Wafer processing method

Abstract

To provide a wafer processing method capable of appropriately removing a chamfered part of a first wafer when the first wafer is processed in a bonded wafer assembly in which the first wafer and a second wafer are bonded to each other.SOLUTION: A wafer processing method includes: a provisionally bonded wafer producing step of producing a provisionally bonded wafer assembly WA in which a first wafer 10A and a second wafer 10B are provisionally bonded to each other with a relatively weak bonding force; a modified layer forming step of forming a modified layer 100 by irradiating, with a laser beam LB, a region positioned on an inner side of and adjacent to a chamfered portion 17A formed on an outer periphery of the first wafer 10A; a chamfered portion removing step of removing the chamfered portion 17A of the first wafer 10A from the modified layer 100 as an initiating point; a completely bonded wafer assembly generation step of annealing the provisionally bonded wafer assembly WA from which the chamfered portion 17A of the first wafer 10A has been removed to generate a completely bonded wafer assembly WB having an increased bonding force; and a finish grinding step of grinding the first wafer 10A to a desired thickness after the chamfered portion removal step and before or after the completely bonded wafer assembly generation step.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present invention relates to a method for processing a wafer in which a first wafer and a second wafer are bonded and the first wafer is processed.

Background Art

[0002] A wafer on which a plurality of devices such as ICs and LSIs are partitioned by a dicing line and formed on the surface is ground on the back surface to a predetermined thickness, and then divided into individual device chips by a dicing device or a laser processing device, and used in electrical devices such as mobile phones and personal computers.

[0003] In addition, a chamfered portion is formed on the outer periphery of the wafer. When the back surface of the wafer is ground, the chamfered portion becomes a sharp knife edge, cracks occur from the knife edge and reach the inside, damaging the devices formed in the region closer to the center, or the operator being injured by the chamfered portion that has become a knife edge. Therefore, a technique for removing the chamfered portion of the wafer has been proposed (see Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the technique of bonding a first wafer and a second wafer to form a bonded wafer and then processing the first wafer in order to improve the function of the device, there is a problem that it is relatively difficult to remove the chamfered portion from the first wafer. That is, (1) Wafers joined by siloxane bonds or the like have a high bonding strength. When irradiating the focus point of a laser beam with a wavelength that is transmissive to the first wafer adjacent to the chamfered portion inside, even if a modified layer is formed inside the first wafer, it is difficult to remove the chamfered portion. (2) When attempting to remove the chamfered portion of the first wafer by forming the modified layer shown in (1) with a high adhesion state between the first wafer and the second wafer, the laser beam during the formation of the modified layer may reach the second wafer and damage the second wafer. (3) Even when attempting to remove the chamfered portion from the first wafer using a cutting blade, it is difficult to remove the chamfered portion without damaging the second wafer. (4) When there are irregularities on the back surface of the first wafer or when the surface is coated with a film, during the process of forming the modified layer shown in (1), the laser beam is diffusely reflected or reflected, and an appropriate modified layer cannot be formed. As a result, there is a problem that the chamfered portion cannot be properly removed. There is such a problem.

[0006] The present invention has been made to solve the problems shown in (1) to (4) above, and its main technical problem is to provide a wafer processing method capable of appropriately removing the chamfered portion of the first wafer when processing the first wafer in a bonded wafer obtained by bonding the first wafer and the second wafer.

Means for Solving the Problems

[0007] In order to solve the above main technical problem, according to the present invention, there is provided a wafer processing method for bonding a first wafer and a second wafer and processing the first wafer, the method including: a temporary bonding wafer generation step of generating a temporarily bonded wafer in which the first wafer and the second wafer are temporarily bonded with a relatively weak bonding force; a modified layer formation step of irradiating a laser beam to the inside adjacent to a chamfered portion formed on the outer periphery of the first wafer of the temporarily bonded wafer to form a modified layer; a chamfered portion removal step of removing the chamfered portion of the first wafer starting from the modified layer; a main bonding wafer generation step of annealing the temporarily bonded wafer from which the chamfered portion of the first wafer has been removed to increase the bonding force and generating a main bonded wafer; and a finishing grinding step of grinding the first wafer after the chamfered portion removal step and before or after the main bonding wafer generation step to finish it to a desired thickness.

[0008] It is preferable to perform a pre-grinding step of grinding the first wafer after the temporary bonding wafer generation step and before the modified layer formation step to remove a layer that obstructs the laser beam irradiated in the modified layer formation step. Further, the first wafer and the second wafer are silicon wafers, the temporarily bonded wafer is a wafer in which Si and Si are bonded with OH, and the main bonded wafer is preferably a wafer in which Si and Si are bonded with O.

Effect of the Invention

[0009] The wafer processing method of the present invention includes a temporary bonding wafer generation step of generating a temporarily bonded wafer in which a first wafer and a second wafer are temporarily bonded with a relatively weak bonding force, a modified layer formation step of irradiating a laser beam to the inside adjacent to the chamfered portion formed on the outer periphery of the first wafer of the temporarily bonded wafer to form a modified layer, a chamfered portion removal step of removing the chamfered portion of the first wafer starting from the modified layer, a main bonding wafer generation step of annealing the temporarily bonded wafer from which the chamfered portion of the first wafer has been removed to increase the bonding force to generate a main bonded wafer, and a finish grinding step of grinding the first wafer after the chamfered portion removal step and before or after the main bonding wafer generation step to finish it to a desired thickness. Therefore, when processing the first wafer in the bonded wafer in which the first wafer and the second wafer are bonded, the chamfered portion of the first wafer can be appropriately removed.

Brief Description of the Drawings

[0010]

Figure 1

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Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments of a wafer processing method configured based on the present invention will be described in detail with reference to the accompanying drawings.

[0012] (Temporary Bonding Wafer Generation Step) When implementing the wafer processing method of the present embodiment, first, a temporary bonding wafer generation step of generating a temporarily bonded wafer in which a first wafer and a second wafer are temporarily bonded with a relatively weak bonding force is performed.

[0013] FIG. 1 shows an embodiment of the temporary bonding wafer generation step of generating a temporarily bonded wafer WA. When performing the temporary bonding wafer generation step, a first wafer 10A and a second wafer 10B as shown in the figure are prepared. The first wafer 10A is, for example, a silicon (Si) wafer having a diameter of 300 mm and a thickness of 300 μm, and a plurality of devices 12A are formed on the surface 10Aa partitioned by a dicing line 14A. The first wafer 10A has a surface 10Aa and a back surface 10Ab, and includes an effective region 16A near the center where the devices 12A used as products are formed, and an outer peripheral surplus region 18A surrounding the effective region 16A with a chamfered portion 17A formed on the outer periphery. The second wafer 10B also has the same configuration as the first wafer 10A, with a chamfered portion 17B formed on the outer periphery, and is a silicon wafer having an effective region formed by partitioning a plurality of devices by a dicing line on the surface 10Ba facing the lower surface side in the figure (not shown).

[0014] The temporary bonding wafer generation process joins the surface 10Aa of the first wafer 10A and the surface 10Ba of the second wafer 10B together with hydroxyl groups (OH). For example, the surface 10Aa of the first wafer 10A and the surface 10Ba of the second wafer 10B are wet cleaned to form hydroxyl groups (OH) on the surfaces and then adhered together to form an interface 20 by Si-OH-OH-Si bonds, thereby generating a temporarily bonded wafer WA with a relatively weak bonding force.

[0015] (Modified layer formation process, pre-grinding process) If the temporary bonding wafer generation process is carried out as described above, a modified layer formation process is performed by positioning the focus point of the laser beam inside adjacent to the chamfered portion 17A formed on the outer periphery of the first wafer 10A of the temporary bonding wafer WA and irradiating it to form a modified layer. In this modified layer formation process, a laser beam with a wavelength that is transmissive to the first wafer 10A is irradiated from the back surface 10Ab of the first wafer 10A. However, if there are irregularities on the back surface 10Ab of the first wafer 10A or if it is covered with some film (such as an oxide film, etc.), it may interfere with the laser beam, and the modified layer formation process may not be properly carried out. Therefore, preferably, after the above temporary bonding wafer generation process and before the modified layer formation process described below, a pre-grinding process described below is carried out. The pre-grinding process is carried out, for example, according to the procedure shown below.

[0016] FIG. 2 shows the chuck table 31 of the grinding apparatus 30 that performs the pre-grinding process, and FIG. 3 shows the grinding means 32 that grinds the temporarily bonded wafer WA held on the chuck table 31. FIGS. 2 and 3 show only a part of the grinding apparatus 30 for convenience of explanation. The chuck table 31 includes a suction chuck 31a formed of a member having a holding surface for holding the workpiece and having air permeability, and is connected to a suction means (not shown) to generate a negative pressure on the upper surface of the suction chuck 31a. The grinding means 32 includes a rotary spindle 33 rotated by a rotary drive mechanism (not shown), a wheel mount 34 attached to the lower end of the rotary spindle 33, and a grinding wheel 35 attached to the lower surface of the wheel mount 34. A plurality of grinding wheels 36A are annularly disposed on the lower surface of the grinding wheel 35. The grinding wheel 36A is a grinding wheel for grinding the back surface 10Ab of the first wafer 10A to remove a layer that obstructs the laser beam, and a relatively fine-grit grinding wheel is employed.

[0017] The above-mentioned temporarily bonded wafer WA is transported to the above-mentioned grinding device 30, placed on the suction chuck 31a of the chuck table 31, and the above-mentioned suction means is operated to suck and hold it. Next, while rotating the rotary spindle 33 of the grinding means 32 in the direction indicated by the arrow R1 in FIG. 3, for example, at 6000 rpm, the chuck table 31 is rotated in the direction indicated by the arrow R2, for example, at 300 rpm. Then, while supplying grinding water onto the back surface 10Ab of the first wafer 10A of the temporarily bonded wafer WA by a grinding water supply means (not shown), the grinding wheel 36A is brought into contact with the back surface 10Ab of the first wafer 10A, and the grinding wheel 35 is fed downward in the direction indicated by the arrow R3, for example, at a speed of 0.1 μm / second. At this time, grinding can be advanced while measuring the thickness of the temporarily bonded wafer WA with a contact type or non-contact type measuring gauge (not shown), and a predetermined amount of the back surface 10Ab of the first wafer 10A is ground to remove a layer that obstructs the laser beam on the back surface 10Ab of the first wafer 10A. The thickness ground and removed in this pre-grinding process may be a thickness sufficient to remove the film or minute irregularities coated on the back surface 10Ab of the first wafer 10A, and it is not to be ground to such an extent as to substantially thin the thickness of the first wafer 10A itself. If the removal of the layer is possible, the grinding means 32 is stopped and the pre-grinding process is completed. In addition, if it is determined in advance that there is no layer such as irregularities or an oxide film that obstructs the laser beam on the back surface 10Ab of the first wafer 10A to which the laser beam is to be irradiated, this pre-grinding process may be omitted.

[0018] As described above, the following modified layer forming process is carried out with no layer obstructing the laser beam from the back surface 10Ab of the first wafer 10A.

[0019] When implementing the modified layer forming process of this embodiment, the temporary bonding wafer WA is transported to a laser processing apparatus 40 (only a part is shown) shown in FIG. 4(a). The laser processing apparatus 40 includes a chuck table 41 as shown in the figure, a laser beam irradiation means 42 that irradiates a laser beam LB having a wavelength that is transmissive to the first wafer 10A of the temporary bonding wafer WA held on the chuck table 41, a moving means (not shown in the figure) that relatively moves the chuck table 41 and the laser beam irradiation means 42, and a control means (not shown in the figure).

[0020] The temporary bonding wafer WA transported to the laser processing apparatus 40 is placed on the chuck table 41 with the first wafer 10A facing upward and is sucked and held. The temporary bonding wafer WA held on the chuck table 41 is imaged by an alignment means (not shown in the figure) to perform alignment. The outer peripheral position where the chamfered portion 17A of the temporary bonding wafer WA is formed, the center position of the temporary bonding wafer WA, the height of the back surface 10Ab of the first wafer 10A, etc. are detected. Inside the first wafer 10A adjacent to the chamfered portion 17A formed on the outer periphery, the processing position where the condensing point of the laser beam LB should be positioned and irradiated is detected. More specifically, it is a position set within the outer peripheral surplus region 18A where the chamfered portion 17A is formed outside the effective region 16A. For example, a position at a radius of 147 mm from the center point of the first wafer 10A is detected. Information regarding the processing position detected in this way is stored in a control means (not shown in the figure).

[0021] Based on the information of the processing position detected by the above alignment, the above moving means is actuated to move the chuck table 41, and as shown in Fig. 4(a), the processing position is positioned directly below the condenser 43 of the laser beam irradiating means 42. Next, in addition to Fig. 4(a), as can be understood from Fig. 4(b), from the back surface 10Ab side of the first wafer 10A, the condensing point of the laser beam LB is positioned and irradiated inside the processing position in the first wafer 10A, and the chuck table 41 is rotated in the direction indicated by the arrow R4 in Fig. 4(a) to form a ring-shaped modified layer 100 along the inside of the chamfered portion 17A of the first wafer 10A.

[0022] The modified layer 100 formed by the modified layer forming step of the present embodiment is preferably formed of a plurality of layers in the vertical direction, as shown in Fig. 4(b). For example, the modified layer 100 shown in Fig. 4(b) is composed of four modified layers in the vertical direction. When forming the modified layer 100 including such a plurality of layers, first, the condensing point of the laser beam LB is positioned and irradiated at a position set at the deepest part (for example, a depth of 180 μm from the back surface 10Ab) close to the interface 20 inside the inner side adjacent to the chamfered portion 17A of the first wafer 10A, and the chuck table 41 is rotated to form a first-layer ring-shaped modified layer along the chamfered portion 17A. Then, while rotating the chuck table 41, the condensing point is directed toward the back surface 10Ab side (upward) three times, and for example, the depth from the back surface 10Ab is increased to depths of 170 μm → 160 μm → 150 μm. Thereby, a total of four ring-shaped modified layers are formed in the vertical direction along the chamfered portion 17A. Note that the modified layer 100 shown in Fig. 4(b) is conceptually shown for convenience of explanation, and the size and depth position of the modified layer 100 are not along the actual dimensions. Thus, the modified layer forming step is completed. Note that the form of the modified layer 100 formed by the modified layer forming step is not limited to the form of forming the above four layers, and is appropriately set according to the material constituting the first wafer 10A, the thickness of the first wafer 10A, the wavelength, output, etc. of the laser beam irradiating means 42.

[0023] When performing the above-described modified layer forming process, the laser processing conditions are set as follows, for example. Wavelength: 1099 nm Repetition frequency: 80 kHz Average output: 2.0 W Processing feed rate: 450 mm / s Or Wavelength: 1342 nm Repetition frequency: 90 kHz Average output: 1.9 W Processing feed rate: 400 mm / s

[0024] In the above-described modified layer forming process, for example, as shown in FIG. 5, a radial modified layer 110 extending in the direction of the outer peripheral end where the chamfered portion 17A is formed may be formed from the region where the modified layer 100 is formed. The illustrated modified layer 110 is a modified layer that functions to more finely divide the chamfered portion 17A when removing the ring-shaped chamfered portion 17A, and can be formed, for example, under the same laser processing conditions as those for forming the above-described modified layer 100, and is formed at a plurality of locations (four locations in the illustrated embodiment) at equal intervals inside the outer periphery of the first wafer 10A. By forming this modified layer 110, when removing the chamfered portion 17A from the first wafer 10A in the chamfered portion removing process described later, the chamfered portion 17A is finely divided, and the removal of the chamfered portion 17A is favorably realized.

[0025] (Chamfered Portion Removing Process) After performing the above-described modified layer forming step, starting from the modified layer 100, as shown in FIG. 6, a chamfer removal step of removing the chamfer 17A formed on the outer periphery of the first wafer 10A is performed. As described above, the above-described modified layer forming step is performed in the state of the temporary bonding wafer WA, and the bonding force at the interface 20 between the first wafer 10A and the second wafer 10B is weak. Therefore, starting from the above-described modified layer 100, it is possible to easily remove and remove the outer peripheral surplus region 18A including the chamfer 17A. The specific method of performing the illustrated chamfer removal step is not particularly limited. For example, a fluid such as air is injected from the side of the chuck table 41 toward the interface 20, or a thin blade is inserted from the side to apply an external force, so that the chamfer 17A can be removed from the first wafer 10A. When the above-described radial modified layer 110 is formed on the first wafer 10A, in this chamfer removal step, the chamfer 17A is removed in a plurality of fragments.

[0026] (This bonded wafer generation step, finishing grinding step) If the chamfer removal step is performed as described above, an annealing process is performed on the temporary bonding wafer WA from which the chamfer 17A of the first wafer 10A has been removed to generate a bonded wafer WB with an increased bonding force at the interface 20, and before or after the bonded wafer generation step, a finishing grinding step of grinding the first wafer 10A to a desired thickness is performed. In the following description, it will be described as performing the bonded wafer generation step first and then the finishing grinding step. However, the finishing grinding step described later may be performed before the bonded wafer generation step.

[0027] When carrying out the step of generating the bonded wafer, the temporary bonded wafer WA from which the chamfered portion 17A has been removed by the chamfered portion removal step is carried into a predetermined heating container (not shown) provided with the heating means 50 shown in FIG. 7, and the temporary bonded wafer WA is heated by the heating means 50. The heating means 50 is, for example, an infrared heater and can be heated by the radiant heat of the infrared heater. The temporary bonded wafer WA is heated by the heating means 50 to a predetermined temperature (for example, about 1000° C.) for a certain period of time. Thereby, the bonding at the interface 20 between the first wafer 10A and the second wafer 10B is changed from a relatively weak Si-OH-OH-Si bond by a hydroxyl group (OH) to a Si-O-Si bond (siloxane bond) that strongly bonds the first wafer 10A and the second wafer 10B, and an annealing process is performed. As a result, a bonded wafer WB is generated in which the bonding force at the interface 20 is increased as compared with the temporary bonded wafer WA. Thus, the step of generating the bonded wafer is completed.

[0028] As described above, if the step of generating the bonded wafer is carried out, it is transported to the grinding device 30 shown in FIGS. 8(a) and 8(b), and a finish grinding step is performed in which the first wafer 10A is ground to a desired thickness. The illustrated grinding device 30 is the same grinding device as the grinding device 30 described with reference to FIG. 3. However, in this finish grinding step, for example, a grinding wheel 35 having a coarsely gritty grinding wheel 36B disposed on the grinding means 32 shown is attached to perform the first grinding. Next, a grinding wheel 35 having the finely gritty grinding wheel 36A disposed on the grinding means 32 as described above is attached to perform the second grinding, and the bonded wafer WB can be finished to a desired thickness.

[0029] The above-mentioned bonded wafer WB is transported to a grinding device 30. As shown in Fig. 8(a), the back surface 10Ab of the first wafer 10A is placed upward on the suction chuck 31a of the chuck table 31, and the above-mentioned suction means is operated to suck and hold it. The finish grinding process of this embodiment is to thin the thickness of the first wafer 10A, which is 300 μm thick, to a desired thickness, for example, 100 μm. A grinding wheel 35 equipped with a coarsely grained grinding stone 36B is attached to the grinding means 32, and while rotating the rotary spindle 33 in the direction indicated by the arrow R1 in Fig. 8(b), for example, at 6000 rpm, the chuck table 31 is rotated in the direction indicated by the arrow R2, for example, at 300 rpm. Then, while supplying grinding water onto the back surface 10Ab of the first wafer 10A by a grinding water supply means (not shown), the grinding stone 36B is brought into contact with the back surface 10Ab of the first wafer 10A, and the grinding wheel 35 is fed downward in the direction indicated by the arrow R3, for example, at a grinding feed rate of 1.0 μm / second for grinding by 170 μm (first grinding). At this time, grinding can be advanced while measuring the thickness of the bonded wafer WB by a contact or non-contact measuring gauge (not shown). Next, the grinding wheel 35 is replaced with one equipped with a finely grained grinding stone 36A, and second grinding is carried out in the same procedure as the above-mentioned first grinding to grind by 30 μm to the desired thickness (100 μm), and the back surface 10Ab of the first wafer 10A can be finished smoother. In the finish grinding process, it is not necessarily limited to carrying out the first grinding and the second grinding as described above, and it may be possible to carry out only one of them as necessary. Thus, the finish grinding process of this embodiment is carried out, and the method for processing the wafer of this embodiment is completed.

[0030] According to the above-described embodiment of the present invention, since the chamfering portion removing step of removing the chamfering portion 17A is performed at the stage of the temporarily bonded wafer WA that is relatively weakly bonded, the chamfering portion 17A can be easily removed, and the above-described problem (1) is solved. Further, since the modified layer forming step is performed at the stage of the temporarily bonded wafer WA to form the modified layer 100, the adhesion between the first wafer 10A and the second wafer 10B is low, and in a state where there are minute gaps, the laser beam LB is irradiated from the back surface 10Ab of the first wafer 10A. Thus, the above-described problem (2) in which the laser beam LB is blocked by the gaps and the laser beam LB reaches the second wafer 10B to damage the second wafer 10B is also avoided. Furthermore, when there are irregularities or a film is coated on the back surface 10Ab of the first wafer 10A, if the above-described pre-grinding step is performed at the stage of the temporarily bonded wafer WA, a layer that obstructs the laser beam can be removed, and in the above-described modified layer forming step, it becomes possible to appropriately form the modified layer by irradiating the laser beam LB, and the above-described problem (4) is also solved. And according to the present embodiment, it becomes unnecessary to use a cutting blade to remove the chamfering portion 17A, and as a result, the above-described problem (3) is also solved.

Explanation of Signs

[0031] 10A: First wafer 10Aa: Front surface 10Ab: Back surface 12A: Device 14A: Scribing line 16A: Active area 17A: Chamfering portion 18A: Outer peripheral surplus area 10B: Second wafer 10Ba: Front surface 10Bb: Back surface 17B: Chamfering portion 20: Interface 30: Grinding device 31: Chuck table 32: Grinding means 35: Grinding wheel 36A, 36B: Grinding stones 40: Laser processing apparatus 41: Chuck table 42: Laser beam irradiation means 43: Condenser 50: Heating means 100: Modified layer 110: Radial modified layer WA: Temporarily bonded wafer WB: Permanently bonded wafer

Claims

1. A method for processing a wafer, which joins a first wafer and a second wafer and performs processing on the first wafer, comprising: a temporary bonding wafer generation step of generating a temporarily bonded wafer in which the first wafer and the second wafer are temporarily bonded with a relatively weak bonding force; a modified layer formation step of irradiating a laser beam to the inside adjacent to the chamfered portion formed on the outer periphery of the first wafer of the temporarily bonded wafer to form a modified layer; a chamfered portion removal step of removing the chamfered portion of the first wafer starting from the modified layer; a main bonding wafer generation step of annealing the temporarily bonded wafer from which the chamfered portion of the first wafer has been removed to increase the bonding force and generating a main bonded wafer; a finishing grinding step of grinding the first wafer after the chamfered portion removal step and before or after the main bonding wafer generation step to finish it to a desired thickness, the wafer processing method being configured to include the steps.

2. The wafer processing method according to claim 1, wherein after the temporary bonding wafer generation step and before the modified layer formation step, a pre-grinding step of grinding the first wafer to remove a layer that obstructs the laser beam irradiated in the modified layer formation step is performed.

3. The first wafer and the second wafer are silicon wafers, the temporarily bonded wafer is a wafer in which Si and Si are bonded by OH, the main bonded wafer is a wafer in which Si and Si are bonded by O, the wafer processing method according to claim 1.

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