has been made in consideration of the above-mentioned problems, and its object is to provide a method for grinding a workpiece that can grind the surface of a workpiece while optically and non-contact measuring the top surface height of a workpiece having a transparent member on its upper surface side or a workpiece that is entirely made of a transparent member. [Means for solving the problem]

[0008] In order to achieve the above-mentioned object, the present invention provides a method for grinding a workpiece, in which the top surface of a workpiece having a transparent member on its upper surface side or a workpiece entirely made of a transparent member is ground with a grinding wheel, and is characterized by comprising a holding step in which the workpiece is held on a chuck table with the surface to be ground facing up, and a grinding step in which the top surface height of the workpiece is measured with a non-contact height measuring device and the workpiece is ground with the grinding wheel until the top surface height reaches a predetermined height. Effect of the Invention

[0009] According to the present invention, a scratching grindstone is brought into contact with the transparent member or the top surface of a workpiece entirely made of a transparent material formed on the top surface of the workpiece held on the chuck table in the holding step, and scratches the top surface in the subsequent scratching step, so that the measurement light emitted from the non-contact height measuring device is reflected by the top surface of the transparent member (the workpiece entirely made of a transparent material). Therefore, the top surface height of the transparent member or the workpiece entirely made of a transparent material can be optically measured in a non-contact manner by the non-contact height measuring device that receives the light reflected by the top surface of the transparent member (or the workpiece entirely made of a transparent material).

[0010] Then, in the next grinding step, the transparent member (or the workpiece entirely made of a transparent member) can be ground with a grinding wheel until the top surface height of the transparent member (or the workpiece entirely made of a transparent member) reaches a predetermined height while scratches on the top surface of the transparent member (or the workpiece entirely made of a transparent member) are removed with a grinding wheel, while the top surface height of the transparent member (or the workpiece entirely made of a transparent member) reaches a predetermined height, while a probe of a contact height measuring device is brought into contact with the holding surface of the chuck table, and the thickness of the workpiece including the transparent member or the workpiece entirely made of a transparent member is measured based on the difference between the height of the holding surface measured by the contact height measuring device and the top surface height of the transparent member measured in a non-contact manner, while the top surface of the transparent member or the workpiece entirely made of a transparent member is ground with a grinding wheel until the thickness of the workpiece reaches a predetermined thickness.

[0011] Therefore, according to the present invention, it is possible to obtain the effect of grinding the surface of a workpiece while optically measuring the top surface height of a workpiece having a transparent member on its upper surface side or a workpiece entirely made of a transparent member in a non-contact manner. [Brief description of the drawings]

[0012] [Figure 1] 1 is a perspective view of a workpiece to be ground by the method of the present invention; [Diagram 2] 2 is a cross-sectional view taken along line AA in FIG. 1. [Diagram 3] 1 is a flowchart showing the steps of the method of the present invention. [Figure 4] 1 is a perspective view of a grinding apparatus for carrying out a method of the present invention; [Diagram 5] FIG. 4 is a partial vertical sectional view showing a holding step in the method of the present invention. [Figure 6] FIG. 4 is a partial vertical cross-sectional view showing a top surface height measuring step in the method of the present invention. [Figure 7] FIG. 2 is a partial vertical sectional view showing a scratching step in the method of the present invention. [Figure 8] FIG. 2 is a partial vertical sectional view showing a grinding step (before the grinding wheel comes into contact with the upper surface of the workpiece) in the method of the present invention. [Figure 9] FIG. 2 is a partial vertical sectional view showing a grinding step (a state in which a grinding wheel is grinding an upper surface of a workpiece) in the method of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0014] The grinding method according to the present embodiment is a method for grinding an SiO2 layer F of a work (support wafer) W having a transparent SiO2 layer (insulating layer) F formed on its surface during the manufacturing process of an SOI substrate. Here, as shown in Figs. 1 and 2, the work W is constructed by forming an SiO2 layer F as an insulating layer on the upper surface of a thin, disk-shaped support wafer W1 by a plasma CVD method or the like, and a tape T is attached to its lower surface. The support wafer W1 is constructed of, for example, single crystal silicon (Si).

[0015] [Grinding equipment configuration] Next, the configuration of a grinding device 1 for carrying out the method of the present invention will be described below with reference to Fig. 3. Fig. 3 is a perspective view of the grinding device 1, and in the following description, the directions of the arrows shown in Fig. 3 are the X-axis direction (left-right direction), the Y-axis direction (front-back direction), and the Z-axis direction (up-down direction), respectively.

[0016] That is, the grinding apparatus 1 has as its main components a chuck table 10 that holds the workpiece W, a grinding mechanism 20 that grinds the workpiece W held on the chuck table 10, a lifting mechanism 30 that moves the grinding mechanism 20 up and down in a direction perpendicular to the holding surface of the chuck table 10 (Z-axis direction), a contact height gauge 40 that measures the thickness of the workpiece W, a non-contact height gauge 50 that optically measures the height of the top surface of the workpiece W (SiO layer F) in a non-contact manner, and a control unit 60.

[0017] Next, the configurations of the main components of the grinding apparatus 1, that is, the chuck table 10, the grinding mechanism 20, the lifting mechanism 30, the contact height measuring device 40, the non-contact height measuring device 50, and the control unit 60 will be described.

[0018] (Chuck table) The chuck table 10 is a disk-shaped member, and as shown in FIG. 5, a disk-shaped porous member 10A is assembled in the center of a metal frame 11. Here, the porous member 10A is made of porous ceramics or the like, and its upper surface constitutes a holding surface that suction-holds the disk-shaped workpiece W. As shown in FIG. 5, the porous member 10A of the chuck table 10 is connected to a suction source 13 such as a vacuum pump via a pipe 12, and an electromagnetic (solenoid) on-off valve V is provided on the pipe 12. Here, the on-off valve V is electrically connected to a control unit 60, and its opening and closing operation is controlled by the control unit 60. Therefore, the on-off valve V is opened and closed by the control unit 60, so that the porous member 10A of the chuck table 10 is selectively connected to the suction source 13.

[0019] As shown in FIG. 5, the chuck table 10 is supported horizontally by a rotating shaft 10a whose center is vertical, and the rotating shaft 10a is rotated by an electric motor (not shown) which serves as a rotational drive source, thereby causing the chuck table 10 to rotate at a predetermined speed around the axial center of the rotating shaft 10a.

[0020] 3, the grinding device 1 has a rectangular box-shaped base 2 that is long in the Y-axis direction (front-back direction), and a chuck table 10 faces a rectangular opening 2a that is long in the Y-axis direction and opens on the top surface of the base 2. The periphery of the chuck table 10 at the opening 2a is covered by a rectangular plate-shaped cover 3, and the front and rear (-Y and +Y directions) parts of the cover 3 at the opening 2a are respectively covered by bellows-shaped expandable covers 4 and 5 that move and expand together with the cover 3.

[0021] (Grinding mechanism) The grinding mechanism 20 includes a spindle motor 22 housed in a holder 21, a vertical spindle 23 rotated around its axis by the spindle motor 22, a disk-shaped mount 24 attached to the lower end of the spindle 23, and a grinding wheel 25 detachably attached to the lower surface of the mount 24. Here, the grinding wheel 25 is composed of a disk-shaped base 25a and a plurality of grinding wheels 25b, which are processing tools arranged in an annular shape and attached to the lower surface of the base 25a. The grinding wheels 25b are rectangular block-shaped processing tools for grinding the workpiece W, and their lower surfaces form a grinding surface that contacts the upper surface (surface to be ground) of the workpiece W. The spindle motor 22 is electrically connected to a control unit 60, and its operation (rotation / stop and rotation speed) is controlled by the control unit 60.

[0022] (Lifting mechanism) The lifting mechanism 30 lifts and lowers the grinding mechanism 20 in a direction perpendicular to the holding surface of the chuck table 10 (Z-axis direction), and is disposed on the -Y-axis direction end face (front face) of a rectangular box-shaped column 6 vertically erected on the +Y-axis direction end face (rear end face) of the upper surface of the base 2. The lifting mechanism 30 lifts and lowers a rectangular plate-shaped lifting plate 31 attached to the back face of the holder 21 of the grinding mechanism 20, together with the holder 21 and the spindle 23 and grinding wheel 25 held by the holder 21, in the Z-axis direction along a pair of left and right guide rails 32. Here, the pair of left and right guide rails 32 are disposed perpendicular to the front face of the column 6 and parallel to each other.

[0023] Between the pair of left and right guide rails 32, a rotatable ball screw 33 is vertically installed along the Z-axis direction (up-down direction), and the upper end of the ball screw 33 is connected to a servo motor 34, which is a drive source and can rotate forward and backward. Here, the servo motor 34 is attached in a vertical state to the column 6 via a rectangular plate-shaped bracket 35 attached to the upper surface of the column 6. The lower end of the ball screw 33 is rotatably supported by the column 6, and a nut member (not shown) that is horizontally protrudes backward (in the +Y-axis direction) from the back surface of the lift plate 31 is screwed into the ball screw 33. The servo motor 34 is electrically connected to the control unit 60, and its operation (rotation / stop, rotation speed, etc.) is controlled by the control unit 60.

[0024] Therefore, by starting the servo motor 34 and rotating the ball screw 33 forward and backward, the lifting plate 31, to which a nut member (not shown) that screws into the ball screw 33 is attached, moves up and down together with the grinding mechanism 20 along a pair of guide rails 32, so that the grinding mechanism 20 rises and falls and the grinding amount (grinding allowance) of the grinding wheel 25b on the workpiece W is adjusted.

[0025] (Contact height measuring device and non-contact height measuring device) The contact height measuring device 40 is a height gauge for measuring the thickness of the workpiece W held on the chuck table 10, and includes a first probe 41 that contacts the top surface of the workpiece W and a second probe 42 that contacts the top surface of the frame 11 of the chuck table 10 (a surface at the same height as the top surface of the holding surface). Here, in the contact height measuring device 40, the top surface height of the workpiece W is measured by the first probe 41, and the thickness of the workpiece W is obtained from the difference between the top surface height of the workpiece W measured by the first probe 41 and the top surface height of the frame 11 of the chuck table 10 measured by the second probe 42. The contact height measuring device 40 is electrically connected to the control unit 60, and when detection signals of the first probe 41 and the second probe 42 of the contact height measuring device 40 are transmitted to the control unit 60, the control unit 60 calculates the thickness of the workpiece W based on these detection signals.

[0026] On the other hand, the non-contact height measuring device 50 measures the height of the top surface of the SiO2 layer F of the workpiece W in a non-contact optical manner, and is disposed above the holding surface of the chuck table 10. As shown in Figures 8 and 9, the non-contact height measuring device 50 is equipped with a light-projecting unit (not shown) that projects measurement light L1 toward the top surface of the SiO2 layer F of the workpiece W held on the chuck table 10, and a light-receiving unit (not shown) that receives reflected light L2 reflected by the top surface of the SiO2 layer F.

[0027] As shown in FIG. 3, the non-contact height measuring device 50 is attached to the tip of an arm 52 extending horizontally from the upper end of a rotatable vertical rotation shaft 51. As the rotation shaft 51 rotates, the non-contact height measuring device 50 rotates together with the arm 52 within a horizontal plane, and can move horizontally between the measurement position (the center position of the workpiece W) shown in FIG. 3 and a retracted position outside the chuck table 10 from the measurement position.

[0028] (Control unit) The control unit 60 controls each of the components constituting the grinding device 1, and includes a CPU (Central Processing Unit) that performs arithmetic processing according to a control program, and memories such as a ROM (Read Only Memory) and a RAM (Random Access Memory). In particular, in this embodiment, as described later, the control unit 60 functions to control the operation of the spindle motor 22 of the grinding mechanism 20 and the servo motor 34 of the lifting mechanism 30 based on the thickness of the workpiece W measured by the contact height measuring device 40 and the top surface height of the workpiece W (SiO2 layer F) measured by the non-contact height measuring device 50.

[0029] [Workpiece grinding method] Next, a grinding method according to the present invention, which is performed on the workpiece W configured as above, will be described. As shown in FIG. 4, the grinding method includes the following steps: 1) Holding process 2) Top surface height measurement process 3) Scratching process 4) Grinding process The above steps are carried out in this order to grind the upper surface of the SiO2 layer F until the workpiece W has a predetermined thickness. Here, 1) the holding step, 2) the upper surface height measuring step, 3) the scratching step, and 4) the grinding step in the method of the present invention will be described below with reference to Figs.

[0030] 1) Holding process: The holding process is a process of holding the workpiece W on the holding surface of the chuck table 10. In this holding process, as shown in FIG. 5, the workpiece W is placed on the holding surface of the chuck table 10 with the SiO2 layer (transparent member) F facing up (with the tape T facing down). From this state, when the control unit 60 (see FIG. 3) opens the on-off valve V and connects the porous member 10A of the chuck table 10 to the suction source 13 via the piping 12, the porous member 10A is suctioned by the suction source 13, generating a negative pressure in the porous member 10A. Then, the workpiece W is sucked and held on the holding surface of the chuck table 10 by the negative pressure generated in the porous member 10A. In this holding process, the chuck table 10 and the workpiece W held thereon are not rotating but are stationary.

[0031] 2) Top surface height measurement process: The top surface height measuring process is a process of measuring the top surface height of the workpiece W held on the chuck table 10 by the contact height measuring device 40. In this top surface height measuring process, as shown in Fig. 6, the first probe 41 of the contact height measuring device 40 contacts the top surface of the workpiece W (SiO2 layer F), and the second probe 42 contacts the top surface of the frame 11 of the chuck table 10. In this state, the top surface height of the workpiece W (SiO2 layer F) is measured by the first probe 41, and the signal is transmitted to the control unit 60. Note that, even in this top surface height measuring process, the chuck table 10 and the workpiece W and grinding wheel 25 held thereon are stationary without rotating.

[0032] 3) Scratching process: The scratching process is a process of scratching the top surface of the workpiece W (SiO2 layer F) held on the chuck table 10. In this scratching process, as shown in Fig. 7, the chuck table 10 and the workpiece W held thereon are rotated at a predetermined speed in the direction of the arrow in the figure, while the scratching grindstone 15b1 rotating in the direction of the arrow in the figure is rotated in contact with the top surface of the workpiece W (SiO2 layer F), thereby scratching the top surface of the workpiece W (SiO2 layer F). The size of this scratch depends on the size of the abrasive grains of the scratching grindstone 25b1, but is set to a size that allows the SiO2 layer F, which is a transparent member, to reflect the measurement light L1.

[0033] In this scratching step, the control unit 60 controls the lifting mechanism 30 to position the lower surface (grinding surface) of the scratching grindstone 25b1 at the upper surface height of the workpiece W (SiO2 layer F) measured by the first probe 41 of the contact height measuring device 40 in the upper surface height measuring step, which is the previous step, and scratches the upper surface of the workpiece W (SiO2 layer F) with the scratching grindstone 25b1. In this scratching step, as shown in FIG. 7, the first probe 41 of the contact height measuring device 40 is separated from the upper surface of the workpiece W (SiO2 layer F) and does not contact the upper surface of the workpiece W (SiO2 layer F). Therefore, no contact marks due to the contact of the first probe 41 are left on the upper surface of the workpiece W (SiO2 layer F).

[0034] 4) Grinding process: The grinding process is a process for removing scratches made on the upper surface of the SiO2 layer F in the previous scratching process by grinding. Specifically, in this grinding process, as shown in FIG. 8, the non-contact height measuring device 50 projects a measurement light L1 from above the workpiece W toward the SiO2 layer F, which is a transparent member, and receives the reflected light L2 reflected by the SiO2 layer F to measure the upper surface height of the workpiece W (SiO2 layer F), while grinding the upper surface of the workpiece W (SiO2 layer F) with the grinding wheel 25b2 until the upper surface reaches a predetermined height, thereby removing the scratches made on the upper surface of the SiO2 layer F in the scratching process. Here, the abrasive grains of the grinding wheel 25b2 are smaller in roughness than the abrasive grains of the scratching wheel 25b1. In other words, since the upper surface of the SiO2 layer F is scratched by the grinding wheel 25b2, the non-contact height measuring device 50 can measure the upper surface height of the SiO2 layer F even in the grinding process.

[0035] Thus, as shown in FIG. 8, when the top surface height of the workpiece W (SiO2 layer F) is optically measured in a non-contact manner using the non-contact height measuring device 50, the top surface of the workpiece W (SiO2 layer F) is scratched by grinding with the scratching grindstone 25b1 in the previous scratching process, and therefore the measurement light L1 emitted from the non-contact height measuring device 50 toward the top surface of the SiO2 layer F, which is a transparent member, is reflected by the scratched top surface of the SiO2 layer F, and the reflected light L2 is received by the non-contact height measuring device 50, making it possible to measure the top surface height of the workpiece W (SiO2 layer F) using the non-contact height measuring device 50.

[0036] Meanwhile, when grinding the upper surface of the workpiece W (SiO2 layer F) with the grinding wheel 25b2, the control unit 60 calculates the thickness of the workpiece W including the SiO2 layer F based on the difference between the upper surface height (height of the holding surface) of the frame 11 of the chuck table 10 measured by the second probe 42 of the contact height measuring device 40 and the upper surface height of the workpiece W (SiO2 layer F) measured by the non-contact height measuring device 50, and adjusts the amount of descent of the grinding wheel 25b2 by lowering the lifting mechanism 30 in the direction of the arrow (downward) in Figure 8, i.e., the amount of grinding of the upper surface of the SiO2 layer F by the grinding wheel 25b2, and continues grinding the workpiece W (SiO2 layer F) with the grinding wheel 25b2 until the thickness of the workpiece W including the SiO2 layer F reaches a predetermined value (or until the upper surface height of the SiO2 layer F reaches a predetermined height).

[0037] As described above, according to the present invention, in the holding step, the SiO2 layer F, which is a transparent member formed on the upper surface of the workpiece W held on the chuck table 10, is brought into contact with the scratching grindstone 25b1 in the subsequent scratching step to scratch the upper surface of the SiO2 layer F, so that the measurement light L1 emitted from the non-contact height measuring device 50 is reflected on the surface of the SiO2 layer F. Therefore, even if the SiO2 layer F is a transparent member, the upper surface height of the SiO2 layer F can be optically measured in a non-contact manner by the non-contact height measuring device 50 that receives the reflected light L2 reflected on the surface.

[0038] Then, in the next grinding step, the SiO2 layer F can be ground by the grinding wheel 25b2 until the upper surface height of the SiO2 layer F reaches a predetermined height while the upper surface height of the SiO2 layer F is measured in a non-contact manner by the non-contact height measuring device 50 and scratches on the upper surface of the SiO2 layer F are ground and removed by the grinding wheel 25b2. At this time, the second probe 42 of the contact height measuring device 40 is brought into contact with the upper surface of the frame 11 of the chuck table 10, and the upper surface of the SiO2 layer F can be ground by the grinding wheel 25b2 until the thickness of the workpiece W including the SiO2 layer F reaches a predetermined thickness while the thickness of the workpiece W is measured based on the difference between the height of the holding surface of the chuck table 10 measured by the second probe 42 and the upper surface height of the SiO2 layer F measured in a non-contact manner by the non-contact height measuring device 50.

[0039] Therefore, according to the present invention, it is possible to obtain an effect that the workpiece W having the SiO2 layer F, which is a transparent member, on its upper surface side can be ground while the thickness of the workpiece W is being measured in a non-contact manner.

[0040] Although the above describes a method for grinding a workpiece W (one of the workpieces constituting an SOI substrate) having a SiO2 layer F as a transparent member on its upper surface, the present invention is similarly applicable to other workpieces having any transparent member other than a SiO2 layer F on their surface side.

[0041] In the above embodiment, the method for grinding the workpiece W having a SiO2 layer F on the upper surface side has been described, but the present invention can also be applied to a workpiece entirely made of a transparent material such as glass. In this case, the upper surface of the workpiece is scratched in the scratching step, and the scratches on the upper surface of the workpiece can be removed by grinding while the height of the upper surface of the workpiece is optically measured in a non-contact manner in the subsequent grinding step.

[0042] The non-contact height measuring device 50 is not limited to one that uses light. The non-contact height measuring device 50 may be one that does not use light, such as a back pressure sensor or an ultrasonic sensor. When using a non-contact height measuring device 50 that does not use light in this way, the scratching step in the above embodiment can be made unnecessary.

[0043] In addition, the present invention is not limited to the application of the embodiments described above, and various modifications are possible within the scope of the claims and the technical ideas described in the specification and drawings. [Explanation of symbols]

[0044] 1: grinding device, 2: base, 2a: opening of base, 3: cover, 4, 5: expandable cover, 6: column, 10: chuck table, 10A: porous member, 10a: rotating shaft, 11: frame, 12: piping, 13: suction source, 20: grinding mechanism, 21: holder, 22: spindle motor, 23: spindle, 24: mount, 25: grinding wheel, 25a: base, 25b: grinding wheel, 25b1: scratching wheel, 25b2: grinding wheel, 30: lifting mechanism, 31: lifting plate, 32: guide rail, 33: ball screw, 34: servo motor, 35: bracket, 40: contact height measuring device, 41: first probe, 42: second probe, 50: non-contact height measuring device, 51: rotation axis, 52: arm, 60: control unit, F: SiO2 (transparent member), L1: measurement light, L2: reflected light, T: tape, V: Opening and closing valve, W: Workpiece, W1: Support wafer

Claims

1. A method for grinding a workpiece, comprising the steps of: grinding an upper surface of a workpiece having a transparent member on an upper surface side thereof or an upper surface of a workpiece entirely made of a transparent member with a grinding wheel, comprising: a holding step of holding the workpiece on a chuck table with the surface to be ground facing up; a grinding step of grinding the workpiece with the grinding wheel while measuring the top surface height of the workpiece with a non-contact height measuring device until the top surface height reaches a predetermined height.

2. a scratching step of scratching the entire top surface of the workpiece with a scratching grindstone before the grinding step; and a grinding step of removing the scratches made on the top surface of the workpiece by grinding the top surface of the workpiece with the grinding grindstone until the top surface reaches a predetermined height, while measuring the top surface height of the workpiece by projecting measurement light from above the workpiece toward the transparent member using the non-contact height measuring device and receiving the light reflected from the top surface of the workpiece.

2. The method for grinding a workpiece according to claim 1, comprising:

3. a top surface height measuring step of measuring a top surface height of the workpiece held on the chuck table by a contact height measuring device before the scratching step; 3. A method for grinding a workpiece according to claim 2, wherein in said scratching step, a lower surface of said scratching grindstone is positioned at the height of the upper surface of said workpiece measured in said upper surface height measuring step, and said scratching grindstone scratches the upper surface of said workpiece.

4. 4. The method for grinding a workpiece according to claim 3, wherein in the grinding process, a thickness of the workpiece is calculated from a difference between the height of the top surface of the workpiece measured by the non-contact height measuring device and the height of the holding surface of the chuck table measured by the contact height measuring device.

5. The transparent member is formed on the upper surface of the silicon member. ２ The SiO layer of the workpiece ２ 5. The method for grinding a workpiece according to claim 1, wherein an upper surface of the layer is ground.

6. 2. The method for grinding a workpiece according to claim 1, wherein the workpiece entirely made of the transparent member is any one of quartz glass, SiC, sapphire, and diamond.

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