Grinding method, method for calculating residual amount of cutting edge, and grinding device

Abstract

Provided is a method for grinding a substrate held by a substrate holding part of a grinding device having a plurality of substrate holding parts and a grinding wheel. The method includes: grinding an Nth (N ≥ 1) substrate with the grinding wheel; grinding an N+1th substrate with the grinding wheel; and adjusting the reference position of the grinding wheel. When adjusting the reference position, the method determines whether the substrate holding part holding the Nth substrate and the substrate holding part holding the N+1th substrate are the same or not. When the substrate holding part holding the Nth substrate is different from the substrate holding part holding the N+1th substrate, an error in top surface height between the different substrate holding parts is taken into consideration. When the substrate holding part holding the Nth substrate is the same as the substrate holding part holding the N+1th substrate, the error in top surface height is not taken into consideration.

Description

Grinding method, cutting edge remaining amount calculation method, and grinding device

[0001] The present disclosure relates to a grinding method, a method for calculating a cutting edge remaining amount, and a grinding device.

[0002] Patent Document 1 discloses a grinding machine that grinds wafers with a grinding wheel. The grinding machine controls a spindle feed mechanism to move the grinding wheel closer to the wafer by an amount corresponding to the amount of wear of the grinding wheel, which is calculated by subtracting the amount of grinding of the wafer from the amount of displacement of the spindle relative to the processed wafer.

[0003] Patent Document 2 discloses a method for adjusting the heights of multiple chuck tables in a grinding machine that has multiple chuck tables for holding workpieces. The adjustment method includes the steps of measuring the height of each chuck table, setting the lowest of the measured values ​​thus obtained as a reference value, and grinding the surfaces of the chuck tables other than the chuck table for which the reference value has been set while measuring their heights until the reference value is reached.

[0004] Japanese Patent Publication No. 2019-155488 Japanese Patent Publication No. 2000-354962

[0005] The technology according to the present disclosure appropriately controls the position of a grinding wheel when grinding a substrate with the grinding wheel.

[0006] One aspect of the present disclosure is a method for grinding a substrate held by a substrate holding part in a grinding device having a plurality of substrate holding parts and grinding wheels, the method including: grinding an Nth substrate (N≧1) with the grinding wheel; grinding an N+1th substrate with the grinding wheel; and adjusting a reference position of the grinding wheel; when adjusting the reference position, determining whether the substrate holding parts holding the Nth substrate and the N+1th substrate are the same, and if the substrate holding part holding the Nth substrate and the substrate holding part holding the N+1th substrate are different, taking into account an error in top surface height between the different substrate holding parts; and if the substrate holding part holding the Nth substrate and the substrate holding part holding the N+1th substrate are the same, not taking into account the error in top surface height.

[0007] According to the present disclosure, the position of the grinding wheel can be appropriately controlled when grinding a substrate with the grinding wheel.

[0008] FIG. 1 is a plan view showing an outline of the configuration of a grinding apparatus according to this embodiment; FIG. 2 is a side view showing an example of the configuration of a grinding unit and a chuck; FIG. 3 is a flow chart showing a series of wafer processing steps performed on a single wafer in the grinding apparatus; FIG. 4 is a flow chart showing a series of wafer processing steps performed successively on a plurality of wafers in the grinding apparatus; FIG. 5 is an explanatory diagram showing the state of grinding processing in the grinding unit; FIG. 6 is an explanatory diagram explaining a method of calculating a setup position; FIG. 7 is an explanatory diagram explaining an error in upper surface height that occurs between chucks; FIG. 8 is an explanatory diagram showing the state of updating the setup position; and FIG. 9 is an explanatory diagram explaining another method of calculating the setup position.

[0009] In the manufacturing process of semiconductor devices, semiconductor substrates (hereinafter referred to as wafers) are subjected to a grinding process to thin the wafers. This wafer grinding is performed, for example, by lowering a grinding wheel while rotating it, and bringing the grinding wheel into contact with the wafer held by a chuck.

[0010] When grinding a wafer, the reference position of the grinding wheel relative to the chuck, for example, the setup position, is adjusted to uniformly control the thickness of the processed wafer. The setup position is adjusted so that the position of the bottom surface (grinding surface) of the grinding wheel coincides with the position of the top surface of the chuck or is a predetermined distance away from the position of the top surface of the chuck. During this process, the grinding wheel wears and thins as the wafer is repeatedly ground. Therefore, as in the grinding machine disclosed in Patent Document 1, for example, it is necessary to control the spindle feed mechanism to move the grinding wheel closer to the wafer by the amount of wear, and update the setup position.

[0011] Furthermore, when multiple chuck tables are arranged as disclosed in Patent Document 2, the heights of the chuck tables relative to the grinding wheel must be the same in order to uniformly control the thickness of the wafer being processed.

[0012] However, even when an operation is performed to align the heights of the chuck tables as in the method disclosed in Patent Document 2, a minute error on the order of several μm may actually occur in the height position of each chuck table. Furthermore, before the wafer grinding process, chuck grinding may be performed to improve the parallelism between the grinding surface of the grinding wheel and the upper surface (holding surface) of the chuck, but this chuck grinding may also cause a minute error in the height of each chuck table.

[0013] These minute errors in the height of each chuck table have not been taken into consideration in conventional semiconductor device manufacturing processes, and they may cause problems due to the recent trend toward higher performance and miniaturization of semiconductor devices. Specifically, there is concern that minute errors in the height of each chuck table will cause minute errors in the setup position described above, making it impossible to control the thickness of the processed wafer uniformly. Therefore, there is room for improvement in conventional wafer grinding methods.

[0014] The technology disclosed herein has been developed in consideration of the above circumstances, and appropriately controls the position of a grinding wheel when grinding a substrate with the grinding wheel. Hereinafter, a grinding device and a grinding method according to this embodiment will be described with reference to the drawings. Note that in this specification and the drawings, elements having substantially the same functional configuration are designated by the same reference numerals, and redundant description will be omitted. Note that in the technology disclosed herein, "grinding" of a wafer W includes so-called "polishing." Therefore, although the following description will be given using a "grinding device" as an example, the technology disclosed herein may also be applied to a "polishing device."

[0015] 1, a grinding apparatus 1 grinds and thins a wafer W as a substrate. The wafer W is a semiconductor wafer such as a silicon wafer or a compound semiconductor wafer. The wafer W to be ground has a front surface Wa and a back surface Wb opposite the front surface Wa. The grinding apparatus 1 performs a grinding process on each of the front surface Wa and the back surface Wb.

[0016] The grinding apparatus 1 has a configuration in which a loading / unloading station 2 and a processing station 3 are integrally connected. In the loading / unloading station 2, for example, a cassette C capable of accommodating a plurality of wafers W is loaded and unloaded between the loading / unloading station 2 and the outside. The processing station 3 is equipped with various processing devices that perform desired processing on the wafers W.

[0017] A cassette mounting table 10 is provided in the loading / unloading station 2. A wafer transfer area 20 is provided adjacent to the cassette mounting table 10 on the positive side of the Y axis.

[0018] The wafer transfer area 20 is provided with a wafer transfer device 22 that is configured to be freely movable on the transfer path 21. The wafer transfer device 22 has a transfer fork 23 that holds and transfers the wafer W. The wafer transfer device 22 is configured to be able to transfer the wafer W to the cassette C on the cassette mounting table 10, an alignment unit 50 (described later), and a first cleaning unit 70 (described later).

[0019] In the processing station 3, processing such as grinding and cleaning is performed on the wafer W. The processing station 3 includes a transfer unit 30 that transfers the wafer W, a grinding unit 40 that performs a grinding process on the wafer W, an alignment unit 50 that adjusts the horizontal orientation of the wafer W, an inversion unit 60 that inverts the front and back surfaces of the wafer W, and a first cleaning unit 70 and a second cleaning unit 80 that clean the wafer W after grinding. In one example, the alignment unit 50 and the first cleaning unit 70 are stacked, and the inversion unit 60 and the second cleaning unit 80 are stacked, but the arrangement of these various devices can be determined as desired.

[0020] The transfer unit 30 is an articulated robot equipped with a plurality of, for example, three, arms 31. Each of the three arms 31 is configured to be freely rotatable. A transfer pad 32 that suction-holds the wafer W is attached to the arm 31 at the tip end. The arm 31 at the base end is attached to an elevating mechanism 33 that vertically raises and lowers the arm 31. The transfer unit 30 is configured to be able to transfer the wafer W to and from transfer positions A1 and A2 of the grinding unit 40, the alignment unit 50, the reversing unit 60, the first cleaning unit 70, and the second cleaning unit 80, which will be described later.

[0021] The grinding unit 40 has a rotary table 41. On the rotary table 41, four chucks 42a to 42d (hereinafter, these may be collectively referred to as "chucks 42") are provided for suction-holding the wafer W. A porous chuck, for example, is used as the chucks 42. The surface of the chuck 42, i.e., the surface for holding the wafer W, has a convex shape in which the center protrudes compared to the edges in a side view. Note that although the protrusion of the center of the chuck 42 is very small, this protrusion is exaggerated in the drawings used in the following explanation for clarity of explanation.

[0022] As shown in FIG. 2 , four chucks 42 serving as substrate holders are held by corresponding chuck bases 43. The chuck bases 43 are provided with tilt adjustment units 44 that adjust the relative tilt of the chucks 42 with respect to a first grinding unit 90 or a second grinding unit 100 (described later). The tilt adjustment units 44 have a fixed shaft 45 provided on the underside of the chuck bases 43 and multiple, for example, two, lift shafts 46. Each lift shaft 46 is configured to be extendable and retractable, and raises and lowers the chuck bases 43. The tilt adjustment units 44 tilt the chucks 42 and chuck bases 43 by vertically raising and lowering the other end of the chuck bases 43 using the lift shafts 46, starting from one end of the outer periphery of the chuck bases 43 (a position corresponding to the fixed shaft 45). This makes it possible to adjust the relative inclination between the grinding surface of the first grinding unit 90 or the second grinding unit 100 at processing positions B1 and B2 (described later) and the surface (holding surface) of the chuck 42. Note that the configuration of the inclination adjustment unit 44 is not limited to this, and it is sufficient if it can adjust the relative angle (parallelism) of the surface (holding surface) of the chuck 42 with respect to the grinding surface of each grinding unit.

[0023] 1, the four chucks 42a to 42d can be moved to delivery positions A1, A2 and processing positions B1, B2 by rotation of the rotary table 41. Furthermore, each of the four chucks 42a to 42d is configured to be rotatable about a vertical axis by a rotation mechanism (not shown).

[0024] At the transfer positions A1 and A2, the wafer W is transferred between the transfer unit 30 and the chuck 42. At the transfer positions A1 and A2, a thickness measurement unit 110 is provided to measure the thickness of the wafer W before or after grinding at the processing positions B1 and B2. The thickness measurement unit 110 measures the thickness of the wafer W at multiple points, for example, three points equally spaced in the radial direction (the center point, the outer periphery point, and the midpoint between the center point and the outer periphery point of the wafer W). The thickness measurement unit 110 may have any configuration, but may include, for example, a non-contact sensor (not shown) and a calculation unit (not shown).

[0025] In this embodiment, the thickness measuring unit 110 is provided at the transfer positions A1 and A2, but the location of the thickness measuring unit 110 is not limited to this. For example, the thickness measuring unit 110 may be provided at the processing positions B1 and B2, or may be provided independently from the grinding unit 40.

[0026] A first grinding unit 90 is disposed at the processing position B1. A second grinding unit 100 is disposed at the processing position B2. The first grinding unit 90 and the second grinding unit 100 each grind the wafer W held by the chuck 42.

[0027] As shown in FIG. 2 , the first grinding unit 90 includes an annular grinding stone 91, a grinding wheel 92 equipped with the grinding stone 91, a mount 93 supporting the grinding wheel 92, a spindle 94 that rotates the grinding wheel 92 via the mount 93, and a drive unit 95 that supports the spindle 94. The grinding stone 91 has a grinding surface 91 a on its underside. The drive unit 95, which serves as a movement mechanism, incorporates, for example, a motor (not shown) and rotates the spindle 94. As shown in FIG. 1 , the first grinding unit 90 is configured to be movable vertically along a support 96 by the drive unit 95. In this embodiment, the first grinding unit 90 measures the position of the grinding stone 91 during the grinding process, as described below, using a position measurement unit (not shown) that measures the Z-axis position of the motor of the drive unit 95. The position measurement unit may directly detect, for example, the underside (grinding surface) of the grinding stone 91, the underside of the grinding wheel 92, or the underside of the mount 93. Furthermore, for example, the position measurement unit may measure the boundary position between the lower surface of the mount 93 and the upper surface of the grinding wheel 92 .

[0028] The grinding wheel 92 is detachable from the mount 93. By removing the grinding wheel 92 from the mount 93 in this manner, the grinding stone 91 that has worn down due to grinding the wafer W can be replaced, as will be described later.

[0029] Also provided at the processing position B1 is a thickness measuring unit 97 that measures the thickness of the wafer W. The thickness measuring unit 97 may have any configuration, but may include, for example, a non-contact sensor (not shown) and a calculation unit (not shown).

[0030] The second grinding unit 100 has the same configuration as the first grinding unit 90. That is, as shown in Fig. 2, the second grinding unit 100 has an annular grinding stone 101, a grinding wheel 102, a mount 103, a spindle 104, a drive unit 105 as a movement mechanism, a position measurement unit (not shown), a support 106, and a thickness measurement unit 107. The grinding stone 101 has a grinding surface 101a on its underside. The grinding wheel 102 is configured to be detachable from the mount 103.

[0031] As described above, the holding surface of the chuck 42 has a convex shape. Therefore, when the wafer W is ground using the first grinding unit 90 or the second grinding unit 100, a portion of the annular grinding wheels 91, 101 comes into contact with the wafer W. More specifically, the annular grinding wheels 91, 101 come into contact with the wafer W in an arc-shaped manner from the center to the outer peripheral edge. By rotating the chuck 42 and the grinding wheels 92, 102 in this state, the entire surface of the wafer W is ground.

[0032] The grinding apparatus 1 described above is provided with a control unit 120. The control unit 120 is, for example, a computer equipped with a CPU, memory, etc., and has a program storage unit (not shown). The program storage unit stores programs for controlling various operations performed using the grinding apparatus 1. The programs may be recorded on a computer-readable storage medium H and installed from the storage medium H into the control unit 120. The storage medium H may be temporary or non-temporary.

[0033] The grinding device 1 according to this embodiment is configured as described above, but the embodiment disclosed herein should be considered to be illustrative in all respects and not restrictive. The above embodiment may be omitted, substituted, or modified in various ways without departing from the scope and spirit of the appended claims.

[0034] For example, in the above embodiment, a so-called two-axis grinding unit 40 having two grinding units (first grinding unit 90 and second grinding unit 100) in the grinding apparatus 1 is employed. However, the configuration of the grinding unit 40 is not limited thereto. Specifically, the grinding unit 40 may have a single-axis configuration having only one grinding unit, or a three-axis configuration having three grinding units for sequentially performing rough grinding, medium grinding, and finish grinding. Even in the case of a two-axis configuration as shown in the figure, the grinding unit 40 may be configured to sequentially perform rough grinding and finish grinding on the same surface of the wafer W, rather than performing grinding on both the front surface Wa and the back surface Wb of the wafer W as in the present application. Furthermore, the number of chucks 42 arranged in the grinding unit 40 is not particularly limited. Two or more chucks 42 may be arranged as appropriate depending on the configuration and number of the grinding units to be arranged.

[0035] Next, a series of wafer processing steps performed in the grinding apparatus 1 configured as described above will be described with reference to Figures 3 to 5. Figure 3 shows the flow of wafer processing steps performed on a single wafer W in the grinding apparatus 1. Figure 4 shows the overall flow of wafer processing steps performed successively on multiple wafers W in the grinding apparatus 1. Figure 5 shows a detailed flow of the grinding process in the grinding unit.

[0036] In the following description, an example will be given in which one lot of 25 wafers W is accommodated in cassette C, and grinding processing is sequentially performed on each of these 25 wafers W. In the following description, for convenience, the 25 wafers W accommodated in cassette C may be referred to as wafers W1 to W25 in the order in which they are processed in grinding apparatus 1. Furthermore, because the processing performed in first grinding section 90 and second grinding section 100 of grinding unit 40 is the same, the following description will be given in which one lot of 25 wafers W is processed in first grinding section 90.

[0037] First, a cassette C containing a plurality of wafers W, in this embodiment 25 wafers per lot, is placed on the cassette mounting table 10 of the carry-in / out station 2. The wafers W are contained in the cassette C with their front surfaces Wa facing upward and their back surfaces Wb facing downward.

[0038] Next, the wafer W1 is removed from the cassette C by the transfer fork 23 of the wafer transfer device 22 and transferred to the processing station 3. The wafer W1 transferred to the processing station 3 is delivered to the alignment unit 50. In the alignment unit 50, the horizontal orientation of the wafer W1 is adjusted by adjusting the position of a notch (not shown) formed in the wafer W1 (S1 in FIG. 3).

[0039] Next, the wafer W1 is transferred by the transfer unit 30 from the alignment unit 50 to the grinding unit 40 and transferred to the chuck 42a at the transfer position A1. At the transfer position A1, the thickness of the wafer W1 before grinding is measured at multiple points by the thickness measurement unit 110 (S2 in FIG. 3). The measured thickness is output to, for example, the control unit 120.

[0040] Next, the wafer W1 held by the chuck 42a is moved to the processing position B1. At the processing position B1, the first grinding unit 90 grinds the front surface Wa of the wafer W1 (S3 in FIG. 3 and P1 in FIG. 4). A detailed method for grinding the wafer W at the processing position B1 will be described below with reference to FIG. 5. The left diagram in FIG. 5 is an explanatory diagram showing the positional relationship between the grinding wheel 91 and the wafer W during grinding by the first grinding unit 90. The right diagram in FIG. 5 is a graph showing the time-series change in the height position of the grinding wheel 91, with the vertical axis representing the height position of the grinding surface 91a of the grinding wheel 91 and the horizontal axis representing time.

[0041] First, the grinding wheel 91 (and grinding wheel 92) is lowered at high speed from the standby position H1 to the air cut start position H2 (from T0 to T1 in FIG. 5). At this time, the high speed lowering is performed in order to improve throughput. However, if the grinding wheel 91 is allowed to contact the wafer W1 at this high speed, there is a concern that the grinding wheel 91 may be damaged or the wafer W1 may be broken. Therefore, the lowering speed of the grinding wheel 91 is slowed down at the air cut start position H2, and the grinding wheel 91 is lowered at a low speed to the contact position H3 with the wafer W1 (from T1 to T2 in FIG. 5: air cut).

[0042] The height position of the grinding surface 91a of the grinding wheel 91 when starting the air cut shown in FIG. 5 (air cut start position H2) is set by adding the thickness of the wafer W1 before grinding and the air cut amount to the setup position (described later). The air cut amount is set in advance in a recipe and is the distance the grinding wheel 91 descends from the air cut start position H2 to the contact position H3 shown in FIG. 5. In this case, the air cut start position H2 is set so that the grinding wheel 91 does not collide with the wafer W1 but the air cut amount is as small as possible. The thickness of the wafer W1 before grinding used to adjust the air cut start position H2 may be measured by the thickness measuring unit 110 at the transfer position A1 or may be measured by the thickness measuring unit 97 at the processing position B1.

[0043] After the grinding wheel 91 is lowered and brought into contact with the wafer W1, the grinding wheel 91 is further lowered to grind the wafer W1 to a grinding end position H4 (the target thickness of the wafer W1 in S3) in the first grinding section 90 (T2 to T5 in FIG. 5: grinding step). Note that in the grinding step, the lowering speed of the grinding wheel 91 may be changed stepwise between T2 and T5 (for example, T3 and T4 in FIG. 5), or the lowering speed may be controlled to a constant value.

[0044] When the grinding wheel 91 reaches the grinding end position H4 and stops descending, the grinding wheel 91 is held at the grinding end position H4 for a certain period of time (T5 to T6 in FIG. 5: spark out). In the spark out state, the grinding wheel 91 continues to rotate. At this time, the position of the grinding wheel 91, specifically the boundary position between the bottom surface of the mount 93 and the top surface of the grinding wheel 92 (hereinafter referred to as the Z position), is measured from the Z-axis position of the motor of the drive unit 95 obtained by the position measurement unit. The measured Z position is output to, for example, the control unit 120.

[0045] After the spark-out is completed, the grinding wheel 91 starts to rise while continuing to rotate (T6 to T7 in FIG. 5: escape cut). In the escape cut state, the grinding wheel 91 is raised at a low speed to prevent wheel marks from remaining on the surface Wa of the wafer W1 when the wafer W1 and the grinding wheel 91 are separated from each other.

[0046] After the wafer W1 and the grinding wheel 91 are separated from each other, the upward movement speed of the grinding wheel 91 is accelerated to move the grinding wheel 91 to the standby position H1 (T7 onwards), and grinding of the surface Wa of the wafer W1 in the first grinding section 90 is completed.

[0047] Next, the thickness of the wafer W1 after grinding is measured by the thickness measuring unit 97 (S4 in FIG. 3). The measured thickness is output to, for example, the control unit 120. Note that the thickness measurement of the wafer W1 by the thickness measuring unit 97 is also performed during the grinding process by the first grinding unit 90.

[0048] Next, based on the thickness of the ground wafer W1 measured by the thickness measuring unit 97, the reference position of the grinding wheel 91 relative to the chuck 42a, i.e., the so-called setup position, is adjusted (S5 in FIG. 3). This setup position adjustment is performed to adjust the setup position for the grinding process of the next wafer W in the first grinding unit 90. The setup position is a position where the position of the lower surface (grinding surface) of the grinding wheel 91 coincides with the position of the upper surface (holding surface) of the chuck 42a, or is a predetermined distance away from the position of the upper surface (holding surface) of the chuck 42a. This predetermined distance from the upper surface of the chuck 42a can be set arbitrarily. The method for adjusting the setup position will be described in detail below.

[0049] In this embodiment, the setup position adjustment (S5) is performed immediately after the thickness measurement (S4) of the wafer W1, but the timing of the setup position adjustment is not limited to this. Specifically, the setup position adjustment may be performed at least before the grinding process of the next wafer W in the first grinding unit 90 (the grinding process of the front surface Wa of the wafer W2, which will be described later, P2 in FIG. 4).

[0050] Next, the wafer W1 held by the chuck 42a is moved to the transfer position A1. At the transfer position A1, the front surface Wa of the wafer W1 after grinding may be cleaned by a cleaning unit (not shown). Next, the wafer W1 is transferred from the transfer position A1 by the transfer unit 30 and transferred to the second cleaning unit 80. At the second cleaning unit 80, the front surface Wa and back surface Wb of the wafer W1 are cleaned (S6 in FIG. 3).

[0051] When the wafer W1 is unloaded from the transfer position A1, the wafer W2 to be next ground in the first grinding unit 90 is transferred to the chuck 42a at the transfer position A1. At the transfer position A1, the thickness of the wafer W2 before grinding is measured at multiple points by the thickness measuring unit 110. The measured thickness is output to, for example, the control unit 120.

[0052] Next, the wafer W2 held by the chuck 42a is moved to the processing position B1. At the processing position B1, the first grinding unit 90 grinds the surface Wa of the wafer W2 (P2 in FIG. 4). The grinding method for the wafer W2 at the processing position B1 is the same as the grinding method for the wafer W1 (P1) described above. That is, as shown in FIG. 5, by controlling the height position of the grinding wheel 91, air cutting (from T1 to T2), grinding steps (from T2 to T5), spark-out (from T5 to T6), and escape cutting (T6 to T7) are performed in sequence.

[0053] While the wafer W2 is positioned at the processing position B1, the wafer W1 cleaned in the second cleaning unit 80 is removed by the transfer unit 30 and transferred to the inversion unit 60. In the inversion unit 60, the front and back surfaces of the wafer W1 are inverted (S7 in FIG. 3). That is, the wafer W1 is inverted so that the ground front surface Wa faces downward and the unground back surface Wb faces upward. The inverted wafer W1 is then transferred to the chuck 42c at the transfer position A1 by the transfer unit 30. At the transfer position A1, the thickness of the wafer W1 may be measured at multiple points by the thickness measuring unit 110 (S8 in FIG. 3). The measured thickness is output to, for example, the control unit 120.

[0054] When grinding of the front surface Wa of the wafer W2 is completed, the thickness of the wafer W2 after grinding is measured by the thickness measuring unit 97. The measured thickness is output to, for example, the control unit 120. Note that the thickness measurement of the wafer W2 by the thickness measuring unit 97 is also performed during the grinding process by the first grinding unit 90.

[0055] Then, in the first grinding unit 90, the setup position for the grinding process of the next wafer W is adjusted until the grinding process of the next wafer W (the grinding process of the back surface Wb of the wafer W1, which will be described later, P3 in FIG. 4) in the first grinding unit 90, based on the thickness of the wafer W2 after grinding measured by the thickness measuring unit 97. The method for adjusting the setup position will be described in detail later.

[0056] Next, the wafer W2 held by the chuck 42a is moved to the transfer position A1 by rotation of the turntable 41. At the transfer position A1, the front surface Wa of the wafer W2 after grinding may be cleaned by a cleaning unit (not shown). Next, the wafer W2 is transferred by the transfer unit 30 to the second cleaning unit 80, where the front surface Wa and back surface Wb of the wafer W2 are cleaned.

[0057] When the chuck 42a (wafer W2) is moved from the processing position B1 to the delivery position A1 by the rotation of the turntable 41, the chuck 42c (wafer W1) disposed at the delivery position A1 moves to the processing position B1. At the processing position B1, the back surface Wb of the wafer W1 is ground by the first grinding unit 90 (S9 in FIG. 3 and P3 in FIG. 4). The method for grinding the back surface Wb of the wafer W1 at the processing position B1 is the same as that described above for P1 and P2.

[0058] While wafer W1 is positioned at processing position B1, wafer W3, which is to be next ground in first grinding unit 90, is transferred to chuck 42a at transfer position A1. At transfer position A1, thickness measurement unit 110 measures the thickness of wafer W3 at multiple points before grinding. The measured thickness is output to control unit 120, for example.

[0059] When grinding of the back surface Wb of the wafer W1 is completed, the thickness measuring unit 97 measures the thickness of the wafer W1 after grinding (S10 in FIG. 3). Then, in the first grinding unit 90, the setup position for the grinding process of the next wafer W (front surface Wa of wafer W3) is adjusted (S11 in FIG. 3) based on the measured thickness of the wafer W1. The wafer W1 held by the chuck 42c is moved to the transfer position A1. At the transfer position A1, the front surface Wa of the wafer W1 after grinding may be cleaned by a cleaning unit (not shown). Next, the wafer W1 after the grinding process is transferred to the first cleaning unit 70 by the transfer unit 30. At the first cleaning unit 70, the front surface Wa and back surface Wb of the wafer W1 are cleaned (S12 in FIG. 3).

[0060] Thereafter, the wafer W1 that has been subjected to all the processes is transferred to the cassette C on the cassette mounting table 10 by the transfer fork 23 of the wafer transfer device 22. In this way, the series of wafer processes for the wafer W1 is completed.

[0061] Thereafter, the grinding apparatus 1 continues the series of wafer processing steps for all wafers W accommodated in the cassette C. That is, when the chuck 42c holding the wafer W1 after grinding its backside Wb moves from the processing position B1 to the transfer position A1, the chuck 42a (wafer W3) disposed at the transfer position A1 moves to the processing position B1. Then, at the processing position B1, the front side Wa of the wafer W3 is ground (P4 in FIG. 4 ). While the wafer W3 is positioned at the processing position B1, the wafer W2 cleaned in the second cleaning unit 80 is removed by the transfer unit 30, and after being inverted from its front side to its backside in the inverting unit 60, the transfer unit 30 transfers the wafer W2 to the chuck 42c at the transfer position A1.

[0062] After the grinding process of the front surface Wa of the wafer W3 at the processing position B1 is completed, the thickness of the wafer W3 is measured. Then, in the first grinding unit 90, the setup position for the grinding process of the next wafer W (the back surface Wb of the wafer W2) is adjusted based on the measured thickness of the wafer W3. The wafer W3 is then moved from the processing position B1 to the transfer position A1, and then the transfer unit 30 transfers the wafer W3 to the second cleaning unit 80. When the wafer W3, whose front surface Wa has been ground, moves from the processing position B1 to the transfer position A1, the chuck 42c (wafer W2) positioned at the transfer position A1 moves to the processing position B1, and then the back surface Wb of the wafer W2 is ground (P5 in FIG. 4 ). Furthermore, while the wafer W2 is positioned at the processing position B1, the wafer W4, which is to be ground next in the first grinding unit 90, is transferred to the chuck 42a at the transfer position A1. After the grinding process of the back surface Wb of the wafer W2 is completed, the wafer W4 held by the chuck 42a is moved to the processing position B1, where the front surface Wa is ground (P6 in FIG. 4).

[0063] Then, as shown in Figure 4, when processing of all wafers W contained in cassette C is completed, i.e., when the grinding process of the back surface Wb of wafer W25 (P50 in Figure 4) is completed and wafer W25 is transported to cassette C on cassette mounting table 10, the series of wafer processing in grinding apparatus 1 is completed.

[0064] As described above, the second grinding unit 100 also performs the same processing as the first grinding unit 90. That is, the front surfaces Wa and back surfaces Wb of a plurality of wafers W housed in a cassette C, i.e., 25 wafers in one lot in this embodiment, are sequentially ground. At this time, the wafers W to be ground in the second grinding unit 100 are held by the chuck 42b or the chuck 42d, for example. The wafers W to be processed in the second grinding unit 100 may be housed in a cassette C different from the wafers W transferred to the first grinding unit 90, or may be housed in the same cassette C. In other words, the plurality of wafers W housed in the cassette C may be continuously processed using the same grinding unit, or may be shared and processed using different grinding units. In this case, for example, control may be performed so that odd-numbered wafers W (W1, W3, W5, etc.) contained in cassette C are processed in the first grinding unit 90, and even-numbered wafers W (W2, W4, W6, etc.) are processed in the second grinding unit 100.

[0065] Next, the above-mentioned method for adjusting the setup position (S5, S11) will be described. Below, the method for adjusting the setup position in the first grinding unit 90 will be described, but the method for adjusting the setup position in the second grinding unit 100 is similar. In the following example, a case will be described in which the setup position in P4 (grinding process on the front surface Wa of the wafer W3) is adjusted and updated using the setup position SP1 in P2 (grinding process on the front surface Wa of the wafer W2) and the setup position SP2 in P3 (grinding process on the back surface Wb of the wafer W1) shown in FIG. 4 .

[0066] In this embodiment, of the two most recent grinding processes performed by the first grinding unit 90 used to adjust the setup position, the wafer W ground first (in the example shown in Figure 6 below, wafer W2 whose front surface Wa is ground) corresponds to the "Nth substrate (N≧1)" according to the technology of the present disclosure, and the wafer W ground last (in the example shown in Figure 6 below, wafer W1 whose back surface Wb is ground) corresponds to the "N+1th substrate" according to the technology of the present disclosure.

[0067] FIG. 6 is an explanatory diagram illustrating a conventional method for calculating the wear amount of a grinding wheel. In the conventional method, the setup position is adjusted based on the wear amount, as described below. FIG. 6(a) shows the state of spark-out during grinding of the front surface Wa of wafer W2 (P2 in FIG. 4), and FIG. 6(b) shows the state of spark-out during grinding of the back surface Wb of wafer W1 (P3 in FIG. 4). In FIG. 6, Z1 and Z2 respectively represent the Z position (the position of the grinding wheel 91 calculated from the Z-axis position of the motor of the drive unit 95; more specifically, the boundary position between the bottom surface of the mount 93 and the top surface of the grinding wheel 92). D1 and D2 respectively represent the length of the grinding wheel 91 including the grinding wheel 92. Wt1 and Wt2 respectively represent the thicknesses of wafers W1 and W2 after grinding.

[0068] As described above, the grinding wheel 91 of the first grinding unit 90 wears and thins as it repeatedly grinds wafers. α shown in FIG. 6 is the amount of wear of the grinding wheel 91 caused by grinding the wafer W (in the illustrated example, grinding the back surface Wb of the wafer W1), and can be expressed by the following formula (1): α=D1-D2 (1)

[0069] At this time, if the distance from the home position at the top end of the Z position to the holding surface of the chuck 42 is constant as shown in FIG. 6, for example, by aligning the height of the upper surface of the chuck 42, the following equation (2) is established: Z1+D1+Wt1=Z2+D2+Wt2 (2)

[0070] In the conventional method, the setup position for the grinding process of the next wafer W in the first grinding unit 90 is adjusted based on this wear amount α. That is, in order to control the position of the grinding surface of the grinding wheel 91 relative to the holding surface of the chuck 42 to be constant in each grinding process, the grinding wheel 91 is moved closer to the chuck 42 by the amount of wear amount α of the grinding wheel 91, and this position is used as the setup position for the grinding process of the next wafer W. In other words, the amount of movement of the grinding wheel 91 for updating the setup position corresponds to the wear amount α of the grinding wheel 91.

[0071] However, as mentioned above, there may be a small error in the upper surface height of each of the chucks 42a to 42d arranged in the grinding unit 40 due to changes in the holding height caused by chuck grinding and machine differences, as shown in FIG. 7. β shown in FIG. 7 indicates the error in the holding surface height between the chucks 42. Therefore, when this error β is taken into consideration, the above formula (2) can be expressed as the following formula (3). As shown in FIG. 7, for example, the error β is a positive value (a value that increases the amount of movement M, described below) when the upper surface height of the chuck 42 is lower than immediately before, and a negative value (a value that decreases the amount of movement M, described below) when the upper surface height of the chuck 42 is higher than immediately before. Z1+D1+Wt1=Z2+D2+Wt2-β (3)

[0072] 8 is an explanatory diagram showing how the setup position is updated in this embodiment. In the following description, at the setup position, the position of the lower surface (grinding surface) of the grinding wheel 91 coincides with the position of the upper surface (holding surface) of the chuck 42a.

[0073] 8(a) shows the setup position (SP1 in the figure) after grinding the front surface Wa of the wafer W2 (P2 in FIG. 4), and FIG. 8(b) shows the setup position (SP2 in the figure) after grinding the back surface Wb of the wafer W1 (P3 in FIG. 4). The movement amount M from the setup position SP1 to the setup position SP2 is determined taking into consideration the amount of wear α that occurs when the grinding wheel 91 wears down due to grinding the back surface Wb of the wafer W1, and the error β in the holding surface height between the chucks 42. That is, the movement amount M of the setup position is calculated by the following equation (4) by modifying the above equation (3): M=α+β=(D1-D2)+β=(Z2-Z1)+(Wt2-Wt1) (4)

[0074] At this time, the amount of wear α of the grinding wheel 91 caused by grinding the wafer W (in the illustrated example, grinding the back surface Wb of the wafer W1) can be calculated by subtracting the error β in the holding surface height between the chucks 42 from the movement amount M of the setup position described above, as shown in the following formula (5). The error β can be determined by measuring the upper surface height of the chucks 42, for example, with a contact sensor (not shown) arranged at the processing position B1. α=M-β (5)

[0075] In the grinding unit 40 according to this embodiment, for example, the initial length of the grinding wheel 91 at the start-up of the grinding apparatus 1 is output in advance to the control unit 120. Then, by calculating the remaining amount (current length) of the grinding wheel 91 from this initial length and the wear amount α each time the setup position is updated (S5, S11), it is possible to update the remaining amount of the grinding wheel 91 at the end of grinding of the wafer W together with the updated setup position.

[0076] As described above, the error β described in the above formulas (3) and (4) represents the error in the holding surface height between the chucks 42. Therefore, this error β needs to be taken into consideration only when the chucks holding the wafer W in the two most recent grinding processes used to adjust the setup position are different, specifically, in the example shown in FIG. 4 , when updating the setup position at P4 (see P2 and P3) to updating the setup position at P50 (see P48 and P49). In other words, when the chucks holding the wafer W in the two most recent grinding processes used to adjust the setup position are the same, specifically, in the example shown in FIG. 4 , when updating the setup position at P3 (see P1 and P2) or when updating the setup position at P1 in the next process (PJ2 in the figure) (see P49 and P50 of PJ1), the error β does not occur, and therefore does not need to be taken into consideration.

[0077] From this viewpoint, when updating the setup position (S5, S11), it is desirable to determine in advance whether the chuck holding the wafer W is the same in the two most recent grinding processes, based on the process recipe for the grinding apparatus 1 (for example, the grinding recipe for the wafer W in the first grinding unit 90 shown in FIG. 4). That is, if the chuck holding the wafer W is the same in the two most recent grinding processes based on the process recipe, the movement amount M is calculated from the following formula (6) obtained by modifying the above formula (2) without taking the error β into consideration, and only when the chucks are different, the movement amount M is calculated based on the above formulas (4) and (5) taking the error β into consideration. M=α=(D1-D2)=(Z2-Z1)+(Wt2-Wt1) (6)

[0078] In this way, by calculating the movement amount M without considering the error β only when the same chuck holds the wafer W in the two most recent grinding processes, the calculation for calculating the movement amount M is simplified, and the setup position can be updated more efficiently. This also simplifies the calculation of the air cut start position H2, which is set based on this setup position. Furthermore, when the same chuck holds the wafer W in the two most recent grinding processes and there is no need to consider the error β, the movement amount M can be considered to be equal to the wear amount α of the grinding wheel 91, as shown in equation (6) above. Therefore, there is no need to separately calculate the wear amount α to determine the remaining cutting edge of the grinding wheel 91, and control related to the grinding process of the wafer W can be further simplified.

[0079] As described above, in the grinding process according to this embodiment, the setup position is adjusted and updated based on the Z position of the wafer W at the time of spark-out measured in S3 and S9 and the thickness of the wafer W measured in S4 and S10. At the same time, the remaining cutting edge of the grinding wheel is calculated and updated based on the amount of wear of the grinding wheel caused by grinding the wafer W. As a result, even if the grinding wheel is worn, the grinding wheel before grinding can be appropriately positioned with respect to the wafer W on the chuck, and the wafer W can be appropriately ground.

[0080] Furthermore, in this embodiment, regardless of whether the chucks holding the wafer W in the two most recent grinding processes are the same or not, the setup position is updated by referring to the Z position and the thickness of the wafer W in the two most recent grinding processes. As a result, even if an error β occurs in the upper surface height between the chucks 42 used to adjust the setup position, the setup position can be appropriately adjusted and updated.

[0081] As described above, the amount of wear α of the grinding wheel 91 can be calculated, and the remaining amount of cutting edge of the grinding wheel 91 can be determined based on this. By determining the remaining amount of cutting edge in this manner, the timing for replacing the grinding wheel 91 can be appropriately set, and breakdowns of the grinding unit 40 caused by performing a grinding process when there is no grinding wheel 91 remaining can be prevented. Furthermore, replacement of the grinding wheel 91 when there is more cutting edge remaining than expected can be prevented.

[0082] As described above, the updated setup position is calculated taking into account the wear amount α and error β, and the thickness of the wafer W before grinding is taken into account to calculate the updated setup position, and the air cut start position H2 is adjusted to a position a predetermined distance away from the updated setup position. For example, when the grinding wheel is worn, the air cut start position becomes higher, and it takes time for the grinding wheel to reach the wafer W. In this regard, according to this embodiment, even if the grinding wheel is worn, the time required for air cut can be shortened by appropriately adjusting the air cut start position, thereby improving throughput.

[0083] In the above setup position update operation, the movement amount M associated with the adjustment of the setup position was calculated taking into account the wear amount α and error β, as shown in the above equation (4). Furthermore, at this time, whether or not the error β is used in adjusting the setup position was determined by referring to whether or not the chuck 42 used in the two most recent grinding processes used in adjusting the setup position was the same. However, during actual grinding processes in the grinding unit 40, in addition to the wear amount α and error β, thermal expansion due to frictional heat generated during the grinding process may change the relative position of the lower surface (grinding surface) of the grinding wheel with respect to the upper surface (holding surface) of the chuck 42.

[0084] Therefore, in the setup position adjustment method (S5, S11) according to this embodiment, it is desirable to calculate the movement amount M of the setup position by further considering the thermal expansion amount γ (see FIG. 9) associated with this thermal expansion in addition to the wear amount α and error β. γ shown in FIG. 9 indicates this thermal expansion amount, and is shown as the relative thermal expansion of the chuck 42 with respect to the grinding wheel 91, for example. Therefore, for convenience, FIG. 9 shows the chuck 42 as if it has thermally expanded, but the grinding wheel 91 may also thermally expand in addition to or instead of the chuck 42.

[0085] The setup position can be updated taking into account the amount of thermal expansion γ using the following formula (7) or formula (8). Formula (7) is used when the chucks holding the wafer W are different in the two most recent grinding processes (when the error β is taken into account), while formula (8) is used when the chucks holding the wafer W are the same in the two most recent grinding processes (when the error β is not taken into account). As shown in FIG. 9, the amount of thermal expansion γ is, in principle, a positive value (a value that reduces the amount of movement M). M=α+β-γ=(Z2-Z1)+(Wt2-Wt1)-γ (7) M=α-γ=(Z2-Z1)+(Wt2-Wt1)-γ (8)

[0086] The amount of thermal expansion γ can be calculated by the following formula (9), for example: γ=n×γu−I(0≦γ≦γmax) (9) In formula (9), n represents the number of wafers W ground in the grinding unit (first grinding unit 90 in this embodiment), γu represents the amount of thermal expansion generated per grinded wafer W, which has been previously acquired, I represents the amount of thermal contraction generated by cooling during the interval between grinding processes (i.e., the amount of thermal expansion eliminated), and γmax represents the maximum value of the amount of thermal expansion γ.

[0087] As described above, when updating the setup position in S5 and S11, the wear amount α is usually calculated as a positive value (determining that the grinding wheel has become thinner due to wear). However, due to various factors, it may be calculated as a negative value (mistakenly determining that the grinding wheel has become thicker after wear). In this case, even though the grinding wheel has actually become thinner due to wear or its thickness has not changed, it is determined that the thickness of the grinding wheel has increased, resulting in a discrepancy between the actual thickness of the grinding wheel and the calculated thickness. This makes it impossible to properly determine the timing for replacing the grinding wheel 91.

[0088] Therefore, when the amount of wear α is calculated as a negative value in this way, instead of determining that the thickness of the grinding wheel has increased after the grinding process, it is desirable to calculate the amount of movement M by assuming that the amount of wear α due to the grinding process is "0" and that the thickness of the grinding wheel has not changed (the update of the setup position is invalidated). This makes it possible to avoid at least problems caused by a large misjudgment of the thickness of the grinding wheel, such as a collision between the grinding wheel and the wafer W due to missing the timing to replace the grinding wheel 91, or a decrease in throughput due to estimating the timing to replace the grinding wheel 91 earlier than expected.

[0089] In the above embodiment, when the same chuck was used to hold the wafer W in the two most recent grinding processes used to adjust the setup position, the movement amount M and the wear amount α were calculated based on the above formula (6), without taking into account the error β in the top surface height between the chucks 42. However, even when the same chuck was used in the grinding processes used to adjust the setup position, if there is a possibility that the top surface height position of the chuck may change, for example, when chuck grinding is performed between the adjustments of the setup position, the movement amount M and the wear amount α may be calculated taking into account the error β.

[0090] In the above embodiment, the case where the two most recent grinding processes used to adjust the setup position were performed on different wafers W (wafers W2 and W1 in the example of FIG. 6 ) has been described as an example. However, even when the two most recent grinding processes are performed on the same wafer W, such as when processes are performed consecutively on the front surface Wa and back surface Wb of the same wafer W, the adjustment of the setup position according to the technology of the present disclosure can be applied.

[0091] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The above-described embodiments may be omitted, substituted, or modified in various ways without departing from the scope and spirit of the appended claims. For example, the components of the above-described embodiments may be arbitrarily combined. Such an arbitrary combination naturally provides the functions and effects of each of the components involved in the combination, and also provides other functions and effects that are apparent to those skilled in the art from the description of this specification.

[0092] Furthermore, the effects described herein are merely descriptive or exemplary and are not limiting. In other words, the technology according to the present disclosure may achieve other effects that are apparent to those skilled in the art from the description of this specification, in addition to or in place of the above-described effects.

[0093] 1 Grinding device 42a to 42d Chuck 91 Grinding wheel 95 Drive unit 101 Grinding wheel 105 Drive unit 120 Control unit β Error SP1 Setup position SP2 Setup position W1 to W25 Wafer

Claims

1. A grinding apparatus comprising multiple substrate holders and grinding wheels, wherein a method for grinding a substrate held in the substrate holders is provided, The grinding wheel is used to grind the Nth substrate (N≧1), The (N+1)th substrate is ground using the aforementioned grinding wheel, This includes adjusting the reference position of the grinding wheel, When adjusting the aforementioned reference position, It is determined whether the substrate holding portion that holds the Nth substrate and the N+1th substrate are the same, If the substrate holding portion that holds the Nth substrate and the substrate holding portion that holds the N+1th substrate are different, the difference in upper surface height between the different substrate holding portions will be taken into consideration. If the substrate holding portion that holds the Nth substrate and the substrate holding portion that holds the N+1th substrate are the same, then the difference in upper surface height is not considered. When adjusting the reference position, the relative thermal expansion of the substrate holding portion with respect to the grinding wheel is taken into consideration. A grinding method in which the amount of thermal expansion is calculated based on the number of substrates ground by the grinding wheel, the amount of thermal expansion that occurs per substrate ground, and the interval time of the grinding process.

2. The grinding method according to claim 1, wherein the reference position is a position where the lower surface of the grinding wheel coincides with the upper surface of the substrate holder, or a position separated from the upper surface of the substrate holder by a predetermined set distance.

3. The adjustment of the aforementioned reference position is as follows: To measure the position of the grinding wheel at the end of grinding the Nth substrate and the thickness of the Nth substrate after grinding, To measure the position of the grinding wheel at the end of grinding the N+1th substrate and the thickness of the N+1th substrate after grinding, The grinding method according to claim 1, comprising calculating the amount of movement of the reference position based on the measured position of the grinding wheel and the thickness of the Nth substrate and the N+1th substrate.

4. The grinding method according to claim 3, comprising calculating the amount of wear of the grinding wheel based on the difference between the amount of movement and the upper surface height.

5. The grinding method according to claim 4, further comprising calculating the remaining cutting edge length of the grinding wheel after grinding the N+1th substrate based on the amount of wear of the grinding wheel.

6. The grinding method according to claim 5, wherein, when adjusting the reference position, if it is determined that the remaining cutting edge length after grinding the N+1th substrate is greater than the remaining cutting edge length after grinding the Nth substrate, the wear amount is considered to be 0.

7. A method for calculating the remaining cutting edge length of a grinding wheel after grinding a substrate in a grinding apparatus equipped with multiple substrate holders and grinding wheels, The grinding wheel is used to grind the Nth substrate (N≧1), The (N+1)th substrate is ground using the aforementioned grinding wheel, This includes calculating the remaining cutting edge length of the grinding wheel, When calculating the remaining cutting edge length, It is determined whether the substrate holding portion that holds the Nth substrate and the N+1th substrate are the same, If the substrate holding portion that holds the Nth substrate and the substrate holding portion that holds the N+1th substrate are different, the difference in upper surface height between the different substrate holding portions will be taken into consideration. If the substrate holding portion that holds the Nth substrate and the substrate holding portion that holds the N+1th substrate are the same, then the difference in upper surface height is not considered. Considering the relative thermal expansion of the substrate holding portion with respect to the grinding wheel, A method for calculating the amount of thermal expansion, based on the number of substrates ground by the grinding wheel, the amount of thermal expansion that occurs per substrate ground, and the interval time of the grinding process.

8. The calculation of the remaining cutting edge length is performed by: To measure the position of the grinding wheel at the end of grinding the Nth substrate and the thickness of the Nth substrate after grinding, To measure the position of the grinding wheel at the end of grinding the N+1th substrate and the thickness of the N+1th substrate after grinding, Based on the measured position of the grinding wheel and the thickness of the Nth substrate and the N+1th substrate, the amount of movement of the reference position of the grinding wheel is calculated, Based on the difference between the aforementioned displacement and the aforementioned upper surface height, the amount of wear on the grinding wheel is calculated, The calculation method according to claim 7, comprising calculating the remaining cutting edge length of the grinding wheel after grinding the N+1 substrate based on the remaining cutting edge length of the grinding wheel and the amount of wear before grinding the N+1 substrate.

9. The calculation method according to claim 8, wherein the amount of wear is deemed to be 0 if it is determined that the remaining cutting edge length after grinding the (N+1)th substrate is greater than the remaining cutting edge length after grinding the Nth substrate.

10. A grinding apparatus for grinding a substrate, A plurality of substrate holding parts for holding the substrate, A moving mechanism for moving a grinding wheel relative to the substrate held in the substrate holding part, It has a control unit and The control unit, Control for grinding the Nth substrate (N≧1), Control for grinding the N+1th substrate, The control to adjust the reference position of the grinding wheel is performed, When adjusting the aforementioned reference position, It is determined whether the substrate holding portion that holds the Nth substrate and the N+1th substrate are the same, If the substrate holding portion that holds the Nth substrate and the substrate holding portion that holds the N+1th substrate are different, the difference in upper surface height between the different substrate holding portions will be taken into consideration. If the substrate holding portion that holds the Nth substrate and the substrate holding portion that holds the N+1th substrate are the same, then the difference in upper surface height is not considered. When adjusting the reference position, the control unit takes into consideration the relative thermal expansion of the substrate holding portion with respect to the grinding wheel. A grinding apparatus in which the control unit performs control to calculate the amount of thermal expansion based on the number of substrates to be ground by the grinding wheel, the amount of thermal expansion that occurs per substrate to be ground, and the interval time of the grinding process.

11. A thickness measuring unit for measuring the thickness of the substrate after grinding, It has a position measuring unit for measuring the position of the grinding wheel, The control unit, Control for measuring the position of the grinding wheel at the end of grinding the Nth substrate and the thickness of the Nth substrate after grinding, Control for measuring the position of the grinding wheel at the end of grinding the N+1th substrate and the thickness of the N+1th substrate after grinding, The grinding apparatus according to claim 10, which performs control to calculate the amount of movement of the reference position based on the measured position of the grinding wheel and the thickness of the Nth substrate and the N+1th substrate.

12. The grinding apparatus according to claim 11, wherein the control unit performs control to calculate the amount of wear of the grinding wheel based on the difference between the amount of movement and the upper surface height.

13. The grinding apparatus according to claim 12, wherein the control unit performs control to calculate the remaining cutting edge length of the grinding wheel after grinding the N+1th substrate, based on the amount of wear of the grinding wheel.

14. The grinding apparatus according to claim 13, wherein the control unit, when adjusting the reference position, determines that the remaining cutting edge length after grinding the N+1th substrate is greater than the remaining cutting edge length after grinding the Nth substrate, executes control to consider the amount of wear to be 0.