Wafer processing apparatus

Abstract

To provide a wafer processing apparatus capable of solving the problem that it is difficult to remove a chamfered portion even when a modified layer is formed by irradiating a first wafer of a bonded wafer with a laser beam having a wavelength transmittable through the first wafer while positioning a condensing point of the laser beam on an inner side adjacent to the chamfered portion of the first wafer.SOLUTION: A holding table 44 for holding the second wafer of the bonded wafer W, laser beam applying means 8 for applying a laser beam while positioning a focal point of the laser beam at an inner side adjacent to a chamfered portion formed at an outer periphery of the first wafer of the bonded wafer W held on the holding table 44, to form a ring-shaped modified layer, and fluid supplying means 6 for supplying a fluid for weakening a bonding force to an interface of the chamfered portion where the first wafer and the second wafer are bonded to each other.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a wafer processing apparatus for processing a bonded wafer in which a first wafer and a second wafer are bonded together. [Background technology]

[0002] Wafers have multiple devices such as ICs and LSIs formed on their surface along planned dividing lines. The back surface is ground to a specified thickness, and then the wafer is divided into individual device chips using a dicing machine and laser processing machine. These chips are then used in electrical devices such as mobile phones and personal computers.

[0003] Furthermore, a chamfer is formed on the outer periphery of the wafer, and when the back surface of the wafer is ground, the chamfer becomes a sharp knife edge, which can cause cracks to form from the knife edge and penetrate into the device, damaging it or injuring an operator when handling the wafer. Therefore, a technique for removing the chamfer from the wafer has been proposed (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-088187 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the technology of bonding a first wafer and a second wafer to improve device functionality and then grinding the back surface of the first wafer to form it to a desired thickness, there is a problem in that it is relatively difficult to remove the chamfered portion from the first wafer.

[0006] That is, wafers bonded by siloxane bonding or the like have a strong bonding strength, and even if a modified layer is formed inside the first wafer by irradiating the first wafer with a laser beam having a wavelength that is transparent to the wafer and positioned at a focal point inside the chamfered portion, it is difficult to remove the chamfered portion. Also, when the region of the chamfered portion to be removed on the first wafer is cut and removed with a cutting blade, there is a problem in that the second wafer may be damaged.

[0007] The present invention has been made in view of the above facts, and its main technical object is to provide a wafer processing apparatus that can solve the problem that, when processing a bonded wafer formed by bonding a first wafer and a second wafer, it is difficult to remove the chamfered portion even if a modified layer is formed by irradiating the first wafer with a laser beam having a wavelength that is transparent to the first wafer and positioned at a focal point inside the chamfered portion of the first wafer. [Means for solving the problem]

[0008] In order to solve the above-mentioned main technical problem, according to the present invention, there is provided a wafer processing apparatus for processing a bonded wafer formed by bonding a first wafer and a second wafer, comprising: a holding table for holding the second wafer of the bonded wafers; laser beam application means for positioning a focal point of a laser beam inside adjacent to a chamfered portion formed on the outer periphery of the first wafer of the bonded wafers held on the holding table and irradiating the first wafer to form a ring-shaped modified layer; and fluid supply means for supplying a fluid that weakens the bonding force to the interface of the chamfered portion where the first wafer and second wafer are bonded.

[0009] The fluid supply means preferably includes a fluid supply nozzle having a tip for ejecting the fluid, and positioning means for positioning the tip of the fluid supply nozzle at the interface of the chamfered portion of the bonded wafer. Also, a fluid removal means is preferably provided for removing the fluid adhering to the upper surface of the first wafer to be irradiated with the laser beam. Furthermore, the fluid removal means preferably ejects gas from a nozzle to remove the fluid from the upper surface of the first wafer.

[0010] It is preferable that a centering means be provided for aligning the center of the bonded wafer held on the holding table with the center of the holding table. It is also preferable that a chamfer removing means be provided for removing a chamfer from the outer periphery of the first wafer on which a modified layer has been formed. It is also preferable that an imaging means be provided for imaging the outer periphery of the bonded wafer held on the holding table to confirm the state of adhesion of the fluid or the tip position of the fluid supply nozzle. Furthermore, it is preferable that the first wafer and the second wafer are bonded by Si-O-Si siloxane bonds, and that the fluid that weakens the bonding strength contains water, water vapor, mist, or ammonia and is supplied from the fluid supply means to convert Si-O-Si bonds to Si-OH-OH-Si bonds, thereby weakening the bonding strength. [Effects of the Invention]

[0011] The wafer processing apparatus of the present invention is a wafer processing apparatus for processing a bonded wafer formed by bonding a first wafer and a second wafer, and includes a holding table for holding the second wafer of the bonded wafers, a laser beam application means for irradiating the first wafer of the bonded wafers held on the holding table with a laser beam focused on an inner side adjacent to a chamfered portion formed on the outer periphery of the first wafer and forming a ring-shaped modified layer, and a fluid supply means for supplying a fluid that weakens the bonding force to the interface of the chamfered portion where the first and second wafers are bonded. This weakens the bonding force in the region of the bonded wafer W corresponding to the chamfered portion, and allows the chamfered portion of the first wafer to be easily removed starting from the ring-shaped modified layer, thereby eliminating the problem of difficulty in removing the chamfered portion. Furthermore, there is no need to remove the chamfered portion using, for example, a cutting blade, and there is no problem of scratching the second wafer to which the first wafer is bonded. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a perspective view of a bonded wafer processed by the processing apparatus of the present embodiment. FIG. [Figure 2] 1 is an overall perspective view of a laser processing apparatus according to an embodiment of the present invention; [Figure 3] 3 is a perspective view of a support column and a holding table of a holding means attached to the laser processing machine shown in FIG. 2. FIG. [Figure 4] 1A is a perspective view showing a manner in which a fluid is supplied to the interface of bonded wafers held on a holding table, and FIG. 1B is a side view showing an enlarged view of a part of the manner in which the fluid is supplied shown in FIG. [Figure 5] FIG. 10 is a perspective view showing an embodiment in which a gas is jetted onto the outer periphery of a first wafer of bonded wafers to remove a fluid. [Figure 6] FIG. 10 is a perspective view showing an embodiment in which a modified layer is formed on the outer periphery of a first wafer of a bonded wafer. [Figure 7](a) A partially enlarged cross-sectional view showing the modified layer formed by the first step, (b) A partially enlarged cross-sectional view showing the modified layer formed by the second step in addition to the modified layer formed by the first step. [Figure 8] FIG. 2 is a plan view showing a radial modified layer formed on a first wafer. [Figure 9] FIG. 10 is a perspective view showing how a chamfer is removed from the outer periphery of the first wafer. [Figure 10] 2(a) is an enlarged perspective view of the motor and chamfer removing unit of the chamfer removing means attached to the laser processing apparatus shown in FIG. 1, (b) is a perspective view of the chamfer removing unit shown in (a) as seen obliquely from below, and (c) is a conceptual diagram showing how the chamfer is removed by the chamfer removing means. [Figure 11] FIG. 10 is a perspective view showing a mode in which grinding is performed on the bonded wafer from which the chamfered portion has been removed. [Figure 12] FIG. 1A is a perspective view showing a manner in which grinding is performed to remove a chamfered portion, and FIG. 1B is a perspective view showing a manner in which grinding is performed on a bonded wafer from which a chamfered portion has been removed. DETAILED DESCRIPTION OF THE INVENTION

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of a wafer processing apparatus constructed based on 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 apparatus of this embodiment. The bonded wafer W is a wafer formed by bonding a first wafer 10A and a second wafer 10B together as shown. The first wafer 10A is, for example, a silicon (Si) wafer having a diameter of 200 mm and a thickness of 700 μm. A plurality of devices 12A are formed on a front surface 10Aa, which is partitioned by planned division lines 14A. The first wafer 10A has a front surface 10Aa and a back surface 10Ab. The first wafer 10A includes a central effective region 16A in which the devices 12A to be used as products are formed, and a peripheral excess region 18A surrounding the effective region 16A, which has a chamfered portion 17A formed on the periphery.

[0015] The second wafer 10B also has a similar configuration to the first wafer 10A, with a chamfered portion 17B formed on the outer periphery, and although not shown, on the surface 10Ba facing downward in the figure, a plurality of devices corresponding to the devices 12A of the first wafer 10A are formed by division along planned dividing lines, and is a silicon wafer with a diameter of 200 mm and a thickness of 700 μm.

[0016] In the present embodiment, the first wafer 10A and the second wafer 10B of the bonded wafer W are integrated by, for example, bonding a surface 10Aa of the first wafer 10A to a surface 10Ba of the second wafer 10B and forming an interface 20 by siloxane bonding. The siloxane bond is an Si-O-Si bond in which silicon (Si) and oxygen (O) are alternately bonded, and since the first wafer 10A and the second wafer 10B are bonded by heat treatment, a strong bonded state is maintained even at high temperatures.

[0017] By using the laser processing apparatus 1 (see FIG. 2) of this embodiment, which constitutes the wafer processing apparatus of the present invention, a laser beam is focused on the inside adjacent to the chamfered portion 17A formed on the outer periphery of the first wafer 10A of the bonded wafer W, and the laser beam is irradiated to form a ring-shaped modified layer, and a fluid that weakens the bonding force is supplied to the chamfered portion 17A where the first wafer 10A and the second wafer 10B are bonded and to the interface 20 near the chamfered portion 17B. The laser processing apparatus 1 of this embodiment will be described in more detail below.

[0018] The laser processing apparatus 1 shown in FIG. 2 is disposed on a base 2 and includes a holding means 4 for holding the bonded wafer W described above, a moving means 5 for moving the holding means 4, an imaging means 7 for imaging the bonded wafer W held by the holding means 4 to perform alignment, a laser beam application means 8 for irradiating a laser beam toward the bonded wafer W held by the holding means 4, a frame 3 consisting of a vertical wall portion 3a erected on the side of the moving means 5 and a horizontal wall portion 3b extending horizontally from the upper end of the vertical wall portion 3a, and a fluid supply means 6 for supplying a fluid that weakens the bonding force to an interface 20 of the chamfered portion where the first wafer 10A and the second wafer 10B are bonded.

[0019] 2, the holding means 4 includes a rectangular X-axis direction movable plate 41 mounted on the base 2 so as to be movable in the X-axis direction, a rectangular Y-axis direction movable plate 42 disposed on the X-axis direction movable plate 41 so as to be movable in the Y-axis direction, a substantially cylindrical support pillar 43 fixed to the upper surface of the Y-axis direction movable plate 42, and a holding table 44 disposed on the upper end of the support pillar 43. The holding table 44 is configured to be rotatable by a rotation drive means (not shown) housed in the support pillar 43.

[0020] 3, the holding table 44 is composed of a suction chuck 441 made of a porous material having air permeability, and a frame 442 surrounding the suction chuck 441. The suction chuck 441 is connected to a suction means (not shown) by a flow path passing through the support 43. By operating the suction means, a negative pressure is generated on the upper surface of the suction chuck 441, and the bonded wafer W can be sucked and held on the holding table 44.

[0021] The holding means 4 of this embodiment includes a centering means 45. The centering means 45 is a means for moving the bonded wafer W placed on the holding table 44 toward the center to align the center of rotation of the holding table 44 with the center of the bonded wafer W. Three centering means 45 of this embodiment are arranged at intervals of 120° so as to sandwich the bonded wafer W placed on the holding table 44 from three sides. The centering means 45 is operated by a centering mechanism (not shown), and the centering mechanism is accommodated in a centering mechanism accommodating portion 43a formed on the outer periphery of the support column 43.

[0022] The illustrated centering means 45 includes a lifting rod 451 that is configured to be rotatable and raised and lowered in the vertical direction (Z-axis direction) indicated by arrow R1 by the above-described centering mechanism, and claws 452 that are horizontally disposed at the upper end of the lifting rod 451. The claws 452 rotate in the direction indicated by arrow R2, and tip ends 452a of the three claws 452 come into contact with the outer periphery of the bonded wafer W placed on the holding table 44 from three sides, thereby aligning the center of the bonded wafer W with the center of rotation of the holding table 44.

[0023] 2, the movement means 5 includes an X-axis movement means 5a that moves the holding means 4 in the X-axis direction, and a Y-axis movement means 5b that moves the holding means 4 in the Y-axis direction perpendicular to the X-axis direction. The X-axis movement means 5a converts the rotational motion of the motor 51 into linear motion via a ball screw 52 and transmits the linear motion to the X-axis movable plate 41, moving the X-axis movable plate 41 in the X-axis direction along a pair of guide rails 2a, 2a arranged on the base 2 along the X-axis direction. The Y-axis movement means 5b converts the rotational motion of the motor 53 into linear motion via a ball screw 54 and transmits the linear motion to the Y-axis movable plate 42, moving the Y-axis movable plate 42 along a pair of guide rails 41a, 41a arranged on the X-axis movable plate 41 along the Y-axis direction.

[0024] An optical system constituting the laser beam application means 8 is housed inside the horizontal wall 3b of the frame 3. A condenser 81, which constitutes part of the laser beam application means 8 and which condenses a laser beam having a wavelength that is transparent to at least the first wafer 10A, and irradiates the bonded wafer W with the laser beam, is disposed on the lower surface side of the tip of the horizontal wall 3b. Furthermore, an imaging means 7 is disposed at a position adjacent to the condenser 81 in the X-axis direction. The imaging means 7 is a camera that captures an image of the bonded wafer W held on the holding table 44 of the holding means 4, and detects the position and orientation of the bonded wafer W, the processing position to be irradiated with the laser beam, etc.

[0025] The fluid supply means 6 is a means for supplying a fluid that weakens the bonding force to the interface 20 of the chamfered portions 17A and 17B where the first wafer 10A and the second wafer 10B are bonded. As shown in FIG. 2, the fluid supply means 6 includes a positioning means 62 that positions the tip of a fluid supply nozzle 68 from the side in the X-axis direction at the interface 20 of the chamfered portions 17A and 17B of the bonded wafer W held on the holding table 44. As shown in the figure, the fluid supply nozzle 68 is disposed so as to extend in the X-axis direction from the upper end of an extension rod 66 that extends vertically. The height position of the extension rod 66 is controlled by an elevating cylinder 64 that constitutes the positioning means 62, and the position of the elevating cylinder 64 in the X-axis direction is moved by the positioning means 62. The fluid supplied from the fluid supply nozzle 68 is preferably, for example, water (pure water), water vapor, mist, or ammonia. The illustrated laser processing device 1 is equipped with a display means M, and each operating unit is controlled by a control means (not shown). The effects obtained by the above-described configuration will be described below.

[0026] First, the bonded wafer W is loaded into the laser processing apparatus 1 by a transport means (not shown) and placed on the holding table 44 with the second wafer 10B facing downward and the back surface 10Ab of the first wafer 10A facing upward. Although not shown, a protective tape may be attached to the back surface 10Bb of the second wafer 10B positioned below. When the center of the first wafer 10A of the bonded wafer W is to be aligned with the center of rotation of the holding table 44, the suction means for generating negative pressure in the holding table 44 is not activated, and the three centering means 45 are activated to rotate the claws 452 in the direction indicated by arrow R2 in FIG. 3 , so that the tip ends 452a of the claws 452 a abut against the outer periphery of the bonded wafer W. The tip ends 452a of the three claws 452 then move the bonded wafer W toward the center of rotation of the holding table 44. As a result, the center of the bonded wafer W coincides with the center of rotation of the holding table 34. Then, the suction means is activated to suction-hold the bonded wafer W on the holding table 44. Next, the centering means 45 is activated to move the claws 452 to a retracted position where they come into close contact with the upper surfaces of the support columns 43, as shown in FIG. 4(a).

[0027] Next, the positioning means 62 of the fluid supply means 6 is operated to adjust the position of the fluid supply nozzle 68 in the direction indicated by arrow R3 (X-axis direction) and the vertical direction indicated by arrow R4 (Z-axis direction) shown in FIG. 4(a). As shown in FIG. 4(b), the tip 68a of the fluid supply nozzle 68 is positioned to face the interface 20 of the bonded wafers W held on the holding table 44. At this time, the distance between the tip 68a of the fluid supply nozzle 68 and the outer peripheral edge of the chamfered portion 17A of the first wafer 10A of the bonded wafers W is set to, for example, 500 μm. When the tip 68a of the fluid supply nozzle 68 is positioned to face the interface 20 of the bonded wafers W, the holding table 44 is moved to position the tip 68a of the fluid supply nozzle 68 directly below the imaging means 7 and capture an image. This makes it possible to precisely control the distance between the tip 68a of the fluid supply nozzle 68 and the outer peripheral edge of the bonded wafers W.

[0028] As described above, once the fluid supply nozzle 68 is positioned at a predetermined position, the fluid supply means 6 is operated to spray the fluid L (e.g., pure water) toward the interface 20, while rotating the holding table 44. As described above, the interface 20 in this embodiment is bonded by a siloxane bond (Si-O-Si bond). When the fluid L is supplied from the side toward the interface 20, water molecules gradually penetrate the interface 20, and the penetrated region changes to an Si-OH-OH-Si bond. This weakens the bonding strength of the interface 20, and as shown in FIG. 4(b), a bonding strength weakened region 22 is formed on the outer periphery of the interface 20. The fluid L supplied from the fluid supply nozzle 68 is not limited to being supplied in liquid form, but may be in the form of water vapor or mist.

[0029] As described above, after the fluid L is supplied to the interface 20 of the bonded wafers W by the fluid supply means 6 to form the bonding strength reduced region 22, as will be described later, the laser beam application means 8 is used to position the focal point of the laser beam and apply it to the outer peripheral excess region 18A, which is adjacent to the chamfered portion 17A formed on the outer periphery of the first wafer 10A of the bonded wafers W held on the holding table 44 and in which no device 12A is formed, to form a ring-shaped modified layer.

[0030] Incidentally, when the fluid L is supplied to the interface 20 of the bonded wafer W using the above-described fluid supply means 6 to form the bonding strength reduced region 22, the fluid L may be attached to the back surface 10Ab of the first wafer 10A. Therefore, before forming a ring-shaped modified layer on the outer periphery of the first wafer 10A, it is preferable to remove the fluid L attached to the back surface 10Ab of the first wafer 10A using the fluid removal means 9 shown in FIG. 5 in addition to FIG. 1. Whether or not to remove the fluid L can be determined by positioning the holding table 44 directly below the imaging means 7, capturing an image of the first wafer 10A of the bonded wafer W, and determining whether or not the fluid L is attached to the outer periphery excess region 18A. If it is determined that the fluid L is not attached, the removal of the fluid L by the fluid removal means 9 described below can be omitted.

[0031] 5, the fluid removal means 9 is a means for injecting gas and is composed of a pipe-shaped member (only a portion of which is shown) disposed near the condenser 81 of the laser beam application means 8, and a gas supply source (not shown) is connected to the fluid removal means 9. The fluid removal means 9 is configured to be able to inject gas, more specifically, high-pressure air 91, from a tip 9a on the lower end side obliquely downward and toward the outside of the holding table 44.

[0032] After the fluid L is ejected onto the interface 20 of the bonded wafers W to form the bonding strength reduced region 22, to remove the fluid L adhering to the outer circumferential excess region 18A, the holding table 44 is moved so that the tip 9a of the fluid removal means 9 disposed near the condenser 81 is positioned near the outer circumferential excess region 18A of the first wafer 10A of the bonded wafers W, as shown in FIG. 5. Next, high-pressure air 91 is ejected from the tip 9a of the fluid removal means 9, and the holding table 44 is rotated in the direction indicated by arrow R5 at a predetermined rotational speed (e.g., 100 rpm). This removes the fluid L adhering to the outer periphery of the first wafer 10A of the bonded wafers W, preventing it from interfering with the laser processing described below.

[0033] The fluid removing means 9 is not limited to the above-described means for spraying high-pressure air 91. Various means can be selected as the fluid removing means 9 as long as they are capable of removing the fluid L adhering to the first wafer 10A of the bonded wafers W. For example, it is possible to employ a means for removing the fluid L by bringing a sponge having excellent absorbency for the fluid L into contact with the peripheral excess region 18A of the first wafer 10A and rotating the holding table 44, a means for irradiating light from a halogen lamp to heat the fluid L and evaporate the fluid L, or a means for removing the fluid L by centrifugal force by rotating the holding table 44 at high speed.

[0034] Once the fluid L on the first wafer 10A has been removed by the fluid removal means 9, a modified layer is formed by laser processing, which will be described below.

[0035] When forming the modified layer, alignment is performed on the bonded wafer W held by suction on the holding table 44 using the imaging means 7 arranged in the laser processing apparatus 1. By this alignment, the position of the outer circumferential edge where the chamfered portion 17A of the first wafer 10A is formed and the center position of the first wafer 10A are detected, and the height of the upper surface of the back surface 10Ab of the first wafer 10A is detected. The focal point of the laser beam LB is positioned in an area corresponding to the inner outer circumferential excess area 18A adjacent to the chamfered portion 17A formed on the outer periphery of the first wafer 10A, and the processing position to be irradiated (for example, a position 98 mm in radius from the center point of the first wafer 10A) is detected.

[0036] The process for forming the modified layer carried out in the present invention can be carried out, for example, including the first step and the second step described below.

[0037] (First step) Based on the position information of the processing position detected by the above-described alignment, the holding table 44 is moved to position the processing position set in a region corresponding to the outer peripheral excess region 18A of the first wafer 10A of the bonded wafer W directly below the condenser 81 of the laser beam application means 8, as shown in Fig. 6. Next, as can be seen from Fig. 7(a) in addition to Fig. 6, the laser beam LB is irradiated from the back surface 10Ab side of the first wafer 10A with the focal point positioned inside the processing position on the first wafer 10A, and the holding table 44 is rotated in the direction indicated by arrow R5 to form a ring-shaped first modified layer 100 around the entire circumference along the inside of the chamfered portion 17A of the first wafer 10A. As described above, the center of rotation of the holding table 44 is aligned with the center of the first wafer 10A, and therefore, by rotating the holding table 44 while irradiating the laser beam LB by the laser beam application means 8, a modified layer 100 can be formed accurately at the processing position set in the peripheral excess region 18A of the first wafer 10A.

[0038] The first modified layer 100 formed by the first step of this embodiment is preferably formed of multiple layers in the vertical direction, as shown in Fig. 7(a). For example, the first modified layer 100 shown in Fig. 7(a) is composed of four modified layers in the vertical direction. To form the first modified layer 100 including such multiple layers, for example, the focal point of the laser beam LB is positioned at a position set at the deepest part (700 μm deep from the back surface 10Ab) inside the first wafer 10A adjacent to the chamfered portion 17A and in contact with the interface 20, and the holding table 44 is rotated to form a first ring-shaped modified layer along the chamfered portion 17A. Then, while rotating the chuck table 34, the focal point is raised three times toward the back surface 10Ab (upward) to a depth from the back surface 10Ab of 500 μm, 300 μm, and 150 μm, thereby forming a total of four ring-shaped modified layers along the chamfered portion 17A. By forming the first modified layer 100 in this relatively deep region, cracks are formed along the first modified layer 100 to the front surface 10Aa of the first wafer 10A, i.e., the interface 20. 7(a) is a conceptual illustration for the sake of convenience, and the depth positions of each layer do not correspond to actual dimensions. Thus, the first step is completed. The first modified layer 100 formed in the first step is not limited to being formed of four layers, and can be appropriately set depending on the thickness of the first wafer 10A, the material constituting the first wafer 10A, the wavelength and output of the laser beam LB irradiated by the laser beam application means 8, etc.

[0039] (Second step) After the first modified layer 100 is formed in the first step described above, a second step is performed to form a second modified layer at a relatively shallow position outside or inside the first modified layer 100, but not reaching the interface 20 of the bonded wafer W. In the second step of this embodiment, as shown in FIG. 7(b), the laser beam LB is focused at positions adjacent to the outside of the uppermost modified layer (150 μm deep from the back surface 10Ab) and the lower modified layer (300 μm deep from the back surface 10Ab) of the first modified layer 100, and the holding table 44 is rotated to form ring-shaped second modified layers 102, 104. The second modified layers 102, 104 are preferably formed by adjacently forming multiple ring-shaped modified layers (three in the illustrated embodiment) at the same depth but with different diameters, as shown in the figure.

[0040] In the modified layer forming process described above, in addition to forming the first modified layer 100 in the first step, second modified layers 102, 104 are formed in the second step adjacent to the first modified layer 100 at relatively shallow positions that do not reach the interface 20. This makes it possible to generate an external force starting from the first modified layer 100 in a direction that warps the chamfered portion 17A, indicated by arrow R6, away from the interface 20. As a result, it is possible to more reliably reduce the bonding strength in the bonding strength reduced region 22 formed at the interface 20, and also to further extend cracks formed along the first modified layer 100.

[0041] The laser processing conditions for forming the modified layer are set, for example, as follows. Wavelength: 1099nm or 1342nm Repetition frequency: 80kHz Average power: 2.0W Holding table rotation speed: 60 rpm

[0042] In addition to the modified layers 100, 102, and 104 described above, for example, as shown in FIG. 8 , a radial modified layer 110 may be formed extending from the region where the first modified layer 100 and the second modified layers 102 and 104 are formed toward the outer circumferential edge where the chamfered portion 17A is formed. The modified layer 110 shown in the figure is formed, for example, by irradiating the first wafer 10A with a laser beam LB under the same laser processing conditions as those used to form the first modified layer 100 described above, and is formed at multiple locations (four locations in the illustrated embodiment) at equal intervals on the outer periphery of the first wafer 10A. By forming this modified layer 110, the chamfered portion 17A is divided into smaller parts when removing the chamfered portion 17A from the first wafer 10A, which allows the chamfered portion 17A to be more easily removed.

[0043] As described above, after the modified layer is formed in the peripheral excess region 18A of the first wafer 10A, the chamfered portion 17A is removed from the outer periphery of the first wafer 10A on which the modified layer has been formed, as shown in Fig. 9. By forming the modified layer as described above, the peripheral excess region 18A including the chamfered portion 17A can be easily removed by applying a simple external force. The laser processing apparatus 1 of this embodiment is equipped with a chamfered portion removing means 30 as shown in Figs. 2 and 10.

[0044] 2, the chamfer removing means 30 includes a casing 32 extending upward from the ends of the guide rails 2a, 2a on the base 2, and an arm 34 that is supported by the casing 32 so as to be movable up and down and extends in the X-axis direction. The casing 32 contains an elevating means (not shown) for raising and lowering the arm 34. A motor 36 is installed at the tip of the arm 34, and a chamfer removing part 38 that is rotated by the motor 36 around an axis that extends in the vertical direction is connected to the underside of the motor 36.

[0045] Fig. 10(a) shows an enlarged view of the motor 36 and chamfer removing unit 38 of the chamfer removing means 30, and Fig. 10(b) shows the chamfer removing unit 38 shown in Fig. 10(a) as viewed obliquely from below. As can be seen from Fig. 10(b), the chamfer removing unit 38 is ring-shaped, and a blade 384 for removing the chamfer 17A of the first wafer 10A is disposed on the inner surface of the ring-shaped chamfer removing unit 38. This blade 384 is a thin, razor-like blade, and when the chamfer removing unit 38 is driven by the motor 36 and rotates forward and backward in the direction indicated by arrow R7, it protrudes inward as indicated by arrow R8 in the figure or is retracted into the chamfer removing unit 38.

[0046] As described above, after the modified layer is formed in the outer peripheral excess region 18A of the first wafer 10A, in order to remove the chamfered portion 17A, the X-axis moving means 5a and the Y-axis moving means 5b are operated to position the holding table 44 below the chamfer-removing unit 38. Next, the arm 34 is lowered to bring the lower surface 382 of the chamfer-removing unit 38 shown in FIG. 10(b) into close contact with the back surface 10Ab of the first wafer 10A of the bonded wafer W. Next, the motor 36 of the chamfer-removing means 30 operates the chamfer-removing unit 38 to move the blade 384 into the bonding strength reduced region 22 formed at the interface 20, as shown by arrow R9 in FIG. 10(c), while rotating the holding table 44, thereby fracturing the outer peripheral excess region 18A including the chamfered portion 17A, starting from the modified layer.

[0047] After the outer peripheral excess region 18A including the chamfered portion 17A has been broken, the motor 36 is operated to house the blade 384 inside the chamfered portion removing part 38, and the arm 34 of the chamfered portion removing means 30 is raised, whereby the chamfered portion 17A is removed from the first wafer 10A of the bonded wafers W, as shown in FIG. 9 .

[0048] As described above, once the chamfered portion 17A has been removed from the first wafer 10A of the bonded wafer W, a grinding process is carried out as necessary to grind the back surface 10Ab of the first wafer 10A to a desired thickness.

[0049] When grinding is performed, the bonded wafer W from which the chamfered portion 17A has been removed is transferred to a grinding apparatus 70 (only a portion of which is shown) shown in Fig. 11. As shown, the grinding apparatus 70 includes a grinding means 72 for grinding and thinning the bonded wafer W held by suction on a chuck table 71. The grinding means 72 includes a rotating spindle 72a rotated by a rotation drive mechanism (not shown), a wheel mount 72b attached to the lower end of the rotating spindle 72a, and a grinding wheel 72c attached to the lower surface of the wheel mount 72b, and a plurality of grinding stones 72d are annularly arranged on the lower surface of the grinding wheel 72c.

[0050] After the bonded wafer W is transported to the grinding apparatus 70, as shown in Fig. 11, it is placed on the chuck table 71 with the second wafer 10B side facing downward, and suction is held by operating a suction means (not shown). Next, the rotating spindle 72a of the grinding means 72 is rotated in the direction indicated by arrow R10 in Fig. 11 at, for example, 6000 rpm, while the chuck table 71 is rotated in the direction indicated by arrow R11 at, for example, 300 rpm. Then, while grinding water is supplied onto the back surface 10Ab of the first wafer 10A by a grinding water supply means (not shown), a grinding feed means (not shown) is operated to bring the grinding stone 72d into contact with the back surface 10Ab of the first wafer 10A, and the grinding wheel 72c is ground and fed downward as indicated by arrow R12 at a grinding feed rate of, for example, 1.0 µm / sec. At this time, grinding can be carried out while measuring the thickness of the bonded wafer W with a contact or non-contact measuring gauge (not shown), and the thickness can be reduced to a desired thickness.

[0051] When the back surface 10Ab of the first wafer 10A is ground by a predetermined amount to obtain the bonded wafer W with a desired thickness, the grinding means 72 is stopped and retreated upward, completing the grinding process. After the grinding process is completed, cleaning, drying, and other processes (details of which are omitted) are carried out as appropriate.

[0052] According to the above-described embodiment, the bonding strength of the regions corresponding to the chamfered portions 17A and 17B at the interface 20 of the bonded wafers W, which have been bonded in advance by siloxane bonding, is weakened, and the chamfered portion 17A of the first wafer 10A can be easily removed starting from the modified layer formed in a ring shape, thereby solving the problem of difficulty in removing the chamfered portion 17A. Furthermore, there is no need to use a cutting blade to remove the chamfered portion 17A, and there is no problem of scratching the second wafer 10B to which the first wafer 10A is bonded.

[0053] The present invention is not limited to the above-described embodiment. Although the laser processing apparatus 1 in the above-described embodiment is provided with the chamfered portion removing means 30, the laser processing apparatus 1 does not necessarily have to be provided with the chamfered portion removing means 30. In a case where the chamfered portion removing means 30 is not provided, after the modified layer is formed on the first wafer 10A of the bonded wafer W, the bonded wafer W is transported to the grinding apparatus 70 as shown in FIG. 12(a), and is placed on the chuck table 71 with the second wafer 10B side facing downward and the back surface 10Ab of the first wafer 10A facing upward, and is held by suction.

[0054] 12(a), the rotating spindle 72a of the grinding means 72 is rotated in the direction indicated by arrow R10 at, for example, 6000 rpm, while the chuck table 71 is rotated in the direction indicated by arrow R11 at, for example, 300 rpm. Then, while grinding water is supplied onto the back surface 10Ab of the first wafer 10A by a grinding water supply means (not shown), the grinding feed means (not shown) is operated to bring the grinding stone 72d into contact with the back surface 10Ab of the first wafer 10A, and the grinding wheel 72c is fed downward as indicated by arrow R12 at a grinding feed rate of, for example, 0.1 μm / sec. This applies an external force to the back surface 10Ab of the first wafer 10A, and the outer peripheral excess region 18A including the chamfered portion 17A is removed, with the modified layer 100 serving as the starting point for division. At this time, it is preferable that the radial modified layer 110 is formed as described above, and the chamfered portion 17A is appropriately divided at the outer periphery so as to be removed well from the first wafer 10A.

[0055] As described above, after the chamfered portion 17A has been removed from the first wafer 10A, the grinding wheel 72c is fed downward as indicated by the arrow R12 at a grinding feed rate of, for example, 1.0 μm / sec. The thickness of the bonded wafer W is measured using a contact or non-contact measuring gauge (not shown) while grinding until the desired thickness is reached. Once a predetermined amount of the back surface 10Ab of the first wafer 10A has been ground to the desired thickness, the grinding means 72 is stopped and retracted upward, completing the grinding process. As shown on the left side of FIG. 12(b), the desired bonded wafer W can be obtained. After the grinding process is completed, cleaning, drying, and other processes (details of which are omitted) may be performed as appropriate.

[0056] The bonded wafer W described above is formed by bonding a first wafer 10A and a second wafer 10B together using siloxane bonding. However, the bonded wafer processed by the processing apparatus of the present invention is not limited to wafers bonded by siloxane bonding. For example, the first wafer 10A and the second wafer 10B may be bonded together using a nitride bond (SiCN bond), a TEOS bond that converts tetraethyl orthosilicate molecules into a solid with Si-O-Si bonds, or a ThOx bond that forms a silicon oxide (SiO) film by heating the silicon wafer in an oxygen atmosphere to oxidize the surface. Regardless of the bonding method, the bonding force can be weakened by the fluid L. Furthermore, the processing apparatus of the present invention can be applied to bonded wafers W that have been bonded by subjecting the bonding surfaces to O plasma treatment or N plasma treatment as pretreatment for forming the interface 20.

[0057] Furthermore, in the above-described embodiment, before performing laser processing to form modified layers 100, 102, 104, 110, etc. on the first wafer 10A of the bonded wafers W, fluid L is sprayed from the fluid supply nozzle 68 of the fluid supply means 6 onto the interface 20 of the bonded wafer W to form the bonding strength reduced region 22, and then each of the modified layers described above is formed. However, the bonding strength reduced region 22 may be formed by supplying fluid L to the interface 20 at the same time as forming the modified layer by laser processing or after forming the modified layer and before removing the chamfered portion 17A from the first wafer 10A.

[0058] Furthermore, in the laser processing apparatus 1 of the above-described embodiment, a fluid removal means 9 is provided to spray gas toward the back surface 10Ab of the first wafer 10A positioned above the bonded wafer W held by suction on the holding table 44, thereby removing the fluid L adhering to the area corresponding to the peripheral excess area 18A. However, for example, if the diameter of the bonded wafer W is larger than the holding table 44 and protrudes outward from the outer periphery of the holding table 44, there is a risk that the fluid L will remain adhering to the outer periphery of the back surface 10Bb of the second wafer 10B positioned below. In this case, a fluid removal means may be added that sprays high-pressure air from below the holding table 44 toward the outer periphery of the second wafer 10B of the bonded wafer W held by suction on the holding table 44, and operates simultaneously with the above-mentioned fluid removal means 9 to spray gas toward both the outer periphery of the back surface 10Ab of the first wafer 10A of the bonded wafer W held on the holding table 44 and the outer periphery of the back surface 10Bb of the second wafer 10B, thereby removing the fluid L.

[0059] Furthermore, in the above-described embodiment, the holding table 44 is provided with the center positioning means 45, but the center positioning means 45 may be omitted. In this case, when the bonded wafer W is placed on the holding table 44 and held by suction, the center of rotation of the holding table 44 may be misaligned with the center of the bonded wafer W. Therefore, before the bonded wafer W is held by suction on the holding table 44 and a modified layer is formed, the holding table 44 holding the bonded wafer W by suction is moved directly below the imaging means 7 and an image is taken, and the center of the bonded wafer W is detected based on positional information about the outer periphery of the bonded wafer W. Then, the direction and amount of misalignment of the center of the bonded wafer W with respect to the center of rotation of the holding table 44 are calculated and stored in control means (not shown). When forming the modified layer inside the outer periphery of the bonded wafer W held by suction on the holding table 44, the X-axis moving means 5a and the Y-axis moving means 5b are operated in accordance with the oscillation of the bonded wafer W when the holding table 44 is rotated, and the position of the holding table 44 relative to the condenser 81 of the laser beam application means 8 is corrected so that the position of the laser beam LB irradiated from the condenser 81 of the laser beam application means 8 is a constant distance (for example, 98 mm from the center) from the center of the bonded wafer W. By performing laser processing in this manner, the ring-shaped modified layer can be formed at a desired position that is a uniform distance from the center of the bonded wafer W.

[0060] Furthermore, when the fluid L is supplied from the fluid supply nozzle 68 of the fluid supply means 6 from the outer periphery toward the interface 20 of the bonded wafer W, the positioning means 62 of the fluid supply means 6 is operated based on the direction and amount of deviation of the center of the bonded wafer W from the center of rotation of the holding table 44 described above. This makes it possible to supply the fluid L toward the interface 20 while keeping the distance from the outer periphery edges of the chamfered portions 17A and 17B of the bonded wafer W to the tip 68a of the fluid supply nozzle 68 to the desired distance (e.g., 500 μm), thereby avoiding variations in the width of the bonding strength reduced region 22 formed at the interface 20 of the bonded wafer W. [Explanation of symbols]

[0061] 1: Laser processing equipment 2: Base 3: Frame 4: Holding means 41:X-axis movable plate 42: Y-axis direction movable plate 43: Strut 43a: Center positioning mechanism housing 44: Holding table 441: Vacuum chuck 442: Frame 45: Center positioning means 451: Lifting rod 452: Nails 452a: Tip 5: Transportation 5a:X-axis movement means 5b: Y-axis movement means 6:Fluid supply means 62: Positioning means 64: Lifting cylinder 66: Extension rod 68: Fluid supply nozzle 68a: Nozzle tip 7: Imaging means 8: Laser beam irradiation means 81: Concentrator 9: Fluid removal means 10A: First wafer 10Aa: Surface 10Ab: Back 12A:Device 14A: Planned division line 16A: Effective area 17A: Chamfered part 18A: Surplus outer area 10B: Second wafer 17B: Chamfered part 20: Interface 22: Bonding force reduction area 30: Chamfer removal means 32: Casing 34: Arm 36: Motor 38: Chamfered part removed 382: Bottom surface 384: Blade 70: Grinding equipment 71: Chuck table 72: Grinding means 72d: Grinding wheel 100, 102, 104, 110: Modified layers W: Bonded wafer

Claims

1. A wafer processing apparatus for processing a bonded wafer formed by bonding a first wafer and a second wafer, a holding table for holding a second wafer of the bonded wafers; a laser beam application means for irradiating a first wafer of the bonded wafers held on the holding table with a laser beam focused at a focal point inside the first wafer adjacent to a chamfered portion formed on the outer periphery of the first wafer, thereby forming a ring-shaped modified layer; a fluid supplying means for supplying a fluid that weakens the bonding force to the interface of the chamfered portion where the first wafer and the second wafer are bonded.

2. 2. The wafer processing apparatus according to claim 1, wherein the fluid supply means comprises a fluid supply nozzle having a tip for ejecting the fluid, and positioning means for positioning the tip of the fluid supply nozzle at the interface of the chamfered portion of the bonded wafer.

3. 2. The wafer processing apparatus according to claim 1, further comprising a fluid removing means for removing the fluid adhering to the upper surface of the first wafer onto which the laser beam is irradiated.

4. 4. The processing apparatus according to claim 3, wherein said fluid removing means ejects gas from a nozzle to remove said fluid from the upper surface of the first wafer.

5. 2. A wafer processing apparatus according to claim 1, further comprising a centering means for aligning the center of the bonded wafer held on said holding table with the center of said holding table.

6. 2. The processing apparatus according to claim 1, further comprising chamfer removing means for removing a chamfer from the outer periphery of the first wafer on which the modified layer is formed.

7. 3. The processing apparatus according to claim 1, further comprising an imaging means for imaging the outer periphery of the bonded wafer held on the holding table to confirm the state of adhesion of the fluid or the position of the tip of the fluid supply nozzle.

8. the first wafer and the second wafer are bonded together by a Si—O—Si siloxane bond, the fluid that weakens the bonding force includes water, water vapor, mist, or ammonia and is supplied from the fluid supply means; 2. The wafer processing device according to claim 1, wherein the bonding strength is weakened by converting Si--O--Si bonds into Si--OH--OH--Si bonds.

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