Grinding device

Abstract

To shorten a polishing time and to uniformize the in-plane thickness of a wafer after polishing, in a polishing device.SOLUTION: A polishing device 1 is equipped with a chuck table 50 that holds a wafer 90 on a holding surface 502, a slider 59 that moves the chuck table 50 to a position where the held wafer 90 can be polished, and control means 19. The polishing device is also equipped with first polishing means 30 that disposes a first polishing pad 306 having a lower surface with an area covering at least an upper surface of the wafer 90, at a lower end of a first spindle 300, and second polishing means 32 that disposes a second polishing pad 326 having a lower surface with a diameter smaller than a diameter of the wafer 90, at a lower end of a second spindle 320. The control means 19 controls moving the chuck table 50 under the first polishing pad 306 and polishing the wafer 90 held on the holding surface 502 with the first polishing pad 306, and polishing a predetermined place of a radius area of the wafer 90 polished with the first polishing pad 306, with the second polishing pad 326.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a polishing apparatus for polishing a workpiece such as a semiconductor wafer.

Background Art

[0002] For example, a polishing apparatus that polishes a wafer using a polishing pad as disclosed in Patent Document 1 mounts a polishing pad having an area covering the upper surface of the wafer held on a chuck table on a spindle, rotates the spindle, rotates the chuck table holding the wafer, and presses the polishing pad against the wafer to polish the wafer.

[0003] When the wafer is polished in this way, concentric ripples-like thickness unevenness may occur centering around the center of the wafer. Therefore, for example, as disclosed in Patent Document 2, the polishing process is performed while relatively reciprocating the chuck table and the polishing pad in a horizontal direction parallel to the holding surface, so as not to form thickness unevenness on the wafer and to reduce the thickness difference of the polished wafer.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, even when polishing is performed while relatively reciprocating the polishing pad and the wafer held on the chuck table in the horizontal plane direction, a slight thickness difference remains in the polished wafer. In addition, there is a problem that the polishing time becomes long by reciprocating the polishing pad in contact with the wafer in the horizontal direction.

[0006] Therefore, a polishing apparatus for polishing a wafer has a problem to be solved, which is to shorten the polishing time and to make the in-plane thickness of the polished wafer uniform.

Means for Solving the Problem

[0007] The present invention for solving the above problems includes a chuck table for holding a wafer on a holding surface, table rotation means for rotating the chuck table, polishing means for arranging a polishing pad for polishing the wafer at the lower end of a spindle and polishing the wafer with the lower surface of the polishing pad, a slider for rotating the chuck table about a rotation axis whose axial direction is vertical or linearly moving it horizontally so that the polishing means can polish the wafer held on the holding surface at a polishing position, and control means. The polishing means includes first polishing means for arranging a first polishing pad having a lower surface with an area covering at least the entire upper surface of the wafer at the lower end of a first spindle, second polishing means for arranging a second polishing pad having a lower surface with a diameter smaller than the diameter of the wafer at the lower end of a second spindle, horizontal movement means for horizontally moving the second polishing means, third polishing means for arranging a third polishing pad having a diameter smaller than the radius of the wafer and large enough to surround the second polishing pad at the lower end of a third spindle, and X-axis movement means for horizontally moving the third polishing means, a thickness measuring device for measuring the thickness of the wafer polished by the first polishing pad and held on the holding surface. The control means moves the chuck table under the first polishing pad to polish the wafer held on the holding surface with the first polishing pad, measures a plurality of thickness values of the wafer in an arcuate or linear radius area between the center and the outer peripheral edge of the wafer with the thickness measuring device, and based on the plurality of thickness values of the wafer measured by the thickness measuring device, at a location where the thickness is larger and there is a thickness difference in an annular shape in a plan view centered on the center of the wafer positioned by the X-axis moving means polishes it so as to trace with the third polishing pad, and based on the plurality of thickness values of the wafer measured by the thickness measuring device, at a location where the thickness is larger and there is a thickness difference in an annular shape in a plan view centered on the center of the wafer by the horizontal moving means positions it and polishes it with the second polishing padfinishing A polishing apparatus that controls polishing. Preferably, the polishing apparatus according to the present invention includes two or more of the second polishing means. The present invention is also a method for polishing a wafer using the above polishing apparatus, the method including: a step of polishing the wafer held on the chuck table with a first polishing pad; a step of measuring a plurality of thickness values of the wafer in an arcuate or linear radius area between the center and the outer peripheral edge of the wafer with the thickness measuring device on the holding surface of the wafer after the step of polishing the wafer with the first polishing pad; a step of polishing in a tracing manner with the third polishing pad positioned by the X-axis moving means at a location having a greater thickness and a thickness difference than others in an annular shape in a plan view centered on the center of the wafer based on the plurality of thickness values of the wafer measured by the thickness measuring device; and a step of performing finishing polishing with the second polishing pad positioned by the horizontal moving means at a location having a greater thickness and a thickness difference than others in an annular shape in a plan view centered on the center of the wafer based on the plurality of thickness values of the wafer measured by the thickness measuring device after the step of polishing in a tracing manner with the third polishing pad.

Advantages of the Invention

[0012] The polishing apparatus according to the present invention includes: a first polishing means in which a first polishing pad having a lower surface with an area at least covering the upper surface of the wafer is disposed at the lower end of a first spindle; and a second polishing means in which a second polishing pad having a lower surface with a diameter smaller than the diameter of the wafer is disposed at the lower end of a second spindle. By this configuration, the control means moves the chuck table under the first polishing pad to polish the wafer held on the holding surface with the first polishing pad, and polishes a predetermined location in the radius area of the wafer polished by the first polishing pad, that is, a location having a thickness difference compared to other locations of the wafer generated by polishing the wafer with the first polishing pad, with the second polishing pad. By controlling these operations, compared to the case of polishing the wafer while horizontally moving a single-axis polishing means in which the polishing pad is in contact with the wafer, the total polishing time can be shortened, and the in-plane thickness of the wafer after polishing with the second polishing pad can be made uniform.

[0013] The polishing apparatus according to the present invention includes a horizontal movement means for horizontally moving the second polishing means, and a thickness measuring device for measuring the thickness of the wafer polished by the first polishing pad and held on the holding surface of the chuck table. The predetermined location is the location having the largest thickness value among a plurality of thickness values of the wafer measured by the thickness measuring device, and by being able to position the second polishing pad of the second polishing means at the predetermined location with the horizontal movement means, compared to the case of polishing the wafer while horizontally moving a single-axis polishing means in which the polishing pad is in contact with the wafer, the total polishing time can be shortened, and the in-plane thickness of the wafer after polishing with the second polishing pad can be made uniform.

[0014] The polishing apparatus according to the present invention includes a conveying means for loading a wafer onto a holding surface or unloading the wafer from the holding surface. The slider can position the chuck table at a first polishing position for polishing a wafer held on the holding surface by a first polishing pad, or at a second polishing position for polishing a wafer held on the holding surface by a second polishing pad, or at a loading / unloading position for loading the wafer onto the holding surface or unloading the wafer from the holding surface by the conveying means. The control means can control polishing a wafer held on the holding surface with the first polishing pad, moving the wafer polished with the first polishing pad to the loading / unloading position and measuring the thickness with a thickness measuring device, and polishing a portion with the largest thickness value among a plurality of thickness values of the wafer measured by the thickness measuring device with the second polishing pad as a predetermined portion. By being able to do this, compared with the case of polishing the wafer while moving the uniaxial polishing means in the horizontal direction, the polishing time can be shortened, and the in-plane thickness of the wafer after polishing with the second polishing pad can be made uniform.

[0015] The polishing apparatus according to the present invention includes a third polishing means in which a third polishing pad having a diameter smaller than the radius of the wafer and capable of surrounding the second polishing pad is disposed at the lower end of a third spindle. By this, a predetermined portion with an in-plane thickness difference of the wafer polished with the first polishing pad is polished in a short time so as to trace with the third polishing pad, and then a predetermined portion with an in-plane thickness difference of the wafer is finish-polished with the second polishing pad, and the in-plane thickness of the polished wafer can be made even more uniform.

[0016] The polishing apparatus according to the present invention can improve the throughput of the polishing process of the wafer by including two or more second polishing means.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Mode for Carrying Out the Invention

[0018] (Embodiment 1) The polishing apparatus 1 shown in FIG. 1 (hereinafter referred to as the polishing apparatus 1 of Embodiment 1) includes, for example, a first polishing means 30 and a second polishing means 32, and is an apparatus for polishing a wafer 90 held on any one of the chuck tables 50 by the first polishing means 30 and the second polishing means 32. The polishing apparatus 1 is configured, for example, by connecting a second apparatus base 11 to the rear (+Y direction side) of the first apparatus base 10. On the first apparatus base 10, there is a wafer preparation area 102 where loading / unloading of the wafer 90 from / to the cassette, centering, and cleaning are performed. On the second apparatus base 11, there is a processing area 115 where the wafer 90 held by the chuck table 50 is processed by the first polishing means 30 or the second polishing means 32. In a part of it, there is a loading / unloading position 114 for loading the wafer 90 onto the holding surface 502 of the chuck table 50 or unloading it from the holding surface 502 by the transfer means 4.

[0019] The wafer 90 shown in FIG. 1 is, for example, a circular plate-shaped semiconductor wafer made of a silicon base material or the like. The lower surface 901 of the wafer 90 facing downward in FIG. 1 has a plurality of devices formed thereon, and is protected by a protective tape (not shown) being adhered thereto. The upper surface 902 facing upward of the wafer 90 is a surface to be processed on which polishing is performed.

[0020] On the front side (-Y direction side) of the first apparatus base 10, a first cassette mounting portion 150 and a second cassette mounting portion 151 are provided. A first cassette 1500 in which the wafer 90 before processing is accommodated is mounted on the first cassette mounting portion 150, and a second cassette 1510 in which the wafer 90 after processing is accommodated is mounted on the second cassette mounting portion 151.

[0021] Behind the opening of the first cassette 1500, a robot 155 is arranged to carry out the wafer 90 before processing from the first cassette 1500 and carry the wafer 90 after processing into the second cassette 1510. The robot 155 shown in FIG. 1 can swing and move the robot hand in a horizontal plane (within the X-axis Y-axis plane) by a multi-joint arm.

[0022] An intermediate placement area 152 is provided at a position adjacent to the robot 155, and alignment means 153 is arranged in the intermediate placement area 152. The alignment means 153 aligns (centers) the wafer 90 carried out from the first cassette 1500 and placed in the intermediate placement area 152 at a predetermined position with a reduced-diameter alignment pin to determine the center position of the wafer 90.

[0023] In the example shown in FIG. 1, a loading arm 40 that swings while holding the wafer 90 is arranged at a position adjacent to the alignment means 153. The loading arm 40 holds the wafer 90 aligned by the alignment means 153 and conveys it to the chuck table 50 positioned at the loading / unloading position 114. An unloading arm 41 that swings while holding the wafer 90 after processing is provided adjacent to the loading arm 40. In this embodiment, the loading arm 40 and the unloading arm 41 constitute a conveying means 4 for carrying the wafer 90 onto the holding surface 502 of the chuck table 50 or unloading the wafer 90 from the holding surface 502.

[0024] Within the movable range of the unloading arm 41, a single-wafer cleaning means 156 for cleaning the wafer 90 after processing conveyed by the unloading arm 41 is arranged. The wafer 90 cleaned by the cleaning means 156 is carried into the second cassette 1510 by the robot 155.

[0025] As shown in FIG. 1, on the second apparatus base 11, a slider 59 is disposed which moves the chuck table 50 to respective polishing positions where the first polishing means 30 or the second polishing means 32 can polish the wafer 90 held on the holding surface 502 of the chuck table 50. The slider 59 is a turntable that is circular in plan view in the first embodiment. On the upper surface of the slider 59, a plurality (for example, three) of chuck tables 50 having holding surfaces 502 for holding the wafer 90 are disposed at equal intervals (for example, at 120-degree intervals) in the circumferential direction of the slider 59 with the center of the slider 59 as the center. Note that the slider may be a linear motion slider on which the chuck table 50 can be disposed on the upper surface and which linearly moves in the Y-axis direction.

[0026] A rotation shaft (not shown) for rotating the slider 59 is connected to the center of the slider 59, and the rotation shaft whose axial direction is the Z-axis direction can be rotated by a motor (not shown). By rotating the slider 59 about the center of the slider 59, a plurality of chuck tables 50 holding the wafer 90 are revolved, and the chuck table 50 can be sequentially positioned from the vicinity of the temporary placement area 152, below the first polishing means 30, below the second polishing means 32, to the loading / unloading position 114. For example, the slider 59 floats on the second apparatus base 11 with air sprayed on the lower surface and is rotatable as described above.

[0027] As shown in FIG. 1, the chuck table 50 includes, for example, a porous plate 500 having a holding surface 502 for holding the wafer 90 and whose outer shape is circular in plan view, and a frame body 501 having a recess for exposing the holding surface 502 and accommodating the porous plate 500. A suction source (not shown) communicates with the holding surface 502, and the suction force generated by the suction source is transmitted.

[0028] The polishing apparatus 1 of Embodiment 1 includes, as polishing means for polishing the wafer 90 with a polishing pad disposed at the lower end of a spindle and polishing the wafer 90 with the lower surface of the polishing pad, a first polishing means 30 in which a first polishing pad 306 having a lower surface with an area at least covering the upper surface 902 of the wafer 90 is disposed at the lower end of a first spindle 300, and a second polishing means 32 in which a second polishing pad 326 having a lower surface with a diameter smaller than the diameter of the wafer 90 is disposed at the lower end of a second spindle 320.

[0029] As shown in FIG. 1, a first column 12 is erected at the rear on the second apparatus base 11, and a first polishing feed means 20 is disposed on the front surface of the first column 12. The first polishing feed means 20 includes a ball screw 200 having an axis in the vertical direction (Z-axis direction), a pair of guide rails 201 disposed in parallel with the ball screw 200, a motor 202 connected to the ball screw 200 and rotating the ball screw 200, and a lifting plate 203 in which an internal nut is screwed onto the ball screw 200 and the side portion is in sliding contact with the guide rail 201. When the motor 202 rotates the ball screw 200, the lifting plate 203 is guided by the guide rail 201 and reciprocates in the Z-axis direction accordingly, and the first polishing means 30 attached to the lifting plate 203 also reciprocates in the Z-axis direction.

[0030] The first polishing means 30 includes, for example, a first spindle 300 whose axial direction is the Z-axis direction, a housing 301 rotatably supporting the first spindle 300, a motor 302 rotationally driving the first spindle 300, a circular plate-shaped mount 303 fixed to the lower end of the first spindle 300, and a circular first polishing pad 306 detachably attached to the lower surface of the mount 303 via a platen (not shown). The first polishing pad 306 is made of, for example, a non-woven fabric such as felt. The diameter of the first polishing pad 306 is approximately the same as the diameter of the mount 303 and is also larger than the diameter of the wafer 90. Note that the first polishing pad 306 may have abrasive grains adhered thereto with an adhesive, may be for dry polishing, or may be for CMP (chemical mechanical polishing) using a polishing liquid. When performing CMP polishing, lattice-shaped grooves for spreading the slurry over the entire surface may be formed on the lower surface of the first polishing pad 306.

[0031] The first polishing means 30 may be configured to perform CMP polishing by supplying the slurry through the first spindle 300 to the contact portion between the wafer 90 and the first polishing pad 306, or by directly supplying the slurry sprayed from an external nozzle (not shown) to the contact portion between the wafer 90 and the first polishing pad 306, or may be configured to perform dry polishing on the wafer 90 without supplying the slurry.

[0032] As shown in FIG. 1, a second column 13 is erected in the X-axis direction parallel to the first column 12 behind the second apparatus base 11, and a second polishing feed means 22 is disposed on the front surface of the second column 13. The second polishing feed means 22 includes a ball screw 220 having an axis in the vertical direction (Z-axis direction), a pair of guide rails 221 disposed in parallel with the ball screw 220, a motor 222 connected to the ball screw 220 to rotate the ball screw 220, and a lifting plate 223 having an internal nut screwed onto the ball screw 220 and a side portion slidably contacting the guide rail 221. When the motor 222 rotates the ball screw 220, the lifting plate 223 is guided by the guide rail 221 and reciprocates in the Z-axis direction, and the second polishing means 32 attached to the lifting plate 223 also reciprocates in the Z-axis direction.

[0033] The second polishing means 32 includes, for example, a second spindle 320 whose axial direction is the Z-axis direction, a housing 321 that rotatably supports the second spindle 320, a motor 322 that rotationally drives the second spindle 320, a circular plate-shaped mount 323 fixed to the lower end of the second spindle 320, and a circular second polishing pad 326 detachably attached to the lower surface of the mount 323 via a platen (not shown). The second polishing pad 326 is made of, for example, a non-woven fabric such as felt. The diameter of the second polishing pad 326 is smaller than the radius of the wafer 90 and is set, for example, to about 1 / 3 to 1 / 4 of the diameter of the wafer 90, but is not limited thereto. Note that the second polishing pad 326 may have abrasive grains adhered thereto with an adhesive, may be for dry polishing, or may be for CMP (chemical mechanical polishing) using a polishing liquid. When performing CMP polishing, lattice-shaped grooves for spreading slurry, for example, may be formed on the lower surface of the second polishing pad 326.

[0034] For example, the polishing apparatus 1 of Embodiment 1 may include two or more second polishing means 32. In this case, for example, a column is erected on the side (+X direction side) of the second apparatus base 11, and a second second polishing means 32 is disposed on the side surface of the column via a second second polishing feed means. In this case, it is possible to improve the throughput of the polishing process of the wafer 90.

[0035] The second polishing means 32 may be configured to perform CMP polishing by supplying slurry through the second spindle 320 to the contact portion between the wafer 90 and the second polishing pad 326, or by directly supplying the slurry sprayed from an external nozzle (not shown) to the contact portion between the wafer 90 and the second polishing pad 326, or may be configured to perform dry polishing on the wafer 90 without supplying slurry.

[0036] The polishing apparatus 1 in this embodiment includes, for example, a horizontal movement means 23 that moves the second polishing means 32 in the horizontal direction (X-axis direction). The horizontal movement means 23 disposed on the front surface of the second column 13 includes a ball screw 230 having an axis in the X-axis direction, a pair of guide rails 231 disposed in parallel with the ball screw 230, a motor 232 connected to the ball screw 230 to rotate the ball screw 230, and a movable plate 233 whose internal nut is screwed onto the ball screw 230 and whose side portion is in sliding contact with the guide rail 231. When the motor 232 rotates the ball screw 230, the movable plate 233 is guided by the guide rail 231 and moves in the X-axis direction, and the second polishing means 32 disposed on the movable plate 233 via the second polishing feed means 22 also moves in the X-axis direction.

[0037] For example, at the center of the upper surface of the slider 59, a lifting cylinder 590 that raises and lowers the rod 591 in the Z-axis direction is disposed. And on the upper end side of the rod 591, an arm member 592 extending in the horizontal direction is disposed, and at the tip of the arm member 592, a thickness measuring device 57 that can be positioned above the chuck table 50 and measures the thickness of the wafer 90 is disposed. For example, the lifting cylinder 590 can rotate about the Z-axis, and thereby, the thickness measuring device 57 disposed at the tip of the arm member 592 can also pivot and move within the horizontal plane.

[0038] The thickness measuring device 57 is, for example, a reflection-type photoelectric sensor that includes a light projecting unit and a light receiving unit and can measure the thickness of the wafer 90 non-contact. The thickness measuring device 57 irradiates the wafer 90 positioned below it with measurement light (infrared light). Then, the thickness of the wafer 90 is measured from the optical path difference of the respective reflected lights by analyzing the interference light of the reflected light reflected from the upper surface 902 of the wafer 90 and the reflected light reflected from the lower surface 901 of the wafer 90 after passing through the wafer 90 by spectroscopic interference. For example, the spectroscopic interference type wafer thickness gauge "SI-F80R series" provided by Keyence Corporation can be used. The thickness measuring device 57 may be a contact type measuring gauge that measures, for example, the height of the upper surface 902 of the wafer 90. In this case, the thickness measuring device 57 has previously measured and grasped the height position of the holding surface 502 of the chuck table 50 with a contact type measuring gauge. Therefore, it includes a calculation unit that calculates the thickness of the wafer 90 by subtracting the height of the holding surface 502 of the chuck table 50 from the height position of the upper surface 902 of the wafer 90 before polishing held by the holding surface 502. Thus, the thickness measuring device 57 measures the amount (removal amount) removed by polishing the wafer 90 from the difference between the height position of the upper surface 902 of the wafer 90 before polishing held by the holding surface 502 and the height position of the upper surface 902 of the wafer 90 measured after the polishing process, and can measure the thickness of the wafer 90 from the difference with the height position of the holding surface 502 of the chuck table 50 measured in advance. Note that the measuring gauge may be a non-contact type. For example, it can measure the height position of the upper surface 902 of the wafer 90 or the height position of the holding surface 502 of the chuck table 50 based on the principle of triangulation with a light projecting unit and a light receiving unit. It may also be a type that includes an oscillation unit that oscillates ultrasonic waves and a vibration receiving unit that receives the reflected ultrasonic vibration. In the case of such a non-contact type, the thickness measuring device 57 does not necessarily need to be able to move up and down.

[0039] The polishing apparatus 1 includes control means 19 that can control each component of the polishing apparatus 1 described as above. The control means 19, which is composed of a CPU and storage elements such as a memory, is electrically connected to, for example, the first polishing feed means 20, the first polishing means 30, the slider 59, and the thickness measuring device 57. Under the control of the control means 19, the polishing feed operation of the first polishing means 30 by the first polishing feed means 20, the rotation operation of the first polishing pad 306 in the first polishing means 30, and the positioning operation of the chuck table 50 by the slider 59 with respect to the second polishing means 32 are controlled. Also, information about, for example, the in-plane thickness of the wafer 90 after the first polishing measured by the thickness measuring device 57 is sent from the thickness measuring device 57 to the control means 19.

[0040] For example, as an example of the control of the first polishing feed means 20 by the control means 19, the motor 202 shown in FIG. 1 is, for example, a servo motor, and a rotary encoder (not shown) of the motor 202 is connected to the control means 19 which also functions as a servo amplifier. When an operation signal is supplied from the output interface of the control means 19 to the motor 202, the ball screw 200 rotates, and the rotation speed detected by the rotary encoder (not shown) is output as an encoder signal to the input interface of the control means 19. Then, the control means 19 that has received the encoder signal can sequentially recognize the height of the first polishing means 30 that is polished and fed by the first polishing feed means 20, and can perform feedback control on the polishing feed speed of the first polishing means 30. For example, the rotational movement control of the slider 59 by the control means 19 and the like are also performed by controlling a motor that rotates a rotating shaft connected to the slider 59 and the like.

[0041] Hereinafter, the case of polishing the wafer 90 using the polishing apparatus 1 shown in FIG. 1 will be described. First, by the control of the slider 59 by the control means 19, the slider 59 shown in FIG. 1 rotates, and the chuck table 50 in a state where the wafer 90 is not placed rotates, for example, in the clockwise direction when viewed from the +Z direction side, and the chuck table 50 moves to the vicinity of the loading arm 40. That is, the chuck table 50 is positioned at the loading / unloading position 114. Then, the robot 155 pulls out one wafer 90 from the first cassette 1500 and moves the wafer 90 to the temporary placement area 152.

[0042] After the center position of the wafer 90 is detected on the temporary placement area 152 by the alignment means 153, the loading arm 40 transports the wafer 90 onto the chuck table 50 and places the wafer 90 on the holding surface 502 so that the center of the holding surface 502 of the chuck table 50 and the center of the wafer 90 substantially coincide. Then, a suction source (not shown) operates, and the chuck table 50 sucks and holds the wafer 90 on the holding surface 502 with the upper surface 902 exposed.

[0043] After the chuck table 50 sucks and holds the wafer 90, the slider 59 shown in FIG. 1 rotates, and the chuck table 50 holding the wafer 90 is positioned at a position below the first polishing means 30. This positioning is always such that the entire upper surface 902 of the wafer 90 is in contact with the first polishing pad 306 during the polishing process, that is, the first polishing pad 306 covers the upper surface 902 of the wafer 90 held by the chuck table 50.

[0044] Next, under the control of the first polishing feed means 20 by the control means 19, the first polishing means 30 descends by the first polishing feed means 20, and the first polishing pad 306 rotating at a predetermined rotational speed comes into contact with the entire upper surface 902 of the wafer 90, so that, for example, dry polishing is performed in the present embodiment. Also, while the chuck table 50 is rotating, after the entire upper surface 902 of the wafer 90 has been polished for a predetermined time, the first polishing means 30 is raised by the first polishing feed means 20 to separate the first polishing pad 306 from the wafer 90. Note that the polishing of the wafer 90 by the first polishing means 30 is performed in a shorter time compared to the case of reciprocating the polishing pad in contact with the upper surface 902 of the wafer 90 in the horizontal direction as in the prior art.

[0045] Next, for example, the arm member 592 shown in FIG. 1 pivots, and the thickness gauge 57 is positioned at a position where it can pass over the center position of the upper surface 902 of the wafer 90 polished by the first polishing pad 306. Further, for example, the non-contact thickness gauge 57 pivots while passing once or a plurality of times over the arc-shaped radius area R1 shown in FIG. 2(A) between the center and the outer peripheral edge of the wafer 90 above the wafer 90, and the light projecting unit irradiates the measurement light toward the lower wafer 90. Then, by spectroscopic interference for analyzing the interference light between the reflected light reflected from the upper surface 902 of the wafer 90 and the reflected light reflected from the lower surface 901 of the wafer 90 after passing through the wafer 90, a plurality of thicknesses in the radius area R1 of the wafer 90 shown in FIG. 2(A) are measured from the optical path difference of each reflected light. Each measurement information about the thickness is sent to the control means 19 shown in FIG. 1.

[0046] For example, the control means 19 calculates the average value of a plurality of thickness values in the radius area R1 of the wafer 90 sent from the thickness measuring device 57 and each difference from the average value, and has a polishing portion recognition unit 191 capable of recognizing the X-axis and Y-axis coordinate positions of the portions with thickness differences within the radius area R1 of the wafer 90. Note that the polishing portion recognition unit 191 may be capable of recognizing only one of the X-axis coordinate position or the Y-axis coordinate position of the portion with thickness. As shown in FIGS. 2(A) and (B), on the wafer 90 polished by the first polishing means 30, there may be portions with thickness differences like ripples in a concentric circle centered on the center of the wafer 90 (for example, portions with a difference of several micrometers from other portions), that is, portions 905 with greater thickness in an annular shape in plan view that are difficult to polish. Then, the coordinate position of the thicker portion 905 than others in the radius area R1 of the wafer 90 is recognized by the polishing portion recognition unit 191 shown in FIG. 1. And the portion 905 is recognized as a predetermined portion 905 to be polished by the second polishing pad 326. Note that the predetermined portion 905 recognized as the portion to be polished by the second polishing pad 326 within the radius area R1 of the wafer 90 polished by the first polishing pad 306 in the present embodiment is the portion with the largest thickness value among the plurality of thickness values of the wafer 90 measured by the thickness measuring device 57. For the predetermined portion recognized as the portion to be polished by the second polishing pad 326 next, for example, if there are a plurality of other portions within the radius area R1 where the thickness difference exceeds the allowable tolerance from the average value, the plurality of portions may also be recognized by the polishing portion recognition unit 191 as the portions to be polished by the second polishing pad 326. Note that the difference between adjacent thickness values among the plurality of thickness values may be calculated, and if the calculated difference exceeds a preset allowable value, it may be determined as the portion to be polished by the second polishing pad 326.

[0047] Next, under the control of the slider 59 and the horizontal movement means 23 by the control means 19 shown in FIG. 1, the slider 59 shown in FIG. 1 rotates in the clockwise direction as viewed from the +Z direction side, and the second polishing means 32 is moved in the X-axis direction by the horizontal movement means 23, so that a predetermined position 905 to be polished within the radius area R1 of the wafer 90 held on the chuck table 50 is covered by the second polishing pad 326 of the second polishing means 32. Alignment is performed between the wafer 90 held on the chuck table 50 and the second polishing pad 326.

[0048] Under the control of the second polishing feed means 22 by the control means 19, the second polishing means 32 descends by the second polishing feed means 22, and the second polishing pad 326 rotating at a predetermined rotational speed abuts against a predetermined position 905 in the radius area R1 of the wafer 90 polished by the first polishing pad 306, so that, for example, dry polishing is performed in the present embodiment. Further, as the chuck table 50 rotates, the entire circumference of the thicker, annular portion 905 of the wafer 90 in plan view is polished by the second polishing pad 326. Since the thickness difference between the predetermined position 905 of the wafer 90 and other portions is a small value of about several μm, the polishing time by the second polishing pad 326 is significantly shorter than the polishing time by the first polishing pad 306.

[0049] After the entire circumference (one revolution around the holding surface 502 as the axis) of the predetermined position 905 in the radius area R1 is polished for a predetermined time to further improve the flatness of the wafer 90, the second polishing means 32 is raised by the second polishing feed means 22 to separate the second polishing pad 326 from the wafer 90. Next, the unloading arm 41 sucks and holds the upper surface 902 of the wafer 90 positioned at the loading / unloading position 114 and transports it from the chuck table 50 to the cleaning means 156. After the wafer 90 is cleaned and dried in the cleaning means 156, the robot 155 unloads the wafer 90 from the cleaning means 156 and accommodates it in the second cassette 1510.

[0050] As described above, the polishing apparatus 1 according to the present invention includes a first polishing means 30 in which a first polishing pad 306 having a lower surface with an area at least covering the upper surface 902 of the wafer 90 is disposed at the lower end of a first spindle 300, and a second polishing means 32 in which a second polishing pad 326 having a lower surface with a diameter smaller than the diameter of the wafer 90 is disposed at the lower end of a second spindle 320. By this configuration, the control means 19 moves the chuck table 50 under the first polishing pad 306 to polish the wafer 90 held on the holding surface 502 with the first polishing pad 306, and polishes a predetermined portion 905 in the radius area R1 of the wafer 90 polished with the first polishing pad 306, that is, a portion 905 having a thickness difference from other portions of the wafer 90 generated by polishing the wafer 90 with the first polishing pad 306, for example, a portion 905 that is concentric with the center of the wafer 90 and is annular in plan view, with the second polishing pad 326. By controlling these operations, compared with the case of polishing the wafer 90 while horizontally moving a single-axis polishing means in which a conventional polishing pad is brought into contact with the wafer, the total polishing time can be shortened, and the in-plane thickness of the polished wafer 90 can be made uniform.

[0051] The polishing apparatus 1 according to the present invention includes a horizontal movement means 23 for horizontally moving the second polishing means 32, and a thickness measuring instrument 57 for measuring the thickness of the wafer 90 polished with the first polishing pad 306 and held on the holding surface 502 of the chuck table 50. The predetermined portion to be polished with the second polishing pad 326 is the portion 905 having the largest thickness value among a plurality of thickness values of the wafer 90 measured by the thickness measuring instrument 57. Since the horizontal movement means 23 can position the second polishing pad 326 of the second polishing means 32 at the predetermined portion, compared with the case of polishing the wafer 90 while horizontally moving a single-axis polishing means in which a polishing pad is brought into contact with the wafer, the total polishing time can be shortened, and the in-plane thickness of the polished wafer 90 can be made uniform.

[0052] (Embodiment 2) The polishing apparatus 18 shown in FIG. 3 (hereinafter referred to as the polishing apparatus 18 of Embodiment 2) is a modification of a part of the configuration of the polishing apparatus 1 of Embodiment 1 shown in FIG. 1. For the same configurations, the same reference symbols as those of the polishing apparatus 1 are used and the description thereof is omitted. For example, the configuration on the first apparatus base 10 of the polishing apparatus 18 of Embodiment 2 is the same as that of the polishing apparatus 1 of Embodiment 1.

[0053] Hereinafter, the configuration of the polishing apparatus 18 of Embodiment 2 that is different from the polishing apparatus 1 of Embodiment 1 shown in FIG. 1 will be described. For example, as shown in FIG. 3, on the first apparatus base 10, a conveying means 4 for loading the wafer 90 onto the holding surface 502 of the chuck table 50 or unloading the wafer 90 from the holding surface 502 is disposed. Only one first column 12 is erected at the rear on the second apparatus base 11, and a first polishing means 30 is disposed on the front surface of the first column 12 via a first polishing feed means 20. For example, on the upper surface of the slider 59, two chuck tables 50 having holding surfaces 502 for holding the wafer 90 are disposed at equal intervals in the circumferential direction of the slider 59 around the center of the slider 59. The slider 59 can be positioned at a first polishing position for polishing the wafer 90 held on the holding surface 502 by the first polishing pad 306, that is, a position below the first polishing means 30, or a second polishing position for polishing the wafer 90 held on the holding surface 502 by the second polishing pad 364, that is, a position below the second polishing means 36, or a loading / unloading position 114 for loading the wafer 90 onto the holding surface 502 or unloading the wafer 90 from the holding surface 502 by the conveying means 4.

[0054] In the polishing apparatus 18 of Embodiment 2, a portal column 110 is erected on the second apparatus base 11 so as to straddle substantially the center of the slider 59. On the front surface of the portal column 110, a horizontal movement means 23 for movably moving the second polishing means 36 in the X-axis direction is disposed. On the movable plate 233 of the horizontal movement means 23, a second polishing feed means such as an electric slider (not shown) for raising and lowering the second polishing means 36 in the Z-axis direction is disposed.

[0055] The second polishing means 36 that can be moved in the X-axis direction by the horizontal movement means 23 and can be moved up and down in the Z-axis direction by a second polishing feed means (not shown) has a second spindle 362 supported in a non-contact manner by a housing 361 incorporating an air bearing or the like. A second polishing pad 364 is attached to the lower end of the second spindle 362 via a mount 363 and a platen (not shown). The material and diameter of the second polishing pad 364 are the same as those of the second polishing pad 326 shown in FIG. 1.

[0056] For example, a support block 235 having a substantially L-shaped side view is disposed on the movable plate 233 of the horizontal movement means 23. The thickness measuring instrument 57 is supported by the support block 235 so as to be opposed to the wafer 90 held on the holding surface 502 of the chuck table 50 in the Z-axis direction at the loading / unloading position 114 below it.

[0057] Hereinafter, the case of polishing the wafer 90 using the polishing apparatus 18 of Embodiment 2 shown in FIG. 3 will be described. From the holding of the wafer 90 by the chuck table 50 to the polishing of the wafer 90 by the first polishing means 30, the same operations as those of the polishing apparatus 1 of Embodiment 1 shown in FIG. 1 are also performed in the polishing apparatus 18.

[0058] Next, for example, under the control of the slider 59 by the control means 19, the slider 59 rotates in the clockwise direction when viewed from the +Z direction side, and the chuck table 50 holding the wafer 90 polished by the first polishing means 30 is positioned at the loading / unloading position 114. Also, the thickness measuring device 57 is moved in the X-axis direction by the horizontal movement means 23 and positioned at a position where it can pass over the center position of the upper surface 902 of the wafer 90 held by the chuck table 50 positioned at the loading / unloading position 114. Further, for example, the non-contact thickness measuring device 57 moves horizontally in the X-axis direction so as to pass once or a plurality of times through a radius area (in this embodiment, the radius area is linear, i.e., a radius) between the center and the outer peripheral edge of the wafer 90 above the wafer 90, and the light projecting unit irradiates the measurement light toward the lower wafer 90. Then, a plurality of thicknesses in the radius area of the wafer 90 are measured. Each measurement information about the thickness is sent to the control means 19.

[0059] Then, the polishing location recognition unit 191 recognizes the coordinate positions of the locations 905 shown in FIGS. 2(A) and (B) that are thicker than others in the radius area of the wafer 90. Note that the location 905 in this embodiment is the location with the largest thickness value among the plurality of thickness values of the wafer 90 measured by the thickness measuring device 57. Next, under the control of the slider 59 or the horizontal movement means 23 by the control means 19 shown in FIG. 2, alignment is performed between the wafer 90 and the second polishing pad 364 so that a predetermined location 905 to be polished on the wafer 90 held by the chuck table 50 is covered by the second polishing pad 364 of the second polishing means 36.

[0060] Then, the second polishing means 36 descends, and the second polishing pad 364 rotating at a predetermined rotational speed comes into contact with a predetermined position 905 in the radial area of the wafer 90, whereby, in this embodiment, for example, dry polishing is performed. Also, as the chuck table 50 rotates, the entire circumference of the thicker, annular portion 905 of the wafer 90 in plan view is polished by the second polishing pad 364. Since the thickness difference between the predetermined position 905 of the wafer 90 and other portions is a small value on the order of several μm, the polishing time by the second polishing pad 364 is significantly shorter than the polishing time by the first polishing pad 306. After the entire circumference of the predetermined position 905 in the radial area is polished for a predetermined time and the flatness of the wafer 90 is further improved, the second polishing pad 364 separates from the wafer 90 and the polishing process ends.

[0061] As described above, the polishing apparatus 18 according to the present invention includes a transfer means 4 for loading the wafer 90 onto the holding surface 502 of the chuck table 50 or unloading the wafer 90 from the holding surface 502. The slider 59 can position the chuck table 50 at a first polishing position for polishing the wafer 90 held on the holding surface 502 by the first polishing pad 306, or a second polishing position for polishing the wafer 90 held on the holding surface 502 by the second polishing pad 364, or a loading / unloading position 114 for loading the wafer 90 onto the holding surface 502 or unloading the wafer 90 from the holding surface 502 by the transfer means 4. The control means 19 can control polishing the wafer 90 held on the holding surface 502 with the first polishing pad 306, moving the wafer 90 polished with the first polishing pad 306 to the loading / unloading position 114 and measuring its thickness with the thickness measuring device 57, and polishing the portion 905 with the largest thickness value among the plurality of thickness values of the wafer 90 measured by the thickness measuring device 57 with the second polishing pad 364 as the predetermined portion 905. Thus, compared with the case of polishing the wafer 90 while horizontally moving a single-axis polishing means in which a polishing pad contacts the wafer 90 as in the prior art, the polishing time can be shortened, and the in-plane thickness of the polished wafer 90 can be made uniform.

[0062] (Embodiment 3) The polishing apparatus 17 shown in FIG. 4 (hereinafter referred to as the polishing apparatus 17 of Embodiment 3) is a modification of a part of the configuration of the polishing apparatus 1 of Embodiment 1 shown in FIG. 1. For the same configuration, the same symbols as those of the polishing apparatus 1 are used and the description thereof is omitted. Hereinafter, the configuration different from that of the polishing apparatus 1 of Embodiment 1 of the polishing apparatus 17 of Embodiment 3 will be described.

[0063] The polishing apparatus 17 of Embodiment 3 includes the portal column 110 described in the polishing apparatus 18 of Embodiment 2. On the front surface of the portal column 110, X-axis moving means 38 for movably moving the third polishing means 37 in the X-axis direction is disposed. The X-axis moving means 38 includes a ball screw 380 having an axis in the X-axis direction, a pair of guide rails 381 disposed in parallel with the ball screw 380, a motor 382 connected to the ball screw 380 to rotate the ball screw 380, and a movable plate 383 whose internal nut is screwed to the ball screw 380 and whose side portion is in sliding contact with the guide rail 381. When the motor 382 rotates the ball screw 380, the movable plate 383 is guided by the guide rail 381 and moves in the X-axis direction, and the third polishing means 37 disposed on the movable plate 383 via third polishing feed means (not shown) also moves in the X-axis direction.

[0064] On the movable plate 383 of the X-axis moving means 38, third polishing feed means such as an electric slider (not shown) for raising and lowering the third polishing means 37 in the Z-axis direction is disposed. The third polishing means 37 that can be moved in the X-axis direction by the X-axis moving means 38 and can be raised and lowered in the Z-axis direction by third polishing feed means (not shown) has a third spindle 372 supported by a housing 371 incorporating an air bearing or the like. A third polishing pad 375 is attached to the lower end of the third spindle 372 via a mount 373 and a platen (not shown).

[0065] The third polishing pad 375 is made of, for example, the same material as the first polishing pad 306 and the second polishing pad 326 shown in FIG. 1, and is set to a diameter smaller than the radius of the wafer 90 and larger than the second polishing pad 326 so as to surround it.

[0066] Incidentally, the X-axis moving means 38 and the third polishing means 37 may be disposed on the back surface of the gantry column 110, or the disposition positions of the third polishing means 37 and the second polishing means 32 may be interchanged. In the example shown in FIG. 4, a thickness measuring device 57 that can be pivotally moved by an arm member 592 on a slider 59 and a thickness measuring device 57 that can be moved in the X-axis direction together with the third polishing means 37 by the X-axis moving means 38 on the front surface of the gantry column 110 are disposed, but at least one of them may be disposed.

[0067] Hereinafter, a case of polishing the wafer 90 using the polishing apparatus 17 of Embodiment 3 shown in FIG. 4 will be described. Holding of the wafer 90 by the chuck table 50, polishing of the wafer 90 by the first polishing means 30, thickness measurement of the wafer 90 within the radius area R1 shown in FIGS. 2(A) and (B) by the thickness measuring device 57 on the slider 59 for example, and recognition of the portion 905 to be polished of the wafer 90 by the polishing location recognition unit 191 are also performed in the polishing apparatus 17 in the same manner as in the polishing apparatus 1 of Embodiment 1 shown in FIG. 1.

[0068] Next, by controlling the slider 59 and the X-axis moving means 38 by the control means 19, the slider 59 shown in FIG. 4 rotates, and the third polishing means 37 is moved in the X-axis direction by the X-axis moving means 38, so that the chuck table 50 is positioned such that a predetermined portion 905 shown in FIGS. 2(A) and (B) to be polished of the wafer 90 held by the chuck table 50 is covered by the third polishing pad 375 of the third polishing means 37.

[0069] Then, the third polishing means 37 descends, and the third polishing pad 375 rotating at a predetermined rotational speed comes into contact with a predetermined location 905 in the radius area R1 shown in FIGS. 2(A) and 2(B) of the wafer 90, whereby, in this embodiment, for example, dry polishing is performed. Further, as the chuck table 50 rotates, the entire circumference of the thicker, annular portion in plan view of the wafer 90 is polished by the third polishing pad 375 in a short time so as to trace it, and then the third polishing pad 375 separates from the wafer 90.

[0070] Next, by controlling the slider 59 and the horizontal movement means 23 by the control means 19, the slider 59 rotates and the second polishing means 32 is moved in the X-axis direction by the horizontal movement means 23, and a predetermined location 905 of the wafer 90 held by the chuck table 50 and polished so as to be traced by the third polishing pad 375 is covered by the second polishing pad 326 of the second polishing means 32, positioning the chuck table 50 holding the wafer 90. Thereafter, through the same steps as the polishing of the wafer 90 in the polishing apparatus 1 of Embodiment 1 described above, the portion 905 having a thickness difference from the other portions of the wafer 90 is polished by the second polishing pad 326, and a flat wafer 90 can be produced.

[0071] As described above, the polishing apparatus 17 of Embodiment 3 includes the third polishing means 37 having the third polishing pad 375 disposed at the lower end of the third spindle, the diameter of which is smaller than the radius of the wafer 90 and can surround the second polishing pad 326. By this, a predetermined location 905 having an in-plane thickness difference of the wafer 90 polished by the first polishing pad 306 is polished in a short time so as to be traced by the third polishing pad 375, and then, the predetermined location 905 having an in-plane thickness difference of the wafer 90 is finish-polished by the second polishing pad 326, making it possible to further uniformize the in-plane thickness of the polished wafer 90.

[0072] Note that the polishing apparatus according to the present invention is not limited to the polishing apparatus 1 of Embodiment 1, the polishing apparatus 18 of Embodiment 2, and the polishing apparatus 17 of Embodiment 3, and can be appropriately modified within the range where the effects of the present invention can be exhibited.

Description of Reference Numerals

[0073] 90: Wafer 902: Upper surface 901: Lower surface 1: Polishing apparatus of Embodiment 1 10: First apparatus base 11: Second apparatus base 115: Processing area 102: Wafer preparation area 114: Loading / unloading position 12: First column 13: Second column 150: First cassette mounting part 1500: First cassette 151: Second cassette mounting part 1510: Second cassette 155: Robot 4: Transfer means 40: Loading arm 41: Unloading arm 153: Alignment means 152: Temporary placement area 156: Cleaning means 50: Chuck table 500: Porous plate 502: Holding surface 501: Frame body 59: Slider 590: Lifting cylinder 591: Rod 592: Arm member 57: Thickness measuring instrument 20: First polishing feed means 200: Ball screw 201: Pair of guide rails 202: Motor 203: Lifting plate 30: First polishing means 300: First spindle 301: Housing 302: Motor 303: Mount 306: First polishing pad 22: Second polishing feed means 220: Ball screw 221: Pair of guide rails 222: Motor 223: Lifting plate 32: Second polishing means 320: Second spindle 321: Housing 322: Motor 323: Mount 326: Second polishing pad 23: Horizontal movement means 230: Ball screw 231: Pair of guide rails 232: Motor 233: Movable plate 19: Control means 191: Polishing location recognition part 18: Polishing apparatus of Embodiment 2 110: Gantry column 36: Second polishing means 360: Second spindle 364: Second polishing pad 17: Polishing apparatus of Embodiment 3 38: X-axis moving means 37: Third polishing means 372: Third spindle 375: Third polishing pad

Claims

1. A polishing apparatus comprising: a chuck table for holding a wafer on a holding surface; table rotation means for rotating the chuck table; polishing means for arranging a polishing pad for polishing the wafer at the lower end of a spindle and polishing the wafer with the lower surface of the polishing pad; a slider for rotating the chuck table about a rotation axis whose axial direction is vertical or linearly moving it horizontally so that the polishing means can polish the wafer held on the holding surface at a polishing position; and control means, wherein the polishing means includes: first polishing means in which a first polishing pad having a lower surface with an area covering at least the entire upper surface of the wafer is arranged at the lower end of a first spindle; and second polishing means in which a second polishing pad having a lower surface with a diameter smaller than the diameter of the wafer is arranged at the lower end of a second spindle, horizontal movement means for horizontally moving the second polishing means, third polishing means in which a third polishing pad having a diameter smaller than the radius of the wafer and capable of surrounding the second polishing pad is arranged at the lower end of a third spindle, X-axis movement means for horizontally moving the third polishing means, and a thickness measuring device for measuring the thickness of the wafer polished by the first polishing pad and held on the holding surface, wherein the control means, moves the chuck table under the first polishing pad and polishes the wafer held on the holding surface with the first polishing pad, measures a plurality of thickness values of the wafer in an arcuate or linear radial area between the center and the outer peripheral edge of the wafer with the thickness measuring device, polishes along the contour with the third polishing pad positioned by the X-axis movement means at a location having a greater thickness and a thickness difference than others in an annular shape in plan view centered on the center of the wafer based on the plurality of thickness values of the wafer measured by the thickness measuring device, and finish-polishes with the second polishing pad positioned by the horizontal movement means at a location having a greater thickness and a thickness difference than others in an annular shape in plan view centered on the center of the wafer based on the plurality of thickness values of the wafer measured by the thickness measuring device.

2. The polishing apparatus according to claim 1, comprising two or more of the second polishing means.

3. A method for polishing a wafer using the polishing apparatus according to any one of claims 1 or 2, comprising: a step of polishing the wafer held on the chuck table with the first polishing pad, After the step of polishing the wafer with the first polishing pad, measuring a plurality of thickness values of the wafer in an arcuate or linear radius area between the center and the outer peripheral edge of the wafer with the thickness measuring device for the thickness of the wafer held on the holding surface. Based on the plurality of thickness values of the wafer measured by the thickness measuring device, polishing in a tracing manner with the third polishing pad positioned by the X-axis moving means at a location having a greater thickness and a thickness difference than others in an annular shape in a plan view centered on the center of the wafer. After the step of polishing in a tracing manner with the third polishing pad, finish polishing with the second polishing pad positioned by the horizontal moving means at a location having a greater thickness and a thickness difference than others in an annular shape in a plan view centered on the center of the wafer based on the plurality of thickness values of the wafer measured by the thickness measuring device. A wafer polishing method including the above steps.

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