Edge trimming method for bonded wafer

Abstract

To provide an edge trimming method for bonded wafers, capable of efficiently removing the outer peripheral portion of a wafer to be ground in a short time.SOLUTION: An edge trimming method for a bonded wafer W obtained by bonding a ground wafer W1 and a support wafer W2 includes a holding step of holding the bonded wafer W on a chuck table 1, a grinding step of rotating the bonded wafer W held on the chuck table 1 and grinding the outer peripheral portion of the ground wafer W1 with a rotating grinding wheel 22 until the outer peripheral portion reaches a predetermined thickness t0 while measuring the thickness of the outer peripheral portion of the ground wafer W1 with a thickness gauge 10, and a removing step of spraying high-pressure water from above the ground surface of the ground wafer W1 ground in the grinding step, thereby fracturing and removing the ring-shaped unground portion W10 of the ground wafer W1 on the support wafer W2.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a method for edge trimming of a bonded wafer in which a wafer to be ground and a support wafer are bonded together. [Background technology]

[0002] In recent years, bonded wafers such as SOI (Silicon On Insulator) substrates that can realize high integration, low power consumption, high speed, high reliability, etc. of semiconductor devices have been put to practical use. Such bonded wafers are obtained by forming an insulating layer such as a silicon thermal oxide film (SiO2 film) on the entire surface of a support wafer with a chamfered outer periphery, and then stacking a ground wafer as an active layer on this support wafer and bonding the two together. In the bonded wafer obtained in this way, the ground wafer as the active layer is ground until it reaches a predetermined thickness.

[0003] In grinding the grinding target wafer of such a bonded wafer, since the outer peripheral portion of the grinding target wafer is easily peeled off from the support wafer, edge trimming is performed before grinding the grinding target wafer in order to remove only the outer peripheral portion of the grinding target wafer that is easily peeled off by grinding it into a ring shape.

[0004] Incidentally, as edge trimming for removing a ring-shaped peripheral portion of a ground wafer, a method using a laser beam is proposed in Patent Document 1. This method is a method in which a laser beam having a wavelength that passes through the ground wafer is irradiated along a ring-shaped planned processing line set inside the outer peripheral edge of the ground wafer to form a ring-shaped modified layer along the planned processing line inside the outer peripheral portion of the ground wafer, and then the ring-shaped region outside the modified layer of the ground wafer is cut and removed to a predetermined thickness.

[0005] Furthermore, Patent Document 2 proposes an edge trimming method in which the outer periphery of a wafer to be ground is ground to a predetermined thickness, and a ring-shaped unground portion remaining on the outer periphery of the wafer to be ground is removed by etching. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2022-176203 [Patent Document 2] JP 2017-004989 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, the method of forming a modified layer inside the ground wafer by irradiating a laser beam proposed in Patent Document 1 and the method of removing the unground portion remaining on the outer periphery of the ground wafer by etching proposed in Patent Document 2 have the problem that the outer periphery of the ground wafer cannot be removed efficiently in a short time.

[0008] The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for edge trimming of bonded wafers, which can efficiently remove the outer peripheral portion of the wafer to be ground in a short time. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems, the present invention provides a method for edge trimming of a bonded wafer, which removes a ring-shaped outer peripheral portion of a bonded wafer obtained by bonding a ground wafer and a support wafer together, and is characterized by including: a holding step of holding the bonded wafer on a chuck table with the support wafer facing down; a grinding step of rotating the bonded wafer held on the chuck table and grinding the outer peripheral portion of the ground wafer with a rotating grinding wheel until it reaches a predetermined thickness while measuring the thickness of the outer peripheral portion of the ground wafer with a thickness gauge; and a removing step of spraying high-pressure water from above the ground surface against the ground surface of the ground wafer ground in the grinding step, thereby breaking and removing the ring-shaped unground portion of the ground wafer on the support wafer. Effect of the Invention

[0010] According to the present invention, high pressure water is sprayed from above onto the ring-shaped unground portion remaining on the outer periphery of the ground wafer after grinding the outer periphery of the ground wafer in the grinding process, so that the impact of the high pressure water causes cracks in the unground portion of the ground wafer, and the unground portion is broken and removed on the support wafer. In this way, the unground portion can be easily and quickly removed by simply spraying high pressure water from above onto the unground portion of the ground wafer, so that, for example, the work of removing the etching solution by cleaning after etching, which is required when removing the unground portion by etching, is not required, and the labor required for cleaning is eliminated, and the outer periphery of the ground wafer can be efficiently removed (edge ​​trimmed) in a short time. [Brief description of the drawings]

[0011] [Figure 1] FIG. [Diagram 2] 1A and 1B are cross-sectional views showing a manufacturing process of a bonded wafer. [Diagram 3] 3 is a flow chart illustrating steps of an edge trimming method according to the present invention. [Figure 4]5A to 5C are vertical cross-sectional views showing a holding step in the edge trimming method according to the present invention. [Diagram 5] 5A to 5C are vertical cross-sectional views showing a grinding step in the edge trimming method according to the present invention. [Figure 6] 5A to 5C are vertical cross-sectional views showing a removing step in the edge trimming method according to the present invention. [Figure 7] 1 is a vertical cross-sectional view of a bonded wafer whose outer periphery has been removed by an edge trimming method according to the present invention. [Figure 8] 3 is a flowchart showing a procedure of an edge trimming method according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0013] The bonded wafer W to which the edge trimming method according to the present invention is applied is used as an SOI substrate, and is constructed by stacking and bonding a thin, disk-shaped ground wafer W1 and a support wafer W2 having the same diameter one on top of the other as shown in Fig. 1. The ground wafer W1 and the support wafer W2 are made of, for example, single crystal silicon (Si). Here, a manufacturing method of this bonded wafer W will be described below with reference to Fig. 2.

[0014] In manufacturing the bonded wafer W shown in Fig. 1, a grinding wafer W1 and a support wafer W2 are prepared, which are disk-shaped and have the same diameter and have an outer periphery chamfered into a curved surface, as shown in Fig. 2(a). An insulating film f such as a silicon thermal oxide film (SiO2 film) is formed on the entire surface of the support wafer W2. The grinding wafer W1 and the support wafer W2 are then stacked one on top of the other as shown in Fig. 2(b) and bonded together by heat treatment to obtain a bonded wafer W. In this bonded wafer W, an insulating film f is interposed between the grinding wafer W1 and the support wafer W2 to prevent current leakage.

[0015] [Method for edge trimming of bonded wafers] Next, a method for edge trimming of a bonded wafer W according to the present invention will be described. As shown in FIG. 3, the edge trimming method includes the following steps: 1) Holding process 2) Grinding process 3) Removal process The above steps are carried out in order to remove the ring-shaped outer peripheral portion of the ground wafer W1 of the bonded wafer W. Each step will be described below.

[0016] 1) Holding process: The holding step is a step of holding the bonded wafer W on the chuck table 1 with the support wafer W2 facing down, as shown in Fig. 4 (step S1 in Fig. 8). Here, the chuck table 1 is a disk-shaped member having a diameter larger than that of the bonded wafer W, and is configured by incorporating a porous member 1B, which is a porous disk-shaped member, in the center of a metal frame 1A.

[0017] The porous member 1B has a smaller diameter than the bonded wafer W, and its surface constitutes a holding surface. The porous member 1B is connected to a suction source 3 such as a vacuum pump via a pipe 2, and an electromagnetic (solenoid) on-off valve V1 is provided on the pipe 2. The on-off valve V1 is electrically connected to a control unit 4, and its opening and closing operation is controlled by the control unit 4. The control unit 4 includes a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and other memory elements.

[0018] The center of the chuck table 1 is attached horizontally to the upper end of a rotating shaft 1a, and the rotating shaft 1a is rotated by an electric motor 5, which is a rotation drive source, causing the chuck table 1 to rotate around the central axis of the rotating shaft 1a. The electric motor 5 is electrically connected to a control unit 4, which controls its operation (start (ON) / stop (OFF), rotation speed, etc.). Note that the chuck table 1 does not rotate during this holding process.

[0019] Thus, in the holding step (step S1 in FIG. 8), the bonded wafer W is placed on the holding surface of the chuck table 1 (porous member 1B) with the support wafer W2 facing down, as shown in FIG. 4. Thereafter, when the control unit 4 opens the on-off valve V1, the porous member 1B is evacuated by the suction source 3 through the piping 2, generating a negative pressure in the porous member 1B. Therefore, the bonded wafer W placed on the holding surface of the porous member 1B is attracted by the negative pressure generated in the porous member 1B and is suction-held on the holding surface of the porous member 1B.

[0020] 2) Grinding process: The grinding process performed after the holding process is a process in which, as shown in FIG. 5, the bonded wafer W held on the chuck table 1 is rotated, and the thickness t of the outer peripheral ground portion W11 of the ground wafer W1 is measured by a thickness gauge 10, while the outer peripheral portion of the ground wafer W1 is ground by a rotating grinding wheel 22 until it reaches a predetermined thickness t0 (see FIG. 6) (step S2 in FIG. 8).

[0021] a 5 is disposed above the chuck table 1, and includes a spindle housing 21 disposed horizontally along the radial direction of the chuck table 1. A spindle motor (not shown) serving as a rotary drive source is built into the spindle housing 21, and a disk-shaped grinding wheel 22 is attached to the tip of a spindle (not shown) that is rotated by the spindle motor. The spindle (not shown) is disposed horizontally along the radial direction of the chuck table 1 (the left-right direction in FIG. 5), and the grinding wheel 22 is attached to the tip protruding from the spindle housing 21.

[0022] The grinding wheel 22 is disposed above the outer periphery (part to be edge-trimmed) of the wafer W1 to be ground of the bonded wafer W held on the chuck table 1 so that its rotation axis is perpendicular to the rotation axis of the chuck table 1, and its width B is set to be larger than the grinding width H of the outer periphery of the wafer W1 to be ground (B>H). The grinding unit 20 can be raised and lowered by a lifting mechanism 23, and the grinding amount (grinding allowance) of the outer periphery of the wafer W1 to be ground by the grinding wheel 22 is adjusted by lowering the grinding unit 20 by the lifting mechanism 23. Here, the spindle motor (not shown) and the lifting mechanism 23 built in the spindle housing 21 are electrically connected to the control unit 4, and the control unit 4 controls the operation of the spindle motor (start (ON) / stop (OFF), rotation speed, etc.) and the lifting operation of the grinding wheel 22.

[0023] 5, a thickness gauge 10 for measuring the thickness t of the outer peripheral portion (ring-shaped ground portion W11) of the ground wafer W1 is disposed above the outer peripheral portion of the bonded wafer W held on the chuck table 1. The thickness gauge 10 irradiates light having a wavelength that is optically transparent to the ground wafer W1 toward the outer peripheral ground portion W11 of the ground wafer W1, and measures the thickness t of the ground portion W11 of the ground wafer W1 optically and non-contactly based on the difference between the time when the light is emitted and the time when the reflected light reflected by the lower surface (insulating film f) of the ground wafer W1 returns. The thickness gauge 10 is electrically connected to the control unit 4, and the thickness t of the ground portion W11 of the ground wafer W1 measured by the thickness gauge 10 is transmitted to the control unit 4.

[0024] In this grinding step, the outer periphery of the wafer W1 to be ground is ground by the grinding wheel 22 of the grinding unit 20 over a predetermined width H shown in FIG. 5 (step S2 in FIG. 8).

[0025] That is, as shown in FIG. 5, when the grinding wheel 22 of the grinding unit 20 is positioned at a predetermined position above the outer periphery of the wafer W1 to be ground, and then a spindle motor (not shown) built into the spindle housing 21 is started, the spindle motor rotates the grinding wheel 22 at a predetermined speed in the direction of the arrow a shown in the figure.

[0026] When the electric motor 5 is started and its rotation is transmitted to the chuck table 1 via the rotary shaft 1a, the chuck table 1 is rotated around the axis of the rotary shaft 1a together with the bonded wafer W in the direction of the arrow b shown in the figure at a predetermined speed. Then, when the grinding unit 20 is lowered together with the grinding wheel 22 by the lifting mechanism 23 from this state, the grinding wheel 22 rotating in the direction of the arrow a shown in the figure comes into contact with the outer peripheral portion of the upper surface of the wafer W1 to be ground of the bonded wafer W rotating in the direction of the arrow b together with the chuck table 1, and grinding of the outer peripheral portion of the upper surface of the wafer W1 to be ground by the grinding wheel 22 is started. During grinding of the wafer W1 to be ground, grinding water (pure water) is supplied from a grinding water supply source (not shown) to the contact portion (grinding portion) between the grinding wheel 22 and the wafer W1 to be ground, and frictional heat and grinding chips generated at the contact portion by grinding are removed by the grinding water.

[0027] Then, when the grinding wheel 22 is further lowered, the outer periphery of the upper surface of the grinding wafer W1 is ground (trimmed) into a ring shape by a predetermined width H by the grinding wheel 22. At this time, the thickness t of the ring-shaped ground portion W11 of the grinding wafer W1 is optically measured in a non-contact manner by the thickness measuring device 10 (step S3 in FIG. 8), and the measured value is transmitted to the control unit 4. The control unit 4 then determines whether the measured thickness t of the ring-shaped ground portion W11 of the ground wafer W1 has reached a predetermined thickness t0 (see Figure 6) (t = t0?) (step S4 in Figure 8), and if the measured thickness t has not reached the predetermined thickness t0 (t > t0) (step S4: No), it repeats grinding the outer peripheral portion of the ground wafer W1 with the grinding wheel 22 (step S4), measuring the thickness t of the ground portion W11 of the ground wafer W1 (step S3), and determining whether the measured thickness t has reached the predetermined thickness t0 (step S4).

[0028] Then, when the thickness t of the ground portion W11 of the ground wafer W1 measured by the thickness measuring device 10 reaches a predetermined thickness t0 (t=t0), that is, when the outer periphery of the ground wafer W1 is ground to the predetermined thickness t0 (step S4 in FIG. 8: Yes), the next removal process is carried out.

[0029] 3) Removal process: The removal process is a process of breaking and removing an unground portion W10 of thickness t0 remaining on the outer periphery of a ground wafer W1, the outer periphery of which has been ground into a ring shape in the preceding grinding process, by injecting high-pressure water.

[0030] That is, in this removal step, a jet nozzle 30 shown in FIG. 6 is used. This jet nozzle 30 is vertically disposed above the outer peripheral portion (ground surface of the unground portion W10) of the ground wafer W1 of the bonded wafer W held on the chuck table 1, and an injection port (not shown) formed on the lower surface of the jet nozzle 30 opens toward the surface (ground surface) of the unground portion W10 of the ground wafer W1 below. The jet nozzle 30 is connected to a high-pressure water supply source 32 by a pipe 31, and an electromagnetic (solenoid) opening / closing valve V2 is provided on the pipe 31. Here, the opening / closing valve V2 is electrically connected to the control unit 4, and its opening / closing operation is controlled by the control unit 4.

[0031] In this removal step, the electric motor 5 is started to rotate the chuck table 1 and the bonded wafer W held thereon at a predetermined speed in the direction of arrow b in Fig. 6 around the axis of the rotating shaft 1a, while the on-off valve V2 is opened to spray high-pressure water supplied from the high-pressure water supply source 32 from a spray port (not shown) of the spray nozzle 30 vertically from above to below toward the surface of the ring-shaped unground portion W10 on the outer periphery of the ground wafer W1 (step S5 in Fig. 8). In addition, while spraying this high-pressure water, the thickness of the unground portion W10 of the ground wafer W1 is optically measured in a non-contact manner by the thickness gauge 10 (step S6 in Fig. 8).

[0032] As described above, when high-pressure water is sprayed from the spray nozzle 30 vertically from above onto the unground portion W10 on the outer periphery of the wafer W1 to be ground, while the chuck table 1 is rotated at a predetermined speed in the direction of arrow b together with the bonded wafer W held thereon, the impact of the high-pressure water causes cracks to form in the unground portion W10 of the wafer W1 to be ground, and the unground portion W10 is broken off and removed on the support wafer W2.

[0033] In this embodiment, the thickness of the unground portion W10 of the ground wafer W1 is measured by the thickness gauge 10 while high-pressure water is sprayed from the spray nozzle 30 toward the unground portion W10 of the ground wafer W1 (step S6 in FIG. 8). However, as described above, when the entire ring-shaped unground portion W10 of the ground wafer W1 is removed by fracture due to the impact of the high-pressure water, the thickness measured by the thickness gauge 10 becomes 0 (that is, thickness measurement becomes impossible). Note that the spray area sprayed with high-pressure water from the spray nozzle 30 may be smaller than the width of the unground portion W10, and the spray nozzle 30 may be moved horizontally in the radial direction of the ground wafer W1, and the spray area may be moved in the width direction of the unground portion W10 to remove the unground portion W10 by fracture.

[0034] Therefore, in this embodiment, the control unit 4 determines whether the thickness of the unground portion W10 of the ground wafer W1 transmitted from the thickness measuring device 10 is 0 or not (step S7 in Figure 8), and if the thickness of the unground portion W10 is not 0 (if the thickness of the unground portion W10 can be measured) (step S7: No), it determines that the unground portion W10 remains on the outer periphery of the ground wafer W1, and repeats the injection of high-pressure water (step S5), the measurement of the thickness of the unground portion W10 of the ground wafer W1 (step S6), and the determination of whether the measured thickness is 0 or not (step S7).

[0035] Then, if the thickness of the unground portion W10 of the ground wafer W1 measured by the thickness measuring device 10 is 0 (thickness cannot be measured) (step S7: Yes), the control unit 4 determines that all of the unground portion W10 of the ground wafer W1 has been removed by spraying high-pressure water, and ends the series of edge trimming steps for the ground wafer W1 (step S8 in Figure 8).

[0036] 7, which includes the ground wafer W1 whose outer periphery has been removed in a ring shape by the above edge trimming, the insulating film f covering the upper surface of the support wafer W2 having an outer diameter φD2 (>φD1) larger than the outer diameter φD1 is exposed as a ring of width H on the outer periphery side of the ground wafer W1 having an outer diameter φD1, and this exposed portion of the insulating film f is not damaged even when the unground portion W10 of the ground wafer W1 is removed by high-pressure water. The ground wafer W1 whose outer periphery has been removed by the above edge trimming is ground to a predetermined thickness, and the bonded wafer W is used as an SOI substrate.

[0037] As is clear from the above description, according to the present invention, in the grinding process, high-pressure water is sprayed from above onto the ring-shaped unground portion W10 remaining on the outer periphery of the ground wafer W1 by grinding the outer periphery of the ground wafer W1, so that the impact of the high-pressure water causes cracks to occur in the unground portion W10 of the ground wafer W1, and the unground portion W10 is broken and removed on the support wafer W2. In this way, since the unground portion W10 of the ground wafer W1 can be removed simply by spraying high-pressure water from above, it is not necessary to remove the etching solution by cleaning after etching, as in the case of removing the unground portion W10 by etching, for example, and the effort required for cleaning is eliminated, and the outer periphery of the ground wafer W1 can be efficiently removed in a short time.

[0038] In this embodiment, the unground portion W10 having a thickness t0 remaining on the outer periphery of the ground wafer W1 due to grinding in the grinding process is removed by fracturing it with a jet of high-pressure water, so that the insulating film f formed on the upper surface of the support wafer W2 is not damaged and there is no deterioration in the performance of the SOI substrate obtained by grinding the ground wafer W1 to a predetermined thickness.

[0039] Although the above describes the method of the present invention applied to a bonded wafer used as an SOI substrate, the present invention can be similarly applied to edge trimming of a bonded wafer (laminated wafer) formed by bonding two wafers with an adhesive. For example, the present invention can be similarly applied to edge trimming of a bonded wafer as disclosed in JP 2016-004799 A.

[0040] In addition, the present invention is not limited to the application of the embodiments described above, and various modifications are possible within the scope of the claims and the technical ideas described in the specification and drawings. [Explanation of symbols]

[0041] 1: chuck table, 1A: frame, 1B: porous member, 1a: rotating shaft, 2: piping, 3: suction source, 4: control unit, 5: electric motor, 10: grinding unit, 20: grinding unit, 21: spindle housing, 22: grinding wheel, 23: lifting mechanism, 30: injection nozzle, 31: piping, 32: high pressure water supply source, B: width of grinding wheel, φD1: outer diameter of the wafer to be ground, D2: supporting wafer, f: insulating film, H: grinding width of the wafer to be ground, t: thickness of the outer periphery of the wafer to be ground, t0: predetermined thickness, V1, V2: On-off valve, W: Bonded wafer, W1: Wafer to be ground, W10: unground portion of the wafer to be ground, W11: ground portion of the wafer to be ground, W2: Support wafer

Claims

[Claim 1] 1. A method for edge trimming a bonded wafer, comprising the steps of: removing an outer peripheral portion of a ground wafer in a ring shape from a bonded wafer obtained by bonding a ground wafer and a support wafer; a holding step of holding the bonded wafer on a chuck table with the support wafer facing down; a grinding step of rotating the bonded wafer held on the chuck table and grinding the outer peripheral portion of the grinding wafer to a predetermined thickness with a rotating grinding wheel while measuring the thickness of the outer peripheral portion of the grinding wafer with a thickness measuring device; a removing step of injecting high-pressure water from above the ground surface of the ground wafer ground in the grinding step to break and remove the ring-shaped unground portion of the ground wafer on the support wafer; 1. A method for edge trimming of a bonded wafer, comprising:

Images