Grinding method for workpieces

Abstract

To enable changing of a ring width or the like without changing a grinding wheel when a workpiece is ground by a TAIKO grinding technique.SOLUTION: A method for grinding a workpiece comprises: a rotation-shaft direction grinding step of bringing a grinding wheel having a circle diameter defined by the outer peripheral side surfaces of a plurality of grindstones is equal to or smaller than a radius of the workpiece and a chuck table holding the front surface side of the workpiece close to each other along an axis of a rotary shaft of the chuck table to grind the back side of the workpiece; and a radial grinding step of moving the grinding wheel and the chuck table relative to each other in the radial direction of the chuck table. The radial grinding step includes one or both of an inside-direction grinding step of moving from a position where a moving track of the bottom surfaces of the grindstones and the axis of the chuck table do not overlap each other to a position where they overlap and an outside-direction grinding step of moving from the position where the moving track and the axis overlap each other to the position where they do not overlap each other.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for grinding a workpiece having a device region and an outer peripheral excess region surrounding the device region on its surface side, by grinding the back side of the workpiece to form a recess, thereby forming a circular thin plate portion and an annular protrusion surrounding the circular thin plate portion. [Background technology]

[0002] With the increasing prevalence of SiP (System in Package) and other systems that encapsulate multiple IC (Integrated Circuit) chips in a single package, there is a growing demand for grinding technologies that can efficiently thin disc-shaped workpieces, such as wafers, on which multiple ICs are formed.

[0003] One known grinding technique for thinning workpieces is the TAIKO® grinding technique (hereinafter, for convenience, abbreviated as TAIKO grinding technique). In the TAIKO grinding technique, for workpieces having a device region on the surface side where devices such as ICs are formed, the circular region on the back side corresponding to the device region is ground.

[0004] In particular, by grinding a circular area, a disc-shaped recess is formed on the back side, while leaving an annular protrusion surrounding the outer circumference of the recess (see, for example, Patent Document 1). By leaving the annular protrusion, the strength of the workpiece can be increased compared to when the entire back side is thinned uniformly, thereby suppressing warping of the workpiece after thinning and cracking of the workpiece during transport.

[0005] When grinding a workpiece using TAIKO grinding technology, the surface side of the workpiece is first held in place by suction using a chuck table. Then, the chuck table is rotated at a predetermined speed, and a grinding unit having a spindle equipped with an annular grinding wheel is lowered toward the chuck table while the grinding wheel is rotated.

[0006] The grinding wheel has an annular base. Multiple grinding wheels are arranged at approximately equal intervals along the circumference of the base on the underside of the base. The grinding wheel is mounted to the spindle via a mount, by fixing the upper side of the base to a disc-shaped mount.

[0007] In order to grind a workpiece using TAIKO grinding technology, a grinding wheel of a predetermined diameter is typically selected such that the grinding surface, defined by the trajectories of the bottom surfaces of multiple grinding wheels, passes directly above the rotation center of the chuck table, and the outer edge of the grinding surface is located on the inner circumference of the annular protrusion.

[0008] Therefore, when changing the width of the annular protrusion (i.e., the ring width) or when grinding workpieces with different diameters using TAIKO grinding technology, a grinding wheel with a predetermined diameter corresponding to the ring width or the diameter of the workpiece is mounted to the mount each time.

[0009] However, since the grinding wheel is usually replaced manually by the operator, replacing the grinding wheel increases the number of steps required, which reduces the work efficiency when grinding workpieces using TAIKO grinding technology. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Japanese Patent Publication No. 2007-19461 [Overview of the project] [Problems that the invention aims to solve]

[0011] This invention has been made in view of the aforementioned problems, and aims to provide a grinding method that enables grinding of workpieces with different ring widths or different diameters without changing the grinding wheel when grinding a workpiece using TAIKO grinding technology. [Means for solving the problem]

[0012] According to one aspect of the present invention, a grinding method of a workpiece for forming a circular thin plate portion and an annular convex portion surrounding the circular thin plate portion by grinding the back surface side of a workpiece having a device region and an outer peripheral surplus region surrounding the device region on the front surface side to form a concave portion, the method comprising: a holding step of holding the front surface side of the workpiece on a holding surface of a chuck table rotatable around a predetermined rotation axis; a grinding wheel including an annular base and a plurality of grinding wheels annularly arranged on one surface of the base, the grinding wheel having a spindle with the grinding wheel having a diameter of a circle defined by the outer peripheral side surfaces of the plurality of grinding wheels being equal to or less than the radius of the workpiece attached to a tip portion; a rotational axis direction grinding step of grinding the back surface side of the workpiece by relatively approaching the chuck table and the grinding unit along an axis of the predetermined rotation axis of the chuck table; and a radial direction grinding step of grinding the back surface side of the workpiece by relatively moving the grinding unit and the chuck table in a radial direction of the chuck table orthogonal to the axis, the radial direction grinding step including either or both of an inner direction grinding step of grinding the workpiece while relatively moving the grinding unit and the chuck table from a position where a movement locus of a bottom surface of the plurality of grinding wheels accompanying rotation of the spindle and the axis of the chuck table do not overlap to a position where they overlap, and an outer direction grinding step of grinding the workpiece while relatively moving the grinding unit and the chuck table from a position where the movement locus and the axis overlap to a position where they do not overlap. The circular thin plate portion and the annular protrusion are formed by sequentially performing the rotational axial grinding step and the radial grinding step, or by repeating them, or by simultaneously performing the rotational axial grinding step and the radial grinding step, or by repeating them. A grinding method of a workpiece is provided.

[0013] Preferably, in the radial direction grinding step, the inner direction grinding step and the outer direction grinding step are alternately repeated to grind the workpiece.

[0014] Preferably, the workpiece is ground by simultaneously performing the rotational axis direction grinding step and the radial direction grinding step, and the radial direction grinding step includes both the inner direction grinding step and the outer direction grinding step.

[0015] Preferably, in the holding step, the workpiece is held by the holding surface having flatness with irregularities less than 10 μm, and in the radial grinding step and the radial grinding step, the workpiece held by the holding surface is ground.

[0016] Preferably, in the axial grinding step and the radial grinding step, the workpiece is ground with the axis of the spindle of the grinding unit arranged non-parallel to the axis of the chuck table.

Advantages of the Invention

[0017] A method for grinding a workpiece according to an aspect of the present invention includes an axial grinding step of relatively approaching a grinding unit and a chuck table along the axis of a predetermined rotation axis of the chuck table, and a radial grinding step of relatively moving the grinding unit and the chuck table in the radial direction of the chuck table. The radial grinding step includes either or both of an inner direction grinding step and an outer direction grinding step.

[0018] In the inner direction grinding step, the grinding unit and the chuck table are relatively moved from a position where the movement locus of the bottom surfaces of the plurality of grinding wheels does not overlap with the axis of the rotation axis of the chuck table to a position where they overlap. In the outer direction grinding step, the grinding unit and the chuck table are relatively moved from a position where the movement locus and the axis overlap to a position where they do not overlap.

[0019] [[ID=((19))]]Thus, in either or both of the inner direction grinding step and the outer direction grinding step, the workpiece is ground while relatively moving the grinding unit and the chuck table in the radial direction of the chuck table. Therefore, without changing the grinding wheel, it is possible to perform grinding with a different ring width or a workpiece having a different diameter.

Brief Description of the Drawings

[0020] [Figure 1] It is a flowchart of a method for grinding a workpiece in the first embodiment. [Figure 2]This is a perspective view showing protective members and the like that are attached to a workpiece. [Figure 3] Figure 3(A) is a partial cross-sectional side view of the holding step, and Figure 3(B) is a perspective view of the holding step. [Figure 4] This is a cross-sectional view of a chuck table typically used in TAIKO grinding technology. [Figure 5] This is a partial cross-sectional side view showing the grinding step in the rotational axis direction. [Figure 6] Figure 6(A) is a partial cross-sectional side view of the internal grinding step, and Figure 6(B) is a perspective view of the internal grinding step. [Figure 7] This is a partial cross-sectional side view of the workpiece after grinding is complete. [Figure 8] This is a flowchart of the grinding method for a workpiece in the second embodiment. [Figure 9] This is a partial cross-sectional side view showing the grinding step in the rotational axis direction. [Figure 10] Figure 10(A) is a partial cross-sectional side view of the outward grinding step, and Figure 10(B) is a perspective view of the outward grinding step. [Figure 11] This is a flowchart of the grinding method for a workpiece in the third embodiment. [Figure 12] This is a partial cross-sectional side view showing the inner grinding step and the outer grinding step. [Figure 13] This is a flowchart of the grinding method for a workpiece in the fourth embodiment. [Figure 14] This is a partial cross-sectional side view showing the rotational axial grinding step and the radial grinding step. [Figure 15] Figure 15(A) is a partial cross-sectional side view showing the rotational axial grinding step and radial grinding step in the fifth embodiment, and Figure 15(B) is a top view showing the rotational axial grinding step and radial grinding step in the fifth embodiment. [Modes for carrying out the invention]

[0021] An embodiment of one aspect of the present invention will be described with reference to the attached drawings. Figure 1 is a flowchart of the grinding method for a workpiece 11 (see Figure 2, etc.) in the first embodiment. In this embodiment, the workpiece 11 is ground according to each step shown in Figure 1.

[0022] First, let's refer to Figure 2 and explain the workpiece 11. As shown in Figure 2, the workpiece 11 has a disc-shaped wafer 13 made of single-crystal silicon. Multiple division lines (stories) 15 are set in a grid pattern on the surface 13a side of the wafer 13.

[0023] Each of the rectangular regions demarcated by multiple division lines 15 has a device 17, such as an IC (Integrated Circuit), formed within it. The region on the surface 13a side where multiple devices 17 are formed is referred to as the device region 13a1. There are no restrictions on the type, quantity, shape, structure, size, or arrangement of the devices 17 in the workpiece 11.

[0024] The area on the surface 13a side surrounding the device region 13a1 is referred to as the outer peripheral excess region 13a2. The surface 13a side of the wafer 13 may be read as the surface side of the workpiece 11, and the back side 13b side of the wafer 13 may be read as the back side of the workpiece 11. However, a functional layer (not shown) having a metal wiring layer, an interlayer insulating film, etc. may be provided so as to cover the surface 13a of the wafer 13 and the device 17.

[0025] When grinding the workpiece 11, a portion of the wafer 13 is thinned by grinding the circular region on the back surface 13b that corresponds to the device region 13a1. This circular region has a diameter smaller than the outer diameter of the wafer 13 and is concentric with the wafer 13.

[0026] Before grinding the wafer 13, a resin protective member 19, approximately the same diameter as the wafer 13, is attached to the surface 13a side. Figure 2 is a perspective view showing the protective member 19 and the like attached to the surface 13a side of the wafer 13.

[0027] The protective member 19 is, for example, a circular tape having a base layer and an adhesive layer, with the adhesive layer of the tape being attached to the surface 13a side. By attaching the protective member 19 to the surface 13a side, the impact on the device 17 during grinding can be mitigated.

[0028] The protective member 19 may have only a base layer and no adhesive layer. In this case, the protective member 19 is heat-pressed to the surface 13a. By heat-pressing the protective member 19 to the surface 13a, it is possible to prevent the adhesive layer from partially remaining on the surface 13a when the protective member 19 is peeled off.

[0029] After the protective member 19 is attached to the surface 13a side, the surface 13a side is held by suction using the chuck table 4 of the grinding device 2 (see Figure 3(A)) (holding step S10). Figure 3(A) is a partial cross-sectional side view of the holding step S10, and Figure 3(B) is a perspective view of the holding step S10. The Z-axis direction shown in Figures 3(A) and 3(B) is parallel to the height direction (i.e., the vertical direction) of the grinding device 2.

[0030] The chuck table 4 has a disc-shaped frame 6 made of non-porous ceramics. A circular recess is formed on the upper surface of the frame 6. A disc-shaped porous plate 8 made of porous ceramics is fixed to this recess.

[0031] The upper surface of the frame 6 and the upper surface of the porous plate 8 are substantially flush, forming a substantially flat holding surface 4a. The holding surface 4a has higher flatness than the holding surface 12a of the chuck table 12 (see Figure 4) that is normally used in TAIKO grinding technology.

[0032] Figure 4 is a cross-sectional view of a chuck table 12 typically used in TAIKO grinding technology. Figure 4 shows a cross-section of the chuck table 12 in a plane that passes through the radial center 12a1 of the chuck table 12 and is perpendicular to the bottom surface of the chuck table 12.

[0033] The chuck table 12 also has a frame 14 and a porous plate 16. The upper surface of the frame 14 and the upper surface of the porous plate 16 are substantially flush, forming a holding surface 12a that holds the workpiece 11 by suction.

[0034] However, on the holding surface 12a, the central part 12a1 and the outer peripheral part 12a2 in the radial direction of the chuck table 12 protrude more than other areas, and the holding surface 12a in cross-sectional view has a so-called double-concave shape.

[0035] On the holding surface 12a, the central part 12a1 and the outer peripheral part 12a2 protrude by a predetermined length 12b of 10 μm to 30 μm in the thickness direction of the chuck table 12, with reference to the most recessed bottom part 12a3.

[0036] In contrast, the holding surface 4a of the chuck table 4 in this embodiment shown in Figure 3(A) is substantially flat, with irregularities of less than 10 μm. One of the features of TAIKO grinding technology is that the workpiece 11 is held by suction on a substantially flat holding surface 4a.

[0037] The irregularities of the holding surface 4a are evaluated, for example, by the arithmetic mean roughness (Ra) of the contour curve in a cross-section of the chuck table 4 in a plane that passes through the center of the chuck table 4 in the radial direction 4b (see Figure 6) and is perpendicular to the bottom surface of the chuck table 12.

[0038] The arithmetic mean roughness (Ra) is defined, for example, in JIS (Japanese Industrial Standards) B 0601:2013. The Ra of the retaining surface 4a in this embodiment is 2.99 μm (i.e., less than 10 μm).

[0039] As shown in Figure 3(A), a radial flow path 6b is formed at the bottom of the recess of the frame 6, and a cylindrical flow path 6c is formed that penetrates the radial center of the frame 6. A suction source (not shown), such as a vacuum pump, is connected to the flow path 6c via a valve (not shown), such as a solenoid valve.

[0040] When the valve is opened while the suction source is operating, negative pressure is transmitted to the holding surface 4a, and the workpiece 11 is held by suction on the holding surface 4a. A cylindrical rotating shaft (a predetermined rotating shaft) 10 is fixed to the lower side of the frame 6. The longitudinal direction of the rotating shaft 10 is approximately parallel to the Z-axis direction and approximately perpendicular to the holding surface 4a.

[0041] A driven pulley (not shown) is fixed near the lower end of the rotating shaft 10. A rotational drive source (not shown), such as a motor, is provided below the chuck table 4. A drive pulley (not shown) is fixed to the output shaft of the rotational drive source.

[0042] A toothed endless belt (not shown) is fitted over the drive pulley and the driven pulley. When power from the rotational drive source is transmitted to the rotating shaft 10, the chuck table 4 rotates around the rotating shaft 10. The longitudinal direction of the rotating shaft 10 is positioned approximately parallel to the Z-axis direction.

[0043] After the holding step S10, the back surface 13b of the wafer 13, which is held by suction on the holding surface 4a, is ground by the grinding unit 20 (see Figure 5). As shown in Figure 5, the grinding unit 20 has a cylindrical spindle housing (not shown).

[0044] A ball screw type Z-axis movement mechanism (not shown) is connected to the spindle housing, and the grinding unit 20 moves along the Z-axis direction by the Z-axis movement mechanism. A portion of a cylindrical spindle 22 is rotatably housed inside the spindle housing.

[0045] The longitudinal direction of the spindle housing and spindle 22 is aligned along the Z-axis direction. In Figure 5, in addition to the spindle 22, an axis 22b is shown that passes through the rotation center of the spindle 22 and the longitudinal centroid of the spindle 22 and is substantially parallel to the Z-axis direction.

[0046] A rotational drive source (not shown), such as a motor, is provided on a portion of the upper side of the spindle 22. The lower end (tip) 22a of the spindle 22 protrudes below the lower end of the spindle housing. A disc-shaped mount 24, smaller in diameter than the holding surface 4a, is fixed to the lower end 22a of the spindle 22.

[0047] An annular grinding wheel 26 is mounted on the lower side of the mount 24. In other words, the grinding wheel 26 is mounted on the lower end 22a of the spindle 22 via the mount 24.

[0048] The grinding wheel 26 has an annular wheel base (base) 26a made of a metal such as an aluminum alloy. On the lower surface (one side) 26a1 of the wheel base 26a, a plurality of grinding wheels 26b are arranged in an annular shape at approximately equal intervals along the circumferential direction of the wheel base 26a.

[0049] Each grinding wheel 26b has abrasive grains made of cBN (cubic boron nitride), diamond, etc., and a bonding material such as a vitrified bond or resin bond for fixing the abrasive grains.

[0050] When the spindle 22 is rotated, the annular region defined by the movement trajectories of the bottom surfaces 26b1 of the multiple grinding wheels 26b becomes the grinding surface 26b2 that grinds the back surface 13b of the wafer 13. In Figure 5, the position of the grinding surface 26b2 in the Z-axis direction is shown.

[0051] The diameter (outer diameter) of the grinding surface 26b2 corresponds to the diameter 26b3 of the circle defined by the outer circumferential surfaces of the multiple grinding wheels 26b in a plane perpendicular to the axis 22b. The diameter 26b3 of the multiple grinding wheels 26b is less than or equal to the radius 11a of the workpiece 11.

[0052] On the wheel base 26a, on the inner circumference side of the grinding wheel 26b, there are multiple openings (not shown) formed at approximately equal intervals along the circumferential direction of the wheel base 26a, which are capable of supplying grinding fluid such as pure water to the grinding wheel 26b. During grinding, the grinding fluid is used for cooling and removal of grinding debris.

[0053] The Z-axis movement mechanism brings the grinding unit 20 and the chuck table 4 relatively closer together along the axis 10a of the rotation axis 10 of the chuck table 4, thereby grinding the back surface 13b of the wafer 13 (rotation axis grinding step S20).

[0054] Figure 5 is a partial cross-sectional side view showing the rotational axis grinding step S20. In Figure 5 and subsequent figures, the rotation axis 10 of the chuck table 4 is simplified and shown by axis 10a. Axis 10a is a straight line passing through the rotation center of the rotation axis 10 and the centroid in the longitudinal direction of the rotation axis 10.

[0055] In this embodiment, the grinding wheel 26 is rotated at 4000 rpm, and the chuck table 4 is rotated at 300 rpm and lowered along the Z-axis at 0.6 μm / s (i.e., ground feed). The flow rate of the grinding water is, for example, 4.0 L / min.

[0056] As described above, the diameters 26b3 of the multiple grinding wheels 26b are less than or equal to the radius 11a of the workpiece 11. Also, when the grinding unit 20 is fed for grinding, the position of the chuck table 4 is such that the grinding surface 26b2 of the grinding wheel 26 does not overlap with the axis 10a of the chuck table 4, as shown in Figure 5. A It has been adjusted to be so.

[0057] Therefore, as shown in Figure 6(A), when the grinding surface 26b2 is fed from the back surface 13b to the desired predetermined depth 11b, a cylindrical projection 11c (i.e., an ungrinded area) is formed in the center of the back surface 13b. After the projection 11c is formed, the grinding feed of the grinding unit 20 is stopped.

[0058] Then, by moving the grinding unit 20 and the chuck table 4 relative to each other in the radial direction 4b of the chuck table 4, the protrusion 11c on the back surface 13b side is ground and removed (radial grinding step S30).

[0059] As shown in Figure 6(A), the radial direction 4b of the chuck table 4 is perpendicular to the axis 10a of the rotation axis 10. The radial direction 4b is approximately parallel to the X-axis direction (not shown), which is perpendicular to the Z-axis direction in the grinding device 2.

[0060] In the radial grinding step S30, the chuck table 4 and the grinding wheel 26 are rotated respectively, and for example, the chuck table 4 is moved outward in the radial direction 4b, thereby moving the grinding wheel 26 inward in the radial direction 4b.

[0061] As a result, the aforementioned position P A Therefore, position P where the grinding surface 26b2 and the axis 10a overlap. B Next, the grinding wheel 26 is moved toward the center of the holding surface 4a, and the projection 11c is removed from the outer peripheral surface of the grinding wheel 26b (i.e., the back surface 13b is ground) (inward grinding step).

[0062] Figure 6(A) is a partial cross-sectional side view of the internal grinding step, and Figure 6(B) is a perspective view of the internal grinding step. Position P A From position P B The movement speed when moving to the next location will be, for example, 1.0 μm / s.

[0063] In this embodiment, the wafer 13 is ground to a predetermined thickness by sequentially performing the rotational axial grinding step S20 and the radial grinding step (inward grinding step) S30 (YES at S40), and the grinding is terminated (see Figure 1).

[0064] In contrast, if the initial grinding feed rate is shallower than the target predetermined depth 11b (NO in S40), the rotational axial grinding step S20 and the radial grinding step (inner grinding step) S30 are repeated (see Figure 1).

[0065] Figure 7 is a partial cross-sectional side view of the workpiece 11 after grinding is complete. By forming a recess 13b1 on the back surface 13b side, the workpiece 11 is formed with a circular thin plate portion 11d including a device region 13a1 and an annular protrusion 11e surrounding the outer periphery of the circular thin plate portion 11d.

[0066] In this embodiment, although the diameters 26b3 of the multiple grinding wheels 26b are less than or equal to the radius 11a of the workpiece 11, the grinding unit 20 and the chuck table 4 are moved relative to each other in the radial direction 4b of the chuck table 4 during the inward grinding step, so that the grinding of the workpiece 11 can be performed without changing the grinding wheels 26.

[0067] Furthermore, by applying the grinding method of this embodiment, the ring width of the annular protrusion 11e can be changed by changing the position of the grinding wheel 26 relative to the workpiece 11 in the rotational axial grinding step S20, and other workpieces 11 having a different diameter from the workpiece 11 can also be ground.

[0068] (Second Embodiment) Next, the second embodiment will be described with reference to Figures 8, 9, 10(A), and 10(B). Figure 8 is a flowchart of the grinding method for the workpiece 11 in the second embodiment.

[0069] In the second embodiment as well, the rotational axial grinding step S20 is performed after the holding step S10. Figure 9 is a partial cross-sectional side view showing the rotational axial grinding step S20 in the second embodiment.

[0070] However, in the rotational axial grinding step S20 of this embodiment, as shown in Figure 9, the grinding surface 26b2 of the grinding wheel 26 coincides with the axis 10a of the chuck table 4 at position P. B After adjusting the position of the chuck table 4 to achieve this, the grinding unit 20 is fed for grinding.

[0071] In this embodiment, the grinding wheel 26 is rotated at 4000 rpm, the chuck table 4 is rotated at 300 rpm, and grinding feed is performed at 0.6 μm / s along the Z-axis direction. The flow rate of the grinding water is, for example, 4.0 L / min.

[0072] As shown in FIG. 10(A), after the grinding wheel 26 is fed in grinding from the back surface 13b to a predetermined depth 11b, the grinding feed of the grinding unit 20 is stopped. Then, after the rotational axis direction grinding step S20, a radial grinding step S32 is performed.

[0073] In the radial grinding step S32, from the above-described position P B to a position P A where the grinding surface 26b2 and the axis 10a do not overlap, while relatively moving the grinding wheel 26 to the outside of the holding surface 4a, the back surface 13b side is ground (outer direction grinding step).

[0074] While rotating the chuck table 4 and the grinding wheel 26 respectively, for example, by moving the chuck table 4 to the inside in the radial direction 4b, the grinding wheel 26 is moved to the outside in the radial direction 4b.

[0075] Position P B to position P A The moving speed when moving is, for example, 1.0 μm / s. FIG. 10(A) is a partial cross-sectional side view of the outer direction grinding step, and FIG. 10(B) is a perspective view of the outer direction grinding step.

[0076] Also in this embodiment, the grinding of the workpiece 11 can be performed without replacing the grinding wheel 26. Further, if the grinding method of this embodiment is applied, the ring width of the annular convex portion 11e can be changed, and grinding of other workpieces 11 having a diameter different from that of the workpiece 11 can also be performed.

[0077] (Third Embodiment) Next, a third embodiment will be described with reference to Figures 11 and 12. Figure 11 is a flowchart of the grinding method for the workpiece 11 in the third embodiment. In the third embodiment as well, the rotational axis grinding step S20 is performed after the holding step S10.

[0078] In the rotational axis grinding step S20 of this embodiment, position P A and position P B The position of the chuck table 4 is adjusted so that the grinding unit 20 is positioned between the chuck table and the grinding unit 20, and then the grinding unit 20 is fed forward for grinding. Then, as shown in Figure 12, the grinding wheel 26 is fed forward for grinding to a depth 11b1 which is shallower than the predetermined depth 11b, and then the grinding feed is stopped.

[0079] In the subsequent radial grinding step S34, the grinding unit 20 is moved relative to the chuck table 4 along the radial direction 4b. For example, first the grinding unit 20 is moved to position P B Move it relatively inward in the radial direction 4b (inward grinding step).

[0080] Next, the grinding unit 20 is positioned P B From position P A Move it relatively outward in the radial direction 4b (outward grinding step). Figure 12 is a partial cross-sectional side view showing the inward grinding step and the outward grinding step in the radial grinding step S34.

[0081] In the radial grinding step S34, both the inner grinding step and the outer grinding step may be performed once or multiple times. If performed multiple times, the inner grinding step and the outer grinding step are repeated alternately.

[0082] Furthermore, if the process is repeated alternately, either the inner grinding step or the outer grinding step may be performed first. In this manner, the back surface 13b is ground until the desired predetermined depth 11b is reached (i.e., until YES is reached in S40), forming a circular thin plate portion 11d and an annular protrusion 11e on the workpiece 11.

[0083] In this embodiment as well, grinding of the workpiece 11 can be performed without changing the grinding wheel 26. Furthermore, by applying the grinding method of this embodiment, the ring width of the annular protrusion 11e can be changed, and other workpieces 11 having a different diameter from the workpiece 11 can also be ground.

[0084] Alternatively, after the grinding wheel 26 is fed to a predetermined depth 11b in the first rotational axial grinding step S20, the radial grinding step S34 may be performed to form the circular thin plate portion 11d and the annular protrusion portion 11e.

[0085] (Fourth Embodiment) Next, the fourth embodiment will be described with reference to Figures 13 and 14. Figure 13 is a flowchart of the grinding method for the workpiece 11 in the fourth embodiment. In the fourth embodiment, after the holding step S10, a rotational axial grinding step and a radial grinding step S22 are performed.

[0086] In other words, after the holding step S10, the back surface 13b of the wafer 13 is ground by simultaneously performing the rotational axial grinding step and the radial grinding step. Specifically, both the inward grinding step and the outward grinding step are performed by oscillating the chuck table 4 along the radial direction 4b while the grinding unit 20 is fed by the Z-axis movement mechanism (see Figure 14).

[0087] Figure 14 is a partial cross-sectional side view showing the rotational axial grinding step and the radial grinding step S22. In the radial grinding step, both the inner grinding step and the outer grinding step may be performed once or multiple times. If performed multiple times, the inner grinding step and the outer grinding step are repeated alternately.

[0088] In this manner, the back surface 13b is ground until the desired predetermined depth 11b is reached (i.e., until the result is YES in S40), thereby forming a circular thin plate portion 11d and an annular protrusion 11e on the workpiece 11.

[0089] In this embodiment as well, grinding of the workpiece 11 can be performed without changing the grinding wheel 26. Furthermore, by applying the grinding method of this embodiment, the ring width of the annular protrusion 11e can be changed, and other workpieces 11 having a different diameter from the workpiece 11 can also be ground.

[0090] (Fifth Embodiment) Next, the fifth embodiment will be described with reference to Figures 15(A) and 15(B). In the fifth embodiment, similar to the fourth embodiment (see Figure 13), after the holding step S10, the rotational axial grinding step and the radial grinding step S22 are performed.

[0091] However, in the fifth embodiment, the back surface 13b of the wafer 13 is ground with the axis 22b of the spindle 22 (i.e., the longitudinal direction of the spindle 22) positioned non-parallel to the axis 10a of the rotation axis 10 of the chuck table 4.

[0092] For example, the grinding feed of the grinding unit 20 and the oscillation of the chuck table 4 are performed while the axis 22b of the spindle 22 is tilted by a predetermined angle with respect to the axis 10a of the rotation axis 10.

[0093] Figure 15(A) is a partial cross-sectional side view showing the rotational axial grinding step and the radial grinding step S22 in the fifth embodiment. In Figure 15(A), a straight line 10a1 parallel to the axis 10a is drawn near the spindle 22 to clearly show the inclination of the spindle 22.

[0094] In the rotational axial grinding step and the radial grinding step S22, the back surface 13b of the wafer 13 is ground by oscillating the chuck table 4 along the radial direction 4b while feeding the grinding wheel 26 downward.

[0095] In addition, during the rotational axial grinding step and the radial grinding step S22, the inner grinding step and the outer grinding step are repeated alternately, and both the inner grinding step and the outer grinding step are performed multiple times.

[0096] In particular, in the fifth embodiment, instead of grinding surfaces 26b2 of multiple grinding wheels 26b, the back surface 13b side of the wafer 13 is ground by the arc-shaped outer peripheral edge 26b4 of the bottom surface 26b1 of a single grinding wheel 26b.

[0097] Therefore, as shown in Figure 15(B), the arc-shaped outer edge 26b4 of the bottom surface 26b1 of the grinding wheel 26b is positioned at the center P of the back surface 13b. C And a point P on the outer circumference of the circular thin plate portion 11d, which corresponds to the inner periphery of the annular protrusion 11e. D It moves back and forth between and .

[0098] As grinding progresses, the center P of the back surface 13b C It gradually moves toward the surface 13a. Similarly, at a point P on the outer circumference of the circular thin plate portion 11d. D However, as grinding progresses, it gradually moves towards the surface 13a. Point P on the outer circumference. D It is located at the boundary between the circular thin plate portion 11d and the annular protrusion portion 11e in the plane defined by the axis 22b of the spindle 22 and the axis 10a of the rotation axis 10.

[0099] Figure 15(B) is a top view showing the rotational axial grinding step and the radial grinding step S22 in the fifth embodiment. In Figure 15(B), the arc-shaped outer edge 26b4 of the bottom surface 26b1 of the grinding wheel 26b is exaggerated with a thick line.

[0100] The arc-shaped outer edge 26b4 corresponds, for example, to the outer periphery of the bottom surface 26b1 of a single grinding wheel 26b, but the entire edge does not necessarily contribute to grinding. For example, only a portion of the arc-shaped outer edge 26b4 located at the lowest end (i.e., the machining point) may contribute to grinding.

[0101] The reciprocating movement of the outer edge 26b4 is achieved, for example, by oscillating the chuck table 4 along the radial direction 4b, but the center of the holding surface 4a and the center P of the back surface 13b C Taking into account the positional misalignment, center P C A point P on the outer perimeter is more likely to be a point P on the outer perimeter. DThe arc-shaped outer edge 26b4 may be moved to a position on the opposite side, to the outside.

[0102] In any case, the back surface 13b is ground until the desired predetermined depth 11b is reached (i.e., until the result is YES in S40), thereby forming a circular thin plate portion 11d and an annular protrusion 11e on the workpiece 11.

[0103] In this embodiment as well, grinding of the workpiece 11 can be performed without changing the grinding wheel 26. Furthermore, by applying the grinding method of this embodiment, the ring width of the annular protrusion 11e can be changed, and other workpieces 11 having a different diameter from the workpiece 11 can also be ground.

[0104] Furthermore, in order to keep the grinding volume of the workpiece 11 per unit time approximately constant, the rotational speed of the chuck table 4, the rotational speed of the spindle 22, and the radial movement speed 4b of the chuck table 4 may be adjusted according to the position of the outer edge 26b4.

[0105] For example, the machining point is center P C When this is the case, the rotational speed of the chuck table 4 is set to 300 rpm, the rotational speed of the spindle 22 is set to 4000 rpm, and the radial movement speed of the chuck table 4 in the 4b direction is set to 1.0 mm / s.

[0106] In contrast, the machining point is a single point P on the outer circumference. D When this is the case, the rotational speed of the chuck table 4 is set to 100 rpm, the rotational speed of the spindle 22 is set to 6000 rpm, and the radial movement speed of the chuck table 4 in the 4b direction is set to 0.1 mm / s.

[0107] The processing point is center P C and one point P on the outer perimeter D If the position is between these two ranges, the rotational speed of the chuck table 4 may be varied within the range of 100 rpm to 300 rpm, the rotational speed of the spindle 22 within the range of 4000 rpm to 6000 rpm, and the radial movement speed of the chuck table 4 4b within the range of 0.1 mm / s to 1.0 mm / s, depending on the position of the outer edge 26b4.

[0108] This allows the grinding volume per unit time to be kept approximately constant, thus improving the flatness of the circular thin plate portion 11d after grinding compared to the case where the rotational speed of the chuck table 4 and spindle 22, and the radial movement speed of the chuck table 4 4b are kept constant regardless of the position of the outer edge 26b4. In other words, the TTV (Total Thickness Variation) can be improved.

[0109] Furthermore, the structures, methods, etc., according to the above embodiments can be modified as appropriate without departing from the scope of the object of the present invention. For example, in the first to fourth embodiments (excluding the fifth embodiment), the wafer 13 can also be ground using a chuck table 12 having a double-concave holding surface 12a as shown in Figure 4.

[0110] However, when using a chuck table 12 having a double-concave holding surface 12a, at least one of the spindle 22 (axis 22b) and the rotation axis 10 (axis 10a) of the chuck table 4 is tilted so that the processing area (i.e., the contact area between the multiple grinding wheels 26b and the back surface 13b of the wafer 13) is arc-shaped.

[0111] By the way, in the fifth embodiment as well, the rotational axial grinding step S20 and the radial grinding step S30 (S32, S34) may be performed separately, as in the first embodiment (Figure 1), the second embodiment (Figure 8), and the third embodiment (Figure 11). [Explanation of Symbols]

[0112] 2: Grinding device, 4: Chuck table, 4a: Holding surface, 4b: Radial direction 6: Frame, 6b, 6c: Flow channel, 8: Porous plate 10: axis of rotation (predetermined axis of rotation), 10a: axis line, 10a1: straight line 11: Workpiece, 11a: Radius, 11b, 11b1: Depth, 11c: Projection 11d: Circular thin plate portion, 11e: Annular protrusion portion 12: Chuck table, 12a: Holding surface 12a1: Center, 12a2: Outer perimeter, 12a3: Bottom, 12b: Length 13: Wafer, 13a: Surface, 13a1: Device area, 13a2: Outer periphery area 13b: Reverse side, 13b1: Recess 14: Frame, 16: Porous board 15: Planned division line, 17: Device, 19: Protective component 20: Grinding unit, 22: Spindle, 22a: Lower end (tip), 22b: Axis 24: Mount 26: Grinding wheel, 26a: Wheel base (base), 26a1: Bottom surface (one side) 26b: grinding wheel, 26b1: bottom surface, 26b2: grinding surface, 26b3: diameter, 26b4: outer edge P A ,P B :Position, P C :Center, P D : A point on the outer perimeter S10: Holding step, S20: Rotational axis grinding step S22: Rotary axial grinding step and radial grinding step S30, S32, S34: Radial grinding step

Claims

1. A method for grinding a workpiece, wherein the back side of the workpiece having a device region and an outer peripheral excess region surrounding the device region is ground to form a recess, thereby forming a circular thin plate portion and an annular protrusion surrounding the circular thin plate portion, A holding step includes holding the surface side of the workpiece with the holding surface of a chuck table that is rotatable around a predetermined axis of rotation, A grinding unit having a spindle to which a grinding wheel is mounted at its tip, the grinding wheel comprising an annular base and a plurality of grinding wheels arranged in a ring on one surface of the base, wherein the diameter of the circle defined by the outer peripheral surfaces of the plurality of grinding wheels is less than or equal to the radius of the workpiece, and a chuck table, and a rotational axial grinding step of grinding the back side of the workpiece by bringing the chuck table relatively closer to the chuck table along the axis of the predetermined rotation axis, A radial grinding step in which the grinding unit and the chuck table are moved relative to each other in the radial direction of the chuck table perpendicular to the axis, thereby grinding the back side of the workpiece, Equipped with, The radial grinding step is, An internal grinding step in which the workpiece is ground while the grinding unit and the chuck table are moved relative to each other from a position where the movement trajectories of the bottom surfaces of the multiple grinding wheels as the spindle rotates and the axis of the chuck table do not overlap to a position where they overlap, The process includes either or both of the following: an outward grinding step, in which the workpiece is ground while the grinding unit and the chuck table are moved relative to each other from a position where the movement trajectory and the axis line overlap to a position where they do not overlap; A method for grinding a workpiece, characterized by forming the circular thin plate portion and the annular protrusion by sequentially performing the rotational axial grinding step and the radial grinding step or by repeating them, or by simultaneously performing the rotational axial grinding step and the radial grinding step or by repeating them.

2. The method for grinding a workpiece according to claim 1, characterized in that the radial grinding step involves alternately repeating the inward grinding step and the outward grinding step to grind the workpiece.

3. The workpiece is ground by simultaneously performing the rotational axial grinding step and the radial grinding step. The method for grinding a workpiece according to claim 1, characterized in that the radial grinding step includes both the inward grinding step and the outward grinding step.

4. In the holding step, the workpiece is held on the holding surface having a flatness with irregularities of less than 10 μm. A method for grinding a workpiece according to any one of claims 1 to 3, characterized in that the radial grinding step and the radial grinding step involve grinding the workpiece held by the holding surface.

5. The method for grinding a workpiece according to claim 4, characterized in that, in the rotational axial grinding step and the radial grinding step, the workpiece is ground with the axis of the spindle of the grinding unit positioned non-parallel to the axis of the chuck table.

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