Processing method of wafer

Abstract

To provide a processing method of a wafer, capable of solving the following problem: if a wafer having high cleavability and bonded on a silicon substrate or the like is ground to a thickness of 5 to 1 μm by a grinding machine, cracks spreading from an outer periphery to an inside occur in the course of grinding processing, resulting in causing deterioration in quality.SOLUTION: There is provided a processing method of a wafer for grinding and thinning a first wafer of a bonded wafer, the bonded wafer including the first wafer having a chamfered portion formed on an outer periphery thereof and a second wafer bonded with the first wafer. The processing method includes: a protective film arrangement step of arranging a protective film on a side of the second wafer; a chamfered-portion removing step of holding a side of the protective film on a chuck table constituting a processing machine configured to remove the chamfered portion and removing the chamfered portion formed on the outer periphery of the first wafer; a cleaning step of cleaning the bonded wafer from which the chamfered portion has been removed; a peeling step of peeling off the protective film; and a grinding step of holding the side of the second wafer on a chuck table constituting a grinding machine and grinding the first wafer.SELECTED DRAWING: Figure 8

Description

[Technical field]

[0001] The present invention relates to a wafer processing method in which a bonded wafer is formed by bonding a first wafer having a chamfered portion on its outer periphery to a second wafer, and the second wafer is thinned by grinding the second wafer. [Background technology]

[0002] A wafer having a plurality of devices such as ICs and LSIs formed on its front surface along division lines is ground on its back surface by a grinding device to form it into the desired thickness, and then separated into individual device chips by a cutting device or the like for use in electrical devices such as mobile phones and personal computers.

[0003] In addition, TF-SAW devices, which excite surface acoustic waves using a thin piezoelectric film or a regular comb-shaped electrode formed on a substrate, which are indispensable for communication devices such as mobile phones, are made by bonding a lithium tantalate (LiTaO3=LT) wafer (hereinafter referred to as an "LT wafer") or a lithium niobate (LiNbO3=LN) wafer (hereinafter referred to as an "LN wafer") used as a piezoelectric material onto a wafer such as silicon, sapphire, quartz, or glass, which serves as a supporting substrate, to form a bonded wafer, and the LT wafer or LN wafer is thinned to a desired thickness (for example, 5 μm) using a grinding device, after which electrodes are formed in the effective area toward the center of the surface, and the wafer is divided into individual TF-SAW device chips that are then mounted on various types of communication devices.

[0004] Furthermore, as smartphones are becoming more multiband, enabling them to handle multiple frequency bands, attention is being focused on devices made from the above-mentioned LT and LN materials.

[0005] A known processing apparatus for grinding the above-mentioned bonded wafer includes a grinding apparatus including a rotatable chuck table that holds the wafer by suction, a moving means for moving the chuck table to a mounting and demounting area where the wafer is mounted and detached, and a grinding area where the wafer is ground, a loading means for loading the wafer onto the chuck table in the mounting and demounting area, a loading means for unloading the ground wafer from the chuck table, and a grinding means that is disposed in the grinding area and has a rotatable grinding wheel that grinds the wafer held on the chuck table while supplying grinding water to the wafer (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2015-230971 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, the above-mentioned LT wafer and LN wafer are materials with high cleavage and grinding is very difficult, and when a LT wafer or LN wafer with a thickness of 350 μm bonded to a silicon substrate or the like is ground to a thickness of 5 to 1 μm by a grinding device, a sharp, thin and brittle area like a knife edge is formed on the outer periphery during the grinding process, and cracks are generated from the outer periphery to the effective area inside, resulting in deterioration of quality. Such a problem is not limited to the case where a bonded wafer is composed of an LT wafer or LN wafer and the LT wafer or LN wafer is ground to a thickness of 5 to 1 μm, but may also occur in bonded wafers composed of other materials with high cleavage.

[0008] The present invention has been made in view of the above-mentioned facts, and its main technical object is to provide a wafer processing method capable of solving the problem that when a wafer having high cleavage property, such as an LT wafer or an LN wafer, bonded to a silicon substrate or the like, is ground to a thickness of 5 to 1 μm by a grinding device, a sharp, thin and brittle area like a knife edge is formed on the outer periphery during the grinding process, and cracks are generated from the outer periphery to the effective area inside, resulting in deterioration of quality. [Means for solving the problem]

[0009] In order to solve the above-mentioned main technical problem, according to the present invention, there is provided a wafer processing method for grinding and thinning a bonded wafer, which is formed by bonding a first wafer and a second wafer having a chamfered portion on their outer periphery, the method including: a protective film disposing step of disposing a protective film on the second wafer side; a chamfer removing step of holding the protective film side on a chuck table constituting a processing device that removes the chamfered portion and removing the chamfered portion formed on the outer periphery of the first wafer; a cleaning step of cleaning the bonded wafer from which the chamfered portion has been removed; a peeling step of peeling off the protective film; and a grinding step of holding the second wafer side on a chuck table constituting a grinding device and grinding the first wafer.

[0010] The first wafer is preferably configured to include lithium tantalate or lithium niobate, and the second wafer is preferably configured to include any one of silicon, sapphire, quartz, and glass. In addition, the protective film disposed in the protective film disposing step is preferably a thermocompression film. Effect of the Invention

[0011] The wafer processing method of the present invention is a wafer processing method for grinding and thinning a bonded wafer formed by bonding a first wafer and a second wafer, the first wafer having a chamfered portion on its outer periphery, and includes a protective film providing step of providing a protective film on the second wafer side, a chamfer removing step of holding the protective film side on a chuck table constituting a processing device that removes the chamfered portion and removing the chamfered portion formed on the outer periphery of the first wafer, a cleaning step of cleaning the bonded wafer from which the chamfered portion has been removed, a peeling step of peeling off the protective film, and a grinding step of holding the second wafer side on a chuck table constituting a grinding device and grinding the first wafer. Therefore, when the first wafer is ground to thin it, a sharp area like a knife edge is not formed on the outer periphery of the first wafer, and no cracks reaching from the outer periphery to the inside are generated during the process of thinning the first wafer, thereby solving the problem of deterioration in quality. Furthermore, as described above, by disposing a protective film on the second wafer side in the protective film disposition step before carrying out the chamfered portion removal step, contaminants including cutting debris generated in the chamfered portion removal step do not adhere to the second wafer side. Furthermore, by carrying out the peeling step, the protective film with contaminants adhered thereto is peeled off and removed. Therefore, when the bonded wafer is held on the chuck table constituting the grinding apparatus during the grinding step, it is possible to prevent contaminants from being trapped between the second wafer and the chuck table. This makes it possible to grind the first wafer to a uniform thickness even when the first wafer is ground thin. [Brief description of the drawings]

[0012] [Figure 1] FIG. 2 is a perspective view showing a mode of forming a bonded wafer which is a workpiece. [Diagram 2] 2 is a perspective view showing an embodiment in which a protective film is provided on the bonded wafer shown in FIG. 1. FIG. [Diagram 3] FIG. 2A is a perspective view showing how a protective film is thermocompression-bonded to a bonded wafer in a protective film disposing step, and FIG. 2B is an enlarged cross-sectional view showing a portion of the outer periphery of the bonded wafer to which the protective film is attached. [Figure 4] FIG. 2A is a perspective view showing a manner in which a bonded wafer is placed on a chuck table, and FIG. 2B is a perspective view showing a manner in which a chamfered portion of a first wafer is removed in a chamfered portion removing step. [Diagram 5] FIG. 1 is a perspective view showing an embodiment of a cleaning process. [Figure 6] FIG. 11 is a perspective view showing an embodiment of a peeling step. [Figure 7] 1 is an overall perspective view of a grinding device for carrying out a grinding step of the present invention; [Figure 8] FIG. 2A is a perspective view showing an embodiment of rough grinding in the grinding step, and FIG. 2B is a perspective view showing an embodiment of finish grinding in the grinding step. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a wafer processing method according to the present invention will be described in detail with reference to the accompanying drawings.

[0014] FIG. 1 shows an example of a mode of forming a bonded wafer W processed by the wafer processing method of the present embodiment. As shown in the figure, the bonded wafer W is composed of a first wafer 10 to be ground by a wafer processing method described later, and a second wafer 20 bonded to the first wafer 10 and supporting the first wafer 10. The diameter of the bonded wafer W shown in the figure is, for example, 200 mm, and the first wafer 10 is, for example, a LT (lithium tantalate (LiTaO3)) wafer with a thickness of 350 μm. The second wafer 20 is a silicon wafer bonded as a support substrate supporting the first wafer 10, and has the same dimensions as the first wafer 10. The bonded wafer W is integrally formed by bonding a surface 10a of the first wafer 10 and a surface 20a of the second wafer 20 by, for example, well-known room temperature bonding. The first wafer 10 has its outer periphery chamfered to form a chamfered portion 10c, and the second wafer 20 also has its outer periphery chamfered to form a chamfered portion 20c.

[0015] According to the wafer processing method of the present embodiment described below, the back surface 10b of the first wafer 10 is ground to a desired thickness, and then electrodes are formed in each area defined by division lines (not shown) in the first wafer 10, and the first wafer 10 is divided along the division lines to form a TF-SAW device (details are omitted). The wafer bonded to the second wafer 20 to form the bonded wafer W is not limited to the above-mentioned LT wafer, and may be an LN (lithium niobate (LiNbO3)) wafer, and the second wafer 20 supporting the first wafer 10 is not limited to the above-mentioned silicon wafer, and may be, for example, any of sapphire, quartz, and glass wafers.

[0016] The wafer processing method of this embodiment, which is performed on the above-mentioned bonded wafer W, is a wafer processing method in which a bonded wafer W in which a first wafer 10 and a second wafer 20, each having a chamfered portion 10c on its outer periphery, are bonded together, in which the back surface 10b of the first wafer 10 is ground to thin the first wafer 10. The wafer processing method is performed in the following manner.

[0017] (Protective film application process) In carrying out the wafer processing method of this embodiment, once the bonded wafer W is prepared, as shown in FIG. 2, a protective film T is laid on the back surface 20b of the second wafer 20. The protective film T used in this protective film disposition step is preferably selected from thermocompression films that are formed to have dimensions equal to or slightly larger than the second wafer 20 and that are suitable for thermocompression bonding and do not have a glue or the like having adhesive properties on the attachment surface. The material suitable for thermocompression bonding is a material that softens and exhibits adhesive properties when heated to a predetermined temperature, and is selected from polyolefin-based films, for example. In the embodiment described below, a polyethylene (PE) film, which is a polyolefin-based film, is selected as the protective film T. Note that the protective film T of the present invention does not exclude films other than the thermocompression films described above, and may be an adhesive film with a glue agent on its surface. Even in this case, it is preferable that the film be softened by heating.

[0018] After the protective film T is laid on the back surface 20b of the second wafer 20 of the bonded wafer W as described above, the thermocompression roller 100 is positioned above the protective film T as shown in Fig. 3(a). The thermocompression roller 100 is equipped with a heater and a temperature sensor (not shown) inside, and its surface is coated with a fluororesin that prevents the protective film T from being rolled in. The surface of the thermocompression roller 100 is heated to a predetermined temperature (e.g., 100°C) at which the protective film T softens and exerts adhesive force, and is pressed against the protective film T from above while rotating in the direction indicated by the arrow R1 and moving in the direction indicated by the arrow R2 to thermocompress the protective film T to the back surface 20b of the second wafer 20. 3(b), the protective film T is heated and softened to be thermocompression-bonded to the back surface 20b of the second wafer 20, so that the protective film T is in close contact with the back surface 20b of the second wafer 20 and is attached so as to wrap around the outer periphery of the second wafer 20 on which the chamfered portion 20c is formed, as indicated by Ta in the figure, completing the protective film disposing step. Note that the form of thermocompression-bonding the protective film T in the protective film disposing step is not limited to the above-mentioned form, and for example, a heating plate may be pressed against the protective film T from above to thermocompression-bond the protective film T to the back surface 20b of the second wafer 20, or hot air may be blown from above to heat the protective film T, and the protective film T may be thermocompression-bonded to the back surface 20b of the second wafer 20 by the air pressure.

[0019] When the protective film T is selected from polyolefin-based sheets, it can be selected from the polyethylene films described above, polypropylene (PP) films, and polystyrene (PS) films. However, the heating temperature during thermocompression bonding must be appropriately adjusted to the softening temperature of the selected film.

[0020] (Beveled part removal process) Next, the bonded wafer W with the protective film T attached to the back surface 20b of the second wafer 20 is transferred to a processing device for removing the chamfered portion 10c of the first wafer 10, for example, a cutting device 80 (only a part of which is shown) shown in Fig. 4(a) and (b). The cutting device 80 includes at least a chuck table 81 shown in Fig. 4(a) and a cutting means 82 shown in Fig. 4(b). The holding surface of the chuck table 81 is made of a breathable material and is connected to a suction means (not shown) to generate negative pressure on the upper surface. The cutting means 82 includes a disk-shaped cutting blade 85 attached to the tip of a rotating shaft 84 rotatably held by a rotating shaft housing 83. As described above, after the bonded wafer W is transported to the cutting device 80, as shown in FIG. 4(a), the side on which the protective film T is provided faces downward and the back surface 10b side of the first wafer 10 faces upward, and the suction means is operated to hold the bonded wafer W by suction. Next, the cutting blade 85 of the cutting means 82 is rotated at a predetermined speed in the direction indicated by the arrow R3 to position the cutting blade 85 at the outer periphery of the first wafer 10 where the chamfered portion 10c is formed. Next, the chuck table 81 is rotated in the direction indicated by the arrow R4 while being cut to a depth corresponding to the thickness of the first wafer 10. As a result, the outer periphery including the chamfered portion 10c of the first wafer 10 is completely removed over the entire circumference, exposing the front surface 20a of the second wafer 20, and the chamfered portion removing process is completed. The thickness of the cutting blade 85 is preferably equal to or greater than the width of the chamfered portion 10c to be removed (e.g., 3 mm), but does not necessarily have to be equal to the width of the chamfered portion 10c, and may be smaller than the width of the chamfered portion 10c to be removed. In that case, the outer periphery of the first wafer 10 may be cut in multiple steps to remove the width equivalent to the chamfered portion 10c.

[0021] The chamfered portion removing step is not limited to the above-mentioned embodiment. In the first wafer 10, a ring-shaped cut groove is formed from the first wafer 10 to the second wafer 20 at the boundary (not shown) between the chamfered portion 10c and an effective area from the center where an electrode is formed, and an external force is applied to the chamfered portion 10c to remove the chamfered portion 10c.

[0022] (Cleaning process) As described above, after the chamfered portion 10c of the first wafer 10 has been removed, a moving means (not shown) for moving the chuck table 81 is operated to position the bonded wafer W directly under the cleaning means 86 as shown in Fig. 5. Next, the chuck table 81 is rotated in the direction indicated by the arrow R4, and cleaning water (e.g., pure water L) is sprayed from the cleaning water spray port 86a of the cleaning means 86 to clean the bonded wafer W from which the chamfered portion 10c has been removed. Note that after spraying the pure water L from the cleaning means 86 for a predetermined time, a drying process may be performed in which air is sprayed to remove moisture from the bonded wafer W.

[0023] (Peeling process) After the cleaning step is performed as described above, a peeling step is performed to peel off the protective film T disposed on the back surface 20b of the second wafer 20, as shown in Fig. 6. When peeling off the protective film T, it is preferable to cool or heat the protective film T according to its characteristics so that the protective film T can be easily peeled off.

[0024] (Grinding process) As described above, after the peeling step is performed, a grinding step is performed to grind the first wafer 10. The grinding step described below will be described based on an example in which grinding is divided into a rough grinding process for grinding the thickness of the first wafer 10 from 350 μm to 20 μm, and a finish grinding process for grinding the first wafer 10 from 20 μm to 5 μm.

[0025] Fig. 7 shows a grinding apparatus 1 suitable for the wafer processing method of the present invention. As shown in Fig. 7, the grinding apparatus 1 includes a roughly rectangular parallelepiped apparatus housing 2, and a support wall 2a is erected on the rear end side of the apparatus housing 2. Two pairs of guide rails 2b, 2b and 2c, 2c extending in the vertical direction are provided on the inner surface of the support wall 2a. A first grinding means 3 as a means for performing rough grinding is mounted on one of the guide rails 2b, 2b so as to be movable in the vertical direction, and a second grinding means 4 as a means for performing finish grinding is mounted on the other guide rails 2c, 2c so as to be movable in the vertical direction.

[0026] The first grinding means 3 comprises a unit housing 31, a wheel mount 33 arranged at the lower end of a rotating shaft 32 supported rotatably on the unit housing 31, a grinding wheel 34 attached to the wheel mount 33 and having a ring-shaped grinding wheel 35 for rough grinding arranged on its underside, an electric motor 36 attached to the upper end of the unit housing 31 for rotating the wheel mount 33 in the direction indicated by arrow R6, and a movable base 38 supporting the unit housing 31 via a support member 37.

[0027] The movable base 38 is provided with a guided groove that slidably engages with the guide rails 2b, 2b, and supports the first grinding means 3 so as to be movable in the vertical direction. The illustrated grinding device 1 is provided with a grinding feed means 39 that raises and lowers the movable base 38 of the first grinding means 3 along the guide rails 2b, 2b, and moves the first grinding means 3 toward and away from the bonded wafer W held on the chuck table 6 described below. The grinding feed means 39 is provided with a male screw rod 391 that is rotatably supported on the support wall 2a and disposed in parallel with the guide rails 2b, 2b in the vertical direction, a pulse motor 392 for rotating the male screw rod 391, and a female screw block (not shown) that is attached to the movable base 38 and screwed with the male screw rod 391. The male screw rod 391 is driven in the forward and reverse directions by the pulse motor 392 to move the first grinding means 3 in the vertical direction.

[0028] The second grinding means 4 for performing finish grinding is also configured in a manner substantially similar to the first grinding means 3 described above, and includes a unit housing 41, a wheel mount 43 disposed at the lower end of a rotating shaft 42 supported rotatably on the unit housing 41, a grinding wheel 44 attached to the wheel mount 43 and having a plurality of grinding wheels 45 for finish grinding arranged in a ring shape on its underside, an electric motor 46 attached to the upper end of the unit housing 41 for rotating the wheel mount 43 in the direction indicated by arrow R7, and a movable base 48 for supporting the unit housing 41 via a support member 47.

[0029] The movable base 48 is provided with a guided groove that slidably engages with the guide rails 2c, 2c provided on the support wall 2a, and the second grinding means 4 is supported so as to be movable in the vertical direction. The illustrated grinding device 1 is provided with a grinding feed means 49 that raises and lowers the movable base 48 of the second grinding means 4 along the guide rails 2c, 2c, and moves the second grinding means 4 toward and away from the bonded wafer W held on the chuck table 6 described below. The grinding feed means 49 is provided with a male screw rod 491 that is rotatably supported and disposed in parallel with the guide rails 2c, 2c on the support wall 2a in the vertical direction, a pulse motor 492 for rotating the male screw rod 491, and a female screw block (not shown) that is attached to the movable base 48 and screwed with the male screw rod 491. The male screw rod 491 is driven in the forward and reverse directions by the pulse motor 492 to move the second grinding means 4 in the vertical direction.

[0030] The grinding apparatus 1 includes a turntable 5 disposed in front of the support wall 2a so as to be substantially flush with the upper surface of the apparatus housing 2. The turntable 5 is formed in a relatively large-diameter disk shape, and is rotated appropriately by a rotary drive mechanism (not shown in FIG. 7) in a drain pan 2d that collects grinding water containing grinding chips on the upper surface of the apparatus housing 2. The turntable 5 is provided with three chuck tables 6 disposed as holding means for holding the bonded wafer W at an angle of 120 degrees. Each chuck table 6 is configured to be rotatable in the direction indicated by the arrow R8. The holding surface (upper surface) of the chuck table 6 is formed in a disk shape using a breathable member, and is connected to a suction means (not shown).

[0031] The three chuck tables 6 arranged on the turntable 5 are moved in sequence from a carry-in / out area A where the bonded wafer W is carried in and out of the chuck table 6, to a first grinding area B where the first grinding means 3 performs rough grinding, to a second grinding area C where the second grinding means 4 performs finish grinding, and to the carry-in / out area A, by rotating the turntable 5 in the direction indicated by the arrow R9. That is, the turntable 5 functions as a positioning means for positioning the chuck table 6 in the carry-in / out area A, the first grinding area B, and the second grinding area C. Furthermore, optical non-contact thickness detection means 71 and 72 for detecting the thickness (height) of the bonded wafer W held on the chuck table 6 are arranged in positions adjacent to the first grinding area B and the second grinding area C in the above-mentioned drain pan 2d.

[0032] The grinding apparatus 1 includes a first cassette 7 disposed on one side of the loading / unloading area A and accommodating a plurality of bonded wafers W before grinding, from which the chamfered portion 10c of the first wafer 10 has been removed by the above-mentioned chamfered portion removing step; a second cassette 8 disposed on the other side of the loading / unloading area A and accommodating a plurality of bonded wafers W after grinding; an alignment means 9 disposed between the first cassette 7 and the loading / unloading area A and on which the bonded wafers W are temporarily placed and their center positions are aligned; a cleaning means 11 disposed between the loading / unloading area A and the second cassette 8; and a cleaning unit 12 disposed in the first cassette 7. The wafer carrying machine includes a workpiece carrying-in / out means 12 for carrying out the accommodated bonded wafer W to the alignment means 9 and carrying the bonded wafer W cleaned by the cleaning means 11 into a second cassette 8, a transport means 13 for transporting the bonded wafer W aligned on the alignment means 9 onto the chuck table 6 positioned in the load / unload area A, and a transport means 14 for carrying out the bonded wafer W after finish grinding, which is obtained by grinding the first wafer 10 by the second grinding means 4 and is held on the chuck table 6 positioned in the load / unload area A, and transporting it to the cleaning means 11.

[0033] A control means 90 including an operation panel for instructing grinding and specifying processing conditions is disposed on the front side of the device housing 2 where the workpiece carrying-in / out means 12 is disposed. The control means 90 includes a central processing unit (CPU) that performs calculations according to a control program, a read-only memory (ROM) that stores the control program, etc., a readable / writable random access memory (RAM) as a storage means for storing calculation results, etc., an input interface, and an output interface (all of which are omitted from the drawing). The control means 90 configured in this manner controls each operating part of the grinding device 1, and also appropriately displays information related to the processing on a display means (not shown).

[0034] The grinding device 1 has a configuration generally as described above, and the grinding process of this embodiment is carried out as follows.

[0035] The above-mentioned bonded wafer W is transported to the chuck table 6 positioned in the load / unload area A, and is placed and held with the second wafer 20 side facing downward and the first wafer 10 side facing upward. Holding the bonded wafer W on the chuck table 6 includes a carry-out step of carrying the bonded wafer W out of the first cassette 7 by the workpiece carry-in / out means 12, an alignment step of placing the bonded wafer W carried out by the workpiece carry-in / out means 12 on the alignment means 9 and aligning the center of the bonded wafer W, and a holding step of operating the transport means 13 to transport the bonded wafer W from the alignment means 9 to the chuck table 6 positioned in the load / unload area A, placing the second wafer 20 side facing downward, and operating a suction means (not shown) to hold the bonded wafer W by suction.

[0036] Next, the turntable 5 is rotated 120° in the direction indicated by the arrow R9, and the chuck table 6 holding the bonded wafer W is positioned in the first grinding region B shown in Fig. 7. Next, as shown in Fig. 8(a), the chuck table 6 is rotated in the direction indicated by the arrow R8 at a predetermined rotational speed (e.g., 300 rpm) to rotate the bonded wafer W held on the chuck table 6, and the grinding wheel 34 of the first grinding means 3 is rotated in the direction indicated by the arrow R6 at a predetermined rotational speed (e.g., 6000 rpm). Next, the grinding feed means 39 is operated to lower the first grinding means 3 in the direction indicated by the arrow R10, and the grinding wheel 35 is brought into contact with the back surface 10b of the first wafer 10 while grinding water is supplied to the grinding location where the bonded wafer W and the grinding wheel 35 come into contact by a grinding water supply means (not shown), and then the grinding wheel 35 is fed at a predetermined grinding feed speed (for example, 1.0 μm / sec) to roughly grind the first wafer 10 with the grinding wheel 35. This rough grinding can be performed while detecting the thickness of the bonded wafer W by the non-contact thickness detection means 71 (not shown in FIG. 8(a)), and the rough grinding is performed until the thickness (350 μm) of the first wafer 10 before processing becomes 20 μm.

[0037] When the rough grinding is completed, the turntable 5 is rotated 120° in the direction indicated by the arrow R9, and the bonded wafer W after the rough grinding is moved from the first grinding area B to the second grinding area C. At this time, the bonded wafer W before the rough grinding is transferred and held on the chuck table 6 moved from the carry-in / out area A to the first grinding area B, and the bonded wafer W before the rough grinding is positioned in the first grinding area B. Then, when the bonded wafer W is positioned in the second grinding area C, as shown in FIG. 8(b), the chuck table 6 is rotated in the direction indicated by the arrow R8 at a predetermined rotation speed (e.g., 300 rpm) to rotate the bonded wafer W held on the chuck table 6, and the rotating shaft 42 of the second grinding means 4 is rotated in the direction indicated by the arrow R7 at a predetermined rotation speed (e.g., 6000 rpm) to rotate the grinding wheel 44.

[0038] Next, the above-mentioned grinding feed means 49 is operated to lower the second grinding means 4 in the direction indicated by the arrow R11 in the figure so that it comes into contact with the back surface 10b of the first wafer 10, and while grinding water is supplied to the grinding point by a grinding water supply means (not shown), the grinding is fed at a predetermined grinding feed speed (e.g., 0.1 μm / sec), and the back surface 10b of the first wafer 10 is finish-ground by the grinding wheel 45. Note that this finish grinding can be performed while detecting the thickness of the bonded wafer W by the above-mentioned non-contact thickness detection means 72, and is performed until the thickness (20 μm) of the first wafer 10 before the finish grinding is reduced to, for example, 5 μm. It should be noted that while the finish grinding process is being carried out in the second grinding area C, the above-mentioned rough grinding process is being carried out simultaneously in the first grinding area B, and the bonded wafer W before the rough grinding process is transported from the first cassette 7 to the chuck table 6 positioned in the loading / unloading area A, where it is placed and held by suction.

[0039] As described above, when the finish grinding is performed in the second grinding area C and the first wafer 10 is ground to a desired thickness, the grinding process for the bonded wafer W in this embodiment is completed, and the wafer processing method of the present invention is completed. Thereafter, the turntable 5 is rotated to move the chuck table 6 again to the carry-in / out area A, and the bonded wafer W is carried out by the carry-out means 14. After being cleaned and dried in the cleaning means 11, the workpiece carry-in / out means 12 is operated to store the cleaned bonded wafer W in the second cassette 8.

[0040] According to the wafer processing method of the embodiment described above, before carrying out the grinding step of grinding the first wafer 10, a chamfer removing step of removing the chamfer 10c formed on the outer periphery of the first wafer 10 is carried out. As a result, when the back surface 10b of the first wafer 10 is ground to thin it, a sharp area like a knife edge is not formed on the outer periphery of the first wafer 10, and in the process of thinning to 5 μm or less, no cracks are generated from the outer periphery to the internal effective area, thereby solving the problem of quality deterioration.

[0041] As described above, the protective film T is provided on the second wafer 20 side in the protective film providing step before the chamfer removing step is performed, thereby preventing contaminants including cutting chips generated in the chamfer removing step from adhering to the second wafer 20 side, and the peeling step is performed after the cleaning step described above. This allows the contaminants that have entered between the chuck table 81 and the protective film T during the chamfer removing step to be removed together with the protective film T, and the second wafer 20 side can be held on the chuck table 6 of the grinding device 1 in a clean state free of contaminants. As a result, even when the first wafer 10 is ground to an extremely thin thickness of, for example, 5 to 1 μm, the bonded wafer W can be ground to a uniform thickness with high precision without being partially lifted off the chuck table due to the influence of contaminants.

[0042] Furthermore, by selecting the protective film T in the above-mentioned protective film disposition process from a thermocompression film, the protective film can be attached so as to wrap around the outer periphery of the second wafer 20, and thus it is possible to reliably prevent contamination from entering between the second wafer 20 and the protective film T in the chamfered portion removal process. [Explanation of symbols]

[0043] 1: Grinding device 2: Device housing 2a: Support wall 2b: Guide rail 2c: Guide rail 2d: Drain pan 3: First grinding method 31: Unit housing 32: Rotation axis 33: Wheel mount 34: Grinding wheel 35: Grinding wheel 36: Electric motor 37: Support member 38: Mobile base 39: Grinding feed means 4: Second grinding method 41: Unit housing 42: Rotation axis 43: Wheel mount 44: Grinding wheel 45: Grinding wheel 46: Electric motor 47: Support member 48: Mobile base 49: Grinding feed means 5: Turntable 6: Chuck table 7: First Cassette 8: Second Cassette 9: Alignment means 10: First wafer 10a: surface 10b: Back side 10c: Chamfered part 11: Cleaning method 12: Workpiece loading / unloading means 13: Means of transportation 14:Export means 20: Second wafer 20a: Surface 20b: Back side 20c: Chamfered part 71, 72: Non-contact thickness detection means 80:Cutting equipment 81: Chuck table 82: Cutting means 83: Rotating shaft housing 84: Rotation axis 85: Cutting blade 86: Cleaning methods 100: Heat pressing roller A: Loading / unloading area B: First grinding area C: Second grinding area T: Protective film W: Bonded wafer

Claims

1. A wafer processing method for thinning a bonded wafer in which a first wafer and a second wafer having a chamfered portion on an outer periphery are bonded together, comprising the steps of: a protective film providing step of providing a protective film on the second wafer side; a chamfer removing step of removing the chamfer formed on the outer periphery of the first wafer by holding the protective film side on a chuck table constituting a processing device for removing the chamfer; a cleaning step of cleaning the bonded wafer from which the chamfered portion has been removed; a peeling step of peeling off the protective film; a grinding step of grinding the first wafer while holding the second wafer side on a chuck table constituting a grinding device; A wafer processing method comprising the steps of:

2. 2. The wafer processing method according to claim 1, wherein the first wafer contains lithium tantalate or lithium niobate, and the second wafer contains any one of silicon, sapphire, quartz, and glass.

3. 2. The wafer processing method according to claim 1, wherein in the protective film providing step, the protective film is a thermocompression film.

Images