Wafer polishing method and bonded workpiece polishing method

Abstract

To polish a wafer so that the wafer has a uniform thickness, in polishing the wafer in which a difference in a thickness forming a cross section thereof into a wedge shape is generated.SOLUTION: A wafer 10 in which a difference in a thickness is generated in a diameter direction is held on a holding surface 210, and a thickness of an outer periphery part of the wafer 10 is measured. A lower surface of a polishing pad 351 is caused to contact an upper surface 100 of the wafer 10 while matching a thickest portion of the outer periphery part of the wafer 10 with an outer periphery of the polishing pad. The thickest part of the outer periphery part of the wafer 10 is polished in a large quantity and then is polished in a smaller quantity toward the diameter direction, utilizing a circumferential velocity difference of the polishing pad 351 that is rotated, without rotating a chuck table 20, so as to eliminate a difference in a thickness in the diameter direction of the wafer 10, and the lower surface of the polishing pad 351 is caused to contact the whole surface of the upper surface 100 of the wafer 10 so as to reduce the thickness of the wafer 10.SELECTED DRAWING: Figure 4

Description

[Technical Field]

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

[0002] A polishing apparatus for polishing a wafer holds a wafer on the holding surface of a chuck table, rotates the chuck table around an axis passing through the center of the holding surface and perpendicular to the holding surface, and presses the underside of the polishing pad, which rotates around an axis passing through the center of the underside of the polishing pad and perpendicular to the underside of the polishing pad, against the wafer to polish it. Wafers polished in this manner may have a thicker or thinner outer periphery than the central portion. To eliminate such thickness differences in the next wafer to be polished, it has been proposed to change the inclination of the rotation axis of the chuck table relative to the rotation axis of the polishing pad depending on the thickness difference of the wafer, as disclosed in Patent Document 1. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-093381 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in a bonded workpiece in which a wafer is bonded to a support substrate, the support substrate may have a wedge-shaped thickness difference in its cross section in the diameter direction, and in such a case, the wafer cannot be polished to a uniform thickness even if the tilt of the chuck table is changed.Furthermore, even when a wafer with a protective tape attached, rather than a bonded workpiece, is polished with a polishing pad, a wedge-shaped thickness difference may occur in the cross section in the diameter direction of the wafer.

[0005] Therefore, when polishing a wafer having a wedge-shaped cross section with varying thickness, there is a problem to be solved: how to polish the wafer to a uniform thickness. [Means for solving the problem]

[0006] The present invention is directed to a method for polishing a wafer by holding the wafer on a holding surface of a chuck table and polishing the wafer by a circular polishing pad having a radius equal to or larger than the diameter of the wafer. The polishing surface of the polishing pad rotates around the center of the polishing surface. The method includes a holding step of holding a wafer having a thickness difference in the diameter direction on the holding surface, a first thickness measurement step of measuring the thickness of the outer periphery of the wafer, and a step of aligning the thickest part of the outer periphery of the wafer with the outer periphery of the polishing pad after the first thickness measurement step. Rotate The polishing pad The polished surface and a thickness difference correction polishing step in which, without rotating the chuck table, the polishing amount is large at the thickest part of the outer periphery of the wafer and decreases toward the diameter direction by utilizing the difference in peripheral speed of the rotating polishing pad, thereby eliminating the thickness difference in the diameter direction of the wafer. After the thickness difference correction polishing step, the chuck table is rotated around the center of the holding surface as an axis, and the upper surface of the wafer is polished by rotating the chuck table around the center of the holding surface. Rotate The polishing pad The polished surface and a polishing step of polishing the entire surface of the wafer by contacting the wafer with a polishing agent to reduce the thickness of the wafer. In this wafer polishing method, it is desirable to carry out a second thickness measurement step between the thickness difference correction polishing step and the full surface polishing step, in which the thickness of the outer peripheral portion of the wafer is measured, and to carry out the thickness difference correction polishing step if the difference between the maximum and minimum measured values ​​in the second thickness measurement step exceeds a predetermined value, and to carry out the full surface polishing step if the measured values ​​in the second thickness measurement step do not exceed the predetermined value. The present invention also provides a method for polishing a workpiece, in which a wafer and a support substrate are bonded together, by holding the support substrate on a holding surface of a chuck table, and polishing the workpiece with a circular polishing pad having a radius equal to or larger than the diameter of the wafer. The polishing surface of the polishing pad rotates around the center of the polishing surface.The method for polishing a bonded workpiece includes a holding step of holding the support substrate of the bonded workpiece on the holding surface, rotating the chuck table around the center of the holding surface as an axis, rotating the polishing pad around the center of the polishing surface as an axis, and polishing the upper surface of the wafer. Rotate a full surface polishing step of contacting the polishing surface of the polishing pad to reduce the thickness of the wafer; a third thickness measurement step of measuring the thickness of the outer periphery of the wafer after the full surface polishing step; and a third thickness measurement step of measuring the thickness of the outer periphery of the wafer after the third thickness measurement step by aligning the thickest part of the outer periphery of the wafer with the outer periphery of the polishing pad without rotating the chuck table. contacting the polishing surface of the rotating polishing pad with the upper surface of the wafer; and a thickness difference correction polishing step in which the polishing amount is large at the outer periphery of the wafer that coincides with the outer periphery of the polishing pad and decreases toward the diameter by utilizing the difference in peripheral speed of the rotating polishing pad, thereby making the thickness of the wafer uniform. In this method for polishing bonded workpieces, after the thickness difference correction polishing process, it is desirable to carry out a fourth thickness measurement process in which the thickness of the outer peripheral portion of the wafer is measured, and if the difference between the maximum and minimum measured values ​​in the fourth thickness measurement process exceeds a predetermined value, to carry out the thickness difference correction polishing process. [Effects of the Invention]

[0007] In the present invention, since the thickness difference of the wafer can be eliminated in the thickness difference correction polishing process, the in-plane thickness of the wafer can be made uniform even if there is a wedge-shaped thickness difference in the wafer, and further, the thickness of the wafer can be made thinner in the full surface polishing process. Furthermore, even if a wedge-shaped thickness difference occurs in the support substrate constituting the bonded workpiece, the in-plane thickness of the wafer can be made uniform in the thickness difference correction polishing process.Even if a wedge-shaped thickness difference occurs in the adhesive layer bonding the support substrate and the wafer, the in-plane thickness of the wafer can be made uniform in the same way. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a perspective view showing an example of a polishing apparatus. [Figure 2] FIG. 2 is a cross-sectional view schematically showing a polishing mechanism. [Figure 3] 5A to 5C are cross-sectional views schematically showing a holding step and a first thickness measuring step in the first polishing method. [Figure 4] 10A and 10B are cross-sectional views schematically showing a thickness difference correction polishing step in the first polishing method. [Figure 5] FIG. 10 is a plan view showing the difference in peripheral speed depending on the radial position of the polishing pad in the first polishing method. [Figure 6] 3A to 3C are cross-sectional views schematically showing a full surface polishing step in the first polishing method. [Figure 7] 10A to 10C are cross-sectional views schematically showing a holding step and an entire surface polishing step in a second polishing method. [Figure 8] FIG. 10 is a cross-sectional view schematically showing a third thickness measuring step in the second polishing method. [Figure 9] 10A and 10B are cross-sectional views schematically showing a thickness difference correction polishing step in the second polishing method. [Figure 10] FIG. 10 is a cross-sectional view schematically showing a wafer having a uniform thickness. DETAILED DESCRIPTION OF THE INVENTION

[0009] 1 Polishing equipment 1 is an apparatus that polishes a wafer 10 held on a chuck table 20 using a polishing mechanism 30. The chuck table 20 is supported by a horizontal movement mechanism 40 so as to be movable in the Y-axis direction (horizontal direction). The polishing mechanism 30 is supported by a polishing feed mechanism 50 so as to be movable in the Z-axis direction (direction perpendicular to the Y-axis direction).

[0010] The chuck table 20 includes a porous member 21 having a holding surface 210 on its surface for holding the wafer 10 by suction, and a frame 22 for accommodating the porous member 21, with the holding surface 210 exposed from the inner periphery of the frame 22. The holding surface 210 and an upper surface 220 of the frame 22 are formed flush with each other.

[0011] A rotating shaft 23 is connected to the lower part of the frame body 22, and the rotating shaft 23 is rotatably supported by a support plate 24. The support plate 24 is supported at least at three points by three support shafts 25 (only two are shown in FIG. 1). At least two of these support shafts 25 have tilt adjustment mechanisms 26 that adjust the height of the chuck table 20 to adjust the tilt of the holding surface 210. The rotating shaft 23 is driven to rotate by a motor 27, and the amount of rotation is recognized by an encoder 28.

[0012] The horizontal movement mechanism 40 includes a ball screw 41 having a rotation axis in the Y-axis direction, a motor 42 that rotates the ball screw 41, a pair of guide rails 43 arranged parallel to the ball screw 41, and a slide plate 44 whose bottom is in sliding contact with the guide rails 43 and has a nut (not shown) inside that screws onto the ball screw 41. A support shaft 25 is provided on the top of the slide plate 44. When the ball screw 41 rotates, the slide plate 44 is guided by the guide rails 43 and moves in the Y-axis direction, and as the slide plate 44 moves in the Y-axis direction, the chuck table 20 also moves in the Y-axis direction.

[0013] The polishing mechanism 30 is disposed to the side of the movement path of the chuck table 20 and includes a spindle 31 having a rotation axis extending in the Z-axis direction, a spindle rotation mechanism 32 that rotates the spindle 31, a spindle housing 33 that rotatably supports the spindle 31, a mount 34 connected to the lower end of the spindle 31, and a polishing wheel 35 attached to the mount 34. When the spindle rotation mechanism 32 rotates the spindle 31, the polishing wheel 35 also rotates. The polishing wheel 35 is composed of a base 350 fixed to the mount 34 and a polishing pad 351 fixed in an annular shape to the underside of the base 350. The polishing pad 351 has a radius equal to or greater than the diameter of the wafer 10 to be polished.

[0014] The polishing mechanism 30 is supported by a polishing feed mechanism 50 so that it can move up and down. The polishing feed mechanism 50 includes a ball screw 51 having a rotation axis in the Z-axis direction, a motor 52 that rotates the ball screw 51, a pair of guide rails 53 arranged parallel to the ball screw 51, a lifting plate 54 whose side portions are in sliding contact with the guide rails 53 and which has a nut (not shown) inside that screws onto the ball screw 51, and a holder 55 that is connected to the lifting plate 54 and supports the spindle housing 33. When the ball screw 51 rotates, the lifting plate 54 is guided by the guide rails 53 and moves in the Z-axis direction, and the polishing mechanism 30 also moves in the Z-axis direction accordingly.

[0015] A thickness gauge 60 for measuring the thickness of the wafer held on the chuck table 20 is disposed at the upper end of the spindle 31. A polishing liquid inlet 70 is formed on the side of the upper part of the spindle 31, and the polishing liquid inlet 70 is connected to a polishing liquid supply source 71.

[0016] 2, the spindle rotation mechanism 32 is composed of a rotor (not shown) fixed to the outer peripheral surface of the upper end of the spindle 31, and a stator 321 fixed to the inner peripheral surface of the spindle housing 33 so as to surround the rotor. When a predetermined voltage is applied to the stator 321, the rotor rotates, causing the spindle 31 to rotate about its axis. A cooling path 322 for removing heat from the stator 321 is disposed near the stator 321. A cooling water supply source (not shown) is connected to the cooling path 322, and the stator 321 can be cooled by supplying cooling water to the cooling path 322.

[0017] The spindle housing 33 is provided with an air supply passage 332 connected to an air source 331, and an outlet 333 that ejects high-pressure air into the gap between the spindle housing 33 and the spindle 31. The spindle 31 housed inside the spindle housing 33 is rotatably supported in a non-contact state by the high-pressure air ejected from the outlet 333 into the gap.

[0018] The mount 34 is formed in a disk shape, and its lower surface serves as a mounting surface 340 to which the grinding wheel 35 is attached. The mounting surface 340 is a flat surface parallel to the horizontal direction perpendicular to the Z-axis direction.

[0019] A first through-hole 36 is formed through the center of the spindle 31, the center of the mount 34, and the center of the polishing wheel 35. The first through-hole 36 opens at the upper end of the spindle 31 and the lower surface of the polishing pad 351. A second through hole 37 is formed on the outer periphery of the first through hole 36, penetrating the spindle 31, the mount 34, and the grinding wheel 35. The second through hole 37 opens at the upper end of the spindle 31 and at the lower surface of the grinding pad 351.

[0020] A rotary joint 38 is attached to the upper end of the spindle 31. A first communication passage 381 communicating with the first through-hole 36 is formed in the rotary joint 38, and this first communication passage 381 is connected to the thickness measuring device 60. A second communication passage 382 communicating with the second through-hole 37 is also formed in the rotary joint 38, and a slurry supply source 384 is connected to the second communication passage 382 via a connecting pipe 383. A valve 385 is provided in the connecting pipe 383.

[0021] The thickness measuring device 60 includes at least a measuring unit 61 that irradiates measuring light downward through the first communication passage 381 and the first through-hole 36 and receives the reflected light of the measuring light reflected on the upper and lower surfaces of the wafer, and a collimator lens 62 that converts the measuring light irradiated by the measuring unit 61 into parallel light, and can calculate the thickness of the wafer from the difference in the optical path length of the reflected light received by the measuring unit 61.

[0022] The polishing apparatus 1 includes a control unit 80 having a CPU, a memory, and other storage elements, etc. The control unit 80 controls the chuck table 20, the polishing mechanism 30, the horizontal movement mechanism 40, the polishing feed mechanism 50, the thickness measuring device 60, etc.

[0023] 2. First polishing method (polishing wafers with protective tape attached) (1) Holding process 3, a protective tape 11 is attached to the underside 101 of a wafer 10, and the protective tape 11 side is suction-held on the holding surface 210 of a chuck table 20, with the upper surface 100 of the wafer 10 exposed upward. The wafer 10 has a thickness difference in the diameter direction, being thickest at one end in the diameter direction and thinnest at the other end in the diameter direction, forming a wedge shape. There is a thickness difference 102 between the thickest and thinnest parts.

[0024] (2) First thickness measurement process Next, the thickness of the outer peripheral portion of the wafer 10, which includes the thickest portion, is measured using the thickness gauge 60 shown in FIGS. 1 and 2. This outer peripheral portion is preferably the edge (periphery) of the wafer 10, but may also be, for example, a position several micrometers or so toward the center from the outer peripheral edge. Furthermore, if the outer peripheral edge is chamfered, the outer peripheral portion is the side closer to the center than the chamfered portion. During this measurement, as shown in FIG. 3, the chuck table 20 is moved in the Y-axis direction to position the thickness gauge 60 above the outer peripheral portion of the wafer 10. Note that the thickness gauge 60 is illustrated in a simplified form in FIG. 3.

[0025] With the thickness measuring device 60 positioned above the outer periphery of the wafer 10, the motor 27 shown in FIG. 1 rotates the chuck table 20, while the horizontal movement mechanism 40 moves the chuck table 20 in the Y-axis direction to measure the thickness of the wafer 10. The measurement unit 61 receives light reflected from the upper surface 100 of the wafer 10 and light reflected from the lower surface 101 of the wafer 10, and measures the thickness of the wafer 10, for example, from the optical path length difference between the two reflected lights. The measured thickness value is stored in the control unit 80 in association with the rotation angle detected by the encoder 28 shown in FIG. 1. This allows the thickest portion of the outer periphery of the wafer 10 to be identified in relation to the rotation angle of the chuck table 20. Here, the rotation angle of the chuck table 20 at which the measured thickness is greatest is identified by the rotation angle θ1 from a certain reference position.

[0026] (3) Thickness difference correction polishing process Next, as shown in FIG. 4, the circumferential position of the thickest portion of the outer periphery of the wafer 10 detected in the first thickness measurement step is aligned with the outer periphery of the polishing pad 351. This alignment is achieved by rotating the chuck table 20 from the reference position by θ1 degrees, which is stored in the control unit 80. Then, in this positional relationship, without rotating the chuck table 20, the spindle rotation mechanism 32 shown in FIG. 1 rotates the polishing pad 351. While the polishing mechanism 30 is lowered by the polishing feed mechanism 50, the rotating polishing pad 351 is brought into contact with the upper surface 100 of the wafer 10, thereby polishing the upper surface 100 of the wafer 10. During polishing, a polishing liquid is introduced from the polishing liquid supply source 71 shown in FIG. 1 to the polishing liquid inlet 70, and the polishing liquid is supplied between the polishing pad 351 and the wafer 10 through the second through hole 37 shown in FIG. 2. Note that the first through hole 36 and the second through hole 37 are not shown in FIG. 4 and subsequent figures. Alternatively, a polishing liquid nozzle may be disposed below the polishing pad 351, and the polishing liquid may be sprayed onto the underside of the polishing pad from the polishing liquid nozzle.

[0027] In this process, since the chuck table 20 is not rotated, a peripheral speed difference occurs depending on the contact position of the polishing pad 351. For example, as shown in FIG. 5, when the polishing pad 351 is rotated in the direction of arrow 300, the relative speeds in the relationship with the wafer 10 at positions where the distances from the center 352 of the polishing pad 351 are d1, d2, d3, d4, d5, and d6 are d1ω, d2ω, d3ω, d4ω, d5ω, and d6, respectively (ω is the angular velocity). Since d1 < d2 < d3 < d4 < d5 < d6, the value of d6ω becomes the largest. Therefore, the outer peripheral portion 354 at a distance d6 from the center 352 of the polishing pad 351 has the highest polishing rate, and the portion 353 at a distance d1 from the center 352 of the polishing pad has the lowest polishing rate. Further, the radius of the polishing pad 351 is not less than the diameter of the wafer 10, and the circumferential position of the thickest portion and the position of the outer periphery of the polishing pad 351 are aligned. Therefore, the polishing amount of the portion of the wafer 10 aligned with the outer peripheral portion of the polishing pad 351, that is, the thickest formed portion, becomes the largest and is polished the fastest. As the polishing amount gradually decreases toward the opposite side in the diameter direction of the wafer 10, the polishing amount of the thinnest formed portion becomes the smallest and is polished the slowest. Therefore, the thickness difference at both ends gradually decreases.

[0028] In this process, the control unit 80 can adjust the polishing amount per unit time by controlling the rotation speed of the polishing pad 351 by the spindle rotation mechanism 32. Therefore, when the thickness difference measured in the first thickness measurement process is large, polishing is performed at a high rotation speed of the polishing pad 351. When there is a thickness difference that cannot be corrected by the rotation speed of the polishing pad 351, the inclination of the chuck table 20 may be changed. That is, before the start of polishing, the thickness difference in the diameter direction of the wafer 10 is measured, and based on the measurement result, it is determined whether or not to change the inclination of the chuck table 20. The inclination of the chuck table 20 is changed by the inclination adjustment mechanism 26 shown in FIG. 1. If the thickness difference measured in the first thickness measurement process is large, polishing can be performed without changing the rotation speed of the polishing pad 351, by increasing the speed at which the polishing mechanism 30 is lowered by the polishing feed mechanism 50, thereby increasing the vertical load pressing the polishing pad 351 against the wafer 10.

[0029] (4) Second thickness measurement process Next, using the same method as in Figure 3, that is, with the thickness gauge 60 positioned above the outer periphery of the wafer 10, the chuck table 20 is rotated and moved in the Y-axis direction to measure the thickness of the wafer 10. Then, the difference between the maximum and minimum measured values ​​is calculated, and if the calculated value exceeds a value previously set in the control unit 80, the process returns to the thickness difference correction polishing process. On the other hand, if the calculated value of the difference between the maximum and minimum measured values ​​is within a range of values ​​previously set in the control unit 80, the process proceeds to the next full surface polishing process. Note that the measured thickness in this process is a value greater than the finished thickness of the wafer 10.

[0030] (5)Full surface polishing process As shown in FIG. 6, the motor 27 shown in FIG. 1 rotates the chuck table 20 around the center 230 of the holding surface 210, rotates the polishing pad 351 around the center 310 of the polishing surface of the lower surface of the polishing pad 351, and the polishing feed mechanism 50 lowers the polishing mechanism 30, thereby polishing the entire upper surface 100 of the wafer 10. During polishing, a polishing liquid is introduced from the polishing liquid supply source 71 shown in FIG. 1 to the polishing liquid inlet 70, and the polishing liquid is supplied between the polishing pad 351 and the wafer 10 through the second through-hole 37 shown in FIG. 2. During this polishing, the thickness of the wafer 10 is measured using the thickness gauge 60 shown in FIG. 1. When the measured thickness reaches a predetermined value, the polishing feed mechanism 50 raises the polishing mechanism 30, thereby completing the polishing. Since the chuck table 20 is also rotated in this process, the entire upper surface 100 of the wafer 10 is polished.

[0031] In this way, by performing the thickness difference correction polishing process in which polishing is performed without rotating the chuck table 20, while aligning the position of the thickest part of the outer periphery of the wafer 10 with the position of the outer periphery of the polishing pad 351, it is possible to finish the wafer 10 to a uniform thickness even if there is a difference in thickness in the diameter direction of the wafer 10.

[0032] 3. Second polishing method (polishing of bonded wafers bonded to a support substrate) Next, we will explain the case of polishing a wafer 12 that constitutes a bonded workpiece in which the lower surface 121 of the wafer 12 is attached to the upper surface 130 of a support substrate 13, as shown in Figure 7. The support substrate 13 has a thickness difference in the diameter direction, and is wedge-shaped, with one end in the diameter direction being the thickest and the other end in the diameter direction being the thinnest. There is a thickness difference 132 between the thickest and thinnest parts.

[0033] (1) Holding process First, the lower surface 131 of the support substrate 13 is suction-held on the holding surface 210 of the chuck table 20, and the upper surface 120 of the wafer 12 is exposed upward. Since the support substrate 13 has a wedge-shaped thickness difference in the diameter direction, the upper surface 120 of the wafer 12 is also inclined correspondingly.

[0034] (2)Full surface polishing process Next, with the polishing pad 351 covering the entire upper surface 120 of the wafer 12, the polishing feed mechanism 50 moves the polishing mechanism 30 downward, bringing the rotating polishing pad 351 into contact with the upper surface 120 of the wafer 12 to perform polishing. During polishing, a polishing liquid is introduced from the polishing liquid supply source 71 shown in FIG. 1 to the polishing liquid inlet 70, and the polishing liquid is supplied between the polishing pad 351 and the wafer 10 through the second through-hole 37 shown in FIG. 2. During this polishing, the thickness of the wafer 12 is measured using the thickness gauge 60 shown in FIG. 1. When the measured thickness of the thinnest portion of the wafer 10 reaches a predetermined value, this process is completed. At the end of this process, a thickness difference occurs in the diameter direction of the wafer 10, as shown in FIG. 8.

[0035] (3) Third thickness measurement process Next, as shown in Fig. 8, thickness measuring device 60 is positioned above the outer periphery of wafer 10. Then, in this state, motor 27 shown in Fig. 1 measures the thickness of wafer 10 while rotating chuck table 20, and the rotation angle detected by encoder 28 shown in Fig. 1 is stored in control unit 80 in association with the thickness of wafer 10. As a result, the thickest part of the outer periphery of wafer 10 is identified in relation to the rotation angle of chuck table 20. Here, it is assumed that the rotation angle of chuck table 20 when the measured thickness is the thickest is θ2 degrees.

[0036] (4) Thickness difference correction polishing process 9, the chuck table 20 is rotated by θ2 degrees from a reference position to align the position of the thickest portion of the outer periphery of the wafer 10 detected in the third thickness measurement step with the position of the outer periphery of the polishing pad 351. Then, without rotating the chuck table 20, the spindle rotation mechanism 32 shown in FIG. 1 rotates the polishing pad 351, bringing the rotating polishing pad 351 into contact with the upper surface 100 of the wafer 10. The polishing mechanism 30 is then lowered by the polishing feed mechanism 50 to polish the upper surface 120 of the wafer 10. During polishing, a polishing liquid is introduced from the polishing liquid supply source 71 shown in FIG. 1 to the polishing liquid inlet 70, and the polishing liquid is supplied between the polishing pad 351 and the wafer 10 through the second through-hole 37 shown in FIG. 2.

[0037] During this polishing, the chuck table 20 is not rotated, and therefore, as shown in FIG. 5, a difference in peripheral speed occurs depending on the contact position of the polishing pad 351. Therefore, the polishing rate is highest at the outer peripheral portion 354 of the polishing pad 351, which is farthest from the center 352 of the polishing pad, and the polishing rate is lowest at the portion closest to the center 352 of the polishing pad. Therefore, the polishing amount is greatest at the portion of the wafer 12 aligned with the outer peripheral portion of the polishing pad 351, i.e., the thickest portion, and is polished the fastest. The polishing amount gradually decreases toward the opposite side of the diameter of the wafer 12, and the polishing amount is smallest at the thinnest portion and is polished the slowest. As a result, the difference in thickness between both ends gradually decreases, and the thickness of the wafer 12 becomes uniform, as shown in FIG. 10.

[0038] If the thickness difference measured in the third thickness measurement step is large, polishing is performed by increasing the rotation speed of the polishing pad 351. If the thickness difference cannot be corrected by the rotation speed of the polishing pad 351, the inclination of the chuck table 20 is changed.

[0039] (5) Fourth thickness measurement process 10, with the thickness gauge 60 positioned above the outer periphery of the wafer 12, the chuck table 20 is rotated while moving in the Y-axis direction to measure the thickness of the wafer 12. The difference between the maximum and minimum measured values ​​is then calculated, and if the calculated value exceeds a value previously set in the control unit 80, the process returns to the thickness difference correction polishing step. On the other hand, if the calculated value of the difference between the maximum and minimum measured values ​​is within a range of values ​​previously set in the control unit 80, polishing of the wafer 10 is terminated.

[0040] As described above, by performing the thickness difference correction polishing process in which polishing is performed without rotating the chuck table 20, while aligning the position of the thickest part of the outer periphery of the wafer 10 with the position of the outer periphery of the polishing pad 351, the wafer 12 can be finished to a uniform thickness even if there is a difference in thickness in the diameter direction of the support substrate 13.

[0041] The first method can also be applied to polishing the wafer 12 that constitutes the bonded workpiece. [Explanation of symbols]

[0042] 1: Polishing device 10: Wafer 100: Upper surface 101: Lower surface 102: Thickness difference 11: Protective tape 12: Wafer 120: Top surface 121: Bottom surface 13: Support substrate 130: Upper surface 131: Lower surface 132: Thickness difference 20: Chuck table 21: Porous member 210: Holding surface 22: Frame body 220: Top surface 23: Rotation axis 230: Center 24: Support plate 25: Support shaft 26: Tilt adjustment mechanism 27: Motor 28: Encoder 30: Polishing mechanism 31: Spindle 32: Spindle rotation mechanism 321: Stator 322: Cooling path 33: Spindle housing 331: Air source 332: Air supply path 333: Spout 34: Mount 340: Mounting surface 35: Grinding wheel 310: Center 350: Base 351: Polishing pad 352: Center 353: Part 354: Outer part 36: First through hole 37: Second through hole 38: Rotary joint 381: First communication passage 382: Second communication passage 383: Connection pipe 384: Slurry supply source 385: Valve 40: Horizontal movement mechanism 41: Ball screw 42: Motor 43: Guide rail 44: Slide plate 50: Polishing feed mechanism 51: Ball screw 52: Motor 53: Guide rail 54: Lifting plate 55: Holder 60: Thickness measuring instrument 61: Measurement unit 62: Collimator lens 70: Polishing liquid inlet 71: Polishing liquid supply source 80: Control unit

Claims

1. A method for polishing a wafer, comprising: holding a wafer on a holding surface of a chuck table; and polishing the wafer on a polishing surface of a circular polishing pad that has a radius equal to or greater than the diameter of the wafer and that rotates around an axis that is the center of the polishing surface of the lower surface of the polishing pad, the method comprising: a holding step of holding a wafer having a thickness difference in a diameter direction on the holding surface; a first thickness measuring step of measuring the thickness of the outer peripheral portion of the wafer; a thickness difference correction polishing step in which, after the first thickness measurement step, the thickest part of the outer periphery of the wafer is aligned with the outer periphery of the polishing pad, the polishing surface of the rotating polishing pad is brought into contact with the upper surface of the wafer, and the polishing amount is increased at the thickest part of the outer periphery of the wafer and decreased toward the diameter by utilizing the difference in peripheral speed of the rotating polishing pad without rotating the chuck table, thereby eliminating the thickness difference in the diameter direction of the wafer; an entire surface polishing step of rotating the chuck table about the center of the holding surface as an axis after the thickness difference correction polishing step, and bringing the polishing surface of the rotating polishing pad into contact with the upper surface of the wafer to reduce the thickness of the wafer; A method for polishing a wafer comprising:

2. a second thickness measurement step for measuring the thickness of the outer peripheral portion of the wafer is carried out between the thickness difference correction polishing step and the entire surface polishing step; If the difference between the maximum and minimum values ​​measured in the second thickness measurement step exceeds a preset value, the thickness difference correction polishing step is carried out, and if the measured value in the second thickness measurement step does not exceed the preset value, the entire surface polishing step is carried out.

2. The method for polishing a wafer according to claim 1.

3. A method for polishing a bonded workpiece, comprising: holding a support substrate of a bonded workpiece, which is formed by bonding a wafer and a support substrate, on a holding surface of a chuck table; and polishing the wafer on the polishing surface of a circular polishing pad which rotates around an axis at the center of the polishing surface of the lower surface of the circular polishing pad having a radius equal to or greater than the diameter of the wafer, a holding step of holding the support substrate of the bonded workpiece on the holding surface; an entire surface polishing step of rotating the chuck table about an axis at the center of the holding surface, rotating a polishing pad about an axis at the center of the polishing surface, and bringing the polishing surface of the rotating polishing pad into contact with the upper surface of the wafer to reduce the thickness of the wafer; a third thickness measurement step of measuring the thickness of the outer peripheral portion of the wafer after the entire surface polishing step; a thickness difference correction polishing step in which, after the third thickness measurement step, the thickest part of the outer periphery of the wafer is made to coincide with the outer periphery of the polishing pad, and the polishing surface of the rotating polishing pad is brought into contact with the upper surface of the wafer without rotating the chuck table, and the amount of polishing is made larger at the outer periphery of the wafer that coincides with the outer periphery of the polishing pad and becomes smaller toward the diameter by utilizing the difference in peripheral speed of the rotating polishing pad, thereby making the thickness of the wafer uniform.

4. After the thickness difference correction polishing step, a fourth thickness measurement step is carried out to measure the thickness of the outer peripheral portion of the wafer; If the difference between the maximum and minimum values ​​measured in the fourth thickness measurement step exceeds a preset value, the thickness difference correction polishing step is carried out.

4. The method for polishing bonded workpieces according to claim 3.

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