JP2024068261A - Method for grinding workpiece - Google Patents

Abstract

To provide a method for grinding a workpiece capable of suppressing degradation of the workpiece.SOLUTION: A method for grinding a workpiece with use of a first grinding wheel provided with a first grinding grindstone including first abrasive grains and a second grinding wheel provided with a second grinding grindstone including second abrasive grains, includes: a first grinding step of grinding a ground surface side of a workpiece by having the first grinding grindstone brought into contact with the workpiece while supplying grinding liquid; a second grinding step of grinding the ground surface side of the workpiece by having the second grinding grindstone brought into contact with the workpiece while supplying grinding liquid; a separation step of separating the workpiece and the second grinding grindstone while supplying grinding liquid; and a third grinding step of grinding the ground surface side of the workpiece until the workpiece attains a predetermined thickness by having the second grinding grindstone brought into contact with the workpiece while supplying grinding liquid.SELECTED DRAWING: Figure 4

Description

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

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

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 undivided wafers and package substrates. The grinding device is equipped with a chuck table that holds the workpiece and a grinding unit that performs grinding on the workpiece, and the grinding unit is equipped with an annular grinding wheel equipped with multiple grinding stones. The workpiece is held on the chuck table, and the grinding wheel is rotated while the grinding stones are brought into contact with the workpiece, thereby grinding and thinning the workpiece (see Patent Document 1).

JP 2014-124690 A

Grinding wheels are formed by fixing abrasive grains with a binder (bond material). When a workpiece is ground with a grinding wheel, the wheel collides with the workpiece, causing the binder to wear away, causing the abrasive grains protruding from the binder to fall off and exposing new abrasive grains embedded in the binder. This phenomenon is called self-sharpening, and the self-sharpening keeps the grinding wheel in good condition and maintains its grinding ability.

When a workpiece is thinned by grinding, a rough grinding process is carried out in which the workpiece is ground with a grinding wheel for rough grinding that contains large grains, and a finish grinding process is carried out in which the workpiece is ground with a grinding wheel for finish grinding that contains small grains. When the workpiece is rough ground, arc-shaped grinding marks (saw marks) remain on the grinding surface of the workpiece, but the grinding marks are removed by the subsequent finish grinding. This makes it possible to prevent grinding marks from remaining on the workpiece after grinding.

However, during the finish grinding of the workpiece, the binder of the grinding wheel wears away and the abrasive grains fall off. In particular, when the grinding wheel for finish grinding first comes into contact with the grinding surface of the workpiece on which the grinding marks have been formed, the binder is likely to wear away, and a large amount of abrasive grains fall off. The abrasive grains that have fallen off from the grinding wheel get between the workpiece and the grinding wheel during finish grinding, and are pressed against the grinding surface of the workpiece by the grinding wheel. This can result in new deep grinding marks being formed on the grinding surface of the workpiece. In this case, grinding marks remain on the workpiece after finish grinding, reducing the quality of the workpiece.

The present invention was made in consideration of these problems, and aims to provide a method for grinding a workpiece that can suppress deterioration in the quality of the workpiece.

According to one aspect of the present invention, a method for grinding a workpiece using a first grinding wheel having a first grinding stone containing first abrasive grains and a second grinding wheel having a second grinding stone containing second abrasive grains having an average grain size smaller than that of the first abrasive grains, the method comprising: a first grinding step in which the first grinding stone is brought into contact with the workpiece while supplying a grinding fluid, thereby grinding the grinding surface side of the workpiece; and after the first grinding step, a second grinding stone is brought into contact with the workpiece while supplying a grinding fluid, thereby grinding the grinding surface side of the workpiece. A method for grinding a workpiece includes a second grinding step in which the workpiece is ground on the side of the workpiece, a separation step in which the workpiece and the second grinding wheel are separated from each other while supplying a grinding fluid after the second grinding step, and a third grinding step in which the workpiece is ground on the side of the workpiece to be ground until the workpiece has a predetermined thickness by bringing the second grinding wheel into contact with the workpiece while supplying a grinding fluid after the separation step, and the amount of the workpiece ground in the third grinding step is less than the amount of the workpiece ground in the second grinding step.

Preferably, the method for grinding the workpiece further includes a cleaning step for cleaning the grinding surface side of the workpiece after the separating step and before the third grinding step.

According to another aspect of the present invention, there is provided a method for grinding a workpiece using a first grinding wheel having a first grinding stone containing first abrasive grains and a second grinding wheel having a second grinding stone containing second abrasive grains having an average grain size smaller than that of the first abrasive grains, the method comprising: a first grinding step in which the first grinding stone is brought into contact with the workpiece while supplying a grinding fluid, thereby forming a recess in the workpiece and leaving an annular reinforcing portion surrounding the recess; and after the first grinding step, a second grinding stone is brought into contact with the workpiece while supplying a grinding fluid, thereby forming a recess in the workpiece and leaving an annular reinforcing portion surrounding the recess. A method for grinding a workpiece includes a second grinding step for grinding the bottom surface of the recess, a separation step for separating the workpiece from the second grinding wheel while supplying a grinding fluid after the second grinding step, and a third grinding step for grinding the bottom surface of the recess until the area of the workpiece where the recess is formed reaches a predetermined thickness by contacting the second grinding wheel with the workpiece while supplying a grinding fluid after the separation step, in which the amount of the workpiece ground in the third grinding step is less than the amount of the workpiece ground in the second grinding step.

Preferably, the method for grinding the workpiece further includes a cleaning step for cleaning the bottom surface of the recess after the separating step and before the third grinding step.

In one embodiment of the present invention, a method for grinding a workpiece includes grinding the workpiece with a first grinding wheel, and then grinding the workpiece with a second grinding wheel. Then, before the thickness of the workpiece reaches the finishing thickness, the workpiece and the second grinding wheel are separated while supplying grinding fluid, and the workpiece is again ground with the second grinding wheel. This makes it less likely that grinding marks will be formed due to abrasive grains that have fallen off during finish grinding, and reduces deterioration in the quality of the workpiece.

FIG. FIG. FIG. 4 is a cross-sectional view showing a chuck table. 4 is a flowchart showing a method for machining a workpiece. FIG. 5A is a partially sectional side view showing the grinding device in the first grinding step, and FIG. 5B is a plan view showing the grinding device in the first grinding step. FIG. 6A is a partially sectional side view showing the grinding device in the second grinding step, and FIG. 6B is a plan view showing the grinding device in the second grinding step. FIG. 4 is a partial cross-sectional side view showing the grinding device in a separating step. FIG. 8A is a partially sectional side view showing the grinding apparatus in the cleaning step, and FIG. 8B is a plan view showing the grinding apparatus in the cleaning step. FIG. 9A is a partially sectional side view showing the grinding device in the third grinding step, and FIG. 9B is a plan view showing the grinding device in the third grinding step. FIG. 10A is a partially sectional side view showing a grinding apparatus that performs rough grinding on the central portion of a workpiece, and FIG. 10B is a plan view showing the grinding apparatus that performs rough grinding on the central portion of a workpiece. FIG. 11(A) is a partially sectional side view showing a grinding apparatus that performs finish grinding on the central portion of a workpiece, and FIG. 11(B) is a plan view showing the grinding apparatus that performs finish grinding on the central portion of a workpiece.

(Embodiment 1)
Hereinafter, an embodiment according to one aspect of the present invention will be described with reference to the accompanying drawings. First, a configuration example of a grinding device that can be used in the grinding method of 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-back direction) are perpendicular to each other. In addition, the Z-axis direction (processing feed direction, height direction, vertical direction, up-down direction) is perpendicular to the X-axis direction and the Y-axis direction.

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 top 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. For example, a transport robot equipped with a robot hand (end effector) capable of holding the workpiece 11 is used as the transport unit 6.

Cassette installation areas 8A and 8B are provided on both sides of the transport unit 6. Cassettes 10A and 10B capable of accommodating multiple workpieces 11 are placed on the cassette installation areas 8A and 8B, respectively.

Figure 2 is a perspective view showing the workpiece 11 to be ground by the grinding device 2. For example, the workpiece 11 is a disk-shaped wafer made of a semiconductor material such as single crystal silicon, and includes 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 number of rectangular regions by a number of streets (planned division lines) 13 arranged in a grid pattern so as to intersect with one another. Furthermore, devices 15 such as ICs (Integrated Circuits), LSIs (Large Scale Integration), LEDs (Light Emitting Diodes), and MEMS (Micro Electro Mechanical Systems) devices are formed on the surface 11a side of each of the multiple regions divided by the streets 13.

The workpiece 11 has, on the surface 11a side, a substantially circular device region 17 in which multiple devices 15 are formed, and an annular peripheral surplus region 19 surrounding the device region 17. The peripheral surplus region 19 corresponds to a strip-shaped region of a predetermined width (e.g., about 2 mm) that includes the outer periphery of the surface 11a. In the peripheral surplus region 19, no devices 15 are formed, or only devices 15 (dummy devices) that are not used in the product are formed. In FIG. 2, the imaginary boundary between the device region 17 and the peripheral surplus region 19 is shown by a dashed line.

By dividing the workpiece 11 along the streets 13, multiple device chips, each of which includes a device 15, are manufactured. In addition, if the back surface 11b side of the workpiece 11 is ground to thin the workpiece 11 before dividing it, a thinned device chip can be obtained.

There are no limitations on the material, shape, structure, size, etc. of the workpiece 11. For example, the workpiece 11 may be a substrate (wafer) made of a semiconductor other than silicon (GaAs, InP, GaN, SiC, etc.), glass (quartz glass, borosilicate glass, etc.), ceramics, resin, metal, etc. Furthermore, there are no limitations on the type, number, shape, structure, size, arrangement, etc. of the device 15.

As shown in FIG. 1, an alignment mechanism 12 is provided diagonally behind the opening 4a. The workpieces 11 stored in the cassettes 10A and 10B are transported to the alignment mechanism 12 by the transport unit 6. The alignment mechanism 12 then clamps the workpieces 11 and positions them 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 has a suction pad that holds the top side of the workpiece 11 by suction. The transport unit 14 holds the workpiece 11, which has been aligned by the alignment mechanism 12, with the suction pad, and then 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 to rotate the turntable 16 around a rotation axis that is generally parallel to the Z-axis direction.

On the turntable 16, multiple chuck tables (holding tables) 18 for holding the workpieces 11 are provided. Figure 1 shows an example in which three chuck tables 18 are arranged at approximately equal intervals (120° intervals) around the circumference of the turntable 16. However, there is no limit to the number of chuck tables 18.

Figure 3 is a cross-sectional view of the chuck table 18. The chuck table 18 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. The recess 20b is formed concentrically with 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 many pores that communicate 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 the workpiece 11 is held by the chuck table 18.

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 is connected to a suction source (not shown) such as an ejector via pores contained in the holding member 22, a flow path 20c formed inside the frame 20, a valve (not shown), etc.

The holding surface 18a of the chuck table 18 is formed in a cone shape with the apex at the center of the holding surface 18a, and is slightly inclined with respect to the radial direction of the holding surface 18a. The chuck table 18 is arranged in a slightly inclined state so that the holding area 18b, which corresponds to a part of the holding surface 18a and extends from the center of the holding surface 18a to the outer periphery, is approximately parallel to the horizontal plane (XY plane).

A rotational drive source (not shown), such as a motor, that rotates the chuck table 18 is connected to the chuck table 18. The rotational drive source rotates the chuck table 18 around a rotation axis 24. The rotation axis 24 is set along a direction perpendicular to the radial direction of the holding surface 18a, and passes through the center of the holding surface 18a while intersecting with the holding surface 18a. The rotation axis 24 is also slightly inclined with respect to the Z-axis direction.

For ease of explanation, the inclination of the holding surface 18a is exaggerated in FIG. 3 (the same applies to FIG. 5(A) and subsequent figures). However, 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 (corresponding to the height of the cone) is set to approximately 20 μm or more and 40 μm or less.

The turntable 16 shown in FIG. 1 rotates clockwise in a plan view. This positions each chuck table 18 in the following order: transport position A, rough grinding position (first grinding position) B, finish grinding position (second grinding position) C, and transport position A.

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

Columnar support structures 28A and 28B are arranged behind the rough grinding position B and the finish grinding position C, respectively. 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.

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 as to be able to 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 is disposed between the pair of guide rails 32 along the Z-axis direction and is screwed into 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 (rough grinding unit) 40A that performs rough grinding on the workpiece 11 is attached to the moving plate 34 of the moving unit 30A. The grinding unit 40A grinds the workpiece 11 held by the chuck table 18 positioned at the rough grinding position B.

Specifically, the grinding unit 40A includes a housing 42A formed in a hollow cylindrical shape. The housing 42A is fixed to the front side (surface side) of the moving plate 34. The housing 42A accommodates a cylindrical spindle 44A (see FIG. 5(A)) arranged along the Z-axis direction, and the tip (lower end) of the spindle 44A is exposed from the housing 42A. A rotation drive source 46A such as a motor that rotates the spindle 44A is connected to the base end (upper end) of the spindle 44A, and a disk-shaped wheel mount 48A made of metal or the like is fixed to the tip of the spindle 44A.

A grinding wheel (rough grinding wheel, first grinding wheel) 50A for rough grinding is attached to the underside of the wheel mount 48A. The grinding wheel 50A is a processing tool that can be attached and detached to the wheel mount 48A and is used to perform rough grinding on the workpiece 11, and is fixed to the wheel mount 48A by a fastener such as a fastening bolt.

A grinding unit (finish grinding unit) 40B that performs finish grinding on the workpiece 11 is attached to the moving plate 34 of the moving unit 30B. The grinding unit 40B grinds the workpiece 11 held by the chuck table 18 positioned at the finish grinding position C.

Specifically, grinding unit 40B includes a housing 42B and a spindle 44B (see FIG. 6A) housed in housing 42B. A rotary drive source 46B such as a motor that rotates spindle 44B is connected to the base end (upper end) of spindle 44B, and a disk-shaped wheel mount 48B is fixed to the tip end (lower end) of spindle 44B. The configurations and functions of the components of grinding unit 40B are the same as those of grinding unit 40A.

A grinding wheel (finish grinding wheel, second grinding wheel) 50B for finish grinding is attached to the underside of the wheel mount 48B. The grinding wheel 50B is a processing tool that can be attached and detached to the wheel mount 48B and is used to perform finish grinding on the workpiece 11, and is fixed to the wheel mount 48B by a fastener such as a fastening bolt.

The grinding wheel 50A includes an annular wheel base (first wheel base) 52A and a plurality of grinding wheels 54A (first grinding wheels) (see FIG. 5A). The grinding wheel 50B includes an annular wheel base (second wheel base) 52B and a plurality of grinding wheels (second grinding wheels) 54B (see FIG. 6A). The configuration and function of the grinding wheels 50A and 50B will be described in detail below.

The moving unit 30A moves the grinding unit 40A up and down along the Z-axis direction, thereby moving the chuck table 18 and the grinding wheel 50A, which are positioned at the rough grinding position B, closer to and farther away from each other along the Z-axis direction. Similarly, the moving unit 30B moves the grinding unit 40B up and down along the Z-axis direction, thereby moving the chuck table 18 and the grinding wheel 50B, which are positioned at the finish grinding position C, closer to and farther away from each other along the Z-axis direction.

A transport unit (transport mechanism, unloading arm) 56 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 56 has a suction pad that holds the top side of the workpiece 11 by suction. The transport unit 56 holds the workpiece 11 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.

A cleaning unit (cleaning mechanism, cleaning device) 58 that cleans the workpiece 11 is provided in front of the transport unit 56. The cleaning unit 58 cleans the workpiece 11 transported from the chuck table 18 by the transport unit 56. For example, the cleaning unit 58 includes a spinner table that holds and rotates the workpiece 11, and a nozzle that supplies cleaning liquid (pure water, etc.) to the workpiece 11 held by the spinner table.

The grinding device 2 also includes a controller (control unit, control section, control device) 60 connected to each of the components that make up the grinding device 2 (the transport unit 6, the alignment mechanism 12, the transport unit 14, the turntable 16, the chuck table 18, the thickness gauge 26, the moving units 30A and 30B, the grinding units 40A and 40B, the transport unit 56, the cleaning unit 58, etc.). The controller 60 controls the grinding device 2 by outputting control signals to each of the components of the grinding device 2.

For example, the controller 60 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 memories such as a ROM (Read Only Memory) and a RAM (Random Access Memory).

When the workpiece 11 is processed by the grinding device 2, first, a cassette 10A or cassette 10B containing multiple workpieces 11 is placed on the cassette installation area 8A or cassette installation area 8B. Then, the transport unit 6 transports the workpiece 11 from the cassette 10A or cassette 10B to the alignment mechanism 12, which aligns the workpiece 11. Thereafter, the transport unit 14 transports the workpiece 11 to the chuck table 18 located at the transport position A, and the workpiece 11 is held by the chuck table 18.

Next, the turntable 16 rotates, and the chuck table 18 holding the workpiece 11 is positioned at the rough grinding position B. The workpiece 11 is then ground by the grinding wheel 50A attached to the grinding unit 40A. This results in rough grinding of the workpiece 11.

Next, the turntable 16 rotates, and the chuck table 18 holding the workpiece 11 is positioned at the finish grinding position C. The workpiece 11 is then ground by the grinding wheel 50B attached to the grinding unit 40B. This completes the finish grinding of the workpiece 11.

When the rough grinding and finish grinding of the workpiece 11 are completed, the turntable 16 rotates and the chuck table 18 holding the workpiece 11 is again positioned at the transport position A. The workpiece 11 is then transported from the chuck table 18 to the cleaning unit 58 by the transport unit 56, and is cleaned by the cleaning unit 58. After cleaning, the workpiece 11 is transported by the transport unit 6 and stored in the cassette 10A or cassette 10B.

Next, a specific example of the method for grinding the workpiece according to this embodiment will be described. FIG. 4 is a flowchart showing the method for processing the workpiece. As an example, the following describes a case where the workpiece 11 is thinned by grinding the back surface 11b side of the workpiece 11 using the grinding device 2. In other words, the back surface 11b of the workpiece 11 corresponds to the surface (grinding surface) that is ground by the grinding wheels 50A and 50B.

First, the grinding surface side (back surface 11b side) of the workpiece 11 is ground with a grinding wheel 50A (first grinding step S1). Figure 5(A) is a partially sectional side view showing the grinding device 2 in the first grinding step S1, and Figure 5(B) is a plan view showing the grinding device 2 in the first grinding step S1.

When grinding the workpiece 11, the workpiece 11 is held by the chuck table 18. As described above, the workpiece 11, which has been aligned by the alignment mechanism 12 (see FIG. 1), is transported by the transport unit 14 (see FIG. 1) and placed on the chuck table 18, which is placed at the transport position A.

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 (the surface to be ground) is exposed upward. At this time, the workpiece 11 is positioned 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. In addition, the entire suction surface 22a (see Figure 3) of the chuck table 18 is covered by the workpiece 11. In this state, when the suction force (negative pressure) of the suction source is applied to the holding surface 18a, the workpiece 11 is suction-held by the chuck table 18.

As mentioned above, the holding surface 18a of the chuck table 18 is formed in a cone shape. When the workpiece 11 is held by the chuck table 18, the workpiece 11 deforms slightly along the holding surface 18a. As a result, the back surface 11b side of the area of the workpiece 11 supported by the holding area 18b (see FIG. 3) of the holding surface 18a is positioned approximately parallel to the horizontal plane (XY plane).

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 and the device 15 (see FIG. 2) with the protective sheet. In this case, the workpiece 11 is held by the holding surface 18a of the chuck table 18 via the protective sheet.

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-curing resin that is cured by exposure to ultraviolet light.

Next, the turntable 16 (see FIG. 1) rotates, and the chuck table 18 holding the workpiece 11 is positioned at the rough grinding position B (see FIG. 1). This positions the workpiece 11 below the grinding wheel 50A.

As shown in FIG. 5A, 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 to have approximately the same diameter as the wheel mount 48A. In addition, a plurality of 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 along the circumferential direction of the wheel base 52A.

The grinding wheel 54A includes abrasive grains (first abrasive grains) and a bonding material (bond material) that fixes the abrasive grains. Diamond, cBN (cubic boron nitride), etc. are used as the abrasive grains, and metal bond, resin bond, vitrified bond, etc. are used as the bonding material. However, there are no restrictions on the material, shape, structure, size, etc. of the grinding wheel 54A, and the number and arrangement of the grinding wheels 54A can be set as desired.

When the rotary drive source 46A (see FIG. 1) is driven, the spindle 44A and the grinding wheel 50A rotate around a rotation axis that is roughly parallel to the Z-axis direction. This causes each of the multiple grinding stones 54A to revolve along annular orbits (paths) centered on the rotation axes of the spindle 44A and the grinding wheel 50A.

When the chuck table 18 holding the workpiece 11 is positioned at the rough grinding position B (see FIG. 1), the positional relationship between the chuck table 18 and the grinding wheel 50A is adjusted so that the center of the workpiece 11 and the orbit of the grinding wheel 54A overlap in the Z-axis direction. The diameter of the orbit of the grinding wheel 54A is larger than the radius of the workpiece 11. Therefore, the multiple grinding wheels 54A are positioned so that they overlap with an arc-shaped area extending from the center of the workpiece 11 to the outer periphery.

Next, the chuck table 18 is rotated around the rotation axis 24, and the grinding wheel 50A is rotated around the rotation axis of the spindle 44A. 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 speeds of the spindle 44A and the grinding wheel 50A are set to 1000 rpm or more and 3000 rpm or less.

Then, while rotating the chuck table 18 and the grinding wheel 50A, the grinding unit 40A is lowered at a predetermined speed along the Z-axis direction (a direction parallel to the rotation axis of the spindle 44A and the grinding wheel 50A) to bring the holding surface 18a of the chuck table 18 and the grinding wheel 50A relatively close to each other. The relative movement speed of the chuck table 18 and the grinding wheel 50A in the Z-axis direction at this time corresponds to the processing feed speed in the first grinding step S1. For example, the processing feed speed is set to 1.0 μm/s or more and 6.0 μm/s or less.

When the grinding wheel 54A comes into contact with the workpiece 11, the grinding wheel 54A rotates to pass through the rotation axis 24 of the chuck table 18, grinding the entire back surface 11b of the workpiece 11. This causes the entire workpiece 11 to be thinned.

While the workpiece 11 is being ground by the grinding wheel 50A, grinding fluid 74 is supplied to the workpiece 11 and the grinding wheel 54A. The grinding fluid 74 cools the workpiece 11 and the grinding wheel 54A and washes away debris (grinding debris) generated by grinding the workpiece 11.

For example, the grinding device 2 is provided with a grinding fluid supply unit 70A that supplies grinding fluid 74. The grinding fluid supply unit 70A includes a nozzle 72A that is provided below the grinding unit 40A. For example, the nozzle 72A is installed at a position that overlaps with the inside of the orbit of the grinding wheel 54A, and supplies grinding fluid 74 such as pure water to the workpiece 11 held by the chuck table 18 and the grinding wheel 54A.

As described above, in the first grinding step S1, the grinding wheel 54A is brought into contact with the workpiece 11 while supplying grinding fluid 74 to the workpiece 11 and the grinding wheel 54A, thereby grinding the grinding surface side (back surface 11b side) of the workpiece 11. Then, when the workpiece 11 is thinned to a predetermined thickness, the grinding wheel 50A is raised and the grinding wheel 54A is separated from the workpiece 11. This completes the rough grinding of the workpiece 11. Note that after the first grinding step S1, arc-shaped grinding marks (saw marks) 11c formed along the trajectory of the grinding wheel 54A remain on the back surface 11b side of the workpiece 11 (see FIG. 5B).

Next, the grinding surface side (back surface 11b side) of the workpiece 11 is ground with the grinding wheel 50B (second grinding step S2). Figure 6(A) is a partially sectional side view showing the grinding device 2 in the second grinding step S2, and Figure 6(B) is a plan view showing the grinding device 2 in the second grinding step S2.

When the rough grinding of the workpiece 11 (first grinding step S1) is completed, the turntable 16 (see FIG. 1) rotates and the chuck table 18 holding the workpiece 11 is positioned at the finish grinding position C (see FIG. 1). This positions the workpiece 11 below the grinding wheel 50B.

As shown in FIG. 6A, the grinding wheel 50B includes an annular wheel base 52B and a plurality of grinding wheels 54B fixed to the wheel base 52B. The material, structure, function, etc. of the wheel base 52B and the grinding wheels 54B are the same as those of the wheel base 52A and the grinding wheels 54A of the grinding wheel 50A (see FIG. 5A). However, the average grain size of the abrasive grains (second abrasive grains) contained in the grinding wheels 54B is smaller than the average grain size of the abrasive grains (first abrasive grains) contained in the grinding wheels 54A.

When the rotary drive source 46B (see FIG. 1) is driven, the spindle 44B and the grinding wheel 50B rotate around a rotation axis that is roughly parallel to the Z-axis direction. This causes each of the multiple grinding stones 54B to revolve along annular orbits (paths) centered on the rotation axes of the spindle 44B and the grinding wheel 50B.

When the chuck table 18 holding the workpiece 11 is positioned at the finish grinding position C (see FIG. 1), the positional relationship between the chuck table 18 and the grinding wheel 50B is adjusted so that the center of the workpiece 11 and the orbit of the grinding wheel 54B overlap in the Z-axis direction. The diameter of the orbit of the grinding wheel 54B is larger than the radius of the workpiece 11. Therefore, the multiple grinding wheels 54B are positioned so that they overlap with an arc-shaped area extending from the center of the workpiece 11 to the outer periphery.

Next, the chuck table 18 is rotated around the rotation axis 24, and the grinding wheel 50B is rotated around the rotation axis of the spindle 44B. 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 speeds of the spindle 44B and the grinding wheel 50B are set to 1000 rpm or more and 3000 rpm or less.

Then, while rotating the chuck table 18 and the grinding wheel 50B, the grinding unit 40B is lowered at a predetermined speed along the Z-axis direction (a direction parallel to the rotation axis of the spindle 44B and the grinding wheel 50B) to bring the holding surface 18a of the chuck table 18 and the grinding wheel 50B relatively close to each other. The relative movement speed of the chuck table 18 and the grinding wheel 50B in the Z-axis direction at this time corresponds to the processing feed speed in the second grinding step S2. For example, the processing feed speed is set to 0.1 μm/s or more and 1.0 μm/s or less.

When the grinding wheel 54B comes into contact with the workpiece 11, the grinding wheel 54B rotates to pass through the rotation axis 24 of the chuck table 18, grinding away the back surface 11b of the workpiece 11. This causes the back surface 11b of the workpiece 11 to be ground away, thinning the entire workpiece 11.

While the workpiece 11 is being ground by the grinding wheel 50B, grinding fluid 74 is supplied to the workpiece 11 and grinding wheel 54B. For example, the grinding device 2 is provided with a grinding fluid supply unit 70B that supplies grinding fluid 74. The grinding fluid supply unit 70B includes a nozzle 72B provided below the grinding unit 40B. For example, the nozzle 72B is installed at a position overlapping with the inside of the orbit of the grinding wheel 54B, and supplies grinding fluid 74 such as pure water to the workpiece 11 and grinding wheel 54B held by the chuck table 18.

As described above, in the second grinding step S2, the grinding wheel 54B is brought into contact with the workpiece 11 while supplying grinding fluid 74 to the workpiece 11 and the grinding wheel 54B, thereby grinding the grinding surface side (back surface 11b side) of the workpiece 11. This applies finish grinding to the workpiece 11, and removes the grinding marks 11c (see FIG. 5B) formed on the back surface 11b side of the workpiece 11 in the first grinding step S1.

When the back surface 11b of the workpiece 11 is ground with the grinding wheel 54B, the binder of the grinding wheel 54B wears away, causing the exposed abrasive grains to fall off and newly exposing the abrasive grains embedded within the binder. This phenomenon is called self-sharpening, and the grinding ability of the grinding wheel 54B is maintained by the self-sharpening. In particular, when the grinding wheel 54B first comes into contact with the back surface 11b of the workpiece 11 on which the grinding marks 11c (see FIG. 5B) remain, the binder is likely to wear away, promoting the self-sharpening. This allows the grinding wheel 54B to be in good condition when the finish grinding of the workpiece 11 begins.

However, abrasive grains that fall off the grinding wheel 54B get between the workpiece 11 and the grinding wheel 54B during finish grinding and are pressed against the back surface 11b of the workpiece 11 by the grinding wheel 54B. As a result, new deep grinding marks (saw marks) 11d may be formed on the back surface 11b of the workpiece 11 (see FIG. 6B). In this case, the grinding marks 11d remain on the workpiece 11 after finish grinding, degrading the quality of the workpiece 11.

Therefore, in this embodiment, grinding of the workpiece 11 is temporarily interrupted at the end of the finish grinding, and the abrasive grains that have fallen off the grinding wheel 54B are removed from the workpiece 11, and then the finish grinding is resumed. This makes it difficult for grinding marks 11d to form on the workpiece 11 at the end of the finish grinding, and suppresses deterioration in the quality of the workpiece 11.

Specifically, first, before the thickness of the workpiece 11 reaches the target value (finishing thickness) of the final thickness of the workpiece 11, the workpiece 11 and the grinding wheel 54B are separated while supplying the grinding fluid 74 to the workpiece 11 (separation step S3). Figure 7 is a partial cross-sectional side view showing the grinding device 2 in separation step S3.

In the separation step S3, the grinding unit 40B is raised by the moving unit 30B (see FIG. 1) while the grinding fluid 74 is being supplied to the workpiece 11 from the nozzle 72B of the grinding fluid supply unit 70B. This causes the grinding wheel 54B to be separated from the back surface 11b of the workpiece 11, and the finish grinding of the workpiece 11 is temporarily interrupted. Then, in the second grinding step S2 (see FIG. 6(B) and FIG. 6(B)), the abrasive grains that have fallen off the grinding wheel 54B and adhered to the back surface 11b of the workpiece 11 or that have entered between the workpiece 11 and the grinding wheel 54B are washed away from the back surface 11b of the workpiece 11 by the grinding fluid 74 and removed.

After the separation step S3, a cleaning step S4 may be performed to further clean the grinding surface side (back surface 11b side) of the workpiece 11. FIG. 8(A) is a partially sectional side view showing the grinding device 2 in the cleaning step S4, and FIG. 8(B) is a plan view showing the grinding device 2 in the cleaning step S4.

For example, the grinding device 2 includes a cleaning fluid supply unit 80 that supplies cleaning fluid 86 to the workpiece 11, separate from the grinding fluid supply unit 70B (see FIG. 7). The cleaning fluid supply unit 80 includes an L-shaped support arm 82, the base end of which is connected to a rotational drive source (not shown), such as a motor, that rotates the support arm 82.

A nozzle 84 that supplies cleaning fluid 86 is attached to the tip of the support arm 82. A fluid supply source (not shown) that supplies the fluid 86 to the nozzle 84 is connected to the nozzle 84. When the rotation drive source is driven, the support arm 82 and the nozzle 84 rotate, and the chuck table 18 and the nozzle 84 move relatively along a direction parallel to the horizontal plane (XY plane).

The amount of movement (amount of lift) of the grinding unit 40B in the aforementioned separation step S3 (see FIG. 7) is set so that the nozzle 84 can move between the workpiece 11 and the grinding wheel 50B. Then, in the cleaning step S4, the nozzle 84 is moved above the workpiece 11 while spraying fluid 86 from the nozzle 84 with the chuck table 18 rotating. For example, the nozzle 84 moves back and forth along an arc-shaped trajectory that passes through an area overlapping with the center of the workpiece 11 (see FIG. 8(B)).

The fluid 86 can be a mixed fluid containing a liquid such as pure water and a gas such as air. When the fluid 86 is sprayed from the nozzle 84 toward the back surface 11b of the workpiece 11, the abrasive grains present on the back surface 11b of the workpiece 11 are blown away or washed away (two-fluid washing). This removes the abrasive grains from the back surface 11b of the workpiece 11.

In addition, during the separation step S3 and cleaning step S4, it is preferable to keep the chuck table 18 and grinding wheel 50B rotating. This makes it possible to quickly resume finish grinding of the workpiece 11 in the third grinding step S5 described below.

In addition, if the abrasive grains can be sufficiently removed by the grinding fluid 74 supplied to the workpiece 11 in the aforementioned separation step S3 (see FIG. 7), the cleaning step S4 may be omitted. In this case, the cleaning fluid supply unit 80 is not required.

Next, the grinding surface side (back surface 11b side) of the workpiece 11 is ground with the grinding wheel 50B until the workpiece 11 has a predetermined finishing thickness (third grinding step S5). Figure 9(A) is a partially sectional side view showing the grinding device 2 in the third grinding step S5, and Figure 9(B) is a plan view showing the grinding device 2 in the third grinding step S5.

In the third grinding step S5, the workpiece 11 is ground in the same procedure as in the second grinding step S2 (see FIG. 6(B) and FIG. 6(B)). Specifically, while the chuck table 18 and the grinding wheel 50B are rotating, the grinding unit 40B is lowered at a predetermined speed along the Z-axis direction to bring the holding surface 18a of the chuck table 18 and the grinding wheel 50B relatively close to each other. In addition, grinding fluid 74 is supplied to the workpiece 11 and the grinding wheel 54A from the nozzle 72A of the grinding fluid supply unit 70A.

When the grinding wheel 54B comes into contact with the workpiece 11, the back surface 11b of the workpiece 11 is ground by the grinding wheel 54B. This restarts the finish grinding of the workpiece 11, and the grinding marks 11d (see FIG. 8B) remaining on the back surface 11b of the workpiece 11 are removed.

As described above, in the first grinding step S1, the grinding surface side (back surface 11b side) of the workpiece 11 is ground by bringing the grinding wheel 54B into contact with the workpiece 11 while supplying grinding fluid 74 to the workpiece 11 and the grinding wheel 54A. Then, when the workpiece 11 is ground until its thickness reaches the finishing thickness, the grinding unit 40B rises and the grinding wheel 54B is separated from the workpiece 11. This completes the finish grinding of the workpiece 11.

In the third grinding step S5, the finish grinding of the workpiece 11 is resumed after the abrasive grains have been removed from the back surface 11b of the workpiece 11 by the separation step S3 and/or cleaning step S4. This significantly reduces the amount of abrasive grains that get between the workpiece 11 and the grinding wheel 54B in the third grinding step S5, making it difficult for new grinding marks to form on the back surface 11b of the workpiece 11.

Note that in the second grinding step S2 described above, most of the finish grinding of the workpiece 11 is completed. Therefore, in the third grinding step S5, the workpiece 11 is ground to the extent that the grinding marks 11d (see FIG. 8B) remaining on the back surface 11b of the workpiece 11 are removed. In other words, the amount of grinding of the workpiece 11 in the third grinding step S5 is less than the amount of grinding of the workpiece 11 in the second grinding step S2. Note that the amount of grinding of the workpiece 11 corresponds to the difference in thickness of the workpiece 11 before and after grinding.

Furthermore, if the amount of grinding of the workpiece 11 in the third grinding step S5 is large, the amount of abrasive grains that fall off the grinding wheel 54B during the third grinding step S5 also increases, making it easier for new grinding marks to form on the workpiece 11. Therefore, it is preferable that the amount of grinding of the workpiece 11 in the third grinding step S5 is set to a small value within a range that allows the grinding marks 11d formed on the workpiece 11 to be removed. For example, the amount of grinding of the workpiece 11 in the third grinding step S5 is set to 10 μm or less, preferably 5 μm or less, and more preferably 3 μm or less.

The rotation speed of the chuck table 18, the rotation speed of the grinding wheel 50B, and the relative movement speed (processing feed speed) between the chuck table 18 and the grinding wheel 50B in the Z-axis direction in the third grinding step S5 can be set in the same manner as in the second grinding step S2. However, the processing feed speed in the third grinding step S5 may be lower than the processing feed speed in the second grinding step S2. Because the amount of grinding of the workpiece 11 in the third grinding step S5 is small, the effect on processing efficiency is small even if the processing feed speed in the third grinding step S5 is set to a low speed.

For example, the processing feed rate in the third grinding step S5 is set to 3/4 or less, preferably 2/3 or less, and more preferably 1/2 or less of the processing feed rate in the second grinding step S2. This reduces the load on the grinding wheel 54B in the third grinding step S5 and reduces the amount of abrasive grains that fall off the grinding wheel 54B, making it less likely that new grinding marks will be formed on the workpiece 11.

By carrying out the above-mentioned first grinding step S1 to third grinding step S5, the workpiece 11 is subjected to rough grinding and finish grinding, and is thinned to a predetermined finishing thickness. The workpiece 11 is then divided along the streets 13 (see FIG. 2) to separate the workpiece 11 into individual pieces, and thin device chips equipped with devices 15 (see FIG. 2) are obtained. Note that, to divide the workpiece 11, a processing device such as a cutting device that cuts the workpiece 11 with an annular cutting blade or a laser processing device that performs laser processing on the workpiece 11 can be used.

As described above, in the method for grinding a workpiece according to this embodiment, the workpiece 11 is first ground with grinding wheel 54A, and then ground with grinding wheel 54B. Then, before the thickness of the workpiece 11 reaches the finishing thickness, the workpiece 11 and grinding wheel 54B are separated while supplying grinding fluid, and the workpiece 11 is ground again with grinding wheel 54B. This makes it less likely that grinding marks will be formed due to abrasive grains that fall off during finish grinding, and reduces deterioration in the quality of the workpiece 11.

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

(Embodiment 2)
In the first embodiment, an example was described in which the entire workpiece 11 was thinned by grinding the entire back surface 11b side of the workpiece 11. However, when the entire workpiece 11 is thinned, the rigidity of the workpiece 11 is reduced, and the workpiece 11 is likely to be deformed or damaged during subsequent handling (transportation, holding, etc.). Therefore, only the center of the back surface 11b side of the workpiece 11 may be thinned by grinding. In this case, a circular recess is formed in the center of the workpiece 11, while the outer periphery of the workpiece 11 is not thinned but is maintained in a thick state and remains as an annular reinforcing part. This suppresses the reduction in the rigidity of the workpiece 11.

A grinding device 2A (see Figs. 10(A) to 11(B)) is used to grind the center of the workpiece 11. The grinding device 2A corresponds to a modified version of the grinding device 2 shown in Fig. 1, and performs rough grinding and finish grinding on the center of the workpiece 11. Specifically, the grinding device 2A includes a chuck table 18, a grinding unit (rough grinding unit) 100A (see Fig. 10(A)) that performs rough grinding on the workpiece 11, and a grinding unit (finish grinding unit) 100B (Fig. 11(A)) that performs finish grinding on the workpiece 11. The configurations and functions of the components of the grinding device 2A other than the grinding units 100A and 100B are the same as those of the grinding device 2.

The grinding method for a workpiece according to this embodiment will be described below. In this embodiment, the grinding unit 100A performs rough grinding on the workpiece 11 (first grinding step S1), and then the grinding unit 100B performs finish grinding on the workpiece 11 (second grinding step S2 to third grinding step S5). Note that the specific steps of the grinding method for a workpiece according to this embodiment are the same as those of embodiment 1, except for the matters described below.

First, the workpiece 11 is ground by the grinding unit 100A to form a recess in the workpiece 11 while leaving an annular reinforcing portion surrounding the recess (first grinding step S1). FIG. 10(A) is a partially sectional side view showing a grinding device 2A that performs rough grinding on the central portion of the workpiece 11, and FIG. 10(A) is a plan view showing a grinding device 2A that performs rough grinding on the central portion of the workpiece 11.

The grinding unit 100A includes a spindle 102A and a wheel mount 104A, and the spindle 102A rotates around a rotation axis set along the Z-axis direction. The configurations and functions of the spindle 102A and the wheel mount 104A are similar to those of the spindle 44A and the wheel mount 48A of the grinding unit 40A (see FIG. 5A), respectively. However, the diameter of the wheel mount 104A is smaller than the diameter of the wheel mount 48A.

A grinding wheel 106A is attached to the wheel mount 104A. The grinding wheel 106A includes an annular wheel base 108A and multiple grinding stones 110A fixed to the wheel base 108A. When the spindle 102A is rotated, the grinding wheel 106A rotates around the rotation axis of the spindle 102A, and the multiple grinding stones 110A each revolve along an annular orbit (path).

The grinding wheel 106A, wheel base 108A, and grinding wheel 110A have the same configurations and functions as the grinding wheel 50A, wheel base 52A, and grinding wheel 54A (see FIG. 5A), respectively. However, the diameter of the wheel base 108A is smaller than the diameter of the wheel base 52A, and the diameter of the orbit of the grinding wheel 110A is smaller than the diameter of the orbit of the grinding wheel 54A.

In the first grinding step S1, the workpiece 11 is first held by the chuck table 18. Then, the positional relationship between the chuck table 18 and the grinding wheel 106A is adjusted so that the center of the workpiece 11 and the trajectory of the grinding wheel 110A overlap in the Z-axis direction.

The diameter of the orbit of the grinding wheel 110A is smaller than the radius of the workpiece 11. For example, the diameter of the orbit of the grinding wheel 110A is set to be approximately the same as the radius of the device region 17 (see FIG. 2) of the workpiece 11. In this case, the multiple grinding wheels 110A are arranged so as to overlap the device region 17 of the workpiece 11, but not to overlap the outer periphery of the workpiece 11.

Next, the chuck table 18 and the grinding wheel 106A are rotated. For example, the rotation speed of the chuck table 18 is set to 10 rpm or more and 300 rpm or less, and the rotation speed of the grinding wheel 106A (the rotation speed of the spindle 102A) is set to 1000 rpm or more and 6000 rpm or less.

Then, with the chuck table 18 and grinding wheel 106A rotating, the grinding unit 100B is lowered along the Z-axis direction (a direction parallel to the rotation axis of the spindle 102A and grinding wheel 106A). This causes the chuck table 18 and grinding wheel 106A to move relatively along the Z-axis direction, bringing the workpiece 11 and grinding wheel 110A closer together. The relative movement speed (processing feed speed) between the chuck table 18 and grinding wheel 106A in the Z-axis direction is set to, for example, 1.0 μm/s or more and 6.0 μm/s or less.

When the grinding wheel 110A comes into contact with the workpiece 11, the grinding wheel 110A rotates to pass through the rotation axis 24 of the chuck table 18, grinding the center of the back surface 11b of the workpiece 11. As a result, only the center of the workpiece 11 is thinned, and a circular recess (groove) 21 is formed in the center of the back surface 11b of the workpiece 11.

The recess 21 includes a circular bottom surface 21a that is generally parallel to the front surface 11a and back surface 11b of the workpiece 11, and an annular side surface (side wall, inner wall) 21b that is connected to the bottom surface 21a and back surface 11b. The diameter of the recess 21 is generally the same as the diameter of the device region 17, and the recess 21 is formed to overlap multiple devices 15 (see FIG. 2).

In addition, an annular reinforcing portion 23 remains on the outer periphery of the workpiece 11, which corresponds to the area that has not been subjected to the grinding process. The reinforcing portion 23 includes the outer periphery excess area 19 (see FIG. 2) and surrounds the device area 17 (see FIG. 2) and the recess 21.

As described above, when only the central portion of the workpiece 11 is thinned, the outer periphery (reinforcement portion 23) of the workpiece 11 remains thick, and the reinforcement portion 23 functions as a reinforcing region that reinforces the workpiece 11. This prevents the rigidity of the workpiece 11 from decreasing, making the workpiece 11 less likely to deform or break.

When the thickness of the center of the workpiece 11 (depth of the recess 21) reaches a predetermined value, the grinding unit 100A rises and the grinding wheel 110A moves away from the workpiece 11. This completes the rough grinding of the workpiece 11 by the grinding wheel 106A. After the rough grinding, arc-shaped grinding marks (saw marks) 11e formed along the trajectory of the grinding wheel 110A remain on the bottom surface 21a of the recess 21 of the workpiece 11 (see FIG. 10B).

In the first grinding step S1, as in the first embodiment, the grinding wheel 110A is brought into contact with the workpiece 11 while supplying grinding fluid to the workpiece 11 and the grinding wheel 110A. For example, a grinding fluid supply passage (not shown) through which the grinding fluid is supplied is provided inside the wheel mount 104A and the wheel base 108A. The grinding fluid supply passage opens inside the multiple grinding wheels 110A. Then, while the workpiece 11 is being ground with the grinding wheel 110A, the grinding fluid flows out of the grinding fluid supply passage and is supplied to the workpiece 11 and the grinding wheel 110A. This cools the workpiece 11 and the grinding wheel 110A and washes away the grinding debris.

However, there are no limitations on the method of supplying the grinding fluid. For example, a grinding fluid supply unit 70A (see Figures 5(A) and 5(B)) may be provided around the chuck table 18. In this case, the grinding fluid is supplied to the workpiece 11 and grinding wheel 110A from the nozzle 72A of the grinding fluid supply unit 70A.

Next, the workpiece 11 is subjected to finish grinding. FIG. 11(A) is a partially sectional side view showing a grinding device 2A that performs finish grinding on the central portion of the workpiece 11, and FIG. 11(A) is a plan view showing a grinding device 2A that performs finish grinding on the central portion of the workpiece 11.

Specifically, first, the bottom surface 21a of the recess 21 of the workpiece 11 is ground by the grinding unit 100B (second grinding step S2). The grinding unit 100B includes a spindle 102B and a wheel mount 104B, and the spindle 102B rotates around a rotation axis set along the Z-axis direction. The configurations and functions of the spindle 102B and the wheel mount 104B are similar to those of the spindle 102A and the wheel mount 104A of the grinding unit 100A (see FIG. 10(A)).

A grinding wheel 106B is attached to the wheel mount 104B. The grinding wheel 106B includes an annular wheel base 108B and a number of grinding stones 110B fixed to the wheel base 108B. When the spindle 102B is rotated, the grinding wheel 106B rotates around the rotation axis of the spindle 102B, and the multiple grinding stones 110B each revolve along an annular orbit (path).

The material, structure, function, etc. of the wheel base 108B and grinding wheel 110B are the same as those of the wheel base 108A and grinding wheel 110A of the grinding wheel 106A (see FIG. 10A). However, the average grain size of the abrasive grains (second abrasive grains) contained in the grinding wheel 110B is smaller than the average grain size of the abrasive grains (first abrasive grains) contained in the grinding wheel 110A.

In the second grinding step S2, first, the workpiece 11 is held by the chuck table 18. Then, the positional relationship between the chuck table 18 and the grinding wheel 106B is adjusted so that the center of the workpiece 11 and the trajectory of the grinding wheel 110B overlap in the Z-axis direction.

The diameter of the orbit of the grinding wheel 110B is smaller than the radius of the workpiece 11. For example, the diameter of the orbit of the grinding wheel 110B is set to be approximately the same as the radius of the device region 17 (see FIG. 2) of the workpiece 11. The multiple grinding wheels 110B are arranged so as to overlap the recesses 21 of the workpiece 11, but not to overlap the reinforcing portions 23 of the workpiece 11.

Next, the chuck table 18 and the grinding wheel 106B are rotated. For example, the rotation speed of the chuck table 18 is set to 10 rpm or more and 300 rpm or less, and the rotation speed of the grinding wheel 106B (the rotation speed of the spindle 102B) is set to 1000 rpm or more and 6000 rpm or less.

Then, with the chuck table 18 and grinding wheel 106B rotating, the grinding unit 100B is lowered along the Z-axis direction (a direction parallel to the rotation axis of the spindle 102B and grinding wheel 106B). This causes the chuck table 18 and grinding wheel 106B to move relatively along the Z-axis direction, bringing the workpiece 11 and grinding wheel 110B closer together. The relative movement speed (processing feed speed) between the chuck table 18 and grinding wheel 106B in the Z-axis direction is set to, for example, 0.1 μm/s or more and 1.0 m/s or less.

When the grinding wheel 110B comes into contact with the workpiece 11, the grinding wheel 110B rotates to pass through the rotation axis 24 of the chuck table 18 while grinding the bottom surface 21a of the recess 21 of the workpiece 11. That is, in the second grinding step S2, the bottom surface 21a of the recess 21 corresponds to the surface (grinding surface) to be ground by the grinding wheel 106B. As a result, the bottom surface 21a of the recess 21 of the workpiece 11 is subjected to finish grinding, and the grinding marks 11e (see FIG. 10B) formed on the bottom surface 21a of the recess 21 in the first grinding step S1 are removed.

In the second grinding step S2, as in the first embodiment, the grinding wheel 110B is brought into contact with the workpiece 11 while supplying grinding fluid to the workpiece 11 and the grinding wheel 110B. For example, a grinding fluid supply passage (not shown) through which the grinding fluid is supplied is provided inside the wheel mount 104B and the wheel base 108B. The grinding fluid supply passage opens inside the multiple grinding wheels 110B. Then, while the workpiece 11 is being ground with the grinding wheel 110B, the grinding fluid flows out of the grinding fluid supply passage and is supplied to the workpiece 11 and the grinding wheel 110B. This cools the workpiece 11 and the grinding wheel 110B and washes away the grinding debris.

However, there are no limitations on the method of supplying the grinding fluid. For example, a grinding fluid supply unit 70B (see Figures 6(A) and 6(B)) may be provided around the chuck table 18. In this case, the grinding fluid is supplied to the workpiece 11 and grinding wheel 110B from nozzles 72B of the grinding fluid supply unit 70B.

Then, before the thickness of the center of the workpiece 11 reaches the final target thickness (finishing thickness), the workpiece 11 and the grinding wheel 110B are separated while supplying grinding fluid to the workpiece 11 (separation step S3). Specifically, the grinding unit 100B is raised while the grinding fluid is still being supplied to the workpiece 11. As a result, the grinding wheel 110B is separated from the bottom surface 21a of the recess 21, and the finish grinding is temporarily interrupted.

In addition, in the second grinding step S2, the abrasive grains that have fallen off the grinding wheel 110B and adhered to the recess 21 of the workpiece 11, or that have entered between the bottom surface 21a of the recess 21 and the grinding wheel 110B, are washed away from the recess 21 of the workpiece 11 by the grinding fluid and removed. The details of the procedure of the separation step S3 are the same as those of embodiment 1 (see FIG. 7).

After the separation step S3, a cleaning step S4 may be performed to further clean the bottom surface 21a of the recess 21 of the workpiece 11. The cleaning method for the workpiece 11 is the same as in the first embodiment. For example, a cleaning fluid 86 is sprayed onto the bottom surface 21a of the recess 21 from a nozzle 84 of the cleaning fluid supply unit 80 (see Figures 8(A) and 8(B)). This removes abrasive grains from the bottom surface 21a of the recess 21.

Next, the bottom surface 21a of the recess 21 is ground with the grinding wheel 106B until the central portion of the workpiece 11 (the area where the recess 21 is formed) has a predetermined finishing thickness (third grinding step S5). In the third grinding step S5, the workpiece 11 is ground in the same procedure as in the second grinding step S2.

Specifically, while rotating the chuck table 18 and the grinding wheel 106B, the grinding unit 100B is lowered at a predetermined speed along the Z-axis direction to bring the holding surface 18a of the chuck table 18 and the grinding wheel 106B relatively close to each other. Note that in the third grinding step S5, similar to the second grinding step S2, the grinding wheel 110B is brought into contact with the workpiece 11 while supplying grinding fluid to the workpiece 11 and the grinding wheel 110B.

When the grinding wheel 110B comes into contact with the workpiece 11, the bottom surface 21a of the recess 21 is ground by the grinding wheel 110B. This restarts the finish grinding of the workpiece 11, and any grinding marks remaining on the bottom surface 21a of the recess 21 are removed. Then, when the workpiece 11 is ground until the thickness of the center of the workpiece 11 reaches the finish thickness, the grinding unit 40B rises and the grinding wheel 110B is separated from the workpiece 11. This completes the finish grinding of the workpiece 11.

As described above, in the third grinding step S5, the finish grinding of the workpiece 11 is resumed after the abrasive grains have been removed from the bottom surface 21a of the recess 21 by the separation step S3 and/or cleaning step S4. This significantly reduces the amount of abrasive grains that get between the workpiece 11 and the grinding wheel 110B in the third grinding step S5, making it difficult for new grinding marks to form on the bottom surface 21a of the recess 21.

As in the first embodiment, the amount of workpiece 11 ground in the third grinding step S5 is less than the amount of workpiece 11 ground in the second grinding step S2. For example, the amount of workpiece 11 ground in the third grinding step S5 is set to 10 μm or less, preferably 5 μm or less, and more preferably 3 μm or less.

In addition, the rotation speed of the chuck table 18, the rotation speed of the grinding wheel 106B, and the relative movement speed (processing feed rate) between the chuck table 18 and the grinding wheel 106B in the Z-axis direction in the third grinding step S5 can be set in the same manner as in the second grinding step S2. However, the processing feed rate in the third grinding step S5 may be lower than the processing feed rate in the second grinding step S2. For example, the processing feed rate in the third grinding step S5 is set to 3/4 or less, preferably 2/3 or less, and more preferably 1/2 or less of the processing feed rate in the second grinding step S2.

By carrying out the above-mentioned first grinding step S1 to third grinding step S5, rough grinding and finish grinding are performed on the central portion of the workpiece 11, and the central portion of the workpiece 11 is thinned to a predetermined finishing thickness. The workpiece 11 is then divided along the streets 13 (see FIG. 2), whereby the device regions 17 (see FIG. 2) of the workpiece 11 are separated into individual pieces, and thin device chips equipped with devices 15 (see FIG. 2) are obtained.

As described above, the method for grinding a workpiece according to this embodiment can also be applied to cases where a recess 21 is ground into the center of the workpiece 11, leaving a reinforcing portion 23 on the outer periphery of the workpiece 11. This embodiment can be appropriately combined with embodiment 1.

11 Workpiece 11a Surface (first surface)
11b Back side (second surface)
11c, 11d, 11e Grinding marks (saw marks)
13th Street (Planned division line)
15 Device 17 Device region 19 Peripheral excess region 21 Recess (groove)
21a Bottom surface 21b Side surface (side wall, inner wall)
23 Reinforcement portion 2 Grinding device 4 Base 4a Opening 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 Upper surface 20b Recess 20c Flow path 22 Holding member 22a Suction surface 24 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 Wheel mount 50A, 50B Grinding wheel 52A, 52B Wheel base 54A, 54B Grinding stone 56 Transport unit (transport mechanism, unloading arm)
58 Cleaning unit (cleaning mechanism, cleaning device)
60 Controller (control unit, control unit, control device)
70A, 70B Grinding fluid supply unit 72A, 72B Nozzle 74 Grinding fluid 80 Cleaning fluid supply unit 82 Support arm 84 Nozzle 86 Fluid 100A, 100B Grinding unit 102A, 102B Spindle 104A, 104B Wheel mount 106A, 106B Grinding wheel 108A, 108B Wheel base 110A, 110B Grinding stone

Claims (4)

A method for grinding a workpiece, comprising: using a first grinding wheel having a first grinding stone including first abrasive grains; and a second grinding wheel having a second grinding stone including second abrasive grains having an average grain size smaller than that of the first abrasive grains,
a first grinding step of grinding a surface of the workpiece by bringing the first grinding wheel into contact with the workpiece while supplying a grinding fluid;
a second grinding step of grinding the grinding surface side of the workpiece by bringing the second grinding wheel into contact with the workpiece while supplying a grinding fluid after the first grinding step;
a separating step of separating the workpiece from the second grinding wheel while supplying a grinding fluid after the second grinding step;
and a third grinding step of grinding the workpiece on the grinding surface side until the workpiece has a predetermined thickness by bringing the second grinding wheel into contact with the workpiece while supplying a grinding fluid after the separating step,
A method for grinding a workpiece, wherein a grinding amount of the workpiece in the third grinding step is smaller than a grinding amount of the workpiece in the second grinding step. The method for grinding a workpiece according to claim 1, further comprising a cleaning step for cleaning the grinding surface side of the workpiece after the separating step and before the third grinding step. A method for grinding a workpiece, comprising: using a first grinding wheel having a first grinding stone including first abrasive grains; and a second grinding wheel having a second grinding stone including second abrasive grains having an average grain size smaller than that of the first abrasive grains,
a first grinding step in which the first grinding wheel is brought into contact with the workpiece while supplying a grinding fluid, thereby forming a recess in the workpiece and leaving an annular reinforcing portion surrounding the recess;
a second grinding step of grinding a bottom surface of the recess by bringing the second grinding wheel into contact with the workpiece while supplying a grinding fluid after the first grinding step;
a separating step of separating the workpiece from the second grinding wheel while supplying a grinding fluid after the second grinding step;
and a third grinding step of, after the separating step, bringing the second grinding wheel into contact with the workpiece while supplying a grinding fluid, thereby grinding a bottom surface of the recess until a region of the workpiece where the recess is formed reaches a predetermined thickness,
A method for grinding a workpiece, wherein a grinding amount of the workpiece in the third grinding step is smaller than a grinding amount of the workpiece in the second grinding step. 4. The method for grinding a workpiece according to claim 3, further comprising a cleaning step of cleaning a bottom surface of the recess after the separating step and before the third grinding step.

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