Grinding method for laminated wafer

Abstract

To appropriately adjust a grinding amount of a device wafer in rough grinding.SOLUTION: In a first rough grinding step, a device wafer 112 is ground by a rough grinding grindstone 306 in such a manner that a thickness of the device wafer 112 becomes a thickness T1 which can be measured by a non-contact thickness measuring instrument. Therefore, even in a case where a support wafer 110 is thick, excessive grinding of the device wafer 112 in the first rough grinding step can be suppressed. Accordingly, a grinding amount of the device wafer 112 in a finish grinding step can be secured sufficiently, thereby suppressing a rough ground surface of the device wafer 112 after the finish grinding. Further, grinding damage such as cracking formed on the device wafer 112 in the rough grinding can be appropriately removed by the finish grinding.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for grinding a bonded wafer. [Background technology]

[0002] The bonded wafer disclosed in Patent Documents 1 and 2 includes a support wafer and a device wafer. In grinding the bonded wafer, rough grinding and finish grinding are performed to grind the device wafer. The thickness of the support wafer and the device wafer before grinding is, for example, 500 μm. In rough grinding, the device wafer is ground to a thickness of, for example, 20 μm. In finish grinding, the device wafer is ground to a thickness of, for example, 2 μm. That is, in this example, the amount of device wafer ground in finish grinding is 18 μm.

[0003] In the finish grinding, the device wafer is ground while the thickness of the device wafer is measured by a non-contact thickness measuring instrument as disclosed in Patent Document 3.

[0004] On the other hand, in rough grinding, the device wafer is ground while measuring the thickness of the bonded wafer with a height gauge. The height gauge measures the height of the wafer's top surface and the height of the holding surface that holds the wafer, and the difference between these is the thickness of the bonded wafer. That is, in rough grinding, in order to make the device wafer 20 μm thick, the device wafer is ground until the thickness of the bonded wafer measured with the height gauge reaches the specified thickness (520 μm in the above example). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-230971 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-134849 [Patent Document 3] Japanese Patent Publication No. 2023-000307 Summary of the Invention [Problem to be solved by the invention]

[0006] In the above example, the thickness error of both the support wafer and the device wafer is ±15 μm. Therefore, the thickness of the support wafer may be 515 μm. In this case, if the device wafer is ground in rough grinding until the thickness of the bonded wafer is 520 μm, the thickness of the device wafer will be 5 μm. In this case, the amount of device wafer ground in finish grinding will be small, at 3 μm. As a result, the ground surface of the device wafer after finish grinding will be rough. Furthermore, it will be difficult to remove grinding damage, such as cracks, formed in the device wafer during rough grinding by finish grinding. This may result in device defects.

[0007] Therefore, an object of the present invention is to appropriately adjust the amount of device wafer ground in rough grinding. [Means for solving the problem]

[0008] The method for grinding a bonded wafer of the present invention (the present grinding method) is a method for grinding a bonded wafer, in which a device wafer formed by bonding a support wafer and a device wafer together is ground by a rough grinding wheel, and then ground by a finish grinding wheel until the device wafer reaches a predetermined finish thickness. The method comprises measuring the height of a holding surface and the height of an upper surface of the bonded wafer held on the holding surface with a height gauge, measuring the thickness of the bonded wafer measured as the difference between the height of the holding surface and the height of the upper surface of the bonded wafer, and grinding the device wafer to a thickness that can be measured by a non-contact thickness measuring device. The method includes a first rough grinding step of grinding the device wafer with a rough grinding wheel, a thickness measuring step of measuring the thickness of the device wafer of the bonded wafer ground in the first rough grinding step with the non-contact thickness measuring device, a second rough grinding step of grinding the device wafer with the rough grinding wheel after the thickness measuring step until the thickness of the device wafer reaches a predetermined finish grinding starting thickness, and a finish grinding step of grinding the device wafer with the finish grinding wheel after the second rough grinding step while measuring the thickness of the device wafer with the non-contact thickness measuring device until the thickness of the device wafer reaches the finish thickness. [Effects of the Invention]

[0009] In this grinding method, in the first rough grinding step, the device wafer is ground with a rough grinding wheel until the thickness of the device wafer reaches a thickness that can be measured by a non-contact thickness measuring device. Furthermore, in the second rough grinding step, the device wafer is ground with the rough grinding wheel until the thickness of the device wafer reaches a predetermined finish grinding starting thickness. Therefore, even if the support wafer is thick, it is possible to prevent the device wafer from being over-ground in the first rough grinding step and the second rough grinding step.

[0010] Therefore, since the amount of grinding of the device wafer in the finish grinding step can be sufficiently ensured, it is possible to prevent the ground surface of the device wafer from becoming rough after the finish grinding. Also, grinding damage such as cracks formed in the device wafer in the first rough grinding step and the second rough grinding step can be appropriately removed by the finish grinding, which makes it possible to reduce the possibility of device defects.

[0011] Furthermore, in the second rough grinding step, the thickness of the device wafer is set to a predetermined thickness at the start of the finish grinding step, which prevents the device wafer from becoming too thick at the start of the finish grinding step. Therefore, it is possible to effectively prevent the finish grinding from taking too long due to an insufficient amount of rough grinding for the device wafer. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 2 is a perspective view showing the configuration of a grinding device. [Figure 2] FIG. 2 is a cross-sectional view showing the structure of a wafer. [Figure 3] FIG. 4 is a cross-sectional view showing a first rough grinding step. [Figure 4] FIG. 10 is a cross-sectional view showing a thickness measurement step. [Figure 5] FIG. 4 is a cross-sectional view showing a second rough grinding step. [Figure 6] FIG. 4 is a cross-sectional view showing a finish grinding step. DETAILED DESCRIPTION OF THE INVENTION

[0013] The grinding apparatus 1 shown in FIG. 1 grinds a wafer held on a chuck table 5 by means of a rough grinding mechanism 30 and a finish grinding mechanism 31 .

[0014] In this embodiment, the grinding apparatus 1 grinds a wafer 100 as shown in Fig. 2. The wafer 100 is a bonded wafer in which a support wafer 110 and a device wafer 112, both of which have a substantially uniform thickness, are bonded together.

[0015] As shown in FIG. 1, the grinding device 1 has a first device base 10 and a second device base 11 disposed behind the first device base 10 (on the +Y direction side).

[0016] A first cassette stage 160 and a second cassette stage 162 for placing cassettes are provided on the front side (-Y direction side) of the first equipment base 10. A first cassette 161 and a second cassette 163 for accommodating wafers 100 are placed on the first cassette stage 160 and the second cassette stage 162, respectively.

[0017] The first cassette 161 and the second cassette 163 each have a plurality of shelves therein, and each shelf accommodates one wafer 100. That is, the first cassette 161 and the second cassette 163 accommodate a plurality of wafers 100 in a shelf-like manner.

[0018] The openings (not shown) of the first cassette 161 and the second cassette 163 face the +Y direction. A robot 155 is disposed on the +Y direction side of these openings. The robot 155 carries the processed wafers 100 into the first cassette 161 or the second cassette 163. The robot 155 also takes out the unprocessed wafers 100 stored in the first cassette 161 or the second cassette 163 and places them on the temporary placement table 154 of the temporary placement mechanism 152.

[0019] The temporary placement mechanism 152 is used to temporarily place the wafers 100 taken out from the first cassette 161 or the second cassette 163, and is provided at a position adjacent to the robot 155. The temporary placement mechanism 152 has a temporary placement table 154 and an alignment member 153. The alignment member 153 has a plurality of alignment pins arranged on the outside so as to surround the temporary placement table 154, and a slider that moves the alignment pins in the radial direction of the temporary placement table 154.

[0020] In the alignment member 153, the alignment pins are moved toward the center in the radial direction of the temporary placement table 154, thereby reducing the diameter of the circle connecting the alignment pins. As a result, the wafer 100 placed on the temporary placement table 154 with the device wafer 112 facing up is aligned (centered) at a predetermined position.

[0021] A carry-in mechanism 170 is provided at a position adjacent to the temporary placement mechanism 152. The carry-in mechanism 170 transports the wafer 100 temporarily placed on the temporary placement mechanism 152 to the chuck table 5 located at a transfer position 501 near the temporary placement mechanism 152, and places the wafer 100 on its holding surface 50. The transfer position 501 is the position of the chuck table 5 when the wafer 100 is carried in and out of the holding surface 50.

[0022] 3, the chuck table 5 includes a porous member 51 and a frame 53 that houses the porous member 51 so that the upper surface of the porous member 51 is exposed. The upper surface of the porous member 51 is a holding surface 50 that holds the wafer 100 by suction. The holding surface 50 is connected to a suction source (not shown) to hold the support wafer 110 side of the wafer 100 by suction. In addition, a frame surface 54, which is the upper surface of the frame 53, surrounds the holding surface 50 and is formed to be on the same plane (flush) as the holding surface 50.

[0023] While the chuck table 5 holds the wafer 100 by suction on the holding surface 50, it can be rotated around a rotation axis that passes through the center of the holding surface 50 and extends in the Z-axis direction by a table rotation mechanism (not shown) provided below it.

[0024] In this embodiment, three chuck tables 5 are arranged on the upper surface of a turntable 6 disposed on the second device base 11. The sides of each chuck table 5 are covered by a chuck table cover 61 provided on the upper surface of the turntable 6.

[0025] The turntable 6 is also divided into three regions at approximately equal intervals by three partition plates 62, and a chuck table 5 is disposed in each region. Therefore, the three chuck tables 5 are disposed at equal intervals on a circle centered on the center of the turntable 6, and the partition plates 62 separate the chuck tables 5.

[0026] The grinding device 1 also has a rotation mechanism 60 that rotates the turntable 6. The rotation mechanism 60 allows the turntable 6 to rotate about a central axis that passes through the center of the turntable 6 and extends in the Z-axis direction. When the turntable 6 rotates, the three chuck tables 5 revolve.

[0027] As a result, the turntable 6 can move the chuck table 5 horizontally to position the chuck table 5 at a transfer position 501 near the temporary placement mechanism 152, a first processing position 502 below the rough grinding mechanism 30, and a second processing position 503 below the finish grinding mechanism 31. The first processing position 502 and the second processing position 503 are positions of the chuck table 5 where the wafer 100 held on the holding surface 50 can be processed by a grinding wheel.

[0028] In addition, in this embodiment, the three chuck tables 5 are configured so that when one chuck table 5 is positioned at the first processing position 502, the other two chuck tables 5 are positioned at the transport position 501 and the second processing position 503, respectively.

[0029] A first column 12 is erected at the rear (+Y direction side) of the second apparatus base 11. A rough grinding mechanism 30 that rough grinds the wafer 100 and a rough grinding feed mechanism 20 that feeds the rough grinding mechanism 30 are disposed in front of the first column 12. The rough grinding mechanism 30 is a grinding mechanism for performing a first rough grinding step and a second rough grinding step.

[0030] The rough grinding feed mechanism 20 includes a pair of guide rails 201 parallel to the Z-axis direction, a lifting table 203 that slides on the guide rails 201, a ball screw 200 parallel to the guide rails 201, a motor 202 that rotates the ball screw 200, and a holder 204 attached to the lifting table 203. The holder 204 holds the rough grinding mechanism 30.

[0031] The lift table 203 is slidably installed on the guide rail 201. A nut portion (not shown) is fixed to the lift table 203. A ball screw 200 is threadedly engaged with this nut portion. The motor 202 is connected to one end of the ball screw 200.

[0032] In the rough grinding feed mechanism 20, the motor 202 rotates the ball screw 200, causing the lifting table 203 to move in the Z-axis direction along the guide rail 201. As a result, the holder 204 attached to the lifting table 203 and the rough grinding mechanism 30 held by the holder 204 also move in the Z-axis direction together with the lifting table 203. In this way, the rough grinding feed mechanism 20 feeds the rough grinding mechanism 30 for grinding along the Z-axis direction.

[0033] The rough grinding mechanism 30 includes a spindle housing 301 fixed to the holder 204, a spindle 300 rotatably held in the spindle housing 301, a motor 302 that rotates the spindle 300, a wheel mount 303 attached to the lower end of the spindle 300, and a grinding wheel 304 detachably connected to the lower surface of the wheel mount 303.

[0034] The spindle housing 301 is held by the holder 204 so as to extend in the Z-axis direction. The spindle 300 extends in the Z-axis direction so as to be perpendicular to the holding surface 50 of the chuck table 5, and is rotatably supported by the spindle housing 301.

[0035] The motor 302 is connected to the upper end side of the spindle 300. The motor 302 causes the spindle 300 to rotate about a rotation axis extending in the Z-axis direction.

[0036] The wheel mount 303 is formed in a disk shape, is fixed to the lower end of the spindle 300, and rotates in accordance with the rotation of the spindle 300. The wheel mount 303 holds a grinding wheel 304.

[0037] The grinding wheel 304 is formed to have an outer diameter approximately equal to the outer diameter of the wheel mount 303. The grinding wheel 304 includes an annular wheel base 305 made of a metal material. A plurality of roughly rectangular parallelepiped rough grinding wheels 306 are fixed to the underside of the wheel base 305 in an annular arrangement around the entire circumference. The rough grinding wheels 306 are rotated by the rotation of the spindle 300, and grind the device wafer 112 of the wafer 100 held on the chuck table 5. The rough grinding wheels 306 are grinding wheels containing relatively large abrasive grains.

[0038] A contact-type thickness measuring device 81 is disposed adjacent to the chuck table 5 disposed below the rough grinding mechanism 30. The contact-type thickness measuring device 81 measures the thickness of the wafer 100 in a contact manner, for example, during rough grinding.

[0039] 3, the contact-type thickness measuring device 81 has a holding surface height gauge 811, an upper surface height gauge 812, and a thickness calculation unit 813. The holding surface height gauge 811 measures the height of the holding surface 50 by contacting the frame surface 54 of the frame 53, which is flush with the holding surface 50 of the chuck table 5. The upper surface height gauge 812 measures the height of the upper surface of the wafer 100 by contacting the upper surface of the device wafer 112, which is the upper surface of the wafer 100 held on the holding surface 50. The thickness calculation unit 813 then calculates the thickness of the wafer 100 based on the difference between the measurement value of the holding surface height gauge 811 and the measurement value of the upper surface height gauge 812.

[0040] In this way, the contact thickness measuring device 81 measures the height of the holding surface 50 of the chuck table 5 and the height of the top surface of the wafer 100 held on the holding surface 50 (the height of the top surface of the device wafer 112), and measures the thickness of the wafer 100, which is measured as the difference between the height of the holding surface 50 and the height of the top surface of the wafer 100.

[0041] Furthermore, a second column 13 is erected at the rear of the second apparatus base 11 so as to be adjacent to the first column 12 along the X-axis direction. A finish grinding mechanism 31 that finish-grinds the wafers 100 and a finish grinding feed mechanism 21 that feeds the finish grinding mechanism 31 are disposed in front of the second column 13. The finish grinding mechanism 31 is a grinding mechanism for carrying out the finish grinding process.

[0042] The finish grinding feed mechanism 21 has a configuration similar to that of the rough grinding feed mechanism 20, and can feed the finish grinding mechanism 31 for grinding along the Z-axis direction. The finish grinding mechanism 31 has a configuration similar to that of the rough grinding mechanism 30, except that it is equipped with a finish grinding wheel 307 instead of the rough grinding wheel 306. The finish grinding wheel 307 is a grinding wheel containing relatively small abrasive grains.

[0043] The grinding device 1 also includes a processing chamber 120 that is provided to cover a portion of the turntable 6. The processing chamber 120 is configured to accommodate the chuck table 5 that has been moved to a first processing position 502 and a second processing position 503, and a rough grinding wheel 306 and a finish grinding wheel 307 that are processing tools.

[0044] A non-contact thickness gauge 90 is attached between the rough grinding mechanism 30 and the finish grinding mechanism 31 on the rear surface of the top plate 121 of the processing chamber 120. The non-contact thickness gauge 90 measures, in a non-contact manner, the thickness of the device wafer 112 of the wafer 100 held on the chuck table 5 arranged at the first processing position 502 and the second processing position 503. That is, the non-contact thickness gauge 90 irradiates the device wafer 112 with measurement light having a wavelength that is transparent to the device wafer 112 from above, receives the upper surface reflected light reflected from the upper surface of the device wafer 112 and the lower surface reflected light reflected from the lower surface of the device wafer 112 through the device wafer 112, and measures the thickness of the device wafer 112 by spectral interference.

[0045] In this embodiment, the non-contact thickness measuring device 90 is capable of measuring the thickness of the device wafer 112 during and after grinding by the rough grinding mechanism 30, and the thickness of the device wafer 112 during and after grinding by the finish grinding mechanism 31.

[0046] The wafer 100 after the finish grinding is carried out by the carry-out mechanism 172. The carry-out mechanism 172 carries the wafer 100 after the finish grinding, which is held on the chuck table 5 located at the transfer position 501, out of the chuck table 5, and transfers it to the spinner table 157 of the single-wafer type spinner cleaning mechanism 156.

[0047] The spinner cleaning mechanism 156 includes a spinner table 157 that holds the wafer 100 , and a nozzle 158 that sprays cleaning water and dry air toward the spinner table 157 .

[0048] In the spinner cleaning mechanism 156, a spinner table 157 holding the wafer 100 rotates, and cleaning water is sprayed toward the wafer 100, thereby spinner-cleaning the wafer 100. Dry air is then blown onto the wafer 100, thereby drying the wafer 100.

[0049] The wafer 100 cleaned by the spinner cleaning mechanism 156 is carried by the robot 155 into the first cassette 161 or the second cassette 163 (for example, the cassette from which the wafer 100 was removed).

[0050] The grinding apparatus 1 also includes a control unit 7 for controlling the grinding apparatus 1. The control unit 7 includes a CPU that performs calculations according to a control program, and a storage medium such as a memory. The control unit 7 executes various processes and comprehensively controls each component of the grinding apparatus 1. For example, the control unit 7 controls each of the above-mentioned members of the grinding apparatus 1 to execute a grinding method for the wafer 100.

[0051] The following describes a method for grinding the wafer 100 in the grinding apparatus 1 controlled by the control unit 7. This grinding method is a method in which the device wafer 112 of the wafer 100, which is a bonded wafer formed by bonding a support wafer 110 and a device wafer 112, is ground by a rough grinding wheel 306 and then ground by a finish grinding wheel 307 until it reaches a preset finish thickness.

[0052] [Holding process] 1 to remove the unprocessed wafer 100 from the first cassette 161 or the second cassette 163, place it on the temporary placement table 154 of the temporary placement mechanism 152, and position the wafer 100. Furthermore, the control unit 7 controls the carry-in mechanism 170 to hold the wafer 100 on the temporary placement table 154, and place it on the holding surface 50 of the chuck table 5 arranged near the temporary placement mechanism 152 with the device wafer 112 facing upward. Thereafter, the control unit 7 connects the holding surface 50 to a suction source (not shown). As a result, the chuck table 5 suction-holds the wafer 100 on the holding surface 50.

[0053] [1st rough grinding process] After the holding step, a first rough grinding step is carried out. In this step, the height of the holding surface 50 and the height of the upper surface of the wafer 100 held on the holding surface 50 are measured by a contact thickness gauge 81, and the thickness of the wafer 100 is measured as the difference between the height of the holding surface 50 and the height of the upper surface of the wafer 100. At the same time, the device wafer 112 is ground by a rough grinding wheel 306 until the thickness of the device wafer 112 becomes a thickness that can be measured by a non-contact thickness gauge 90.

[0054] Specifically, after the holding step, the control unit 7 rotates the turntable 6 (see Figure 1) so that the chuck table 5 holding the wafer 100 is positioned at the first processing position 502 below the rough grinding mechanism 30. 3, the control unit 7 rotates the rough grinding wheel 306 of the rough grinding mechanism 30 (arrow 401) and also rotates the chuck table 5 holding the wafer 100 (arrow 402). Thereafter, the control unit 7 uses the rough grinding feed mechanism 20 to lower the rough grinding mechanism 30, bringing the rough grinding wheel 306 into contact with the upper surface of the device wafer 112, and performing a first rough grinding on the device wafer 112.

[0055] At this time, the control unit 7 grinds the device wafer 112 until the thickness of the wafer 100 measured using the contact-type thickness measuring device 81 becomes a predetermined thickness so that the thickness of the device wafer 112 becomes a thickness T1 (see Figures 2 and 3) that can be measured by the non-contact thickness measuring device 90.

[0056] In this embodiment, the thicknesses of the support wafer 110 and the device wafer 112 in the wafer 100 before grinding are, for example, 500 μm each. Furthermore, since the non-contact thickness gauge 90 has high resolution, the thickness T1 of the device wafer 112 that can be measured by the non-contact thickness gauge 90 is 1 μm or more and 50 μm or less. Therefore, in the first rough grinding step, the device wafer 112 is ground by the rough grinding wheel 306 until the thickness of the wafer 100 becomes 550 μm, for example, so that the thickness of the device wafer 112 becomes 50 μm or less. In other words, the wafer 100 is ground until the value measured by the contact-type thickness gauge 81 becomes 550 μm.

[0057] The thickness error of both the support wafer 110 and the device wafer 112 is, for example, ±15 μm, so the range of the thickness of the support wafer 110 is 485 to 515 μm. Therefore, in the first rough grinding step of this embodiment, as an example, the device wafer 112 is ground by the rough grinding wheel 306 until the thickness of the wafer 100 becomes 565 μm so that the thickness of the device wafer 112 becomes 50 μm or less, taking into account the error (±15 μm) in the thickness of the support wafer 110. In other words, the wafer 100 is ground until the value measured by the contact-type thickness gauge 81 becomes 565 μm.

[0058] [Thickness measurement process] After the first rough grinding step, a thickness measurement step is carried out, in which the thickness of the device wafer 112 of the wafer 100 ground in the first rough grinding step is measured by the non-contact thickness measuring device 90.

[0059] Specifically, as shown in FIG. 4, the control unit 7 uses a non-contact thickness measuring device 90 to measure the thickness of the device wafer 112 after the first rough grinding step.

[0060] As described above, the thickness of the support wafer 110 ranges from 485 to 515 μm. When the support wafer 110 is at its thickest (515 μm), if the device wafer 112 is ground in the first rough grinding step until the thickness of the wafer 100 reaches 565 μm, the thickness of the device wafer 112 will be 50 μm, which is less than the thickness T1 that can be measured by the non-contact thickness gauge 90. Therefore, in this case, the thickness of the device wafer 112 can be measured by the non-contact thickness gauge 90. Therefore, the control unit 7 acquires the thickness of the device wafer 112 measured by the non-contact thickness gauge 90 and performs the next second rough grinding step.

[0061] On the other hand, even when the support wafer 110 is at its thinnest (485 μm), the device wafer 112 is ground in the first rough grinding step until the thickness of the wafer 100 becomes 565 μm. Therefore, the thickness of the device wafer 112 becomes 80 μm, which is thicker than the thickness T1 that can be measured by the non-contact thickness gauge 90. Therefore, in this case, the device wafer 112 is too thick and its thickness cannot be measured by the non-contact thickness gauge 90. Therefore, in this case, for example, the thickness of the device wafer 112 cannot be measured by the non-contact thickness gauge 90.

[0062] When the thickness of the device wafer 112 cannot be measured by the non-contact thickness gauge 90 in this way, the control unit 7 determines that the device wafer 112 is too thick and resumes the first rough grinding step described above. That is, while measuring the thickness of the wafer 100 by the contact-type thickness gauge 81, the control unit 7 grinds the device wafer 112 so that the thickness of the device wafer 112 becomes a thickness T1 that can be measured by the non-contact thickness gauge 90.

[0063] At this time, the control unit 7 grinds the device wafer 112 by, for example, 15 μm, which is the absolute value of the thickness error of the support wafer 110. That is, the control unit 7 grinds the device wafer 112 until the thickness of the wafer 100 becomes 550 μm. Thereafter, the control unit 7 again performs a thickness measurement step in which the non-contact thickness gauge 90 is used to measure the thickness of the device wafer 112.

[0064] At this time, the thickness of the device wafer 112 is 65 μm, which is thicker than the thickness T1 that can be measured by the non-contact thickness gauge 90, and so it is again impossible to measure the thickness of the device wafer 112 by the non-contact thickness gauge 90. Therefore, the control unit 7 again measures the thickness of the wafer 100 by the contact thickness gauge 81, while grinding the device wafer 112 by 15 μm to make the thickness of the wafer 100 535 μm. Thereafter, the control unit 7 measures the thickness of the device wafer 112 by the non-contact thickness gauge 90.

[0065] At this time, the thickness of the device wafer 112 is 50 μm. In this manner, the control unit 7 measures the thickness of the device wafer 112 with the non-contact thickness measuring device 90 while repeating the first rough grinding step.

[0066] As a result of the repeated first rough grinding step as described above, the thickness of the device wafer 112, which was 80 μm, becomes 50 μm. Therefore, in the third and subsequent thickness measurement steps, it becomes possible to measure the thickness of the device wafer 112 with the non-contact thickness gauge 90. Therefore, the control unit 7 acquires the thickness of the device wafer 112 measured with the non-contact thickness gauge 90, and performs the next second rough grinding step.

[0067] [Second rough grinding process] After the thickness measurement step, a second rough grinding step is performed. In this step, after the thickness measurement step, the device wafer 112 is ground by the rough grinding wheel 306 until the thickness of the device wafer 112 reaches a predetermined finish grinding starting thickness. In this second rough grinding step, the device wafer 112 is ground while the thickness of the wafer 100 is measured by, for example, the contact-type thickness gauge 81.

[0068] 5, the control unit 7 rotates the rough grinding wheel 306 of the rough grinding mechanism 30 (arrow 401) and also rotates the chuck table 5 holding the wafer 100 (arrow 402). Thereafter, the control unit 7 uses the rough grinding feed mechanism 20 to lower the rough grinding mechanism 30, bringing the rough grinding wheel 306 into contact with the upper surface of the device wafer 112, and performing the second rough grinding on the device wafer 112.

[0069] At this time, the control unit 7 performs the second rough grinding until the thickness of the device wafer 112 reaches a predetermined finish grinding start thickness T2 (see FIGS. 2 and 5) while measuring the thickness of the wafer 100 using the contact-type thickness gauge 81. In this embodiment, this finish grinding start thickness T2 is, for example, 20 μm. Therefore, when the support wafer 110 is thick (thickness: 515 μm), the thickness of the wafer 100 when the device wafer 112 reaches the finish grinding starting thickness T2 is 535 μm. Furthermore, when the support wafer 110 is thin (thickness: 485 μm), the thickness of the wafer 100 when the device wafer 112 reaches the finish grinding starting thickness T2 is 505 μm.

[0070] That is, if the thickness of the device wafer 112 obtained in the thickness measurement process is T0 (see Figure 5), the control unit 7 grinds the device wafer 112 using the rough grinding wheel 306 so that the thickness of the wafer 100 measured by the contact-type thickness gauge 81 becomes thinner by T0-T2 (20 μm).

[0071] For example, if the thickness of the wafer 100 after the first rough grinding process is 550 μm and the thickness T0 of the device wafer 112 obtained in the thickness measurement process is 50 μm, the control unit 7 grinds the device wafer 112 using the rough grinding wheel 306 so that the thickness of the wafer 100 becomes thinner by 30 μm (50 μm - 20 μm) (i.e., so that the thickness of the wafer 100 becomes 520 μm). As a result, the thickness of the device wafer 112 becomes 20 μm, which is the predetermined finish grinding start thickness T2.

[0072] When a non-contact thickness gauge similar to the non-contact thickness gauge 90 is disposed near the rough grinding mechanism 30, the control unit 7 may use the non-contact thickness gauge in place of the contact type thickness gauge 81 in the second rough grinding step. That is, the control unit 7 may grind the device wafer 112 until the thickness of the device wafer 112 reaches a predetermined finish grinding starting thickness T2 (20 μm) while measuring the thickness of the device wafer 112 with the non-contact thickness gauge. The non-contact thickness gauge arranged near the rough grinding mechanism 30 may have a lower resolution than the non-contact thickness gauge 90 arranged near the finish grinding mechanism 31. In this case, the thickness measurement accuracy of this non-contact thickness gauge will be lower than that of the non-contact thickness gauge 90.

[0073] [Finishing grinding process] After the rough grinding step, a finish grinding step is carried out. In this step, after the second rough grinding step, the device wafer 112 is ground by a finish grinding wheel 307 until the thickness of the device wafer 112 reaches a predetermined finish thickness while the thickness of the device wafer 112 is measured by a non-contact thickness measuring device 90.

[0074] Specifically, after the second rough grinding process, the control unit 7 rotates the turntable 6 (see Figure 1) so that the chuck table 5 holding the wafer 100 after the second rough grinding process is positioned at the second processing position 503 below the finish grinding mechanism 31. 6, the control unit 7 rotates the finish grinding wheel 307 of the finish grinding mechanism 31 (arrow 403) and also rotates the chuck table 5 holding the wafer 100 (arrow 402). Thereafter, the control unit 7 uses the finish grinding feed mechanism 21 to lower the finish grinding mechanism 31, bringing the finish grinding wheel 307 into contact with the upper surface of the device wafer 112, and performing finish grinding on the device wafer 112.

[0075] At this time, the control unit 7 grinds the device wafer 112 with the finish grinding wheel 307 until the thickness reaches a predetermined finish thickness T3 (see FIGS. 2 and 6) while measuring the thickness of the device wafer 112 using the non-contact thickness measuring device 90. In this embodiment, the finish thickness T3 is, for example, 2 μm.

[0076] After the finish grinding process, the control unit 7 performs a cleaning process on the wafer 100 using the spinner cleaning mechanism 156 (see Figure 1), and then stores the wafer 100 in the second cassette 163 (the cassette from which the wafer 100 was removed) of the first cassette 161 using the robot 155.

[0077] As described above, in this embodiment, in the first rough grinding step, the device wafer 112 is ground by the rough grinding wheel 306 until the thickness of the device wafer 112 reaches a thickness T1 (e.g., 50 μm) that can be measured by the non-contact thickness measuring device 90. Furthermore, in the second rough grinding step, the device wafer 112 is ground by the rough grinding wheel 306 until the thickness of the device wafer 112 reaches a preset finish grinding starting thickness T2 (e.g., 20 μm). Therefore, even if the support wafer 110 is thick, it is possible to prevent the device wafer 112 from being ground too much in the first rough grinding step and the second rough grinding step.

[0078] Therefore, the amount of grinding of the device wafer 112 in the finish grinding step can be ensured sufficiently, and the ground surface of the device wafer 112 after the finish grinding can be prevented from becoming rough. Furthermore, grinding damage such as cracks formed on the device wafer 112 in the first rough grinding step and the second rough grinding step can be properly removed by finish grinding, thereby reducing the possibility of device defects.

[0079] Furthermore, in the second rough grinding step, the thickness of the device wafer 112 is set to the finish grinding starting thickness T2, so that the device wafer 112 can be prevented from becoming too thick at the start of the finish grinding step. Therefore, it is possible to effectively prevent the finish grinding from taking too long due to an insufficient amount of rough grinding of the device wafer 112.

[0080] In the first rough grinding step described above, the device wafer 112 is ground by the rough grinding wheel 306 until the thickness of the wafer 100 becomes 565 μm, taking into account the thickness error (±15 μm) of the support wafer 110 so that the thickness of the device wafer 112 becomes 50 μm or less. In this regard, in the first rough grinding step, the device wafer 112 may be ground so that the thickness of the device wafer 112 is equal to or greater than a preset finish grinding start thickness T2 (for example, 20 μm) and equal to or less than 50 μm, which is measurable by the non-contact thickness measuring device 90. That is, in the first rough grinding step, the device wafer 112 may be ground so that the thickness of the device wafer 112 is equal to or greater than 20 μm and equal to or less than 50 μm.

[0081] In this regard, in the first rough grinding step, when the support wafer 110 is thick (515 μm), in order for the thickness of the device wafer 112 to be 20 μm or more and 50 μm or less, the device wafer 112 should be ground so that the thickness of the wafer 100 is 535 μm or more and 565 μm or less.

[0082] Furthermore, in the first rough grinding step, when the support wafer 110 is thin (485 μm), in order for the thickness of the device wafer 112 to be 20 μm or more and 50 μm or less, the device wafer 112 is ground so that the thickness of the wafer 100 is 505 μm or more and 535 μm or less.

[0083] Therefore, in the first rough grinding step, the device wafer 112 may be ground by the rough grinding wheel 306 until the thickness of the wafer 100 becomes 535 μm. In this case, the thickness of the device wafer 112 after the first rough grinding step will be 20 μm or more and 50 μm or less, regardless of whether the support wafer 110 is thick or thin. [Explanation of symbols]

[0084] 1: grinding device, 5: chuck table, 6: turntable, 7: control unit, 10: first device base; 11: second device base; 12: first column; 13: second column, 20: rough grinding feed mechanism, 21: finish grinding feed mechanism, 30: rough grinding mechanism, 31: finish grinding mechanism, 50: holding surface, 51: porous member, 53: Frame body, 54: Frame body surface, 60: Rotation mechanism, 61: Chuck table cover, 62: Partition plate, 81: Contact type thickness measuring device, 90: Non-contact thickness measuring device, 100: wafer, 110: support wafer, 112: device wafer, 120: processing chamber, 152: temporary placement mechanism, 153: alignment member, 154: temporary placement table, 155: robot, 156: spinner cleaning mechanism, 157: spinner table, 158: nozzle, 160: first cassette stage, 161: first cassette, 162: second cassette stage, 163: second cassette, 170: Loading mechanism, 172: Loading mechanism, 200: Ball screw, 201: Guide rail, 202: motor, 203: lift table, 204: holder, 300: spindle, 301: Spindle housing, 302: Motor, 303: Wheel mount, 304: Grinding wheel, 305: Wheel base, 306: Rough grinding stone, 307: Finish grinding wheel, 501: Transfer position, 502: First processing position, 503: second processing position, 811: holding surface height gauge, 812: upper surface height gauge, 813: thickness calculation unit, T0: the thickness of the device wafer obtained in the thickness measurement process, T1: Thickness measurable by non-contact thickness measuring instrument, T2: Thickness at the start of finish grinding, T3: Finished thickness

Claims

[Claim 1] A method for grinding a bonded wafer, in which a device wafer is bonded to a support wafer, is ground by a rough grinding wheel, and then ground by a finish grinding wheel until the device wafer reaches a predetermined finish thickness, a first rough grinding step of measuring the height of a holding surface and the height of an upper surface of the bonded wafer held on the holding surface with a height gauge, and measuring the thickness of the bonded wafer as a difference between the height of the holding surface and the height of the upper surface of the bonded wafer, while grinding the device wafer with the rough grinding wheel so that the thickness of the device wafer becomes a thickness that can be measured with a non-contact thickness measuring device; a thickness measuring step of measuring the thickness of the device wafer of the bonded wafer ground in the first rough grinding step by the non-contact thickness measuring device; a second rough grinding step of grinding the device wafer with the rough grinding wheel until the thickness of the device wafer reaches a predetermined finish grinding starting thickness after the thickness measuring step; a finish grinding step of grinding the device wafer with the finish grinding wheel until the thickness of the device wafer reaches the finish thickness while measuring the thickness of the device wafer with the non-contact thickness measuring device after the second rough grinding step; A method for grinding a bonded wafer, comprising:

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