Grinding method and grinding device

Abstract

A substrate grinding method including: lowering a grinding wheel onto a first substrate that is held by a substrate holding part, and grinding the first substrate with the grinding wheel; adjusting a reference position of the grinding wheel with respect to the substrate holding part at the time of grinding a second substrate that is to be ground after the first substrate is ground; and setting an upper limit and a lower limit for moving the reference position when adjusting the reference position.

Description

Grinding method and grinding device

[0001] The present disclosure relates to a grinding method and a grinding apparatus.

[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 displacement of the spindle relative to the processed wafer.

[0003] JP 2019-155488 A

[0004] The technology according to the present disclosure appropriately controls the position of a grinding wheel when grinding a substrate with the grinding wheel.

[0005] One aspect of the present disclosure is a method for grinding a substrate, comprising: lowering a grinding wheel onto a first substrate held by a substrate holder; grinding the first substrate with the grinding wheel; adjusting a reference position of the grinding wheel relative to the substrate holder when grinding a second substrate that is ground after grinding the first substrate; and setting upper and lower limits for movement of the reference position when adjusting the reference position.

[0006] According to the present disclosure, the position of the grinding wheel can be appropriately controlled when grinding a substrate with the grinding wheel.

[0007] FIG. 1 is a plan view showing an outline of the configuration of a grinding apparatus according to an embodiment of the present invention; FIG. 2 is a side view showing an example of the configuration of a grinding unit and a chuck; FIG. 3 is a flow diagram showing a series of wafer processing procedures by the grinding apparatus; FIG. 4 is an explanatory diagram showing the state of rough grinding in the rough grinding unit; FIG. 5 is an explanatory diagram explaining a method of calculating a setup position; FIG. 6 is an explanatory diagram showing the state of updating a setup position; FIG. 7 is an explanatory diagram showing the upper limit position and the lower limit position of the setup position after updating when updating the setup position; FIG. 8 is an explanatory diagram showing the upper limit position and the lower limit position of the setup position after updating when updating the setup position;

[0008] 2. Description of the Related Art In the semiconductor manufacturing process, a semiconductor substrate (hereinafter referred to as a wafer) is thinned by grinding the back surface of the wafer.

[0009] Wafer grinding is performed, for example, by lowering a grinding wheel onto a wafer held in a chuck and rotating the grinding wheel to bring it into contact with the backside of the wafer. Repeated wafer grinding causes the grinding wheel to wear and become thinner. Therefore, in a grinding machine disclosed in Patent Document 1, for example, a spindle feed mechanism is controlled to move the grinding wheel closer to the wafer by the amount of wear of the grinding wheel.

[0010] Furthermore, when grinding a wafer, the reference position of the grinding wheel relative to the chuck, for example, the setup position, is adjusted. The setup position is a height position where the position of the upper surface of the chuck coincides with the position of the grinding surface of the grinding wheel, or a position a set distance away from that height position. As described above, since the grinding wheel wears out when the wafer is ground, the setup position is adjusted and updated each time a wafer is ground. Specifically, the position of the grinding wheel when wafer grinding is completed (spark out, described below) and the thickness of the wafer after grinding are measured, and the setup position is updated based on the measured position of the grinding wheel and the wafer thickness. Then, based on the setup position, the air cut start position, described below, before starting wafer grinding is determined.

[0011] However, if the wafer thickness is not measured properly, the setup position cannot be updated properly. For example, if the wafer thickness is measured incorrectly and is larger than the actual thickness, the grinding wheel length is calculated to be shorter than the actual thickness, which results in the setup position for the next wafer being lower than the actual position, and there is a risk of the next wafer colliding with the grinding wheel. Also, if the wafer thickness is measured incorrectly and is smaller than the actual thickness, the grinding wheel length is calculated to be longer than the actual position, which results in the setup position for the next wafer being higher than the actual position, which may reduce the throughput for the next wafer.

[0012] The technology disclosed herein has been made 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 the present embodiment will be described with reference to the drawings. Note that in this specification and the drawings, elements having substantially the same functional configurations are designated by the same reference numerals, and redundant description will be omitted.

[0013] 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 front surface Wa is a holding surface that is held by a chuck 42 (described later) in the grinding apparatus 1. The back surface Wb of the wafer W, which is opposite the front surface Wa, is a grinding surface that is ground in the grinding apparatus 1.

[0014] 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.

[0015] 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.

[0016] The wafer transfer region 20 is provided with a wafer transfer device 22 that is movable on a transfer path 21 extending in the X-axis direction. The wafer transfer device 22 has a transfer fork 23 that holds and transfers a wafer W. The transfer fork 23 is movable horizontally, vertically, around a horizontal axis, and around a vertical axis. 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 60 (described later).

[0017] 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, and a first cleaning unit 60 and a second cleaning unit 70 that clean the wafer W after grinding.

[0018] 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 raises and lowers the arm 31 in the vertical direction. The transfer unit 30 is configured to be able to transfer the wafer W to the grinding unit 40, the alignment unit 50, the first cleaning unit 60, and the second cleaning unit 70.

[0019] The grinding unit 40 has a rotary table 41. Four chucks 42 are provided on the rotary table 41 as substrate holders that suction-hold the wafer W. A porous chuck, for example, is used as the chucks 42. The surface of the chucks 42, i.e., the surface that holds the wafer W, has a convex shape in which the center protrudes compared to the edges in a side view. Note that although this protrusion in the center is very small, in the following explanation, the protrusion in the center of the chuck 42 is illustrated enlarged for clarity.

[0020] As shown in FIG. 2 , the four chucks 42 are respectively held by four chuck bases 43. The chuck bases 43 are provided with tilt adjustment mechanisms 44 that adjust the relative tilt between each grinding unit (a rough grinding unit 90, a medium grinding unit 100, and a finish grinding unit 110, described below) and the chucks 42. The tilt adjustment mechanism 44 has a fixed shaft 45 provided on the underside of the chuck base 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 base 43. The tilt adjustment mechanism 44 tilts the chucks 42 and the chuck bases 43 by vertically raising and lowering the other end of the chuck base 43 using the lift shafts 46, with one end of the outer periphery of the chuck base 43 (a position corresponding to the fixed shaft 45) as a base point. This allows the relative tilt between the grinding surface of each grinding unit at processing positions A1 to A3 and the upper surface of the chuck 42 to be adjusted. The configuration of the tilt adjustment mechanism 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 portion.

[0021] 1, the four chucks 42 can be moved to a transfer position A0 and processing positions A1 to A3 by rotating the rotary table 41. Furthermore, each of the four chucks 42 is configured to be rotatable about a vertical axis by a rotation mechanism (not shown).

[0022] At the transfer position A0, the transfer unit 30 transfers the wafer W. A thickness measurement unit 80 is provided at the transfer position A0 to measure the thickness of the wafer W before or after grinding. The thickness measurement unit 80 measures the thickness of the wafer W at multiple points, for example, three points (center point, middle point, and outer periphery point) equally spaced in the radial direction. The thickness measurement unit 80 also acquires the in-plane distribution of the thickness of the wafer W and calculates the flatness (TTV: Total Thickness Variation) of the wafer W. The thickness measurement unit 80 may have any configuration, but may include, for example, a non-contact sensor (not shown) and a calculation unit (not shown).

[0023] In this embodiment, the thickness measuring unit 80 is provided at the delivery position A0, but the location of the thickness measuring unit 80 is not limited to this. For example, the thickness measuring unit 80 may be located independently of the grinding unit 40.

[0024] A rough grinding unit 90 is disposed at the processing position A1 and performs rough grinding of the wafer W. A medium grinding unit 100 is disposed at the processing position A2 and performs medium grinding of the wafer W. A finish grinding unit 110 is disposed at the processing position A3 and performs finish grinding of the wafer W.

[0025] As shown in FIG. 2 , the rough grinding unit 90 at the processing position A1 includes an annular rough grinding stone 91, a rough grinding wheel 92 supporting the rough grinding stone 91, a mount 93 supporting the rough grinding wheel 92, a spindle 94 that rotates the rough grinding wheel 92 via the mount 93, and a drive unit 95 that supports the spindle 94. The drive unit 95 incorporates, for example, a motor (not shown) and rotates the spindle 94. As shown in FIG. 1 , the rough grinding unit 90 is configured to be movable vertically along a support 96 by the drive unit 95. In this embodiment, the drive unit 95 and the support 96 constitute a movement mechanism of the present disclosure that moves the rough grinding stone 91. The drive unit 95 also uses a measurement unit (not shown) that measures the Z-axis position of the motor to measure the position of the rough grinding stone 91 during spark-out, specifically, the boundary position between the lower surface of the mount 93 and the upper surface of the rough grinding wheel 92, thereby constituting a first measurement unit of the present disclosure.

[0026] As described above, the holding surface of the chuck 42 has a convex shape. Therefore, when the wafer W is ground using the rough grinding unit 90, a portion of the annular rough grinding wheel 91 comes into contact with the wafer W. More specifically, the annular rough grinding wheel 91 comes into contact with the wafer W in an arc-shaped manner from the center to the outer peripheral edge of the wafer W. By rotating the chuck 42 and the rough grinding wheel 92 in this state, the entire back surface Wb of the wafer W is ground.

[0027] Also provided at the processing position A1 is a thickness measurement unit 97 serving as a second measurement unit in the present disclosure for measuring the thickness of the wafer W. The thickness measurement unit 97 may have any configuration, but may include, for example, a non-contact sensor (not shown) and a calculation unit (not shown).

[0028] The medium grinding unit 100 at the processing position A2 has the same configuration as the rough grinding unit 90. That is, as shown in Fig. 2, the medium grinding unit 100 has an annular medium grinding stone 101, a medium grinding wheel 102, a mount 103, a spindle 104, a drive unit 105, and a support 106. The grain size of the abrasive grains in the medium grinding stone is smaller than the grain size of the abrasive grains in the rough grinding stone.

[0029] 1, a thickness measurement unit 107 is provided at the processing position A2 as a second measurement unit in the present disclosure, which measures the thickness of the wafer W. The thickness measurement unit 107 may have any configuration, but may include, for example, a non-contact sensor (not shown) and a calculation unit (not shown).

[0030] The finish grinding unit 110 at the processing position A3 has a configuration similar to that of the rough grinding unit 90. That is, as shown in Fig. 2, the finish grinding unit 110 has an annular finish grinding stone 111, a finish grinding wheel 112, a mount 113, a spindle 114, a drive unit 115, and a support 116. The grit size of the abrasive grains in the finish grinding stone is smaller than the grit size of the abrasive grains in the medium grinding stone.

[0031] 1, a thickness measurement unit 117 is provided at the processing position A3 as a second measurement unit in the present disclosure, which measures the thickness of the wafer W. The thickness measurement unit 117 may have any configuration, but may include, for example, a non-contact sensor (not shown) and a calculation unit (not shown).

[0032] The grinding apparatus 1 described above is provided with a display panel 120. The display panel 120 is, for example, a monitor or a touch panel, and may be directly attached to the grinding apparatus 1 or may be remotely viewable. A selection screen for enabling or disabling the update of the setup position, which will be described later, is displayed on the display panel 120, and the operator can set the update to enabled or disabled from the selection screen on the display panel 120. The display panel 120 may also display an input screen for inputting the upper and lower limit positions of the setup position, which will be described later, or an input screen for inputting the upper and lower limits of the movement amount from the setup position. The upper and lower limit positions of the setup position can also be controlled by information set by the control unit 130 based on the grinding amount, and this set information may be input from the input screen on the display panel 120.

[0033] The grinding apparatus 1 described above is provided with at least one control unit 130. The control unit 130 processes computer-executable instructions that cause the grinding apparatus 1 to perform the various steps described in this disclosure. The control unit 130 may be configured to control each element of the grinding apparatus 1 to perform the various steps described herein. In one embodiment, part or all of the control unit 130 may be included in the grinding apparatus 1. The control unit 130 may include a processing unit, a storage unit, and a communication interface. The control unit 130 is realized, for example, by a computer. The processing unit may be configured to read from the storage unit a program that provides logic or routines that enable various control operations and execute the read program to perform various control operations. This program may be stored in the storage unit in advance or may be acquired via a medium when needed. The acquired program is stored in the storage unit and read from the storage unit by the processing unit for execution. The medium may be various computer-readable storage media or a communication line connected to the communication interface. The storage medium may be temporary or non-temporary. The processing unit may be a CPU (Central Processing Unit) or one or more circuits. The storage unit may include a RAM (Random Access Memory), a ROM (Read Only Memory), a HDD (Hard Disk Drive), an SSD (Solid State Drive), or a combination thereof. The communication interface may communicate with the grinding device 1 via a communication line such as a LAN (Local Area Network).

[0034] Next, a series of wafer processing steps performed in the grinding apparatus 1 configured as above will be described.

[0035] First, a cassette C containing a plurality of wafers W is placed on the cassette mounting table 10 of the carry-in / out station 2. Next, the wafers W in the cassette C are removed by the transfer fork 23 of the wafer transfer device 22 and transferred to the processing station 3. The wafers W transferred to the processing station 3 are delivered to the alignment unit 50. In the alignment unit 50, the horizontal orientation of the wafers W is adjusted by adjusting the position of a notch (not shown) formed in the wafers W (S1 in FIG. 3).

[0036] Next, the wafer W is transferred by the transfer unit 30 from the alignment unit 50 to the grinding unit 40 and transferred to the chuck 42 at the transfer position A0. At the transfer position A0, the thickness of the wafer W before grinding is measured at multiple points by the thickness measurement unit 80 (S2 in FIG. 3). The measured thickness is output to, for example, the control unit 130.

[0037] Next, the wafer W held by the chuck 42 is moved to the processing position A1. At the processing position A1, first, the rough grinding unit 90 adjusts the air cut start position (S3 in FIG. 3), as will be described later. The air cut start position may be adjusted based on the thickness of the wafer W before grinding measured in S2, or the thickness of the wafer W before rough grinding may be measured by the thickness measuring unit 97 in S3, and the air cut start position may be adjusted based on the measured thickness. The method for adjusting the air cut start position will be described in detail below.

[0038] Next, the back surface Wb of the wafer W is roughly ground by the rough grinding unit 90 (S4 in FIG. 3). A detailed method of rough grinding the wafer W at the processing position A1 will be described below with reference to FIG. 4. The left diagram in FIG. 4 is an explanatory diagram showing the positional relationship between the rough grinding wheel 91 and the wafer W during rough grinding. The right diagram in FIG. 4 is a graph showing the time-series change in the height position of the rough grinding wheel 91, with the vertical axis representing the height position of the grinding surface 91a of the rough grinding wheel 91 and the horizontal axis representing time.

[0039] First, the rough grinding wheel 91 (and the rough grinding wheel 92) is lowered at high speed from the standby position H1 to the air cut start position H2 (time T0 to T1). At this time, the rough grinding wheel 91 is lowered at high speed from the viewpoint of improving throughput. However, if the rough grinding wheel 91 is allowed to contact the wafer W at this high speed, the rough grinding wheel 91 may be broken or the wafer W may be damaged. Therefore, the rough grinding wheel 91 is then decelerated and lowered at low speed to the contact position H3 with the wafer W (time T1 to T2: air cut).

[0040] After the rough grinding wheel 91 is lowered to bring the rough grinding wheel 91 into contact with the wafer W, the rough grinding wheel 91 is further lowered to grind the wafer W to a grinding end position H4 (the target thickness of the wafer W in the rough grinding section 90) in the rough grinding section 90 (times T2 to T5: grinding step). Note that in the grinding step, the lowering speed of the rough grinding wheel 91 may be changed stepwise between times T2 and T5 (for example, at times T3 and T4), or the lowering speed may be controlled to a constant value.

[0041] When the rough grinding wheel 91 reaches the grinding end position H4 and stops descending, the rough grinding wheel 91 is held at the grinding end position H4 for a certain period of time (time T5 to T6: spark out). In the spark out state, the rough grinding wheel 91 continues to rotate. At this time, the position of the rough grinding wheel 91, specifically the boundary position between the bottom surface of the mount 93 and the top surface of the rough 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 (S5 in FIG. 3). The measured Z position is output to, for example, the control unit 130.

[0042] After the spark-out is completed, the rough grinding wheel 91 starts to rise while continuing to rotate (time T6 to T7: escape cut). In the escape cut state, the rough grinding wheel 91 is raised at a low speed to prevent wheel marks from remaining on the back surface Wb of the wafer W when the wafer W and the rough grinding wheel 91 are separated from each other.

[0043] After the wafer W and the rough grinding wheel 91 are separated, the rough grinding wheel 91 is then accelerated to move to the standby position H1 (after time T7), and rough grinding of the back surface Wb of the wafer W in the rough grinding section 90 is completed.

[0044] Next, the thickness of the wafer W after rough grinding is measured by the thickness measuring unit 97 (S6 in FIG. 3). The measured thickness is output to, for example, the control unit 130. Note that the thickness measurement of the wafer W by the thickness measuring unit 97 is also performed during rough grinding.

[0045] Next, based on the thickness of the wafer W after rough grinding measured in S6, the reference position of the rough grinding wheel 91 relative to the chuck 42, i.e., the so-called setup position, is adjusted (S7 in FIG. 3). In S7, the setup position for grinding the next wafer W in the rough grinding unit 90 is adjusted. The setup position is a height position at which the position of the upper surface of the chuck 42 coincides with the position of the grinding surface of the rough grinding wheel 91. Alternatively, the setup position may be a position spaced a predetermined distance from the height position. The predetermined distance can be set arbitrarily. The method for adjusting the setup position will be described in detail later. The setup position adjustment is performed before grinding the next wafer W to be processed using the same chuck 42 and the same processing position A1.

[0046] Next, the wafer W held by the chuck 42 is moved to the processing position A2. At the processing position A2, first, the air cut start position is adjusted in the intermediate grinding unit 100 (S8 in FIG. 3). At this time, the thickness of the wafer W before intermediate grinding is measured by the thickness measuring unit 107, and the air cut start position is adjusted based on the measured thickness.

[0047] Next, the back surface Wb of the wafer W is medium-ground by the medium grinding unit 100 (S9 in FIG. 3). The medium grinding by the medium grinding unit 100 is performed, for example, in the same manner as the rough grinding by the rough grinding unit 90 shown in FIG. 4. That is, by controlling the height position of the medium grinding wheel 101, air cut, grinding step, spark out, and escape cut are performed in sequence. Furthermore, the Z position is measured during spark out (S10 in FIG. 3). The measured Z position is output to, for example, the control unit 130.

[0048] Next, the thickness of the wafer W after intermediate grinding is measured by the thickness measuring unit 107 (S11 in FIG. 3). The measured thickness is output to, for example, the control unit 130. Note that the thickness measurement of the wafer W by the thickness measuring unit 107 is also performed during intermediate grinding.

[0049] Next, based on the thickness of the wafer W after the intermediate grinding measured in S6, the reference position of the intermediate grinding wheel 101 relative to the chuck 42, that is, the so-called setup position, is adjusted (S12 in FIG. 3). In S12, the setup position is adjusted when the next wafer W is ground in the intermediate grinding unit 100.

[0050] Next, the wafer W held by the chuck 42 is moved to the processing position A3. At the processing position A3, first, the air cut start position is adjusted in the finish grinding unit 110 (S13 in FIG. 3). At this time, the thickness of the wafer W before finish grinding is measured by the thickness measuring unit 117, and the air cut start position is adjusted based on the measured thickness.

[0051] Next, the back surface Wb of the wafer W is finish-ground by the finish grinding unit 110 (S14 in FIG. 3). The finish grinding in the finish grinding unit 110 is performed, for example, by a method similar to the rough grinding by the rough grinding unit 90 shown in FIG. 4. That is, by controlling the height position of the finish grinding wheel 111, air cut, grinding step, spark out, and escape cut are performed in sequence. Furthermore, the Z position is measured during spark out (S15 in FIG. 3). The measured Z position is output to, for example, the control unit 130.

[0052] Next, the thickness of the wafer W after the finish grinding is measured by the thickness measuring unit 117 (S16 in FIG. 3). The measured thickness is output to, for example, the control unit 130. Note that the thickness measurement of the wafer W by the thickness measuring unit 117 is also performed during the finish grinding.

[0053] Next, based on the thickness of the wafer W after finish grinding measured in S16, the reference position of the finish grinding wheel 111 relative to the chuck 42, that is, the so-called setup position, is adjusted (S117 in FIG. 3). In S17, the setup position is adjusted when the next wafer W is ground in the finish grinding unit 110.

[0054] Next, the wafer W held by the chuck 42 is moved to the transfer position A0. At the transfer position A0, the thickness of the wafer W after finish grinding is measured at multiple points by the thickness measuring unit 80 to obtain the in-plane thickness distribution of the wafer W and the flatness of the wafer W (S18 in FIG. 3). The obtained thickness distribution and flatness are output to, for example, the control unit 130.

[0055] Next, the wafer W is transferred from the delivery position A0 to the second cleaning unit 70 by the transfer unit 30, and the front surface Wa and / or the back surface Wb are cleaned while being held on the transfer pad 32 (S19 in FIG. 3).

[0056] Next, the wafer W is transported from the second cleaning unit 70 to the first cleaning unit 60 by the transport unit 30, and the front surface Wa and / or back surface Wb are further cleaned using a cleaning liquid nozzle (not shown) (S20 in Figure 3).

[0057] Thereafter, the wafer W that has undergone 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 manner, the series of wafer processes is completed. Note that in the grinding device 1, the series of wafer processes is continuously performed on the plurality of wafers W accommodated in the cassette C.

[0058] Next, the above-mentioned method for adjusting the air cut start position (S3, S8, S13) and the method for adjusting the setup position (S7, S12, S17) will be described. Below, the method for adjusting the air cut start position (S3) and the method for adjusting the setup position (S7) in the rough grinding unit 90 will be described, but the methods for adjusting the air cut start position and the setup position (S8, S13, S12, S17) in the intermediate grinding unit 100 and the finish grinding unit 110 are also similar.

[0059] First, a method for adjusting the setup position will be described. In the following example, a third setup position P3 for a third wafer W3 is adjusted and updated using a first setup position P1 for a first wafer W1 and a second setup position P2 for a second wafer W2.

[0060] FIG. 5 is an explanatory diagram illustrating a method for calculating the setup position. FIG. 5(a) shows the state of spark-out during rough grinding of the first wafer W1, and FIG. 5(b) shows the state of spark-out during rough grinding of the second wafer W2. In FIG. 5, Z1 and Z2 are respectively the Z position (the position of the rough 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 rough grinding wheel 92). D1 and D2 are respectively the length of the rough grinding wheel 91 including the rough grinding wheel 92. T1 and T2 are respectively the thicknesses of the wafers W1 and W2 after rough grinding. The distance from the home position at the top end of the Z position to the holding surface of the chuck 42 is constant, and the following equation (1) holds: Z1 + D1 + T1 = Z2 + D2 + T2 (1)

[0061] 6 is an explanatory diagram showing how the setup position is updated. FIG. 6(a) shows the second setup position P2, and FIG. 6(b) shows the third setup position P3. The movement amount M from the second setup position P2 to the third setup position P3 is the amount of wear (D1-D2) that occurs when the rough grinding wheel 91 wears down due to rough grinding of the second wafer W2. That is, the movement amount M of the setup position is calculated by the following equation (2) by modifying the above equation (1): M=D1-D2=(Z2-Z1)+(T2-T1) (2)

[0062] As described above, the third setup position P3 for the third wafer W3 is adjusted and updated based on the Z positions Z1 and Z2 of the wafers W1 and W2 at the time of spark-out measured in S5 and the thicknesses T1 and T2 of the wafers W1 and W2 measured in S6 (S3).

[0063] Next, a method for adjusting the air cut start position will be described. In the following example, a case will be described in which the air cut start position for the second wafer W2 is adjusted based on the first setup position P1 for the first wafer W1.

[0064] The air cut start position is the height position of the grinding surface 91a of the rough grinding wheel 91 when air cut starts, and is the air cut start position H2 shown in FIG. 4. The air cut start position is set by adding the thickness of the second wafer W2 before rough grinding and the air cut amount to the first setup position P1. In this case, the air cut start position is set to an amount that is as small as possible without causing the rough grinding wheel 91 to collide with the second wafer W2. The thickness of the second wafer W2 before rough grinding may be measured by the thickness measuring unit 80 in S2 or by the thickness measuring unit 97 in S3. The air cut amount is set in advance in a recipe and is the distance that the rough grinding wheel 91 descends from the air cut start position H2 to the contact position H3 shown in FIG. 4.

[0065] Note that there are cases where S2 is omitted and the thickness measurement of the second wafer W2 before rough grinding by the thickness measurement unit 80 is not performed, or where the thickness measurement of the second wafer W2 before rough grinding in S3 is not performed. In these cases, when the setup position is adjusted and updated after rough grinding of the first wafer W1 (S7), the air cut start position of the second wafer W2 is adjusted based on the thickness of the second wafer W2 that is estimated in advance.

[0066] As described above, the setup positions are adjusted in the rough grinding unit 90, the medium grinding unit 100, and the finish grinding unit 110. By appropriately adjusting the setup positions, even if the grinding wheels are worn, the grinding wheels before grinding can be appropriately positioned. Therefore, grinding (rough grinding, medium grinding, and finish grinding) of the back surface Wb of the wafer W can be appropriately performed.

[0067] As described above, the air cut start position is adjusted in each of the rough grinding unit 90, the medium grinding unit 100, and the finish grinding unit 110. 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 and throughput can be improved by appropriately adjusting the air cut start position.

[0068] Here, for example, in S6, there are cases where the thickness measurement of the wafer W after rough grinding is not performed appropriately. For example, if the measured thickness value of the wafer W measured in S6 differs from the set thickness, a warning (alarm) is issued. Furthermore, if the measured thickness value differs from the set thickness in this way, an upper and lower tolerance range is set for the set thickness, and if the measured thickness value falls outside the tolerance range, rough grinding of the next wafer W is stopped.

[0069] Furthermore, for example, if the thickness measurement value of the wafer W measured in S6 is the same as the set thickness but different from the actual thickness, there is a risk that the setup position of the rough grinding unit 90 cannot be properly adjusted and updated in S3.

[0070] For example, if the actual thickness of the wafer W after rough grinding is 700 μm and the thickness measuring unit 97 erroneously measures the thickness of the wafer W as 900 μm, the length of the rough grinding wheel 91 will be calculated to be 200 μm shorter than the actual length. In this case, the setup position is set lower than the actual position, which may cause the rough grinding wheel 91 to collide with the wafer W, resulting in breakage of the rough grinding wheel 91 or damage to the wafer W.

[0071] Furthermore, for example, if the actual thickness of the wafer W after rough grinding is 700 μm and the thickness measuring unit 97 erroneously measures the thickness of the wafer W as being smaller at 500 μm, the length of the rough grinding wheel 91 will be calculated to be 200 μm longer than the actual length. In this case, the setup position will be set to a position higher than the actual length, which may increase the time required for air cutting, for example, and may result in a decrease in throughput.

[0072] Therefore, in this embodiment, when updating the setup position, upper and lower limits are set for movement of the setup position. The upper and lower limits for movement of the setup position are set for each of the rough grinding unit 90, the medium grinding unit 100, and the finish grinding unit 110. Below, a method for setting the upper and lower limits for movement of the setup position in the rough grinding unit 90 will be described, but the same applies to the medium grinding unit 100 and the finish grinding unit 110.

[0073] FIG. 7 shows the upper limit position P after the setup position P is updated.Ｕ and the updated lower limit position P of the setup position P. Ｌ 1 is an explanatory diagram showing the upper limit M of the movement amount from the setup position P. Ｕ The position moved upward by (the upper limit threshold) is the upper limit position P Ｕ In addition, the lower limit M of the movement amount from the setup position P Ｌ The position moved downward by (the lower limit threshold) is the lower limit position P Ｌ is.

[0074] Upper limit M of the movement of the setup position P Ｕ is set based on the amount of rough grinding of the wafer W. For example, the upper limit M can be determined by multiplying the amount of rough grinding of the wafer W set by the recipe by an arbitrarily set percentage (%). Ｕ The method for setting the ratio is arbitrary, but for example, an allowable range of 0%-200% may be set and the operator may set it arbitrarily. For example, if the rough grinding amount of the wafer W is 30 μm and the set ratio is 10%, the upper limit M Ｕ is set to 3 μm.

[0075] Lower limit M of the movement of the setup position P Ｌ Also, the upper limit M Ｕ Similarly, the lower limit M is set based on the amount of rough grinding of the wafer W. For example, the lower limit M can be set by multiplying the amount of rough grinding of the wafer W set by the recipe by an arbitrarily set percentage (%). Ｌ Calculate.

[0076] As described above, when the setup position P is automatically updated in S3, the movement amount M of the setup position is calculated from the above formula (2) based on the Z position of the wafer W at the time of spark-out measured in S5 and the thickness of the wafer measured in S6. The upward movement amount M during this automatic update is the upper limit M. Ｕ If the amount of downward movement M during automatic update is larger than the lower limit M Ｌ If it is smaller, a warning is issued, and the rough grinding of the subsequent wafer W is stopped by this warning.

[0077] In this case, the setup position P is updated to the upper limit position P Ｕ and the lower limit position P ＬAs a result, it is possible to avoid a collision between the rough grinding wheel 91 and the wafer W caused by an erroneous measurement of the thickness of the wafer W being too large. It is also possible to avoid a decrease in throughput caused by an erroneous measurement of the thickness of the wafer W being too small.

[0078] As shown in FIG. 8, the setup position P is located below the upper limit position P Ｕ and the lower limit position P Ｌ Even in such a case, the setup position P is updated to the upper limit position P Ｕ and the lower limit position P Ｌ This can be appropriately performed between the above, and the above-mentioned effects can be obtained.

[0079] Here, if the wafer W before grinding is abnormal and has a large thickness, for example, in the air cut range, there is a risk of collision between the rough grinding wheel 91 and the wafer W. In particular, if the setup position is updated in S3, that is, if the setup position is moved downward in response to wear of the rough grinding wheel 91, the possibility of collision between the rough grinding wheel 91 and the wafer W described above increases.

[0080] Therefore, if it is known that the thickness of the wafer W before grinding is large, the updating of the setup position of the rough grinding unit 90 in S3 is invalidated. Whether the updating of the setup position is valid or invalid may be determined by an operator, or may be determined by the control unit 130 based on the thickness of the wafer W that has been determined in advance. By invalidating the updating of the setup position in this way, it is possible to prevent the above-mentioned collision between the rough grinding wheel 91 and the wafer W.

[0081] Furthermore, the validity or invalidity of updating the setup position may be determined by comparing the thickness of the wafer W before grinding with the air cut amount. If it is expected that the front surface height (height of the back surface Wb) of the wafer W before grinding will be higher than the air cut start position or the height of the rough grinding wheel 91 in the air cut range (contact position H3 shown in FIG. 4), the updating of the setup position is invalidated.

[0082] Although the grinding device 1 described above has a three-axis configuration including the rough grinding unit 90, the medium grinding unit 100, and the finish grinding unit 110, it may have a one-axis or two-axis configuration. Whether it is a one-axis or two-axis configuration, the technology of the present disclosure can be applied to each grinding unit.

[0083] 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.

[0084] 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.

[0085] REFERENCE SIGNS LIST 1 Grinding device 42 Chuck 91 Rough grinding stone 95 Drive unit 96 Support 101 Medium grinding stone 105 Drive unit 106 Support 111 Finish grinding stone 115 Drive unit 116 Support 130 Control unit W Wafer

Claims

1. A method for grinding a substrate comprising: lowering a grinding wheel onto a first substrate held by a substrate holding part and grinding the first substrate with the grinding wheel; adjusting a reference position of the grinding wheel relative to the substrate holding part when grinding a second substrate which is ground after grinding of the first substrate; and setting upper and lower limits for movement of the reference position when adjusting the reference position.

2. The grinding method according to claim 1, wherein the upper limit and the lower limit are set based on the amount of grinding of the second substrate.

3. A grinding method as described in claim 1, wherein the reference position is a height position where the position of the upper surface of the substrate holding part coincides with the position of the grinding surface of the grinding wheel, or a position a set distance away from said height position.

4. A grinding method as described in claim 1, comprising: measuring the position of the grinding wheel at the end of grinding and the thickness of the first substrate after grinding; calculating the amount of movement of the reference position based on the measured position of the grinding wheel and the thickness of the first substrate; and issuing a warning if the calculated amount of upward movement of the reference position is greater than the upper threshold value, or if the calculated amount of downward movement of the reference position is less than the lower threshold value.

5. The grinding method according to claim 1, further comprising adjusting an air-cut start position for said second substrate based on said reference position and the thickness of said second substrate before grinding.

6. The grinding method according to claim 1, comprising: determining whether the adjustment of the reference position is valid or invalid; and grinding the second substrate based on the determined information on whether the adjustment is valid or invalid.

7. The grinding method according to claim 6, wherein adjustment of the reference position is invalidated when the surface height of the second substrate before grinding is higher than an air-cut start position or an air-cut range for the second substrate.

8. An apparatus for grinding a substrate comprising: a substrate holding part for holding the substrate; a moving mechanism for moving a grinding wheel relative to the substrate held by the substrate holding part; and a control part capable of setting upper and lower limits for movement of a reference position of the grinding wheel relative to the substrate holding part when grinding a second substrate which is ground after grinding a first substrate.

9. The grinding device according to claim 8, wherein the control unit sets the upper limit and the lower limit based on the amount of grinding of the second substrate.

10. A grinding device as described in claim 8, wherein the control unit sets the reference position to a height position where the position of the upper surface of the substrate holding part coincides with the position of the grinding surface of the grinding wheel, or to a position a set distance away from that height position.

11. A grinding device as described in claim 8, comprising: a first measuring unit that measures the position of the grinding wheel at the end of grinding; and a second measuring unit that measures the thickness of the substrate after grinding, wherein the control unit calculates the amount of movement of the reference position based on the position of the grinding wheel measured by the first measuring unit and the thickness of the first substrate measured by the second measuring unit, and executes control to issue a warning if the calculated amount of upward movement of the reference position is greater than the upper threshold value, or if the calculated amount of downward movement of the reference position is less than the lower threshold value.

12. The grinding device according to claim 8, wherein the control unit executes control to adjust an air cut start position for the second substrate based on the reference position and the thickness of the second substrate before grinding.

13. The grinding device according to claim 8, wherein the control unit determines whether adjustment of the reference position is valid or invalid, and executes control for grinding the second substrate based on the determined information on whether adjustment is valid or invalid.

14. The grinding apparatus of claim 13, wherein the control unit determines the adjustment of the reference position to be invalid when the surface height of the second substrate before grinding is higher than the air cut start position or air cut range for the second substrate.