Wafer grinding apparatus and wafer grinding method

Abstract

To minimize in-plane thickness differences and grind the wafer to a uniform thickness across its entire surface. [Solution] The grinding apparatus 1 comprises a chuck table 10, a grinding unit 20 for grinding a wafer W, a lifting mechanism 30 for raising and lowering the grinding unit 20, and a grinding water supply means 40 for supplying grinding water. It also includes a spray nozzle 60 for spraying hot or cold water onto the holding surface 10a of the chuck table 10, a thickness measuring instrument 50 for measuring the thickness of multiple locations on the wafer W held on the holding surface 10a, and a control unit 70 that, among the multiple thickness values ​​of the wafer W measured by the thickness measuring instrument 50, sprays hot water from the spray nozzle 60 on locations that are thicker than a set thickness, or sprays cold water from the spray nozzle 60 on locations that are thinner than a set thickness, thereby expanding or contracting the chuck table 10 via the wafer W to change the height of the holding surface 10a.

Description

[Technical Field]

[0001] The present invention relates to a wafer grinding apparatus and a wafer grinding method for grinding a wafer held on the holding surface of a chuck table using a grinding wheel. [Background technology]

[0002] In a grinding apparatus for grinding wafers on which devices are formed, a chuck table is used which has a conical holding surface that is slightly inclined downward along the outer circumference with the center as the apex. A wafer with protective tape attached to its surface is held on the holding surface of this chuck table, and the lower surface of an annular grinding wheel is brought into contact with the radial portion of the back surface of the wafer, which rotates together with the chuck table, in order to grind the entire back surface of the wafer (see, for example, Patent Documents 1 to 3).

[0003] In this grinding method, the wafer is ground to a uniform in-plane thickness by adjusting the inclination of the chuck table so that the radial portion of the holding surface of the chuck table is parallel to the lower surface of the grinding wheel. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2008-264913 [Patent Document 2] Japanese Patent Publication No. 2013-119123 [Patent Document 3] Japanese Patent Publication No. 2014-226749 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, simply adjusting the inclination between the rotation axis of the chuck table and the rotation axis of the grinding wheel is insufficient, or at least difficult, to meet the recent requirement of keeping the in-plane thickness difference of wafers below 0.1 μm.

[0006] Furthermore, in a grinding method in which a bonded wafer, formed by bonding a support wafer and a device wafer, is held on a chuck table with the support wafer facing downwards, and the back surface (top surface) of the device wafer of the bonded wafer is ground, the surface of the device wafer may have ring-shaped irregularities due to the adhesive used to bond the surface of the device wafer (the bottom surface which is the bonding surface to the support wafer) to the support wafer. In such cases, there is a problem that the thickness of the ground device wafer will not be uniform.

[0007] The present invention has been made in view of the above problems, and its object is to provide a wafer grinding apparatus and a wafer grinding method that can grind a wafer to a uniform thickness over its entire surface while minimizing the difference in in-plane thickness. [Means for solving the problem]

[0008] The invention described in claim 1 is a grinding apparatus comprising: a chuck table that holds a wafer by a holding surface; a grinding unit that rotates an annular grinding wheel around a grinding wheel rotation axis passing through the center of the grinding wheel to grind the wafer with the grinding wheel; a lifting mechanism that moves the grinding unit and the chuck table up and down relative to each other; and a grinding water supply means that supplies grinding water to the location where the grinding wheel contacts the wafer, wherein the apparatus comprises: a spray nozzle that sprays hot water or cold water from above the holding surface onto at least a part of the holding surface or a part of the wafer held on the holding surface; and The device is characterized by comprising: a thickness measuring instrument that measures the thickness of multiple locations on the wafer; and a control unit that, among the multiple thickness values ​​of the wafer measured by the thickness measuring instrument, sprays hot water from a spray nozzle at locations that are thicker than a preset thickness or that show a value greater than the average of the multiple thickness values ​​measured, or sprays cold water from a spray nozzle at locations that are thinner than the preset thickness or that show a value less than the average of the multiple thickness values ​​measured, thereby expanding or contracting the chuck table via the wafer to change the height of the holding surface.

[0009] The invention described in claim 2 is a method for grinding a wafer using the grinding apparatus described in claim 1, comprising: a holding step of holding the wafer on the holding surface of the chuck table; and a grinding step of grinding the wafer to a preset finish thickness while rotating the chuck table around a table rotation axis passing through the center of the holding surface and grinding the wafer with the grinding wheel, measuring the thickness of multiple locations on the radial portion of the wafer with a thickness measuring instrument, and spraying hot water from the spray nozzle to locations that are thicker than a preset set thickness or that show a value greater than the average of the multiple measured thickness values, or spraying cold water from the spray nozzle to locations that are thinner than the set thickness or that show a value less than the average of the multiple measured thickness values.

[0010] The invention described in claim 3 is a method for grinding a wafer using the grinding apparatus described in claim 1, comprising: a holding step of holding the wafer on the holding surface of the chuck table; a pre-grinding step of grinding the wafer to a thickness not reaching a preset finish thickness; a thickness measuring step of measuring the thickness of multiple locations on the wafer pre-grinded in the pre-grinding step using a thickness measuring instrument; a holding surface height changing step of changing the height of the holding surface by expanding or contracting the chuck table via the pre-grinded wafer, by spraying hot water from the spray nozzle on locations that are thicker than a preset set thickness or on locations that show a value greater than the average of the multiple thickness values ​​measured in the thickness measuring step, or by spraying cold water from the spray nozzle on locations that are thinner than the set thickness or on locations that show a value smaller than the average of the multiple thickness values ​​measured; and a finish grinding step of grinding the pre-grinded wafer to a preset finish thickness.

[0011] The invention described in claim 4 is a method for grinding a wafer using the grinding apparatus described in claim 1, comprising: a first holding step of holding a first wafer on the holding surface of the chuck table; a first grinding step of grinding the first wafer to a preset finish thickness; a thickness measuring step of measuring the thickness of multiple locations of the first wafer ground in the first grinding step using a thickness measuring instrument; a storage step of storing, from among the multiple thickness values ​​measured in the thickness measuring step, a first location that is thicker than the finish thickness and a second location that is thinner than the finish thickness; and the chuck table The method is characterized by comprising: a separation step of separating the first wafer from the holding surface; a second holding step of holding the second wafer on the holding surface of the chuck table; a holding surface height correction step of correcting the height of the holding surface via the second wafer by spraying hot water from the spray nozzle to a first location stored in the control unit of the second wafer, or by spraying cold water from the spray nozzle to a second location; and a second grinding step of grinding the second wafer to the finished thickness after the holding surface height correction step or while the holding surface height correction step is being performed.

[0012] The invention described in claim 5 is a bonded wafer in which, in the invention described in any of claims 2 to 4, the wafer comprises a support wafer and a device wafer having a device formed on a bonding surface to be bonded to the support wafer, wherein the holding step, the first holding step or the second holding step is to hold the support wafer by suction using the chuck table, and the grinding step, the preliminary grinding step, the finish grinding step, the first grinding step or the second grinding step is to grind the device wafer.

[0013] The invention described in claim 6 is a grinding apparatus comprising: a chuck table that holds a wafer by a holding surface; a grinding unit that rotates a grinding wheel on a grinding wheel rotation axis passing through the center of an annular grinding wheel and grinds the wafer with the grinding wheel; a lifting mechanism that moves the chuck table and the grinding unit up and down relative to each other; a grinding water supply means that supplies grinding water to the location where the grinding wheel contacts the wafer; and a thickness measuring instrument that measures the thickness of multiple locations on the wafer held by the holding surface, the apparatus comprising: a spot heater that partially heats the wafer held by the holding surface; and a holding surface height changing control unit that heats the wafer with the spot heater at locations where the thickness values ​​measured by the thickness measuring instrument are thicker than a preset thickness, or at locations where the measured thickness values ​​are greater than the average value of the multiple locations, thereby partially expanding the chuck table via the wafer and raising the holding surface.

[0014] The invention described in claim 9 is a method for grinding a wafer using the grinding apparatus described above, comprising: a holding step of holding the wafer on the holding surface; and a grinding step of rotating the chuck table around a table rotation axis passing through the center of the holding surface to grind the wafer with the grinding wheel, measuring the thickness of the wafer at multiple locations with the thickness measuring instrument, and partially heating the wafer with the spot heater at locations that are thicker than a preset finish thickness or thicker than the average value of the multiple measured thickness values, thereby partially raising the holding surface through the wafer and grinding to the finish thickness.

[0015] The invention described in claim 10 is a method for grinding a wafer using the grinding apparatus described above, comprising: a holding step of holding the wafer on the holding surface; a pre-grinding step of pre-grinding the wafer to a predetermined thickness that does not reach a predetermined finish thickness; a thickness measuring step of measuring the thickness of the pre-grinded wafer at multiple locations using a thickness measuring instrument; a holding surface raising step of partially heating the wafer with a spot heater at locations that are thicker than the predetermined thickness among the multiple thickness values ​​measured in the thickness measuring step, or at locations that show a value greater than the average of the multiple thickness values ​​measured, thereby partially expanding the chuck table through the pre-grinded wafer and partially raising the holding surface through the wafer; and a finish grinding step of grinding the pre-grinded wafer to the finish thickness after the holding surface raising step, or while the holding surface raising step is being performed.

[0016] The invention described in claim 11 is a method for grinding a wafer using the grinding apparatus described above, comprising: a first holding step of holding a first wafer on the holding surface; a first grinding step of grinding the first wafer to a finish thickness; a thickness measuring step of measuring the thickness of the first wafer ground in the first grinding step with the thickness measuring instrument; a storage step of storing the portion of the plurality of thickness values ​​measured in the thickness measuring step that is thicker than the finish thickness; a separation step of separating the first wafer from the holding surface; a second holding step of holding a second wafer on the holding surface; a holding surface raising step of partially heating the second wafer with the spot heater at the portion stored in the storage step, thereby partially raising the holding surface via the second wafer; and a second grinding step of grinding the second wafer to a preset finish thickness after the holding surface raising step, or while performing the holding surface raising step. [Effects of the Invention]

[0017] According to the wafer grinding method of claim 2, which is carried out using the grinding apparatus of claim 1, the thickness of the wafer during grinding is measured, and hot water is sprayed from the spray nozzle to the parts where the measured thickness is thicker than a predetermined set thickness, or cold water is sprayed from the spray nozzle to the parts where the thickness is thinner than the set thickness. As a result, the wafer held on the holding surface of the chuck table and ground during the grinding process has a small difference in in-plane thickness and is ground to a uniform thickness over the entire surface.

[0018] According to the invention of claim 3, which is carried out using the grinding apparatus of claim 1, the wafer is pre-ground to a thickness that does not reach a preset finish thickness, the thickness of multiple locations on the radial portion of the pre-ground wafer is measured, and hot water is sprayed from the spray nozzle to the locations that are thicker than the preset thickness, or cold water is sprayed from the spray nozzle to the locations that are thinner than the preset thickness, thereby expanding or contracting the chuck table via the pre-ground wafer to change the height of the holding surface. As a result, the ground wafer is ground to a uniform thickness over its entire surface with minimal in-plane thickness differences.

[0019] According to the invention of claim 4, implemented using the grinding apparatus of claim 1, the first wafer is ground to a preset finish thickness, the thickness of the ground first wafer is measured and stored by the control unit as the first location where the first wafer is thicker than the finish thickness and the second location where the first wafer is thinner than the finish thickness, hot water is sprayed from a spray nozzle to heat and expand the portion of the chuck table's holding surface corresponding to the first location via the second wafer, and cold water is sprayed from a spray nozzle to cool and contract the portion of the chuck table's holding surface corresponding to the second location via the second wafer, thereby correcting the height of the chuck table's holding surface. As a result, the second wafer held on the chuck table's holding surface can be ground to a uniform thickness over its entire surface while minimizing the difference in its in-plane thickness.

[0020] According to the invention described in claim 5, even if the wafer is a bonded wafer made by bonding two wafers together, the grinding method described in claims 2 to 4 makes it possible to grind one of the two wafers of the bonded wafer to a uniform thickness over its entire surface while minimizing the difference in its in-plane thickness.

[0021] According to the inventions of claims 9 to 11, implemented using the grinding apparatus of claim 6, the portion of the multiple thickness values ​​measured by the thickness measuring unit that is thicker than a preset thickness is heated with a spot heater, causing the chuck table to expand and the height of the holding surface to be changed. This allows the grinding wheel to come into contact with the thicker portion of the wafer before other portions, enabling the wafer to be ground to a uniform thickness across its entire surface and minimizing the in-plane thickness difference of the wafer. [Brief explanation of the drawing]

[0022] [Figure 1] This is a perspective view showing a part of a wafer grinding apparatus according to the first embodiment of the present invention, with the part shown in a fractured state. [Figure 2] Figure 2A is a side cross-sectional view of the main part of a grinding apparatus showing the grinding process in the wafer grinding method according to the first invention of the first embodiment, and Figure 2B is a diagram showing the thickness distribution in the radial direction of the wafer. [Figure 3] This is a side cross-sectional view of the main part of a grinding apparatus showing the positioning of the injection nozzle and the wafer grinding process in a wafer grinding method according to the first embodiment of the first invention. [Figure 4] This is a flowchart showing the procedure for a wafer grinding method according to the first embodiment of the first invention. [Figure 5] This is a block diagram showing the steps of the wafer grinding method according to the second invention of the first embodiment. [Figure 6] Figure 6A is a side cross-sectional view of the main part of a grinding apparatus showing the thickness measurement step in the wafer grinding method according to the second invention of the first embodiment, and Figure 6B is a diagram showing the radial thickness distribution of the wafer. [Figure 7]This is a side cross-sectional view of the main part of a grinding apparatus showing the holding surface height changing step in a wafer grinding method according to the second invention of the first embodiment. [Figure 8] This is a flowchart showing the procedure for a wafer grinding method according to the second invention of the first embodiment. [Figure 9] This is a block diagram showing the steps of the wafer grinding method according to the third invention of the first embodiment. [Figure 10] Figure 10A is a side cross-sectional view of the main part of a grinding apparatus showing the thickness measurement step in the wafer grinding method according to the third invention of the first embodiment, and Figure 10B is a diagram showing the thickness distribution in the radial direction of the wafer. [Figure 11] This is a side cross-sectional view of the main part of a grinding apparatus showing the holding surface height correction step in a wafer grinding method according to the third invention of the first embodiment. [Figure 12] This is a flowchart showing the procedure for a wafer grinding method according to the third invention of the first embodiment. [Figure 13] This is a side cross-sectional view of the main part of a grinding apparatus showing the grinding process of a bonded wafer according to the first embodiment. [Figure 14] This is a schematic perspective view of a grinding apparatus according to a second embodiment. [Figure 15] This is a schematic diagram showing a partial longitudinal cross-sectional view of the grinding apparatus of the second embodiment, and is an explanatory diagram of the holding process of the first grinding method in the second embodiment. [Figure 16] This is a schematic diagram showing a partial longitudinal cross-sectional view of the grinding apparatus of the second embodiment, and is an explanatory diagram of the processing steps performed in the grinding step of the first grinding method in the second embodiment. [Figure 17] This is a flowchart of each step of the first grinding method in the second embodiment. [Figure 18] Figure 18A is an explanatory diagram of the thickness measurement process performed in the grinding step of the first grinding method in the second embodiment, and Figure 18B is a diagram showing the radial distribution of the wafer thickness. [Figure 19] This is an explanatory diagram of the spot heater positioning process performed in the grinding step of the first grinding method in the second embodiment. [Figure 20] This is an explanatory diagram of the holding surface raising process performed in the grinding step of the first grinding method in the second embodiment. [Figure 21] This is an explanatory diagram of the holding surface raising process performed in the grinding step of the first grinding method in the second embodiment. [Figure 22] This is an explanatory diagram of the discharge process of the first grinding method in the second embodiment. [Figure 23] This is a flowchart of each step of the second grinding method in the second embodiment. [Figure 24] This is an explanatory diagram of the thickness measurement step in the second grinding method according to the second embodiment. [Figure 25] This is an explanatory diagram of the holding surface raising step in the second grinding method according to the second embodiment. [Figure 26] This is a flowchart of each step of the third grinding method in the second embodiment. [Figure 27] This is an explanatory diagram of the thickness measurement process in the third grinding method in the second embodiment. [Figure 28] This is an explanatory diagram of the separation step in the third grinding method in the second embodiment. [Figure 29] This is an explanatory diagram of the holding surface raising step in the third grinding method in the second embodiment. [Figure 30] This is a schematic diagram similar to Figure 16, showing the grinding process of a bonded wafer. [Figure 31] Figure 31A is a schematic diagram of a partial longitudinal cross-section of the grinding apparatus of the first modified example, Figure 31B is a partial enlargement of Figure 31A, and Figure 31C is a schematic perspective view of the nozzle of the first modified example from below. [Figure 32] This is a schematic diagram showing a partial longitudinal cross-section of the grinding apparatus of the second modified example. [Modes for carrying out the invention]

[0023] Embodiments of the present invention will be described below with reference to the accompanying drawings.

[0024] <First Embodiment> [Configuration of the grinding machine] First, the configuration of the grinding apparatus according to the first embodiment of the present invention will be described. In the following description, the arrow directions shown in Figure 1 will be the X-axis direction (left and right direction), the Y-axis direction (front and back direction), and the Z-axis direction (up and down direction, vertical direction), respectively. The X-axis, Y-axis, and Z-axis directions are perpendicular to each other. The X-axis and Y-axis directions are approximately horizontal. Of the two arrows indicating the Z-axis direction, the +Z side is considered upward and the -Z side is considered downward.

[0025] The grinding apparatus 1 shown in Figure 1 is used to grind a thin, disc-shaped wafer W (including a first wafer, a second wafer, and a bonded wafer), which is the workpiece, and comprises the following components.

[0026] In other words, the grinding apparatus 1 includes a chuck table 10 that holds and rotates the wafer W, a table rotation mechanism 12 (see Figure 2) that rotates the chuck table 10, a grinding unit 20 that grinds the wafer W held on the chuck table 10, a lifting mechanism 30 that moves the grinding unit 20 up and down in a direction perpendicular to the holding surface 10a (see Figure 2) of the chuck table 10 (in the Z-axis direction), a grinding water supply means 40 that supplies grinding water toward the inside of the annular grinding wheel 25b (see Figure 2A) during the grinding of the wafer W, and the wafer W during grinding The main components of the device are: a thickness measuring instrument 50 that measures the thickness at multiple locations on the radial portion of wafer W; an injection nozzle 60 that sprays hot or cold water onto at least a portion of the radial portion of the holding surface 10a of the chuck table 10, or onto the upper surface of wafer W held on the holding surface 10a; and a control unit 70 that positions the injection nozzle 60 at locations where the thickness at multiple locations on the radial portion of wafer W measured by the thickness measuring instrument 50 is thinner or thicker than a preset set thickness, and sprays hot or cold water from the injection nozzle 60 onto wafer W. The preset set thickness may be the average or median value of the thicknesses at multiple locations measured by the thickness measuring instrument 50.

[0027] Here, the wafer W is made of, for example, a single-crystal silicon matrix, and in the state shown in Figure 1, a plurality of devices (not shown) are formed on the downward-facing surface, and these devices are protected by a protective tape (not shown) attached to the surface of the wafer W. The wafer W is held by suction on its surface (bottom surface in Figure 1) to the holding surface 10a of the chuck table 10 via the protective tape (not shown), and its back surface (top surface in Figure 1) is ground by the grinding wheel 25b (see Figure 2A) of the grinding unit 20 while receiving grinding water from the grinding water supply means 40.

[0028] Next, the configurations of the main components of the grinding apparatus 1, namely the chuck table 10, the table rotation mechanism 12, the grinding unit 20, the lifting mechanism 30, the grinding water supply means 40, the thickness measuring instrument 50, the spray nozzle 60, and the control unit 70, will be explained.

[0029] (Chuck table and table rotation mechanism) The chuck table 10 is a disc-shaped member, and as shown in Figure 2, a disc-shaped porous member 11 is incorporated in its center, with the upper surface of this porous member 11 forming a holding surface 10a for holding the wafer W. The porous member 11 is made of porous ceramic or the like and is selectively connected to a suction source (not shown), such as a vacuum pump or ejector.

[0030] Here, the upper surface of the chuck table 10 (porous member 11), as shown in Figure 2, forms a conical holding surface 10a that slopes downward toward the outer circumference with the center as the apex, and the surface of the wafer W (the bottom surface in Figure 2) is held on this holding surface 10a with a protective tape (not shown) facing downwards. Note that in Figure 2, the slope of the conical holding surface 10a of the chuck table 10 is exaggerated in the illustration, but in reality, this slope is so slight that it cannot be seen with the naked eye.

[0031] The chuck table 10 is rotated counterclockwise in the direction of the arrow by the table rotation mechanism 12 shown in Figure 2, with respect to the table rotation axis CL1 which passes through the apex of the holding surface 10a (the center of the holding surface 10a). In other words, the chuck table 10 has a rotation axis (not shown) that extends vertically downward from its center, and this rotation axis is rotated at a predetermined speed around the table rotation axis CL1 by the table rotation mechanism 12. Here, the table rotation mechanism 12 is composed of a servo motor (not shown) which is the drive source, and an encoder (not shown) which detects the rotation speed, rotation direction, rotation angle, etc. of the servo motor.

[0032] As shown in Figure 1, the grinding apparatus 1 according to this embodiment is equipped with a rectangular box-shaped base 100 that is long in the Y-axis direction (front-to-back direction), and a chuck table 10 faces a rectangular opening 100a that is long in the Y-axis direction and opens on the upper surface of this base 100. The area around the chuck table 10 in the opening 100a is covered by a rectangular plate-shaped cover 2, and the front and rear portions of the cover 2 in the opening 100a (-Y direction and +Y direction) are covered by bellows-shaped expandable covers 3 and 4 that move and expand together with the cover 2. Therefore, no matter what position the chuck table 10 is at on the Y-axis, the opening 100a is always closed by the cover 2 and the expandable covers 3 and 4, preventing foreign matter from entering the base 100 from the opening 100a.

[0033] Furthermore, the chuck table 10 can be tilted by a tilt adjustment mechanism (not shown). Specifically, the table rotation axis CL1 of the chuck table 10 can be tilted by an angle α shown with respect to the vertical, and the tilt can be adjusted so that the radial portion of the holding surface 10a of the chuck table 10 is parallel to the lower surface of the grinding wheel 25b.

[0034] Furthermore, the chuck table 10 is movable horizontally (in the Y-axis direction) by a horizontal movement mechanism 13 (see Figure 2) housed within the base 100. Since the horizontal movement mechanism 13 is composed of a known ball screw mechanism, detailed illustration and explanation of it are omitted.

[0035] (Grinding unit) As shown in Figure 1, the grinding unit 20 includes a spindle motor 22, which is a rotational drive source housed in a holder 21; a vertical spindle 23 that is rotationally driven by the spindle motor 22; a disc-shaped mount 24 attached to the lower end of the spindle 23; and a grinding wheel 25 that is detachably mounted on the lower surface of the mount 24. Here, the grinding wheel 25 is composed of a disc-shaped base 25a and a plurality of grinding wheels 25b, which are processing tools that are mounted in an annular shape on the lower surface of the base 25a. The grinding wheels 25b are rectangular block-shaped processing tools for grinding wafers W, and their lower surfaces constitute a grinding surface that contacts the upper surface (workpiece surface) of the wafer W.

[0036] The spindle 23 of the grinding unit 20 rotates together with the mount 24 and the grinding wheel 25 around the grinding wheel rotation axis CL2. However, in the grinding apparatus 1 according to this embodiment, the grinding wheel rotation axis CL2 is positioned vertically and cannot be tilted. In contrast, the table rotation axis CL1 of the chuck table 10 can be tilted by a predetermined angle α relative to the vertical grinding wheel rotation axis CL2 by a tilt adjustment mechanism (not shown), for example as shown in Figure 2. This tilts the holding surface 10a of the chuck table 10 by an angle α with respect to the horizontal plane.

[0037] (Lifting mechanism) The lifting mechanism 30 is a mechanism that moves the grinding unit 20 closer to and further away from the holding surface 10a of the chuck table 10. As shown in Figure 1, it is positioned on the -Y-axis end face (front) of a rectangular box-shaped column 101 that is erected vertically on the +Y-axis end (rear end) of the upper surface of the base 100. This lifting mechanism 30 raises and lowers a rectangular plate-shaped lifting plate 31, which is attached to the back of the holder 21 of the grinding unit 20, along a pair of left and right guide rails 32 in the Z-axis direction, together with the holder 21 and the spindle 23 and grinding wheel 25 held in the holder 21. Here, the pair of left and right guide rails 32 are arranged perpendicularly and parallel to each other on the front surface of the column 101.

[0038] Furthermore, a rotatable ball screw 33 is erected vertically along the Z-axis direction (up and down direction) between a pair of left and right guide rails 32, and the upper end of the ball screw 33 is connected to a reversible servo motor 34, which is the drive source. Here, the servo motor 34 is mounted vertically on the column 101 via a rectangular plate-shaped bracket 35 attached to the upper surface of the column 101. The lower end of the ball screw 33 is rotatably supported on the column 101, and a nut member (not shown) that protrudes horizontally toward the rear (+Y-axis direction) from the back of the lifting plate 31 is screwed onto the ball screw 33. The servo motor 34 is provided with an encoder 36 that detects the rotation direction and rotation speed of the servo motor 34, and the detection signal from the encoder 36 is transmitted to the control unit 70, and the control unit 70 that receives this detection signal drives and controls the servo motor 34 based on the detection signal. The amount of movement of the lifting plate 31 and the grinding unit 20 may be obtained by the pulse signal output from the encoder 36.

[0039] Therefore, by starting the servo motor 34 and rotating the ball screw 33 in both forward and reverse directions, the lifting plate 31, to which a nut member (not shown) that screws onto the ball screw 33 is attached, moves up and down along a pair of guide rails 32 together with the grinding unit 20, causing the grinding unit 20 to move up and down and setting the amount of grinding (grinding allowance) of the grinding wheel 25b relative to the wafer W.

[0040] (Means for supplying grinding water) The grinding water supply means 40 supplies grinding water, such as pure water, to the grinding region, which is the contact area between the grinding wheel 25b and the wafer W during grinding, and ejects the grinding water from the inside of the annular grinding wheel 25b that rotates during grinding. More specifically, as shown in Figure 1, the grinding water supply means 40 is equipped with a grinding water supply source 41 such as a water pump, and a pipe 42 extending from this grinding water supply source 41 is connected to a supply passage (not shown) formed perpendicular to the axis of the spindle motor 22. The supply passage (not shown) formed in the spindle motor 22 is connected to a supply passage 23a formed perpendicular to the axis of the spindle 23 shown in Figure 2A, and the supply passage 23a is connected to a plurality of supply passages 24a that extend radially outward from the center of the mount 24. Furthermore, the base 25a of the grinding wheel 25 has multiple nozzles 25c that extend vertically downward from each supply passage 24a formed in the mount 24.

[0041] Therefore, the grinding water supplied from the grinding water supply source 41 to the spindle motor 22 via the piping 42 is sprayed from multiple nozzles 25c formed on the base 25a of the grinding wheel 25 toward the upper surface of the wafer W through a supply passage 23a formed in the spindle 23 and multiple supply passages 24a formed in the mount 24, as shown in Figure 2A.

[0042] (Thickness measuring instrument) The thickness measuring instrument 50 measures the thickness of multiple locations on the radial portion of the wafer W being ground by the grinding unit 20 in a non-contact manner. As shown in Figure 1, it is equipped with a thickness sensor 53 attached to the tip of an arm 52 that extends horizontally from the upper end of a support shaft 51 that is rotatably erected vertically near the chuck table 10 on the base 100. The thickness sensor 53 may be an optical interferometer or the like, which measures the thickness of the wafer W by irradiating the wafer W with light of a wavelength that passes through the wafer W (infrared light) and observing the interference between the reflected light from the upper surface of the wafer W and the reflected light from the lower surface of the wafer W. Alternatively, the thickness measuring instrument 50 may measure the thickness of the wafer W by emitting ultrasonic vibrations toward the wafer W and receiving the ultrasonic vibrations reflected from the back surface and the front surface of the wafer W, respectively. Furthermore, the thickness measuring instrument 50 may measure the thickness of the wafer W by calculating the difference between the height of the holding surface 10a and the height of the wafer W, using a holding surface height measuring instrument that measures the height of the holding surface 10a non-contactually and a wafer top surface height measuring instrument that measures the height of the top surface of the wafer W non-contactually. This thickness measuring instrument 50 also uses light or ultrasound.

[0043] Here, the support shaft 51 incorporates a motor 54, which is a drive source for rotating the support shaft 51, and an encoder 55 that detects the rotation angle and direction of the motor 54. The motor 54 and encoder 55 are electrically connected to the control unit 70, and when a detection signal is transmitted from the encoder 55 to the control unit 70, the control unit 70 drives the motor 54 based on the received detection signal. In other words, the control unit 70 recognizes the position of the measurement point being measured by the thickness sensor 53 in the radial direction of the wafer W based on the detection signal from the encoder 55.

[0044] Therefore, by starting the motor 54 to rotate the support shaft 51, and as the support shaft 51 rotates, the arm 52 is swung above the holding surface 10a of the chuck table 10, thereby causing the thickness sensor 53 attached to the tip of the arm 52 to reciprocate horizontally in the radial direction of the wafer W being held on the holding surface 10a of the rotating chuck table 10 and being ground by the grinding wheel 25b, the thickness of any multiple locations on the radial portion of the surface of the wafer W being ground can be measured. In addition to horizontally moving the thickness sensor 53 as described above, the thickness measuring device 50 may also consist of multiple thickness sensors 53 arranged on the radial portion of the holding surface 10a.

[0045] (Spray nozzle) The injection nozzle 60 injects cold water or hot water (hot water in this embodiment) from a cold water supply source 61 or a hot water supply source 62 shown in Figure 1 to at least one location (see Figure 3) on the wafer W being ground. It is attached to the tip of an arm 64 that extends horizontally from the upper end of a support shaft 63 which is rotatably erected vertically near the chuck table 10 on the base 100. The support shaft 63 incorporates a motor 65, which is a drive source for rotating the support shaft 63, and an encoder 66 that detects the rotation angle and direction of the motor 65. The motor 65 constitutes a horizontal movement mechanism that moves (rotates horizontally) the injection nozzle 60 horizontally above the wafer W. The motor 65 and the encoder 66 are electrically connected to the control unit 70. When a detection signal from the encoder 66 is transmitted to the control unit 70, the control unit 70 drives and controls the motor 65 based on the received detection signal.

[0046] As shown in Figure 1, the pipes 67 and 68 extending from the chilled water supply source 61 and the hot water supply source 62, respectively, merge into a single pipe 69, which is connected to the injection nozzle 60. Each of the pipes 67 and 68 is provided with on-off valves V1 and V2, respectively, which are electrically connected to the control unit 70, and their opening and closing operations are controlled by the control unit 70.

[0047] Therefore, by activating the motor 65 that constitutes the horizontal movement mechanism and causing the arm 64 to swing around the pivot shaft 63, the injection nozzle 60 attached to the tip of the arm 64 can be moved horizontally above the wafer W in the radial direction of the wafer W, thereby allowing cold or hot water to be injected at any point in the radial portion of the wafer W (see Figure 3). In addition to moving one injection nozzle 60 horizontally in the radial direction of the wafer W as described above, two or more injection nozzles 60 may be moved horizontally. Furthermore, multiple injection nozzles 60 may be arranged in the radial portion of the holding surface 10a.

[0048] (Control Unit) The control unit 70 shown in Figure 1 includes a CPU (Central Processing Unit) that performs calculations according to a control program, and a storage unit such as ROM (Read Only Memory) and RAM (Random Access Memory). In particular, in this embodiment, the control unit 70 positions the spray nozzle 60 at the portion of the wafer W being ground where the thickness (thickness value) measured by the thickness sensor 53 is greater than or less than a preset thickness, and while rotating the chuck table 10 together with the wafer W, it sprays hot or cold water from the spray nozzle 60 to partially expand or contract at least a part of the holding surface 10a of the chuck table 10 via the wafer W. Details of this will be described later.

[0049] [Wafer grinding method] Next, embodiments of the wafer grinding method according to the first to third inventions, which is carried out using the grinding apparatus 1 configured as described above, will be explained.

[0050] <First Invention> The method for grinding a wafer W according to the first invention is: 1) Holding process: 2) Grinding process: This method grinds the wafer W by performing the steps in this order. Each step will be explained below in steps S1 to S10 of the flowchart in Figure 4.

[0051] 1) Holding process: The holding step is a step of holding the wafer W on the holding surface 10a of the chuck table 10. As shown in Figure 2, the wafer W is placed with a protective tape (not shown) facing downwards on the holding surface 10a of the chuck table 10, which is tilted by a tilt adjustment mechanism (not shown) so that the table rotation axis CL1 is tilted at an angle α with respect to the vertical. Then, when the porous member 11 of the chuck table 10 is connected to a suction source (not shown), the porous member 11 is evacuated by the suction source (not shown), generating negative pressure on the porous member 11. Therefore, the wafer W is attracted and held on the conical holding surface 10a of the chuck table 10 by this negative pressure (step S1). In this case, the thin wafer W deforms into an umbrella shape with its center as the apex, following the shape of the holding surface 10a of the chuck table 10.

[0052] 2) Grinding process: In the grinding process, the chuck table 10 is moved horizontally in the +Y axis direction (to the right in Figure 3) by the horizontal movement mechanism 13 along with the wafer W held therein, and the chuck table 10 is positioned so that the circumscribed circle of the annular grinding wheel 25b of the grinding wheel 25 passes through the center of the wafer W. The inclination angle α of the chuck table 10 is set to a value such that the radial portion of the holding surface 10a of the chuck table 10 (the right half in Figure 3) is parallel to the horizontal lower surface (grinding surface) of the grinding wheel 25b, as shown in Figure 3.

[0053] In the above state, the chuck table 10 and the wafer W held therein are driven to rotate at a predetermined speed in the direction of the arrow shown (counterclockwise) around the table rotation axis CL1 by the table rotation mechanism 12, and the grinding wheel 25 is driven to rotate at a predetermined speed in the same direction as the rotation direction of the chuck table 10 (counterclockwise) around the grinding wheel rotation axis CL2 by the spindle motor 22 of the grinding unit 20 shown in Figure 1. Then, the grinding unit 20 is lowered by the lifting mechanism 30, and when the grinding wheel 25b of the grinding wheel 25 comes into contact with the radial portion of the upper surface of the wafer W, the entire surface of the wafer W is ground by the grinding wheel 25b (step S2). At this time, grinding water is supplied from the grinding water supply source 41 of the grinding water supply means 40 through the piping 42 (see Figure 1), a supply passage (not shown) formed on the axis of the spindle motor 22, a supply passage 23a formed on the axis of the spindle 23 shown in Figure 2A, and a plurality of supply passages 24a formed on the mount 24, and is sprayed toward the upper surface of the wafer W from a plurality of nozzles 25c formed perpendicular to the base 25a of the grinding wheel 25. As a result, grinding debris generated by grinding the wafer W is removed by the grinding water, and the frictional heat generated at the contact point between the grinding wheel 25b and the wafer W is removed by the grinding water, cooling the contact point.

[0054] In the above grinding process, while the upper surface (back surface) of the wafer W is being ground by the grinding wheel 25b, the thickness (thickness value) at a plurality of locations in the radial portion of the wafer W is measured by the thickness sensor 53 of the thickness measuring device 50 (step S3). Specifically, when the support shaft 51 of the thickness measuring device 50 shown in FIG. 1 rotates within a predetermined angular range by the motor 54, the arm 52 attached to the upper end of the support shaft 51 pivots horizontally about the support shaft 51. Therefore, the thickness sensor 53 attached to the tip of the arm 52 moves above the wafer W from the center portion toward the outer peripheral portion as shown in FIG. 2A. In the present embodiment, the thickness of the wafer W is measured by the thickness sensor 53 at five locations in the radial direction, namely, the center point A and the outer peripheral point B of the wafer W, the intermediate point C between them, the measurement point D between the center point A and the intermediate point C, and the measurement point E between the intermediate point C and the outer peripheral point B. Note that the measurement locations of the wafer W are not limited to five points. Further, in the present embodiment, as the thickness measuring device 50, one configured by attaching the thickness sensor 53 to the tip of the arm 52 that pivots horizontally about the support shaft 51 is used, but one in which the thickness sensor 53 is attached to five points on the non-pivoting horizontal arm 52 may also be used.

[0055] As described above, FIG. 2B shows the results of measuring the thicknesses at the center point A, the measurement point D, the intermediate point C, the measurement point E, and the outer peripheral point B of the wafer W by the thickness sensor 53. In the present embodiment, the thickness t at the measurement point E of the wafer W E is the largest, and the thicknesses t A 、t D 、t C 、t B measured at the other center point A, measurement point D, intermediate point C, and outer peripheral point B respectively show the same value (set thickness t0 described later).

[0056] And, as described above, the thicknesses t A 、t D 、t C 、t E 、t BOnce measured, the control unit 70 determines whether these thicknesses match a preset set thickness t0 (see Figure 2B) (before hot or cold water is sprayed from the spray nozzle 60 as described later) (step S4).

[0057] In this embodiment, as shown in Figure 2B, the thickness t at the center point A, measurement point D, midpoint C, and outer edge point B of the wafer W, excluding the measurement point E, is measured. A t D t C t B This is equal to the set thickness t0, but the thickness t measured at measurement point E is equal to the set thickness t E (t) is thicker than the set thickness t0 E >t0) Therefore, the result of the judgment in step S4 is No, and the injection nozzle 60 is positioned (step S5).

[0058] Specifically, when the motor 65 shown in Figure 1 is activated and the support shaft 63 is rotated by a predetermined angle, the arm 64 attached to the upper end of the support shaft 63 rotates horizontally, causing the injection nozzle 60 attached to the tip of the arm 64 to move horizontally above the wafer W, and as shown in Figure 3, the injection nozzle 60 is positioned directly above the circumference passing through the measurement point E of the wafer W. In other words, in this positioning of the injection nozzle 60, as shown in Figure 3, the thickness t E The injection nozzle 60 is positioned directly above the measurement point E of the wafer W, where the set thickness t0 exceeds the set thickness.

[0059] As described above, when the injection nozzle 60 is positioned directly above the circumference passing through the measurement point E of the wafer W (step S5), the control unit 70 shown in Figure 1 measures the thickness t at the measurement point E of the wafer W. E It is determined whether the thickness exceeds the set thickness t0 (step S6).

[0060] As a result of the above determination, the thickness t at the measurement point E of the wafer W is determined to be as in this embodiment. E The set thickness t0 is exceeded (t EIf (t0) (Step S6 in Figure 4: Yes), as shown in Figure 3, the chuck table 10 is rotated at a predetermined speed in the direction of the arrow by the table rotation mechanism 12, and hot water is sprayed from the spray nozzle 60 toward the measurement point E of the wafer W, so that the ring-shaped portion of the holding surface 10a corresponding to the measurement point E is heated by the hot water through the wafer W (Step S7). Specifically, as shown in Figure 3, the control unit 70 opens one on-off valve V2 and closes the other on-off valve V1. Then, hot water is supplied from the hot water supply source 62 through the pipes 68 and 69 to the spray nozzle 60, and hot water is sprayed from the spray nozzle 60 toward the measurement point E of the wafer W, so that the ring-shaped portion of the wafer W passing through the measurement point E is heated by the hot water and this portion expands due to thermal expansion.

[0061] Here, the thickness t at measurement point E of wafer W. E The thickness t at the other center point A, measurement point D, midpoint C, and outer perimeter point B. A t D t C t B Because it is larger than and exceeds the set thickness t0, when the holding surface 10a corresponding to the measurement point E of the wafer W is heated by hot water through the wafer W, the area directly below the measurement point E of the holding surface 10a expands in a ring shape, causing the portion of the wafer W at the measurement point E to become thinner than before the hot water was sprayed, and the thickness of each of the other measurement points t A t D t C t B It is ground to the same thickness.

[0062] Conversely, for example, the measured thickness t at measurement point E of wafer W. E (t EIn the case of <t0) (step S6: No), the control unit 70 closes one of the on-off valves V2 and opens the other on-off valve V1. Then, cold water is supplied from the cold water supply source 61 to the injection nozzle 60 through the pipes 67 and 69, and cold water is injected from the injection nozzle 60 toward the measurement point E of the wafer W. As a result, the holding surface 10a corresponding to the measurement point E of the wafer W is cooled in a ring shape (step S8 in FIG. 4). Then, since the area directly below the measurement point E of the holding surface 10a shrinks in a ring shape, the portion of the measurement point E of the wafer W becomes thicker than before the cold water is injected, and the respective thicknesses t A , t D , t C , t B is ground to the same thickness as that. When there are a plurality of measurement points on the wafer W where the thickness exceeds the set thickness t0, the positioning of the injection nozzle 60 and the injection of warm water or cold water from the injection nozzle 60 are repeated by the number of those measurement points.

[0063] Then, when warm water is injected from the injection nozzle 60 toward the wafer W (step S7), or when cold water is injected from the injection nozzle 60 toward the wafer W (step S8), the control unit 70 determines whether the thickness of the wafer W measured by the thickness measuring device 50 is a predetermined finish thickness. When the thickness of the wafer W has been ground to the finish thickness (step S9: Yes), a series of grinding processes for the wafer W is completed (step S10).

[0064] On the other hand, when the wafer W has not been ground until it reaches the predetermined thickness (step S9: No), the processes of steps S2 to S9 are repeated until the thickness of the wafer W reaches the finish thickness.

[0065] As described above, in the wafer grinding method according to the first invention, the thickness of the wafer W is measured while grinding, and hot water is sprayed from the spray nozzle 60 to the portion where the measured thickness is thicker than a predetermined set thickness, or cold water is sprayed from the spray nozzle 60 to the portion where the thickness is thinner than the set thickness. As a result, the wafer W held on the holding surface 10a of the chuck table 10 and ground during the grinding process has a small difference in in-plane thickness and is ground to a uniform thickness over the entire surface.

[0066] In the above embodiment, hot or cold water is sprayed depending on whether the thickness of the wafer W measured by the thickness measuring instrument 50 matches the set thickness. However, a range (set range) may be set for the set thickness, and hot or cold water may be sprayed if the measured thickness exceeds that set range. The set thickness may also be the average value (moving average), median value (moving median), or mode of the thickness measured by the thickness measuring instrument 50.

[0067] <Second Invention> Next, a method for grinding a wafer W according to the second invention, which is carried out using the grinding apparatus 1 shown in Figure 1, will be explained based on Figures 5 to 8. This grinding method is as shown in Figure 5, 1) Holding process: 2) Pre-grinding process: 3) Thickness measurement process: 4) Process for changing the height of the retaining surface: 5) Finish grinding process: This method grinds the wafer W by performing the steps in this order. Each step will be explained below in steps S11 to S21 of Figure 8.

[0068] 1) Holding process: The holding step is the step of holding the wafer W on the holding surface 10a of the chuck table 10 (step S11). Since this holding step is the same as the holding step in the first invention, its illustration and explanation are omitted.

[0069] 2) Pre-grinding process: The preliminary grinding process is a process in which one wafer W is ground up to a certain point, and in this preliminary grinding process, the wafer W is ground to a thickness that does not reach a predetermined finish thickness (a set thickness that is thicker than the finish thickness) (step S12).

[0070] In the pre-grinding process, the chuck table 10 is positioned so that the circumscribed circle of the annular grinding wheel 25b of the grinding wheel 25 passes through the center of the wafer W. In this state, the chuck table 10 and the wafer W held therein are driven to rotate at a predetermined speed in the direction of the arrow shown (counterclockwise) around the table rotation axis CL1 by the table rotation mechanism 12, and the grinding wheel 25 of the grinding unit 20 shown in Figure 1 is driven to rotate at a predetermined speed in the same direction as the rotation direction of the chuck table 10 (counterclockwise) around the grinding wheel rotation axis CL2. From this state, the grinding unit 20 is lowered by the lifting mechanism 30, and when the grinding wheel 25b of the grinding wheel 25 contacts the radial portion of the upper surface of the wafer W, the wafer W being ground by the grinding wheel 25b is ground to a thickness that does not reach the preset finish thickness (set thickness) (pre-grinding).

[0071] 3) Thickness measurement process: The thickness measurement step is a step in which the thickness of the wafer W that has been pre-ground in the preceding pre-grinding step is measured by the thickness sensor 53 of the thickness measuring instrument 50 at multiple locations on the radial portion of the wafer W (step S13). Specifically, as shown in Figure 6A, the thickness sensor 53 moves over the wafer W from the center to the outer edge. In this embodiment, the thickness of the wafer W is measured by the thickness sensor 53 at five radial points: the center point A, the outer edge point B, the midpoint between the two C, the measurement point D between the center point A and the midpoint C, and the measurement point E between the midpoint C and the outer edge point B. Note that the measurement locations on the wafer W are not limited to five points.

[0072] As described above, Figure 6B shows the results of measuring the thickness at the center point A, measurement point D, midpoint C, measurement point E, and outer edge point B of the wafer W using the thickness sensor 53. In this embodiment, the thickness t at measurement point E of the wafer W is measured. E The largest thickness was measured at the other center point A, measurement point D, midpoint C, and outer perimeter point B, respectively. A t D t C t B These represent the same value (set thickness t0).

[0073] 4) Process for changing the height of the retaining surface: As described above, the thickness t at the center point A, measurement point D, midpoint C, measurement point E, and outer edge point B of the wafer W. A t D t C t B Once measured, the control unit 70 determines whether these thicknesses match a pre-set thickness t0 (see Figure 6B) (as described later, before hot or cold water is sprayed from the spray nozzle 60) (step S14).

[0074] In this embodiment, as shown in Figure 6B, the thickness t at the measurement point E of the wafer W is E Since this does not match the set thickness (Step S14; No), the injection nozzle 60 is positioned (Step S15). That is, in positioning the injection nozzle 60, as shown in Figure 7, the thickness t E The injection nozzle 60 is positioned directly above the measurement point E of the wafer W, where the set thickness t0 exceeds the set thickness (step S15).

[0075] Specifically, when the motor 65 shown in Figure 1 is activated and the support shaft 63 is rotated by a predetermined angle, the arm 64 attached to the upper end of the support shaft 63 rotates horizontally, causing the injection nozzle 60 attached to the tip of the arm 64 to move horizontally above the wafer W, and as shown in Figure 7, the injection nozzle 60 is positioned directly above the circumference passing through the measurement point E of the wafer W.

[0076] As described above, when the injection nozzle 60 is positioned directly above the circumference passing through the measurement point E of the wafer W, the control unit 70 shown in Figure 1 measures the thickness t at the measurement point E of the wafer W. E It is determined whether the thickness exceeds the set thickness t0 (step S16).

[0077] As a result of the above determination, the thickness t at the measurement point E of the wafer W is determined to be as in this embodiment. E The set thickness t0 is exceeded (t E If (t0) (step S16: Yes), as shown in Figure 7, the chuck table 10 is rotated at a predetermined speed in the direction of the arrow by the table rotation mechanism 12, and hot water is sprayed from the spray nozzle 60 toward the measurement point E of the wafer W, so that the holding surface 10a directly below the measurement point E is heated in a ring shape through the wafer W (step S17). Specifically, as shown in Figure 7, the control unit 70 opens one on-off valve V2 and closes the other on-off valve V1. Then, hot water is supplied from the hot water supply source 62 through the pipes 68 and 69 to the spray nozzle 60, and hot water is sprayed from the spray nozzle 60 toward the ring-shaped portion of the wafer W passing through the measurement point E, so that the holding surface 10a of the chuck table 10 is heated in a ring shape through this ring-shaped portion of the wafer W and thermally expands, causing the height of the holding surface 10a to rise.

[0078] Here, the thickness t at measurement point E of wafer W. E The thickness t at the other center point A, measurement point D, midpoint C, and outer perimeter point B. A t D t C t B Because it is larger than and exceeds the set thickness t0, when the holding surface 10a is heated through the wafer W by spraying hot water from the spray nozzle 60 to the measurement point E of the wafer W, the area directly below the measurement point E of the holding surface 10a expands in a ring shape, so that the portion of the wafer W at the measurement point E becomes thinner than before the hot water was sprayed, and the thickness of each of the other measurement points t A t D t C t B It is ground to the same thickness.

[0079] Conversely, for example, the measured thickness t at the measurement point E on the wafer W E is less than the set thickness t0 (t E < t0). In this case (step S16: No), the control unit 70 closes one on-off valve V2 and opens the other on-off valve V1. Then, cold water is supplied from the cold water supply source 61 to the injection nozzle 60 through the pipes 67 and 69, and while the chuck table 10 is rotated at a predetermined speed in the direction of the illustrated arrow by the table rotation mechanism 12, cold water is injected from the injection nozzle 60 toward the measurement point E of the wafer W (step S18). As a result, the holding surface 10a directly below the measurement point E of the wafer W is cooled and shrunk in a ring shape through the wafer W, so that the height of the holding surface 10a is decreased. The thickness t of the wafer W measured by the thickness measuring device 50 A , t D , t C , t E , t B If there are a plurality of measurement points where the thickness does not match the set thickness t0, the positioning of the injection nozzle 60 and the injection of warm water or cold water from the injection nozzle 60 are repeated by the number of the exceeded measurement points.

[0080] 5) Finishing grinding process: The finishing grinding process is a process of finishing grinding the wafer W sucked and held on the holding surface 10a of the chuck table 10 whose height has been changed (corrected) in the previous holding surface height changing process until the thickness of the wafer W that has been preliminarily ground reaches a predetermined finishing thickness when the thickness of the wafer W does not match the set thickness t0.

[0081] In this finishing grinding, the chuck table 10 is positioned so that the outer circumcircle of the annular grinding wheel 25b of the grinding wheel 25 passes through the center of the wafer W. At this time, the chuck table 10 is tilted by an angle α with respect to the grinding wheel rotation axis CL2 perpendicular to the table rotation axis CL1 so that the radius portion of its holding surface 10a is parallel to the horizontal lower surface (grinding surface) of the grinding wheel 25b.

[0082] In the above state, the chuck table 10 and the wafer W held therein are driven to rotate at a predetermined speed in the direction of the arrow shown (counterclockwise) around the table rotation axis CL1 by the table rotation mechanism 12, and the grinding wheel 25 is driven to rotate at a predetermined speed in the same direction as the rotation direction of the chuck table 10 (counterclockwise) around the grinding wheel rotation axis CL2 by the spindle motor 22 of the grinding unit 20 shown in Figure 1. Then, the grinding unit 20 is lowered by the lifting mechanism 30, and when the grinding wheel 25b of the grinding wheel 25 comes into contact with the radial portion of the upper surface of the wafer W, the entire surface of the wafer W is finished grinding by the grinding wheel 25b (step S19).

[0083] As described above, when the wafer W is finished grinding (step S19), the control unit 70 determines whether the thickness of the wafer W has been ground down to the finish thickness. If the thickness of the wafer W has been ground down to the finish thickness (step S20: Yes), the series of grinding operations on the wafer W is completed (step S21).

[0084] On the other hand, if the wafer W has not been ground to a predetermined thickness (step S20: No), the finish grinding of the wafer W is repeated until it reaches the final thickness.

[0085] As described above, in the wafer grinding method according to the second invention, the wafer W is pre-ground to a thickness that does not reach a predetermined finish thickness, the thickness of multiple locations on the radial portion of the pre-ground wafer W is measured, and hot water is sprayed from the spray nozzle 60 to the locations that are thicker than the set thickness, or cold water is sprayed from the spray nozzle 60 to the locations that are thinner than the set thickness, thereby expanding or contracting the chuck table 10 via the pre-ground wafer W to change the height of the holding surface 10a. As a result, the temperature of the holding surface 10a of the chuck table 10 becomes uniform over the entire surface, and the entire surface of the holding surface 10a becomes a uniform flat surface without irregularities or undulations, so that in the subsequent finish grinding, the wafer W is ground to a uniform thickness over the entire surface with minimal in-plane thickness differences.

[0086] <Third Invention> Next, a method for grinding a wafer W according to the third invention, which is carried out using the grinding apparatus 1 shown in Figure 1, will be explained based on Figures 9 to 12. This grinding method is as shown in Figure 9, 1) First holding step: 2) First grinding process: 3) Thickness measurement process: 4) Storage process: 5) Separation process: 6)Second holding step: 7) Retaining surface height correction process: 8) Second grinding process: This method grinds the wafer W by performing the steps in this order. Each step will be explained below in steps S31 to S48 of Figure 12.

[0087] 1) First holding step: The first holding step is a step of holding the first wafer W1 on the holding surface 10a of the chuck table 10 (step S31), in which the first wafer W1 is placed on the holding surface 10a of the chuck table 10 with a protective tape (not shown) facing downwards. Then, when the porous member 11 of the chuck table 10 is connected to a suction source (not shown), the porous member 11 is evacuated by the suction source (not shown), so a negative pressure is generated in the porous member 11. Therefore, the first wafer W1 is attracted and held on the conical holding surface 10a of the chuck table 10 by this negative pressure.

[0088] 2) First grinding process: The first grinding step is a step of grinding the first wafer W1, which was held by suction on the holding surface 10a of the chuck table 10 in the preceding first holding step, to a predetermined finish thickness. In this first grinding step, the chuck table 10 is positioned so that the circumscribed circle of the annular grinding wheel 25b of the grinding wheel 25 passes through the center of the first wafer W1. The inclination angle α of the chuck table 10 is set to a value such that the radial portion of the holding surface 10a of the chuck table 10 (the right half of Figure 14) is parallel to the horizontal lower surface (grinding surface) of the grinding wheel 25.

[0089] In the above state, the chuck table 10 and the first wafer W1 held therein are driven to rotate at a predetermined speed in the direction of the arrow shown (counterclockwise) around the table rotation axis CL1 by the table rotation mechanism 12, and the grinding wheel 25 is driven to rotate at a predetermined speed in the same direction as the rotation direction of the chuck table 10 (counterclockwise) around the grinding wheel rotation axis CL2 by the spindle motor 22 of the grinding unit 20 shown in Figure 1. Then, the grinding unit 20 is lowered by the lifting mechanism 30, and when the grinding wheel 25b of the grinding wheel 25 comes into contact with the radial portion of the upper surface of the first wafer W1, the entire surface of the first wafer W1 is first ground to the finish thickness by the grinding wheel 25b (step S32).

[0090] 3) Thickness measurement process: The thickness measurement step is a step in which the thickness of the first wafer W1, which has been ground to the finish thickness in the preceding first grinding step, is measured by the thickness sensor 53 of the thickness measuring instrument 50 at multiple locations on the radial portion of the first wafer W1 (step S33). Specifically, as shown in Figure 10A, the thickness sensor 53 moves over the first wafer W1 from the center to the outer edge. In this embodiment, the thickness of the first wafer W1 is measured by the thickness sensor 53 at five radial points: the center point A, the outer edge point B, the midpoint between the two C, the measurement point D between the center point A and the midpoint C, and the measurement point E between the midpoint C and the outer edge point B. Note that the measurement locations of the first wafer W1 are not limited to five points.

[0091] As described above, Figure 10B shows the results of measuring the thickness of the first wafer W1 at the center point A, measurement point D, midpoint C, measurement point E, and outer edge point B using the thickness sensor 53. In this embodiment, the thickness t at measurement point E of the first wafer W1 is E The largest thickness was measured at the other center point A, measurement point D, midpoint C, and outer perimeter point B, respectively. A t D t C t B These indicate the same value (finished thickness).

[0092] 4) Memory process: In the memory process, the control unit 70 determines whether the thicknesses t A , t B , t C , t D , t E measured at the center point A, outer peripheral point B, intermediate point C, measurement point D, intermediate point C, and measurement point E of the first wafer W1 respectively match the finished thickness t0 (step S34). In the present embodiment, the thicknesses t A , t D , t C , t B measured at the center point A, measurement point D, intermediate point C, and outer peripheral point B respectively match the finished thickness t0, but the thickness t E measured at the measurement point E does not match the finished thickness t0 (see FIG. 10B). Therefore, the determination result in step S34 is No, and it is determined whether the thickness t E is greater than the finished thickness t0 (step S35).

[0093] In the present embodiment, since the thickness t E measured at the measurement point E is greater than the finished thickness t0 (t E > t0), this measurement point E is stored in the memory unit of the control unit 70 as the first location (step S36). On the other hand, for example, as shown by the dashed line in FIG. 10B, when the thickness t D of the first wafer W1 measured at the measurement point D is less than the finished thickness t0 (t D < t0), the measurement point D is stored in the memory unit of the control unit 70 as the second location (step S37).

[0094] On the other hand, when the thicknesses t A , t B , t C , t D , t E measured at the center point A, outer peripheral point B, intermediate point C, measurement point D, and measurement point E of the first wafer W1 respectively match the finished thickness t0 (step S34: Yes), the subsequent separation process described below, which is the next process, is performed (step S38).

[0095] 5) Separation process: The separation process involves measuring the thickness t at multiple points on the radial portion of the first wafer W1 during the thickness measurement process, namely, the center point A, the outer edge point B, the midpoint point C, the measurement point D, and the measurement point E. A t B t C t D t E Once the measurement is complete, the first wafer W1 is separated from the holding surface 10a of the chuck table 10.

[0096] In this separation process, the lifting mechanism 30 raises the grinding wheel 25 and other components, moving them above the chuck table 10. Then, the connection between the porous member 11 of the chuck table 10 and a suction source (not shown) is disconnected to release the suction force caused by the negative pressure on the first wafer W1. From this state, the first wafer W1 is separated upward from the holding surface 10a of the chuck table 10 and removed (step S38). As a result, the holding surface (upper surface of the porous member 11) 10a is exposed on the upper surface of the chuck table 10.

[0097] 6)Second holding step: The second holding step is to hold the second wafer W2 on the holding surface 10a of the chuck table 10 from which the first wafer W1 was removed in the preceding separation step (step S39). In this second holding step, as shown in Figure 16, the second wafer W2 is placed on the holding surface 10a of the chuck table 10 with a protective tape (not shown) facing downwards. Then, when the porous member 11 of the chuck table 10 is connected to a suction source (not shown), the porous member 11 is evacuated by the suction source (not shown), generating negative pressure on the porous member 11. Consequently, the second wafer W2 is attracted and held on the conical holding surface 10a of the chuck table 10 by this negative pressure.

[0098] 7) Retaining surface height correction process: The holding surface height correction step is a step of correcting the height of the holding surface 10a of the chuck table 10, and in this holding surface height correction step, it is determined whether or not a first location (a location where the thickness of the first wafer W1 is greater than the finished thickness t0) or a second location (a location where the thickness of the first wafer W1 is less than the finished thickness t0) is stored in the memory unit of the control unit 70 (step S40).

[0099] If the memory unit of the control unit 70 stores either a first or second location (step S40: Yes), it is determined whether the stored location is the first location or not (step S41). If the memory unit stores the first location (step S41: Yes), as shown in Figure 11, the injection nozzle 60 is positioned above the measurement point E, which is the first location (step S42), and the chuck table 10 and the second wafer W2 held therein are rotated around the table rotation axis CL1 in the direction of the arrow by the table rotation mechanism 12, while hot water is injected from the injection nozzle 60 to the location on the second wafer W2 corresponding to the measurement point E (step S43).

[0100] In the injection of hot water from the injection nozzle 60 onto the second wafer W2, as shown in Figure 11, one on-off valve V1 is closed while the other on-off valve V2 is opened. Then, hot water is supplied from the hot water supply source 62 to the injection nozzle 60 via pipes 68 and 69, and the hot water is injected from the injection nozzle 60 toward the location corresponding to the measurement point E of the rotating second wafer W2. When hot water is injected toward the location corresponding to the measurement point E of the second wafer W2 in this way, the location of the holding surface 10a of the chuck table 10 corresponding to the measurement point E is heated in a ring shape by the hot water via the second wafer W2, and this ring-shaped portion of the holding surface 10a expands due to thermal expansion.

[0101] The measured thickness t of the first wafer W1 E The portion of the holding surface 10a of the chuck table 10 corresponding to a measurement point E where the thickness is greater than the finished thickness t0 has a lower temperature than the other portions. By heating this portion with hot water, the height of the holding surface 10a is corrected. As a result, the holding surface 10a becomes a flat plane without irregularities.

[0102] On the other hand, as shown by the dashed line in FIG. 10B, since the thickness t at the measurement point D is smaller than the finished thickness t0, when this measurement point D is stored as the second location in the storage unit of the control unit 70 (step S41: No), as shown in FIG. 11, the injection nozzle 60 is positioned above the position corresponding to the measurement point D of the second wafer W2 (step S44), and cold water is injected from the injection nozzle 60 toward the portion corresponding to the measurement point D of the second wafer W2 (step S45). That is, in the injection of cold water from the injection nozzle 60 to the second wafer W2, as shown in FIG. 11, while one of the on-off valves V4 is closed, the other on-off valve V3 is opened. Then, cold water is supplied from the cold water supply source 61 to the injection nozzle 60 through the path indicated by the arrow, and cold water is injected from the injection nozzle 60 toward the location corresponding to the measurement point D of the rotating second wafer W2. Then, the portion of the holding surface 10a of the chuck table 10 corresponding to the measurement point D is cooled through the second wafer W2. Here, since the portion of the holding surface 10a of the chuck table 10 corresponding to the measurement point D where the thickness of the first wafer W1 is smaller than the finished thickness t0 is at a higher temperature and expanded than other portions, this portion can be cooled and contracted by cold water. As a result, the height of the holding surface 10a is corrected, and the holding surface 10a becomes a flat plane without irregularities. In the above description, hot water or cold water is injected from the injection nozzle 60 to the second wafer W2 to change the height of the holding surface 10a through the second wafer W2. However, hot water or cold water may be injected from the injection nozzle 60 to the holding surface 10a to change the height of the holding surface 10a, and then the second wafer W2 may be held and ground.

[0103] ​​In this embodiment, the case where there is only one point on the first wafer W1 with a thickness greater than the finished thickness (measurement point E) was described as an example. However, if there are multiple such points, the spray nozzle 60 will spray hot water to multiple locations on the second wafer W2. Furthermore, if the first wafer W1 has a mixture of locations with a thickness greater than and less than the finished thickness t0, hot water and cold water will be sprayed from the spray nozzle 60 to the locations on the second wafer W2 corresponding to those points.

[0104] 8) Second grinding process: The second grinding step is a step (step S46) in which the second wafer W2, which is held by suction on the holding surface 10a of the chuck table 10 whose height was corrected in the preceding holding surface height correction step, is ground to the finished thickness (second grinding). In this second grinding step, the chuck table 10 is positioned so that the circumscribed circle of the annular grinding wheel 25b of the grinding wheel 25 passes through the center of the second wafer W2. At this time, the chuck table 10 is tilted by the angle α shown in the figure with respect to the vertical grinding wheel rotation axis CL2 so that the radial portion of its holding surface 10a is parallel to the horizontal lower surface (grinding surface) of the grinding wheel 25b.

[0105] In the above state, the chuck table 10 and the second wafer W2 held therein are driven to rotate at a predetermined speed in the direction of the arrow (counterclockwise) around the table rotation axis CL1 by the table rotation mechanism 12, and the grinding wheel 25 is driven to rotate at a predetermined speed in the same direction as the rotation direction of the chuck table 10 (counterclockwise) around the grinding wheel rotation axis CL2 by the spindle motor 22 of the grinding unit 20 shown in Figure 1. Then, the grinding unit 20 is lowered by the lifting mechanism 30, and when the grinding wheel 25b of the grinding wheel 25 comes into contact with the radial portion of the upper surface of the wafer W, the entire surface of the wafer W is finished grinding by the grinding wheel 25b.

[0106] As described above, when the second wafer W2 is finished grinding (step S46), the control unit 70 determines whether the thickness of the second wafer W2 has been ground down to the finished thickness t0. If the thickness of the second wafer W2 has been ground down to the finished thickness t0 (step S47: Yes), the series of grinding operations on the second wafer W2 is completed (step S48).

[0107] On the other hand, if the second wafer W2 has not been ground to a predetermined finish thickness t0 (step S47: No), the grinding of the second wafer W2 is repeated until the finish thickness t0 is reached.

[0108] In this embodiment, the second grinding step is performed after the retaining surface height correction step, but the second grinding step may be performed simultaneously with the retaining surface height correction step.

[0109] As described above, in the grinding method for the second wafer W2 according to the third invention, the first wafer W1 is ground to a preset finish thickness t0, the thickness of the ground first wafer W1 is measured and stored by the control unit 70 as the first location where the first wafer W1 is thicker than the finish thickness t0 and the second location where the first wafer W1 is thinner than the finish thickness t0. Hot water is sprayed from the spray nozzle 60 to the first location to heat and expand the portion of the holding surface 10a of the chuck table 10 corresponding to the first location via the second wafer W2, and cold water is sprayed from the spray nozzle 60 to cool and contract the portion of the holding surface 10a of the chuck table 10 corresponding to the second location via the second wafer W2. As a result, the height of the holding surface 10a of the chuck table 10 is corrected, and the holding surface 10a becomes a flat plane without irregularities. As a result, the second wafer W2 held on the holding surface 10a of the chuck table 10 can be ground to a uniform thickness across its entire surface while minimizing the difference in thickness within its plane.

[0110] Incidentally, the grinding methods according to the first to third inventions described above can also be applied to grinding the bonded wafer W shown in Figure 13. Here, the bonded wafer W is composed of a support wafer WS and a device wafer WD bonded to the support wafer WS, and a plurality of devices (not shown) are formed on the bonding surface of the device wafer WD to the support wafer WS (the lower surface in Figure 13).

[0111] Then, as shown in Figure 13, the bonded wafer W is held by suction on the holding surface 10a of the chuck table 10 with the support wafer WS facing downwards, and the back surface (top surface) of the device wafer WD is ground by the grinding wheel 25b of the rotating grinding wheel 25. In other words, when grinding the device wafer WD of the bonded wafer W, as in the first invention, the thickness of the device wafer WD is measured with a thickness measuring instrument 50, and hot or cold water is sprayed onto the holding surface 10a from a spray nozzle 60 to correct the height of the holding surface 10a, while grinding the device wafer WD to a predetermined finished thickness. Alternatively, as in the second invention, the thickness of the pre-ground device wafer WD is measured with a thickness measuring instrument 50, and then hot or cold water is sprayed onto the holding surface 10a from a spray nozzle 60 to correct the height of the holding surface 10a, while grinding the device wafer WD to a predetermined finished thickness.

[0112] Furthermore, as in the third invention, the device wafer WD of the bonded wafer W is ground to a finish thickness, the thickness of the device wafer WD is measured with a thickness measuring instrument 50, and then hot or cold water is sprayed onto the holding surface 10a from a spray nozzle 60 to correct the height of the holding surface 10a, and then the device wafer WD of the next (subsequent) bonded wafer W is ground to a predetermined finish thickness.

[0113] <Second Embodiment> Next, Figures 14 to 29 will describe embodiments of the present invention other than those described above. Figure 14 is a schematic perspective view of a grinding apparatus according to the second embodiment. In the following description, the same reference numerals may be used for components that are the same as or equivalent to those in the first embodiment, and their descriptions may be omitted or simplified. In the second embodiment, instead of the configuration in the first embodiment in which hot or cold water is sprayed from the spray nozzle 60, a heating unit 160 is installed. As shown in Figure 14, the heating unit 160 is installed on the base 100 at a position through which the chuck table 10 passes.

[0114] The heating unit 160 includes a support shaft 161 that is rotatably erected vertically near the chuck table 10 on the base 100, an arm 162 that extends horizontally from the upper end of the support shaft 161, and a spot heater 163 attached to the tip of the arm 162. The support shaft 161 incorporates a motor 164, which is a drive source for rotating the support shaft 161, and an encoder 165 that detects the rotation angle and direction of the motor 164.

[0115] The spot heater 163 is configured by combining a concave reflective mirror and a near-infrared lamp such as a halogen heater lamp, and can be exemplified as a heater unit that enhances the directivity of the irradiated high-temperature beam (heat ray). The spot heater 163 partially heats the wafer W held below on the holding surface 10a by irradiating it with a high-temperature beam, and is provided so that the height of the holding surface 10a can be changed by expanding the porous member 11 of the chuck table 10 via the wafer W.

[0116] In the heating section 160, the motor 164 is driven to swing the arm 162 above the wafer W around the pivot shaft 161, causing the spot heater 163 attached to the tip of the arm 162 to move radially around the wafer W. This movement allows the spot heater 163 to partially heat and expand the porous member 11 (holding surface 10a) of the wafer W and, consequently, the chuck table 10 at any point in the radial region of the wafer W.

[0117] The wafer W to be ground by the grinding apparatus 1 may be protected by attaching a protective tape (not shown) to the downward-facing surface WA in the state shown in Figure 14. In the grinding process, the surface WA of the wafer W is the surface to be held by the holding surface 10a of the chuck table 10, and the back surface WB of the wafer W (the top surface in Figure 14) is the surface to be ground.

[0118] When grinding a wafer W held on a chuck table 10, the chuck table 10 and wafer W are moved and positioned below the grinding unit 20 via a horizontal movement mechanism 13. In this state, the grinding wheel 25 in the grinding unit 20 rotates and descends at a predetermined speed to feed the wafer for processing, and the back surface WB of the wafer W is ground by the grinding wheel 25b. During this grinding, the chuck table 10 rotates, for example, in the same direction as the grinding wheel 25, causing the wafer W to rotate. The outer diameter of the grinding edge by the grinding wheel 25b is larger than the radius of the holding surface 10a, and by passing through the center of the wafer W, the entire surface of the wafer W is uniformly ground by the grinding wheel 25b.

[0119] The operation of each part of the grinding apparatus 1 is controlled by the control unit 70 (see Figure 14). The control unit 70 is composed of a processor that performs various processes, as well as a memory unit 71 that stores various parameters and programs. The memory unit 71 of the control unit 70 stores, as part of the control program, a program for controlling the operation of, for example, the lifting mechanism 30, the grinding unit 20, the grinding water supply means 40, the thickness measuring instrument 50, the heating unit 160, etc. The control unit 70 also includes a holding surface height change control unit 72. In the operation of each part of the grinding apparatus 1 described below, unless the main control entity is specified, it is assumed that the operation is controlled by a control signal sent from the control unit 70.

[0120] [Wafer grinding method] Next, the first to third methods for grinding a wafer W, performed using the grinding apparatus 1 in the second embodiment configured as described above, will be explained.

[0121] <First grinding method> First, the first grinding method for wafer W in the second embodiment will be described below. Figure 17 is a flowchart of each step of the first grinding method. As shown in Figure 17, the first grinding method for wafer W according to this embodiment is a method of grinding wafer W through 1) a holding step, 2) a grinding step, and 3) a discharge step, and each of these steps will be described below.

[0122] 1) Holding process Figure 15 is an explanatory diagram of the holding process in the first grinding method. In the holding process, first, as shown in Figure 15, the chuck table 10 is tilted by a tilt adjustment mechanism (not shown) such that its table rotation axis CL1 is tilted by an angle α shown with respect to the Z-axis direction. In this state, for example, a wafer W is placed on the holding surface 10a of the chuck table 10 by a transport device (not shown), and the porous member 11 of the chuck table 10 is connected to a suction source (not shown). Then, a negative pressure is generated in the porous member 11 by the vacuum drawn by the suction source, and the wafer W is attracted and held to the holding surface 10a by this negative pressure. At this time, the wafer W is deformed into an umbrella shape with its center as the apex, following the shape of the holding surface 10a.

[0123] 2) Grinding process After the holding process is performed, the grinding process is carried out as shown in Figure 17. In the grinding process of the first grinding method, the following steps are performed: 2-1) processing step, 2-2) thickness measurement step, 2-3) calculation step, 2-4) spot heater positioning step, and 2-5) holding surface raising step. Each step in the grinding process is described below. Figure 16 is an explanatory diagram of the processing step performed in the grinding process of the first grinding method. Figure 18A is an explanatory diagram of the thickness measurement step performed in the grinding process of the first grinding method. Figure 18B is a diagram showing the radial distribution of the wafer thickness. Figure 19 is an explanatory diagram of the spot heater positioning step performed in the grinding process of the first grinding method. Figures 20 and 21 are explanatory diagrams of the holding surface raising step performed in the grinding process of the first grinding method. In the first grinding method, the thickness measurement process, calculation process, spot heater positioning process, and holding surface raising process are carried out simultaneously with the processing process of grinding the back surface WB of the wafer W.

[0124] 2-1) Processing process In the processing step, the chuck table 10 and the wafer W held on the chuck table 10 are moved horizontally in the Y-axis direction by the horizontal movement mechanism 13, and the chuck table 10 is positioned so that the circumscribed circle of the annular grinding wheel 25b passes through the center of the wafer W. The inclination angle α of the chuck table 10 is set to a value such that the radial region of the holding surface 10a (right half of Figure 15) is parallel to the horizontal lower surface (grinding surface) of the annular grinding wheel 25b.

[0125] Furthermore, the table rotation mechanism 12 rotates the chuck table 10 and the wafer W held on the chuck table 10 at a predetermined speed in the direction of the arrow shown on the table rotation axis CL1. In addition, the spindle motor 22 (see Figure 14) of the grinding unit 20 rotates the grinding wheel 25 at a predetermined speed in the same direction as the rotation of the chuck table 10 on the grinding wheel rotation axis CL2.

[0126] When the grinding unit 20 is lowered by the lifting mechanism 30 from this state, as shown in Figure 16, the grinding wheel 25b comes into contact with the radial region of the back surface WB of the wafer W, and the entire surface of the back surface WB of the wafer W is ground by the grinding wheel 25b.

[0127] At this time, grinding water is supplied from the grinding water source 41 of the grinding water supply means 40 through the pipe 42 and sprayed from multiple nozzles 25c formed on the grinding wheel 25 toward the back surface WB of the wafer W. As a result, grinding debris generated by grinding the wafer W is removed by the grinding water, and the frictional heat generated at the contact point between the grinding wheel 25b and the wafer W is removed by the grinding water, cooling the contact point.

[0128] If only the above processing steps were performed in the grinding process, the back surface WB of the wafer W would be ground, and due to deformation of the chuck table 10 itself, which receives processing heat during grinding, the wafer W may not have a uniform thickness, resulting in thickness differences. Therefore, the following steps are performed in the grinding process.

[0129] 2-2) Thickness measurement process While the wafer W is being ground during the processing stage, a thickness measurement process is carried out. In the thickness measurement process, the thickness of multiple points in the radial region of the wafer W being ground during the processing stage is measured.

[0130] In the thickness measurement process, the support shaft 51 of the thickness measuring device 50 shown in Figure 14 is rotated in forward and reverse directions within a predetermined angular range by a motor 54, and an arm 52 attached to the upper end of the support shaft 51 is reciprocated horizontally around the support shaft 51. As a result, as shown in Figure 18A, the thickness sensor 53 at the tip of the arm 52 moves back and forth over the wafer W from the center A to the outer periphery B, and from the outer periphery B to the center A. In the first grinding method, the thickness of the wafer W is measured by the thickness sensor 53 at five points: the center A, the outer periphery B, the intermediate part C between the center A and the outer periphery B, the measurement part D between the center A and the intermediate part C, and the measurement part E between the intermediate part C and the outer periphery B. The measurement by the thickness sensor 53 is performed optically and non-contact with the wafer W. Note that the measurement locations are not limited to five points.

[0131] In Figure 18B, the thickness of wafer W at the center A, measurement area D, intermediate area C, measurement area E, and outer edge B is the thickness value T. A , T D , T C , T E , T B This is shown as an example of the results measured by the thickness sensor 53. In Figure 18B, the thickness value T at the measurement section E of the wafer W is shown. E However, it is larger compared to other measurement points. The thickness value T is the measurement result of the thickness sensor 53. A , T D , T C , T E , T B This is output to the control unit 70.

[0132] 2-3) Calculation process The calculation process is carried out while continuing the grinding process of the wafer W using the grinding wheel 25b in the processing process and the thickness measurement of the wafer W using the thickness measuring instrument 50 in the thickness measurement process. In the calculation process, the thickness values ​​T at multiple measurement points measured by the thickness sensor 53 of the thickness measuring instrument 50 in the thickness measurement process are calculated. A , T D , T C , T E , T BThe holding surface height change control unit 72 of the control unit 70 is input to this control unit 70. In addition, the holding surface height change control unit 72 receives the thickness values ​​T of multiple measurement points. A , T D , T C , T E , T B A set thickness S used for comparison is predetermined. This set thickness S is determined by the thickness values ​​T of multiple measurement points. A , T D , T C , T E , T B For example, the average or median value may be determined and set in the holding surface height change control unit 72, or the processing information of the wafer W may be stored and set in the storage unit 71 before grinding the wafer W is performed. Alternatively, the set thickness S may be thicker than the pre-set finish thickness after grinding the wafer W is completed, and may be set as a numerical range with an upper limit and a lower limit.

[0133] In the calculation process, the holding surface height change control unit 72 uses a pre-set thickness S and the thickness values ​​T of multiple measurement points. A , T D , T C , T E , T B The two are compared. Then, multiple thickness values ​​T are measured. A , T D , T C , T E , T B Of these, the parts that are thicker than the set thickness S are identified. As shown in Figure 18B, the set thickness S is set to the thickness value T A , T D , T C , T E , T B When the mean (moving average) or median (moving median) of these values ​​is used, these thickness values ​​T A , T D , T C , T E , T B Of these, the one that is thicker than the set thickness S is the one with thickness value T. E As a result, any area thicker than the set thickness S is identified as the "measurement area E".

[0134] 2-4) Spot heater positioning process While the processing and thickness measurement processes continue, the spot heater positioning process is performed after the calculation process. In the spot heater positioning process, the spot heater 163 of the heating unit 160 is positioned directly above the measurement section E of the wafer W, which was set in the calculation process, via the holding surface height change control unit 72. This positioning is achieved by rotating the support shaft 161 by a predetermined angle in the heating unit 160 by the drive of the motor 164 shown in Figure 14. As a result, the spot heater 163 is moved horizontally above the wafer W by the horizontal rotation of the arm 162, and as shown in Figure 19, the spot heater 163 is positioned directly above the measurement section E of the wafer W.

[0135] 2-5) Holding surface raising process While continuing the processing and thickness measurement processes, the holding surface raising process is performed after the spot heater positioning process. In the holding surface raising process, as shown in Figure 20, the spot heater 163, which was positioned directly above the measurement section E of the wafer W in the spot heater positioning process, raises the holding surface 10a A high-temperature beam is irradiated onto the measurement section E of the wafer W held by the chuck table 10. At this time, grinding of the wafer W by the grinding wheel 25b continues, and the rotational drive of the chuck table 10 and the wafer W held by the chuck table 10 continues. Therefore, due to the irradiation of the high-temperature beam from the spot heater 163, the wafer W is partially heated in a ring-shaped region that is concentric with the wafer W and passes through the measurement section E of the wafer W. Due to this heating, the porous member 11 of the chuck table 10 is partially heated in a ring shape through the wafer W directly below the ring-shaped region passing through the measurement section E of the wafer W. As a result, the heated portion of the porous member 11 (chuck table 10) expands in a ring shape, causing the holding surface 10a of the chuck table 10 to be displaced so that it partially rises in a ring shape, and the height of the holding surface 10a is changed to an upward state. As the ring-shaped region passing through the measurement section E on the holding surface 10a is partially raised, the ring-shaped region passing through the measurement section E of the wafer W is partially lifted upward and deformed to bulge.

[0136] Then, as described above, while measuring with the thickness sensor 53, irradiating with a high-temperature beam from the spot heater 163, and changing the height of the holding surface 10a, the back surface WB of the wafer W, which is rotated by the chuck table 10, is ground by the rotating grinding wheel 25b. If the height of the holding surface 10a is not changed as described above, the ring-shaped region passing through the measurement section E of the wafer W will have a thickness value T E As the area becomes larger, the amount of grinding is reduced compared to other areas, resulting in a thickness difference in the wafer W instead of a uniform thickness. In contrast, as described above, the expansion of the chuck table 10 causes the holding surface 10a to rise in a ring shape, allowing the lower surface of the grinding wheel 25b to contact the wafer W before other areas in the area passing through the measurement section E, enabling grinding. This makes it possible to equalize the amount of grinding across the entire surface of the wafer W, and as shown in Figure 21, it is possible to minimize the in-plane thickness difference of the wafer W and grind the wafer W to a uniform thickness across its entire surface.

[0137] As described above, the grinding process of the wafer W proceeds, and when the thickness of the wafer W is ground down to the finish thickness, the thickness value T measured by the thickness sensor 53 is... A , T D , T C , T E , T B The grinding unit 20 is raised by the drive of the lifting mechanism 30 via the output of the device. This completes the grinding of one wafer W in the grinding process.

[0138] 3) Unloading process Figure 22 is an explanatory diagram of the unloading process performed in the grinding step of the first grinding method. After the grinding step is performed, the unloading process is carried out. In the unloading process, the rotation of the chuck table 10 and the grinding wheel 25 is stopped, and the chuck table 10 is moved horizontally in the Y-axis direction by the horizontal movement mechanism 13. Then, as shown in Figure 22, the wafer W is unloaded from the chuck table 10 via a transport mechanism (not shown), and the first grinding method for one wafer W is completed. If grinding of the next wafer W is to be performed, the first grinding method is repeated from the holding step described above.

[0139] According to the first grinding method described above, as stated above, the in-plane thickness difference of the wafer W is kept small, and the wafer W can be ground to a uniform thickness across its entire surface. This overcomes the limitations of grinding the wafer W to a uniform thickness simply by adjusting the angle α of the chuck table 10, and allows the wafer W to be ground to a uniform thickness with high precision.

[0140] Furthermore, in the first grinding method, the thickness measurement process, calculation process, spot heater positioning process, and holding surface raising process are carried out simultaneously with the processing process of grinding the back surface WB of the wafer W. Therefore, it is possible to correct the amount of grinding in real time during the grinding of the wafer W to adjust the amount of grinding in the parts where the thickness value of the wafer W is large.

[0141] Next, a grinding method other than those described above in this embodiment will be explained. In the following explanation, the explanation of a process that is the same as or equivalent to a grinding method described earlier may be omitted or simplified.

[0142] <Second grinding method> Next, the second grinding method for the wafer W in the second embodiment will be described below. Figure 23 is a flow chart of each step of the second grinding method. As shown in Figure 23, the second grinding method for the wafer W according to this embodiment is a method of grinding the wafer W through 1) a holding step, 2) a preliminary grinding step, 3) a thickness measurement step, 4) a holding surface raising step, 5) a finish grinding step, and 6) a discharge step, and each of these steps will be described below. Figure 24 is an explanatory diagram of the thickness measurement step in the second grinding method. Figure 25 is an explanatory diagram of the holding surface raising step in the second grinding method.

[0143] 1) Holding process The holding step of the second grinding method is carried out in the same manner as the holding step of the first grinding method, and the wafer W is held on the holding surface 10a (see Figure 15).

[0144] 2) Pre-grinding process In the second grinding method, a pre-grinding process is performed after the holding process. The pre-grinding process is performed in the same manner as the processing process in the first grinding method, except that the amount of wafer W to be ground is different. In the pre-grinding process, when the wafer W is pre-ground to a predetermined thickness (for example, a predetermined set thickness S) that does not reach the predetermined finish thickness, the grinding unit 20 is raised by the drive of the lifting mechanism 30, as shown in Figure 24, and the grinding process is temporarily suspended.

[0145] 3) Thickness measurement process In the second grinding method, a thickness measurement step is performed after the preliminary grinding step. The thickness measurement step is performed in the same manner as the thickness measurement step of the first grinding method, except that the grinding process of the wafer W is temporarily suspended. The thickness of the preliminary-ground wafer W is measured at multiple locations (for example, the five points mentioned above) using the thickness sensor 53 of the thickness measuring instrument 50 (see Figure 24).

[0146] 4) Holding surface raising process In the second grinding method, after the thickness measurement step, the holding surface raising step is performed. The holding surface raising step is performed in the same manner as the calculation step, spot heater positioning step, and holding surface raising step of the first grinding method, except that the grinding of the wafer W is temporarily suspended during this step. Therefore, in the holding surface raising step, multiple thickness values ​​T measured in the thickness measurement step are used. A , T D , T C , T E , T B In areas where the wafer W is thicker than a preset thickness S (measurement section E), the spot heater 163 partially heats the wafer W. This causes the porous member 11 (chuck table 10) to expand via the pre-ground wafer W, and partially raises the holding surface 10a in a ring shape via the wafer W (see Figure 25).

[0147] 5) Finishing grinding process In the second grinding method, after the holding surface raising step is performed, a finish grinding step is carried out. The finish grinding step is carried out in the same manner as the pre-grinding step to resume the grinding of the wafer W that was temporarily suspended. In the finish grinding step, as in Figure 21, with the holding surface 10a raised in a ring shape in the holding surface raising step, the pre-ground wafer W is ground to the finish thickness.

[0148] 6) Unloading process In the second grinding method, after the finish grinding process, the unloading process is performed. The unloading process is carried out in the same way as the unloading process in the first grinding method, and the wafer W is unloaded from the chuck table 10 (see Figure 22).

[0149] Similar to the first grinding method, the second grinding method also minimizes the in-plane thickness difference of the wafer W and allows for uniform thickness grinding across the entire wafer W. In the second grinding method, the preliminary grinding step and finish grinding step for grinding the back surface WB of the wafer W, and the thickness measurement step and holding surface raising step can be performed at different timings.

[0150] <Third grinding method> Next, a third method for grinding the wafer W will be described below. In this embodiment, the third method for grinding the wafer W involves grinding the first wafer W1 (see Figure 27) as the first wafer W, measuring its thickness, raising the holding surface 10a based on the measurement results, and then grinding the second wafer W2 (see Figure 29).

[0151] Figure 26 is a flowchart of each step of the third grinding method. As shown in Figure 26, the third grinding method is a method of grinding a wafer W through 1) a first holding step, 2) a first grinding step, 3) a thickness measurement step, 4) a storage step, 5) a separation step, 6) a second holding step, 7) a holding surface raising step, 8) a second grinding step, and 9) a discharge step. These steps will be explained below. Figure 14 is an explanatory diagram of the thickness measurement step in the third grinding method. Figure 28 is an explanatory diagram of the separation step in the third grinding method. Figure 29 is an explanatory diagram of the holding surface raising step in the third grinding method.

[0152] 1) First holding process The first holding step of the third grinding method is performed in the same manner as the holding step of the first grinding method, and the first wafer W1 is held on the holding surface 10a (see Figure 15).

[0153] 2) First grinding process In the third grinding method, the first grinding step is performed after the holding step. The first grinding step is performed in the same manner as the processing step of the first grinding method, except that the steps performed simultaneously with the processing step are not performed. In the first grinding step, once the first wafer W1 is ground to a predetermined finish thickness, the grinding unit 20 is raised by the drive of the lifting mechanism 30, as shown in Figure 27, and the grinding process is stopped.

[0154] 3) Thickness measurement process In the third grinding method, a thickness measurement step is performed after the first grinding step. The thickness measurement step is performed in the same manner as the thickness measurement step of the first grinding method, except that the grinding process is not performed simultaneously. The thickness of the first wafer W1 ground in the second grinding step is measured at multiple locations (for example, the five points mentioned above) by the thickness sensors 53 of the thickness measuring instrument 50 (see Figure 27).

[0155] 4) Memory process In the third grinding method, after the thickness measurement step is performed, a memory step is performed. The memory step is performed in the same way as the calculation step of the first grinding method, and further, in this step, multiple thickness values ​​T measured in the thickness measurement step are stored. A , TD , T C , T E , T B Of these, the areas thicker than the finished thickness (measurement section E, see Figure 18B) are stored in memory.

[0156] 5) Separation process In the third grinding method, after the storage process is performed, a separation process is carried out. The separation process is carried out in the same manner as the unloading process in the first grinding method, and the first wafer W1 is separated from the holding surface 10a of the chuck table 10 and unloaded (see Figure 28).

[0157] 6)Second holding process In the third grinding method, the second holding step is performed in the same manner as the first holding step, except that the object to be held is changed, and the second wafer W2 is held on the holding surface 10a (see Figure 15).

[0158] 7) Holding surface raising process In the third grinding method, after the second holding step, a holding surface raising step is performed. The holding surface raising step is performed in the same manner as the spot heater positioning step and the holding surface raising step of the first grinding method, except that the second wafer W2 before grinding is held in the chuck table 10 during the step. Therefore, as shown in Figure 29, in the holding surface raising step, the second wafer W2 is partially heated by the spot heater 163 in the measurement section E, which is thicker than the finished thickness stored in the memory step. This causes the porous member 11 (chuck table 10) to expand via the second wafer W2, and the holding surface 10a is partially raised in a ring shape via the second wafer W2.

[0159] 8) Second grinding process In the third grinding method, the second grinding step is performed after the holding surface raising step, or while the holding surface raising step is being performed. The second grinding step is performed in the same manner as the first grinding step, except that the workpiece is changed to the second wafer W2. In the second grinding step, with the holding surface 10a raised in a ring shape during the holding surface raising step, the second wafer W2 is ground to a predetermined finish thickness (see Figure 21).

[0160] 9) Unloading process In the third grinding method, after the second grinding step is performed, the unloading step is carried out. The unloading step is carried out in the same way as the unloading step in the first grinding method, and the second wafer W2 is unloaded from the chuck table 10 (see Figure 22).

[0161] The third grinding method described above, like the first and second grinding methods, can minimize the in-plane thickness difference of the second wafer W2 and grind the wafer W to a uniform thickness across its entire surface. In the third grinding method, for example, the first wafer W1 can be used as a dummy for grinding as the first wafer W, and at least one of the second wafers W2 from the second onward can be ground without measuring its thickness.

[0162] Furthermore, the present invention is not limited to the embodiments described above, and can be implemented with various modifications. In the embodiments described above, the size, shape, etc., shown in the accompanying drawings are not limited thereto, and can be appropriately modified within the scope that allows the present invention to exert its effects. In addition, the present invention can be implemented with appropriate modifications as long as it does not deviate from the scope of its objectives.

[0163] In the second embodiment described above, the case was explained in which only the thickness value of the measurement section E is larger than the other thickness values ​​on each wafer W, W1. However, the variation in thickness that occurs on each wafer W, W1 is not particularly limited. Therefore, the above-described grinding methods may be performed on each wafer W, W1 in a state of uneven thickness, where the thickness values ​​are larger or smaller at multiple locations.

[0164] Furthermore, in the second embodiment, the wafer W may be a bonded wafer formed by bonding two wafers together with a bonding member (not shown), as shown in Figure 30. The bonded wafer W consists of a support wafer WS located at the bottom of the figure and a device wafer WD located at the top of the figure, which is bonded to the upper surface of the support wafer WS by the bonding member (adhesive). In the device wafer WD, a device (not shown) is formed on the bonding surface (lower surface in the figure) that is bonded to the support wafer WS. When grinding such a bonded wafer W using the grinding methods described above, in each holding step, the lower surface of the support wafer WS is held by suction from the holding surface 10a of the chuck table 10, and in each grinding step, the device wafer WD is ground. Here, a ring-shaped thickness difference may occur in the bonding member. Therefore, when the lower surface of the support wafer WS is held by suction from the holding surface 10a of the chuck table 10, the upper surface of the device wafer WD becomes uneven. Even if irregularities occur on the upper surface of the device wafer WD due to the bonding material (adhesive) in the wafer W that will become the bonded wafer, the thickness of the device wafer WD after grinding can be made uniform by performing the first to third grinding methods described above.

[0165] Furthermore, although the thickness measuring device 50 used in this example consists of a thickness sensor 53 attached to the tip of an arm 52 that rotates horizontally around a support shaft 51, a device with thickness sensors attached to five points on a non-rotating horizontal arm may also be used.

[0166] Furthermore, in the above embodiments, the grinding unit 20 was moved up and down by the lifting mechanism 30, but it is sufficient to move the chuck table 10 and the grinding unit 20 up and down relative to each other. Therefore, the configuration may be changed so that the lifting mechanism 30 moves both the chuck table 10 and the grinding unit 20, or only the chuck table 10.

[0167] Furthermore, the spot heater 163 may be modified to include, instead of the heater unit described above, an irradiation mechanism 80 that irradiates the wafer W with light having an absorbent wavelength as shown in Figure 31, or an injection mechanism 90 that sprays hot air onto the wafer W as shown in Figure 32. Figure 31A is a schematic diagram of a partially longitudinal cross-section of the grinding apparatus of the first modified example, Figure 31B is a partially enlarged view of Figure 31A, and Figure 31C is a schematic perspective view of the nozzle of the first modified example viewed from below.

[0168] As shown in Figure 31A, the irradiation mechanism 80 in the first modified example includes a light source 81, a nozzle 82, and an air source 83.

[0169] The light emitted from the light source 81 is set to a wavelength that can partially heat the wafer W, and examples include laser light, visible light such as red light, far-infrared light, and near-infrared light. When irradiating with a laser beam using the irradiation mechanism 80, the light source 81 focuses the laser beam emitted by an oscillator housed inside the casing and irradiates it from the nozzle 82.

[0170] As shown in Figures 31B and 31C, the nozzle 82 is formed in a double cylindrical shape and is located below the light source 81. The nozzle 82 includes an optical path 85 formed at a central position parallel to the vertical direction (Z-axis direction) with its lower end being an optical passage opening 84, and an air passage 87 formed at a position surrounding the optical path 85 with its lower end being an air injection port 86. The air passage 87 is connected to the air source 83 via an air supply port 88.

[0171] In nozzle 82, light generated from light source 81 passes through optical path 85 and irradiates wafer W vertically downward (-Z side) from optical opening 84. Also in nozzle 82, air supplied from air source 83 passes through air channel 87 and is injected vertically downward onto wafer W from air injection port 86.

[0172] The irradiation mechanism 80 partially heats the wafer W held by the holding surface 10a by irradiating it with light, thereby expanding the porous member 11 of the chuck table 10 via the wafer W and allowing the height of the holding surface 10a to be changed. In addition, the irradiation mechanism 80 simultaneously irradiates the wafer W with light and injects air from an air nozzle 86 at a position surrounding the irradiated light. This injection of air prevents grinding water flowing on the wafer W from flowing into the area of ​​light irradiation on the wafer W. This allows for effective heating of the wafer W by light irradiation from the irradiation mechanism 80.

[0173] Figure 32 is a schematic diagram showing a partial longitudinal cross-section of the grinding apparatus of the second modified example. As shown in Figure 32, the injection mechanism 90 in the second modified example comprises a hot air source 91 and a nozzle 92. The hot air source 91 is configured to generate hot air by heating air, and can be exemplified by a configuration comprising a heating mechanism such as an electric heating wire and a blowing mechanism such as a fan. The nozzle 92 irradiates the wafer W vertically downward (-Z side) with the hot air generated from the hot air source 91.

[0174] The injection mechanism 90 partially heats the wafer W held by the holding surface 10a by injecting hot air onto the wafer W below, thereby expanding the porous member 11 of the chuck table 10 via the wafer W and allowing the height of the holding surface 10a to be changed. In other words, the hot air injected from the injection mechanism 90 is at a temperature that allows the porous member 11 to expand by heating the wafer W, thereby changing the height of the holding surface 10a.

[0175] The above embodiment describes infeed grinding, in which the lower surface of the grinding wheel 25b is brought into contact with the radial portion of the wafer W for grinding, but is not limited to this. Grinding of the wafer W may also be creep-feed grinding, in which the grinding wheel 25b and the chuck table 10 holding the wafer W are moved relative to each other in the horizontal direction, and the wafer W is ground with the side surface of the grinding wheel 25b. In creep-feed grinding, the thickness of the wafer W is measured not at the radial portion of the wafer W, but at multiple locations in the diametrical direction of the wafer W, which is the direction of movement of the wafer W relative to the grinding wheel 25b, and at multiple locations in a direction perpendicular to the diametrical direction. In addition, by spraying hot or cold water from the spray nozzle 60, the linear portion of the holding surface 10a expands or contracts. [Explanation of Symbols]

[0176] 1: Grinding device, 2: Cover, 3,4: Expandable cover, 10: Chuck table, 10a: Holding surface, 11: Porous member, 12: Table rotation mechanism, 13: Horizontal movement mechanism, 20: Grinding unit, 21: Holder, 22: Spindle motor, 23: Spindle, 24: Mount, 25: Grinding wheel, 25a: Base, 25b: Grinding wheel, 25c: Nozzle, 30: Lifting mechanism, 31: Lifting plate, 32: Guide rail, 33: Ball screw, 34: Servo motor, 35: Bracket, 36: Encoder, 40: Grinding water supply means, 41: Grinding water supply source, 42: Piping, 50: Thickness measuring instrument, 51: Support shaft, 52: Arm, 53: Thickness sensor, 54: Motor, 55: Encoder, 60: Injection nozzle, 61: Cold water supply source, 62: Hot water supply source, 63: Support shaft, 64: Arm, 65: Motor, 66: Encoder, 67-69: Piping, 70: Control unit, 72: Holding surface height change control unit, 80: Irradiation mechanism, 90: Spray mechanism, 100: Base, 100a: Base opening, 101: Column, 163: Spot heater, CL1: Table rotation axis, CL2: Grinding wheel rotation axis, V1, V2, V3, V4: On / off valves, W: wafer (bonded wafer), W1: first wafer, W2: second wafer, WD: Device wafer, WS: Support wafer, α: Chuck table tilt angle

Claims

1. A chuck table that holds the wafer by a holding surface, A grinding unit that grinds the wafer with the grinding wheel by rotating the grinding wheel around a rotation axis passing through the center of the annular grinding wheel, A lifting mechanism that moves the grinding unit and the chuck table up and down relative to each other, A grinding water supply means that supplies grinding water to the area where the grinding wheel contacts the wafer, A grinding device equipped with, A spray nozzle for spraying hot or cold water from above the holding surface onto at least a portion of the holding surface or a portion of the wafer held on the holding surface, A thickness measuring device for measuring the thickness of multiple locations on the wafer held on the holding surface, A control unit that, when measuring multiple thickness values ​​of the wafer with the thickness measuring instrument, sprays hot water from the spray nozzle at locations that are thicker than a preset thickness or at locations that show a value greater than the average of the measured multiple thickness values, or sprays cold water from the spray nozzle at locations that are thinner than the preset thickness or at locations that show a value less than the average of the measured multiple thickness values, thereby expanding or contracting the chuck table via the wafer to change the height of the holding surface, A wafer grinding apparatus characterized by comprising the following:

2. A method for grinding a wafer using the grinding apparatus described in claim 1, A holding step of holding the wafer on the holding surface of the chuck table, While grinding the wafer with the grinding wheel by rotating the chuck table around a table rotation axis passing through the center of the holding surface, the thickness measuring instrument measures the thickness at multiple points on the radial portion of the wafer, A grinding process in which, among the multiple thickness values ​​measured by the thickness measuring instrument, hot water is sprayed from the spray nozzle to areas that are thicker than a preset thickness or to areas that show a value greater than the average of the multiple thickness values ​​measured, or cold water is sprayed from the spray nozzle to areas that are thinner than the preset thickness or to areas that show a value less than the average of the multiple thickness values ​​measured, while grinding the wafer to a preset finish thickness, A method for grinding wafers, characterized by including [a certain element].

3. A method for grinding a wafer using the grinding apparatus described in claim 1, A holding step of holding the wafer on the holding surface of the chuck table, A preliminary grinding step in which the wafer is ground to a thickness that does not reach a predetermined finish thickness, A thickness measurement step in which the thickness of multiple locations on the wafer that has been pre-ground in the pre-grinding step is measured using the thickness measuring instrument, A holding surface height changing step is performed in which, among the multiple thickness values ​​measured in the thickness measurement step, hot water is sprayed from the spray nozzle to areas that are thicker than a preset thickness or to areas that show a value greater than the average of the multiple thickness values ​​measured, or cold water is sprayed from the spray nozzle to areas that are thinner than the preset thickness or to areas that show a value less than the average of the multiple thickness values ​​measured, thereby expanding or contracting the chuck table via the pre-ground wafer to change the height of the holding surface. A finish grinding step in which the pre-ground wafer is ground to a predetermined finish thickness, A method for grinding wafers, characterized by including [a certain element].

4. A method for grinding a wafer using the grinding apparatus described in claim 1, A first holding step involves holding the first wafer on the holding surface of the chuck table, A first grinding step in which the first wafer is ground to a predetermined finish thickness, A thickness measurement step in which the thickness of multiple locations on the first wafer ground in the first grinding step is measured using the thickness measuring instrument, A storage step in which, among the multiple thickness values ​​measured in the thickness measurement step, a first location that is thicker than the finished thickness and a second location that is thinner than the finished thickness are stored. A separation step of separating the first wafer from the holding surface of the chuck table, A second holding step involves holding the second wafer on the holding surface of the chuck table, A holding surface height correction step is performed to correct the height of the holding surface via the second wafer by spraying hot water from the spray nozzle at the first location stored in the control unit of the second wafer, or by spraying cold water from the spray nozzle at the second location, A second grinding step, which grinds the second wafer to the finished thickness after the holding surface height correction step or while the holding surface height correction step is being performed, A method for grinding wafers, characterized by including [a certain element].

5. The wafer is a bonded wafer comprising a support wafer and a device wafer having a device formed on the bonding surface to be bonded to the support wafer, The holding step, the first holding step, or the second holding step involves using the chuck table to suction and hold the support wafer. The grinding step, the pre-grinding step, the finish grinding step, the first grinding step, or the second grinding step grinds the device wafer. A method for grinding a wafer according to any one of features 2 to 4.

6. A chuck table that holds the wafer by a holding surface, A grinding unit that rotates a grinding wheel on a grinding wheel rotation axis passing through the center of an annular grinding wheel to grind the wafer with the grinding wheel, A lifting mechanism that moves the chuck table and the grinding unit up and down relative to each other, A grinding water supply means that supplies grinding water to the area where the grinding wheel contacts the wafer, A grinding apparatus comprising a thickness measuring instrument for measuring the thickness of multiple locations on the wafer held on the holding surface, A spot heater for partially heating the wafer held on the holding surface, A wafer grinding apparatus comprising: a holding surface height changing control unit that heats the wafer with a spot heater at locations where the thickness values ​​measured by the thickness measuring instrument are thicker than a preset thickness, or at locations where the measured thickness values ​​are greater than the average value of the multiple locations, thereby partially expanding the chuck table via the wafer and raising the holding surface.

7. The wafer grinding apparatus according to claim 6, wherein the spot heater is equipped with a mechanism for spraying hot air onto the wafer.

8. The wafer grinding apparatus according to claim 6, wherein the spot heater is equipped with a mechanism for irradiating the wafer with light having an absorbing wavelength.

9. A method for grinding a wafer using the grinding apparatus described in claim 6, A holding step of holding the wafer on the holding surface, A method for grinding a wafer, comprising: rotating the chuck table around a table rotation axis passing through the center of the holding surface to grind the wafer with the grinding wheel; measuring the thickness of the wafer at multiple locations with a thickness measuring instrument; and, among the multiple thickness values ​​measured, partially heating the wafer with a spot heater at locations that are thicker than a preset finish thickness or at locations that show a value greater than the average of the multiple thickness values ​​measured, thereby partially raising the holding surface through the wafer and grinding it to the finish thickness.

10. A method for grinding a wafer using the grinding apparatus described in claim 6, A holding step of holding the wafer on the holding surface, A pre-grinding step in which the wafer is pre-ground to a predetermined thickness that does not reach a predetermined finish thickness, A thickness measurement step in which the thickness of the pre-ground wafer is measured at multiple locations using the thickness measuring instrument, A holding surface raising step is performed in which, among the multiple thickness values ​​measured in the thickness measurement step, a portion of the wafer is partially heated with the spot heater in the portion that is thicker than the set thickness, or in the portion that shows a value greater than the average of the multiple thickness values ​​measured, thereby partially expanding the chuck table through the pre-ground wafer and partially raising the holding surface through the wafer. A wafer grinding method comprising: a finishing grinding step of grinding the pre-ground wafer to the finished thickness after the holding surface raising step, or while the holding surface raising step is being performed.

11. A method for grinding a wafer using the grinding apparatus described in claim 6, A first holding step of holding the first wafer on the holding surface, A first grinding step in which the first wafer is ground to a finished thickness, A thickness measurement step in which the thickness of the first wafer ground in the first grinding step is measured using the thickness measuring instrument, A storage step in which the locations among the multiple thickness values ​​measured in the thickness measurement step that are thicker than the finished thickness, A separation step of separating the first wafer from the holding surface, A second holding step involves holding the second wafer on the holding surface, A holding surface raising step is performed in which the second wafer is partially heated with the spot heater at the location stored in the storage step, thereby partially raising the holding surface via the second wafer. A wafer grinding method comprising: a second grinding step of grinding the second wafer to a predetermined finish thickness after the holding surface raising step, or while the holding surface raising step is being performed.

12. The wafer is a bonded wafer formed by bonding a support wafer and a device wafer, on which a device is formed on the bonding surface to be bonded to the support wafer, with a bonding member. In the holding step, the first holding step, or the second holding step, the support wafer is held by the holding surface of the chuck table through suction. A method for grinding a wafer according to any one of claims 9 to 11, wherein the device wafer is ground in the grinding step, the pre-grinding step, the finish grinding step, the first grinding step, or the second grinding step.

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