Grinding method for workpieces

Abstract

To provide a grinding method of workpiece which reduces frequency of dressing of a plurality of grinding stones, and can reduce required time for thinning workpiece.SOLUTION: A grinding method of workpiece for thinning workpiece from initial thickness to finish thickness by creep feed grinding includes: a holding step of holding a surface side of workpiece on a holding surface of a chuck table; a first groove formation step of forming a first groove in which an interval between its bottom face and the holding surface becomes a first distance that is less than the initial thickness and more than the finish thickness, on a rear face side of the workpiece; a first thinning step of thinning a region where the groove is not formed in the workpiece, to thickness corresponding to a second distance that is less than the initial thickness and more than the first distance; and a second thinning step of thinning the whole area of the workpiece to the finish thickness.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a method for grinding a workpiece, which uses a grinding wheel having a plurality of grinding wheels arranged in a ring and rotatable about a straight line along a first direction orthogonal to the direction in which the plurality of grinding wheels are arranged such that the tip surfaces of the plurality of grinding wheels draw an annular locus overlapping each other, to thin the workpiece from an initial thickness to a finished thickness.

Background Art

[0002] Chips of devices such as ICs (Integrated Circuits) are essential components in various electronic devices such as mobile phones and personal computers. Such chips are manufactured, for example, by dividing a workpiece including a wafer or the like having a large number of devices formed on the surface side into regions each including an individual device.

[0003] Furthermore, this workpiece is often thinned before being divided for the purpose of miniaturization and weight reduction of the chip. As a method for thinning the workpiece, grinding by a grinding device can be mentioned. This grinding device includes, for example, a chuck table and a grinding wheel provided above the chuck table and having a plurality of grinding wheels arranged in a ring.

[0004] In such a grinding device, the workpiece may be thinned by a grinding method also called creep feed grinding (see, for example, Patent Document 1). In this grinding method, first, the surface side of the workpiece is held on the upper surface (holding surface) of the chuck table.

[0005] Next, the workpiece is positioned horizontally when viewed from at least one lower end surface (tip surface) of the plurality of grinding wheels, and the positions of the grinding wheel and the chuck table are adjusted so that the height of this lower end surface is the height between the front and back surfaces of the workpiece.

[0006] Next, the grinding wheel is rotated along a vertical axis, and the grinding wheel and the chuck table are moved relative to each other horizontally so that multiple grinding wheels come into contact with the back side of the workpiece. As a result, one end of the back side of the workpiece is ground while the workpiece is pressed towards the chuck table by the multiple grinding wheels.

[0007] Furthermore, in this grinding method, the grinding wheel and the chuck table are moved relative to each other horizontally until the other end of the back side of the workpiece is ground while the workpiece is pressed against the chuck table. As a result, the back side of the workpiece is removed and the workpiece is thinned. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2005-28550 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] When a workpiece is thinned using creep feed grinding, grinding chips tend to clog the lower surfaces of each of the multiple grinding wheels. In this case, the processing load increases when thinning the workpiece, and processing accuracy tends to decrease. Therefore, when performing creep feed grinding on a workpiece, it is necessary to frequently dress the lower surfaces of each of the multiple grinding wheels to clear the clogging.

[0010] This dressing process involves replacing the workpiece held in the chuck table with a dressing board, and then rotating the grinding wheel while bringing the lower surfaces of multiple grinding wheels into contact with the dressing board. In this case, the time required to thin the workpiece is increased.

[0011] In view of this, the object of the present invention is to provide a method for grinding a workpiece that can reduce the time required to thin the workpiece by reducing the frequency of dressing of multiple grinding wheels. [Means for solving the problem]

[0012] According to the present invention, a method for grinding a workpiece to thin it from an initial thickness to a finish thickness is provided, which involves using a grinding wheel that has a plurality of grinding wheels arranged in an annular shape, and is rotatable around a straight line along a first direction perpendicular to the direction in which the plurality of grinding wheels are arranged such that the tip surfaces of each of the plurality of grinding wheels overlap each other to form an annular trajectory, and comprising a holding step of holding the surface side of the workpiece on the holding surface of a chuck table having a holding surface perpendicular to the first direction, and after the holding step, at least one of the plurality of grinding wheels A first preparation step of adjusting the positions of the grinding wheel and the chuck table so that the workpiece is positioned in the first direction when viewed from the end face; a first groove forming step of forming a first groove on the back side of the workpiece by rotating the grinding wheel and bringing the grinding wheel and the chuck table closer together along the first direction, such that the distance between the bottom surface and the holding surface is a first distance less than the initial thickness and greater than the finish thickness; and a first groove forming step of adjusting the positions of the grinding wheel and the chuck table so that the distance between the bottom surface and the holding surface is a first distance less than the initial thickness and greater than the finish thickness when viewed from at least one of the tip faces of the plurality of grinding wheels in the first direction. A second preparation step involves positioning the grinding wheel and the chuck table such that the workpiece is positioned in a second intersecting direction, and the distance between at least one of the multiple grinding wheels' tip faces and the holding face in the first direction is less than the initial thickness and greater than the first distance, and after the second preparation step, the grinding wheel and the chuck table are moved relative to each other along the second direction while rotating the grinding wheel such that one end of the annular trajectory in the second direction passes from one end to the other end of the workpiece in the second direction. This involves a first thinning step in which the area of ​​the workpiece in which the groove is not formed is thinned to a thickness corresponding to the second distance; a third preparation step in which, after the first thinning step, the workpiece is positioned in the second direction as viewed from at least one of the tip faces of the plurality of grinding wheels, and the positions of the grinding wheel and the chuck table are adjusted so that the distance between at least one of the tip faces of the plurality of grinding wheels and the holding surface in the first direction is a third distance corresponding to the finished thickness; and after the third preparation step, while rotating the grinding wheel,A method for grinding a workpiece is provided, comprising: a second thinning step of thinning the entire workpiece to the finish thickness by moving the grinding wheel and the chuck table relatively along the second direction such that one end of the annular trajectory in the second direction passes through the workpiece from one end to the other in the second direction;

[0013] Preferably, the grinding method for a workpiece of the present invention further comprises a fourth preparation step between the first groove forming step and the second preparation step, in which the positions of the grinding wheel and the chuck table are adjusted so that the area of ​​the workpiece in which the groove is not formed is positioned in the first direction when viewed from at least one of the leading surfaces of the plurality of grinding wheels; and a second groove forming step after the first preparation step, in which the grinding wheel and the chuck table are brought closer together along the first direction while the grinding wheel is rotated, thereby forming a second groove on the back side of the workpiece such that the distance between its bottom surface and the holding surface is a fourth distance less than the initial thickness and greater than the finish thickness.

[0014] More preferably, in a plan view, the shape of the second groove corresponds to the shape of the first groove rotated with respect to the center of the workpiece. [Effects of the Invention]

[0015] In the present invention, in the first groove forming step, grooves are formed on the back side of the workpiece, and then in the first thinning step, the area of ​​the workpiece in which grooves have not been formed is thinned by creep feed grinding so as to leave the bottom side of the groove intact.

[0016] In this case, when the trajectory of the tip surface of each rotating grinding wheel overlaps with the groove, the force pressing the workpiece toward the chuck table weakens. As a result, after this trajectory overlaps with the groove, the tip surface of each grinding wheel and the portion of the workpiece's back surface that defines the groove collide over a wide area, and / or, in this case, grinding of the back surface of the workpiece progresses as each grinding wheel collides not only with the side surface of the workpiece but also with the portion that defines the groove, thus increasing the number of times the tip surface of each grinding wheel collides with the back surface of the workpiece.

[0017] Furthermore, when the leading edge of each grinding wheel collides with the back surface of the workpiece in this manner, clogging of the leading edge of each grinding wheel is more easily resolved. Therefore, in this invention, it is possible to reduce the time required to thin the workpiece by reducing the frequency of dressing of multiple grinding wheels. [Brief explanation of the drawing]

[0018] [Figure 1] Figure 1 is a schematic perspective view showing an example of a grinding apparatus. [Figure 2] Figure 2 is a schematic partial cross-sectional side view showing an example of a grinding apparatus. [Figure 3] Figure 3 is a schematic flowchart illustrating an example of a workpiece processing method in a grinding machine, which thins the workpiece from its initial thickness to its finished thickness. [Figure 4] Figure 4(A) is a schematic cross-sectional side view showing the workpiece and chuck table after the holding step, and Figure 4(B) is a schematic plan view showing the workpiece and chuck table after the holding step. [Figure 5] Figure 5(A) is a schematic partial cross-sectional side view showing the workpiece, chuck table, and grinding wheel after the first preparation step, and Figure 5(B) is a schematic plan view showing the workpiece, chuck table, and grinding wheel after the first preparation step. [Figure 6]FIG. 6(A) is a partial cross-sectional side view schematically showing the state of the first groove forming step, FIG. 6(B) is a partial cross-sectional side view schematically showing the workpiece and the chuck table after the first groove forming step, and FIG. 6(C) is a plan view schematically showing the workpiece and the chuck table after the first groove forming step. [Figure 7] FIG. 7(A) is a partial cross-sectional side view schematically showing the workpiece, the chuck table, and the grinding wheel after the second preparation step, and FIG. 7(B) is a plan view schematically showing the workpiece, the chuck table, and the grinding wheel after the second preparation step. [Figure 8] FIG. 8(A) is a partial cross-sectional side view schematically showing the state of the first thinning step, FIG. 8(B) is a plan view schematically showing the state of the first thinning step, and FIG. 8(C) is a partial cross-sectional side view schematically showing the workpiece and the chuck table after the first thinning step. [Figure 9] FIG. 9(A) is a partial cross-sectional side view schematically showing the workpiece, the chuck table, and the grinding wheel after the third preparation step, and FIG. 9(B) is a plan view schematically showing the workpiece, the chuck table, and the grinding wheel after the third preparation step. [Figure 10] FIG. 10(A) is a partial cross-sectional side view schematically showing the state of the second thinning step, FIG. 10(B) is a plan view schematically showing the state of the second thinning step, and FIG. 10(C) is a partial cross-sectional side view schematically showing the workpiece and the chuck table after the second thinning step. [Figure 11] FIG. 11 is a flowchart schematically showing an example (rotation step) of the steps performed between the first groove forming step and the second preparation step. [Figure 12] FIG. 12(A) is a plan view schematically showing the workpiece and the chuck table after the rotation step, and FIG. 12(B) is a plan view schematically showing the state of the first thinning step performed after the rotation step. [Figure 13] FIG. 13 is a flowchart schematically showing another example (movement step and second groove forming step) of the steps performed between the first groove forming step and the second preparation step. [Figure 14] Figure 14(A) is a schematic plan view showing the workpiece and chuck table after the moving step and the second groove forming step, and Figure 14(B) is a schematic plan view showing the first thinning step performed after the moving step and the second groove forming step. [Figure 15] Figure 15 is a flowchart illustrating yet another example of steps performed between the first groove-forming step and the second preparation step (the rotation step and the second groove-forming step). [Figure 16] Figure 16(A) is a schematic plan view showing the workpiece and chuck table after the rotation step and the second groove forming step, and Figure 16(B) is a schematic plan view showing the first thinning step performed after the rotation step and the second groove forming step. [Modes for carrying out the invention]

[0019] Embodiments of the present invention will be described with reference to the attached drawings. Figure 1 is a schematic perspective view showing an example of a grinding apparatus, and Figure 2 is a schematic partial cross-sectional side view showing the grinding apparatus shown in Figure 1. Note that the +X axis direction (forward direction) and the +Y axis direction (left direction) shown in Figures 1 and 2 are mutually orthogonal directions on the horizontal plane, and the +Z axis direction (upward direction) is a direction perpendicular to the +X axis direction and the +Y axis direction, respectively.

[0020] Furthermore, the -X-axis direction (backward direction) shown in Figures 1 and 2 is the opposite direction of the +X-axis direction, the -Y-axis direction (rightward direction) is the opposite direction of the +Y-axis direction, and the -Z-axis direction (downward direction) is the opposite direction of the +Z-axis direction. In the following, the +X-axis direction and the -X-axis direction will be collectively referred to as the X-axis direction (forward / backward direction), the +Y-axis direction and the -Y-axis direction will be collectively referred to as the Y-axis direction (left / right direction), and the +Z-axis direction and the -Z-axis direction will be collectively referred to as the Z-axis direction (up / down direction).

[0021] The grinding apparatus 2 shown in Figures 1 and 2 has a base 4 that supports each component. A rectangular parallelepiped groove 4a extending along the X-axis is formed on the upper surface of the base 4. An X-axis movement mechanism 6 for moving the chuck table 28, which will be described later, along the X-axis is provided on the bottom surface of the groove 4a.

[0022] This X-axis movement mechanism 6 has a pair of guide rails 8, each extending along the X-axis direction. A rectangular parallelepiped X-axis movement plate 10 is attached to the upper side of the pair of guide rails 8 in a manner that allows it to slide along the X-axis direction. A screw shaft 12 extending along the X-axis direction is positioned between the pair of guide rails 8.

[0023] A pulse motor 14 for rotating the screw shaft 12 is connected to the rear end of the screw shaft 12. A nut 16 for housing a number of balls that circulate in accordance with the rotation of the screw shaft 12 is provided on the outer surface of the screw shaft 12 where the screw threads are formed, thus forming a ball screw.

[0024] Furthermore, the nut 16 is fixed to the underside of the X-axis moving plate 10. Therefore, when the screw shaft 12 is rotated by the pulse motor 14, the X-axis moving plate 10 moves along the X-axis direction together with the nut 16.

[0025] A rotating mechanism 18 for rotating a chuck table 28, which will be described later, is provided on the X-axis moving plate 10. This rotating mechanism 18 has a central shaft 20 extending along the Z-axis direction and a rotational drive source (not shown), such as a pulse motor, connected to the central shaft 20 via a pulley.

[0026] This pulley has a driven pulley 22 connected to the lower end of the central shaft 20 and a driving pulley (not shown) connected to a rotational drive source. An endless belt (not shown) is stretched between the driven pulley 22 and the driving pulley. In addition, multiple support shafts 24 for supporting the chuck table 28, which will be described later, are provided on the X-axis moving plate 10.

[0027] The lower end of each of the multiple support shafts 24 is fixed to the X-axis moving plate 10, and its upper end is fixed to the table base 26. A through hole (not shown) is formed in the center of the table base 26, and the central shaft 20 passes through this through hole.

[0028] Furthermore, a disc-shaped chuck table 28 is mounted on the upper end of the central shaft 20. The chuck table 28 is supported by the table base 26, for example, via bearings (not shown), so that it can rotate independently of the table base 26.

[0029] When the aforementioned rotation mechanism 18 is activated, the chuck table 28 rotates. Also, when the aforementioned X-axis movement mechanism 6 is activated, that is, when the pulse motor 14 is activated, the chuck table 28 moves along the X-axis direction together with the table base 26.

[0030] The chuck table 28 has a disc-shaped frame 30 made of ceramics or the like. This frame 30 has a disc-shaped bottom wall and cylindrical side walls that rise from this bottom wall. That is, a disc-shaped recess is formed on the upper surface of the frame 30, defined by the bottom wall and the side walls.

[0031] Furthermore, a channel (not shown) is formed in the bottom wall of the frame 30, which opens at the bottom surface of the recess, and this channel communicates with a suction source (not shown), such as an ejector. In addition, a disc-shaped porous plate 32 having a diameter approximately equal to the diameter of the recess is fixed to the recess formed on the upper side of the frame 30 (see Figure 1).

[0032] The porous plate 32 is made of, for example, porous ceramics. The upper surface of the porous plate 32 and the upper surface of the side wall of the frame 30 are parallel to the X-axis and Y-axis directions. When a suction source communicating with a flow channel formed inside the frame 30 is activated, a suction force acts on the space near the upper surface of the porous plate 32.

[0033] Therefore, the upper surface of the porous plate 32 and the upper surface of the side wall of the frame 30 function as holding surfaces for holding the workpiece 1. This workpiece 1 is made of a semiconductor material such as silicon and has a wafer 11 on its surface 11a side, on which multiple devices are formed.

[0034] Furthermore, a protective tape 13, made of, for example, resin, is attached to the surface 11a of the wafer 11 to prevent damage to the device when grinding the back surface 11b of the wafer 11. For example, a protective tape 13 of known thickness is used. The initial thickness of the workpiece 1, including the wafer 11 and the protective tape 13, is determined prior to grinding, as described later, using a measuring instrument (not shown) provided in the grinding apparatus 2.

[0035] A table cover 34 is provided around the chuck table 28. The width of this table cover 34 (length along the Y-axis) is approximately equal to the width of the groove 4a formed on the upper surface of the base 4. In addition, a pair of dustproof and waterproof covers 36, each expandable and contractible along the X-axis, are provided on either side of the table cover 34, sandwiching the table cover 34.

[0036] Then, when the X-axis movement mechanism 6 is operated to move the chuck table 28 in the X-axis direction, that is, when the pulse motor 14 is operated, the table cover 34 moves along the X-axis direction together with the chuck table 28, and the dustproof and waterproof cover 36 expands and contracts.

[0037] A rectangular prism-shaped support structure 38 is provided in the area of ​​the upper surface of the base 4 located behind the groove 4a. A Z-axis moving mechanism 40 for raising and lowering the grinding unit 54, which will be described later, is provided on the front of this support structure 38. This Z-axis moving mechanism 40 has a pair of guide rails 42, each extending along the Z-axis direction.

[0038] A slider 44 is provided on the front side of each of the pair of guide rails 42 in a manner that allows it to slide along the Z-axis direction (see Figure 2). The front end of the slider 44 is fixed to the rear side of the rectangular parallelepiped Z-axis moving plate 46. Furthermore, a screw shaft 48 extending along the Z-axis direction is positioned between the pair of guide rails 42.

[0039] A pulse motor 50 for rotating the screw shaft 48 is connected to the upper end of the screw shaft 48. Furthermore, a nut 52 for housing a number of balls that circulate in accordance with the rotation of the screw shaft 48 is provided on the outer surface of the screw shaft 48 where the screw threads are formed (see Figure 2), thus forming a ball screw.

[0040] Furthermore, the nut 52 is fixed to the rear side of the Z-axis moving plate 46. Therefore, when the screw shaft 48 is rotated by the pulse motor 50, the Z-axis moving plate 46 moves along the Z-axis direction together with the nut 52. A grinding unit 54 is provided on the front side of the Z-axis moving plate 46.

[0041] The grinding unit 54 has a cylindrical retaining member 56 fixed to the front surface of the Z-axis moving plate 46. Inside the retaining member 56, there is a cylindrical housing 58 that extends along the Z-axis direction. This housing 58 houses a rotating mechanism for rotating the grinding wheel 64, which will be described later.

[0042] This rotating mechanism has a spindle 60 that extends along the Z-axis direction, with its tip (lower end) exposed from the housing 58. The spindle 60 is supported by the housing 58 in a rotatable manner, and a rotational drive source such as a servo motor is connected to its base end (upper end).

[0043] Furthermore, the tip of the spindle 60 has a disc-like shape and functions as a wheel mount 62. An annular grinding wheel 64, having an outer diameter approximately equal to the diameter of the wheel mount 62, is attached to the underside of the wheel mount 62 using fixing members (not shown), such as bolts.

[0044] This grinding wheel 64 has a plurality of grinding wheels 64a arranged in an annular shape along a direction perpendicular to the Z-axis, and a wheel base 64b on which the plurality of grinding wheels 64a are fixed to the lower surface.

[0045] Then, when the rotational drive source connected to the base end of the spindle 60 is activated, the wheel mount 62 and the grinding wheel 64 rotate together with the spindle 60, with a straight line along the Z-axis as the axis of rotation. In other words, the grinding wheel 64 is rotatable in such a way that it traces an annular trajectory in which the lower end faces (tip faces) of each of the multiple grinding wheels 64a overlap each other.

[0046] The multiple grinding wheels 64a each contain abrasive grains such as diamond or cBN dispersed in a bonding material such as a vitrified bond or a resin bond. The wheel base 64b is made of a metal material such as stainless steel or aluminum.

[0047] Figure 3 is a schematic flowchart illustrating an example of a workpiece processing method in which the workpiece 1 is thinned from its initial thickness to its finish thickness using a grinding machine 2. In this method, first, the surface side (protective tape 13 side) of the workpiece 1 is held on the holding surface of the chuck table 28 (holding step S0).

[0048] Figure 4(A) is a schematic partial cross-sectional side view showing the workpiece 1 and chuck table 28 after the holding step S0, and Figure 4(B) is a schematic plan view showing the workpiece 1 and chuck table 28 after the holding step S0. In the holding step S0, first, the workpiece 1 is placed on the holding surface of the chuck table 28 so that the back surface of the workpiece 1 (the back surface 11b of the wafer 11) is exposed, that is, so that the protective tape 13 is facing downwards.

[0049] Then, in this state, the suction source communicating with the flow path formed inside the frame 30 is activated. This causes a suction force to act on the surface side of the workpiece 1. As a result, the surface side of the workpiece 1 is held by the holding surface of the chuck table 28.

[0050] After the holding step S0, the workpiece 1 is positioned downward (in the -Z axis direction) when viewed from at least one lower end surface of the multiple grinding wheels 64a (first preparation step S1). Figure 5(A) is a schematic partial cross-sectional side view showing the workpiece 1, chuck table 28, and grinding wheel 64 after the first preparation step S1, and Figure 5(B) is a schematic plan view showing the workpiece 1, chuck table 28, and grinding wheel 64 after the first preparation step S1.

[0051] In the first preparation step S1, for example, the chuck table 28 is moved along the X-axis so that the center C of the back surface 11b of the wafer 11 is located below the lower end surface of the grinding wheel 64a_F, which is the foremost of the multiple grinding wheels 64a.

[0052] After the first preparation step S1, a groove is formed on the back side of the workpiece 1 such that the distance between its bottom surface and the holding surface is less than the initial thickness and greater than the finished thickness (first groove forming step S2). Figure 6(A) is a schematic partial cross-sectional side view showing the first groove forming step S2, Figure 6(B) is a schematic partial cross-sectional side view showing the workpiece 1 and chuck table 28 after the first groove forming step S2, and Figure 6(C) is a schematic plan view showing the workpiece 1 and chuck table 28 after the first groove forming step S2.

[0053] In the first groove forming step S2, the grinding wheel 64 is first rotated with a straight line along the Z-axis as the axis of rotation. Then, while the grinding wheel 64 is rotating, the grinding wheel 64 is lowered until the distance I1 in the Z-axis direction between the lower end faces of each of the multiple grinding wheels 64a and the holding surface of the chuck table 28 is an arbitrary distance that is less than the initial thickness of the workpiece 1 and greater than the finished thickness.

[0054] As a result, an arc-shaped groove 15 is formed on the back side of the workpiece 1 (the back side of the wafer 11) such that the distance between its bottom surface and the holding surface is a first distance D1. Furthermore, once the groove 15 is formed on the back side of the workpiece 1, the rotation of the grinding wheel 64 is stopped, and the grinding wheel 64 is raised to separate the multiple grinding wheels 64a from the wafer 11.

[0055] After the first groove forming step S2, the workpiece 1 is positioned forward (+X axis direction) when viewed from at least one lower end surface of the multiple grinding wheels 64a, and the vertical distance (Z axis direction) between the lower end surface and the holding surface is set to a second distance which is less than the initial thickness and greater than the first distance D1 (second preparation step S3). Figure 7(A) is a schematic partial cross-sectional side view showing the workpiece 1, chuck table 28 and grinding wheel 64 after the second preparation step S3, and Figure 7(B) is a schematic plan view showing the workpiece 1, chuck table 28 and grinding wheel 64 after the second preparation step S3.

[0056] In the second preparation step S3, first, the chuck table 28 is advanced so that the grinding wheel 64 and the chuck table 28 are separated in a plan view. Then, the grinding wheel 64 is lowered so that the distance in the Z-axis direction between the lower end surface of each of the multiple grinding wheels 64a and the holding surface of the chuck table 28 is less than the initial thickness and greater than the first distance D1, resulting in a second distance D2.

[0057] Following the second preparation step S3, the area of ​​the workpiece 1 in which grooves 15 are not formed is thinned to a thickness corresponding to the second distance D2 by creep feed grinding (first thinning step S4). Figure 8(A) is a schematic partial cross-sectional side view showing the first thinning step S4, Figure 8(B) is a schematic plan view showing the first thinning step S4, and Figure 8(C) is a schematic partial cross-sectional side view showing the workpiece 1 and chuck table 28 after the first thinning step S4.

[0058] In the first thinning step S4, the grinding wheel 64 is first rotated with a straight line along the Z-axis as the axis of rotation. Then, while the grinding wheel 64 is still rotating, the chuck table 28 is retracted so that the leading edge of the annular trajectory of the lower end surface of each of the multiple grinding wheels 64a passes from the rear end to the front end of the workpiece 1.

[0059] As a result, the workpiece 1 is pressed towards the chuck table 28 while the back side of the workpiece 1 (the back side 11b of the wafer 11) is ground. When the leading edge of the annular trajectory passes the leading edge of the workpiece 1, the rotation of the grinding wheel 64 is stopped, and the grinding wheel 64 is raised to separate the multiple grinding wheels 64a from the wafer 11.

[0060] After the first thinning step S4, the workpiece 1 is positioned forward (+X axis direction) when viewed from at least one lower end surface of the multiple grinding wheels 64a, and the vertical distance between the lower end surface and the holding surface is set to a third distance corresponding to the finished thickness (third preparation step S5). Figure 9(A) is a schematic partial cross-sectional side view showing the workpiece 1, chuck table 28 and grinding wheel 64 after the third preparation step S5, and Figure 9(B) is a schematic plan view showing the workpiece 1, chuck table 28 and grinding wheel 64 after the third preparation step S5.

[0061] In the third preparation step S5, first, the chuck table 28 is advanced so that the grinding wheel 64 and the chuck table 28 are separated in a plan view. Then, the grinding wheel 64 is lowered so that the distance in the Z-axis direction between the lower end surface of each of the multiple grinding wheels 64a and the holding surface of the chuck table 28 is a third distance D3 corresponding to the finished thickness of the workpiece 1.

[0062] After the third preparation step S5, the entire workpiece 1 is thinned to the finish thickness (second thinning step S6). Figure 10(A) is a schematic partial cross-sectional side view showing the second thinning step S6, Figure 10(B) is a schematic plan view showing the second thinning step S6, and Figure 10(C) is a schematic partial cross-sectional side view showing the workpiece 1 and chuck table 28 after the second thinning step S6.

[0063] In the second thinning step S6, first, the grinding wheel 64 is rotated with a straight line along the Z-axis as the axis of rotation. Then, while the grinding wheel 64 is still rotating, the chuck table 28 is moved back so that the leading edge of the annular trajectory of the lower end surface of each of the multiple grinding wheels 64a passes from the rear end to the front end of the workpiece 1.

[0064] As a result, the workpiece 1 is pressed towards the chuck table 28 while the back side of the workpiece 1 (the back side 11b of the wafer 11) is ground. Furthermore, once the leading edge of the annular trajectory passes the leading edge of the workpiece 1, the rotation of the grinding wheel 64 is stopped, and the grinding wheel 64 is raised to separate the multiple grinding wheels 64a from the wafer 11.

[0065] In the workpiece grinding method shown in Figure 3, a groove 15 is formed on the back side (back side 11b of the wafer 11) of the workpiece 1 in the first groove formation step S2, and then in the first thinning step S4, the area of ​​the workpiece 1 in which the groove 15 is not formed is thinned by creep feed grinding so as to leave the bottom side of the groove 15 intact.

[0066] In this case, when the trajectory of the lower end surface (tip surface) of each rotating grinding wheel 64a coincides with the groove 15, the force pressing the workpiece 1 toward the chuck table 28 weakens. Therefore, after this trajectory coincides with the groove 15, the lower end surface of each grinding wheel 64a and the portion of the back side of the workpiece 1 that defines the groove 15 collide over a wide area.

[0067] When the lower end surface of each grinding wheel 64a collides with the back surface of the workpiece 1 in this manner, clogging of the lower end surface of each grinding wheel 64a is more easily resolved. Therefore, in the workpiece grinding method shown in Figure 3, it is possible to reduce the time required to thin the workpiece 1 by reducing the frequency of dressing of the multiple grinding wheels 64a.

[0068] It should be noted that the above description represents only one aspect of the present invention, and the present invention is not limited to the above description. For example, the present invention may be a method for grinding a workpiece in which the workpiece 1 is thinned from an initial thickness to a finished thickness by performing creep feed grinding three or more times.

[0069] Furthermore, the present invention may also be a workpiece grinding method comprising another step in addition to the steps S0 to S6 shown in Figure 3. For example, as shown in Figure 11, the present invention may be a workpiece grinding method comprising a rotation step (fourth preparation step) S7 in which the chuck table 28 is rotated between the first groove forming step S2 and the second preparation step S3.

[0070] In this rotation step S7, the chuck table 28 is rotated, for example, 180°, with a straight line passing through the center of the holding surface and along the Z-axis direction as the axis of rotation. Figure 12(A) is a schematic plan view showing the workpiece 1 and the chuck table 28 after this rotation step S7, and Figure 12(B) is a schematic plan view showing the first thinning step S4 performed after this rotation step S7.

[0071] In a workpiece grinding method comprising a rotation step S7, the groove 15 is positioned to protrude in the -X axis direction, and then in the first thinning step S4, the area of ​​the workpiece 1 in which the groove 15 is not formed is thinned by creep feed grinding so as to leave the bottom surface of the groove 15 intact.

[0072] In this case, each grinding wheel 64a collides not only with the side surface of the workpiece 1 (the side surface of the wafer 11) but also with the portion defining the groove 15, as grinding progresses on the back side of the workpiece 1. As a result, the number of times the lower end surface of each grinding wheel 64a collides with the back side of the workpiece 1 increases.

[0073] When the lower end surface of each grinding wheel 64a collides with the back surface of the workpiece 1 in this manner, clogging of the leading surface of each grinding wheel 64a is more easily resolved. Therefore, in a workpiece grinding method that includes a rotation step S7, it is possible to reduce the time required to thin the workpiece 1 by reducing the frequency of dressing of the multiple grinding wheels 64a, similar to the workpiece grinding method shown in Figure 3.

[0074] Furthermore, the present invention may also be a grinding method for a workpiece, as shown in Figure 13, comprising a moving step (fourth preparation step) S8 in which the chuck table 28 is moved along the front-rear direction (X-axis direction) between the first groove forming step S2 and the second preparation step S3, and a second groove forming step S9 in which a groove 17 is formed on the back side of the workpiece 1 such that the distance between its bottom surface and the holding surface is less than the initial thickness and greater than the finish thickness.

[0075] In this movement step S8, the chuck table 28 is moved back by a distance of, for example, about half the radius of the holding surface. In the second groove forming step S9, a groove 17 is formed on the back side of the workpiece 1 (the back side 11b of the wafer 11) such that the fourth distance is, for example, approximately equal to the first distance D1 (see Figure 7(A)).

[0076] Figure 14(A) is a schematic plan view showing the workpiece 1 and chuck table 28 after the moving step S8 and the second groove forming step S9, and Figure 14(B) is a schematic plan view showing the first thinning step S4 which is performed after the moving step S8 and the second groove forming step S9.

[0077] In a workpiece grinding method comprising a moving step S8 and a second groove forming step S9, grooves 15 and 17 are formed on the back side of the workpiece 1 in the first groove forming step S2 and the second groove forming step S9, and then in the first thinning step S4, the area of ​​the workpiece 1 in which grooves 15 are not formed is thinned by creep feed grinding so as to leave the bottom side of grooves 15 and 17 intact.

[0078] In this case, the force pressing the workpiece 1 toward the chuck table 28 weakens not only when the trajectory of the lower end surface (tip surface) of each rotating grinding wheel 64a overlaps with the groove 15, but also when it overlaps with the groove 17. Therefore, after the trajectory overlaps with the groove 15, the lower end surface of each grinding wheel 64a and the portion of the back side of the workpiece 1 that defines the groove 15 collide over a wide area, and after the trajectory overlaps with the groove 17, the lower end surface of each grinding wheel 64a and the portion of the back side of the workpiece 1 that defines the groove 17 also collide over a wide area.

[0079] Furthermore, when the lower end surface of each grinding wheel 64a collides with the back surface of the workpiece 1 in this manner, clogging of the lower end surface of each grinding wheel 64a is more easily resolved compared to the workpiece grinding method shown in Figure 3. Therefore, in the workpiece grinding method comprising the moving step S8 and the second groove forming step S9, it is possible to further reduce the frequency of dressing of the multiple grinding wheels 64a.

[0080] Furthermore, the present invention may also be a method for grinding a workpiece, as shown in Figure 15, comprising the above-described rotation step S7 and the above-described second groove forming step S9 between the first groove forming step S2 and the second preparation step S3.

[0081] Figure 16(A) is a schematic plan view showing the workpiece 1 and chuck table 28 after the rotation step S7 and the second groove forming step S9, and Figure 16(B) is a schematic plan view showing the first thinning step S4 performed after the rotation step S7 and the second groove forming step S9.

[0082] In this case, a portion of the groove 15 formed in the first groove forming step S2 and a portion of the groove 17 formed in the second groove forming step S9 overlap, and the pair of grooves 15 and 17 are connected. Furthermore, the shape of the groove 17 formed in the second groove forming step S9 corresponds to the shape of the groove 15 when rotated with respect to the center of the workpiece 1 (center C of the back surface 11b of the wafer 11) in a plan view.

[0083] In a workpiece grinding method comprising a rotation step S7 and a second groove forming step S9, the groove 15 formed on the back side of the workpiece 1 (the back side 11b of the wafer 11) in the first groove forming step S2 is positioned to protrude in the -X axis direction, and in the second groove forming step S9, a groove 17 having a shape that is like the groove 15 rotated by 180° in a plan view is formed on the back side of the workpiece 1. Then, in the first thinning step S4, the area of ​​the workpiece 1 in which grooves 15 and 17 are not formed is thinned by creep feed grinding, leaving the bottom sides of grooves 15 and 17 intact.

[0084] In this case, when the trajectory of the lower end surface (tip surface) of each rotating grinding wheel 64a coincides with the groove 17, the force pressing the workpiece 1 toward the chuck table 28 weakens. Therefore, after this trajectory coincides with the groove 17, the lower end surface of each grinding wheel 64a collides with the portion of the back side of the workpiece 1 that defines the groove 17 over a wide area. Furthermore, grinding of the back side of the workpiece 1 progresses as each grinding wheel 64a collides not only with the side surface of the workpiece 1 (the side surface of the wafer 11) but also with the portion that defines the groove 15. As a result, the number of times the lower end surface of each grinding wheel 64a collides with the back side of the workpiece 1 increases.

[0085] Furthermore, when the lower end surface of each grinding wheel 64a collides with the back surface of the workpiece 1 in this manner, clogging of the leading edge surfaces of each grinding wheel 64a is more easily resolved compared to the workpiece grinding method shown in Figure 3 and the workpiece grinding method that includes only the rotation step S7 in addition to the steps shown in Figure 3. Therefore, in the workpiece grinding method that includes the rotation step S7 and the second groove forming step S9, it is possible to further reduce the frequency of dressing the multiple grinding wheels 64a.

[0086] Furthermore, the present invention may also be a grinding method for a workpiece in which, after forming three or more grooves on the back side of the workpiece 1 (the back side 11b of the wafer 11), creep feed grinding is performed multiple times to thin the workpiece 1 from its initial thickness to its finished thickness.

[0087] Furthermore, the present invention may be implemented using a grinding apparatus that is equipped with an X-axis movement mechanism for moving the grinding unit 54 along the X-axis direction, in addition to or instead of the X-axis movement mechanism 6. Furthermore, the present invention may be implemented using a grinding apparatus that is equipped with a Y-axis movement mechanism for moving the chuck table 28 or the grinding unit 54 along the Y-axis direction, in addition to or instead of the X-axis movement mechanism 6.

[0088] Furthermore, the present invention may be implemented using a grinding apparatus that is equipped with a Z-axis movement mechanism for moving the chuck table 28 along the Z-axis direction, in addition to or instead of the Z-axis movement mechanism 40. In other words, in the present invention, it is sufficient that the chuck table 28 and the grinding unit 54 can move relative to each other in the X-axis direction, Y-axis direction, and Z-axis direction, and there are no limitations on the structure for this purpose.

[0089] Furthermore, the structures and methods of the embodiments described above can be modified as appropriate without departing from the scope of the present invention. [Explanation of symbols]

[0090] 1: Workpiece 2: Grinding equipment 4: Base (4a: Groove) 6:X-axis movement mechanism 8: Guide rail 10: X-axis movement plate 11: Wafer (11a: Front side, 11b: Back side) 12: Screw shaft 13: Protective tape 14: Pulse motor 15: Groove 16: Nut 17: Groove 18: Rotation mechanism 20: Central axis 22: Driven pulley 24: Support shaft 26: Table base 28: Chuck Table 30:Frame body 32: Porous plate 34: Table cover 36: Dustproof and splashproof cover 38:Support structure 40:Z-axis movement mechanism 42: Guide rail 44: Slider 46: Z-axis movement plate 48: Screw shaft 50: Pulse motor 52: Nut 54: Grinding Unit 56: Retaining member 58: Spindle Housing 60: Spindle 62: Wheel Mount 64: Grinding wheel (64a: Grinding wheel, 64b: Wheel base)

Claims

1. A method for grinding a workpiece to thin it from an initial thickness to a finish thickness, using a grinding wheel that has a plurality of grinding wheels arranged in a ring shape, and is rotatable with a rotation axis along a straight line perpendicular to the direction in which the plurality of grinding wheels are arranged such that the tip surfaces of each of the plurality of grinding wheels overlap each other in a ring shape, A holding step of a chuck table having a holding surface perpendicular to the first direction, which holds the surface side of the workpiece on the holding surface, A first preparation step is to adjust the positions of the grinding wheel and the chuck table after the holding step, so that the workpiece is positioned in the first direction when viewed from at least one of the leading surfaces of the plurality of grinding wheels. A first groove forming step is performed in which, after the first preparation step, the grinding wheel is rotated and the grinding wheel and the chuck table are brought closer together along the first direction, thereby forming a first groove on the back side of the workpiece such that the distance between the bottom surface and the holding surface is less than the initial thickness and greater than the finish thickness. A second preparation step is performed after the first groove forming step, in which the workpiece is positioned in a second direction perpendicular to the first direction when viewed from at least one of the tip faces of the plurality of grinding wheels, and the positions of the grinding wheel and the chuck table are adjusted so that the distance between at least one of the tip faces of the plurality of grinding wheels and the holding surface in the first direction is less than the initial thickness and greater than the first distance, A first thinning step is performed in which, after the second preparation step, the grinding wheel and the chuck table are moved relative to each other along the second direction while the grinding wheel is rotated, such that one end of the annular trajectory in the second direction passes from one end to the other end of the workpiece in the second direction, thereby thinning the area of ​​the workpiece in which the groove is not formed to a thickness corresponding to the second distance. A third preparation step is performed, after the first thinning step, to position the workpiece in the second direction as viewed from at least one of the tip faces of the plurality of grinding wheels, and to adjust the positions of the grinding wheel and the chuck table so that the distance between at least one of the tip faces of the plurality of grinding wheels and the holding surface in the first direction is a third distance corresponding to the finished thickness. A second thinning step is performed, in which, while rotating the grinding wheel, the grinding wheel and the chuck table are moved relative to each other along the second direction such that one end of the annular trajectory in the second direction passes from one end to the other end of the workpiece in the second direction, thereby thinning the entire workpiece to the finish thickness. A method for grinding a workpiece, comprising the following components.

2. Between the first groove forming step and the second preparation step, A fourth preparation step involves adjusting the positions of the grinding wheel and the chuck table such that the area of ​​the workpiece in which the groove is not formed is positioned in the first direction when viewed from at least one of the tip faces of the plurality of grinding wheels, A second groove forming step is performed, in which, after the first preparation step, the grinding wheel is rotated and the grinding wheel and the chuck table are brought closer together along the first direction, thereby forming a second groove on the back side of the workpiece such that the distance between the bottom surface and the holding surface is a fourth distance which is less than the initial thickness and greater than the finish thickness. The method for grinding a workpiece according to claim 1, further comprising:

3. In a plan view, the shape of the second groove corresponds to the shape of the first groove when rotated with respect to the center of the workpiece, as described in claim 2.

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