Grinding wheels and grinding methods for wafers

Abstract

This invention provides a grinding wheel and a grinding method for wafers. The grinding wheel includes: an annular base having a free end; and a plurality of segmented grinding tools, which are circumferentially separated and fixed to the free end of the annular base. The plurality of segmented grinding tools are divided into a plurality of grinding tool groups consisting of a predetermined number of segmented grinding tools. Each segmented grinding tool forming each grinding tool group has a rectangular shape with a long side and a short side on the grinding surface. Regarding the segmented grinding tools of the grinding tool group, from the outer peripheral side of the free end of the annular base toward the inner peripheral side, the long side of the segmented grinding tool is fixed sequentially by changing the inclination from the circumferential direction of the free end toward the diametrical direction.

Description

Technical Field

[0001] The present invention relates to a grinding wheel and a grinding method, wherein the grinding wheel is composed of an annular base and a plurality of segmented grinding tools disposed at the free end of the annular base, for grinding a wafer, and the grinding method uses the grinding wheel to grind the wafer. Background Technology

[0002] The wafer is divided into multiple devices such as ICs and LSIs by intersecting multiple predetermined dividing lines on the front side. After the back side of the wafer is ground to the desired thickness using a grinding device, the wafer is divided into individual device chips by a dicing device. The divided device chips are used in electronic devices such as mobile phones and personal computers.

[0003] The grinding apparatus generally consists of the following parts: a chuck stage for attracting and holding a wafer; a grinding unit for grinding the wafer held by the chuck stage; and a grinding water supply mechanism for supplying grinding water to the grinding wheels constituting the grinding unit. The grinding apparatus is capable of forming a wafer to a desired thickness (see, for example, Patent Document 1).

[0004] Patent Document 1: Japanese Patent Application Publication No. 2009-246098

[0005] In addition, such as Figure 7 As shown in (a) and (b), conventionally known grinding wheels 104 are mounted on a grinding wheel mount 103 formed at the lower end of a rotating shaft 102, and have a configuration in which multiple segmented grinding wheels 106 are arranged concentrically at the free end (lower end face) 105a of an annular base 105. Grinding is performed by positioning the segmented grinding wheels 106 of the grinding wheel, which rotates in the direction indicated by arrow R2, at the center O of a chuck table 110 rotating in the direction indicated by arrow R1, through a protective belt 122, to form the wafer 120 to the desired thickness. However, in conventional structures, since all the segmented grinding wheels 106 always pass through the center O of the wafer 120, therefore, as Figure 7 As shown in (c), for example, the central region 124 (approximately 30 mm in diameter) of a wafer 120 with a diameter of 100 mm is ground slightly more (about 1 μm to 2 μm) than the outer peripheral region 126, resulting in a tendency for the central region 124 to be processed thinner than the outer peripheral region 126. This thickness deviation becomes particularly noticeable when the finished thickness of the wafer 120 is less than 50 μm. Furthermore, Figure 7 (b) is a view of the annular base 104 from the free end 105a side, i.e. the lower end face side, and the position of the wafer 120 being ground is shown together using double dotted lines. Summary of the Invention

[0006] Therefore, the object of the present invention is to provide a grinding wheel capable of reducing thickness deviation and a grinding method for wafers.

[0007] According to one aspect of the present invention, a grinding wheel is provided, comprising: an annular base having a free end; and a plurality of segmented grinding tools, which are fixed separately from each other in the circumferential direction to the free end of the annular base. The plurality of segmented grinding tools are divided into a plurality of grinding tool groups consisting of a predetermined number of segmented grinding tools. Each segmented grinding tool forming each grinding tool group has a rectangular shape with a long side and a short side on the grinding surface. With respect to the segmented grinding tools of the grinding tool group, the long side of the segmented grinding tool is fixed sequentially from the outer circumferential side of the free end of the annular base toward the inner circumferential side by changing the inclination from the circumferential direction of the free end toward the diametrical direction.

[0008] According to another aspect of the present invention, a method for grinding a wafer is provided, using a grinding wheel having: an annular base having a free end; and a plurality of segmented grinding tools, which are circumferentially separated and fixed to the free end of the annular base. The plurality of segmented grinding tools are divided into a plurality of grinding tool groups consisting of a predetermined number of segmented grinding tools. Each segmented grinding tool forming each grinding tool group has a rectangular shape with a long side and a short side on the grinding surface. Regarding the segmented grinding tools of the grinding tool group, from the outer circumferential side of the free end of the annular base toward the inner circumferential side, the long side of the segmented grinding tool is fixed sequentially by changing the inclination from the circumferential direction of the free end toward the diametrical direction. The wafer grinding method includes the following step: holding... The process involves: positioning the center of the wafer at the rotation center of a rotatable chuck table and holding the wafer using the chuck table; positioning the grinding wheel so that it rotates from the outer peripheral segment of the same grinding wheel group toward the inner peripheral segment, and the outermost segment passes through the center of the wafer, wherein the long side of the outer peripheral segment is arranged in the circumferential direction and the long side of the inner peripheral segment is arranged in the diametrical direction; and grinding, after the positioning process, bringing the segment of the rotating grinding wheel into contact with the wafer held by the rotating chuck table, and grinding the wafer while providing grinding water from the center of the grinding wheel.

[0009] According to the grinding wheel of the present invention, the segmented grinding wheel that limits the passage of the wafer through the center during grinding can suppress the tendency of the central region of the wafer to be processed thinner than the outer peripheral region, and eliminate the problem of thickness deviation that cannot be ignored as the finished thickness of the wafer becomes less than 50 μm.

[0010] The wafer grinding method according to the present invention can suppress the tendency for the central region of the wafer to be processed thinner than the outer peripheral region, eliminating the problem of non-negligible thickness deviation as the finished wafer thickness becomes less than 50 μm. Furthermore, since the grinding wheel assembly is configured in an impeller-like structure, if grinding water is supplied from the center of the grinding wheel, the assembly functions like a centrifugal pump, efficiently discharging the grinding water outwards and improving grinding efficiency. Attached Figure Description

[0011] Figure 1 This is an overall perspective view of the grinding apparatus according to an embodiment of the present invention.

[0012] Figure 2 (a) is a perspective view of the grinding wheel according to this embodiment. Figure 2 (b) is Figure 2 (a) is a plan view of the grinding wheel as seen from the lower surface. Figure 2 (c) is Figure 2 (b) is an enlarged view of region A.

[0013] Figure 3 It is a perspective view showing the wafer as the workpiece, the protective tape, and the bonding method.

[0014] Figure 4 This is a perspective view illustrating an embodiment of the holding process of this embodiment.

[0015] Figure 5 This is a perspective view illustrating an embodiment of the positioning process of this embodiment.

[0016] Figure 6 (a) is a perspective view showing an embodiment of the grinding process of this embodiment. Figure 6 (b) is a plan view obtained by observing the grinding wheel during the grinding process from the lower surface side.

[0017] Figure 7 (a) is a perspective view showing an embodiment of a grinding process performed using a conventional grinding wheel. Figure 7 (b) is a plan view obtained from the lower surface of the grinding wheel during a previous grinding process. Figure 7 (c) is a cross-sectional view of a wafer that has undergone conventional grinding processes.

[0018] Label Explanation

[0019] 1: Grinding device; 2: Device housing; 3: Wall; 4: Grinding unit; 41: Motor; 42: Rotary shaft; 42a: Upper end; 43: Grinding wheel mounting base; 44: Grinding wheel; 45: Annular base; 45a: Upper surface; 45b: Threaded hole; 45c: Free end (lower surface); 46, 46a~46h: Segmented grinding wheel; 50: Grinding wheel assembly; 5: Lifting mechanism; 6: Worktable unit 61: Chuck worktable; 61a: Adsorption chuck; 61b: Frame; 62: Cover plate; 10: Wafer; 12: Device; 14: Segmentation pre-line; 102: Rotary shaft; 103: Grinding wheel mounting base; 104: Grinding wheel; 105: Annular base; 105a: Free end; 106: Segmented grinding wheel; 120: Wafer; 124: Central area; 126: Outer peripheral area; T: Protective belt. Detailed Implementation

[0020] Hereinafter, with reference to the accompanying drawings, the grinding wheel of the present invention and the grinding method of the wafer performed using the grinding wheel will be described in detail.

[0021] Figure 1 The figure shows an overall perspective view of a grinding apparatus 1 employing the grinding wheel of this embodiment. The grinding apparatus 1 includes: an apparatus housing 2; a wall portion 3, which is vertically disposed on the apparatus housing 2; a grinding unit 4, which performs grinding processing on a workpiece; a lifting mechanism 5, which is disposed on the front surface of the wall portion 3 to lift the grinding unit 4; and a worktable unit 6, which has a chuck worktable 61 for holding the workpiece.

[0022] The grinding unit 4 includes: a rotating shaft 42 driven to rotate by a motor 41; a grinding wheel mounting base 43 disposed at the lower end of the rotating shaft 42; and a grinding wheel 44 mounted on the lower surface of the grinding wheel mounting base 43. Grinding water L supplied from a grinding water supply mechanism (not shown) is introduced from the upper end 42a of the rotating shaft 42 and supplied to the center portion of the free end side of the grinding wheel 44 via the rotating shaft 42.

[0023] The worktable unit 6 has a chuck worktable 61 and a cover plate 62. As shown, the chuck worktable 61 has a circular plate-shaped suction chuck 61a and a frame 61b surrounding the suction chuck 61a. The chuck worktable 61 is configured to rotate via a rotary drive source (not shown). The cover plate 62 causes the chuck worktable 61 to protrude upwards and covers its circumference. The worktable unit 6 is held within a movable base (not shown) housed in the device housing 2 and has a loading / unloading area (…). Figure 1 The chuck table 61 is positioned in the area where it moves in the direction indicated by arrow Y to move the workpiece in and out; and the moving unit (not shown) positions the chuck table 61 in the grinding area below the grinding unit 4.

[0024] Figure 2 The image shows the grinding wheel 44 of this embodiment, removed from the grinding wheel mounting base 43 of the aforementioned grinding unit 4. (See image for reference.) Figure 2 As shown in (a), the grinding wheel 44 has an annular base 45 and a plurality of segmented grinding tools 46. A threaded hole 45b is formed on the upper surface 45a of the annular base 45 for use when mounted on the grinding wheel mounting seat 43, and a plurality of segmented grinding tools 46 are disposed on the lower end face 45c of the annular base 45. Figure 2 (b) shows a plan view of the state as seen from the free end 45c side of the annular base 45. Figure 2 (c) shows Figure 2 (b) is an enlarged view of a portion of region A.

[0025] In this embodiment, such as Figure 2 (b) Figure 2 As shown in (c), a grinding wheel assembly 50 is formed in the circumferential direction of the free end 45c (indicated by arrow D1), consisting of eight segmented grinding wheels 46a to 46h arranged in an impeller-like manner. The same grinding wheel assembly 50 is arranged in the circumferential direction on the free end 45c of the annular base 45.

[0026] like Figure 2 As shown in (c), the segmented grinding wheels 46a to 46h are rectangular in shape with short sides 461 and long sides 462 on the grinding surface. They are arranged such that, depending on the direction of rotation of the grinding wheel 44 during grinding (which is the same direction as the circumferential direction D1 shown in the figure), the position of the segmented grinding wheels 46a to 46h changes from the outer periphery of the free end 45c of the annular base 45 towards the inner periphery. Furthermore, the orientation of the long side 462 of each segmented grinding wheel gradually changes its inclination from the direction along the circumferential direction D1 to the direction along the diametrical direction D2, which is perpendicular to the circumferential direction D1. Thus, when the grinding wheel assembly 50 composed of the segmented grinding wheels 46a to 46h is considered as a single unit, it has a so-called impeller shape, as shown by the single-dot dashed line.

[0027] The grinding apparatus 1 of this embodiment generally has the structure described above. The effects of the grinding wheel 44 and the grinding method of the wafer using the grinding wheel 44 will be described below.

[0028] First, when implementing the wafer grinding method of this embodiment, such as Figure 3 As shown, a wafer 10 is prepared as the workpiece. The wafer 10 is, for example, a silicon wafer with a diameter of 100 mm, on which a plurality of devices 12 are formed by dividing a predetermined dividing line 14. If such a wafer 10 is prepared, as shown, a protective tape T is attached to the front side 10a to form a single unit.

[0029] After preparing the chip 10 as described above, the chip 10 is then placed according to... Figure 1 The grinding device 1, as described, is conveyed, such as... Figure 4 As shown, with the back side 10b of the wafer 10 facing upward and the protective strip T facing downward, the center O2 of the wafer 10 is positioned at the rotation center O1 of the chuck stage 61 for loading and holding (holding process).

[0030] Next, as Figure 5 As shown, starting from the segmented grinding tool 46a side, which is arranged along the circumferential direction D1 with its long side 462, the segmented grinding tool 46h side, which is arranged along the diametrical direction D2 with its long side 462 (also refer to...) Figure 2 (b) In the direction indicated by arrow R3 in the figure, the grinding wheel 44 is rotated and the moving unit (not shown) is activated to move the chuck table 61, positioning the grinding wheel 44 so that the segmented grinding tool 46a disposed on the outer periphery passes through the center O2 of the wafer 10 (positioning process).

[0031] Next, as Figure 6 As shown in (a), the chuck table 61 is rotated in the direction indicated by R4, and according to Figure 1 The lifting mechanism 5, as described above, operates to lower the grinding unit 4 in the direction indicated by arrow R5, bringing the grinding wheel 44's grinding wheel assembly 50 into contact with the back surface 10b of the wafer 10 for grinding. The thickness is measured using a thickness detection unit (not shown) and ground to the desired thickness (e.g., 50 μm). At this time, as... Figure 6 As shown in (b), a grinding water supply hole 42b, which serves as the lower end of the rotation shaft 42, is provided at the center of the free end 45c of the grinding wheel 44. Grinding water L is supplied from this grinding water supply hole 42b. The grinding water L is guided by centrifugal force to the grinding processing section (grinding process) where the grinding wheel assembly 50, composed of segmented grinding wheels 46, contacts the back surface 10b of the wafer 10.

[0032] In the above grinding process, from Figure 6As can be seen from (b), among the segmented grinding wheels 46a to 46h constituting the grinding wheel assembly 50 disposed on the annular base 45 of the grinding wheel 44, only the segmented grinding wheel 46a disposed on the outermost peripheral side passes through the center O2 of the wafer 10, while the segmented grinding wheels 46b to 46h disposed at other positions (the inner peripheral side of the annular base 45) are restricted from passing through the center O2 of the wafer 10. This prevents the central region of the back surface 10b of the wafer 10 from being processed thinner than the outer peripheral region, thereby eliminating the problem of non-negligible thickness deviation as the finished thickness of the wafer 10 becomes less than 50 μm. Furthermore, as described above, the present invention is not limited to allowing only the segmented grinding wheel 46a disposed on the outermost peripheral side of the segmented grinding wheels 46a to 46h to pass through the center O2 of the wafer 10; in addition to the segmented grinding wheel 46a, the segmented grinding wheels 46b disposed at adjacent positions may also pass through the center O2 of the wafer 10. In this invention, it is important that not all of the multiple segmented grinding tools 46a to 46h forming the grinding tool group 50 pass through the center O2 of the wafer 10, but only a portion of the segmented grinding tools pass through the center O2 of the wafer 10.

[0033] Furthermore, as described above, the grinding wheel assembly 50 of this embodiment is integrally formed in an impeller shape using multiple segmented grinding wheels 46a to 46h, and multiple segments are arranged in the circumferential direction. By having this structure, such as Figure 6 As shown in (b), the grinding water L supplied from the center of the grinding wheel 44 of the grinding unit 4 is guided to the grinding processing part on the outer periphery by centrifugal force. The multiple grinding wheel groups 50, which are in the shape of impellers, function like a centrifugal pump and can efficiently discharge the grinding water L from the inside to the outside of the grinding wheel 44, thereby improving the grinding efficiency.

Claims

1. A grinding wheel, wherein the grinding wheel has: a ring-shaped base having a free end; and a plurality of segmental grinding tools fixed on the free end of the ring-shaped base separately from each other in a circumferential direction, the plurality of segmental grinding tools are divided into a plurality of grinding tool groups each of which is composed of a prescribed number of segmental grinding tools, each of the segmental grinding tools forming each of the grinding tool groups has a rectangular shape having a long side and a short side on a grinding surface, with respect to the segmental grinding tools of the grinding tool group, the long side of the segmental grinding tools is sequentially fixed with a change in inclination from a circumferential direction of the free end to a diametrical direction toward an inner peripheral side from an outer peripheral side of the free end, the segmental grinding tool closest to the outer peripheral side of the free end in the grinding tool group extends along the circumferential direction, and the segmental grinding tool closest to the inner peripheral side of the free end in the grinding tool group extends along the diametrical direction perpendicular to the circumferential direction.

2. A grinding method of a wafer using a grinding wheel, wherein the grinding wheel has: a ring-shaped base having a free end; and a plurality of segmental grinding tools fixed on the free end of the ring-shaped base separately from each other in a circumferential direction, the plurality of segmental grinding tools are divided into a plurality of grinding tool groups each of which is composed of a prescribed number of segmental grinding tools, each of the segmental grinding tools forming each of the grinding tool groups has a rectangular shape having a long side and a short side on a grinding surface, with respect to the segmental grinding tools of the grinding tool group, the long side of the segmental grinding tools is sequentially fixed with a change in inclination from a circumferential direction of the free end to a diametrical direction toward an inner peripheral side from an outer peripheral side of the free end, the segmental grinding tool closest to the outer peripheral side of the free end in the grinding tool group extends along the circumferential direction, and the segmental grinding tool closest to the inner peripheral side of the free end in the grinding tool group extends along the diametrical direction perpendicular to the circumferential direction, wherein the grinding method of the wafer has: a holding step of positioning a center of a wafer at a rotation center of a rotatable chuck table and holding the wafer by the chuck table; a positioning step of positioning the grinding wheel so that the grinding wheel rotates in a direction from the segmental grinding tool of the outer peripheral side toward the segmental grinding tool of the inner peripheral side in the same grinding tool group, and the segmental grinding tool of the outermost peripheral side passes through the center of the wafer, in which the long side of the segmental grinding tool of the outer peripheral side is disposed in the circumferential direction, and the long side of the segmental grinding tool of the inner peripheral side is disposed in the diametrical direction; and a grinding step of bringing the segmental grinding tool of the rotating grinding wheel into contact with the wafer held by the rotating chuck table after the positioning step is performed, and grinding the wafer while supplying grinding water from a central portion of the grinding wheel.

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