Processing methods

Abstract

To provide a processing method which can suppress formation of a level difference on a polishing surface of a polishing pad due to polishing of a surface to be polished of work-piece, so as to maintain a shape of the polishing pad which is suitable for flatting the surface to be polished, even after the polishing of the surface to be polished is performed.SOLUTION: A point on an outer periphery of a surface to be polished positioned at a predetermined coordinate (a first coordinate) included in a coordinate plane which is parallel to a polishing surface is not caused to contact the polishing surface and a point on a surface to be polished positioned at another coordinate (a third coordinate) is caused contact an outer periphery of the polishing surface so as to polish work-piece, so that a whole area of the surface to be polished of the work-piece can be polished and a region in the vicinity of the outer periphery of the polishing surface of the polishing pad can be abraded as much as a region closer to inside than the region in the vicinity of the outer periphery can be abraded. This can suppress formation of a level difference on the polishing surface of the polishing pad due to polishing of the surface to be polished of the work-piece and maintain a shape of the polishing pad suitable for flatting the surface to be polished, even after the polishing of the surface to be polished is performed.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a method for polishing a workpiece having a circular polishing surface by using a polishing pad having a circular polishing surface. [Background technology]

[0002] Chips for electronic devices such as semiconductor devices and optical devices are manufactured using workpieces such as semiconductor wafers made of silicon (Si) or silicon carbide (SiC) or insulator wafers made of sapphire (aluminum oxide (Al2O3)). Such chips are manufactured, for example, by thinning a workpiece on which many devices are formed on its surface, and then dividing the workpiece into regions containing individual devices.

[0003] One method for thinning a workpiece is, for example, grinding the back side of the workpiece. However, when a workpiece is ground, a layer (fractured layer) in which the crystal structure of the material constituting the workpiece is disturbed is formed on the back side (grinding surface), and / or grinding marks remain and fine cracks are formed. Furthermore, when such a workpiece is divided to produce chips, the flexural strength of the resulting chips may be reduced.

[0004] Therefore, in order to remove the fractured layer, grinding marks, and / or cracks formed on the grinding surface side of the workpiece, the grinding surface of the workpiece may be polished after grinding (see, for example, Patent Document 1). This polishing is performed by contacting the polishing surface of the polishing pad with the back surface (polished surface) of the workpiece while rotating both the workpiece and a polishing pad made of resin such as foamed polyurethane or nonwoven fabric such as felt with abrasive grains dispersed therein. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2003-243345 A Summary of the Invention [Problem to be solved by the invention]

[0006] The polishing surface of the polishing pad is worn by polishing the surface of the workpiece. Therefore, when a large number of workpieces having the same size of surface are polished using only a part of the polishing surface of the polishing pad, a step may be formed on the polishing surface of the polishing pad. For example, the area near the outer periphery of the polishing surface may protrude lower than the area inside.

[0007] When such a polishing pad is used to polish the surface of a workpiece, it may be difficult to flatten the surface of the workpiece. Specifically, since polishing pads are generally flexible, the polishing surface of the polishing pad may deform when polishing the surface of the workpiece.

[0008] For example, during polishing, the load applied to the periphery of the workpiece may be large due to the presence of steps formed on the polishing surface of the polishing pad. If a workpiece having a polishing surface of the same size as the above-mentioned multiple workpieces is polished in this state, the area near the periphery may be polished excessively and become thin (sagging may occur).

[0009] In view of the above, an object of the present invention is to provide a processing method that suppresses the formation of steps on the polishing surface of a polishing pad caused by polishing the polished surface of a workpiece, and that can maintain the shape of the polishing pad suitable for planarizing the polished surface even after such polishing has been performed. [Means for solving the problem]

[0010] According to the present invention, there is provided a method for polishing a workpiece having a circular polished surface using a polishing pad having a circular polishing surface, the method comprising the steps of: holding the workpiece on a chuck table having a conical holding surface with a convex center; adjusting an angle between a rotation axis of the chuck table and a rotation axis of the polishing pad so that a line segment connecting a point on the outer periphery of the holding surface that is the shortest distance to the polishing surface in a direction perpendicular to the polishing surface and the center of the holding surface is parallel to the polishing surface; and adjusting an angle between the rotation axis of the chuck table and the rotation axis of the polishing pad, the angle being determined by a coordinate plane parallel to the polishing surface, the point on the outer periphery of the polished surface that overlaps with the line segment. a positioning step of relatively moving the polishing pad and the chuck table in a horizontal direction to position the polishing pad above the chuck table so that one coordinate does not overlap with the polishing pad and a second coordinate where the center of the surface to be polished is located overlaps with the polishing pad; and a polishing step of polishing the workpiece by rotating the polishing pad and the chuck table such that a point on the outer periphery of the surface to be polished located at the first coordinate does not come into contact with the polishing surface and a point on the outer periphery of the surface to be polished located at a third coordinate on the coordinate plane different from the first coordinate does not come into contact with the outer periphery of the polishing surface.

[0011] Furthermore, the present invention further includes a dressing step of dressing the polishing pad prior to the positioning step, in which a recess is formed in a circular central region of the polishing surface, and it is preferable that a portion of the boundary of the interface where the polishing surface and the surface to be polished contact each other during the polishing step is arc-shaped along the outer periphery of the recess. Effect of the Invention

[0012] In the present invention, a workpiece is polished by not contacting a point on the outer periphery of the polished surface located at a predetermined coordinate (first coordinate) included in a coordinate plane parallel to the polishing surface with the polishing surface, and by contacting a point on the outer periphery of the polished surface located at another coordinate (third coordinate) with the outer periphery of the polishing surface. In this case, the entire polished surface of the workpiece can be polished, and the area near the outer periphery of the polishing surface of the polishing pad can be worn to the same extent as the area inside it.

[0013] This suppresses the formation of steps on the polishing surface of the polishing pad caused by polishing the polished surface of the workpiece, and even after such polishing, the shape of the polishing pad can be maintained suitable for planarizing the polished surface. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a perspective view illustrating an example of a processing apparatus. [Diagram 2] FIG. 2 is a perspective view that illustrates an example of a workpiece. [Diagram 3] FIG. 3 is a partial cross-sectional side view that illustrates an example of the chuck table. [Figure 4] FIG. 4 is a flow chart that illustrates a schematic example of a method for processing a workpiece. [Diagram 5] FIG. 5(A) is a top view showing a chuck table positioned at the polishing position and a polishing pad whose position has been adjusted, and FIG. 5(B) is a cross-sectional view showing a cross section taken along line A1B1 shown in FIG. 5(A). [Figure 6] FIG. 6(A) is a top view that shows a schematic diagram of a workpiece being polished by a polishing pad, and FIG. 6(B) is a cross-sectional view that shows a schematic diagram of a cross section taken along line A2B2 shown in FIG. 6(A). [Figure 7] FIG. 7 is a flow chart that illustrates a modified example of the method for processing a workpiece. [Figure 8] FIG. 8 is a side view showing a schematic view of the dressing unit located at the polishing position and the polishing pad whose position has been adjusted. [Figure 9] FIG. 9(A) is a top view showing a schematic diagram of a workpiece being polished by a dressed polishing pad, and FIG. 9(B) is a cross-sectional view showing a schematic diagram of a cross section taken along line A3B3 shown in FIG. 9(A). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] An embodiment of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a perspective view showing a schematic example of a processing device capable of grinding and polishing a workpiece. Note that the X-axis direction (front-back direction) and the Y-axis direction (left-right direction) shown in Fig. 1 are directions perpendicular to each other on a horizontal plane, and the Z-axis direction (up-down direction) is a direction perpendicular to the X-axis direction and the Y-axis direction (vertical direction).

[0016] The processing device 2 shown in Fig. 1 includes a base 4 that supports each component. An opening 4a is formed on the front end side of the upper surface of the base 4, and a transport mechanism 6 for transporting a plate-shaped workpiece is provided within the opening 4a. Fig. 2 is a perspective view that shows a schematic example of a workpiece transported by the transport mechanism 6.

[0017] 2 is, for example, a wafer having a circular front surface 11a and a back surface 11b, and made of a semiconductor material such as silicon (Si). The front surface 11a side of the workpiece 11 is partitioned into a plurality of regions by a plurality of mutually intersecting division lines 13, and a device 15 such as an IC (Integrated Circuit) is formed in each region.

[0018] A film-like tape having a diameter approximately equal to that of the workpiece 11 may be attached to the front surface 11a of the workpiece 11. This tape is made of, for example, resin, and protects the device 15 by absorbing the impact applied to the front surface 11a when the back surface 11b of the workpiece 11 is ground.

[0019] There are no limitations on the material, shape, structure, size, etc. of the workpiece 11. For example, the workpiece 11 may be a substrate made of other semiconductor materials, ceramics, resin, metal, or other materials. Similarly, there are no limitations on the type, number, shape, structure, size, arrangement, etc. of the devices 15. Furthermore, the devices 15 do not have to be formed on the workpiece 11.

[0020] Cassette tables 8a and 8b are provided in front of the opening 4a. Cassettes 10a and 10b capable of accommodating a plurality of workpieces 11 are placed on the cassette tables 8a and 8b, respectively. A position adjustment mechanism 12 for adjusting the position of the workpieces 11 is provided diagonally behind the opening 4a.

[0021] The position adjustment mechanism 12 includes, for example, a table 12a configured to support the central portion of the workpiece 11, and a plurality of pins 12b configured to be able to approach and move away from the table 12a in an area outside the table 12a. For example, when the workpiece 11 carried out from the cassette 10a by the transport mechanism 6 is placed on the table 12a, the central position of the workpiece 11 is aligned with the central portion of the table 12a by the plurality of pins 12b.

[0022] A carry-in mechanism 14 capable of holding and rotating the workpiece 11 is provided near the position adjustment mechanism 12. The carry-in mechanism 14 has a suction pad capable of adsorbing the upper surface side of the workpiece 11, and transports the workpiece 11, the position of which has been adjusted by the position adjustment mechanism 12, backward. A disk-shaped turntable 16 is provided behind the carry-in mechanism 14.

[0023] The turntable 16 is connected to a rotary drive source (not shown) such as a motor, and rotates about a straight line parallel to the Z-axis direction as its rotation axis. On the upper surface of the turntable 16, four chuck tables 18 for supporting the workpiece 11 during processing are provided at approximately equal intervals along the circumferential direction of the turntable 16. There is no limit to the number of chuck tables 18 provided on the turntable 16.

[0024] The loading mechanism 14 sucks the workpiece 11 with a suction pad and loads it onto a chuck table 18 arranged at a load-in / load-out position near the loading mechanism 14. The turntable 16 rotates, for example, in the direction of the arrow shown in Fig. 1, and moves each chuck table 18 to the load-in / load-out position, rough grinding position, finish grinding position, and polishing position in that order.

[0025] 3 is a partial cross-sectional side view that shows a schematic view of the chuck table 18 and the like. The chuck table 18 has a frame 20 made of a metal material such as stainless steel or ceramics. The frame 20 has a disk-shaped bottom wall and an annular side wall that extends upward from the outer periphery of the bottom wall. In the frame 20, a recess is defined by the bottom wall and the side wall.

[0026] A suction passage (not shown) is formed in the bottom wall of the frame 20. One end of the suction passage is exposed at the bottom surface of the recess, and the other end of the suction passage is connected to a suction source (not shown) such as an ejector. A porous plate 22 is fixed to the recess. The lower surface of the porous plate 22 is roughly flat, and the center of the upper surface is convex and conical.

[0027] When the suction source is operated, a negative pressure is generated in the space near the upper surface of the porous plate 22. Therefore, the upper surface of the porous plate 22 functions as the holding surface 18a of the chuck table 18 that holds the workpiece 11. Specifically, when the suction source is operated with the workpiece 11 carried in on the upper surface of the porous plate 22, the workpiece 11 is sucked and held on the chuck table 18.

[0028] The upper part of a cylindrical spindle 24 is connected to the lower part of the chuck table 18. The chuck table 18 is removable from the spindle 24. The lower part of the spindle 24 is connected to a rotation drive source (not shown) such as a motor. When the rotation drive source is operated, the chuck table 18 rotates about a rotation axis 26 that passes through the center of the holding surface 18a.

[0029] An annular bearing 28 that supports the chuck table 18 in a rotatable manner is provided below the chuck table 18. An annular support plate 30 is fixed below the bearing 28. An annular table base 32 is provided below the support plate 30. The spindle 24 is located in an opening provided in the center of each of the bearing 28, the support plate 30, and the table base 32.

[0030] Three support mechanisms (a fixed support mechanism 36a, a first movable support mechanism 36b, and a second movable support mechanism 36c) are provided at approximately equal intervals along the circumferential direction of the table base 32 on the underside of the table base 32. In this specification, these three support mechanisms are collectively referred to as the tilt adjustment unit 36.

[0031] The table base 32 is supported by a fixed support mechanism 36a, a first movable support mechanism 36b, and a second movable support mechanism 36c. The fixed support mechanism 36a has a pillar (fixed shaft) of a predetermined length. The upper part of this pillar is connected to an upper support body fixed to the lower surface of the table base 32, and the lower part of this pillar is fixed to the support base.

[0032] Each of the first movable support mechanism 36b and the second movable support mechanism 36c has a pillar (movable shaft) 38 with a male screw formed at its tip. The tip (upper part) of the pillar 38 is rotatably connected to an upper support 40 fixed to the lower surface of the table base 32. Specifically, the upper support 40 is a metal columnar member such as a rod having a female screw, and the male screw of the pillar 38 is rotatably connected to the female screw of the upper support 40.

[0033] An annular bearing 42 having a predetermined outer diameter is fixed to the outer periphery of the support pillar 38 of the first movable support mechanism 36b and the second movable support mechanism 36c. A portion of the bearing 42 is supported by a stepped support plate 44. In other words, the first movable support mechanism 36b and the second movable support mechanism 36c are supported by the support plate 44.

[0034] A motor 46 that rotates the support pillar 38 is connected to the lower part of the support pillar 38. When the motor 46 is operated to rotate the support pillar 38 in one direction, the upper support 40 rises. When the motor 46 is operated to rotate the support pillar 38 in the other direction, the upper support 40 descends. In this manner, the upper supports 40 of the first movable support mechanism 36b and the second movable support mechanism 36c are raised and lowered, thereby adjusting the inclination of the table base 32 (i.e., the chuck table 18).

[0035] 1 again, the remaining components of the processing apparatus 2 will be described. A dressing unit 48 used to dress the polishing pad 110, which will be described later, is disposed between a pair of chuck tables 18 adjacent to each other along the circumferential direction of the turntable 16. The dressing unit 48 has a cylindrical support member 50, the lower end of which is fixed to the upper surface of the turntable 16. A dressing part 52 is attached to the upper end of the support member 50.

[0036] The dressing portion 52 has a structure in which abrasive grains are dispersed in a bond material such as resin, or a structure in which a plating layer in which abrasive grains are dispersed is provided on the surface of the upper end portion of the support member 50. The abrasive grains are made of materials such as silicon carbide (SiC), cubic boron nitride (cBN), diamond, or metal oxide fine particles. Examples of the metal oxide fine particles include fine particles made of silica (silicon oxide), ceria (cerium oxide), zirconia (zirconium oxide), alumina (aluminum oxide), or the like.

[0037] A columnar support structure 54 is provided behind each of the rough grinding position and the finish grinding position (behind the turntable 16). A Z-axis movement mechanism 56 is provided on the front surface (the surface on the turntable 16 side) of the support structure 54. The Z-axis movement mechanism 56 is fixed to the front surface of the support structure 54 and has a pair of guide rails 58 extending along the Z-axis direction.

[0038] A moving plate 60 is connected to the front side of the pair of guide rails 58 in a manner that allows it to slide along the pair of guide rails 58. A screw shaft 62 extending along the Z-axis direction is disposed between the pair of guide rails 58. A motor 64 for rotating the screw shaft 62 is connected to the upper end of the screw shaft 62.

[0039] A nut portion (not shown) that accommodates balls that roll on the surface of the rotating screw shaft 62 is provided on the surface of the screw shaft 62 on which the helical groove is formed, thereby forming a ball screw. That is, when the screw shaft 62 rotates, the balls circulate inside the nut portion, and the nut portion moves along the Z-axis direction.

[0040] Moreover, this nut portion is fixed to the rear surface (back surface) side of the movable plate 60. Therefore, when the screw shaft 62 is rotated by the motor 64, the movable plate 60 moves along the Z-axis direction together with the nut portion. Furthermore, a fixing device 66 is provided on the obverse surface (front surface) of the movable plate 60.

[0041] The fixture 66 supports a grinding unit 68 for grinding the workpiece 11. The grinding unit 68 includes a spindle housing 70 fixed to the fixture 66. A spindle 72 extending along the Z-axis direction is rotatably accommodated in the spindle housing 70.

[0042] A rotation drive source (not shown) such as a motor is connected to the upper end of the spindle 72, and the spindle 72 rotates by the power of this rotation drive source. The lower end of the spindle 72 is exposed from the lower surface of the spindle housing 70, and a disk-shaped mount 74 is fixed to this lower end.

[0043] A grinding wheel 76a for rough grinding is attached to the underside of the mount 74 of the grinding unit 68 on the rough grinding position side. This grinding wheel 76a for rough grinding has a wheel base formed to have approximately the same diameter as the mount 74. This wheel base is made of a metal material such as stainless steel or aluminum.

[0044] In addition, a plurality of grinding wheels containing abrasive grains suitable for rough grinding are fixed to the underside of the wheel base. The underside (grinding surface) of each of the plurality of grinding wheels is a surface that is approximately perpendicular to the Z-axis direction, and roughly grinds the workpiece 11 that is sucked and held on the chuck table 18 arranged at the rough grinding position.

[0045] Similarly, a grinding wheel 76b for finish grinding is attached to the underside of the mount 74 of the grinding unit 68 on the finish grinding position side. This grinding wheel 76b for finish grinding has a wheel base formed to have approximately the same diameter as the mount 74. This wheel base is made of a metal material such as stainless steel or aluminum.

[0046] In addition, a plurality of grinding wheels containing abrasive grains suitable for finish grinding are fixed to the underside of the wheel base. The underside (grinding surface) of each of the plurality of grinding wheels is a surface that is approximately perpendicular to the Z-axis direction, and finish grinds the workpiece 11 that is sucked and held on the chuck table 18 arranged at the finish grinding position. The grain size of the abrasive grains contained in the grinding wheels for finish grinding is generally smaller than the grain size of the abrasive grains contained in the grinding wheels for rough grinding.

[0047] Furthermore, liquid supply nozzles (not shown) are arranged near the grinding wheels 76a, 76b to supply liquid (grinding fluid) such as pure water to the area (processing point) of the workpiece 11 that comes into contact with the grinding stones. Alternatively, instead of or in addition to this nozzle, openings for supplying liquid may be provided in the grinding wheels 76a, 76b, and the grinding fluid may be supplied to the processing point through these openings.

[0048] A support structure 78 is provided on the side of the polishing area (on the side of the turntable 16). An X-axis movement mechanism 80 is provided on the side of the support structure 78 facing the turntable 16. The X-axis movement mechanism 80 is fixed to the side of the support structure 78 facing the turntable 16, and has a pair of guide rails 82 extending along the X-axis direction.

[0049] A moving plate 84 is connected to the turntable 16 side of the pair of guide rails 82 in a manner that allows it to slide along the pair of guide rails 82. A screw shaft 86 extending along the X-axis direction is disposed between the pair of guide rails 82. A motor 88 for rotating the screw shaft 86 is connected to the front end of the screw shaft 86.

[0050] A nut portion (not shown) that accommodates balls that roll on the surface of the rotating screw shaft 86 is provided on the surface of the screw shaft 86 on which the helical groove is formed, thereby forming a ball screw. That is, when the screw shaft 86 rotates, the balls circulate inside the nut portion, and the nut portion moves along the X-axis direction.

[0051] Furthermore, this nut portion is fixed to the surface (rear surface) of the moving plate 84 that faces the support structure 78. Therefore, when the screw shaft 86 is rotated by the motor 88, the moving plate 84 moves along the X-axis direction together with the nut portion. Furthermore, a Z-axis moving mechanism 90 is provided on the surface (front surface) of the moving plate 84 on the turntable 16 side.

[0052] The Z-axis movement mechanism 90 has a pair of guide rails 92 that are fixed to the surface of the moving plate 84 and extend along the Z-axis direction. A moving plate 94 is connected to the turntable 16 side of the pair of guide rails 92 in a manner that allows it to slide along the pair of guide rails 92.

[0053] A screw shaft 96 extending along the Z-axis direction is disposed between the pair of guide rails 92. A motor 98 for rotating the screw shaft 96 is connected to the upper end of the screw shaft 96. A nut portion (not shown) for accommodating balls that roll on the surface of the rotating screw shaft 96 is provided on the surface of the screw shaft 96 on which a spiral groove is formed, thereby forming a ball screw.

[0054] That is, when the screw shaft 96 rotates, the balls circulate inside the nut portion, causing the nut portion to move along the Z-axis direction. This nut portion is fixed to the surface (back surface) of the moving plate 94 that faces the moving plate 84. Therefore, when the screw shaft 96 is rotated by the motor 98, the moving plate 94 moves along the Z-axis direction together with the nut portion.

[0055] A fixture 100 is provided on the surface (front surface) of the moving plate 94 facing the turntable 16. The fixture 100 supports a polishing unit 102 for polishing the workpiece 11. The polishing unit 102 includes a spindle housing 104 fixed to the fixture 100.

[0056] A spindle 106 extending along the Z-axis direction is rotatably housed in the spindle housing 104. A rotation drive source (not shown) such as a motor is connected to the upper end of the spindle 106, and the spindle 106 rotates by the power of this rotation drive source.

[0057] The lower end of the spindle 106 is exposed from the lower surface of the spindle housing 104, and a disk-shaped mount 108 is fixed to this lower end. A disk-shaped polishing pad 110 is attached to the lower surface of this mount 108. This polishing pad 110 has a diameter longer than the workpiece 11 that is sucked and held on the chuck table 18, and is, for example, a fixed-abrasive polishing pad with abrasive grains dispersed therein.

[0058] The circular lower surface (polishing surface) of the polishing pad 110 is a surface that is approximately perpendicular to the Z-axis direction, and dry polishes the workpiece 11 that is suction-held on the chuck table 18 arranged at the polishing position. The polishing pad 110 is manufactured, for example, by impregnating a polyester nonwoven fabric with a urethane solution in which abrasive grains with an average grain size of 20 μm or less are dispersed, and then drying it.

[0059] The abrasive grains dispersed inside the polishing pad 110 are made of materials such as silicon carbide, cBN, diamond, or metal oxide fine particles. Examples of the metal oxide fine particles include fine particles made of silica, ceria, zirconia, alumina, etc. The polishing pad 110 is flexible and bends slightly in response to the load applied when polishing the workpiece 11.

[0060] A discharge mechanism 112 capable of rotating while holding the workpiece 11 after it has been polished by the polishing unit 102 is provided on the side of the carry-in mechanism 14. A cleaning mechanism 114 configured to clean the workpiece 11 discharged by the carry-out mechanism 112 is disposed in front of the carry-out mechanism 112 and behind the opening 4a. The workpiece 11 cleaned by the cleaning mechanism 114 is transported by the transport mechanism 6 and stored, for example, in a cassette 10b.

[0061] 4 is a flow chart showing a schematic example of a method for processing the workpiece 11 in the processing device 2. In this method, first, the workpiece 11 is held by the chuck table 18 (holding step: S1). Specifically, the workpiece 11 arranged at a predetermined position by the position adjustment mechanism 12 is carried out by the carry-in mechanism 14 and carried into the chuck table 18 arranged at a carry-in / carry-out position, and then the chuck table 18 suction-holds the workpiece 11.

[0062] Next, the inclination of the chuck table 18 is adjusted (inclination adjustment step: S2). Specifically, the inclination adjustment unit 36 ​​adjusts the inclination of the chuck table 18 so that the line segment connecting the highest point among the points on the outer periphery of the holding surface 18a of the chuck table 18 and the center of the holding surface 18a is perpendicular to the Z-axis direction. In other words, the inclination adjustment unit 36 ​​adjusts the inclination of the chuck table 18 so that the line segment is parallel to the lower surface (grinding surface) of the grinding wheel for rough grinding, the lower surface (grinding surface) of the grinding wheel for finish grinding, and the lower surface (polishing surface) of the polishing pad 110.

[0063] Next, the chuck table 18 is positioned at the rough grinding position (first positioning step: S3). Specifically, the turntable 16 is rotated in the direction of the arrow shown in FIG. 1 so that the trajectory of the grinding stone of the grinding wheel 76a for rough grinding when rotated overlaps with one end and the other end of the above-mentioned line segment in a plan view.

[0064] Next, the workpiece 11 is roughly ground (rough grinding step: S4). Specifically, while rotating the chuck table 18 and the grinding wheel 76a for rough grinding, the grinding wheel 76a is lowered so that the lower surface (grinding surface) of the grinding wheel comes into contact with the upper surface (e.g., back surface 11b) of the workpiece 11. A grinding fluid is supplied to the area (processing point) of the workpiece 11 that comes into contact with the grinding wheel via a liquid supply nozzle or the like.

[0065] Next, the chuck table 18 is positioned at the finish grinding position (second positioning step: S5). Specifically, the turntable 16 is rotated in the direction of the arrow shown in Fig. 1 so that the trajectory of the grinding stone of the grinding wheel 76b for finish grinding overlaps with one end and the other end of the line segment in a plan view.

[0066] Next, the workpiece 11 is finish-ground (finish grinding step: S6). Specifically, while rotating the chuck table 18 and the grinding wheel 76b for finish grinding, the grinding wheel 76b is lowered so that the lower surface of the grinding wheel contacts the upper surface (e.g., the back surface 11b) of the workpiece 11. A grinding fluid is supplied to the area (processing point) of the workpiece 11 that contacts the grinding wheel via a liquid supply nozzle or the like.

[0067] Next, the chuck table 18 is positioned at the polishing position, and the position of the polishing pad 110 is adjusted (third positioning step: S7). Fig. 5(A) is a top view showing the chuck table 18 positioned at the polishing position and the polishing pad 110 whose position has been adjusted, and Fig. 5(B) is a cross-sectional view showing the cross section taken along line A1B1 shown in Fig. 5(A).

[0068] 5(A) can also be expressed as showing a coordinate plane parallel to the polishing surface of polishing pad 110, i.e., a coordinate plane parallel to the X-axis direction and the Y-axis direction (XY coordinate plane). In this third positioning step (S7), a point P1 on the outer periphery of the upper surface (e.g., back surface 11b) (polished surface) of workpiece 11 that overlaps with line segment L (corresponding to the above-mentioned line segment) is positioned at first coordinates (X1, Y1), and a center P2 of the polished surface of workpiece 11 is positioned at second coordinates (X2, Y2).

[0069] The first coordinate (X1, Y1) is a point that is located slightly outside the outer periphery of the polishing pad 110 and does not overlap with the polishing pad 110. The second coordinate (X2, Y2) is a point that overlaps with the polishing pad 110. That is, in the third positioning step (S7), the turntable 16 is rotated in the direction of the arrow shown in FIG. 1 and the position of the polishing unit 102 along the X-axis direction is adjusted so that most of the area of ​​the workpiece 11 except for a very small area including point P1 overlaps with the polishing pad 110.

[0070] Next, the workpiece 11 is polished (polishing step: S8). Fig. 6(A) is a top view that shows a schematic view of the workpiece 11 being polished by the polishing pad 110, and Fig. 6(B) is a cross-sectional view that shows a schematic cross section along line A2B2 shown in Fig. 6(A). Fig. 6(A) can also be expressed as showing an XY coordinate plane.

[0071] In this polishing step (S8), the chuck table 18 is rotated about the rotation axis 26, and the polishing pad 110 is rotated about the rotation axis 116 while the polishing pad 110 is lowered so that the lower surface (polishing surface) of the polishing pad 110 comes into contact with the polished surface of the workpiece 11. At this time, the polishing pad 110 bends slightly in response to the load applied when the workpiece 11 is polished.

[0072] In other words, a part of the workpiece 11 bites into the polishing pad 110 (see FIG. 6B). Therefore, not only the uppermost region of the workpiece 11 in the Z-axis direction (the region overlapping with the line segment L shown in FIG. 5A), but also a region (polishing region) R1 located slightly below this region comes into contact with the polishing pad 110.

[0073] This polishing area R1 does not include point P1 located at the first coordinate (X1, Y1), but does include points P3a and P3b on the outer periphery of the polished surface of the workpiece 11 located at third coordinates (X3a, Y3a) and (X3b, Y3b) on the XY coordinate plane which are different from the first coordinates.

[0074] The polishing area R1 changes depending on the relative positions of the chuck table 18 and the polishing pad 110 adjusted in the third positioning step (S7). Therefore, in the third positioning step (S7), the relative positions of the chuck table 18 and the polishing pad 110 are adjusted so that the polishing area R1 does not include point P1 and includes points P3a and P3b.

[0075] 4, the workpiece 11 is polished without contacting a point on the outer periphery of the polished surface of the workpiece 11 located at a first coordinate (X1, Y1) included in the XY coordinate plane with the polishing surface of the polishing pad 110, and with contacting a point on the outer periphery of the polished surface located at a third coordinate (X3a, Y3a), (X3b, Y3b) with the outer periphery of the polishing surface. In this case, the entire polished surface of the workpiece 11 can be polished, and the area near the outer periphery of the polishing surface of the polishing pad 110 can be worn to the same extent as the area inside.

[0076] This suppresses the formation of steps on the polishing surface of the polishing pad 110 caused by polishing the polished surface of the workpiece 11, and even after such polishing, the shape of the polishing pad 110 can be maintained suitable for planarizing the polished surface.

[0077] Furthermore, in this method, when polishing the polished surface of the workpiece 11, a part (unused area) R2 (see FIG. 6(A)) near the center of the polishing surface of the polishing pad 110 may not come into contact with the polished surface of the workpiece 11. In this case, there is a risk that the unused area R2 will protrude downward (a step will be formed) compared to the outer areas due to polishing of the polished surface of the workpiece 11.

[0078] When the polishing surface of the workpiece 11 is polished using the polishing pad 110 with the unused region R2 protruding in this manner, it may be difficult to flatten the polishing surface of the workpiece 11. Specifically, in this case, there is a risk that a ring-shaped depression concentric with the polishing surface of the workpiece 11 may be formed on the polishing surface.

[0079] Therefore, in the present invention, it is preferable to form a recess in the circular region (central region) including the unused region R2 before the third positioning step (S7). Figure 7 is a flow chart showing an example of such a processing method. In this method, first, a holding step (S1) and an inclination adjustment step (S2) are performed.

[0080] Next, the dressing unit 48 is positioned at the polishing position, and the position of the polishing pad 110 is adjusted (fourth positioning step: S9). Fig. 8 is a side view showing the dressing unit 48 positioned at the polishing position and the polishing pad 110 whose position has been adjusted.

[0081] Specifically, in a plan view, the turntable 16 is rotated in the direction of the arrow shown in FIG. 1 so that the dressing unit 48 overlaps with the central region of the polishing surface of the polishing pad 110 (the region including the unused region R2 shown in FIG. 6(A)), and the position of the polishing unit 102 along the X-axis direction is adjusted.

[0082] Next, the polishing pad 110 is dressed (dressing step: S10). Specifically, while rotating the polishing pad 110, the polishing pad 110 is lowered so that the lower surface (polishing surface) of the polishing pad 110 contacts the upper surface of the dressing part 52 of the dressing unit 48. As a result, a recess is formed on the polishing surface of the polishing pad 110. Furthermore, if necessary to form a recess in the central region of the polishing surface of the polishing pad 110, the polishing unit 102 may be moved along the X-axis direction while the polishing pad 110 is being rotated.

[0083] Next, a third positioning step (S7) and a polishing step (S8) are performed. Fig. 9(A) is a top view showing a state where a workpiece 11 is polished by a dressed polishing pad 110, and Fig. 9(B) is a cross-sectional view showing a cross section taken along line A3B3 shown in Fig. 9(A). Fig. 9(A) can also be expressed as showing an XY coordinate plane.

[0084] 9(A) and 9(B), a recess 118 is formed on the polishing surface of the polishing pad 110 so as to define a part of the boundary of the interface (specifically, the polishing area R1) where this polishing surface comes into contact with the polished surface of the workpiece 11. In other words, a part of the boundary of this interface is arc-shaped along the outer periphery of the recess 118.

[0085] When such recesses 118 are formed on the polishing surface of polishing pad 110, the central region of polishing pad 110 does not protrude downward (a step is not formed) beyond the outer regions after polishing step (S8). Therefore, in this case, the entire polished surface of workpiece 11 can be polished without forming an annular recess concentric with the polished surface of workpiece 11 in workpiece 11.

[0086] The above-mentioned method is one aspect of the present invention, and the present invention is not limited to the above-mentioned method. For example, the present invention may be a processing method in which the steps for rough grinding and / or finish grinding the workpiece 11 (the first positioning step (S3) to the finish grinding step (S6)) are omitted from the processing method shown in Fig. 4.

[0087] Furthermore, in the present invention, the moving directions of the chuck table 18 and the polishing unit 102 are not limited. For example, the chuck table 18 may be movable along the Z-axis direction, and the polishing unit 102 may be movable along the Y-axis direction. Furthermore, the chuck table 18 may not be provided on the upper surface of the turntable 16, but may be connected to an X-axis moving mechanism and / or a Y-axis moving mechanism constituted by a ball screw or the like.

[0088] In the present invention, a tilt adjusting unit may be provided to adjust the tilt of the polishing unit 102. In the tilt adjusting step (S2) of the present invention, the tilt of the polishing unit 102 may be adjusted without adjusting the tilt of the chuck table 18.

[0089] In other words, in the present invention, it is sufficient that the angle between the rotation axis 26 of the chuck table 18 and the rotation axis 116 of the polishing pad 110 can be adjusted so that the line segment connecting the point on the outer periphery of the holding surface 18a of the chuck table 18 that has the shortest distance to the polishing surface in a direction perpendicular to the polishing surface of the polishing pad 110 and the center of the holding surface 18a is parallel to the polishing surface.

[0090] In addition, the structures and methods according to the above-described embodiments can be modified as appropriate without departing from the scope of the present invention. [Explanation of symbols]

[0091] 11: Workpiece (11a: front side, 11b: back side) 13: Planned division line 15: Device 2: Processing equipment 4: Base (4a: opening) 6: Transport mechanism 8a, 8b: Cassette table 10a, 10b: Cassette 12: Position adjustment mechanism (12a: table, 12b: pin) 14: Loading mechanism 16: Turntable 18: Chuck table (18a: holding surface) 20:Frame body 22: Porous plate 24: Spindle 26: Rotation axis 28: Bearing 30: Support plate 32: Table base 36: Tilt adjustment unit (36a: fixed support mechanism, 36b, 36c: movable support mechanisms) 38: Strut 40: Upper support 42: Bearing 44: Support plate 46: Motor 48: Dress Unit 50: Support member 52: Dress Department 54 :Support structure 56:Z-axis movement mechanism 58: Guide rail 60: Moving plate 62: Screw shaft 64: Motor 66: Fixtures 68: Grinding unit 70: Spindle housing 72: Spindle 74: Mount 76a, 76b: Grinding wheels 78 :Support structure 80:X-axis movement mechanism 82: Guide rail 84: Moving plate 86: Screw shaft 88: Motor 90:Z-axis movement mechanism 92: Guide rail 94: Moving plate 96: Screw shaft 98: Motor 100: Fixtures 102: Polishing unit 104: Spindle housing 106: Spindle 108: Mount 110: Polishing pad 112: Unloading mechanism 114: Cleaning mechanism 116: Rotation axis 118: Recess

Claims

1. A method for polishing a workpiece having a circular polishing surface using a polishing pad having a circular polishing surface, comprising the steps of: A holding step of holding the workpiece on a chuck table having a cone-shaped holding surface with a convex center; an adjustment step of adjusting an angle between a rotation axis of the chuck table and a rotation axis of the polishing pad so that a line segment connecting a point on the outer periphery of the holding surface that has the shortest distance to the polishing surface in a direction perpendicular to the polishing surface and the center of the holding surface becomes parallel to the polishing surface; a positioning step of relatively moving the polishing pad and the chuck table in a horizontal direction to position the polishing pad above the chuck table so that, in a coordinate plane parallel to the polishing surface, a first coordinate at which a point on the outer periphery of the polished surface that overlaps with the line segment is located does not overlap with the polishing pad, and a second coordinate at which the center of the polished surface is located overlaps with the polishing pad; a polishing step in which, while the polishing pad and the chuck table are rotating, a point on the outer periphery of the polished surface located at the first coordinates is not brought into contact with the polishing surface, and a point on the outer periphery of the polished surface located at a third coordinate on the coordinate plane different from the first coordinates is brought into contact with the outer periphery of the polishing surface to polish the workpiece; A processing method comprising:

2. The method further includes a step of dressing the polishing pad before the positioning step, The dressing step includes forming a recess in a circular central region of the polishing surface; 2. The method according to claim 1, wherein a part of a boundary of an interface where the polishing surface and the surface to be polished come into contact with each other during the polishing step forms an arc shape along an outer periphery of the recess.

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