JP7736591B2 - Grinding method for workpiece - Google Patents

Description

The present invention relates to a method for grinding a workpiece using a grinding device.

By dividing and singulating a wafer on which multiple devices are formed, multiple device chips, each equipped with a device, are manufactured. Furthermore, by mounting multiple device chips on a base substrate and covering the mounted device chips with a resin sealing material (mold resin), a package substrate is formed. By dividing and singulating the package substrate, multiple packaged devices, each equipped with multiple packaged device chips, are manufactured. The device chips and packaged devices are incorporated into various electronic devices such as mobile phones and personal computers.

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

Furthermore, in recent years, with the miniaturization of electronic devices, there is 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 is equipped with a chuck table that holds the workpiece and a grinding unit that grinds the workpiece. The grinding unit is equipped with an annular grinding wheel containing multiple grinding stones. The workpiece is held on the chuck table, and the grinding stones are 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).

JP 2014-124690 A

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 overlaps the movement path (rotation path) of the grinding wheel's grinding stone. Then, while the chuck table and grinding wheel are both rotated, the grinding wheel is lowered toward the workpiece at a predetermined speed (process feed). As a result, the grinding stone, 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.

In in-feed grinding, a grinding wheel moves along an arcuate path from the outer edge to the center of the workpiece, bringing it into contact with the workpiece as it rotates along with the chuck table. When a workpiece is ground using this method, the volume of workpiece removed per unit time is greater at the outer periphery than at the center of the workpiece, 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.

Differences in surface roughness between the center and periphery of a workpiece can cause variations in the mechanical strength of the chips (device chips, packaged devices, etc.) obtained by dividing the workpiece. This can make chip quality control difficult and may result in reduced chip yields.

The present invention was made in consideration of these problems, and aims to provide a method for grinding a workpiece that can reduce variation in the surface roughness of the workpiece.

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 first chuck table having a first holding surface; a second chuck table having a second holding surface; and a grinding unit having a spindle having a grinding wheel with multiple grinding wheels attached to its tip; a first holding step for holding the workpiece on the first holding surface; a first positioning step for adjusting the positional relationship between the first chuck table and the grinding wheel so that an area of the workpiece through which the rotation axis of the first chuck table passes overlaps with the movement path of the grinding wheel; and a first chuck table and the grinding wheel, the tilt of which is adjusted so that the distance between the area of the workpiece through which the rotation axis of the first chuck table passes and the grinding wheel is smaller than the distance between other areas of the workpiece and the grinding wheel, while rotating the first chuck table and the grinding wheel. a first grinding step in which the grinding wheel is brought into contact with the workpiece by relatively approaching the workpiece, thereby grinding the workpiece; a second holding step in which the workpiece is held on the second holding surface; a second positioning step in which the positional relationship between the second chuck table and the grinding wheel is adjusted so that an area of the workpiece through which the rotation axis of the second chuck table passes overlaps with the movement path of the grinding wheel; and a second grinding step in which the grinding wheel is brought into contact with the workpiece by relatively approaching the second holding surface and the grinding wheel while rotating the second chuck table, the tilt of which is adjusted so that the workpiece is not ground on the rotation axis of the second chuck table, and the grinding wheel, respectively, thereby grinding the outer periphery of the workpiece; and the second grinding step in which the grinding wheel is brought into contact with the workpiece by relatively approaching the second holding surface and the grinding wheel, thereby grinding the outer periphery of the workpiece;

Preferably, the rotational speed of the second chuck table in the second grinding step is lower than the rotational speed of the first chuck table in the first grinding step. Also, preferably, the rotational speed of the grinding wheel in the second grinding step is higher than the rotational speed of the grinding wheel in the first grinding step. Also, preferably, the relative approach speed between the second holding surface and the grinding wheel in the second grinding step is lower than the relative approach speed between the first holding surface and the grinding wheel in the first grinding step.

In one aspect of the present invention, a method for grinding a workpiece involves grinding a workpiece held by a first chuck table whose tilt is adjusted so that the central portion of the workpiece can be thinner than the peripheral portion (first grinding step), and then grinding a workpiece held by a second chuck table whose tilt is adjusted so that the peripheral portion of the workpiece can be ground under processing conditions that reduce surface roughness (second grinding step). This reduces the difference in surface roughness between the central and peripheral portions of the workpiece, and reduces variation in surface roughness in the workpiece after grinding.

FIG. FIG. 2(A) is a cross-sectional view showing a chuck table for rough grinding, FIG. 2(B) is a cross-sectional view showing a first chuck table for finish grinding, and FIG. 2(C) is a cross-sectional view showing a second chuck table for finish grinding. FIG. 2 is a front view showing the first grinding unit and the second grinding unit. 1 is a flowchart showing a method for grinding a workpiece. FIG. 10 is a cross-sectional view showing the workpiece in a first holding step. FIG. 6A is a partial cross-sectional side view showing the workpiece in the first positioning step, and FIG. 6B is a partial cross-sectional side view showing the workpiece in the first grinding step. FIG. 4 is a cross-sectional view showing the workpiece after the first grinding step. FIG. 10 is a cross-sectional view showing the workpiece in a second holding step. FIG. 9A is a partial cross-sectional side view showing the workpiece in the second positioning step, and FIG. 9B is a partial cross-sectional side view showing the workpiece in the second grinding step. FIG. 10 is a cross-sectional view showing the workpiece after the second grinding step.

An embodiment of the present invention will now be described with reference to the accompanying drawings. First, an example configuration of a processing device that can be used to implement the workpiece grinding method according to this embodiment will be described. Figure 1 is a perspective view showing a grinding device 2 that grinds a workpiece 11. Note that in Figure 1, the X-axis direction (first horizontal direction, left-right direction) and the Y-axis direction (second horizontal direction, front-back direction) are mutually perpendicular. Furthermore, the Z-axis direction (processing feed direction, vertical direction, up-down direction, height direction) is a direction perpendicular to the X-axis and Y-axis directions.

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 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.

Cassette installation areas 8A and 8B are provided on both sides of the transport unit 6. Cassettes 10A and 10B, each capable of holding multiple workpieces 11, are placed on the cassette installation areas 8A and 8B. Cassette 10A holds the workpiece 11 to be processed by the grinding device 2 (workpiece 11 before processing). Cassette 10B, on the other hand, holds the workpiece 11 that has been processed by the grinding device 2 (workpiece 11 after processing).

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 multiple rectangular regions by multiple streets (planned division lines) arranged in a grid pattern so that they intersect with each other. Furthermore, each region divided by the streets on the front surface 11a of the workpiece 11 contains a device such as an IC (Integrated Circuit), an LSI (Large Scale Integration), an LED (Light Emitting Diode), or a MEMS (Micro Electro Mechanical Systems) device.

By dividing the workpiece 11 along the streets, multiple device chips, each equipped with a device, are manufactured. Furthermore, if the workpiece 11 is ground and thinned using the grinding device 2 before being divided, thinned device chips can be obtained.

However, there are no restrictions on the type, material, size, shape, structure, etc. of the workpiece 11 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 on it.

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 multiple device chips mounted on a base substrate with a resin layer (mold resin). By dividing and singulating the package substrate, multiple package devices each equipped with multiple packaged device chips are manufactured.

An alignment mechanism 12 is provided diagonally behind the opening 4a. The workpiece 11 stored in the cassette 10A is transported to the alignment mechanism 12 by the transport unit 6. The alignment mechanism 12 then clamps the workpiece 11 and positions it in a predetermined position.

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 is equipped with a suction pad that holds the top side of the workpiece 11 by suction. After the transport unit 14 holds the workpiece 11, which has been aligned by the alignment mechanism 12, with the suction pad, it rotates the suction pad to transport the workpiece 11 backward.

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

Three chuck tables (holding tables) 18A, 18B, and 18C that hold the workpiece 11 are provided on the turntable 16. The chuck tables 18A, 18B, and 18C are arranged at approximately equal intervals (120° intervals) around the circumference of the turntable 16.

Chuck table 18A is a chuck table for rough grinding that holds workpiece 11 to be roughly ground by grinding unit 40A (described below). Chuck tables 18B and 18C are chuck tables for finish grinding that hold workpiece 11 to be finish ground by grinding unit 40B (described below).

Figure 2(A) is a cross-sectional view showing the chuck table 18A. The chuck table 18A has 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.

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 contains numerous pores that connect from the top surface to the bottom surface of the holding member 22. The top surface of the holding member 22 forms a circular suction surface 22a that sucks the workpiece 11 when it is held by the chuck table 18A.

The upper surface 20a of the frame 20 and the suction surface 22a of the holding member 22 form the 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 contained in the holding member 22, a flow path 20c formed inside the frame 20, a valve (not shown), etc.

A tilt adjustment mechanism (not shown) that adjusts the tilt of the chuck table 18A is connected to the chuck table 18A. The holding surface 18a of the chuck table 18A is formed in a cone shape with its apex at the center of the holding surface 18a and is slightly tilted in the radial direction of the holding surface 18a. The chuck table 18A is positioned at a slight tilt so that a holding area 18b, which corresponds to a portion of the holding surface 18a and extends from the center to the outer periphery of the holding surface 18a, is roughly parallel to the horizontal plane.

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

Note that for ease of explanation, the inclination of the holding surface 18a is exaggerated in Figure 2(A), but the actual inclination of the holding surface 18a is small. For example, if the diameter of the 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 the holding surface 18a (equivalent to the height of the cone) is set to approximately 20 μm or more and 40 μm or less.

Figure 2(B) is a cross-sectional view showing chuck table 18B, and Figure 2(C) is a cross-sectional view showing chuck table 18C. The configuration of chuck tables 18B and 18C is similar to that of chuck table 18A. However, rotation axis 24B of chuck table 18B and rotation axis 24C of chuck table 18C are each set to be inclined at a predetermined angle relative to rotation axis 24A of chuck table 18A (see Figure 2(A)). Note that for ease of explanation, the inclination of rotation axes 24B and 24C is exaggerated in Figures 2(B) and 2(C). Details of the inclination of rotation axes 24B and 24C will be described later.

The turntable 16 shown in Figure 1 rotates clockwise and/or counterclockwise in a plan view. This allows the chuck tables 18A, 18B, and 18C to be positioned at the transfer position A, first grinding position B, or second grinding position C at the desired timing.

A thickness gauge 26 for measuring the thickness of the workpiece 11 held by the chuck tables 18A, 18B, and 18C is provided near the first grinding position B and near the second grinding position C. For example, the thickness gauge 26 includes a first height gauge (first height gauge) that measures the height of the top surface of the workpiece 11 held by the chuck tables 18A, 18B, and 18C, and a second height gauge (second height gauge) that measures the height of the top surface of the chuck tables 18A, 18B, and 18C.

Columnar support structures 28A and 28B are located behind the first grinding position B and the second grinding position C, respectively. A moving unit (moving mechanism) 30A is provided on the front side of support structure 28A, and a moving unit (moving mechanism) 30B is provided on the front side of support structure 28B.

Each of the moving units 30A and 30B has 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 that it can slide along the guide rails 32.

A nut portion (not shown) is provided on the rear side (back side) of the moving plate 34. A ball screw 36, which is arranged along the Z-axis direction between a 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.

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 hollow, cylindrical housing 42A, which is fixed to the front side (surface side) of the 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 18A positioned at the first grinding position B and the grinding unit 40A closer to and farther away from each other.

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 hollow, cylindrical housing 42B, which 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 grinding unit 40B toward and away from the chuck table 18B or chuck table 18C positioned at the second grinding position C.

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

The grinding unit 40A includes a cylindrical spindle (first spindle) 44A. The spindle 44A is housed in a housing 42A (see Figure 1), with the tip (lower end) of the spindle 44A exposed from the housing 42A. A rotational drive source 46A (see Figure 1), such as a motor, is connected to the base (upper end) of the spindle 44A.

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 can be attached to and detached from the mount 48A and grinds the workpiece 11. It is fixed to the mount 48A with a fastener such as a fastening bolt. This attaches the grinding wheel 50A to the tip of the spindle 44A.

The grinding wheel 50A has an annular wheel base 52A. The wheel base 52A is made of a metal such as aluminum or stainless steel, and is formed with approximately the same diameter as the mount 48A. Furthermore, multiple 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 a ring shape at approximately equal intervals around the circumference of the wheel base 52A.

The grinding unit 40B includes a cylindrical spindle (second spindle) 44B. The spindle 44B is housed in a housing 42B (see Figure 1), with the tip (lower end) of the spindle 44B exposed from the housing 42B. A rotational drive source 46B (see Figure 1), such as a motor, is connected to the base (upper end) of the spindle 44B.

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 can be attached to and detached from the mount 48B and grinds the workpiece 11. It is fixed to the mount 48B with a fastener such as a fastening bolt. This attaches the grinding wheel 50B to the tip of the spindle 44B.

The grinding wheel 50B has 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 roughly the same diameter as the mount 48B. Furthermore, multiple 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 in a ring shape at roughly equal intervals around the circumference of the wheel base 52B.

The grinding wheels 54A, 54B contain abrasive grains such as diamond or cBN (cubic boron nitride) and a bonding material such as a metal bond, resin bond, or vitrified bond that secures the abrasive grains. There are no restrictions on the material, shape, structure, or size of the grinding wheels 54A, 54B, and the number and arrangement of the grinding wheels 54A, 54B can be set as desired.

When the rotational drive source 46A (see FIG. 1) is driven, the spindle 44A and grinding wheel 50A rotate around the rotational axis 56A, and each of the grinding wheels 54A moves along a circular path (orbit) centered on the rotational axis 56A. Similarly, when the rotational drive source 46B (see FIG. 1) is driven, the spindle 44B and grinding wheel 50B rotate around the rotational axis 56B, and each of the grinding wheels 54B moves along a circular path (orbit) centered on the rotational axis 56B. The rotational axis 56A of the spindle 44A and grinding wheel 50A and the rotational axis 56B of the spindle 44B and grinding wheel 50B are each set to be approximately parallel to the Z-axis direction.

Grinding unit 40A is a grinding unit for rough grinding that performs rough grinding on workpiece 11, and a grinding wheel 50A for rough grinding is attached to the tip of spindle 44A. On the other hand, grinding unit 40B is a grinding unit for finish grinding that performs finish grinding on workpiece 11, and a grinding wheel 50B for finish grinding is attached to the tip of spindle 44B. Specifically, the average particle size of the abrasive grains contained in grinding wheel 54B of grinding wheel 50B is smaller than the average particle size of the abrasive grains contained in grinding wheel 54A of grinding wheel 50A.

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

As shown in FIG. 1, a transport unit (transport mechanism, unloading arm) 58 that transports the workpiece 11 is provided adjacent to the transport unit 14 in the X-axis direction. For example, the transport unit 58 is equipped with a suction pad that holds the top surface of the workpiece 11 by suction. The transport unit 58 holds the workpiece 11, which is held by the chuck table 18C located at transport position A, with the suction pad, and then rotates the suction pad to transport the workpiece 11 forward.

A cleaning unit (cleaning mechanism, cleaning device) 60 that cleans the workpiece 11 is provided in front of the transport unit 58. The cleaning unit 60 cleans the workpiece 11 transported from the chuck table 18C 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 cleaning liquid (such as pure water) to the workpiece 11 held by the spinner table.

The grinding device 2 also includes a control unit (controller, controller) 62 connected to each component of the grinding device 2 (transport unit 6, alignment mechanism 12, transport unit 14, turntable 16, chuck tables 18A, 18B, 18C, thickness gauge 26, moving units 30A, 30B, grinding units 40A, 40B, transport unit 58, cleaning unit 60, etc.). The control unit 62 controls the operation of the grinding device 2 by outputting control signals to each component of the grinding device 2.

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

When processing workpieces 11 using the grinding device 2, first, multiple workpieces 11 are placed in a cassette 10A, and the cassette 10A is placed on the cassette installation area 8A. The transport unit 6 then transports the workpieces 11 from the cassette 10A to the alignment mechanism 12, which then aligns the workpieces 11. The transport unit 14 then transports the workpieces 11 to the chuck table 18A located at transport position A, where they are held by the chuck table 18A.

Next, the turntable 16 rotates, and the chuck table 18A is positioned at the first grinding position B. The workpiece 11 is then ground by the grinding unit 40A. This results in a rough grinding of the workpiece 11.

Next, the turntable 16 rotates, and the chuck table 18A is positioned at the transfer position A. After that, the workpiece 11 is lifted from the chuck table 18A by the transfer unit 14, and the turntable 16 rotates further, and the chuck table 18B is positioned at the transfer position A. The workpiece 11 held by the transfer unit 14 is then placed on the chuck table 18B and held by the chuck table 18B.

Next, the turntable 16 rotates, and the chuck table 18B is positioned at the second grinding position C. The workpiece 11 held by the chuck table 18B is then ground by the grinding unit 40B. This completes the first stage of finish grinding on the workpiece 11.

Next, the turntable 16 rotates, and the chuck table 18B is positioned at the transfer position A. After that, the workpiece 11 is lifted from the chuck table 18B by the transfer unit 14, and the turntable 16 rotates further, and the chuck table 18C is positioned at the transfer position A. The workpiece 11 held by the transfer unit 14 is then placed on the chuck table 18C and held by the chuck table 18C.

Next, the turntable 16 rotates, and the chuck table 18C is positioned at the second grinding position C. The workpiece 11 held by the chuck table 18C is then ground by the grinding unit 40B. This completes the second stage of finish grinding on the workpiece 11.

When grinding of the workpiece 11 is complete, the turntable 16 rotates and the chuck table 18C is positioned at transfer position A. The workpiece 11 is then transferred from the chuck table 18C to the cleaning unit 60 by the transfer unit 58, where it is cleaned. After cleaning, the workpiece 11 is transported by the transfer unit 68 to the cassette 10B and stored there.

Next, a specific example of a workpiece grinding method for grinding the workpiece 11 using the grinding device 2 will be described. Figure 4 is a flowchart showing the workpiece grinding method. In this embodiment, the workpiece grinding method involves a first-stage grinding in which the workpiece 11 is held by chuck table 18B and ground by grinding unit 40B, and a second-stage grinding in which the workpiece 11 is held by chuck table 18C and ground by grinding unit 40B, thereby reducing variation in the surface roughness of the workpiece 11 after grinding.

Note that before grinding the workpiece 11 by grinding unit 40B, grinding (rough grinding) of the workpiece 11 is performed by grinding unit 40A as needed. Specifically, first, the workpiece 11 is aligned by the alignment mechanism 12, then transported by the transport unit 14 and placed on the chuck table 18A located at transport position A (see Figure 1).

Next, the turntable 16 rotates, positioning the chuck table 18A at the first grinding position B. This adjusts the relative positions of the chuck table 18A and the grinding wheel 50A. At this time, the chuck table 18A is positioned so that the area of the workpiece 11 through which the rotation axis 24A (see Figure 2A) of the chuck table 18A passes (the center of the workpiece 11) overlaps with the movement path of the grinding stone 54A (see Figure 3) of the grinding wheel 50A.

Next, while rotating the chuck table 18A and grinding wheel 50A, the holding surface 18a (see FIG. 2A) of the chuck table 18A and the grinding wheel 50A are brought relatively close together, bringing the grindstone 54A (see FIG. 3) into contact with the workpiece 11 and grinding the workpiece 11. This performs a rough grinding of the workpiece 11. Then, when the workpiece 11 has been ground to the desired thickness, grinding of the workpiece 11 is stopped.

Note that rough grinding of the workpiece 11 may be performed using a grinding device separate from the grinding device 2. In this case, the chuck table 18A and grinding unit 40A can be omitted from the grinding device 2.

Next, the workpiece 11 is held by the holding surface 18a (first holding surface) of the chuck table 18B (first chuck table) (first holding step S11). In the first holding step S11, the chuck table 18A holding the roughly ground workpiece 11 is first positioned at the transfer position A, and the transfer unit 14 lifts the workpiece 11 from the chuck table 18A. In this state, the turntable 16 rotates, and the chuck table 18B is positioned at the transfer position A. Then, the workpiece 11 held by the transfer unit 14 is placed on the chuck table 18B.

Figure 5 is a cross-sectional view showing the workpiece 11 in the first holding step S11. For example, the workpiece 11 is placed on the chuck table 18B 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 overlaps the center position of the holding surface 18a and the entire suction surface 22a is covered by the workpiece 11. As a result, the workpiece 11 is positioned concentrically with the holding surface 18a so that the rotation axis 24B of the chuck table 18B passes through the center of the workpiece 11.

When the workpiece 11 is placed on the holding surface 18a and the suction force (negative pressure) of the suction source is applied to the suction surface 22a, the workpiece 11 is sucked onto the suction surface 22a. As a result, the workpiece 11 is held by suction on the chuck table 18B in a state where it is slightly deformed along the conical holding surface 18a.

A protective sheet for protecting the workpiece 11 may be attached to the surface 11a of the workpiece 11. This covers and protects the surface 11a of the workpiece 11 (devices, etc.), and the workpiece 11 is held by the holding surface 18a of the chuck table 18B via the protective sheet.

For example, a protective sheet may be a tape comprising a circular film-like substrate and an adhesive layer (glue layer) provided on the substrate. 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 also be an ultraviolet-curing resin that hardens when exposed to ultraviolet light.

Next, the positional relationship between the chuck table 18B 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 18B holding the workpiece 11 is positioned at the second grinding position C (see Figure 1). This positions the workpiece 11 and chuck table 18B in a predetermined position below the grinding wheel 50B.

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

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

Here, the tilt of the chuck table 18B (tilt of the rotation axis 24B) is adjusted in advance so that the distance between the area of the workpiece 11 through which the rotation axis 24B of the chuck table 18B passes (the center of the workpiece 11) and the grinding wheel 54B is smaller than the distance between other areas of the workpiece 11 and the grinding wheel 54B. Specifically, the chuck table 18B is tilted toward the grinding wheel 50B so that the holding area 18b of the chuck table 18B is inclined relative to the grinding surface formed by the underside of the grinding wheel 54B.

Therefore, in the region of the workpiece 11 supported by the holding region 18b, the distance between the workpiece 11 and the grinding wheel 54B increases from the center of the workpiece 11 toward the outer periphery (the farther away from the rotation axis 24B). In other words, the workpiece 11 is positioned so that the distance _S1 between the center of the workpiece 11 and the grinding wheel 54B is smaller than the distance _S2 between the outer periphery of the workpiece 11 and the grinding wheel 54B.

The relative inclination between the chuck table 18B and the grinding wheel 50B can be set as desired depending on the total thickness variation (TTV) required for the workpiece 11. For example, the angle between the rotation axis 24B of the chuck table 18B and the rotation axis 56B of the grinding wheel 50B is set to between 0° and 0.004°, for example, approximately 0.0034°.

Next, while rotating the chuck table 18B and the grinding wheel 50B, the holding surface 18a of the chuck table 18B and the grinding wheel 50B are brought relatively close to each other, causing the grinding wheel 54B to come into contact with the workpiece 11 and grind the workpiece 11 (first grinding step S13). Figure 6(B) is a partial cross-sectional side view showing the workpiece 11 in the first grinding step S13.

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

Next, with the chuck table 18B and grinding wheel 50B rotating, the grinding unit 40B is lowered at a predetermined speed along the Z-axis direction, bringing the holding surface 18a of the chuck table 18B and the grinding wheel 50B relatively closer together. 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 18B (workpiece 11) and the grinding wheel 50B, 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 equal to or greater than 1.5 μm/s and equal to or less than 5.0 μm/s.

When the holding surface 18a of the chuck table 18B and the grinding wheel 50B are brought relatively close together, the rotating grindstones 54B come into contact with the back surface 11b of the workpiece 11, grinding the workpiece 11. Each of the multiple grindstones 54B rotates to pass through the rotation axis 24B of the chuck table 18B, grinding an arc-shaped area from the periphery to the center of the workpiece 11. Furthermore, the rotation of the chuck table 18B brings the grindstones 54B into contact with the entire back surface 11b of the workpiece 11. This grinds and thins the workpiece 11.

When the workpiece 11 has been ground until its thickness reaches a predetermined value, the grinding unit 40B rises and the grinding wheel 54B moves away from the workpiece 11. This stops grinding the workpiece 11 with the grinding wheel 50B.

Figure 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 held by the chuck table 18B, whose tilt is adjusted so that the distance between the area of the workpiece 11 through which the rotation axis 24B of the chuck table 18B passes (the center of the workpiece 11) and the grinding wheel 54B is smaller than the distance between other areas of the workpiece 11 (such as the outer edge of the workpiece 11) and the grinding wheel 54B, and the workpiece 11 is ground by the grinding wheel 50B. Therefore, the center of the workpiece 11 is ground preferentially, and the workpiece 11 is processed so that the center is thinner than the outer edge. As a result, a conical recess is formed on the back surface 11b side of the center of the workpiece 11.

The grinding of the workpiece 11 in the first grinding step S13 is so-called in-feed grinding. Therefore, the volume of workpiece removed per unit time is greater at the outer periphery of the workpiece 11 than at the center of the workpiece 11, where the grinding wheel 54B is always in contact. This results in a greater processing load being applied to 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.

Next, the workpiece 11 is held by the holding surface 18a (second holding surface) of the chuck table 18C (second chuck table) (second holding step S14). In the second holding step S14, first, the chuck table 18B holding the workpiece 11 ground in the first grinding step S13 is positioned at the transfer position A, and the workpiece 11 is lifted from the chuck table 18B by the transfer unit 14. In this state, the turntable 16 rotates, and the chuck table 18C is positioned at the transfer position A. Then, the workpiece 11 held by the transfer unit 14 is placed on the chuck table 18C.

Figure 8 is a cross-sectional view showing the workpiece 11 in the second holding step S14. The workpiece 11 is placed on the chuck table 18C so that the front surface 11a faces the holding surface 18a and the back surface 11b, which was ground in the first grinding step S13, is exposed upward. At this time, the workpiece 11 is positioned so that the center position of the workpiece 11 overlaps the center position of the holding surface 18a and the entire suction surface 22a is covered by the workpiece 11. As a result, the workpiece 11 is positioned concentrically with the holding surface 18a so that the rotation axis 24C of the chuck table 18C passes through the center of the workpiece 11.

When the workpiece 11 is placed on the holding surface 18a and the suction force (negative pressure) of the suction source is applied to the suction surface 22a, the workpiece 11 is sucked onto the suction surface 22a. As a result, the workpiece 11 is held by suction on the chuck table 18C in a state where it is slightly deformed along the conical holding surface 18a.

Next, the positional relationship between the chuck table 18C and the grinding wheel 50B is adjusted (second positioning step S15). In the second positioning step S15, the turntable 16 rotates, and the chuck table 18C holding the workpiece 11 is positioned at the second grinding position C (see Figure 1). This positions the workpiece 11 and chuck table 18C in a predetermined position below the grinding wheel 50B.

Figure 9 (A) is a partial cross-sectional side view showing the workpiece 11 in the second positioning step S15. When the chuck table 18C is positioned at the second grinding position C, the positional relationship between the chuck table 18C and the grinding wheel 50B is adjusted so that the area of the workpiece 11 through which the rotation axis 24C of the chuck table 18C passes overlaps with the movement path of the grinding stone 54B of the grinding wheel 50B.

As mentioned above, the workpiece 11 is positioned so that the rotation axis 24C of the chuck table 18C passes through the center of the workpiece 11. In this case, the chuck table 18C 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.

Here, the tilt of the chuck table 18C (tilt of the rotation axis 24C) is adjusted in advance so that the workpiece 11 is not ground on the rotation axis 24C of the chuck table 18C in the second grinding step S16 described below. For example, the tilt of the grinding wheel 50C is adjusted so that the distance between the area of the workpiece 11 through which the rotation axis 24C of the chuck table 18C passes (the center of the workpiece 11) and the grinding wheel 54B is greater than the distance between other areas of the workpiece 11 and the grinding wheel 54B. Specifically, the chuck table 18C is tilted away from the grinding wheel 50B so that the holding area 18b of the chuck table 18C is inclined relative to the grinding surface formed by the underside of the grinding wheel 54B.

Therefore, in the region of the workpiece 11 supported by the holding region 18b, the distance between the workpiece 11 and the grinding wheel 54B decreases from the center of the workpiece 11 toward the outer periphery (the farther away from the rotation axis 24C). In other words, the workpiece 11 is positioned so that the distance _S3 between the center of the workpiece 11 and the grinding wheel 54B is greater than the distance _S4 between the outer periphery of the workpiece 11 and the grinding wheel 54B.

The relative inclination between the chuck table 18C and the grinding wheel 50B can be set as desired depending on the TTV, etc. required for the workpiece 11. For example, the angle between the rotation axis 24C of the chuck table 18C and the rotation axis 56B of the grinding wheel 50B is set to between 0.007° and 0.012°, inclusive, for example, approximately 0.008°.

Next, while rotating the chuck table 18C and the grinding wheel 50B, the holding surface 18a of the chuck table 18C and the grinding wheel 50B are brought relatively close to each other, causing the grinding wheel 54B to come into contact with the workpiece 11 and grind the outer periphery of the workpiece 11 (second grinding step S16). Figure 9(B) is a partial cross-sectional side view showing the workpiece 11 in the second grinding step S16.

In the second grinding step S16, first, the chuck table 18C is rotated around the rotation axis 24C, and the spindle 44B and grinding wheel 50B are rotated around the rotation axis 56B. Next, with the chuck table 18C and grinding wheel 50B rotating, the grinding unit 40B is lowered at a predetermined speed along the Z-axis direction, bringing the holding surface 18a of the chuck table 18C and the grinding wheel 50B relatively closer to 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 18C (workpiece 11) and the grinding wheel 50B, corresponds to the processing feed rate (grinding feed rate) in the second grinding step S16.

When the holding surface 18a of the chuck table 18C and the grinding wheel 50B are brought relatively close together, 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. When the workpiece 11 has been ground until the thickness of its outer periphery reaches a predetermined value, the grinding unit 40B rises and the grinding wheel 54B moves away from the workpiece 11. This stops grinding the workpiece 11 with the grinding wheel 50B.

Figure 10 is a cross-sectional view showing the workpiece 11 after the second grinding step S16. In the second grinding step S16, the workpiece 11 is held by the chuck table 18C, the tilt of which is adjusted so that the grinding wheel 54B can contact only the outer periphery of the workpiece 11, and is ground by the grinding wheel 50B. Grinding is then stopped before the grinding wheel 54B contacts the workpiece 11 on the rotation axis 24C of the chuck table 18C. As a result, the center of the workpiece 11 is not ground on or near the rotation axis 24C of the chuck table 18C, 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.

As mentioned 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 Figure 7) than at the center. Therefore, in the second grinding step S16, 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 reduce the variation in surface roughness between the center and outer periphery of the workpiece 11.

There are no restrictions on the specific processing conditions for the workpiece 11 in the second grinding step S16, as long as they can reduce the surface roughness of the outer periphery of the workpiece 11 after the second grinding step S16. For example, the surface roughness of the outer periphery of the workpiece 11 can be reduced by adjusting the rotational speed of the chuck table 18C, the rotational speed of the grinding wheel 50B, the processing feed rate, etc.

Specifically, the rotational speed of chuck table 18C in the second grinding step S16 may be set lower than the rotational speed of chuck table 18B in the first grinding step S13. Preferably, the rotational speed of chuck table 18C is set to 1/3 or less of the rotational speed of chuck table 18B. For example, the rotational speed of chuck table 18C can be set to 30 rpm or more and 300 rpm or less. In this case, the processing conditions other than the rotational speed of chuck table 18C can be set the same as those for the first grinding step S13.

The rotational speed of the grinding wheel 50B in the second grinding step S16 may be set higher than the rotational speed of the grinding wheel 50B in the first grinding step S13. Preferably, the rotational speed of the grinding wheel 50B in the second grinding step S16 is set to at least twice the rotational speed of the grinding wheel 50B in the first grinding step S13. For example, the rotational speed of the grinding wheel 50B in the second grinding step S16 can be set to between 2000 rpm and 6000 rpm. In this case, the processing conditions other than the rotational speed of the grinding wheel 50B can be set the same as those for the first grinding step S13.

Furthermore, the processing feed rate in the second grinding step S16 (the relative approach rate between the holding surface 18a of the chuck table 18C 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 of the chuck table 18B and the grinding wheel 50B). Preferably, the processing feed rate in the second grinding step S16 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 S16 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 the same as those in the first grinding step S13.

By setting the processing conditions in the second grinding step S16 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. 10) after the second grinding step S16 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 S16, only one of the three processing conditions described above from the first grinding step S13 may be changed, or any two or more of the three may be changed.

The range of the workpiece 11 ground in the second grinding step S16 can be set as appropriate, as long as the variation in the surface roughness of the workpiece 11 remains within a certain range. For example, in the second grinding step S16, an area of the workpiece 11 whose distance from the outer edge is between 1/3 and 2/3 of the radius of the workpiece 11 is ground. In particular, in the second grinding step S16, it is preferable to grind an area of the workpiece 11 whose distance from the outer edge is between 2/5 and 3/5 of the radius of the workpiece 11.

The storage section (memory) of the control unit 62 shown in FIG. 1 stores a program describing the series of operations of the components of the grinding device 2 required to sequentially perform the first holding step S11, first positioning step S12, first grinding step S13, second holding step S14, second positioning step S15, and second grinding step S16. When processing the workpiece 11, the control unit 62 reads and executes the program from the storage section, and sequentially outputs control signals to each component of the grinding device 2. This controls the operation of the grinding device 2, and the workpiece grinding method according to this embodiment is automatically performed.

As described above, in the workpiece grinding method according to this embodiment, the workpiece 11 held by the chuck table 18B, whose tilt has been adjusted so that the central portion of the workpiece 11 can be made thinner than the peripheral portion, is ground (first grinding step S13). Then, the workpiece 11 held by the chuck table 18C, whose tilt has been adjusted so that the peripheral portion of the workpiece 11 can be ground, is ground under processing conditions that reduce the surface roughness (second grinding step S16). This reduces the difference in surface roughness between the central and peripheral portions of the workpiece 11, thereby reducing the variation in surface roughness of the workpiece 11 after grinding.

Furthermore, in the first grinding step S13, the workpiece 11 held by the chuck table 18B is ground, and in the second grinding step S16, the workpiece 11 held by the chuck table 18C is ground. Therefore, the inclinations of the chuck tables 18B and 18C can be individually adjusted in advance to suit the contents of the first grinding step S13 and the second grinding step S16, respectively, making it possible to omit the work of adjusting the inclination of the chuck table and grinding wheel between the first grinding step S13 and the second grinding step S16. This improves the processing efficiency of the workpiece 11.

The structures, methods, etc., described in the above embodiments can be modified as appropriate without departing from the scope of the present invention.

11 Workpiece 11a Surface (first surface)
11b Back side (second side)
2 Grinding device 4 Base 4a Opening 6 Conveying unit (conveying mechanism)
8A, 8B Cassette installation area 10A, 10B Cassette 12 Alignment mechanism
14 Transport unit (transport mechanism, loading arm)
16 Turntable 18A, 18B, 18C Chuck table (holding table)
18a Holding surface 18b Holding area 20 Frame (main body)
20a Upper surface 20b Recessed portion 20c Flow path 22 Holding member 22a Suction surface 24A, 24B, 24C Rotating shaft 26 Thickness measuring device 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 wheel 52A, 52B Wheel base 54A, 54B Grinding stone 56A, 56B Rotation shaft 58 Transfer unit (transfer mechanism, unloading arm)
60 Cleaning unit (cleaning mechanism, cleaning device)
62 Control unit (control unit, control device)

Claims (4)

A method for grinding a workpiece using a grinding device, comprising:
The grinding device comprises:
a first chuck table having a first holding surface;
a second chuck table having a second holding surface;
a grinding unit including a spindle having a grinding wheel having a plurality of grinding stones attached to a tip thereof;
a first holding step of holding the workpiece on the first holding surface;
a first positioning step of adjusting a positional relationship between the first chuck table and the grinding wheel so that an area of the workpiece through which the rotation axis of the first chuck table passes overlaps with a moving path of the grinding wheel;
a first grinding step in which the first chuck table and the grinding wheel are rotated, the tilt of which is adjusted so that the distance between the grinding wheel and a region of the workpiece through which the rotation axis of the first chuck table passes is smaller than the distance between the grinding wheel and other regions of the workpiece, and the first holding surface and the grinding wheel are brought relatively close to each other, thereby bringing the grinding wheel into contact with the workpiece and grinding the workpiece;
a second holding step of holding the workpiece on the second holding surface;
a second positioning step of adjusting the positional relationship between the second chuck table and the grinding wheel so that an area of the workpiece through which the rotation axis of the second chuck table passes overlaps with a moving path of the grinding wheel;
a second grinding step of rotating the second chuck table, the tilt of which is adjusted so that the workpiece is not ground on the rotation axis of the second chuck table, and the grinding wheel, while bringing the second holding surface and the grinding wheel relatively close to each other, thereby bringing the grinding wheel into contact with the workpiece and grinding the outer periphery 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. The method for grinding a workpiece according to claim 1, characterized in that the rotational speed of the second chuck table in the second grinding step is lower than the rotational speed of the first chuck table in the first grinding step. The method for grinding a workpiece according to claim 1 or 2, wherein the rotational speed of the grinding wheel in the second grinding step is higher than the rotational speed of the grinding wheel in the first grinding step. A method for grinding a workpiece according to any one of claims 1 to 3, wherein the relative approach speed between the second holding surface and the grinding wheel in the second grinding step is lower than the relative approach speed between the first holding surface and the grinding wheel in the first grinding step.