Grinding method for workpiece

Abstract

To provide a grinding method for a work-piece that can reduce variation in surface roughness of the work-piece.SOLUTION: A grinding method for a work-piece includes: a holding step of holding the work-piece on a holding surface of a chuck table; a first positioning step of adjusting a positional relation between the chuck table and a first grinding wheel; a first grinding step of grinding the work-piece with a first grinding stone of the first grinding wheel in contact with the work-piece; a second positioning step of adjusting a positional relation between the chuck table and a second grinding wheel; and a second grinding step of grinding an outer periphery part of the work-piece with a second grinding stone of the second grinding wheel in contact with the work-piece.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for grinding a workpiece using a grinding device. [Background technology]

[0002] A wafer on which a plurality of devices are formed is divided and singulated to produce a plurality of device chips, each including a device. Furthermore, a package substrate is formed by mounting a plurality of device chips on a base substrate and covering the mounted device chips with a resin sealing material (mold resin). A plurality of packaged devices, each including a plurality of packaged device chips, is produced by dividing and singulating the package substrate. The device chips and packaged devices are incorporated into various electronic devices such as mobile phones and personal computers.

[0003] A cutting machine is used to separate wafers and package substrates. The cutting machine is equipped with a chuck table that holds the workpiece and a cutting unit that performs the cutting process on the workpiece, and the cutting unit is equipped with an annular cutting blade. The workpiece is held on the chuck table, and the cutting blade is rotated and cut into the workpiece, cutting and separating the workpiece.

[0004] Furthermore, in recent years, with the miniaturization of electronic devices, there has been a demand for thinner device chips and package devices. Therefore, a grinding device is sometimes used to grind and thin wafers and package substrates before they are divided. The grinding device includes a chuck table that holds the workpiece and a grinding unit that grinds the workpiece, and the grinding unit is equipped with an annular grinding wheel that includes multiple grinding stones. The workpiece is held by the chuck table, and the grinding stone is brought into contact with the workpiece while the chuck table and grinding wheel are rotated, thereby grinding and thinning the workpiece (see Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-124690 Summary of the Invention [Problem to be solved by the invention]

[0006] When grinding a workpiece using a grinding device, the relative positions of the chuck table and grinding wheel are adjusted so that the center of the workpiece held by the chuck table coincides with the movement path (rotation path) of the grinding wheel. Then, while the chuck table and grinding wheel are rotated, the grinding wheel is lowered toward the workpiece at a predetermined speed (process feed). As a result, the grinding wheel, rotating at high speed, comes into contact with the top surface of the workpiece, grinding the top side of the workpiece. This type of grinding method is called in-feed grinding.

[0007] In in-feed grinding, a grinding wheel moves along an arcuate path from the outer edge to the center of the workpiece, contacting the workpiece as it rotates with the chuck table. When grinding a workpiece using this method, the volume of workpiece removed per unit time is greater at the outer periphery than at the center, where the grinding wheel is always in contact. This places a greater processing load on the outer periphery of the workpiece, and the surface roughness of the ground surface tends to be greater at the outer periphery than at the center.

[0008] The difference in surface roughness between the center and periphery of the workpiece causes variations in the mechanical strength of the chips (device chips, packaged devices, etc.) obtained by dividing the workpiece, which makes chip quality control difficult and may result in a decrease in chip yield.

[0009] The present invention has been made in view of the above problems, and has as its object to provide a method for grinding a workpiece that can reduce the variation in the surface roughness of the workpiece. [Means for solving the problem]

[0010] According to one aspect of the present invention, there is provided a method for grinding a workpiece using a grinding device, the grinding device comprising: a chuck table having a holding surface; a first grinding unit having a first spindle having a first grinding wheel with a plurality of first grinding wheels attached to its tip; and a second grinding unit having a second spindle having a second grinding wheel with a plurality of second grinding wheels attached to its tip; and the method includes a holding step of holding the workpiece on the holding surface; a first positioning step of adjusting the positional relationship between the chuck table and the first grinding wheel so that a region of the workpiece through which the rotation axis of the chuck table passes overlaps with a moving path of the first grinding wheel; and a second positioning step of adjusting the positional relationship between the chuck table and the first grinding wheel so that a region of the workpiece through which the rotation axis of the chuck table passes overlaps with a moving path of the first grinding wheel. a first grinding step in which the first grinding wheel is brought into contact with the workpiece and grinds the workpiece by rotating the first grinding wheel and the holding surface and bringing the first grinding wheel relatively close to each other while rotating the first grinding wheel, the tilt of which is adjusted so that the distance between the first grinding wheel and other areas of the workpiece is smaller than the distance between the first grinding wheel and other areas of the workpiece; a second positioning step in which the positional relationship between the chuck table and the second grinding wheel is adjusted so that the area of ​​the workpiece through which the rotation axis of the chuck table passes overlaps with the movement path of the second grinding wheel; and a second positioning step in which the chuck table and the second grinding wheel are rotated and the holding surface and the second grinding wheel are brought into relative proximity to each other while rotating the second grinding wheel and the second grinding wheel, the tilt of which is adjusted so that the workpiece is not ground on the rotation axis of the chuck table, the second grinding wheel is brought into contact with the workpiece and grinds the workpiece. The center of the workpiece is not ground. and a second grinding step of grinding the outer periphery of the workpiece, wherein in the second grinding step, the workpiece is ground under processing conditions that result in a smaller surface roughness of the workpiece than in the first grinding step.

[0011] Preferably, the rotation speed of the chuck table in the second grinding step is lower than the rotation speed of the chuck table in the first grinding step. Also, preferably, the rotation speed of the second grinding wheel in the second grinding step is higher than the rotation speed of the first grinding wheel in the first grinding step. Also, preferably, the relative approach speed between the holding surface and the second grinding wheel in the second grinding step is lower than the relative approach speed between the holding surface and the first grinding wheel in the first grinding step. Also, preferably, the average particle size of the abrasive grains contained in the second grinding stone is smaller than the average particle size of the abrasive grains contained in the first grinding stone. [Effects of the Invention]

[0012] In a method for grinding a workpiece according to one aspect of the present invention, the workpiece is ground with a first grinding wheel whose inclination is adjusted so that the central portion of the workpiece can be thinner than the peripheral portion (first grinding step), and then the workpiece is ground with a second grinding wheel whose inclination is adjusted so that the peripheral portion of the workpiece can be ground under processing conditions that reduce the surface roughness (second grinding step).This reduces the difference in surface roughness between the central portion and the peripheral portion of the workpiece, and reduces the variation in surface roughness of the workpiece after grinding. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. [Figure 2] FIG. 2 is a cross-sectional view showing a chuck table. [Figure 3] FIG. 2 is a front view showing the first grinding unit and the second grinding unit. [Figure 4] 1 is a flowchart showing a method for grinding a workpiece. [Figure 5] FIG. 10 is a cross-sectional view showing the workpiece in the holding step. [Figure 6] FIG. 6(A) is a partial cross-sectional side view showing the workpiece in the first positioning step, and FIG. 6(B) is a partial cross-sectional side view showing the workpiece in the first grinding step. [Figure 7] FIG. 3 is a cross-sectional view showing the workpiece after the first grinding step. [Figure 8] FIG. 8(A) is a partial cross-sectional side view showing the workpiece in the second positioning step, and FIG. 8(B) is a partial cross-sectional side view showing the workpiece in the second grinding step. [Figure 9] FIG. 4 is a cross-sectional view showing the workpiece after the second grinding step. DETAILED DESCRIPTION OF THE INVENTION

[0014] An embodiment according to one aspect of the present invention will be described below with reference to the accompanying drawings. First, an example of the configuration of a processing device that can be used to implement the grinding method for a workpiece according to this embodiment will be described. FIG. 1 is a perspective view showing a grinding device 2 that grinds a workpiece 11. In FIG. 1, the X-axis direction (first horizontal direction, left-right direction) and the Y-axis direction (second horizontal direction, front-rear direction) are perpendicular to each other. Furthermore, the Z-axis direction (processing feed direction, vertical direction, up-down direction, height direction) is perpendicular to the X-axis direction and the Y-axis direction.

[0015] The grinding device 2 includes a base 4 that supports or houses each of the components that make up the grinding device 2. An opening 4a is provided on the upper surface side of the front end of the base 4, and a transport unit (transport mechanism) 6 that transports the workpiece 11 is provided inside the opening 4a.

[0016] Cassette installation areas 8A and 8B are provided on both sides of the transport unit 6. Cassettes 10A and 10B, each capable of accommodating a plurality of workpieces 11, are arranged on the cassette installation areas 8A and 8B. Cassette 10A accommodates workpieces 11 to be processed by the grinding device 2 (workpieces 11 before processing). Meanwhile, cassette 10B accommodates workpieces 11 that have been processed by the grinding device 2 (workpieces 11 after processing).

[0017] For example, the workpiece 11 is a disk-shaped wafer made of a semiconductor material such as single crystal silicon, and has a front surface (first surface) 11a and a back surface (second surface) 11b that are generally parallel to each other. The workpiece 11 is divided into a plurality of rectangular regions by a plurality of streets (planned division lines) arranged in a grid pattern so as to intersect with each other. Furthermore, devices such as ICs (Integrated Circuits), LSIs (Large Scale Integration), LEDs (Light Emitting Diodes), and MEMS (Micro Electro Mechanical Systems) devices are formed in each of the regions divided by the streets on the front surface 11a of the workpiece 11.

[0018] By dividing the workpiece 11 along the streets, a plurality of device chips each equipped with a device are manufactured. Furthermore, if the workpiece 11 is ground and thinned by the grinding device 2 before being divided, thinned device chips can be obtained.

[0019] However, there are no restrictions on the type, material, size, shape, structure, etc. of the workpiece 11 to be ground by the grinding device 2. For example, the workpiece 11 may be a substrate (wafer) made of a semiconductor other than silicon (GaAs, InP, GaN, SiC, etc.), glass, ceramics, resin, metal, etc. Furthermore, there are no restrictions on the type, number, shape, structure, size, arrangement, etc. of devices formed on the workpiece 11, and the workpiece 11 does not necessarily have to have any devices formed thereon.

[0020] Furthermore, the workpiece 11 may be a package substrate such as a CSP (Chip Size Package) substrate or a QFN (Quad Flat Non-leaded package) substrate. For example, a package substrate is formed by sealing a plurality of device chips mounted on a base substrate with a resin layer (mold resin). By dividing the package substrate into individual pieces, a plurality of packaged devices each including a plurality of packaged device chips are manufactured.

[0021] An alignment mechanism 12 is provided diagonally behind the opening 4a. The workpiece 11 accommodated in the cassette 10A is transported to the alignment mechanism 12 by the transport unit 6. The alignment mechanism 12 then sandwiches the workpiece 11 and places it in a predetermined position.

[0022] A transport unit (transport mechanism, loading arm) 14 that transports the workpiece 11 is provided adjacent to the alignment mechanism 12. For example, the transport unit 14 includes a suction pad that holds the upper surface of the workpiece 11 by suction. After the transport unit 14 holds the workpiece 11 that has been aligned by the alignment mechanism 12 with the suction pad, it rotates the suction pad to transport the workpiece 11 backward.

[0023] A disk-shaped turntable 16 is provided behind the transport unit 14. A rotation drive source (not shown), such as a motor, is connected to the turntable 16 to rotate the turntable 16 around a rotation axis that is approximately parallel to the Z-axis direction.

[0024] A plurality of chuck tables (holding tables) 18 for holding the workpieces 11 are provided on the turntable 16. Fig. 1 shows an example in which three chuck tables 18 are arranged at approximately equal intervals along the circumferential direction of the turntable 16.

[0025] 2 is a cross-sectional view showing the chuck table 18. The chuck table 18 includes a cylindrical frame (main body) 20 made of metal such as SUS (stainless steel), glass, ceramics, resin, etc. A cylindrical recess 20b is provided in the center of the upper surface 20a of the frame 20.

[0026] A disk-shaped holding member 22 made of a porous material such as porous ceramics is fitted into the recess 20b of the frame 20. The holding member 22 includes a large number of pores that communicate from the upper surface to the lower surface of the holding member 22. The upper surface of the holding member 22 forms a circular suction surface 22a that sucks the workpiece 11 when the workpiece 11 is held by the chuck table 18.

[0027] The upper surface 20a of the frame 20 and the suction surface 22a of the holding member 22 form a holding surface 18a that holds the workpiece 11. The holding surface 18a (suction surface 22a) is connected to a suction source (not shown) such as an ejector via holes included in the holding member 22, a flow path 20c formed inside the frame 20, a valve (not shown), etc.

[0028] A tilt adjustment mechanism (not shown) that adjusts the tilt of the chuck table 18 is connected to the chuck table 18. The holding surface 18a of the chuck table 18 is formed in a cone shape with its apex at the center of the holding surface 18a and is slightly tilted relative to the radial direction of the holding surface 18a. The chuck table 18 is disposed in a slightly tilted state so that a holding region 18b, which corresponds to a part of the holding surface 18a and extends from the center to the outer periphery of the holding surface 18a, is approximately parallel to the horizontal plane.

[0029] A rotary drive source (not shown), such as a motor, is connected to the chuck table 18 to rotate the chuck table 18. The rotary drive source rotates the chuck table 18 around a rotation axis 24 that intersects with the holding surface 18a. The rotation axis 24 of the chuck table 18 is set to pass through the center of the holding surface 18a along a direction perpendicular to the radial direction of the holding surface 18a, and is slightly inclined with respect to the Z-axis direction.

[0030] 2, for ease of explanation, the inclination of holding surface 18a is exaggerated, but the actual inclination of holding surface 18a is small. For example, when the diameter of holding surface 18a is approximately 290 mm or more and 310 mm or less, the difference in height between the center and the outer periphery of holding surface 18a (corresponding to the height of the cone) is set to approximately 20 μm or more and 40 μm or less.

[0031] 1 rotates clockwise in a plan view, thereby positioning each chuck table 18 at the transfer position A, the first grinding position B, the second grinding position C, and the transfer position A in this order.

[0032] Thickness gauges 26 for measuring the thickness of the workpiece 11 held by the chuck table 18 are provided near the first grinding position B and near the second grinding position C. For example, the thickness gauges 26 include a first height gauge (first height gauge) for measuring the height of the upper surface of the workpiece 11 held by the chuck table 18, and a second height gauge (second height gauge) for measuring the height of the upper surface of the chuck table 18.

[0033] Pillar-shaped support structures 28A and 28B are respectively arranged behind the first grinding position B and the second grinding position C. A moving unit (moving mechanism) 30A is provided on the front side of the support structure 28A, and a moving unit (moving mechanism) 30B is provided on the front side of the support structure 28B.

[0034] Each of the moving units 30A and 30B includes a pair of guide rails 32 arranged along the Z-axis direction. A flat moving plate 34 is attached to the pair of guide rails 32 so as to be slidable along the guide rails 32.

[0035] A nut portion (not shown) is provided on the rear surface side (back surface side) of the moving plate 34. A ball screw 36, which is disposed along the Z-axis direction between the pair of guide rails 32, is threadedly engaged with this nut portion. A pulse motor 38 that rotates the ball screw 36 is connected to the end of the ball screw 36. When the ball screw 36 is rotated by the pulse motor 38, the moving plate 34 moves along the Z-axis direction.

[0036] A grinding unit (first grinding unit) 40A that grinds the workpiece 11 is attached to the moving unit 30A. The grinding unit 40A has a housing 42A formed in a hollow cylindrical shape, and the housing 42A is fixed to the front side (surface side) of a moving plate 34 provided on the moving unit 30A. The moving unit 30A raises and lowers the grinding unit 40A along the Z-axis direction, thereby moving the chuck table 18 positioned at the first grinding position B and the grinding unit 40A toward and away from each other.

[0037] A grinding unit (second grinding unit) 40B that grinds the workpiece 11 is attached to the moving unit 30B. The grinding unit 40B has a housing 42B formed in a hollow cylindrical shape, and the housing 42B is fixed to the front side (surface side) of the moving plate 34 provided on the moving unit 30B. The moving unit 30B raises and lowers the grinding unit 40B along the Z-axis direction, thereby moving the chuck table 18 positioned at the second grinding position C and the grinding unit 40B toward and away from each other.

[0038] 3 is a front view showing grinding units 40A and 40B. Grinding unit 40A grinds the workpiece 11 held by the chuck table 18 positioned at a first grinding position B (see FIG. 1). Meanwhile, grinding unit 40B grinds the workpiece 11 held by the chuck table 18 positioned at a second grinding position C (see FIG. 1).

[0039] The grinding unit 40A includes a cylindrical spindle (first spindle) 44A. The spindle 44A is accommodated in a housing 42A (see FIG. 1), and the tip end (lower end) of the spindle 44A is exposed from the housing 42A. A rotation drive source 46A (see FIG. 1), such as a motor, is connected to the base end (upper end) of the spindle 44A.

[0040] A disk-shaped mount 48A made of metal or the like is fixed to the lower end of the spindle 44A. A grinding wheel (first grinding wheel) 50A is attached to the underside of the mount 48A. The grinding wheel 50A is a processing tool that is detachable from the mount 48A and grinds the workpiece 11, and is fixed to the mount 48A by a fastener such as a fastening bolt. In this way, the grinding wheel 50A is attached to the tip of the spindle 44A.

[0041] The grinding wheel 50A includes an annular wheel base 52A. The wheel base 52A is made of a metal such as aluminum or stainless steel, and is formed to have approximately the same diameter as the mount 48A. A plurality of grinding stones (first grinding stones) 54A are fixed to the underside of the wheel base 52A. For example, the grinding stones 54A are formed in a rectangular parallelepiped shape and are arranged in an annular shape at approximately equal intervals along the circumferential direction of the wheel base 52A.

[0042] The grinding unit 40B includes a cylindrical spindle (second spindle) 44B. The spindle 44B is accommodated in a housing 42B (see FIG. 1), and the tip end (lower end) of the spindle 44B is exposed from the housing 42B. A rotation drive source 46B (see FIG. 1), such as a motor, is connected to the base end (upper end) of the spindle 44B.

[0043] A disk-shaped mount 48B made of metal or the like is fixed to the lower end of the spindle 44B. A grinding wheel (second grinding wheel) 50B is attached to the underside of the mount 48B. The grinding wheel 50B is a processing tool that is detachable from the mount 48B and grinds the workpiece 11, and is fixed to the mount 48B by a fastener such as a fastening bolt. In this way, the grinding wheel 50B is attached to the tip of the spindle 44B.

[0044] The grinding wheel 50B includes an annular wheel base 52B. The wheel base 52B is made of a metal such as aluminum or stainless steel, and is formed to have approximately the same diameter as the mount 48B. A plurality of grinding stones (second grinding stones) 54B are fixed to the underside of the wheel base 52B. For example, the grinding stones 54B are formed in a rectangular parallelepiped shape and are arranged annularly at approximately equal intervals along the circumferential direction of the wheel base 52B.

[0045] The grinding wheels 54A, 54B contain abrasive grains such as diamond, cBN (cubic boron nitride), etc., and a bonding material for fixing the abrasive grains, such as a metal bond, a resin bond, a vitrified bond, etc. There are no restrictions on the material, shape, structure, size, etc. of the grinding wheels 54A, 54B, and the number and arrangement of the grinding wheels 54A, 54B can also be set arbitrarily.

[0046] When the rotary drive source 46A (see FIG. 1) is driven, the spindle 44A and the grinding wheel 50A rotate around the rotation axis 56A, and each of the grinding stones 54A moves along an annular movement path (orbit) centered on the rotation axis 56A. Similarly, when the rotary drive source 46B (see FIG. 1) is driven, the spindle 44B and the grinding wheel 50B rotate around the rotation axis 56B, and each of the grinding stones 54B moves along annular movement path (orbit) centered on the rotation axis 56B.

[0047] The rotation axis 56A of the spindle 44A and the grinding wheel 50A, and the rotation axis 56B of the spindle 44B and the grinding wheel 50B are each set to be inclined at a predetermined angle with respect to the Z-axis direction. For ease of explanation, the inclination of the rotation axes 56A and 56B is exaggerated in Figure 3. Details of the inclination of the rotation axes 56A and 56B will be described later.

[0048] Grinding fluid supply passages (not shown), such as nozzles, for supplying liquid (grinding fluid) such as pure water are provided inside or near the grinding units 40A and 40B. While the workpiece 11 is being ground, the grinding fluid is supplied to the workpiece 11 and the grinding wheels 54A and 54B. This cools the workpiece 11 and the grinding wheels 54A and 54B, and also washes away chips (grinding chips) generated by grinding.

[0049] 1, a transport unit (transport mechanism, unloading arm) 58 that transports the workpiece 11 is provided at a position adjacent to the transport unit 14 in the X-axis direction. For example, the transport unit 58 includes a suction pad that suction-holds the upper surface of the workpiece 11. The transport unit 58 holds the workpiece 11, which is held by the chuck table 18 arranged at transport position A, with the suction pad, and then rotates the suction pad to transport the workpiece 11 forward.

[0050] A cleaning unit (cleaning mechanism, cleaning device) 60 that cleans the workpiece 11 is provided on the front side of the transport unit 58. The cleaning unit 60 cleans the workpiece 11 transported from the chuck table 18 by the transport unit 58. For example, the cleaning unit 60 includes a spinner table that holds and rotates the workpiece 11, and a nozzle that supplies a cleaning liquid (pure water, etc.) to the workpiece 11 held by the spinner table.

[0051] The grinding apparatus 2 also includes a control unit (control section, control device) 62 connected to each of the components (transport unit 6, alignment mechanism 12, transport unit 14, turntable 16, chuck table 18, thickness measuring device 26, moving units 30A and 30B, grinding units 40A and 40B, transport unit 58, cleaning unit 60, etc.) that make up the grinding apparatus 2. The control unit 62 controls the operation of the grinding apparatus 2 by outputting control signals to each of the components of the grinding apparatus 2.

[0052] For example, the control unit 62 is configured by a computer and includes a calculation section that performs calculations necessary for the operation of the grinding device 2, and a storage section that stores various information (data, programs, etc.) used for the operation of the grinding device 2. The calculation section includes a processor such as a CPU (Central Processing Unit). The storage section includes memories such as a ROM (Read Only Memory) and a RAM (Random Access Memory).

[0053] When grinding workpieces 11 with grinding device 2, first, a plurality of workpieces 11 are stored in cassette 10A, and cassette 10A is placed on cassette placement area 8A. Then, workpieces 11 are transferred from cassette 10A to alignment mechanism 12 by transport unit 6, and alignment mechanism 12 aligns workpieces 11. Thereafter, workpieces 11 are transferred by transport unit 14 to chuck table 18 arranged at transfer position A, and are held by chuck table 18.

[0054] Next, the turntable 16 rotates, and the chuck table 18 holding the workpiece 11 is positioned at the first grinding position B. Then, the workpiece 11 is ground by the grinding unit 40A. Thereafter, the turntable 16 rotates, and the chuck table 18 holding the workpiece 11 is positioned at the second grinding position C. Then, the workpiece 11 is ground by the grinding unit 40B. Details of the grinding of the workpiece 11 by the grinding units 40A and 40B will be described later.

[0055] When grinding of the workpiece 11 is completed, the turntable 16 rotates, and the chuck table 18 holding the workpiece 11 is positioned at the transfer position A. Then, the workpiece 11 is transferred from the chuck table 18 to the cleaning unit 60 by the transfer unit 58, and is cleaned by the cleaning unit 60. After cleaning, the workpiece 11 is transferred to the cassette 10B by the transfer unit 68 and stored therein.

[0056] Next, a specific example of a method for grinding a workpiece 11 using the grinding device 2 will be described. Fig. 4 is a flowchart showing the method for grinding a workpiece.

[0057] First, the workpiece 11 is held by the holding surface 18a of the chuck table 18 (holding step S11). In the holding step S11, the workpiece 11, which has been aligned by the alignment mechanism 12, is transported by the transport unit 14 and placed on the chuck table 18, which is placed at the transport position A (see FIG. 1).

[0058] 5 is a cross-sectional view showing the workpiece 11 in the holding step S11. For example, the workpiece 11 is placed on the chuck table 18 so that the front surface 11a faces the holding surface 18a and the back surface 11b is exposed upward. At this time, the workpiece 11 is positioned so that the center position of the workpiece 11 and the center position of the holding surface 18a overlap and the entire suction surface 22a is covered by the workpiece 11. As a result, the workpiece 11 is placed concentrically with the holding surface 18a so that the rotation axis 24 of the chuck table 18 passes through the center of the workpiece 11.

[0059] When the suction force (negative pressure) of the suction source is applied to the suction surface 22a while the workpiece 11 is placed on the holding surface 18a, the workpiece 11 is sucked onto the suction surface 22a. As a result, the workpiece 11 is sucked and held by the chuck table 18 in a state where it is slightly deformed along the conical holding surface 18a. Furthermore, the area of ​​the workpiece 11 supported by the holding area 18b of the chuck table 18 is positioned approximately horizontally.

[0060] A protective sheet for protecting the workpiece 11 may be attached to the surface 11a side of the workpiece 11. As a result, the surface 11a side of the workpiece 11 (devices, etc.) is covered and protected by the protective sheet, and the workpiece 11 is held by the holding surface 18a of the chuck table 18 via the protective sheet.

[0061] For example, a tape including a circular film-like substrate and an adhesive layer (glue layer) provided on the substrate is used as the protective sheet. The substrate is made of a resin such as polyolefin, polyvinyl chloride, or polyethylene terephthalate. The adhesive layer is made of an epoxy-based, acrylic-based, or rubber-based adhesive. The adhesive layer may be an ultraviolet-curable resin that hardens when irradiated with ultraviolet light.

[0062] Next, the positional relationship between the chuck table 18 and the grinding wheel 50A is adjusted (first positioning step S12). In the first positioning step S12, the turntable 16 rotates, and the chuck table 18 holding the workpiece 11 is positioned at the first grinding position B (see FIG. 1). As a result, the workpiece 11 and the chuck table 18 are positioned at predetermined positions below the grinding wheel 50A.

[0063] 6(A) is a partial cross-sectional side view showing the workpiece 11 in the first positioning step S12. When the chuck table 18 is positioned at the first grinding position B, the positional relationship between the chuck table 18 and the grinding wheel 50A is adjusted so that the area of ​​the workpiece 11 through which the rotation axis 24 of the chuck table 18 passes overlaps with the movement path of the grinding stone 54A of the grinding wheel 50A.

[0064] As described above, the workpiece 11 is positioned so that the rotation axis 24 of the chuck table 18 passes through the center of the workpiece 11. In this case, the chuck table 18 is positioned so that the center of the workpiece 11 overlaps in the Z-axis direction with the movement path of the grinding stone 54A when the grinding wheel 50A is rotated around the rotation axis 56A.

[0065] Here, the inclination of the spindle 44A and the grinding wheel 50A (inclination of the rotation axis 56A) is adjusted in advance so that the distance between the grinding wheel 54A and an area of ​​the workpiece 11 through which the rotation axis 24 of the chuck table 18 passes (the center of the workpiece 11) is smaller than the distance between the grinding wheel 54A and other areas of the workpiece 11. Specifically, the grinding wheel 50A is inclined toward the chuck table 18 so that the grinding surface formed by the lower surface of the grinding wheel 54A is inclined with respect to the holding area 18b of the chuck table 18.

[0066] Therefore, in the region of workpiece 11 supported by holding region 18b, the distance between workpiece 11 and grindstone 54A increases from the center of workpiece 11 toward the outer periphery (the farther away from rotation axis 24). In other words, workpiece 11 is positioned so that distance S1 between the center of workpiece 11 and grindstone 54A is smaller than distance S2 between the outer periphery of workpiece 11 and grindstone 54A.

[0067] The relative inclination between the chuck table 18 and the grinding wheel 50A can be set arbitrarily depending on factors such as the total thickness variation (TTV) required for the workpiece 11. For example, the angle formed between the rotation axis 24 of the chuck table 18 and the rotation axis 56A of the grinding wheel 50A is set to be equal to or greater than 0° and equal to or less than 0.004°, for example, approximately 0.0034°.

[0068] Next, while rotating the chuck table 18 and the grinding wheel 50A, the holding surface 18a of the chuck table 18 and the grinding wheel 50A are brought relatively close to each other, thereby bringing the grindstone 54A into contact with the workpiece 11 and grinding the workpiece 11 (first grinding step S13). Fig. 6(B) is a partial cross-sectional side view showing the workpiece 11 in the first grinding step S13.

[0069] In the first grinding step S13, first, the chuck table 18 is rotated around the rotation axis 24, and the spindle 44A and the grinding wheel 50A are rotated around the rotation axis 56A. For example, the rotation speed of the chuck table 18 is set to 100 rpm or more and 900 rpm or less, and the rotation speed of the spindle 44A and the grinding wheel 50A is set to 1000 rpm or more and 3000 rpm or less.

[0070] Next, with the chuck table 18 and the grinding wheel 50A rotating, the grinding unit 40A is lowered at a predetermined speed along the Z-axis direction, bringing the holding surface 18a of the chuck table 18 and the grinding wheel 50A relatively close to each other. The lowering speed of the grinding wheel 50A at this time, i.e., the relative movement speed in the Z-axis direction between the chuck table 18 (workpiece 11) and the grinding wheel 50A, corresponds to the processing feed speed in the first grinding step S13. For example, the processing feed speed in the first grinding step S13 is set to be 1.5 μm / s or more and 5.0 μm / s or less.

[0071] When the holding surface 18a of the chuck table 18 and the grinding wheel 50A are brought relatively close to each other, the rotating grindstone 54A comes into contact with the back surface 11b of the workpiece 11, and the workpiece 11 is ground. At this time, each of the multiple grindstones 54A rotates so as to pass through the rotation axis 24 of the chuck table 18, and grinds an arc-shaped region extending from the outer periphery to the center of the workpiece 11. Furthermore, the rotation of the chuck table 18 brings the grindstone 54A into contact with the entire back surface 11b of the workpiece 11. As a result, the workpiece 11 is ground and thinned.

[0072] When the workpiece 11 has been ground until its thickness reaches a predetermined value, the grinding unit 40A is raised and the grinding wheel 54A is moved away from the workpiece 11. This stops the grinding of the workpiece 11 by the grinding wheel 50A.

[0073] 7 is a cross-sectional view showing the workpiece 11 after the first grinding step S13. In the first grinding step S13, the workpiece 11 is ground using the grinding wheel 50A, the inclination of which is adjusted so that the distance between the area of ​​the workpiece 11 through which the rotation axis 24 of the chuck table 18 passes (the center of the workpiece 11) and the grinding wheel 54A is smaller than the distance between other areas of the workpiece 11 (such as the outer periphery of the workpiece 11) and the grinding wheel 54A. Therefore, the central portion of the workpiece 11 is ground preferentially, and the workpiece 11 is processed so that the central portion is thinner than the outer periphery. As a result, a conical recess is formed on the back surface 11b side of the central portion of the workpiece 11.

[0074] The grinding of the workpiece 11 in the first grinding step S13 is so-called in-feed grinding. Therefore, the volume of the workpiece removed per unit time is larger at the outer periphery of the workpiece 11 than at the center of the workpiece 11, which is always in contact with the grinding wheel 54A. This places a heavy processing load on the outer periphery of the workpiece 11, and the surface roughness of the back surface 11b (the surface to be ground) is greater at the outer periphery of the workpiece 11 than at the center.

[0075] Next, the positional relationship between the chuck table 18 and the grinding wheel 50B is adjusted (second positioning step S14). In the second positioning step S14, the turntable 16 rotates, and the chuck table 18 holding the workpiece 11 is positioned at the second grinding position C (see FIG. 1). As a result, the workpiece 11 and the chuck table 18 are positioned at predetermined positions below the grinding wheel 50B.

[0076] 8(A) is a partial cross-sectional side view showing the workpiece 11 in the second positioning step S14. When the chuck table 18 is positioned at the second grinding position C, the positional relationship between the chuck table 18 and the grinding wheel 50B is adjusted so that the area of ​​the workpiece 11 through which the rotation axis 24 of the chuck table 18 passes overlaps with the movement path of the grinding stone 54B of the grinding wheel 50B.

[0077] As described above, the workpiece 11 is positioned so that the rotation axis 24 of the chuck table 18 passes through the center of the workpiece 11. In this case, the chuck table 18 is positioned so that the center of the workpiece 11 overlaps in the Z-axis direction with the movement path of the grinding stone 54B when the grinding wheel 50B is rotated around the rotation axis 56B.

[0078] Here, the inclination of the spindle 44B and the grinding wheel 50B (inclination of the rotation axis 56B) is adjusted in advance so that the workpiece 11 is not ground on the rotation axis 24 of the chuck table 18 in the second grinding step S15 described below. For example, the inclination of the grinding wheel 50B is adjusted so that the distance between the grinding wheel 54B and an area of ​​the workpiece 11 through which the rotation axis 24 of the chuck table 18 passes (the center of the workpiece 11) is greater than the distance between the grinding wheel 54B and other areas of the workpiece 11. Specifically, the grinding wheel 50B is inclined away from the chuck table 18 so that the grinding surface formed by the lower surface of the grinding wheel 54B is inclined with respect to the holding area 18b of the chuck table 18.

[0079] Therefore, in the region of workpiece 11 supported by holding region 18b, the distance between workpiece 11 and grindstone 54B decreases from the center of workpiece 11 toward the outer periphery (the farther away from rotation axis 24). In other words, workpiece 11 is positioned so that distance S3 between the center of workpiece 11 and grindstone 54B is greater than distance S4 between the outer periphery of workpiece 11 and grindstone 54B.

[0080] The relative inclination between the chuck table 18 and the grinding wheel 50B can be set arbitrarily depending on the TTV required for the workpiece 11. For example, the angle formed between the rotation axis 24 of the chuck table 18 and the rotation axis 56B of the grinding wheel 50B is set to 0.007° or more and 0.012° or less, for example, approximately 0.008°.

[0081] Next, while rotating the chuck table 18 and the grinding wheel 50B, the holding surface 18a of the chuck table 18 and the grinding wheel 50B are brought relatively close to each other, thereby bringing the grindstone 54B into contact with the workpiece 11 and grinding the outer periphery of the workpiece 11 (second grinding step S15). Fig. 8(B) is a partial cross-sectional side view showing the workpiece 11 in the second grinding step S15.

[0082] In the second grinding step S15, first, the chuck table 18 is rotated about the rotation axis 24, and the spindle 44B and the grinding wheel 50B are rotated about the rotation axis 56B. Next, with the chuck table 18 and the grinding wheel 50B rotating, the grinding unit 40B is lowered at a predetermined speed along the Z-axis direction, so that the holding surface 18a of the chuck table 18 and the grinding wheel 50B approach each other. The lowering speed of the grinding wheel 50B at this time, i.e., the relative movement speed in the Z-axis direction between the chuck table 18 (workpiece 11) and the grinding wheel 50B, corresponds to the processing feed rate (grinding feed rate) in the second grinding step S15.

[0083] When the holding surface 18a of the chuck table 18 and the grinding wheel 50B are brought relatively close to each other, the rotating grinding wheel 54B comes into contact with the back surface 11b of the outer periphery of the workpiece 11, grinding the outer periphery of the workpiece 11. Then, when the workpiece 11 has been ground until the thickness of the outer periphery of the workpiece 11 reaches a predetermined value, the grinding unit 40B rises and the grinding wheel 54B is separated from the workpiece 11. This stops grinding of the workpiece 11 by the grinding wheel 50B.

[0084] 9 is a cross-sectional view showing the workpiece 11 after the second grinding step S15. In the second grinding step S15, the workpiece 11 is ground using the grinding wheel 50B, the inclination of which is adjusted so that the grinding wheel 54B can contact only the outer periphery of the workpiece 11. Then, grinding is stopped before the grinding wheel 54B contacts the workpiece 11 on the rotation axis 24 of the chuck table 18. As a result, the center of the workpiece 11 on and near the rotation axis 24 of the chuck table 18 is not ground, and only the outer periphery of the workpiece 11 is ground and thinned. As a result, the difference in height between the center and outer periphery of the workpiece 11 is reduced.

[0085] As described above, after the first grinding step S13, the surface roughness of the back surface 11b (ground surface) is greater at the outer periphery of the workpiece 11 (see FIG. 7) than at the center. Therefore, in the second grinding step S15, the outer periphery of the workpiece 11 is ground under processing conditions that result in a smaller surface roughness of the workpiece 11 than in the first grinding step S13. This makes it possible to suppress variations in surface roughness between the center and outer periphery of the workpiece 11.

[0086] There are no restrictions on the specific processing conditions for the workpiece 11 in the second grinding step S15, as long as they can reduce the surface roughness of the outer periphery of the workpiece 11 after the second grinding step S15. For example, the surface roughness of the outer periphery of the workpiece 11 can be reduced by adjusting the rotation speed of the chuck table 18, the rotation speed of the grinding wheel 50B, the processing feed rate, the average particle size of the abrasive grains contained in the grinding stone 54B, etc.

[0087] Specifically, the rotation speed of the chuck table 18 in the second grinding step S15 may be set lower than the rotation speed of the chuck table 18 in the first grinding step S13. Preferably, the rotation speed of the chuck table 18 in the second grinding step S15 is set to ⅓ or less of the rotation speed of the chuck table 18 in the first grinding step S13. For example, the rotation speed of the chuck table 18 in the second grinding step S15 can be set to 30 rpm or more and 300 rpm or less. In this case, the processing conditions other than the rotation speed of the chuck table 18 can be set to the same as those in the first grinding step S13.

[0088] Furthermore, the rotational speed of the grinding wheel 50B in the second grinding step S15 may be set higher than the rotational speed of the grinding wheel 50A in the first grinding step S13. Preferably, the rotational speed of the grinding wheel 50B is set to at least twice the rotational speed of the grinding wheel 50A. For example, the rotational speed of the grinding wheel 50B can be set to 2000 rpm or higher and 6000 rpm or lower. In this case, the processing conditions other than the rotational speed of the grinding wheel 50B can be set to the same as those in the first grinding step S13.

[0089] Furthermore, the processing feed rate in the second grinding step S15 (the relative approach rate between the holding surface 18a and the grinding wheel 50B) may be set lower than the processing feed rate in the first grinding step S13 (the relative approach rate between the holding surface 18a and the grinding wheel 50A). Preferably, the processing feed rate in the second grinding step S15 is set to 1 / 5 or less of the processing feed rate in the first grinding step S13. For example, the processing feed rate in the second grinding step S15 can be set to 0.3 μm / s or more and 1.0 μm / s or less. In this case, the processing conditions other than the processing feed rate can be set to the same as those in the first grinding step S13.

[0090] Furthermore, the average particle size of the abrasive grains contained in grinding stone 54B of grinding wheel 50B may be smaller than the average particle size of the abrasive grains contained in grinding stone 54A of grinding wheel 50A. Preferably, the average particle size of the abrasive grains contained in grinding stone 54B is between one-third and two-thirds of the average particle size of the abrasive grains contained in grinding stone 54A. For example, the average particle size of the abrasive grains contained in grinding stone 54A is between 3 μm and 5 μm (for example, about 4 μm), and the average particle size of the abrasive grains contained in grinding stone 54B is between 1 μm and 3 μm (for example, about 2 μm). In this case, the processing conditions other than the average particle size of the abrasive grains can be set in the same way as in the first grinding step S13.

[0091] By setting the processing conditions in the second grinding step S15 as described above, the surface roughness of the outer periphery of the workpiece 11 can be controlled independently of the surface roughness of the central portion of the workpiece 11. This makes it possible to keep the surface roughness of the outer periphery of the workpiece 11 (see FIG. 9) after the second grinding step S15 within a range of, for example, ±20% of the surface roughness of the central portion. As a result, the variation in surface roughness of the back surface 11b (ground surface) of the workpiece 11 is reduced. Note that in the second grinding step S15, only one of the four processing conditions described above may be changed from the first grinding step S13, or any two or more of the four conditions may be changed.

[0092] Furthermore, the range of the workpiece 11 to be ground in the second grinding step S15 can be set as appropriate within a range in which the variation in surface roughness of the workpiece 11 falls within a certain range. For example, in the second grinding step S15, an area of ​​the workpiece 11 whose distance from the outer peripheral edge is between 1 / 3 and 2 / 3 of the radius of the workpiece 11 is ground. In particular, in the second grinding step S15, it is preferable to grind an area of ​​the workpiece 11 whose distance from the outer peripheral edge is between 2 / 5 and 3 / 5 of the radius of the workpiece 11.

[0093] 1 stores a program describing a series of operations of the components of the grinding apparatus 2 required to sequentially perform the holding step S11, first positioning step S12, first grinding step S13, second positioning step S14, and second grinding step S15. When processing the workpiece 11, the control unit 62 reads out the program from the storage and executes it, sequentially outputting control signals to each component of the grinding apparatus 2. This controls the operation of the grinding apparatus 2, and the workpiece grinding method according to this embodiment is automatically performed.

[0094] As described above, in the method for grinding a workpiece according to this embodiment, the workpiece 11 is ground using the grinding wheel 50A whose inclination has been adjusted so that the central portion of the workpiece 11 can be made thinner than the outer periphery (first grinding step S13), and then the workpiece 11 is ground using the grinding wheel 50B whose inclination has been adjusted so that the outer periphery of the workpiece 11 can be ground under processing conditions that reduce the surface roughness (second grinding step S15). This reduces the difference in surface roughness between the central portion and the outer periphery of the workpiece 11, and reduces the variation in surface roughness of the workpiece 11 after grinding.

[0095] Furthermore, in the first grinding step S13, the workpiece 11 is ground by the grinding wheel 50A attached to the spindle 44A, and in the second grinding step S15, the workpiece 11 is ground by the grinding wheel 50B attached to the spindle 44B. Therefore, the inclinations of the grinding wheels 50A and 50B can be individually adjusted in advance to suit the contents of the first grinding step S13 and the second grinding step S15, respectively, and it is possible to omit the work of adjusting the inclinations of the chuck table and grinding wheels between the first grinding step S13 and the second grinding step S15. This improves the processing efficiency of the workpiece 11.

[0096] The structures, methods, etc. according to the above-described embodiments can be modified as appropriate without departing from the scope of the object of the present invention. [Explanation of symbols]

[0097] 11 Workpiece 11a Surface (first side) 11b Back side (2nd side) 2 Grinding equipment 4 Foundation 4a aperture 6. Transport unit (transport mechanism) 8A, 8B Cassette installation area 10A, 10B cassette 12 Alignment mechanism 14 Transport unit (transport mechanism, loading arm) 16 Turntable 18 Chuck table (holding table) 18a Holding surface 18b Holding area 20 Frame (main body) 20a top surface 20b Recess 20c Flow path 22 Retaining member 22a Suction surface 24 Rotation Axis 26 Thickness Measuring Instrument 28A,28B Support structure 30A, 30B Moving unit (moving mechanism) 32 guide rail 34 Moving Plate 36 Ball screw 38 Pulse motor 40A, 40B Grinding Unit 42A, 42B housing 44A, 44B Spindle 46A, 46B Rotation drive source 48A, 48B mount 50A, 50B grinding wheels 52A, 52B wheel base 54A, 54B Grindstone 56A, 56B Rotating shaft 58 Transport unit (transport mechanism, unloading arm) 60 Cleaning unit (cleaning mechanism, cleaning device) 62 Control unit (control unit, control device)

Claims

1. A method for grinding a workpiece using a grinding device, comprising: The grinding device comprises: a chuck table having a holding surface; a first grinding unit including a first spindle having a first grinding wheel having a plurality of first grindstones attached to a tip thereof; a second grinding unit including a second spindle having a second grinding wheel having a plurality of second grinding stones attached to a tip end thereof; a holding step of holding the workpiece on the holding surface; a first positioning step of adjusting a positional relationship between the chuck table and the first grinding wheel so that an area of ​​the workpiece through which the rotation axis of the chuck table passes overlaps with a moving path of the first grinding wheel; a first grinding step in which the chuck table and the first grinding wheel, the inclination of which is adjusted so that the distance between the first grinding stone and a region of the workpiece through which the rotation axis of the chuck table passes is smaller than the distance between the first grinding stone and other regions of the workpiece, are respectively rotated, and the holding surface and the first grinding wheel are brought relatively close to each other, thereby bringing the first grinding stone into contact with the workpiece to grind the workpiece; a second positioning step of adjusting the positional relationship between the chuck table and the second grinding wheel so that an area of ​​the workpiece through which the rotation axis of the chuck table passes overlaps with a movement path of the second grinding wheel; a second grinding step in which the holding surface and the second grinding wheel are brought relatively close to each other while rotating the chuck table and the second grinding wheel, the tilt of which is adjusted so that the workpiece is not ground on the rotation axis of the chuck table, thereby bringing the second grinding wheel into contact with the workpiece and grinding the outer periphery of the workpiece without grinding the center of the workpiece, In the second grinding step, the workpiece is ground under processing conditions that result in a smaller surface roughness of the workpiece than in the first grinding step.

2. 2. The method for grinding a workpiece according to claim 1, wherein the rotation speed of the chuck table in the second grinding step is lower than the rotation speed of the chuck table in the first grinding step.

3. 3. The method for grinding a workpiece according to claim 1, wherein the rotational speed of the second grinding wheel in the second grinding step is higher than the rotational speed of the first grinding wheel in the first grinding step.

4. 4. A method for grinding a workpiece according to claim 1, wherein the relative approach speed between the holding surface and the second grinding wheel in the second grinding step is lower than the relative approach speed between the holding surface and the first grinding wheel in the first grinding step.

5. 5. The method for grinding a workpiece according to claim 1, wherein the average particle size of the abrasive grains contained in the second grinding stone is smaller than the average particle size of the abrasive grains contained in the first grinding stone.

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