Wafer grinding method

Abstract

To reduce the number and the size of chipping occurring on an inner peripheral edge of a top face of a ring-shaped reinforcement part.SOLUTION: A wafer grinding method comprises: a first grinding step in which a grinding wheel and a wafer are caused to approach each other by descending the grinding wheel relatively to a chuck table to grind the wafer with a bottom surface of a plurality of grindstones, thereby forming a ring-shaped reinforcement part; a second grinding step in which the grinding wheel is moved to an outer side in a radial direction of the wafer relatively to the wafer, thereby grinding an inner peripheral side surface of the ring-shaped reinforcement part with outer peripheral side surfaces of the plurality of grindstones; a first separation step in which the grinding wheel is moved to an inner side in the radial direction of the wafer relatively to the wafer, thereby separating the outer peripheral side surfaces of the plurality of grindstones from the inner peripheral side surface of the ring-shaped reinforcement part; and a second separation step in which the grinding wheel is raised relatively to the chuck table, separating the bottom surfaces of the plurality of grindstones from a top face of a thin plate part.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for grinding a wafer, which forms a thin plate portion and a ring-shaped reinforcing portion surrounding the outer periphery of a disk-shaped wafer by grinding an area of ​​the wafer that is radially inward from the outer periphery of the wafer. [Background technology]

[0002] With the spread of SiP (System in Package), in which multiple thinned device chips are stacked to form a single package, there is a demand for a grinding technology that can thin a wafer with a good yield before it is divided into multiple device chips. One of the grinding technologies for thinning a wafer is known as a grinding technology called TAIKO (registered trademark) (hereinafter, for convenience, abbreviated as the TAIKO process).

[0003] In the TAIKO process, a wafer has a device region on its front side where multiple devices are formed, and a circular region on the back side corresponding to the device region is ground away, leaving the outer periphery of the wafer as a ring-shaped reinforcement, forming a disk-shaped recess on the back side of the wafer (see, for example, Patent Document 1).

[0004] By adopting the TAIKO process, the strength of the wafer can be increased compared to when the entire back surface is uniformly thinned, which has the advantage of reducing the risk of the wafer warping after thinning and cracking during transportation.

[0005] However, when the TAIKO process is adopted, chipping is formed on the inner peripheral edge of the top surface of the ring-shaped reinforcing part (i.e., the annular surface corresponding to the back surface of the wafer) so as to extend from the inner peripheral edge toward the outside in the radial direction of the wafer. For example, chipping is likely to occur when the bottom surfaces of the multiple grinding stones constituting the grinding wheel bite into the back surface of the wafer.

[0006] In addition, after the multiple grinding wheels bite into the wafer, the grinding wheel is lowered straight down to continue grinding, and as a result, contact between the outer peripheral side of each grinding wheel and the inner peripheral side of the ring-shaped reinforcement portion causes a further increase in the number of chippings on the inner edge of the top surface of the ring-shaped reinforcement portion, and the size of existing chippings becomes larger.

[0007] Chipping on the inner periphery of the top surface of the ring-shaped reinforcement can lead to, for example, cracking of the wafer. In addition, after the TAIKO process, wet etching may be performed on the back side of the wafer, and if chipping is formed on the inner periphery of the top surface of the ring-shaped reinforcement, etching on the inner periphery will progress so as to expand the chipping.

[0008] As a result, the inner periphery becomes a wavy circle with irregular concaves and convexes. When the inner periphery becomes a wavy circle like this, problems such as poor formation of a metal film on the back surface of the wafer and poor application of a dicing tape due to air bubbles getting between the back surface of the wafer and the dicing tape when applying the dicing tape to the back surface of the wafer can occur. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2007-19461 A Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention has been made in consideration of the above problems, and aims to reduce the number and size of chipping that occurs on the inner peripheral edge of the top surface of the ring-shaped reinforcing portion in the TAIKO process. [Means for solving the problem]

[0011] According to one aspect of the present invention, there is provided a method for grinding a wafer, which forms a thin plate portion and a ring-shaped reinforcing portion surrounding the outer periphery of a disk-shaped wafer by grinding an area inside an outer periphery of the wafer in the radial direction of the wafer, the method including: a holding step of holding the wafer on a chuck table rotatable about a rotation axis arranged so as to pass through the center of the chuck table in the radial direction; and, after the holding step, a circular base and a plurality of grinding wheels arranged along the circumferential direction of the base on one side of the base, wherein a grinding wheel having an outer diameter smaller than the outer diameter of the wafer as determined by the plurality of grinding wheels when rotated around a spindle arranged at the center of the base in the radial direction is lowered relatively to the chuck table to bring the grinding wheel and the wafer closer together to grind the plurality of grinding wheels. The present invention provides a method for grinding a wafer, comprising: a first grinding step of forming the ring-shaped reinforcing portion by grinding the wafer with a bottom surface of a grinding wheel; a second grinding step of grinding an inner peripheral side surface of the ring-shaped reinforcing portion with an outer peripheral side surface of the grinding wheels by moving the grinding wheel relatively to the wafer in the radial direction of the wafer after the holding step; a first separating step of separating the outer peripheral side surfaces of the grinding wheels from the inner peripheral side surface of the ring-shaped reinforcing portion by moving the grinding wheel relatively to the wafer in the radial direction of the wafer after the first grinding step and the second grinding step; and a second separating step of separating the bottom surfaces of the grinding wheels from the top surface of the thin plate portion by raising the grinding wheel relatively to the chuck table after the first grinding step and the second grinding step.

[0012] Preferably, the first grinding step and the second grinding step are completed simultaneously.

[0013] Also, preferably, the first and second separating steps are initiated simultaneously.

[0014] Also preferably, each of the plurality of grinding wheels is a rough grinding wheel. Effect of the Invention

[0015] A wafer grinding method according to one embodiment of the present invention includes a second grinding step in which the inner peripheral side surface of the ring-shaped reinforcement portion is ground with the outer peripheral side surfaces of multiple grinding stones by moving the grinding wheel relatively to the wafer in the radial outward direction of the wafer.

[0016] The second grinding process can remove to some extent chipping formed on the inner peripheral side surface of the ring-shaped reinforcement portion when the bottom surfaces of the multiple grinding wheels bite into the back surface of the wafer and when the grinding feed is performed by lowering the grinding wheel straight down.

[0017] Furthermore, the wafer grinding method includes a first separating step of separating the outer peripheral side surfaces of the multiple grinding stones from the inner peripheral side surface of the ring-shaped reinforcement portion by moving the grinding wheel relatively inward in the radial direction of the wafer.

[0018] The first separating step shortens the contact time between the outer peripheral side surfaces of the grinding wheels and the inner peripheral side surface of the ring-shaped reinforcement, compared to when the grinding wheel is raised straight up with the outer peripheral side surfaces of the grinding wheels in contact with the inner peripheral side surface of the ring-shaped reinforcement, and the grinding wheel is moved above the top surface of the ring-shaped reinforcement, thereby reducing the number and length of chipping that occurs on the inner edge of the top surface of the ring-shaped reinforcement. [Brief description of the drawings]

[0019] [Figure 1] FIG. 2 is a flow diagram of a wafer grinding method according to the first embodiment. [Diagram 2] 11 is a perspective view of a wafer and a protective member showing a protective member attaching step. FIG. [Diagram 3] FIG. 4 is a partial cross-sectional side view of the grinding apparatus showing a holding process. [Figure 4] FIG. 4 is a partial cross-sectional side view of the grinding device showing a first grinding step. [Diagram 5] FIG. 5(A) is a plan view of the wafer after the first grinding step, and FIG. 5(B) is a partially enlarged view of FIG. 5(A). [Figure 6]FIG. 4 is a partial cross-sectional side view of the grinding apparatus showing a second grinding step. [Figure 7] FIG. 7(A) is a plan view of the wafer after the second grinding step, and FIG. 7(B) is a partially enlarged view of FIG. 7(A). [Figure 8] FIG. 4 is a partial cross-sectional side view of the grinding apparatus showing a first separating step. [Figure 9] FIG. 11 is a partial cross-sectional side view of the grinding apparatus showing a second separating step. [Figure 10] 13 is a Gantt chart of a grinding step and a separating step in the second embodiment. [Figure 11] 1 is a partial cross-sectional side view of the grinding apparatus showing a state in which the first and second grinding steps are simultaneously completed. FIG. [Figure 12] 13 is a Gantt chart of a grinding step and a separating step in the third embodiment. [Figure 13] 1 is a partial cross-sectional side view of the grinding apparatus illustrating a state in which first and second separating steps are started simultaneously. FIG. [Figure 14] 13 is a Gantt chart of a grinding step and a separating step in the fourth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] (First embodiment) An embodiment according to one aspect of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a flow diagram of a grinding method for a wafer 11 (see Fig. 2 etc.) according to the first embodiment. First, the wafer 11 will be described with reference to Fig. 2.

[0021] 2, the wafer 11 has a disk shape. The wafer 11 has a substrate such as a silicon single crystal substrate, a compound semiconductor single crystal substrate, etc. A plurality of dividing lines 13 are set in a lattice pattern on a surface 11a of the wafer 11.

[0022] Devices 15 such as ICs (Integrated Circuits) are formed in each small area defined by the plurality of division lines 13. There are no limitations on the type, number, shape, structure, size, arrangement, etc. of the devices 15 on the wafer 11.

[0023] In grinding the wafer 11, a circular area of ​​the back surface 11b corresponding to a circular area (ie, device area 15a) containing a plurality of devices 15 on the front surface 11a is ground to thin a portion of the wafer 11.

[0024] Before grinding the wafer 11, a resin protective member 17 having approximately the same diameter as the wafer 11 is attached to the front surface 11a. The protective member 17 is, for example, a tape having a base layer and an adhesive layer. The adhesive layer of the tape is attached to the front surface 11a of the wafer 11.

[0025] However, the protective member 17 may have only a base layer without the adhesive layer. In this case, the protective member 17 is attached to the surface 11a by thermocompression bonding. By attaching the protective member 17 to the surface 11a, it is possible to reduce the impact on the device 15 during grinding.

[0026] The wafer 11 is ground in the form of a laminate 19 in which the wafer 11 and the protective member 17 are bonded together. Next, the grinding device 2 will be described with reference to Figures 3 and 4. As shown in Figure 3 and subsequent figures, the X-axis direction, Y-axis direction, and Z-axis direction (vertical direction, up-down direction) in the grinding device 2 are perpendicular to one another.

[0027] 3, the grinding device 2 includes a disk-shaped chuck table 4. The chuck table 4 has a disk-shaped frame 6 made of, for example, non-porous ceramics. A circular recess is formed on the upper surface of the frame 6. A disk-shaped porous plate 8 made of porous ceramics is fixed in this recess.

[0028] The upper surface of the porous plate 8 has a conical shape in cross section. The center of the porous plate 8 protrudes by, for example, 20 μm compared to the outer periphery. Note that in the drawings, the amount of protrusion of the center of the porous plate 8 is exaggerated for ease of explanation.

[0029] The upper surface of the porous plate 8 and the upper surface of the frame 6 are substantially flush with each other, and function as a holding surface 4a for suction-holding the wafer 11 via the protective member 17. The porous plate 8 is connected to a suction source (not shown) such as a vacuum pump through a predetermined flow path.

[0030] A rotary drive source (not shown) such as a motor is provided below the frame 6 for rotating the chuck table 4. The chuck table 4 can rotate around a rotary shaft 4b by the power of the rotary drive source. In FIG. 3, the rotary shaft 4b is simply indicated by a dashed line.

[0031] The rotation axis 4b is disposed so as to be perpendicular to the bottom surface of the chuck table 4 and pass through the radial center 4c of the chuck table 4. Furthermore, the rotation axis 4b is tilted at a small angle with respect to the Z-axis direction in the XZ plane, and the chuck table 4 is rotatable around the rotation axis 4b in this tilted state.

[0032] The chuck table 4 and the rotary drive source are supported movably along the X-axis direction by an X-axis direction moving mechanism (not shown) including a ball screw (not shown). As shown in FIG 4, a rough grinding unit 10 is disposed above the chuck table 4.

[0033] The rough grinding unit 10 includes a cylindrical spindle housing (not shown). A Z-axis direction moving mechanism (not shown) including a ball screw (not shown) is connected to the spindle housing. The Z-axis direction moving mechanism moves the rough grinding unit 10 along the Z-axis direction.

[0034] A part of the cylindrical spindle 12 is rotatably accommodated in the space inside the spindle housing. In the first embodiment, the longitudinal direction of the spindle housing and the spindle 12 is arranged along the Z-axis direction.

[0035] A rotation drive source (not shown), such as a motor, is provided on a portion of the upper side of the spindle 12. The lower end of the spindle 12 protrudes downward beyond the lower end of the spindle housing. The center of the upper surface of a disk-shaped mount 14 is fixed to the lower end of the spindle 12.

[0036] An annular rough grinding wheel (grinding wheel) 16 is fixed to the underside of the mount 14 using a fixing member (not shown) such as a bolt. In this manner, the rough grinding wheel 16 is attached to the lower end of the spindle 12 via the mount 14. The rough grinding wheel 16 includes an annular wheel base (base) 18 made of a metal such as an aluminum alloy.

[0037] The spindle 12 is disposed in the radial center of the wheel base 18, and the radial center 18a of the wheel base 18, the radial center 14a of the mount 14, and the rotation center 12a of the spindle 12 are approximately aligned.

[0038] A plurality of rough grinding wheels (grinding wheels) 20 are arranged at approximately equal intervals along the circumferential direction of the wheel base 18 on the bottom surface (one surface) 18b side of the wheel base 18. The rough grinding wheels 20 include abrasive grains made of cBN (cubic boron nitride), diamond, or the like, and a bond material, such as a vitrified bond or a resin bond, for fixing the abrasive grains.

[0039] The average grain size of the abrasive grains of the rough grinding wheel 20 is larger than that of the so-called finish grinding wheel. The abrasive grains of the rough grinding wheel 20 have a grain size of, for example, #240 to #1200, more preferably #240 to #1000.

[0040] The grain size is described in JIS R6001-2:2017 (Grain size of abrasives for grinding wheels - Part 2: Fine powder) of the JIS standard established by the Japanese Industrial Standards Committee. Note that the grain sizes of #240 to #1200 and #240 to #1000 may be evaluated by a sedimentation test method or an electrical resistance test method.

[0041] The outer diameters of the rough grinding wheels 20 defined by the outer peripheral side surfaces 20b of the rough grinding wheels 20 are smaller than the outer diameter of the wafer 11 and larger than the radius of the device region 15a on the surface 11a. Also, the inner diameters of the rough grinding wheels 20 defined by the inner peripheral side surfaces of the rough grinding wheels 20 are smaller than the radius of the device region 15a on the surface 11a.

[0042] In one example, the segment width of one rough grinding wheel 20 (i.e., the length of one rough grinding wheel 20 in the radial direction of the wheel base 18) is 4 mm, so the difference between the outer diameter and inner diameter of multiple rough grinding wheels 20 is 8 mm (= 4 mm x 2).

[0043] As described above, the rotation center 12a of the spindle 12 and the radial center 18a of the wheel base 18 are approximately aligned, but a deviation of about 100 μm to 300 μm is permitted. If there is such a deviation between the rotation center 12a and the center 18a, when the rough grinding wheel 16 is rotated around the spindle 12, the rough grinding stones 20 will rotate and run out.

[0044] Even if rotational runout occurs, the outer diameter defined by the multiple rough grinding stones 20 when the rough grinding wheel 16 is rotating around the spindle 12 is smaller than the outer diameter of the wafer 11 and larger than the radius of the device region 15a.

[0045] During grinding, due to the conical holding surface 4a and the slight inclination of the rotation shaft 4b, the wafer 11 is ground in an area corresponding to a 1 / 2 arc of the circumference (i.e., an arc of a semicircle) of a ring formed by a plurality of rough grinding wheels 20 (see FIG. 4) arranged in a ring shape, rather than the entire circumference (see FIG. 5(A)).

[0046] A grinding water supply nozzle (not shown) capable of supplying grinding water such as pure water toward the contact area (i.e., the processing area) between the rough grinding stone 20 and the wafer 11 is provided near the rough grinding wheel 16. During grinding, the grinding water is used to remove heat and grinding debris generated in the processing area.

[0047] Next, a method for grinding the wafer 11 will be described with reference to Fig. 1. As shown in Fig. 1, each step is performed in the order of a protective member attaching step S10, a holding step S20, a grinding step S30, and a separating step S40.

[0048] The grinding step S30 includes a first grinding step S32 and a second grinding step S34, and the separating step S40 includes a first separating step S42 and a second separating step S44. In the first embodiment, particularly, the second grinding step S34 is performed after the first grinding step S32, and then the second separating step S44 is performed after the first separating step S42.

[0049] 2 is a perspective view showing the protective member attachment step S10. As described above, the protective member 17 is attached to the front surface 11a of the wafer 11 to form the laminate 19. After the protective member attachment step S10, the process proceeds to the holding step S20.

[0050] 3 is a partial cross-sectional side view of the grinding apparatus 2 showing the holding step S20. In the holding step S20, first, the stack 19 is placed on the holding surface 4a of the chuck table 4 so that the protective member 17 contacts the holding surface 4a. At this time, the stack 19 is placed on the holding surface 4a so that the center of the holding surface 4a and the center of the back surface 11b (or front surface 11a) of the wafer 11 approximately coincide with each other.

[0051] Then, a negative pressure from a suction source is transmitted to the upper surface of the porous plate 8. As a result, the wafer 11 is suction-held on the holding surface 4a via the protective member 17 so as to follow the shape of the holding surface 4a, with the back surface 11b exposed upward.

[0052] After the holding step S20, the chuck table 4 and the rough grinding unit 10 are used to grind a range to a predetermined depth from the back surface 11b of the wafer 11 (grinding step S30). Fig. 4 is a partial cross-sectional side view of the grinding apparatus 2 showing the first grinding step S32.

[0053] In the first grinding step S32 in the first embodiment, first, the spindle 12 and the chuck table 4 are rotated in a predetermined direction, respectively. The rotation of the spindle 12 and the chuck table 4 continues at least until the flow shown in FIG. 1 is completed.

[0054] Furthermore, the position of the rough grinding unit 10 in the X-axis direction is adjusted by the X-axis direction movement mechanism so that the orbits of the multiple rough grinding wheels 20 overlap with the rotation axis 4b of the chuck table 4 in a plan view. In this state, the rough grinding unit 10 is moved downward by the Z-axis direction movement mechanism, thereby lowering the rough grinding wheel 16 relative to the chuck table 4.

[0055] In this manner, the rough grinding wheel 16 and the wafer 11 are brought close to each other, and a circular area of ​​the back surface 11b that is located inside the outer peripheral edge 11d of the wafer 11 in the radial direction 11c of the wafer 11 and corresponds to the device region 15a is ground by the bottom surfaces 20a of multiple rough grinding stones 20.

[0056] 5(A), a thin plate portion 21a and a ring-shaped reinforcing portion 21b surrounding the outer periphery of the thin plate portion 21a are formed on the wafer 11. The thin plate portion 21a and the ring-shaped reinforcing portion 21b define a recess 21c that is a disk-shaped space. An example of the grinding conditions in the first grinding step S32 is shown below.

[0057] Chuck table rotation speed: 300 rpm Grinding wheel speed: 4000 rpm Grinding feed rate: 6μm / s Grinding water supply rate: 4.0L / min

[0058] Fig. 5(A) is a plan view of the wafer 11 after the first grinding step S32. Fig. 5(A) shows saw marks (i.e., grinding marks) formed on the thin plate portion 21a in the first grinding step S32.

[0059] In Figure 5 (A), the area of ​​the ring formed by multiple rough grinding wheels 20 corresponding to the 1 / 2 arc that contributes to grinding is shown by a relatively thick solid line, and the area corresponding to the remaining 1 / 2 arc that does not contribute to grinding (i.e., does not contact the wafer 11) is shown by a dashed line.

[0060] Incidentally, when the bottom surface 20a of the rough grinding wheel 20 comes into contact with the back surface 11b (i.e., the moment the rough grinding wheel 16 bites into the back surface 11b of the wafer 11), chipping 11e (see Figure 5(B)) is likely to occur on the back surface 11b of the wafer 11 located on the outer periphery of the multiple rough grinding wheels 20.

[0061] Furthermore, when the rough grinding wheel 16 is lowered relative to the chuck table 4, the outer peripheral side surface 20b of each rough grinding stone 20 comes into contact with the inner peripheral side surface 21b1 of the ring-shaped reinforcement portion 21b, so that the number of chippings 11e on the inner peripheral edge of the top surface 21b2 (see Figure 5 (B)) of the ring-shaped reinforcement portion 21b further increases and the size of the existing chippings 11e becomes larger.

[0062] Fig. 5(B) is a partially enlarged view of the area surrounded by the dashed-dotted rectangular frame in Fig. 5(A). As shown in Fig. 5(B), the chipping 11e is formed so as to extend from the inner peripheral edge of the top surface 21b2 of the ring-shaped reinforcing portion 21b toward the outside in the radial direction 11c of the wafer 11.

[0063] If the chipping 11e remains on the ring-shaped reinforcing portion 21b, this can lead to cracking of the wafer 11, poor formation of the metal film on the rear surface 11b, poor application of the dicing tape to the rear surface 11b, and the like, as described above.

[0064] Therefore, in the first embodiment, after the first grinding process S32, the inner peripheral side surface 21b1 of the ring-shaped reinforcing portion 21b is ground with the outer peripheral side surface 20b of multiple rough grinding wheels 20 so as to expand the diameter of the recess 21c (second grinding process S34).

[0065] Fig. 6 is a partial cross-sectional side view of the grinding device 2 showing the second grinding step S34. Note that in Fig. 6, the position of the inner peripheral side surface 21b1 of the ring-shaped reinforcing portion 21 before the start of the second grinding step S34 is shown by a dashed line. However, the dashed line showing the previous position of the inner peripheral side surface 21b1 is shown in an area in Fig. 6 where there is no rough grinding wheel 20.

[0066] In the first embodiment, the position of the rough grinding unit 10 is fixed in the Z-axis direction and within the XY plane, and the chuck table 4 is moved in the -X direction by the X-axis direction moving mechanism, thereby moving the rough grinding unit 10 relatively in the +X direction.

[0067] In this manner, the inner peripheral side surface 21b1 of the ring-shaped reinforcing portion 21b is ground by relatively moving the rough grinding wheel 16 outward in the radial direction 11c of the wafer 11 with respect to the wafer 11. An example of grinding conditions in the second grinding step S34 is shown below.

[0068] Chuck table rotation speed: 300 rpm Grinding wheel speed: 4000 rpm Grinding feed rate: 0mm / s Grinding water supply rate: 4.0L / min Movement of the chuck table in the X-axis direction: A specified value between 100 μm and 200 μm Chuck table movement speed: 20μm / s

[0069] Fig. 7(A) is a plan view of the wafer 11 after the second grinding step S34, and Fig. 7(B) is a partially enlarged view of the area surrounded by the dashed-dotted rectangular frame in Fig. 7(A). By the second grinding step S34, chipping 11e formed on the inner peripheral side surface 21b1 (including the inner peripheral edge of the top surface 21b2) of the ring-shaped reinforcing portion 21b can be removed to a certain extent.

[0070] However, since some new chippings 11e are formed in the second grinding step S34 as well, not all chippings 11e are necessarily removed in the second grinding step S34.

[0071] Meanwhile, in a typical TAIKO process, after the first grinding step S32, the rough grinding unit 10 is raised straight up by the Z-axis movement mechanism, thereby pulling the rough grinding wheel 16 out of the recess 21c and moving the rough grinding wheel 16 above the wafer 11.

[0072] However, at this time, the rough grinding wheel 16 rises with the outer peripheral side surface 20b of the multiple rough grinding stones 20 in contact with the inner peripheral side surface 21b1 of the ring-shaped reinforcement portion 21b, so that new chipping 11e is formed on the inner peripheral edge of the top surface 21b2 of the ring-shaped reinforcement portion 21b, or the size of the existing chipping 11e increases.

[0073] To address this problem, it is considered that the grinding method can be devised to suppress contact between the outer peripheral side surface 20b of the multiple rough grinding stones 20 and the inner peripheral side surface 21b1 of the ring-shaped reinforcement portion 21b when the rough grinding wheel 16 is raised.

[0074] Specifically, first, the rough grinding wheel 16 is lowered along the Z-axis direction, and the chuck table 4 is moved along the X-axis direction so that the rough grinding wheel 16 approaches the center of the radial direction 11c of the wafer 11, thereby grinding the back surface 11b.

[0075] As a result, the inner peripheral side surface 21b1 of the ring-shaped reinforcing portion 21b becomes an inverted truncated cone shape instead of a cylindrical shape. Next, the rough grinding wheel 16 is raised straight along the Z-axis direction. At this time, the outer peripheral side surfaces 20b of the multiple rough grinding stones 20 do not contact the inner peripheral side surface 21b1 of the ring-shaped reinforcing portion 21b.

[0076] However, when such a grinding mode is adopted, the inner peripheral side surface 21b1 becomes an inverted truncated cone shape, which causes a new problem that the area that can be used as the device region 15a is narrowed accordingly. Furthermore, chipping 11e formed on the top surface 21b2 when the bottom surfaces 20a of the multiple rough grinding wheels 20 bite into the back surface 11b of the wafer 11 still remains.

[0077] In order to solve this problem, as shown in FIG. 8, after the second grinding step S34, the rough grinding wheel 16 is moved relatively inward in the radial direction 11c of the wafer 11 with respect to the wafer 11, thereby separating the outer peripheral side surface 20b of the multiple rough grinding stones 20 from the inner peripheral side surface 21b1 of the ring-shaped reinforcement portion 21b (first separating step S42).

[0078] In the first embodiment, the position of the rough grinding unit 10 is fixed in the Z-axis direction and within the XY plane, and the rough grinding unit 10 is moved in the -X direction by moving the chuck table 4 in the +X direction using an X-axis direction moving mechanism.

[0079] 8 is a partial cross-sectional side view of the grinding apparatus 2 showing the first separating step S42. An example of processing conditions in the first separating step S42 is shown below.

[0080] Chuck table rotation speed: 300 rpm Grinding wheel speed: 4000 rpm Grinding feed rate: 0mm / s Grinding water supply rate: 4.0L / min Chuck table movement in the X-axis direction: 1.0 mm Chuck table movement speed: 20μm / s

[0081] The first separation step S42 shortens the contact time between the outer peripheral side surface 20b and the inner peripheral side surface 21b1, compared to the case where the rough grinding wheel 16 is moved straight up with the outer peripheral side surface 20b of the multiple rough grinding wheels 20 in contact with the inner peripheral side surface 21b1 of the ring-shaped reinforcement portion 21b, and the rough grinding wheel 16 is moved above the top surface 21b2 of the ring-shaped reinforcement portion 21b. Therefore, the number and length of chippings 11e generated on the inner peripheral edge of the top surface 21b2 of the ring-shaped reinforcement portion 21b can be reduced.

[0082] In the first embodiment, after the first separation step S42, as shown in FIG. 9, the rough grinding wheel 16 is raised relative to the chuck table 4 to separate the bottom surfaces 20a of the multiple rough grinding stones 20 from the top surfaces 21a1 of the thin plate portions 21a (second separation step S44).

[0083] That is, after the outer peripheral side surface 20b of the multiple rough grinding wheels 20 is separated from the inner peripheral side surface 21b1 of the ring-shaped reinforcement portion 21b in the first separation process S42, the rough grinding unit 10 is moved upward by the Z-axis direction moving mechanism in the second separation process S44.

[0084] 9 is a partial cross-sectional side view of the grinding apparatus 2 showing the second separating step S44. An example of processing conditions in the second separating step S44 is shown below.

[0085] Chuck table rotation speed: 300 rpm Grinding wheel speed: 4000 rpm Rising speed of rough grinding unit: specified value between 10mm / s and 90mm / s Grinding water supply rate: 4.0L / min

[0086] In the first embodiment, the second grinding step S34 can remove chippings 11e formed on the inner peripheral side surface 21b1 of the ring-shaped reinforcing portion 21b to some extent. Also, the first separating step S42 can reduce the number and length of chippings 11e formed on the inner peripheral edge of the top surface 21b2 of the ring-shaped reinforcing portion 21b compared to the case of employing the normal TAIKO process.

[0087] 1, the thin plate portion 21a is subjected to finish grinding. The finish grinding wheel (not shown) has a plurality of finish grinding stones arranged at approximately equal intervals along the circumferential direction of the wheel base 18 on the bottom surface 18b side of the wheel base 18.

[0088] The average grain size of the abrasive grains of the finish grinding stone is smaller than the average grain size of the rough grinding stone 20. As the abrasive grains of the finish grinding stone, for example, abrasive grains having a grain size of #5000 to #10000 are used.

[0089] The grain size may be evaluated by a sedimentation test method or an electrical resistance test method, but for grain sizes not listed in JIS R6001-2:2017, the notation commonly used in the industry that manufactures and sells grinding wheels shall be followed or equivalent.

[0090] However, in the finish grinding, the thin plate portion 21a located inside the ring-shaped reinforcing portion 21b in the radial direction 11c of the wafer 11 is ground in a direction proceeding from the back surface 11b to the front surface 11a. In other words, since the finish grinding wheel does not come into contact with the ring-shaped reinforcing portion 21b, new chipping 11e is not formed on the inner peripheral side surface 21b1 (including the inner peripheral edge of the top surface 21b2) of the ring-shaped reinforcing portion 21b.

[0091] (Second embodiment) Next, a second embodiment will be described with reference to Fig. 10 and Fig. 11. As shown in Fig. 10, in the second embodiment, the second grinding process S34 is started after the start of the first grinding process S32. After that, the first grinding process S32 and the second grinding process S34 are ended simultaneously.

[0092] Fig. 10 is a Gantt chart of the first grinding step S32, the second grinding step S34, the first separating step S42, and the second separating step S44 in the second embodiment. For convenience of explanation, the protective member attaching step S10 and the holding step S20 are omitted in Fig. 10, but in reality, both steps are performed before the first grinding step S32.

[0093] In addition, the second grinding step S34 may be started after the first grinding step S32, as shown by the solid line in FIG. 10, or may be started simultaneously with the first grinding step S32, as shown by the dashed line in FIG.

[0094] 11 is a partial cross-sectional side view of the grinding device 2 showing how the first grinding step S32 and the second grinding step S34 are simultaneously completed. In the second embodiment, in the grinding step S30, there is a time period during which the X-axis direction moving mechanism and the Z-axis direction moving mechanism are simultaneously operated so that the trajectory of the movement of the rough grinding wheel 16 is inclined with respect to the Z-axis direction.

[0095] In this way, since there are time periods during which the first grinding process S32 and the second grinding process S34 are performed simultaneously, the total time required for grinding can be shortened compared to the case in which the second grinding process S34 is started after the first grinding process S32 is completed.

[0096] (Third embodiment) Next, a third embodiment will be described with reference to Fig. 12 and Fig. 13. As shown in Fig. 12, in the third embodiment, the second grinding step S34 is started after the first grinding step S32 is completed. Then, after the second grinding step S34 is completed, the first separating step S42 and the second separating step S44 are simultaneously started.

[0097] Fig. 12 is a Gantt chart of the first grinding step S32, the second grinding step S34, the first separating step S42, and the second separating step S44 in the third embodiment. For convenience of explanation, the protective member attaching step S10 and the holding step S20 are omitted in Fig. 12, but in reality, both steps are performed before the first grinding step S32.

[0098] In addition, the second separation step S44 may continue after the first separation step S42 is completed, as shown by the dashed line in FIG. 12, or may end simultaneously with the completion of the first separation step S42, as shown by the solid line in FIG.

[0099] 13 is a partial cross-sectional side view of the grinding apparatus 2 showing the simultaneous start of the first separating step S42 and the second separating step S44. In the third embodiment, in the separating step S40, there is a time period during which the X-axis direction moving mechanism and the Z-axis direction moving mechanism are operated simultaneously so that the trajectory of the movement of the rough grinding wheel 16 is inclined with respect to the Z-axis direction.

[0100] In this way, since there is a time period during which the first separation step S42 and the second separation step S44 are performed simultaneously, the total time required for grinding can be shortened compared to the case where the second separation step S44 is started after the first separation step S42 is completed.

[0101] (Fourth embodiment) Next, a fourth embodiment will be described with reference to Fig. 14. As shown in Fig. 14, in the fourth embodiment, the first grinding step S32 and the second grinding step S34 are simultaneously completed, and the first separating step S42 and the second separating step S44 are simultaneously started.

[0102] Fig. 14 is a Gantt chart of the first grinding step S32, the second grinding step S34, the first separating step S42, and the second separating step S44 in the fourth embodiment. For convenience of explanation, the protective member attaching step S10 and the holding step S20 are omitted in Fig. 14, but in reality, both steps are performed.

[0103] The second grinding step S34 may be started after the first grinding step S32, as indicated by the solid line in FIG. 14, or may be started simultaneously with the first grinding step S32, as indicated by the dashed line in FIG.

[0104] In addition, the second separation step S44 may continue after the first separation step S42 is completed, as shown by the dashed line in FIG. 14, or may end simultaneously with the first separation step S42, as shown by the solid line in FIG. 14.

[0105] In the fourth embodiment, the total time required for grinding can be further shortened compared to the first to third embodiments. In addition, the structures, methods, etc. according to the above-mentioned embodiments can be appropriately modified without departing from the scope of the present invention. Various modified examples that can be applied to the above-mentioned embodiments will be described below.

[0106] In the above-described embodiment, the rough grinding wheel 16 and the chuck table 4 are moved toward and away from each other in the Z-axis direction by a Z-axis direction moving mechanism fixed to the rough grinding unit 10, but instead of or in addition to this, the chuck table 4 may be moved along the Z-axis direction.

[0107] In addition, in the above-described embodiment, the movement of the rough grinding unit 10 outward and inward in the radial direction 11c of the wafer 11 is performed by an X-axis direction moving mechanism supporting the chuck table 4, but instead of or together with this, the rough grinding unit 10 may be moved along the X-axis direction.

[0108] Furthermore, in the above-described embodiment, the longitudinal direction of the spindle 12 is arranged approximately parallel to the Z-axis direction, and the rotation axis 4b of the chuck table 4 is inclined with respect to the Z-axis direction, but as long as the thin plate portion 21a and the ring-shaped reinforcement portion 21b can be formed, the longitudinal direction of the spindle 12 may be inclined with respect to the Z-axis direction, and the rotation axis 4b of the chuck table 4 may be arranged approximately parallel to the Z-axis direction.

[0109] In the above embodiment, the holding surface 4a of the chuck table 4 has a conical shape, but instead, the holding surface 4a may have a biconcave shape. When the holding surface 4a has a biconcave shape, the outer circumferential edge and the center of the holding surface 4a have a shape that protrudes compared to an intermediate region between the outer circumferential edge and the center in a cross-sectional view.

[0110] The intermediate region between the outer circumferential end and the center is recessed by a predetermined value, for example, of 1 μm or more and 20 μm or less, compared to the outer circumferential end and the center, and a smooth curved surface is formed on the holding surface 4a except for the outer circumferential end and the center.

[0111] Incidentally, the outer diameter defined by the plurality of rough grinding stones 20 when the rough grinding wheel 16 is rotated around the spindle 12 may be smaller than the radius of the device region 15a. When such a small-diameter rough grinding wheel 26 is used, if the wafer 11 is ground according to the flow shown in Fig. 1, a disk-shaped or cylindrical unground region remains in the center of the wafer 11 at the start of the first separation step S42.

[0112] Therefore, after the start of the first separating step S42, the unground area is removed by grinding. As an example, in the first separating step S42, the relative moving distance of the rough grinding wheel 16 with respect to the chuck table 4 is increased compared to the first embodiment, thereby removing the disk-shaped or cylindrical unground area. Then, after the removal of the unground area, the second separating step S44 is performed. [Explanation of symbols]

[0113] 2: grinding device, 4: chuck table, 4a: holding surface, 4b: rotating shaft, 4c: center 6: frame, 8: porous plate, 10: rough grinding unit 11: wafer, 11a: front surface, 11b: back surface 11c: radial direction, 11d: outer periphery, 11e: chipping 12: spindle, 12a: rotation center, 14: mount, 14a: center 13: planned division line, 15: device, 15a: device region, 17: protective member 16: Rough grinding wheel (grinding wheel) 18: Wheel base (base), 18a: Center, 18b: Bottom surface (one side) 19: Laminate 20: rough grinding wheel (grinding wheel), 20a: bottom surface, 20b: outer peripheral side surface 21a: Thin plate part, 21a1: Top surface 21b: ring-shaped reinforcing portion, 21b1: inner peripheral side surface, 21b2: top surface 21c: Recess S10: protective member attachment step, S20: holding step S30: Grinding step, S32: First grinding step, S34: Second grinding step S40: Separation step, S42: First separation step, S44: Second separation step

Claims

1. A method for grinding a wafer, comprising the steps of: grinding a region of a disk-shaped wafer that is inward from an outer periphery of the wafer in a radial direction of the wafer, thereby forming a thin plate portion and a ring-shaped reinforcing portion surrounding the outer periphery of the thin plate portion on the wafer, the method comprising the steps of: a holding step of holding the wafer on a chuck table rotatable around a rotation axis disposed so as to pass through a radial center of the chuck table; a first grinding step after the holding step, in which a grinding wheel including an annular base and a plurality of grinding wheels arranged along a circumferential direction of the base on one side of the base, the grinding wheel having an outer diameter smaller than an outer diameter of the wafer when rotated around a spindle arranged at the center of the base in the radial direction, is lowered relatively to the chuck table to bring the grinding wheel and the wafer closer together and grind the wafer with a bottom surface of the plurality of grinding wheels, thereby forming the ring-shaped reinforcing portion; a second grinding step of grinding an inner peripheral side surface of the ring-shaped reinforcing portion with an outer peripheral side surface of the plurality of grinding stones by moving the grinding wheel relatively to the wafer in a radial direction outward of the wafer after the holding step; a first separation step of, after the first grinding step and the second grinding step, moving the grinding wheel relatively inward in a radial direction of the wafer with respect to the wafer, thereby separating an outer peripheral side surface of the plurality of grinding stones from an inner peripheral side surface of the ring-shaped reinforcing portion; a second separating step of separating bottom surfaces of the plurality of grinding stones from a top surface of the thin plate portion by raising the grinding wheel relatively to the chuck table after the first grinding step and the second grinding step; A method for grinding a wafer, comprising:

2. 2. The method for grinding a wafer according to claim 1, wherein the first grinding step and the second grinding step are completed simultaneously.

3. 3. The method for grinding a wafer according to claim 1, wherein the first separating step and the second separating step are started simultaneously.

4. 2. The method of claim 1, wherein each of said plurality of grinding wheels is a coarse grinding wheel.

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