Method for grinding a workpiece

Abstract

Provided is a grinding method of a workpiece that suppresses occurrence of grinding defects in grinding of a workpiece in which a ring-shaped reinforcing portion is formed on the back surface side of the workpiece. The grinding method of the workpiece grinds a prescribed region corresponding to a device region in the back surface side of the workpiece having the device region and a peripheral remaining region surrounding the device region, to form a circular-plate-shaped recess and a ring-shaped reinforcing portion surrounding the recess, and has the steps of: grinding the prescribed region while feeding a grinding unit in grinding while rotating a main shaft without rotating a chuck table holding the workpiece, thereby forming a groove on the back surface side of the workpiece; starting rotation of the chuck table while keeping the state of rotating the main shaft, thereby grinding a side wall of the groove to remove the groove; and grinding the prescribed region while feeding the grinding unit in grinding while rotating the main shaft and the chuck table, thereby forming the recess and the ring-shaped reinforcing portion.

Description

Technical Field

[0001] The present invention relates to a grinding method for a workpiece, wherein a predetermined area corresponding to the device area on the back side of the workpiece having a device area on the front side and a peripheral remaining area surrounding the device area is ground to form a circular plate-shaped recess and an annular reinforcing portion surrounding the recess. Background Technology

[0002] In order to make the device chips used in electronic devices lighter and thinner, grinding equipment is sometimes used to grind the wafer (workpiece) on the front side with multiple devices formed thereon, for example, to thin the workpiece to less than 100μm.

[0003] However, when the workpiece is too thin, it becomes difficult to transport the thinned workpiece. Therefore, a grinding method is known in which a predetermined area on the back side of the workpiece, corresponding to the device area on the front side where multiple devices are formed, is ground to form a circular plate-shaped recess and an annular reinforcing portion surrounding the recess (for example, see Patent Document 1).

[0004] This grinding method is called TAIKO (registered trademark). By forming a ring-shaped reinforcing portion on the outer periphery of the workpiece, warping of the workpiece can be reduced compared to a workpiece that is uniformly thinned on the back side, and the strength of the workpiece can be improved. In addition, it can suppress chipping of the workpiece starting from the outer periphery.

[0005] To form the annular reinforcing section, a grinding wheel with an outer diameter smaller than that of the workpiece is used. The grinding wheel has an annular grinding wheel base, and multiple grinding tools in various segments are fixed along the circumference of the grinding wheel base on one side of the grinding wheel base.

[0006] Compared to conventional grinding wheels used for uniform grinding of the entire back side, this grinding wheel has a smaller diameter and requires fewer grinding tools. Furthermore, because the circumferential speed during grinding is slower than that of conventional grinding wheels, the workload of each grinding tool is increased compared to that of each grinding tool in a conventional grinding wheel.

[0007] Therefore, compared to grinding wheels in conventional grinding, grinding wheels have a lower grinding capacity, which can easily lead to defects such as flattening, voids, and clogging. For example, when a hard oxide film forms on the back side of the workpiece, grinding defects are more likely to occur, accompanied by a decrease in grinding capacity.

[0008] Patent Document 1: Japanese Patent Application Publication No. 2007-19461 Summary of the Invention

[0009] The present invention was made in view of this problem, and its object is to provide a grinding method that can suppress the occurrence of grinding defects in grinding a ring-shaped reinforcing portion formed on the back side of the workpiece.

[0010] According to one aspect of the present invention, a grinding method for a workpiece is provided, the grinding method using a grinding apparatus comprising: a chuck table for holding the workpiece, and a grinding unit including a spindle, the grinding unit grinding the workpiece held by the chuck table while a grinding wheel having a plurality of grinding tools arranged in a ring is mounted on the spindle and the grinding wheel rotates about the spindle. The grinding method uses the grinding apparatus to grind a predetermined area on the back side of the workpiece corresponding to the device area, which has a device area on the front side having a plurality of devices formed thereon and a remaining area around the device area, using the grinding wheel to form a circular plate-shaped recess and an annular reinforcing portion surrounding the recess. The method comprises the following steps: a groove forming step, in which, without rotating the chuck table holding the workpiece, the grinding unit is fed while rotating the spindle to grind a predetermined area, thereby forming an arc-shaped or annular groove with a depth not reaching the finished thickness on the back side of the workpiece; a groove removal step, after the groove forming step, in which, while keeping the spindle rotated, the chuck table is started to rotate, thereby grinding the sidewall of the groove and removing the groove from the workpiece; and a recess forming step, after the groove removal step, in which, while rotating the spindle and the chuck table, the grinding unit is fed to grind, thereby grinding the predetermined area corresponding to the device area to form the recess, and forming an annular reinforcing portion surrounding the recess.

[0011] Preferably, during the groove removal step, the chuck table is rotated while the grinding unit is being fed through the grinding process.

[0012] In one aspect of the workpiece grinding method of the present invention, the workpiece is ground by rotating the spindle while the grinding unit is fed to grind without rotating the chuck table holding the workpiece, thereby forming an arc-shaped or annular groove with a depth that does not reach the finished thickness on the back side of the workpiece (groove forming step).

[0013] After the groove forming step, while keeping the spindle rotating, the chuck table is rotated to grind the sidewalls of the groove, removing the groove from the workpiece (groove removal step). Following the groove removal step, while rotating the spindle and chuck table, the grinding unit performs a grinding feed, grinding a predetermined area corresponding to the device area to form a recess, and forming a ring-shaped reinforcing portion around the recess (recess forming step).

[0014] In the groove forming step, grinding is mainly performed using the bottom surface of the grinding wheel. However, in the groove removal step, grinding can be performed mainly using the side surface of the grinding wheel. Therefore, in the groove removal step, compared to the case where grinding is performed mainly using the bottom surface of the grinding wheel to grind the entire back side of the workpiece, the deterioration of the bottom surface of the grinding wheel (i.e., the reduction in grinding capability) can be reduced.

[0015] Furthermore, in the recess forming step following the groove removal step, a predetermined area on the back side of the workpiece after the groove removal is ground. In the recess forming step, grinding is primarily performed using the bottom surface of the grinding wheel, and in particular, grinding is performed while minimizing the deterioration of the bottom surface of the grinding wheel. Therefore, even when a relatively hard oxide film is formed on the back side of the workpiece, the occurrence of grinding defects can be suppressed. Attached Figure Description

[0016] Figure 1 It is a three-dimensional view of the workpiece, etc.

[0017] Figure 2 This is a flowchart of the grinding method.

[0018] Figure 3 This is a partial cross-sectional side view showing the groove forming steps.

[0019] Figure 4 (A) is a top view of the workpiece, etc., during the groove forming step. Figure 4 (B) is a top view of the workpiece, showing the groove formed by the groove forming step.

[0020] Figure 5 This is a partial cross-sectional side view showing the groove removal process.

[0021] Figure 6 This is a top view of the workpiece or similar material during the grooving process.

[0022] Figure 7 This is a partial cross-sectional side view showing the steps involved in forming the recess.

[0023] Figure 8 It is a cross-sectional view of the workpiece after grinding.

[0024] Figure 9 This is a top view of the workpiece, showing the groove formed by the groove forming step of the second embodiment.

[0025] Label Explanation

[0026] 2: Grinding device; 4: Chuck table; 4a: Holding surface; 4b: Rotation axis; 6: Grinding unit; 8: Spindle; 10: Mounting base; 11: Workpiece; 11a: Front side; 11b: Back side; 11b1: Center; 11c: Recess; 11d: Annular reinforcement; 11e: Groove; 11e1: Inner peripheral sidewall; 11e2: Outer peripheral sidewall; 11f: Finished thickness; 12: Grinding wheel; 14: Grinding wheel base; 16: Grinding tool; 13: Pre-defined dividing line; 15: Device; 17a: Device area; 17b: Remaining outer peripheral area; 17c: Boundary area; 17d: Defined area; 19: Protective strip; 21: Workpiece unit. Detailed Implementation

[0027] An embodiment of one aspect of the present invention will be described with reference to the accompanying drawings. First, referring to... Figure 1 The workpiece 11 that is the object of grinding in the first embodiment will be described. Figure 1 It is a three-dimensional view of the workpiece 11, etc.

[0028] The workpiece 11 in this embodiment is a circular silicon wafer with a predetermined diameter (e.g., about 200 mm). The workpiece 11 has a front side 11a and a back side 11b, and the length from the front side 11a to the back side 11b (i.e., the thickness of the workpiece 11) is a predetermined value of 200 μm or more and 800 μm or less (e.g., 725 μm).

[0029] Formed on the entire back side 11b with A thermal oxide film of varying thickness (not shown). Multiple pre-defined dividing lines 13 are arranged in a grid pattern on the front side 11a. Devices such as ICs (Integrated Circuits) are formed on the front side 11a of the rectangular area divided by the multiple pre-defined dividing lines 13.

[0030] Furthermore, there are no restrictions on the type, material, size, shape, or structure of the workpiece 11. The workpiece 11 can also be a wafer or substrate formed from compound semiconductors other than silicon (GaN, SiC, etc.), glass, ceramics, resin, metal, etc. Additionally, there are no restrictions on the type, number, shape, structure, size, or arrangement of the devices 15 formed on the workpiece 11.

[0031] In the top view, in a manner surrounding the device region 17a on which multiple devices 15 are formed, there is a generally flat, annular peripheral residual region 17b around the device region 17a on which no devices 15 are formed.

[0032] Before grinding the workpiece 11, a circular protective strip 19 made of resin is attached to the front side 11a to reduce damage to the device 15 during grinding. Thus, a workpiece unit 21 is formed by stacking the workpiece 11 and the protective strip 19.

[0033] During the grinding of the workpiece 11, the designated area 17d (refer to) on the back side 11b that corresponds to the device area 17a is ground. Figure 8 Grinding to the specified depth. Therefore, as... Figure 8 As shown, a circular plate-shaped recess 11c and an annular reinforcing portion 11d surrounding the side of the recess 11c are formed.

[0034] Next, refer to Figure 3 The grinding apparatus 2 used for grinding the workpiece 11 will be described. Figure 3 The +Z and -Z directions shown are parallel to the Z-axis and opposite to each other. For example, the +Z direction is the up direction, and the -Z direction is the down direction.

[0035] In addition, such as Figure 3 as well as Figure 4 As shown, the +X and -X directions are opposite directions to the X-axis direction, which is perpendicular to the Z-axis direction. Similarly, the +Y and -Y directions are opposite directions to the Y-axis direction, which is perpendicular to both the Z-axis and X-axis directions. For example, the XY plane is parallel to the horizontal plane.

[0036] like Figure 3 As shown, the grinding apparatus 2 has a circular chuck table 4 that attracts and holds the front side 11a of the workpiece 11. The chuck table 4 has a circular frame made of ceramic.

[0037] A circular plate-shaped recess (not shown) is formed in the center of the frame. A defined flow path (not shown) is formed inside the frame. One end of the defined flow path is exposed in the recess, and an suction source such as an injector (not shown) is connected to the other end of the defined flow path.

[0038] A porous plate (not shown) made of porous ceramic is fixed in the recess of the frame. Negative pressure from the suction source is transmitted to the upper surface of the porous plate. The upper surface of the porous plate is flush with the upper surface of the frame, and functions as a holding surface 4a for attracting and holding the workpiece 11.

[0039] In addition, the annular region between the outer peripheral end and the center of the retaining surface 4a is more concave than the outer peripheral end and the center of the retaining surface 4a. In a cross-sectional view of the chuck table 4 along the radial direction of the retaining surface 4a, this annular region has a so-called double concave shape.

[0040] However, the depth of the depression is, for example, about 1 μm to 20 μm, therefore in Figure 3 In the illustration, for convenience, the retaining surface 4a is shown as approximately flat. In the following figures, for convenience, the retaining surface 4a will also be shown as approximately flat.

[0041] The chuck table 4 can be rotated around a predetermined axis of rotation 4b (see reference) by a rotary drive source (not shown) such as an electric motor located at the bottom. Figure 5 Rotation. The rotation axis 4b is tilted at a specified angle relative to the Z-axis direction in the XZ plane so that the outer peripheral end of the holding surface 4a on the +X direction side is slightly higher than the outer peripheral end of the holding surface 4a on the -X direction side.

[0042] return Figure 3 The other components of the grinding apparatus 2 will be described below. A grinding unit 6 is positioned above the chuck table 4. The grinding unit 6 has a cylindrical spindle housing (not shown).

[0043] A ball screw-type grinding feed mechanism (not shown) is connected to the spindle housing to move the grinding unit 6 along the Z-axis. A portion of the cylindrical spindle 8 is rotatably held within the spindle housing.

[0044] In this embodiment, the spindle 8 is arranged approximately parallel to the Z-axis. A rotation drive source such as an electric motor (not shown) is provided at the upper end of the spindle 8, and a circular plate-shaped mounting base 10 is fixed at the lower end of the spindle 8.

[0045] A circular grinding wheel 12 is mounted on the lower surface of the mounting base 10. The grinding wheel 12 has a ring-shaped grinding wheel base 14 formed of a metal such as aluminum alloy. The upper surface of the grinding wheel base 14 is fixed to the lower surface of the mounting base 10.

[0046] In this way, the grinding wheel 12 mounted on the spindle 8 can rotate around the spindle 8. On the lower surface of the grinding wheel base 14, a plurality of segmented grinding tools 16 are arranged in a ring around the circumference of the grinding wheel base 14.

[0047] Furthermore, the outer diameter of the region formed by the paths of multiple grinding wheels 16 is approximately half the diameter of the back surface 11b. Next, the grinding method for the workpiece 11 using the grinding apparatus 2 will be described. Figure 2 This is a flowchart of the grinding method.

[0048] First, such as Figure 3As shown, the workpiece 11 is held by the retaining surface 4a through the protective band 19, attracting and holding the front side 11a of the workpiece 11. At this time, the workpiece 11 is deformed according to the shape of the retaining surface 4a (holding step S10). After the holding step S10, the groove forming step S20 is performed.

[0049] In the groove forming step S20, while the chuck table 4 holding the workpiece 11 is not rotated (i.e., stationary), the grinding unit 6 is fed along the Z-axis while the spindle 8 is rotated at a specified speed.

[0050] In this embodiment, the specified rotational speed of the spindle 8 is set to 4000 rpm, and the grinding feed rate is set to 3.0 μm / s. Figure 3 This is a partial cross-sectional side view showing the groove forming step S20. Furthermore, in Figure 3 In subsequent drawings, the protective strip 19 has been omitted for convenience.

[0051] Figure 4 (A) is a top view of the workpiece 11, etc., in the groove forming step S20. Figure 4 In (A), the boundary region 17c on the back side 11b, corresponding to the boundary between the device region 17a and the remaining peripheral region 17b, is indicated by a dashed line. The region inside this boundary region 17c is designated as the region 17d as described above.

[0052] In the groove forming step S20 of this embodiment, the area corresponding to the moving trajectory of the grinding tool 16 in the defined area 17d on the back surface 11b side is ground to form an annular groove 11e passing through the center 11b1 of the back surface 11b. Figure 4 (B) is a top view of the workpiece 11, showing the groove 11e formed by the groove forming step S20.

[0053] The trench 11e formed by trench forming step S20 has a greater thickness than the oxide film formed on the back side 11b and does not reach the finished thickness 11f of the device region 17a (see reference). Figure 8 The depth specified in the regulations.

[0054] For example, the oxide film is 0.2 μm to 0.3 μm. When the grinding feed rate is 3.0 μm / s, after grinding for 1 second after the lower surface of the grinding wheel 16 contacts the back surface 11b, the grinding wheel 16 breaks through the oxide film and forms a groove 11e, with a depth of 3.0 μm to the deepest bottom of the groove 11e.

[0055] Furthermore, since the finished thickness 11f is, for example, 100 μm, the depth of the groove 11e does not reach the finished thickness 11f. After the groove forming step S20, the chuck table 4 is started to rotate while the spindle 8 is kept rotating at a specified speed (groove removal step S30).

[0056] In the groove removal step S30, as Figure 5 and Figure 6 As shown, the groove 11e is removed from the workpiece 11 by grinding the inner peripheral sidewall 11e1 and the outer peripheral sidewall 11e2 of the groove 11e.

[0057] In the groove removal step S30, for example, the chuck table 4 is started to rotate and eventually set to 300 rpm. In the groove removal step S30 of this embodiment, the chuck table 4 is rotated while the grinding unit 6 is fed downward at a speed of 3.0 μm / s, but the chuck table 4 may also be rotated without grinding feed.

[0058] Figure 5 This is a partial cross-sectional side view showing the groove removal step S30. Figure 6 This is a top view of the workpiece 11, etc., in the groove removal step S30. Figure 6 In the diagram, arrows schematically show the grinding of the inner peripheral sidewall 11e1 and the outer peripheral sidewall 11e2 of the groove 11e.

[0059] In the groove forming step S20, grinding is mainly performed using the bottom surface of the grinding tool 16. In contrast, in the groove removal step S30, grinding is mainly performed using the sides (inner and outer circumferential sides) of the grinding tool 16.

[0060] Therefore, in the groove removal step S30, compared with the case where the bottom surface of the grinding wheel 16 is ground as a whole on the back surface 11b side, the deterioration of the bottom surface of the grinding wheel 16 (i.e., the reduction of grinding capability) can be reduced.

[0061] Furthermore, in this embodiment, by performing the groove removal step S30, both the inner and outer peripheral surfaces of the grinding wheel 16 can be used to grind the specified area 17d. Therefore, compared to the case where only one of the inner and outer peripheral surfaces of the grinding wheel 16 is used for grinding in the groove removal step S30, the load on the sides of the grinding wheel 16 can be reduced.

[0062] After the groove removal step S30, the grinding unit 6 is then fed while the spindle 8 and the chuck table 4 are rotated. For example, the grinding unit 6 is fed at 3.0 μm / s while the spindle 8 is rotated at 4000 rpm and the chuck table 4 is rotated at 300 rpm.

[0063] After grinding the specified area 17d until the thickness of the ground portion reaches the specified finished thickness 11f, the grinding feed is stopped. This forms... Figure 7 The recess 11c shown is formed, and an annular reinforcing portion 11d is formed around the recess 11c (recess formation step S40). Figure 7 This is a partial cross-sectional side view showing step S40 of forming the recess. Figure 8 This is a cross-sectional view of the workpiece 11 after grinding.

[0064] In the recess forming step S40, grinding is mainly performed using the bottom surface of the grinding tool 16. In particular, grinding can be performed while mitigating the deterioration of the bottom surface condition of the grinding tool 16. Therefore, even when a relatively hard oxide film is formed on the back side 11b, the occurrence of grinding defects in the workpiece 11 can be suppressed.

[0065] Next, the second embodiment will be described. In the second embodiment, the steps from holding step S10 to recess forming step S40 are also performed sequentially. However, the tilt angle of the rotation axis 4b of the chuck table 4 in the second embodiment is greater than that of the rotation axis 4b in the first embodiment, so the position of the outer peripheral end of the holding surface 4a in the +X direction is higher than that in the first embodiment.

[0066] Therefore, in the groove forming step S20 of the second embodiment, a groove 11e that is not annular but semi-circular arc-shaped passing through the center 11b1 is formed on the +X direction side of the back surface 11b. Figure 9 This is a top view of the workpiece 11, showing the semi-circular groove 11e formed by the groove forming step S20 of the second embodiment.

[0067] In the second embodiment, the semi-circular groove 11e is formed in the groove forming step S20, which is different from the first embodiment. However, in the second embodiment, the groove removal step S30 and the recess forming step S40 can also be performed in the same way as in the first embodiment.

[0068] Furthermore, the shape of the groove 11e formed in the groove forming step S20 of the second embodiment can also be an arc shape with a predetermined central angle. In the groove forming step S20 of the second embodiment, by forming an arc-shaped or semi-arc-shaped groove 11e, the load on the bottom surface of the grinding tool 16 can be reduced compared to forming an annular groove 11e.

[0069] In the groove removal step S30 of the second embodiment, compared with the case where the bottom surface of the grinding tool 16 is ground as a whole on the back surface 11b side, the deterioration of the bottom surface of the grinding tool 16 (i.e., the reduction of grinding ability) can also be reduced.

[0070] Furthermore, in the recess forming step S40 of the second embodiment, grinding can be performed while mitigating the deterioration of the bottom surface condition of the grinding tool 16. Therefore, even when a relatively hard oxide film is formed on the back side 11b, the occurrence of grinding defects in the workpiece 11 can be suppressed.

[0071] Furthermore, the structure and method of the above-described embodiments can be appropriately modified and implemented as long as they do not depart from the scope of the present invention.

Claims

1. A grinding method for a workpiece, the grinding method using a grinding apparatus, This grinding device has the following features: The chuck table holds the workpiece and... A grinding unit, comprising a spindle, grinds a workpiece held in a chuck table while a grinding wheel having a plurality of grinding tools arranged in a ring is mounted on the spindle and the grinding wheel rotates about the spindle. The grinding method for the workpiece uses the grinding apparatus to grind a predetermined area on the back side of the workpiece corresponding to the device area, which has a device area on the front side having multiple devices formed thereon and a remaining area around the outer periphery of the device area, using the grinding wheel to form a circular plate-shaped recess and an annular reinforcing portion around the recess. Its features are, The grinding method for the workpiece comprises the following steps: In the groove forming step, without rotating the chuck table that holds the workpiece, the grinding unit is rotated while grinding the specified area, thereby forming an arc-shaped or annular groove with a depth that has not reached the finished thickness on the back side of the workpiece. In the groove removal step, after the groove forming step, while keeping the spindle rotating, the chuck table begins to rotate, thereby grinding the sidewalls of the groove and removing the groove from the workpiece; and In the recess forming step, after the groove removal step, the grinding unit is fed while rotating the spindle and the chuck table, thereby grinding the specified area corresponding to the device area to form the recess and forming the annular reinforcement around the recess.

2. The grinding method for a workpiece according to claim 1, characterized in that, In the groove removal step, the chuck table is rotated while the grinding unit is being fed through the grinding process.

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