Processing method of wafer

Abstract

To provide a processing method of a wafer, capable of preventing peeling of a first wafer from a second wafer in a course of processing a bonded wafer, the bonded wafer including the first wafer having a chamfered portion formed on an outer periphery thereof and the second wafer bonded with the first wafer.SOLUTION: A processing method of a wafer includes: a cutting groove forming step of holding a side of a second wafer on a chuck table constituting a processing machine configured to form a cutting groove, and positioning a cutting blade in a region adjacent to an effective region inside a chamfered portion formed on an outer periphery of the first wafer to form an annular cutting groove extending to the second wafer; a cutting groove detection step of detecting whether the width of the annular cutting groove is uniformly formed; and a grinding step of, if the width of the cutting groove is detected to be uniform during the cutting groove detection step, holding the side of the second wafer on a chuck table constituting a grinding machine and grinding the first wafer.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a wafer processing method for thinning a bonded wafer in which a first wafer having a chamfered portion on its outer periphery and an effective area in its center is bonded to a second wafer, the first wafer being ground to thin the first 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 side is thinned to a desired thickness (for example, 5 μm) using a grinding device, after which electrodes are formed on the surface and the wafer is divided into individual device chips that are then mounted on various 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 wafers and LN wafers are materials that have high cleavage and are very difficult to grind. In addition, if the bonding when forming a bonded wafer is insufficient, when an attempt is made to grind an LT wafer or LN wafer with a thickness of 350 μm bonded to a silicon substrate or the like to a thickness of 5 to 1 μm using a grinding device, the LT wafer or LN wafer may peel off from the silicon substrate or the like during the grinding process, causing problems during transportation, and the like, which require a lot of time and effort for the operator to deal with.

[0008] The present invention has been made in consideration of the above-mentioned facts, and its main technical object is to provide a wafer processing method capable of preventing the second wafer from peeling off from the second wafer during the process of processing a bonded wafer in which a first wafer having a chamfered portion on its outer periphery and a second wafer are bonded together. [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 formed by bonding a first wafer and a second wafer, the first wafer having a chamfered portion on its outer periphery and an effective area in the center, the method comprising: a cut groove forming step of holding the second wafer on a chuck table constituting a processing device for forming a cut groove, and positioning a cutting blade in an area inside the chamfer formed on the outer periphery of the first wafer and adjacent to the effective area to form an annular cut groove extending to the second wafer; a cut groove detection step of detecting whether the width of the annular cut groove is formed uniformly; and, if it is detected in the cut groove detection step that the width of the cut groove is uniform, a grinding step of holding the second wafer on the chuck table constituting a grinding device, and grinding the first wafer.

[0010] In the cutting groove detection step, if it is detected that the width of the cutting groove is not uniform, it is preferable to determine that the grinding step should not be performed. Also, if it is detected that the width of the cutting groove is uniform in the cutting groove detection step, a chamfer removing step of removing a ring-shaped chamfer existing on the outer periphery of the cutting groove may be performed before the grinding step. Furthermore, it is preferable that the first wafer is configured to include lithium tantalate or lithium niobate, and the second wafer is configured to include any one of silicon, sapphire, quartz, and glass. 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 an effective area in the center, and includes a cut groove forming step of holding the second wafer on a chuck table constituting a processing device for forming a cut groove, and positioning a cutting blade in an area inside the chamfer formed on the outer periphery of the first wafer and adjacent to the effective area to form an annular cut groove reaching the second wafer, a cut groove detection step of detecting whether the width of the annular cut groove is formed uniformly, and a grinding step of holding the second wafer on the chuck table constituting a grinding device and grinding the first wafer if it is detected in the cut groove detection step that the width of the cut groove is uniform. Therefore, it is possible to avoid separation of the second wafer from the second wafer during the process of grinding the bonded wafer formed by bonding a first wafer and a second wafer having a chamfered portion on its outer periphery. [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. 1A is a perspective view showing a mode in which the second wafer side is held on a chuck table constituting a processing device for forming an annular groove, and FIG. 1B is a perspective view showing an embodiment of a cut groove forming step. [Figure 4] FIG. 2A is a perspective view showing an embodiment of a cut groove forming step, and FIG. 2B is a conceptual diagram showing an uneven cut groove formed by the cut groove forming step shown in FIG. 2A. [Diagram 5] FIG. 11 is a perspective view showing an embodiment of a chamfer removing step. [Figure 6] FIG. 2 is a perspective view showing a mode in which a cleaning process is performed. [Figure 7] FIG. 2 is a perspective view showing an embodiment of a protective film peeling treatment. [Figure 8]1 is an overall perspective view of a grinding device for carrying out a grinding step of the present invention; [Figure 9] 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 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 that is ground by a wafer processing method described later, and a second wafer 20 that is bonded to the first wafer 10 and supports 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 that is bonded as a support substrate that supports the first wafer 10, and has the same dimensions as the first wafer 10. The bonded wafer W is 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, to form an integrated structure. The first wafer 10 has a chamfered portion 10c formed on its outer periphery, and the second wafer 20 also has a chamfered portion 20c formed on its outer periphery.

[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 of ​​the first wafer 10 defined by a division line (not shown) and the first wafer 10 is divided along the division line to form a TF-SAW device. The TF-SAW device is formed in an effective area 10d near the center surrounded by a dashed line H of the first wafer 10 shown in FIG. 1. The dashed line H shown in the figure is added for convenience of explanation and is not actually added to the bonded wafer W. The wafer bonded to the second wafer 20 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, a sapphire, quartz, or glass wafer.

[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 having a chamfered portion 10c on their outer periphery are bonded together is produced by grinding the back surface 10b of the first wafer 10 to thin it, and the wafer processing method is performed by the following procedure.

[0017] (Cutting groove formation process) In the wafer processing method of this embodiment, first, the cutting groove forming step described below is performed, but before that, as shown in FIG. 2, it is preferable to perform a protective film disposing step in which the above-mentioned bonded wafer W is inverted and a protective film T is disposed on the back surface 20b of the second wafer 20. The protective film T used in this protective film disposing step is not particularly limited, but is preferably selected from thermocompression films suitable for thermocompression bonding, which do not have a glue or the like disposed on the attachment surface. The material suitable for thermocompression bonding is a material that softens and exhibits adhesiveness when heated to a predetermined temperature, and is selected from polyolefin films, for example, and more specifically, a polyethylene (PE) film is selected. Note that the protective film T does not exclude films other than the above-mentioned thermocompression films, and may be an adhesive film with a glue disposed on the surface. Even in that case, it is preferable that the film be softened by heating. When the protective film T is disposed on the back surface 20b of the second wafer 20, the protective film T is heated by a heating and pressing means (not shown) and pressed against the back surface 20b of the second wafer 20 to adhere thereto.

[0018] Once the bonded wafer W is prepared, the bonded wafer W is transferred to a processing device for forming an annular cut groove in the bonded wafer W, for example, a cutting device 80 (only a part of which is shown) shown in Figs. 3(a) and (b). The cutting device 80 includes at least a chuck table 81 shown in Fig. 3(a) and a cutting means 82 shown in Fig. 3(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 85A for forming the cut groove 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, the second wafer 20 on which the protective film T is provided is placed on the chuck table 81 with the back surface 10b of the first wafer 10 facing upward as shown in Fig. 3(a), and the suction means is operated to hold the first wafer 10 by suction. The thickness of the cutting blade 85A is, for example, 30 µm.

[0019] Next, the cutting blade 85A of the cutting means 82 is rotated at a predetermined speed in the direction indicated by the arrow R1 to position the cutting blade 85A inside the chamfered portion 10c formed on the outer periphery of the first wafer 10 in a region adjacent to the effective region 10d indicated by the dashed line in the figure, and the chuck table 81 is rotated in the direction indicated by the arrow R2 while cutting in at a depth corresponding to the thickness (350 μm) of the first wafer 10 as shown in Fig. 3(b). As a result, a cut groove 100 is formed along the entire periphery along the region inside the chamfered portion 10c on the outer periphery of the first wafer 10 and adjacent to the effective region 10d, reaching the second wafer 20, and the cut groove forming process is completed.

[0020] (Cutting groove detection process) When the above-mentioned cutting groove forming step is completed, the cutting groove 100 formed in the first wafer 10 of the bonded wafer W is positioned directly under the imaging means 86 by operating the chuck table moving means (not shown), as shown in FIG. 4(a). The imaging means 86 is connected to the control means 87 of the cutting device 80. As shown in FIG. 4(a), the image captured by the imaging means 86 can be displayed on the display means M via the control means 87 configured by a computer. Then, the cutting groove 100 is imaged over its entire circumference while the chuck table 81 is rotated in the direction indicated by the arrow R2 by the rotation driving means (not shown), and the image processing program by the control means 87 is operated to measure the width of the cutting groove 100 over its entire circumference. The cutting groove 100 may be measured, for example, at every predetermined rotation angle (for example, 30°).

[0021] If the bonding between the first wafer 10 and the second wafer 20 in the bonded wafer W is sufficient, even if the effective area 10d and the chamfered portion 10c are separated by the above-mentioned cutting groove 100, the first wafer 10 will not peel off from the second wafer 20 outside the cutting groove 100, and as shown on the display means M in Figure 4(a), the width of the cutting groove 100 measured at every predetermined rotation angle (e.g., 30°) is detected as a width (30 μm) corresponding to the thickness of the cutting blade 85A over the entire circumference, and the detection result is output as being uniform.

[0022] However, if the bonding between the first wafer 10 and the second wafer 20 in the bonded wafer W is insufficient, when the effective area 10d and the chamfered portion 10c are separated by the above-mentioned cutting groove 100, the first wafer 10 peels off from the second wafer 20 on the outside of the cutting groove 100, i.e., on the chamfered portion 10c side. As a result, the cutting groove 100 measured over the entire circumference does not have a width (30 μm) corresponding to the cutting blade 85A, and is measured at 10 μm, which is narrower than 30 μm, in some places, as shown in (1) of FIG. 4(b), or the chamfered portion 10c side is broken and scattered due to insufficient bonding, and is measured at a width exceeding the measurement upper limit, as shown in (2) of FIG. 4(b). In this case, the detection result is output that the width of the cutting groove 100 does not correspond to the thickness of the cutting blade 85A and is non-uniform.

[0023] (Bevel removal process) When the above-mentioned cut groove detection step outputs a detection result that the width of the cut groove 100 is uniform, it is determined that the bonding of the bonded wafer W is sufficient, and a grinding step, which will be described later, is carried out. Here, in this embodiment, before carrying out the grinding step, a chamfering portion removing step is carried out to remove the ring-shaped chamfering portion 10c present on the outer periphery of the cut groove 100. The method for removing the ring-shaped chamfering portion 10c is not particularly limited, but can be carried out, for example, as follows.

[0024] When performing the chamfer removing step of this embodiment, the bonded wafer W with the cut groove 100 formed therein is transported to a cutting device 80 (only a part of which is shown) shown in FIG. 5. The cutting device 80 is the cutting device 80 described based on FIG. 3, but the cutting blade 85A with the cut groove 100 formed therein is replaced with a cutting blade 85B with a thickness of, for example, 3 mm, which is suitable for performing the chamfer removing step. After the bonded wafer W is transported to the cutting device 80, as shown in FIG. 5, the second wafer 20 side with the protective film T provided thereon is placed on the chuck table 81 with the side downward and the back surface 10b side of the first wafer 10 upward, and is held by suction. Next, the cutting blade 85B of the cutting means 82 is rotated at a predetermined speed in the direction indicated by the arrow R1, and positioned in the area outside the cut groove 100, i.e., the outer peripheral area where the chamfer 10c of the first wafer 10 is formed. Next, the chuck table 81 is rotated in the direction indicated by the arrow R2 while being fed to a depth corresponding to the thickness (350 μm) 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 surface 20a of the second wafer 20, and completing the chamfered portion removing step. In this embodiment, the chamfered portion removing step is performed by replacing the cutting blade of the cutting device 80 that performed the cut groove forming step, but it may be performed by preparing a separate cutting device that exclusively performs the chamfered portion removing step. In addition, the chamfered portion removing step is not necessarily limited to being performed using the above-mentioned cutting device 80, and may also be performed by other methods in which an external force is applied to the chamfered portion 10c to remove it.

[0025] (Grinding process) In the above-mentioned cut groove detection step, when the bonded wafer W determined to have a uniform width of the cut groove 100 over the entire circumference and sufficient bonding is subjected to the grinding step, it is preferable to perform the cleaning process described below. When performing this cleaning process, a moving means (not shown) for moving the chuck table 81 is operated to position the bonded wafer W directly under the cleaning means 88 as shown in FIG. 6. Next, the chuck table 81 is rotated in the direction indicated by the arrow R2, and cleaning water (e.g., pure water L) is sprayed from the cleaning water spray port 88a of the cleaning means 88 for a predetermined time to clean the bonded wafer W from which the chamfered portion 10c has been removed. After spraying the pure water L from the cleaning means 88, a drying process may be performed to remove moisture from the bonded wafer W by spraying air. By carrying out this cleaning process, contaminants including processing debris generated by carrying out the above-mentioned cut groove forming process and chamfer removing process can be removed from the bonded wafer W, and thus it is possible to prevent contaminants from entering between the bonded wafer W and the chuck table that holds the bonded wafer W during the grinding process described below.

[0026] After the above-mentioned cleaning process is performed, a protective film peeling process is performed to peel off the protective film T arranged on the back surface 20b of the second wafer 20, as shown in FIG. 7. This allows the contamination that has entered between the chuck table 81 and the protective film T during the cutting groove forming process and the chamfered portion removing process to be removed together with the protective film T, and the second wafer 20 side can be made clean and free of contamination and held on the chuck table 6 of the grinding device 1 described later. 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 from the chuck table due to the influence of contamination. When peeling off the protective film T, it is preferable to irradiate ultraviolet rays or perform a cooling or heating process according to the characteristics of the protective film T so that the protective film T can be easily peeled off.

[0027] After the protective film peeling process is performed, a grinding process is performed to grind the first wafer 10 side by using a grinding device 1 shown in Fig. 8. In the grinding process described below, an example is described in which a rough grinding process is performed to grind the thickness of the first wafer 10 from 350 µm to 20 µm, and a finish grinding process is performed to grind the first wafer 10 from 20 µm to 5 µm.

[0028] As shown in Fig. 8, the grinding device 1 includes a roughly rectangular parallelepiped housing 2, and a support wall 2a is erected on the rear end side of the 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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. 8) 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).

[0034] 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 rough grinding is performed by the first grinding means 3, to a second grinding area C where finish grinding is performed by the second grinding means 4, and then to the carry-in / out area A, by rotating the turntable 5 in the direction indicated by the arrow R9. 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 drainage pan 2d.

[0035] 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 device 12 disposed between the loading / unloading area A and the second cassette 8. a workpiece loading / unloading means 12 for loading the bonded wafer W accommodated in the cassette 7 to the alignment means 9 and loading 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 loading / unloading area A, and a transport means 14 for transporting the bonded wafer W after the first wafer 10 has been ground by the second grinding means 4 and held on the chuck table 6 positioned in the loading / unloading area A, and loading the bonded wafer W to the cleaning means 11.

[0036] 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 information related to the grinding process is appropriately displayed on a display means (not shown) via the control means 90.

[0037] The grinding device 1 has a configuration generally as described above, and the grinding process of this embodiment is carried out as follows.

[0038] The bonded wafer W is transported, placed, and held on the chuck table 6 positioned in the carry-in / out area A. When the bonded wafer W is held on the chuck table 6, the following steps are performed: a carry-out step in which the bonded wafer W is carried out from the first cassette 7 by the workpiece carry-in / out means 12, a positioning step in which the bonded wafer W carried out by the workpiece carry-in / out means 12 is placed on the positioning means 9 and the center of the bonded wafer W is aligned, and a holding step in which the transport means 13 is operated to transport the bonded wafer W from the positioning means 9 to the chuck table 6 positioned in the carry-in / out area A, the second wafer 20 side is placed on the chuck table 6 positioned in the carry-in / out area A, and the bonded wafer W is held by suction by operating a suction means (not shown).

[0039] Next, the turntable 5 is rotated 120° in the direction indicated by the arrow R9 described above, and the chuck table 6 holding the bonded wafer W is positioned in the first grinding region B shown in Fig. 8. Once the chuck table 6 holding the bonded wafer W is positioned in the first grinding region B, as shown in Fig. 9(a), the chuck table 6 is rotated in the direction indicated by the arrow R8 described above 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 being supplied by a grinding water supply means (not shown), and then the grinding wheel 35 is fed at a predetermined grinding feed speed (e.g., 1.0 μm / sec) to roughly grind the first wafer 10. 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. 9(a)). The rough grinding is performed until the thickness (350 μm) of the first wafer 10 before processing becomes 20 μm.

[0040] 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. 9(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 grinding wheel 44 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).

[0041] 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 becomes, 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 simultaneously carried out 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.

[0042] As described above, when the first wafer 10 constituting the bonded wafer W is ground to a desired thickness by the finish grinding process in the second grinding area C, the grinding step 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 that has been subjected to the finish grinding process is carried out by the carry-out means 14, and after being cleaned and dried in the cleaning means 11, the workpiece carry-in / out means 12 is operated to carry out the bonded wafer W from the cleaning means 11 and store it in the second cassette 8.

[0043] The grinding step of the wafer processing method of this embodiment is performed after the above-mentioned cut groove forming step and cut groove detecting step are performed, it is detected that the width of the cut groove 100 formed in the bonded wafer W is uniform, and it is determined that the bond between the first wafer 10 and the second wafer 20 of the bonded wafer W is sufficient and that the bond is strong enough that the first wafer 10 does not peel off even in the grinding step. This avoids the problem that the first wafer 10 peels off from the second wafer 20 during the grinding step.

[0044] Furthermore, if the width of the cut groove 100 detected in the above-mentioned cut groove detection process does not correspond to the cutting blade 85A and is detected to be uneven as described based on Fig. 4(b), it is determined that the bonding between the first wafer 10 and the second wafer 20 is insufficient and therefore the grinding process should not be performed, and the wafer is excluded from the processes to be performed after the cut groove detection process. As a result, the problem of the first wafer 10 peeling off from the second wafer 20 during the grinding process is avoided.

[0045] Furthermore, the above-mentioned chamfered portion removal process is performed only when the width of the cut groove 100 is detected to be uniform through the cut groove detection process. This avoids the problem that, when removing the chamfered portion 10c with the cutting blade 85B, the chamfered portion 10c is scattered during the chamfered portion removal process due to insufficient bonding between the first wafer 10 and the second wafer 20, causing damage to the cutting blade 85B.

[0046] As described above, in the wafer processing method configured according to the present invention, the cutting groove detection step detects whether the width of the annular cutting groove is uniform, and determines whether to perform the grinding step of grinding the first wafer. Therefore, during the process of processing a bonded wafer in which a first wafer having a chamfered portion on its outer periphery and a second wafer are bonded together, it is possible to prevent the first wafer (e.g., an LT wafer, an LN wafer) from peeling off from the second wafer (e.g., a silicon substrate, etc.). [Explanation of symbols]

[0047] 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 10d: Effective area 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 85A: Cutting blade (thickness 30 μm) 85B: Cutting blade (thickness 3mm) 86: Imaging means 87: Control means 88: Cleaning methods 100: Cutting groove A: Loading / unloading area B: First grinding area C: Second grinding area L: Pure water T: Protective film W: Bonded wafer

Claims

1. A wafer processing method in which a first wafer having a chamfered portion on an outer periphery and a useful area in a center is bonded to a second wafer, the method comprising: grinding the first wafer to thin it; a cutting groove forming step of holding the second wafer side on a chuck table constituting a processing device for forming a cutting groove, and positioning a cutting blade in an area adjacent to the effective area inside a chamfer formed on the outer periphery of the first wafer, thereby forming an annular cutting groove extending to the second wafer; a cutting groove detection step of detecting whether the width of the annular cutting groove is uniform; a grinding step of holding the second wafer on a chuck table constituting a grinding device and grinding the first wafer if it is detected in the grinding groove detection step that the width of the grinding groove is uniform; A wafer processing method comprising the steps of:

2. 2. The wafer processing method according to claim 1, wherein if it is detected in said cut groove detection step that the width of the cut groove is non-uniform, it is determined that said grinding step should not be carried out.

3. 2. A wafer processing method as described in claim 1, further comprising the steps of: if it is detected in the cut groove detection step that the width of the cut groove is uniform, a chamfer removal step is carried out before the grinding step to remove a ring-shaped chamfer existing on the outer periphery of the cut groove.

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

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