Grinding method for workpiece

Abstract

To provide a grinding method for a work-piece that can reduce the probability that a device may be broken, without substantially extending a time during which grinding is completed, in grinding a tabular work-piece having the device provided at a front surface side, from a rear surface side thereof.SOLUTION: A grinding method for a work-piece includes: a first grinding step of grinding a work-piece from a rear surface side thereof to form, in the work-piece, a first discoid thin plate part and an annular first thick plate part surrounding the first thin plate part; a second grinding step of grinding the first thin plate part from a rear surface side thereof to form, in the first thin plate part, a second discoid thin plate part which is smaller in diameter and thinner than the first thin plate part and an annular second thick plate part surrounding the second thin plate part, after the first grinding step; and a third step of grinding the second thick plate part and the second thin plate part from rear surface sides thereof using a second grinding stone including abrasive grain smaller than abrasive grain of a first grinding stone, to form a third discoid thin plate part which is larger in diameter and thinner than the second thin plate part.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present invention relates to a method for grinding a workpiece, which is applied when grinding a plate-shaped workpiece such as a wafer. [Background technology]

[0002] To realize small and lightweight device chips, there are increasing opportunities to thin wafers with devices such as integrated circuits mounted on their front side. For example, the front side of the wafer is held by a chuck table, and the chuck table and a grinding wheel with a grinding stone containing abrasive grains (grinding stone) are rotated relative to each other, and the grinding stone is pressed against the back side of the wafer while a liquid such as pure water is supplied, thereby grinding and thinning the wafer.

[0003] However, when the entire wafer is thinned using the above-mentioned method, the rigidity of the wafer is significantly reduced, making it difficult to handle in subsequent processes. Therefore, a technique has been proposed in which the central (inner) region of the wafer where the devices are provided is ground, and the outer edge (outer) region is left unground, thereby maintaining a sufficiently high rigidity of the wafer after grinding (see, for example, Patent Document 1).

[0004] In this technique, a grinding wheel having a fixed grinding stone containing abrasive grains of a certain size is first used to roughly grind the central region of the wafer, forming a disk-shaped thin plate portion and an annular thick plate portion surrounding the thin plate portion on the wafer. In this way, the use of a grinding wheel having a fixed grinding stone containing large abrasive grains can shorten the time required to grind the wafer compared to the use of a grinding wheel having a fixed grinding stone containing relatively small abrasive grains.

[0005] On the other hand, when a wafer is ground using a grinding wheel with a fixed grinding stone containing large abrasive grains, a damaged layer containing scratches and distortions caused by the grinding is generated on the ground surface, and the mechanical strength (transverse strength) of the thin plate is likely to be insufficient. Therefore, after the wafer is roughly ground, the thin plate is further ground using a grinding wheel with a fixed grinding stone containing relatively small abrasive grains to remove the damaged layer. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-176896 Summary of the Invention [Problem to be solved by the invention]

[0007] However, when grinding the thin portion to remove the damaged layer, if the grinding wheel comes into contact with the side of the thick portion, the thick portion may be chipped. Therefore, when removing the damaged layer, only the central region of the thin portion is ground to prevent the grinding wheel from coming into contact with the thick portion. However, this method leaves the damaged layer in the outer edge region of the thin portion (the region close to the boundary with the thick portion). As a result, during subsequent transportation, cracks extend from the remaining damaged layer to the front surface of the wafer, easily damaging the device.

[0008] Although it is possible to prevent device damage due to cracks extending from the damaged layer by increasing the thickness of the thinned portion and increasing the distance from the device on the front side to the damaged layer, in this case, a large portion of the wafer must be removed using a grinding wheel with a fixed grinding stone containing relatively small abrasive grains, which can remove only a small amount per unit time, in order to thin the thinned portion to the final thickness. This means that the time required to complete the grinding process is significantly longer.

[0009] The present invention has been made in consideration of such problems, and its object is to provide a method for grinding a workpiece that, when grinding a plate-shaped workpiece having a device on its front surface from its back surface, can reduce the probability of damaging the device without significantly increasing the time required to complete grinding. [Means for solving the problem]

[0010] According to one aspect of the present invention, there is provided a method for grinding a workpiece, in which a plate-shaped workpiece having a plurality of devices provided on a front surface thereof is ground from a back surface thereof opposite to the front surface thereof using a grinding wheel attached to a rotating spindle, the method comprising: a step of attaching a protective member to the front surface of the workpiece; and a step of attaching a first grinding stone containing abrasive grains to the first chuck table while the workpiece is held via the protective member on a first holding surface of the first chuck table. The first grinding stone of the first grinding wheel is brought into contact with the workpiece, The first grinding wheel and the first chuck table While moving the first holding surface in a direction along the first holding surface, a first grinding step in which the workpiece is ground from the back surface side by relatively moving the workpiece in a direction intersecting the first holding surface, thereby forming a disk-shaped first thin plate portion and an annular first thick plate portion surrounding the first thin plate portion on the workpiece; and after the first grinding step, bringing the first grinding stone of the first grinding wheel into contact with the workpiece; The first grinding wheel and the first chuck table While moving the first holding surface in a direction along the first holding surface, a second grinding step in which the first thin plate portion is ground from the back side by relatively moving the first holding surface in a direction intersecting the first holding surface to form a second thin plate portion in the first thin plate portion, the second thin plate portion being disc-shaped and thinner with a diameter smaller than that of the first thin plate portion, and a second thick plate portion in an annular shape surrounding the second thin plate portion; and a second grinding wheel containing abrasive grains smaller than those of the first grinding wheel, in a state in which the workpiece is held by the second holding surface of the second chuck table via the protective member after the second grinding step. The second grinding stone of the second grinding wheel is brought into contact with the workpiece, The second grinding wheel and the second chuck table While moving the second holding surface in a direction along the second holding surface,and a third grinding step in which the second thick plate portion and the second thin plate portion are ground from the back surface side by moving the workpiece relatively in a direction intersecting the second holding surface to form a disk-shaped third thin plate portion that is thinner and has a larger diameter than the second thin plate portion and a smaller diameter than the first thin plate portion, wherein in the first grinding step, a first thin plate portion is formed that has a thickness such that cracks that extend from a first damage layer containing scratches or distortions generated in the workpiece in the first grinding step do not reach the device during subsequent transportation, and the thickness of the workpiece removed in the second grinding step is smaller than the thickness of the workpiece removed in the first grinding step.

[0011] Preferably, the first chuck table is used as the second chuck table. Also, preferably, in the third grinding step, the speed at which the second grinding wheel and the second chuck table are moved relative to each other when grinding only the second thick portion is set to be faster than the speed at which the second grinding wheel and the second chuck table are moved relative to each other when grinding the region including the second thin portion.

[0012] Also preferably 、 In the second grinding step, a second thin plate portion is formed with a thickness such that a second damage layer containing scratches or distortions generated in the workpiece in the second grinding step does not reach the area that will become the third thin plate portion. [Effects of the Invention]

[0013] A method for grinding a workpiece according to one aspect of the present invention includes a first grinding step in which the workpiece is ground using a first grinding wheel equipped with a first grinding stone containing relatively large abrasive grains to form a first circular thin portion and a first thick portion surrounding the first thin portion on the workpiece; a second grinding step in which the first thin portion is ground using the same first grinding wheel to form a second circular thin portion that is smaller in diameter and thinner than the first thin portion and a second annular thick portion surrounding the second thin portion on the first thin portion; and a third grinding step in which the second thick portion and the second thin portion are ground using a second grinding wheel equipped with a second grinding stone containing relatively small abrasive grains to form a third circular thin portion that is larger in diameter and thinner than the second thin portion.

[0014] Therefore, compared to when the third grinding step is performed after the first grinding step without performing the second grinding step, the amount (volume) of the portion to be removed in the third grinding step is smaller by the amount of the portion removed in the second grinding step. In other words, in exchange for adding the second grinding step, which is completed in a short time using the first grinding wheel that can remove a large amount per unit time, the time required for the third grinding step can be shortened, so the time required to complete grinding can be shortened compared to when the third grinding step is performed after the first grinding step without performing the second grinding step.

[0015] Therefore, even if the first thin plate portion is made thicker and the distance from the device to the damaged layer is made sufficiently large to prevent damage to the device due to cracks extending from the damaged layer containing scratches or strain generated in the first grinding step, the time until grinding is completed does not increase significantly. Thus, according to the method for grinding a workpiece according to one aspect of the present invention, the probability of device damage can be reduced without significantly increasing the time until grinding is completed. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a perspective view that schematically shows how a protective member is attached to a plate-shaped workpiece. [Figure 2]FIG. 2 is a cross-sectional view schematically showing a state in which a workpiece is held on a chuck table via a protective member. [Figure 3] FIG. 3 is a cross-sectional view that schematically shows how a workpiece is ground by the first grinding wheel. [Figure 4] FIG. 4 is a cross-sectional view schematically showing a part of the workpiece after being ground by the first grinding wheel. [Figure 5] FIG. 5 is a cross-sectional view that schematically shows how the chuck table and the first grinding wheel are moved relatively in a direction along the upper surface of the chuck table. [Figure 6] FIG. 6 is a cross-sectional view that schematically shows how the first thin plate portion of the workpiece is ground by the first grinding wheel. [Figure 7] FIG. 7 is a cross-sectional view schematically showing a part of the workpiece after the first thin plate portion has been ground by the first grinding wheel. [Figure 8] FIG. 8 is a cross-sectional view that schematically shows how the second thick portion and the second thin portion of the workpiece are ground by the second grinding wheel. [Figure 9] FIG. 9 is a cross-sectional view schematically showing a part of the workpiece after the second thick portion and the second thin portion have been ground by the second grinding wheel. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. In the grinding method for a workpiece according to this embodiment, first, a protective member is attached to a plate-shaped workpiece to be ground (attaching step). Fig. 1 is a perspective view schematically showing how a protective member 21 is attached to a plate-shaped workpiece 11.

[0018] The workpiece 11 is typically a disk-shaped wafer made of a semiconductor such as silicon (Si). The front surface 11a of the workpiece 11 is divided into a plurality of small regions by a plurality of mutually intersecting division lines (streets) 13, and a device 15 such as an IC (Integrated Circuit) is formed in each small region. In this embodiment, a portion of the workpiece 11 corresponding to the region (device region) where the device 15 is formed is ground from the back surface 11b side opposite to the front surface 11a, thereby thinning a portion of the workpiece 11.

[0019] In this embodiment, the workpiece 11 is a disk-shaped wafer made of a semiconductor such as silicon, but there are no limitations on the material, shape, structure, size, etc. of the workpiece 11. For example, a substrate made of other materials such as semiconductors, ceramics, resins, metals, etc. can also be used as the workpiece 11. Similarly, there are no limitations on the type, number, shape, structure, size, arrangement, etc. of the devices 15.

[0020] The protective member 21 attached to the workpiece 11 is typically a circular tape (film) having a diameter roughly equal to that of the workpiece 11, a resin substrate, a wafer of the same or different type as the workpiece 11, etc. An adhesive layer that exhibits adhesive strength to the workpiece 11 is provided on the surface 21a side of this protective member 21.

[0021] Therefore, the protective member 21 can be attached to the workpiece 11 by bringing the front surface 21a side of the protective member 21 into close contact with the workpiece 11. In this embodiment, as shown in Fig. 1 , the front surface 21a side of the protective member 21 is brought into close contact with the front surface 11a of the workpiece 11, and the protective member 21 is attached to the front surface 11a of the workpiece 11. This reduces the impact applied to the front surface 11a when the workpiece 11 is ground from the back surface 11b side, thereby protecting the device 15 and the like.

[0022] After the protective member 21 is attached to the front surface 11a of the workpiece 11, the workpiece 11 is held by the holding surface of the chuck table via the protective member 21 (holding step). That is, the back surface 21b side of the protective member 21 attached to the workpiece 11 is held by the chuck table 4. FIG. 2 is a cross-sectional view that schematically shows how the workpiece 11 is held on the chuck table 4 via the protective member 21. Note that the grinding device 2 shown in FIG. 2 and other figures is used in each of the following steps.

[0023] The grinding device 2 is equipped with chuck tables (first chuck table, second chuck table) 4 configured to hold a workpiece 11. The chuck table 4 includes a disk-shaped frame 6 made of a metal such as stainless steel. A recess 6a having a circular opening at the top end is formed on the upper surface of the frame 6. A porous disk-shaped holding plate 8 made of ceramics or the like is fixed to this recess 6a.

[0024] The upper surface 8a of the holding plate 8 is configured, for example, in a shape corresponding to the side surface of a cone, and functions as a holding surface that holds the protective member 21. In this embodiment, the back surface 21b of the protective member 21 is brought into contact with the upper surface (first holding surface, second holding surface) 8a. The lower surface side of the holding plate 8 is connected to a suction source (not shown) such as an ejector via a flow path 6b provided inside the frame 6, a valve (not shown), etc.

[0025] Therefore, by bringing the back surface 21b of the protective member 21 into contact with the upper surface 8a of the holding plate 8, opening the valve, and applying negative pressure from the suction source, the back surface 21b of the protective member 21 is sucked by the chuck table 4. In other words, the workpiece 11 is held by the chuck table 4 via the protective member 21 attached to the workpiece 11.

[0026] Then, the back surface 11b side of the workpiece 11 is exposed upward, as shown in Fig. 2. Note that although the shape of the upper surface 8a of the holding plate 8 is exaggerated in Fig. 2 and other figures, in reality, the difference in height (height difference) between the apex 8b of the upper surface 8a, which corresponds to the apex of the cone, and the outer periphery of the upper surface 8a is approximately 10 µm to 30 µm.

[0027] A rotational drive source (not shown), such as a motor, is connected to the lower part of the frame 6. The force generated by this rotational drive source causes the chuck table 4 to rotate about an axis along the vertical direction or an axis slightly tilted relative to the vertical direction, with the vertex 8b as the center of rotation. The frame 6 is also supported by a chuck table moving mechanism (not shown), and the force generated by this chuck table moving mechanism causes the chuck table 4 to move horizontally.

[0028] After the workpiece 11 is held by the chuck table 4 via the protective member 21, for example, an area of the workpiece 11 corresponding to an area where the device 15 is formed (device area) is roughly ground from the back surface 11b side (first grinding step). Fig. 3 is a cross-sectional view showing the process of roughly grinding the workpiece 11. Note that for ease of explanation, some elements are shown from the side in Fig. 3.

[0029] 3 and other figures, a first grinding unit (rough grinding unit) 10 is disposed above the chuck table 4 of the grinding device 2. The first grinding unit 10 includes, for example, a cylindrical spindle housing (not shown). A columnar spindle 12 is housed in the space inside the spindle housing.

[0030] A disk-shaped mount 14 having a diameter smaller than, for example, the workpiece 11 or the protective member 21 is provided at the lower end of the spindle 12. A plurality of holes (not shown) penetrating the mount 14 in the thickness direction are formed on the outer periphery of the mount 14, and bolts 16 or the like are inserted into each hole. A disk-shaped first grinding wheel (rough grinding wheel) 18 having roughly the same diameter as the mount 14 is fixed to the underside of the mount 14 by bolts 16 or the like.

[0031] The first grinding wheel 18 includes a disk-shaped wheel base 20 made of metal such as stainless steel or aluminum. A plurality of first grinding stones (coarse grinding stones) 22 are fixed to the underside of the wheel base 20 along the circumferential direction of the wheel base 20. The first grinding stones 22 have a structure in which large abrasive grains made of, for example, diamond or the like are dispersed in a binder made of resin or the like.

[0032] When the first grinding wheel 18 including this first grinding stone 22 is used, the amount of workpiece 11 that can be removed per unit time increases, but a damaged layer containing scratches or distortion is more likely to be formed on the grinding surface of the workpiece 11. A rotational drive source (not shown), such as a motor, is connected to the upper end of the spindle 12. The first grinding wheel 18 rotates around an axis that is aligned vertically or slightly tilted relative to the vertical direction by the force generated by this rotational drive source.

[0033] A nozzle (not shown) configured to supply a grinding liquid (typically water) to the first grinding stone 22 and the like is provided near the first grinding wheel 18 or inside the first grinding wheel 18. The spindle housing is supported, for example, by a first grinding unit moving mechanism (not shown), and the first grinding unit 10 moves in the vertical direction by a force generated by this first grinding unit moving mechanism.

[0034] When grinding the workpiece 11 with the first grinding unit 10 (first grinding wheel 18), first, the chuck table 4 is moved to a position directly below the first grinding unit 10. Specifically, the chuck table 4 is moved horizontally by the chuck table moving mechanism so that the first grinding wheel 18 (all first grinding wheels 22) are positioned directly above the area where the device 15 is formed.

[0035] 3, the chuck table 4 and the first grinding wheel 18 are rotated, and the first grinding unit 10 (first grinding wheel 18) is lowered while supplying liquid from the nozzle. In other words, the first grinding wheel 18 and the chuck table 4 are moved relatively in a direction intersecting with the upper surface 8a, and the workpiece 11 is ground by the first grinding wheel 18. The speed at which the first grinding unit 10 is lowered (grinding feed rate) is adjusted within a range in which the first grinding stone 22 is pressed against the workpiece 11 with an appropriate pressure.

[0036] 4 is a cross-sectional view schematically showing a portion of the workpiece 11 after being ground by the first grinding wheel 18. As described above, by grinding the area of the workpiece 11 corresponding to the area where the device 15 is formed from the rear surface 11b side, it is possible to form a disk-shaped first thin plate portion 11c corresponding to the area where the device 15 is formed and an annular first thick plate portion 11d surrounding the first thin plate portion 11c in the workpiece 11, as shown in FIG.

[0037] A damaged layer (first damaged layer) 11e containing scratches or distortion is formed on the portion (surface to be ground) of the first thin plate portion 11c on the back surface 11b side. Therefore, it is desirable that the first thin plate portion 11c be formed to a thickness such that even if a crack propagates from the damaged layer 11e during subsequent transportation, the crack will not reach the device 15 on the front surface 11a side.

[0038] There are no significant limitations on the specific grinding conditions. To achieve efficient grinding of the workpiece 11, the rotation speed of the chuck table 4 should be set to 100 rpm to 600 rpm, typically 300 rpm, and the rotation speed of the first grinding wheel 18 should be set to 1000 rpm to 7000 rpm, typically 4500 rpm. The descending speed of the first grinding unit 10 should be set to 0.8 μm / s to 10 μm / s, typically 6.0 μm / s.

[0039] After the workpiece 11 is ground from the back surface 11b side to form the disk-shaped first thin plate portion 11c and the annular first thick plate portion 11d surrounding the first thin plate portion 11c, the first thin plate portion 11c is roughly ground from the back surface 11b side with the same first grinding wheel 18 (second grinding step). In this embodiment, first, the chuck table 4 and the first grinding wheel 18 are moved relative to each other to move the first grinding wheel 18 away from the inner side surface of the first thick plate portion 11d.

[0040] More specifically, the chuck table 4 and the first grinding wheel 18 are moved relatively in a direction along the upper surface 8a of the chuck table 4 to form a gap between the first grinding wheel 18 and the first thick plate portion 11d. Fig. 5 is a cross-sectional view schematically showing the state in which the chuck table 4 and the first grinding wheel 18 are moved relatively in a direction along the upper surface 8a.

[0041] For ease of explanation, some elements are shown from the side in Fig. 5. Furthermore, in Fig. 5, the chuck table 4 and the first grinding wheel 18 are moved relatively in a direction along the upper surface 8a while being rotated, but the chuck table 4 and the first grinding wheel 18 may be moved relatively in a direction along the upper surface 8a after stopping their rotation. There are no significant limitations on the speed or distance of movement, but here the speed of movement is set to 1.0 mm / s to 2.0 mm / s, and the distance of movement is set to 3.0 mm to 6.0 mm.

[0042] After the chuck table 4 and the first grinding wheel 18 are moved relatively to form a gap between the first grinding wheel 18 and the first thick plate portion 11d, the first grinding unit 10 (first grinding wheel 18) is lowered while supplying liquid from a nozzle. In other words, the first grinding wheel 18 and the chuck table 4 are moved relatively in a direction intersecting with the upper surface 8a, and the first thin plate portion 11c is ground by the first grinding wheel 18.

[0043] 6 is a cross-sectional view schematically showing how the first thin plate portion 11c of the workpiece 11 is ground by the first grinding wheel 18. For ease of explanation, some elements are shown from the side in FIG. 6. The speed at which the first grinding unit 10 is lowered (grinding feed rate) is adjusted within a range in which the first grinding stone 22 is pressed against the first thin plate portion 11c with an appropriate pressure.

[0044] 7 is a cross-sectional view schematically showing a portion of the workpiece 11 after the first thin portion 11c has been ground by the first grinding wheel 18. As described above, by grinding the first thin portion 11c from the back surface 11b side, a disk-shaped second thin portion 11f and an annular second thick portion 11g surrounding the second thin portion 11f can be formed in the first thin portion 11c of the workpiece 11, as shown in FIG. 7. After the second thin portion 11f and the second thick portion 11g have been formed, the first grinding unit 10 is raised, and grinding by the first grinding wheel 18 is terminated.

[0045] A damaged layer (second damaged layer) 11h including scratches or distortion is formed on the back surface 11b side (the surface to be ground) of the second thin plate portion 11f. Therefore, it is desirable that the second thin plate portion 11f be formed to a thickness that allows the damaged layer 11h to be sufficiently removed by thinning the second thin plate portion 11f to a desired thickness in subsequent grinding.

[0046] There are no significant limitations on the specific grinding conditions. To achieve efficient grinding of the workpiece 11, the rotation speed of the chuck table 4 should be set to 100 rpm to 600 rpm, typically 300 rpm, and the rotation speed of the first grinding wheel 18 should be set to 1000 rpm to 7000 rpm, typically 4500 rpm.

[0047] The speed of the descent of the first grinding unit 10 is preferably set to 0.8 μm / s to 10 μm / s. Furthermore, the speed of the descent of the first grinding unit 10 may be changed in accordance with the progress of grinding. Typically, the speed is set to one of three stages: 6.0 μm / s, 3.0 μm / s, and 1.0 μm / s, in order, in accordance with the progress of grinding.

[0048] After grinding with the first grinding wheel 18, the second thick portion 11g and the second thin portion 11f are ground with higher precision from the back surface 11b side (third grinding step). Figure 8 is a cross-sectional view showing the workpiece 11 being ground with high precision. Note that for ease of explanation, some elements are shown from the side in Figure 8.

[0049] 8, a second grinding unit (finish grinding unit) 24, which is separate from the first grinding unit 10, is disposed above the chuck table 4 of the grinding device 2. The second grinding unit 24 includes, for example, a cylindrical spindle housing (not shown). A columnar spindle 26 is housed in the space inside the spindle housing.

[0050] A disk-shaped mount 28 having a diameter smaller than, for example, the workpiece 11 or the protective member 21 is provided at the lower end of the spindle 26. A plurality of holes (not shown) penetrating the mount 28 in the thickness direction are formed on the outer periphery of the mount 28, and bolts 30 or the like are inserted into each hole. A disk-shaped second grinding wheel (finish grinding wheel) 32 having roughly the same diameter as the mount 28 is fixed to the underside of the mount 28 by bolts 30 or the like.

[0051] The second grinding wheel 32 includes a disk-shaped wheel base 34 made of metal such as stainless steel or aluminum. A plurality of second grinding stones (finish grinding stones) 36 are fixed to the underside of the wheel base 34 along the circumferential direction of the wheel base 34. The second grinding stone 36 has a structure in which small abrasive grains made of, for example, diamond or the like are dispersed in a binder made of resin or the like. Specifically, the size (typically, average particle size) of the abrasive grains contained in the second grinding stone 36 is smaller than the size of the abrasive grains contained in the first grinding stone 22.

[0052] When the second grinding wheel 32 including this second grinding stone 36 is used, the amount of workpiece 11 that can be removed per unit time decreases, but a damaged layer containing scratches or distortion is less likely to form on the grinding surface of the workpiece 11. A rotational drive source (not shown), such as a motor, is connected to the upper end of the spindle 26. The second grinding wheel 32 rotates around an axis that is aligned vertically or slightly tilted relative to the vertical direction by the force generated by this rotational drive source.

[0053] A nozzle (not shown) configured to supply a grinding liquid (typically, water) to the second grinding stone 36 and the like is provided near the second grinding wheel 32 or inside the second grinding wheel 32. The spindle housing is supported, for example, by a second grinding unit moving mechanism (not shown), and the second grinding unit 24 moves in the vertical direction by a force generated by this second grinding unit moving mechanism.

[0054] When grinding the second thick portion 11g and the second thin portion 11f with the second grinding unit 24 (second grinding wheel 32), first, the chuck table 4 is moved to a position directly below the second grinding unit 24. Specifically, the chuck table 4 is moved horizontally by the chuck table moving mechanism so that the second grinding wheel 32 (all second grinding stones 36) are positioned directly above the second thick portion 11g and the second thin portion 11f.

[0055] 8, the chuck table 4 and the second grinding wheel 32 are rotated, and the second grinding unit 24 (second grinding wheel 32) is lowered while supplying liquid from the nozzle. In other words, the second grinding wheel 32 and the chuck table 4 are moved relatively in a direction intersecting with the upper surface 8a. The speed at which the second grinding unit 24 is lowered (grinding feed rate) is adjusted within a range in which the second grinding wheel 36 is pressed against the workpiece 11 with an appropriate pressure.

[0056] 9 is a cross-sectional view schematically illustrating a portion of the workpiece 11 after the second thick portion 11g and the second thin portion 11f have been ground by the second grinding wheel 32. As described above, by grinding the second thick portion 11g and the second thin portion 11f from the rear surface 11b side, as shown in FIG. 9, a disk-shaped third thin portion 11i having a larger diameter and thinner than the second thin portion 11f can be formed in the workpiece 11. Furthermore, by grinding using the second grinding wheel 32, a damaged layer 11h of the second thin portion 11f is removed.

[0057] There are no significant limitations on the specific grinding conditions. In order to achieve efficient and highly accurate grinding of the workpiece 11, the rotation speed of the chuck table 4 should be set to 100 rpm to 600 rpm, typically 300 rpm, and the rotation speed of the second grinding wheel 32 should be set to 1000 rpm to 7000 rpm, typically 4000 rpm.

[0058] In grinding with the second grinding wheel 32, after only the second thick portion 11g is ground, the region including the second thin portion 11f (and the second thick portion 11g) is ground. Here, since the area of the surface to be ground when only the second thick portion 11g is ground is small, it is possible to increase the speed of descending the second grinding unit 24 when only the second thick portion 11g is ground compared to when the region including the second thin portion 11f is ground.

[0059] Therefore, in this embodiment, the speed of descent of the second grinding unit 24 when grinding only the second thick portion 11g is set to 0.8 μm / s to 5.0 μm / s, and the speed of descent of the second grinding unit 24 when grinding the area including the second thin portion 11f is set to 0.1 μm / s to 0.8 μm / s.

[0060] That is, the speed at which the second grinding wheel 32 and the chuck table 4 are moved relative to each other when grinding only the second thick portion 11g is set to be greater than the speed at which the second grinding wheel 32 and the chuck table 4 are moved relative to each other when grinding the area including the second thin portion 11f. Typically, when grinding only the second thick portion 11g, the speed is set to 1.6 μm / s, and when grinding the area including the second thin portion 11f, two speed stages of 0.6 μm / s and 0.3 μm / s are set in sequence as the grinding progresses.

[0061] This shortens the time required for grinding, improving efficiency, while sufficiently reducing the amount of scratches and distortion formed in the third thin plate portion 11i. In other words, it is possible to remove the damaged layer 11h, which is close to the device 15 on the front surface 11a side and is prone to developing cracks that extend to the device 15 during subsequent transportation, without significantly increasing the time required to complete grinding. In particular, when the second thin plate portion 11f is formed with a thickness such that the damaged layer 11h does not reach the region that will become the third thin plate portion 11i, the damaged layer 11h is sufficiently removed as the third thin plate portion 11i is formed.

[0062] Although the damaged layer 11e remains in the outer peripheral portion of the second thick plate portion 11g (the portion in contact with the first thick plate portion 11d) that is not ground by the second grinding wheel 32, the distance from this damaged layer 11e to the device 15 on the front surface 11a side is greater than the distance from the damaged layer 11h to the device 15. Therefore, the probability that a crack will extend from the remaining damaged layer 11e to the device 15 on the front surface 11a side is low, and this does not pose a major problem. In particular, when the first thin plate portion is formed to a thickness that prevents a crack extending from the damaged layer 11e from reaching the device 15, the problem caused by this crack is more appropriately resolved.

[0063] Next, examples and comparative examples conducted to confirm the effects of the grinding method for a workpiece according to this embodiment will be described. In the examples and comparative examples, the time required to grind the first thin plate portion 11c having a thickness of 200 μm to form the third thin plate portion 11i having a thickness of 100 μm was confirmed. In the examples, the first thin plate portion 11c was first ground using the first grinding wheel 18 to form the second thin plate portion 11f having a thickness of 130 μm and the second thick plate portion 11g having a thickness of 200 μm.

[0064] The speed at which the first grinding wheel 18 was lowered when grinding the first thin plate portion 11c (grinding feed rate) was set to 6.0 μm / s, 3.0 μm / s, and 1.0 μm / s. The distance by which the first grinding wheel 18 was lowered at each speed (i.e., the thickness removed by grinding) was 10 μm at the speed of 6.0 μm / s, 30 μm at the speed of 3.0 μm / s, and 30 μm at the speed of 1.0 μm / s.

[0065] Thereafter, the second thick portion 11g and the second thin portion 11f were ground using the second grinding wheel 32 to form a third thin portion 11i having a thickness of 100 μm. Specifically, after only the second thick portion 11g was ground, the area including the second thin portion 11f (and the second thick portion 11g) was ground. The speed at which the second grinding wheel 32 was lowered when grinding only the second thick portion 11g (grinding feed rate) was set to 1.6 μm / s. The distance the second grinding wheel 18 was lowered was 70 μm.

[0066] On the other hand, the speed at which the second grinding wheel 32 was lowered when grinding the region including the second thinner portion 11f was set to 0.6 μm / s and 0.3 μm / s. The distance at which the second grinding wheel 32 was lowered at each speed was 20 μm at a speed of 0.6 μm / s and 10 μm at a speed of 0.3 μm / s. That is, in this example, it took about 152 seconds to complete grinding.

[0067] In the comparative example, the first thin plate portion 11c, which was 200 μm thick, was ground using the second grinding wheel 32 to a thickness of 100 μm (corresponding to the third thin plate portion 11i). The speeds at which the second grinding wheel 32 was lowered when grinding the first thin plate portion 11c were set to 0.6 μm / s and 0.3 μm / s. The distance the second grinding wheel 32 was lowered at each speed was 90 μm at a speed of 0.6 μm / s and 10 μm at a speed of 0.3 μm / s. In other words, in the comparative example, it took approximately 183 seconds to complete grinding.

[0068] Thus, in the example, the time until grinding is completed is about 31 seconds shorter than in the comparative example. In the method for grinding a workpiece according to this embodiment, before grinding the first thin plate portion 11c, an additional time (1.5 seconds to 6.0 seconds) is required to relatively move the chuck table 4 and the first grinding wheel 18 in a direction along the upper surface 8a. Even taking this into consideration, it can be said that the method for grinding a workpiece according to this embodiment is sufficiently effective.

[0069] As described above, in the method for grinding a workpiece according to this embodiment, the workpiece 11 is ground using the first grinding wheel 18 equipped with the first grinding stone 22 containing relatively large abrasive grains, thereby forming the disk-shaped first thin plate portion 11c and the first thick plate portion 11d surrounding the first thin plate portion 11c in the workpiece 11 (first grinding step), and by grinding the first thin plate portion 11c using the same first grinding wheel 18, a first thick plate portion 11d is formed that is straighter than the first thin plate portion 11c. A second thin plate portion 11f having a small diameter and a thin disk shape and a second thick plate portion 11g having an annular shape surrounding the second thin plate portion 11f are formed on the first thin plate portion 11c (second grinding step), and then the second thick plate portion 11g and the second thin plate portion 11f are ground using a second grinding wheel 32 having a second grinding stone 36 containing relatively small abrasive grains to form a third thin plate portion 11i having a larger diameter and a thinner disk shape than the second thin plate portion 11f (third grinding step).

[0070] Therefore, compared to conventional grinding methods for workpieces that do not form the second thin portion 11f and the second thick portion 11g, the amount (volume) of the portion to be removed using the second grinding wheel 32 is reduced by the amount of the portion removed using the first grinding wheel 18 when forming the second thin portion 11f and the second thick portion 11g. In other words, the grinding time using the second grinding wheel 32 can be significantly shortened in exchange for a slight increase in the grinding time using the first grinding wheel 18, which can remove a larger amount per unit time, so that overall the time required to complete grinding can be shortened.

[0071] Therefore, even if the first thin plate portion 11c is made thicker to sufficiently increase the distance from the device 15 to the damage layer 11e in order to prevent damage to the device 15 due to cracks extending from the damage layer (first damage layer) 11e formed in the first thin plate portion 11c, the time until grinding is completed does not increase significantly. Thus, according to the method for grinding a workpiece according to this embodiment, the probability of damage to the device 15 can be reduced without significantly increasing the time until grinding is completed.

[0072] The present invention is not limited to the above-described embodiment and can be implemented with various modifications. For example, in the above-described embodiment, the workpiece 11 held by the chuck table 4 is ground with the first grinding wheel 18, and then the workpiece 11 held by the chuck table 4 is ground with the second grinding wheel 32. In other words, the first chuck table used when grinding the workpiece 11 with the first grinding wheel 18 is used as the second chuck table when grinding the workpiece 11 with the second grinding wheel 32.

[0073] Alternatively, after the workpiece 11 held by the chuck table 4 is ground by the first grinding wheel 18, the workpiece 11 held by a chuck table other than the chuck table 4 can be ground by the second grinding wheel 32. In other words, the first chuck table used when grinding the workpiece 11 by the first grinding wheel 18 and the second chuck table used when grinding the workpiece 11 by the second grinding wheel 32 may be different. Similarly, the method for grinding a workpiece according to the present invention may be performed using a plurality of grinding devices.

[0074] Furthermore, in the above-described embodiment, the first thin plate portion 11c is ground after the chuck table 4 and the first grinding wheel 18 are moved relatively in a direction along the upper surface 8a of the chuck table 4, but the first thin plate portion 11c can also be ground by other methods. For example, the first thin plate portion 11c may be ground while the chuck table 4 and the first grinding wheel 18 are moved relatively in a direction along the upper surface 8a of the chuck table 4. In this case, the inner side surface of the second thick plate portion 11g will be inclined with respect to the surface 11a, etc.

[0075] In the above-described embodiment, the first thin plate portion 11c is ground after the chuck table 4 and the first grinding wheel 18 are moved relatively in a direction along the upper surface 8a of the chuck table 4, so the central region of the first thin plate portion 11c may remain unground. In such a case, for example, when grinding the second thick plate portion 11g with the second grinding wheel 32, the remaining portion of the first thin plate portion 11c may be removed at the same time.

[0076] In addition, the structures, methods, etc. according to the above-described embodiments and modifications can be modified as appropriate without departing from the scope of the present invention. [Explanation of symbols]

[0077] 11: Workpiece 11a: Surface 11b: Back side 11c: 1st thin plate part 11d: First thick plate section 11e: Damage Layer (1st Damage Layer) 11f: 2nd thin plate part 11g: Second thick plate section 11h: Damage layer (second damage layer) 11i: 3rd thin plate part 13: Planned division line (street) 15: Device 21: Protective material 21a: Surface 21b: Back side 2: Grinding equipment 4: Chuck table (1st chuck table, 2nd chuck table) 6: Frame 6a: Recess 6b: Flow path 8: Holding plate 8a:Top surface (1st holding surface, 2nd holding surface) 8b: Vertex 10: First grinding unit (rough grinding unit) 12: Spindle 14: Mount 16: Bolt 18: First grinding wheel (rough grinding wheel) 20: Wheel base 22: No. 1 grinding wheel (rough grinding wheel) 24: Second grinding unit (finish grinding unit) 26: Spindle 28: Mount 30: Bolt 32: Second grinding wheel (finish grinding wheel) 34: Wheel base 36: Second grinding wheel (finishing grinding wheel)

Claims

1. A method for grinding a workpiece, in which a plate-shaped workpiece having a plurality of devices provided on a front surface side is ground from a back surface side opposite to the front surface using a grinding wheel attached to a rotating spindle, comprising: a bonding step of bonding a protective member to the surface of the workpiece; a first grinding step in which, with the workpiece held on a first holding surface of a first chuck table via the protective member, a first grinding wheel having a first grinding stone containing abrasive grains is brought into contact with the workpiece, and the first grinding wheel and the first chuck table are moved relatively in a direction along the first holding surface while also moving relatively in a direction intersecting the first holding surface to grind the workpiece from its back surface, thereby forming a disk-shaped first thin plate portion and an annular first thick plate portion surrounding the first thin plate portion on the workpiece; a second grinding step after the first grinding step, in which the first grinding stone of the first grinding wheel is brought into contact with the workpiece, and the first grinding wheel and the first chuck table are moved relatively in a direction along the first holding surface while being moved relatively in a direction intersecting the first holding surface to grind the first thin plate portion from the back surface side, thereby forming a second thin plate portion in the first thin plate portion, the second thin plate portion being thinner and having a smaller diameter than the first thin plate portion, and an annular second thick plate portion surrounding the second thin plate portion; and a third grinding step of, after the second grinding step, bringing the workpiece into contact with a second grinding stone of a second grinding wheel having a second grinding stone containing smaller abrasive grains than the first grinding stone, while the workpiece is held on a second holding surface of a second chuck table via the protective member, and relatively moving the second grinding wheel and the second chuck table in a direction along the second holding surface and in a direction intersecting the second holding surface to grind the second thick plate portion and the second thin plate portion from the back surface side, thereby forming a disk-shaped third thin plate portion that is thinner and has a diameter larger than that of the second thin plate portion and a diameter smaller than that of the first thin plate portion, In the first grinding step, a first thin plate portion is formed having a thickness such that a crack extending from a first damaged layer including a scratch or a distortion generated in the workpiece in the first grinding step during subsequent transportation does not reach the device; A method for grinding a workpiece, wherein the thickness of the workpiece removed in the second grinding step is smaller than the thickness of the workpiece removed in the first grinding step.

2. 2. The method for grinding a workpiece according to claim 1, wherein the first chuck table is used as the second chuck table.

3. 3. A method for grinding a workpiece as described in claim 1 or claim 2, wherein in the third grinding step, the speed at which the second grinding wheel and the second chuck table are moved relative to each other when grinding only the second thick plate portion is made faster than the speed at which the second grinding wheel and the second chuck table are moved relative to each other when grinding an area including the second thin plate portion.

4. A method for grinding a workpiece described in any one of claims 1 to 3, wherein in the second grinding step, a second thin plate portion is formed having a thickness such that a second damage layer containing scratches or distortions generated in the workpiece in the second grinding step does not reach the area that becomes the third thin plate portion.

Images