JP2024062729A - Method for grinding a workpiece - Google Patents

Abstract

[Problem] To provide a method for grinding a workpiece that can simplify the processing steps of the workpiece while preventing damage to the workpiece. [Solution] The method for grinding a workpiece having a chamfered portion on its outer periphery with a grinding wheel including a grinding wheel includes the following steps: a holding step for holding the workpiece on a chuck table, a recess forming step for grinding the workpiece with the grinding wheel to form a recess in the workpiece while leaving an unground area on the outer periphery of the workpiece, and a slide grinding step for grinding the unground area with the grinding wheel. [Selected Figure] Figure 4

Description

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

In the device chip manufacturing process, a wafer is used that has device regions on its front side, with devices formed in each of the multiple regions partitioned by multiple streets (planned division lines) arranged in a grid pattern. By dividing this wafer along the streets, multiple device chips are obtained, each of which has a device. The device chips 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. Therefore, a grinding device is sometimes used to grind and thin the wafer before it is divided. The grinding device is equipped with a chuck table that holds the workpiece and a grinding unit that grinds the workpiece, and the grinding unit is equipped with an annular grinding wheel that includes a grinding stone. The wafer is held by the chuck table, and the grinding stone is brought into contact with the back side of the wafer while the chuck table and grinding wheel are rotated, thereby grinding and thinning the wafer.

The wafer is chamfered by grinding the outer periphery of the wafer to make the side of the wafer curved. When a chamfered wafer is ground to thin it, the outer periphery of the wafer becomes sharply pointed (sharp edge shape). When the sharp edge of the wafer is pressed against the chuck table by the grinding wheel, chipping or cracking may occur on the outer periphery of the wafer, which may damage the wafer.

Therefore, when grinding a chamfered wafer to thin it, a process called edge trimming is sometimes performed in advance, in which the outer periphery of the wafer is cut into an annular shape using a cutting blade (see Patent Document 1). When edge trimming is performed, the chamfered area of the wafer is removed, so that the outer periphery of the wafer does not have a sharp edge shape even if the wafer is subsequently ground to thin it. This makes it less likely that damage will occur to the wafer.

JP 2000-173961 A

As described above, when edge trimming is performed on a workpiece such as a chamfered wafer, the outer periphery of the workpiece before grinding is cut into a ring shape with a cutting blade. This requires a process in which the workpiece is processed with a cutting device separate from the grinding device, which requires time and cost for preparation for the grinding process.

In addition, if the workpiece is ground to thin it after edge trimming, the diameter of the workpiece changes before and after processing. This requires that the equipment used to handle the workpiece (transport, hold, process, capture images, etc.) must be adjusted to match the dimensions of the workpiece after grinding. Furthermore, if a mark such as a notch or orientation flat indicating the crystal orientation of the workpiece is formed on the outer periphery of the workpiece, the mark will be removed by edge trimming, so the crystal orientation must be confirmed by another method after the workpiece is ground. As a result, the processing process for the workpiece becomes complicated.

The present invention was made in consideration of these problems, and aims to provide a method for grinding a workpiece that can simplify the processing steps of the workpiece while preventing damage to the workpiece.

According to one aspect of the present invention, there is provided a method for grinding a workpiece having a chamfered portion on its outer periphery with a grinding wheel including a grinding wheel, the method including: a holding step for holding the workpiece with a chuck table; a recess forming step for grinding the workpiece with the grinding wheel while leaving an unground area on the outer periphery of the workpiece by relatively moving the chuck table and the grinding wheel in a direction parallel to the rotation axis of the grinding wheel after the holding step while rotating the chuck table and the grinding wheel, thereby forming a recess in the workpiece; and a slide grinding step for grinding the unground area with the grinding wheel by relatively moving the chuck table and the grinding wheel in a direction intersecting the rotation axis of the grinding wheel after the recess forming step while rotating the chuck table and the grinding wheel.

Preferably, the method for grinding the workpiece further includes a pre-grinding step, prior to the recess forming step, of grinding the workpiece to thin the entire workpiece. Also, preferably, in the slide grinding step, the grinding wheel is moved relatively to the outer periphery of the workpiece while moving the grinding wheel relatively in a direction away from the bottom surface of the recess.

Moreover, preferably, the recess forming step and the slide grinding step are performed multiple times to grind the workpiece.

In one aspect of the present invention, a method for grinding a workpiece involves grinding the workpiece with a grinding wheel to form a recess in the workpiece while leaving an unground area on the outer periphery of the workpiece, and then grinding the unground area with a grinding wheel, thereby thinning the workpiece while preventing damage to the outer periphery. This makes it possible to omit edge trimming, in which the outer periphery of the workpiece is cut with a cutting blade, and simplifies the processing steps for the workpiece.

FIG. FIG. 4 is a cross-sectional view showing a chuck table. FIG. 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 holding step, and FIG. 5B is a perspective view showing the grinding device in the holding step. FIG. 6A is a partially sectional side view showing the grinding device in the recess forming step, and FIG. 6B is a perspective view showing the grinding device in the recess forming step. FIG. 7A is a partially sectional side view showing the grinding device in the slide grinding step, and FIG. 7B is a perspective view showing the grinding device in the slide grinding step. FIG. 8A is a partially sectional side view showing the grinding device in the slide grinding step according to the modified example, and FIG. 8B is a perspective view showing the grinding device in the slide grinding step according to the modified example. FIG. 9A is a partially sectional side view showing the grinding device in the pre-grinding step, and FIG. 9B is a perspective view showing the grinding device in the pre-grinding step.

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

The grinding device 2 is equipped with a chuck table (holding table) 4 that holds a workpiece that is the object of grinding by the grinding device 2. The chuck table 4 is equipped with a cylindrical frame (main body) 6 made of metal such as SUS (stainless steel), glass, ceramics, resin, etc. A cylindrical recess 6b is provided in the center of the upper surface 6a of the frame 6.

A disk-shaped holding member 8 made of a porous material such as porous ceramics is fitted into the recess 6b of the frame 6. The holding member 8 contains many pores that communicate from the top surface to the bottom surface of the holding member 8. The top surface of the holding member 8 forms a circular suction surface 8a that sucks in the workpiece when it is held by the chuck table 4.

Figure 2 is a cross-sectional view showing the chuck table 4. The upper surface 6a of the frame 6 and the suction surface 8a of the holding member 8 form the holding surface 4a of the chuck table 4. The holding surface 4a is connected to a suction source (not shown) such as an ejector via pores contained in the holding member 8, a flow path 6c provided inside the frame 6, a valve (not shown), etc.

The holding surface 4a of the chuck table 4 is formed in a cone shape with the apex at the center of the holding surface 4a, and is slightly inclined with respect to the radial direction of the holding surface 4a. The chuck table 4 is arranged in a slightly inclined state so that a holding area 4b, which corresponds to a part of the holding surface 4a and extends from the center to the outer periphery of the holding surface 4a, is roughly parallel to the horizontal plane. The area of the workpiece held by the holding area 4b of the holding surface 4a is ground by the grinding unit 10 described below.

For ease of explanation, the inclination of the holding surface 4a is exaggerated in FIG. 2, but the actual inclination of the holding surface 4a is small. For example, when the diameter of the holding surface 4a is about 290 mm or more and 310 mm or less, the difference in height between the center and the outer periphery of the holding surface 4a (corresponding to the height of the cone) is set to about 20 μm or more and 40 μm or less.

A rotational drive source (not shown), such as a motor, that rotates the chuck table 4 is connected to the chuck table 4. The rotational drive source rotates the chuck table 4 around a rotation axis 4c. The rotation axis 4c of the chuck table 4 is set along a direction perpendicular to the radial direction of the holding surface 4a and is slightly inclined with respect to the Z-axis direction. In addition, the rotation axis 4c passes through the center of the holding surface 4a and intersects with the holding surface 4a.

A moving unit (not shown) that moves the chuck table 4 horizontally (XY plane) is connected to the chuck table 4. For example, the moving unit is configured with a ball screw type X-axis moving mechanism that moves the chuck table 4 along the X-axis direction. In this case, the X-axis moving mechanism includes a ball screw (not shown) arranged along the X-axis direction, a pulse motor (not shown) that rotates the ball screw, and a nut portion (not shown) that is connected to the chuck table 4 and into which the ball screw is screwed.

As shown in FIG. 1, the grinding device 2 includes a grinding unit 10 that performs grinding on a workpiece. The grinding unit 10 includes a cylindrical spindle 12 that is arranged along the Z-axis direction. A rotary drive source (not shown), such as a motor, that rotates the spindle 12 is connected to the base end (upper end) of the spindle 12. When the rotary drive source is driven, the spindle 12 rotates around a rotary axis 12a that is set along the Z-axis direction.

A disk-shaped wheel mount 14 made of metal or the like is fixed to the tip (lower end) of the spindle 12. An annular grinding wheel 16 for grinding the workpiece is removably attached to the underside of the wheel mount 14. For example, the grinding wheel 16 is fixed to the wheel mount 14 by a fastener such as a bolt.

The grinding wheel 16 is made of a metal such as aluminum or stainless steel and has an annular wheel base 18 formed to have roughly the same diameter as the wheel mount 14. The upper surface of the wheel base 18 is fixed to the lower surface of the wheel mount 14.

A number of grinding wheels 20 are fixed to the underside of the wheel base 18. The underside of the grinding wheels 20 constitutes a grinding surface 20a that grinds the workpiece. For example, the grinding wheels 20 are formed in a rectangular parallelepiped shape and are arranged in a ring shape at roughly equal intervals along the circumferential direction of the wheel base 18.

The grinding wheel 20 includes abrasive grains made of diamond, cBN (cubic boron nitride), etc., and a bonding material (bond material) such as a metal bond, a resin bond, or a vitrified bond that fixes the abrasive grains. However, there are no restrictions on the material, shape, structure, size, etc. of the grinding wheel 20. The number of grinding wheels 20 can also be set as desired.

The grinding wheel 16 rotates around the rotation axis 12a by power transmitted from a rotary drive source (not shown) via the spindle 12 and the wheel mount 14. In other words, the rotation axis 12a of the spindle 12 corresponds to the rotation axis of the wheel mount 14 and the grinding wheel 16. When the grinding wheel 16 is rotated, each of the multiple grinding stones 20 revolves around the rotation axis 12a along a circular orbit (path) that is roughly parallel to the horizontal plane (XY plane).

The grinding unit 10 is connected to a moving unit (not shown) that moves the grinding unit 10 along the Z-axis direction. For example, the moving unit is configured with a ball screw type Z-axis moving mechanism that moves the grinding unit 10 along the Z-axis direction. In this case, the Z-axis moving mechanism includes a ball screw (not shown) arranged along the Z-axis direction, a pulse motor (not shown) that rotates the ball screw, and a nut portion (not shown) that is connected to the grinding unit 10 and into which the ball screw is screwed.

When the chuck table 4 is moved by the X-axis movement mechanism, the chuck table 4 and the grinding wheel 16 move relatively along the X-axis direction. Also, when the grinding unit 10 is raised and lowered by the Z-axis movement mechanism, the chuck table 4 and the grinding wheel 16 move relatively along the Z-axis direction.

A grinding fluid supply passage (not shown) for supplying liquid (grinding fluid) such as pure water is provided inside or near the grinding unit 10. When the workpiece is ground with the grinding wheel 16, the grinding fluid is supplied to the workpiece and the grinding wheel 20. This cools the workpiece and the grinding wheel 20 and washes away debris (grinding debris) generated by the grinding process.

The grinding device 2 also includes a controller (not shown) that controls the grinding device 2. The controller is connected to the components of the grinding device 2, and generates control signals that control the operation of each component. For example, the controller 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).

Figure 3 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, and a side surface (chamfered portion) 11c connected to the front surface 11a and the back surface 11b.

The workpiece 11 is chamfered by grinding the outer periphery of the workpiece 11 to make the side 11c curved. This chamfering removes the corners at the boundary between the front surface 11a and the side 11c and at the boundary between the back surface 11b and the side 11c, and shapes the side 11c into a curved (arc-shaped) surface extending from the front surface 11a to the back surface 11b. In other words, the side 11c corresponds to a curved chamfered portion that has been chamfered, and is curved toward the radial outside of the workpiece 11 (see FIG. 5(A) etc.).

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 regions divided by the streets 13.

The workpiece 11 has a substantially circular device region 17 on the surface 11a side, 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. 3, the imaginary boundary between the device region 17 and the peripheral surplus region 19 is shown by a dashed line.

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.

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.

Next, a specific example of a method for grinding a workpiece according to this embodiment will be described. FIG. 4 is a flowchart showing a method for processing a workpiece. In this embodiment, the workpiece 11 is thinned by grinding the back surface 11b side of the workpiece 11 using the grinding device 2.

First, the workpiece 11 is held by the chuck table 4 (holding step S1). FIG. 5(A) is a partially sectional side view showing the grinding device 2 in the holding step S1, and FIG. 5(B) is a perspective view showing the grinding device 2 in the holding step S1. Note that for simplification, the holding surface 4a of the chuck table 4 is shown flat in FIG. 5(A) (the same applies to FIG. 6(A) and subsequent figures). However, as mentioned above, the actual holding surface 4a is formed in a cone shape (see FIG. 2).

In the holding step S1, the workpiece 11 is placed on the chuck table 4 so that the front surface 11a faces the holding surface 4a and the back surface 11b is exposed upward. At this time, the workpiece 11 is positioned concentrically with the holding surface 4a so that the rotation axis 4c of the chuck table 4 passes through the center of the workpiece 11. In addition, the entire suction surface 8a (see Figure 1) of the chuck table 4 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 4a, the workpiece 11 is suction-held by the chuck table 4.

When the workpiece 11 is held by the chuck table 4, a protective member (not shown) may be fixed to the surface 11a of the workpiece 11. For example, a circular sheet formed to have roughly the same diameter as the workpiece 11 is used as the protective member. Specifically, the protective member includes a film-like substrate and an adhesive layer (glue) provided on the substrate. The substrate is made of a resin such as polyolefin, polyvinyl chloride, or polyethylene terephthalate, and 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 irradiation with ultraviolet light.

The protective member is fixed so as to cover the entire surface 11a side of the workpiece 11. As a result, the surface 11a side of the workpiece 11 and the device 15 (see FIG. 3) are protected by the protective member. The workpiece 11 is then held by the holding surface 4a of the chuck table 4 via the protective member.

Next, the workpiece 11 is ground with the grinding wheel 20 to form a recess in the workpiece 11 while leaving an unground area on the outer periphery of the workpiece 11 (recess formation step S2). Figure 6(A) is a partially sectional side view showing the grinding device 2 in the recess formation step S2, and Figure 6(B) is a perspective view showing the grinding device 2 in the recess formation step S2.

In the recess forming step S2, first, the positional relationship between the chuck table 4 and the grinding wheel 16 is adjusted. Specifically, the chuck table 4 is moved along the X-axis direction by a moving unit (not shown) and positioned so that the center of the workpiece 11 and the trajectory of the grinding wheel 20 overlap in the Z-axis direction.

The diameter of the orbit of the grinding wheels 20 is smaller than the radius of the workpiece 11. For example, the diameter of the orbit of the grinding wheels 20 is set to be approximately the same as the radius of the device region 17 (see FIG. 3) of the workpiece 11. Therefore, each of the multiple grinding wheels 20 is positioned so as to overlap with an area of the workpiece 11 that is radially inward of the outer periphery of the workpiece 11.

Next, while rotating the chuck table 4 and the grinding wheel 16, the chuck table 4 and the grinding wheel 16 are moved relatively along a direction parallel to the rotation axis 12a (Z-axis direction). As a result, the back surface 11b side of the workpiece 11 is ground by the grinding surface 20a of the grinding wheel 20, and a circular recess (groove) 21 is formed in the center of the back surface 11b side of the workpiece 11.

Specifically, first, the chuck table 4 is rotated around the rotation axis 4c, and the grinding wheel 16 is rotated around the rotation axis 12a. For example, the rotation speed of the chuck table 4 is set to 100 rpm or more and 300 rpm or less, and the rotation speed of the grinding wheel 16 (the rotation speed of the spindle 12) is set to 2000 rpm or more and 6000 rpm or less.

Next, the grinding unit 10 is lowered along the Z-axis direction by a moving unit (not shown). This causes the chuck table 4 and the grinding wheel 16 to move relatively along a direction parallel to the rotation axis 12a (Z-axis direction), bringing the workpiece 11 and the grinding wheel 20 closer together. The relative movement speed (processing feed speed) between the chuck table 4 and the grinding wheel 16 in the Z-axis direction is set to, for example, 0.1 μm/s or more and 5 μm/s or less.

When the grinding wheel 20 comes into contact with the workpiece 11, the grinding wheel 20 rotates to pass through the rotation axis 4c of the chuck table 4, 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 21 is formed in the center of the back surface 11b of the workpiece 11.

In addition, an annular unground area (convex portion) 23 remains on the outer periphery of the workpiece 11, which corresponds to an area that has not been subjected to grinding. The unground area 23 includes the outer periphery excess area 19 (see FIG. 3) and surrounds the device area 17 (see FIG. 3) and the concave portion 21. The width of the unground area 23 depends on the diameter of the orbit of the grinding wheel 20, and is, for example, 2 mm or less.

Then, when the depth of the recess 21 reaches a predetermined value and the thickness of the center of the workpiece 11 (device region 17, see FIG. 3) reaches a predetermined target value (finishing thickness), the descent of the grinding unit 10 is stopped. This completes the formation of the recess 21 by the grinding wheel 16. The recess 21 formed in the workpiece 11 includes a circular bottom surface 21a that is roughly parallel to the front surface 11a and back surface 11b of the workpiece 11, and an annular side surface (side wall, inner wall) 21b connected to the bottom surface 21a and back surface 11b. The diameter of the recess 21 is roughly the same as the diameter of the device region 17, and the recess 21 is formed to overlap multiple devices 15 (see FIG. 3).

As described above, in the recess formation step S2, the grinding wheel 20 does not come into contact with the outer periphery (unground area 23) of the workpiece 11, and the outer periphery of the workpiece 11 is not ground or thinned. Therefore, the outer periphery of the workpiece 11 that has been chamfered does not become sharply pointed (sharp edge shape) and remains thick. This makes it possible to prevent the outer periphery of the workpiece 11, which has become a sharp edge shape, from being pressed against the holding surface 4a by the grinding wheel 20, suppressing the occurrence of chipping or cracking in the outer periphery of the workpiece 11.

Next, the unground area 23 is ground with the grinding wheel 20 (slide grinding step S3). Figure 7(A) is a partially sectional side view showing the grinding device 2 in slide grinding step S3, and Figure 7(B) is a perspective view showing the grinding device 2 in slide grinding step S3.

In the slide grinding step S3, the chuck table 4 and the grinding wheel 16 are moved relatively along a direction intersecting the rotation axis 12a while maintaining the rotating state of the chuck table 4 and the grinding wheel 16. Specifically, the chuck table 4 is moved along the X-axis direction by a moving unit (not shown), thereby moving the chuck table 4 and the grinding wheel 16 relatively along the X-axis direction.

The direction of movement of the chuck table 4 is set so that the rotation axis 4c of the chuck table 4 moves away from the rotation axis 12a of the grinding wheel 16 and the outer periphery (side surface 11c) of the workpiece 11 approaches the grinding wheel 20. This causes the grinding wheel 16 to slide horizontally relative to the workpiece 11, and the side surface of the grinding wheel 20 is pressed against the side surface 21b (see Figures 6(A) and 6(B)) of the recess 21 formed in the workpiece 11. As a result, the unground area 23 (see Figures 6(A) and 6(B)) remaining in the workpiece 11 is ground from the side surface 21b of the recess toward the side surface 11c of the workpiece 11.

The rotation speeds of the chuck table 4 and the grinding wheel 16 may be the same as or different from those in the recess formation step S2. For example, the rotation speed of the chuck table 4 is set to 100 rpm or more and 300 rpm or less, and the rotation speed of the grinding wheel 16 (the rotation speed of the spindle 12) is set to 2000 rpm or more and 6000 rpm or less. In addition, the relative movement speed (processing feed speed) between the chuck table 4 and the grinding wheel 16 in the X-axis direction is set to, for example, 0.5 mm/s or more and 5 mm/s or less.

When the relative movement distance between the chuck table 4 and the grinding wheel 16 reaches the width of the unground area 23 (see Figures 6(A) and 6(B)), the unground area 23 is removed and the outer periphery of the workpiece 11 is thinned. As a result, as shown in Figures 7(A) and 7(B), the back surface 11b of the workpiece 11 becomes flat, and the overall thickness of the workpiece 11 becomes the finishing thickness.

As described above, in the slide grinding step S3, the grinding wheel 16 is slid horizontally relative to the workpiece 11 to remove the remaining unground area 23 surrounding the recess 21 by grinding it along the radial direction (XY plane direction) of the workpiece 11 rather than along the thickness direction (Z-axis direction). This makes it possible to avoid applying a large load to the outer periphery of the thinned workpiece 11 in the thickness direction of the workpiece 11 during the process of removing the unground area 23. As a result, the occurrence of chipping or cracking in the outer periphery of the workpiece 11 is suppressed, and damage to the outer periphery of the workpiece 11 can be avoided.

Then, the workpiece 11 is divided along the streets 13 (see FIG. 3) to separate the device regions 17 (see FIG. 3) of the workpiece 11, and a thin device chip equipped with a device 15 (see FIG. 3) is obtained. To divide the workpiece 11, various processing devices can be used, 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.

As described above, in the method for grinding a workpiece according to this embodiment, the workpiece 11 is ground with the grinding wheel 20 to form a recess 21 in the workpiece 11 while leaving an unground area 23 on the outer periphery of the workpiece 11, and then the unground area 23 is ground with the grinding wheel 20, thereby thinning the workpiece 11 while preventing damage to the outer periphery of the workpiece 11. This makes it possible to omit edge trimming, in which the outer periphery of the workpiece 11 is cut with a cutting blade, and simplifies the processing process for the workpiece 11.

In the above embodiment, an example has been described in which the recess forming step S2 and the slide grinding step S3 are each performed once to bring the thickness of the workpiece 11 to the finishing thickness. However, the workpiece 11 may be ground by performing the recess forming step S2 and the slide grinding step S3 multiple times. Specifically, after performing the recess forming step S2 and the slide grinding step S3 to grind the entire workpiece 11 to a predetermined amount, the recess forming step S2 and the slide grinding step S3 are further performed on the same workpiece 11. By repeating this operation, the workpiece 11 is thinned until it reaches the finishing thickness.

When the recess forming step S2 and the slide grinding step S3 are performed in multiple steps as described above, the height (volume) of the unground area 23 removed in one slide grinding step S3 is reduced. This reduces the load on the outer periphery of the workpiece 11 in the slide grinding step S3.

In the above embodiment, an example was described in which the chuck table 4 and the grinding wheel 16 are moved relatively along the horizontal direction (X-axis direction) in the slide grinding step S3. However, instead of the slide grinding step S3, a slide grinding step S3' may be performed in which the chuck table 4 and the grinding wheel 16 are moved relatively along a direction inclined with respect to the horizontal direction.

Figure 8 (A) is a partially sectional side view showing the grinding device 2 in the slide grinding step S3', and Figure 8 (B) is a perspective view showing the grinding device 2 in the slide grinding step S3'. The slide grinding step S3' corresponds to a modified example of the slide grinding step S3. In the slide grinding step S3', the grinding wheel 16 is moved relatively to the outer peripheral edge side (side surface 11c side) of the workpiece 11, while the grinding wheel 16 is moved relatively in a direction away from the bottom surface 21a of the recess 21.

Specifically, while the chuck table 4 and grinding wheel 16 are kept rotating, the chuck table 4 is moved along the X-axis direction by a moving unit (not shown), and the grinding unit 10 is raised along the Z-axis direction by a moving unit (not shown). This causes the chuck table 4 and the grinding wheel 16 to move relatively along the X-axis direction and the Z-axis direction, and the grinding wheel 16 to move diagonally upward relative to the chuck table 4. As a result, the grinding wheel 20 grinds the unground area 23 while moving away from the bottom surface 21a of the recess 21 (see Figures 6(A) and 6(B)).

The rotation speed of the chuck table 4 and the grinding wheel 16 and the relative movement speed (first processing feed speed) between the chuck table 4 and the grinding wheel 16 in the X-axis direction can be set in the same manner as in the slide grinding step S3. The relative movement speed (second processing feed speed) between the chuck table 4 and the grinding wheel 16 in the Z-axis direction is set to, for example, 0.1 μm/s or more and 5 μm/s or less. Furthermore, the relative movement distance between the chuck table 4 and the grinding wheel 16 in the Z-axis direction (the amount of lift of the grinding wheel 16) is set to, for example, 0.5 μm or more and 10 μm or less.

As described above, when the unground region 23 is ground while the grinding wheel 20 is spaced from the bottom surface 21a of the recess 21, the grinding wheel 20 does not come into contact with the bottom surface 21a of the recess 21 while the unground region 23 is being ground. This prevents numerous saw marks from being formed in random directions on the bottom surface 21a of the recess 21, and suppresses a decrease in the mechanical strength of the workpiece 11.

Furthermore, before the recess forming step S2, a pre-grinding step may be performed in which the workpiece 11 is ground to thin the entire workpiece 11. Figure 9(A) is a partially sectional side view showing the grinding device 2 in the pre-grinding step, and Figure 9(B) is a perspective view showing the grinding device 2 in the pre-grinding step.

For example, the grinding device 2 includes a grinding unit 30 in addition to the grinding unit 10 (see FIG. 1). The grinding unit 30 includes a spindle 32 and a wheel mount 34, and the spindle 32 rotates around a rotation axis 32a set along the Z-axis direction. The configurations and functions of the spindle 32 and the wheel mount 34 are similar to those of the spindle 12 and the wheel mount 14 of the grinding unit 10 (see FIG. 1). However, the diameter of the wheel mount 34 is larger than the diameter of the wheel mount 14.

A grinding wheel 36 is attached to the wheel mount 34. The grinding wheel 36 includes an annular wheel base 38 and a number of grinding wheels 40 fixed to the wheel base 38. The underside of the grinding wheels 40 forms a grinding surface 40a that grinds the workpiece 11. When the spindle 32 is rotated, the grinding wheel 36 rotates around the rotation axis 32a, and the multiple grinding wheels 40 each revolve along a circular orbit (path) centered on the rotation axis 32a.

The grinding wheel 36, wheel base 38, and grinding wheel 40 have the same configurations and functions as the grinding wheel 16, wheel base 18, and grinding wheel 20 (see FIG. 1), respectively. However, the diameter of the wheel base 38 is larger than the diameter of the wheel base 18, and the diameter of the orbit of the grinding wheel 40 is larger than the diameter of the orbit of the grinding wheel 20.

For example, the pre-grinding step is performed after the holding step S1 (see FIGS. 5(A) and 5(B)) and before the recess forming step S2 (see FIGS. 6(A) and 6(B)). That is, the workpiece 11 held by the chuck table 4 is ground by the grinding stone 40 of the grinding wheel 36.

In the pre-grinding step, first, the positional relationship between the chuck table 4 and the grinding wheel 36 is adjusted. Specifically, the chuck table 4 is moved along the X-axis direction by a moving unit (not shown) and positioned so that the center of the workpiece 11 and the orbit of the grinding wheel 40 overlap in the Z-axis direction. The diameter of the orbit of the grinding wheel 40 is set to be equal to or greater than the radius of the workpiece 11. Therefore, the multiple grinding wheels 40 are positioned so as to overlap an area on a circular arc extending from the center of the workpiece 11 to the outer periphery.

Next, while rotating the chuck table 4 and the grinding wheel 36, the chuck table 4 and the grinding wheel 36 are moved relative to each other along a direction parallel to the rotation axis 32a (Z-axis direction). As a result, the back surface 11b side of the workpiece 11 is ground by the grinding wheel 40.

Specifically, first, the chuck table 4 is rotated around the rotation axis 4c, and the grinding wheel 36 is rotated around the rotation axis 32a. Next, the grinding unit 30 is lowered along the Z-axis direction by a moving unit (not shown). As a result, the chuck table 4 and the grinding wheel 36 move relatively along a direction parallel to the rotation axis 32a (Z-axis direction), and the workpiece 11 and the grinding wheel 40 approach each other. Then, when the grinding wheel 40 comes into contact with the workpiece 11, the grinding wheel 40 rotates so as to pass through the rotation axis 4c of the chuck table 4, grinding the entire back surface 11b side of the workpiece 11. As a result, the entire workpiece 11 is thinned.

When the thickness of the workpiece 11 reaches a predetermined target value, the grinding unit 30 rises and the grinding wheel 40 moves away from the workpiece 11. This completes the grinding of the workpiece 11 by the grinding wheel 36. Note that the grinding of the workpiece 11 in the pre-grinding step is stopped before the outer periphery of the workpiece 11 has a sharp edge shape and cracks or chips occur on the outer periphery of the workpiece 11.

When the pre-grinding step is performed, the entire workpiece 11 is thinned. This reduces the amount of grinding of the central part of the workpiece 11 in the recess formation step S2 and the amount of grinding of the outer periphery of the workpiece 11 in the slide grinding step S3.

The grinding device 2 may be equipped with two or more chuck tables 4. In this case, the chuck table 4 that holds the workpiece 11 in the pre-grinding step and the chuck table 4 that holds the workpiece 11 in the recess forming step S2 and the slide grinding step S3 may be different chuck tables. The pre-grinding step may also be performed by another grinding device prepared separately from the grinding device 2. In the above case, the pre-grinding step is performed before the holding step S1.

In addition, the structures, methods, etc. relating to the above embodiments can be modified as appropriate without departing from the scope of the purpose of the present invention.

11 Workpiece 11a Surface (first surface)
11b Back side (second surface)
11c Side (chamfered portion)
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 Unground area (convex portion)
2 Grinding device 4 Chuck table (holding table)
4a Holding surface 4b Holding area 4c Rotation axis 6 Frame (main body)
6a Upper surface 6b Recess 6c Flow path 8 Holding member 8a Suction surface 10 Grinding unit 12 Spindle 12a Rotating shaft 14 Wheel mount 16 Grinding wheel 18 Wheel base 20 Grinding stone 20a Grinding surface 30 Grinding unit 32 Spindle 32a Rotating shaft 34 Wheel mount 36 Grinding wheel 38 Wheel base 40 Grinding stone 40a Grinding surface

Claims (4)

A method for grinding a workpiece having a chamfered outer periphery with a grinding wheel including a grinding stone, comprising:
A holding step of holding the workpiece on a chuck table;
a recess forming step in which, after the holding step, the chuck table and the grinding wheel are moved relatively along a direction parallel to the rotation axis of the grinding wheel while rotating the chuck table and the grinding wheel, thereby grinding the workpiece with the grinding wheel to form a recess in the workpiece while leaving an unground area on the outer periphery of the workpiece;
a slide grinding step of grinding the unground area with the grinding wheel by moving the chuck table and the grinding wheel relatively along a direction intersecting the rotation axis of the grinding wheel while rotating the chuck table and the grinding wheel after the recess forming step. The method for grinding a workpiece according to claim 1, further comprising a pre-grinding step of grinding the workpiece to thin the entire workpiece before the recess forming step. The method for grinding a workpiece according to claim 1 or 2, characterized in that in the slide grinding step, the grinding wheel is moved relatively toward the outer periphery of the workpiece while the grinding wheel is moved relatively away from the bottom surface of the recess. The method for grinding a workpiece according to claim 1 or 2, characterized in that the workpiece is ground by performing the recess forming step and the slide grinding step multiple times.

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