Wafer processing method

Abstract

The present invention provides a wafer processing method that allows for the appropriate removal of the chamfered portion of the first wafer when processing the first wafer in a bonded wafer obtained by joining a first wafer and a second wafer. [Solution] The method comprises: a modified layer formation step in which a laser beam is focused on the inner side adjacent to the chamfered portion formed on the outer circumference of the first wafer 10A and irradiated to form a ring-shaped modified layer; a chamfered portion removal promotion step in which a fluid that weakens the bonding force is supplied to the interface of the chamfered portion where the first wafer 10A and the second wafer 10B are joined, and the fluid penetrates to an area where the chamfered portion can be removed; and a grinding step in which the second wafer 10B is held in the chuck table 51 that constitutes the grinding device 50, the first wafer 10A is ground to thin it, and the chamfered portion 17A' is removed.

Description

Technical Field

[0001] The present invention relates to a method for processing a wafer by processing the first wafer in a bonded wafer obtained by bonding a first wafer and a second wafer.

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 form a predetermined thickness, and then divided into individual device chips by a dicing device or a laser processing device, and is used in electric devices such as mobile phones and personal computers.

[0003] Also, a chamfer is formed on the outer periphery of the wafer. When the back surface of the wafer is ground, the chamfer 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 is injured by the chamfer that has become a knife edge. Therefore, a technique for removing the chamfer 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 grinding the back surface of the first wafer in order to improve the function of the device, there is a problem that it is relatively difficult to remove the chamfer from the first wafer.

[0006] That is, (1) Wafers bonded by siloxane bonds, etc., have strong bonding forces, and even if a laser beam with a wavelength that is transparent to the first wafer is focused on the inside adjacent to the chamfered portion and irradiated to form a modified layer inside the first wafer, it is difficult to remove the chamfered portion well by this alone. (2) When attempting to remove the chamfered portion of the first wafer by forming a modified layer as described in (1) above, while the first wafer and the second wafer are in high adhesion, the laser beam used to form the modified layer may reach the second wafer and damage it. (3) When removing the chamfered portion from the first wafer using a cutting blade, it is difficult to remove it completely without damaging the second wafer. This presents a problem.

[0007] The present invention has been made to solve the problems described in (1) to (3) above, and its main technical problem is to provide a wafer processing method that can appropriately remove the chamfered portion of the first wafer when processing the first wafer in a bonded wafer formed by joining a first wafer and a second wafer. [Means for solving the problem]

[0008] To solve the above-mentioned main technical problems, the present invention provides a wafer processing method for a bonded wafer in which a first wafer and a second wafer are joined, comprising: a modified layer formation step of positioning the focusing point of a laser beam on the inside adjacent to a chamfer formed on the outer circumference of the first wafer and irradiating it to form a ring-shaped modified layer; a chamfer removal promotion step of supplying a fluid that weakens the bonding force to the interface of the chamfer formed where the first wafer and the second wafer are joined and allowing it to penetrate to an area where the chamfer can be removed; and a grinding step of holding the second wafer on a chuck table constituting a grinding apparatus, grinding the first wafer to thin it, and removing the chamfer.

[0009] The process includes an external force application step in which an external force is applied to the interface, and it is preferable that the bonding force of the interface is weakened in combination with the external force in the chamfer removal acceleration step. Furthermore, the modified layer formation step may include a first step of positioning the focal point of the laser beam near the interface and irradiating it to form a relatively deep first modified layer in which cracks reach the interface, and a second step of forming a relatively shallow second modified layer adjacent to the first modified layer on the outside or inside, which does not reach the interface, and the external force application step may be carried out to apply an external force that bends the chamfer away from the interface, starting from the first modified layer.

[0010] In the modified layer formation process, a radial modified layer may be formed from the ring-shaped modified layer outward. Furthermore, the chamfer removal acceleration process may be performed before the modified layer formation process, after the modified layer formation process, or simultaneously with the modified layer formation process.

[0011] The first wafer and the second wafer are joined by Si-O-Si siloxane bonds, and the fluid that weakens the bonding force includes water, water vapor, or mist. Preferably, in the chamfer removal acceleration step, the Si-O-Si bonds are changed to Si-OH-OH-Si bonds, thereby weakening the bonding force at the interface. [Effects of the Invention]

[0012] The wafer processing method of the present invention is a wafer processing method for a bonded wafer formed by joining a first wafer and a second wafer, and includes: a modified layer formation step of positioning the focusing point of a laser beam on the inside adjacent to a chamfer formed on the outer circumference of the first wafer and irradiating it to form a ring-shaped modified layer; a chamfer removal promotion step of supplying a fluid that weakens the bonding force to the interface of the chamfer formed by joining the first wafer and the second wafer and allowing it to penetrate to an area where the chamfer can be removed; and a grinding step of holding the second wafer on a chuck table constituting a grinding device, grinding the first wafer to thin it, and removing the chamfer. As a result, the bonding force of the chamfer is weakened when performing the grinding step, and the chamfer of the first wafer can be appropriately removed. Furthermore, if the chamfer removal acceleration process is performed before the formation of the modified layer, the adhesion between the first wafer and the second wafer is reduced, and the laser beam is blocked by the gap formed by the chamfer removal acceleration process, allowing the chamfer to be removed without damaging the second wafer. In addition, since it is not necessary to remove the chamfer with a cutting blade, the problem of damaging the second wafer is also eliminated. [Brief explanation of the drawing]

[0013] [Figure 1] This is a perspective view of the bonded wafer processed according to this embodiment. [Figure 2] This is an overall perspective view of the laser processing equipment. [Figure 3] Figure 2 is a perspective view showing how a bonded wafer is held on the chuck table of the laser processing apparatus. [Figure 4] This is a perspective view showing an embodiment of the chamfer removal acceleration process. [Figure 5] This is a perspective view showing an embodiment of the modified layer formation process. [Figure 6] (a) A partially enlarged cross-sectional view showing the first step of the modified layer formation process, and (b) A partially enlarged cross-sectional view showing the second step of the modified layer formation process. [Figure 7]This is a plan view showing the radially modified layers formed on the first wafer. [Figure 8] This is a perspective view showing an embodiment of the grinding process. [Modes for carrying out the invention]

[0014] Hereinafter, embodiments relating to a wafer processing method constructed according to the present invention will be described in detail with reference to the attached drawings.

[0015] Figure 1 shows a bonded wafer W, which is an example of a workpiece processed in this embodiment. The bonded wafer W is a wafer formed by bonding a first wafer 10A and a second wafer 10B together. The first wafer 10A is, for example, a silicon (Si) wafer with a diameter of 300 mm and a thickness of 300 μm, and a plurality of devices 12A are formed on the surface 10Aa, demarcated by division lines 14A. The first wafer 10A has a surface 10Aa and a back surface 10Ab, and comprises an effective region 16A near the center on which the devices 12A used as a product are formed, and an outer peripheral excess region 18A surrounding the effective region 16A, on which a chamfered portion 17A is formed. The second wafer 10B has the same configuration as the first wafer 10A, with a chamfered portion 17B formed on its outer circumference. Although not shown in the figure, it is a silicon (Si) wafer having an effective region on the surface 10Ba facing downwards in the figure, where multiple devices are partitioned by planned division lines. In this embodiment, the bonded wafer W is formed by bonding, for example, the surface 10Aa of the first wafer 10A and the surface 10Ba of the second wafer 10B, and forming an interface 20 by siloxane bonding. Siloxane bonding is a Si-O-Si bond in which silicon (Si) and oxygen (O) are alternately bonded. Since the first wafer 10A and the second wafer 10B are bonded by heat treatment, a strong bond state is maintained even at high temperatures.

[0016] When implementing the wafer processing method of the present embodiment with respect to the first wafer 10A of the bonded wafer W described above, a modified layer forming step is performed in which the condensing point of the laser beam is positioned and irradiated inside adjacent to the chamfered portion 17A formed on the outer periphery of the first wafer 10A to form a ring-shaped modified layer, and a fluid for weakening the bonding force is supplied to the interface 20 near the chamfered portion 17A and the chamfered portion 17B where the first wafer 10A and the second wafer 10B are bonded, and a chamfered portion removal promoting step is performed in which the fluid is immersed to a region where the chamfered portion 17A of the first wafer 10A can be removed.

[0017] FIG. 2 shows a laser processing apparatus 1 configured to be able to perform the modified layer forming step and the chamfered portion removal promoting step of the present embodiment.

[0018] The laser processing apparatus 1 is disposed on a base 2 and includes a holding means 3 for holding the bonded wafer W described above, a moving means 4 for moving the holding means 3, an alignment means 6 for imaging the bonded wafer W held by the holding means 3 and performing an alignment process, a laser beam irradiation means 7 for irradiating a laser beam toward the bonded wafer W held by the holding means 3, a frame body 5 composed of a vertical wall portion 5a erected on the side of the moving means 4 and a horizontal wall portion 5b extending in the horizontal direction from the upper end portion of the vertical wall portion 5a, and a fluid supply means 8.

[0019] As shown in FIG. 2, the holding means 3 includes a rectangular X-axis direction movable plate 31 mounted on the base 2 so as to be movable in the X-axis direction, a rectangular Y-axis direction movable plate 32 disposed on the X-axis direction movable plate 31 so as to be movable in the Y-axis direction, a cylindrical support column 33 fixed to the upper surface of the Y-axis direction movable plate 32, and a chuck table 34 disposed at the upper end of the support column 33. The chuck table 34 is configured to be rotatable by a rotation driving means (not shown) housed in the support column 33, and the upper surface of the chuck table 34 is constituted by an adsorption chuck 35 formed of a porous material having air permeability. The adsorption chuck 35 is connected to a suction means (not shown) by a flow path passing through the support column 33, and by operating the suction means, a negative pressure can be generated on the upper surface of the adsorption chuck 35 to suck and hold the bonded wafer W.

[0020] The moving means 4 includes an X-axis moving means 43 that moves the holding means 3 in the X-axis direction, and a Y-axis moving means 46 that moves the holding means 3 in the Y-axis direction which is perpendicular to the X-axis direction. The X-axis moving means 43 converts the rotational motion of the motor 41 into linear motion via a ball screw 42 and transmits it to the X-axis movable plate 31, moving the X-axis movable plate 31 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 moving means 46 converts the rotational motion of the motor 44 into linear motion via a ball screw 45 and transmits it to the Y-axis movable plate 32, moving the Y-axis movable plate 32 along a pair of guide rails 31a, 31a arranged on the X-axis movable plate 31 along the Y-axis direction.

[0021] The optical system constituting the laser beam irradiation means 7 is housed inside the horizontal wall portion 5b of the frame 5. A light concentrator 71, which constitutes part of the laser beam irradiation means 7, is disposed on the lower surface of the tip of the horizontal wall portion 5b, and focuses a laser beam of a wavelength that is transparent to at least the first wafer 10A described above and irradiates the bonded wafer W with it. An alignment means 6 is disposed adjacent to the light concentrator 71 in the X-axis direction. The alignment means 6 is an imaging means that images the bonded wafer W held by the holding means 3 and detects the position and orientation of the bonded wafer W, the processing position to which the laser beam should be irradiated, etc.

[0022] The fluid supply means 8 in this embodiment is disposed on the Y-axis movable plate 32 and is positioned adjacent to the chuck table 34. The fluid supply means 8 has a nozzle 8a at its upper end and is connected to a fluid supply source (not shown) that supplies fluid L to the nozzle 8a. The fluid supply means 8 is configured to be movable by a drive means (not shown) in the vertical direction indicated by arrow R1 and in the direction toward the center of the chuck table 34 indicated by arrow R2, so that the nozzle 8a can be positioned at a desired location and fluid L can be ejected from the tip of the nozzle 8a.

[0023] In addition to the above-described configuration, the laser processing apparatus 1 is equipped with control means for controlling each operating part, display means, etc. (not shown in the illustration). The control means is composed of a computer and includes a central processing unit (CPU) that performs calculations according to a control program, a read-only memory (ROM) for storing the control program, etc., a read-write random access memory (RAM) for temporarily storing detected values, calculation results, etc., an input interface, and an output interface (details are not shown in the illustration). The control means is connected to the above-described moving means 4, alignment means 6, laser beam irradiation means 7, display means (not shown), etc.

[0024] The laser processing apparatus 1 of this embodiment has a configuration that is generally as described above, and the modified layer formation process and the chamfer removal acceleration process, which are performed before the grinding process (described later) in the wafer processing method of the present invention, will be described.

[0025] The modified layer formation process can be carried out using the laser processing apparatus 1 described above, and the chamfer removal acceleration process can be carried out before the modified layer formation process, after the modified layer formation process, or simultaneously with the modified layer formation process. The following description will explain an example in which the chamfer removal acceleration process is carried out before the modified layer formation process.

[0026] (Process to accelerate removal of chamfered areas) Once the bonded wafer W described in Figure 1 is prepared, the bonded wafer W is transported to the laser processing apparatus 1 described in Figure 2, and as shown in Figure 3, it is placed on the suction chuck 35 that constitutes the holding surface of the chuck table 34 with the first wafer 10A facing upwards and the second wafer 10B facing downwards. Although not shown, if it is necessary to prevent the fluid L supplied in this chamfer removal acceleration process from being sucked in by the negative pressure generated on the suction chuck 35 of the chuck table 34, a protective tape may be attached to the back surface 10Ba of the second wafer 10B. Preferably, the protective tape is formed to be slightly larger than the suction chuck 35 so as to be able to cover at least the entire suction chuck 35 as shown.

[0027] Once the bonded wafer W is placed on the chuck table 34, a suction means (not shown) is activated to generate negative pressure on the suction chuck 35 and hold it in place by suction. Next, the fluid supply means 8 is moved in the vertical direction indicated by arrow R1 in Figure 1 and in the direction toward the center of the chuck table 34 indicated by arrow R2, so that, as shown in Figure 4, the tip of the nozzle 8a of the fluid supply means 8 is positioned at the height of the interface 20 where the first wafer 10A and the second wafer 10B are bonded, and also in a position close to the side of the interface 20.

[0028] Next, a fluid L that weakens the bonding force of the interface 20 is supplied from the tip of the nozzle 8a to the interface 20 where the chamfered portion 17A of the first wafer 10A and the chamfered portion 17B of the second wafer 10B are joined, and the chuck table 34 is rotated. As described above, the interface 20 in this embodiment is joined by siloxane bonds (Si-O-Si bonds), and when the above-mentioned fluid L (for example, pure water) is supplied to the interface 20 from the side, water molecules gradually penetrate the region where the interface 20 is formed from the outer circumference, and the penetrated region changes to Si-OH-OH-Si bonds. As a result, the bonding force of the interface 20 is weakened, and as shown in Figure 4, a bonding force reduction region 21 is formed in the ring shape at the interface 20 of the region where the chamfered portion 17A and the chamfered portion 17B are joined. Note that the fluid L supplied from the nozzle 8a is not limited to pure water (liquid), but may also be vapor or mist.

[0029] In this embodiment, by injecting fluid L at high pressure from the nozzle 8a of the fluid supply means 8, the water pressure of the fluid L also acts as an external force that bends the chamfered portion 17A of the first wafer 10A away from the chamfered portion 17B of the second wafer 10B. In other words, the fluid supply means 8 also functions as an external force applying means that applies an external force that weakens the bonding force of the interface 20, and by injecting the liquid L at high pressure, the process of applying an external force that weakens the bonding force of the interface 20 is carried out simultaneously with the process of promoting the removal of the chamfered portion. In this way, the change in the bonding form at the interface 20 described above and the external force applied by the injection of fluid L at high pressure combine to reduce adhesion in the bonded force reduction region 21 shown in the figure, and the bonded force reduction region 21 can be formed more reliably. Furthermore, the bonding force reduction region 21 is formed so as not to extend to the effective region 16A where the device 12A is formed. By appropriately adjusting the amount of fluid L supplied, the injection pressure of fluid L, the rotation speed of the chuck table 34, the supply time of fluid L, etc., the width of the bonding force reduction region 21 formed on the outer circumference of the interface 20 is adjusted to a desired width.

[0030] (Modified layer formation process) As described above, once the chamfer removal acceleration process has been carried out, the modified layer formation process described below is performed. In this modified layer formation process, alignment is performed on the bonded wafer W, which is held by suction on the chuck table 34, using the alignment means 6 provided in the laser processing apparatus 1. This alignment detects the position of the outer edge where the chamfer 17A of the first wafer 10A is formed, the center position of the first wafer 10A, and the height of the upper surface of the back surface 10Ab of the first wafer 10A. The processing position (for example, a position with a radius of 147 mm from the center point of the first wafer 10A) where the focal point of the laser beam LB should be positioned and irradiated is detected on the inside adjacent to the chamfer 17A formed on the outer circumference of the first wafer 10A.

[0031] The modified layer formation process carried out according to the present invention can be carried out, for example, by including the first step and the second step described below.

[0032] (First step) Based on the positional information of the processing position detected by the alignment means 6 described above, the chuck table 34 is moved to position the processing position set on the first wafer 10A of the bonded wafer W directly below the concentrator 71 of the laser beam irradiation means 7, as shown in Figure 5. Next, as can be understood from Figure 6(a) in addition to Figure 5, the focal point of the laser beam LB is positioned inside the processing position on the first wafer 10A from the back surface 10Ab side of the first wafer 10A and irradiated, and the chuck table 34 is rotated in the direction indicated by arrow R3 in Figure 5 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.

[0033] 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 Figure 6(a). For example, the first modified layer 100 shown in Figure 6(a) is composed of four modified layers in the vertical direction. In forming the first modified layer 100, which includes multiple layers, first, the focal point of the laser beam LB is positioned at the deepest point near the interface 20 (for example, 180 μm from the back surface 10Ab) in the inner interior adjacent to the chamfered portion 17A of the first wafer 10A, and the chuck table 34 is rotated in the direction indicated by R3 to form the first ring-shaped modified layer along the chamfered portion 17A. Then, while rotating the chuck table 34, the focal point is moved three times toward the back surface 10Ab side (upwards), for example, increasing the depth from the back surface 10Ab to a depth of 170 μm → 160 μm → 150 μm, thereby forming a total of four ring-shaped modified layers along the chamfered portion 17A. By positioning the focal point of the laser beam LB closer to the interface 20 and irradiating it in this manner, the first modified layer 100 is formed at a relatively deep position on the first wafer 10A. As a result, cracks are formed along the first modified layer 100 on the surface 10Aa side of the first wafer 10A, i.e., at a position leading to the interface 20. Note that the first modified layer 100 shown in Figure 6 is a conceptual representation for illustrative purposes, and the depth positions of each layer do not correspond to the actual dimensions. With this, the first step is completed. Note that the first modified layer 100 formed in the first step is not limited to being formed of four layers, and the appropriate number of layers is determined by the wavelength and output of the laser beam LB irradiated by the laser beam irradiation means 7, the thickness of the first wafer 10A, the material constituting the first wafer 10A, etc.

[0034] (Second step) If the first modified layer 100 is formed by the first step described above, a second step is performed to form a second modified layer on the outside or inside of the first modified layer 100 at a relatively shallow position that does not reach the interface 20 of the bonded wafer W. In the second step of this embodiment, as shown in Figure 6(b), the focal point of the laser beam LB is positioned adjacent to the outside of the uppermost modified layer of the first modified layer 100 (a modified layer formed to a depth of 150 μm from the back surface 10Ab) and the modified layer formed below it (a depth of 160 μm from the back surface 10Ab), and the chuck table 34 is rotated to form ring-shaped second modified layers 102 and 104. Preferably, the second modified layers 102 and 104 are formed by a plurality of modified layers (three in the illustrated embodiment) formed adjacent to each other in the diametrical direction at the same depth.

[0035] In the modified layer formation process described above, in addition to forming the first modified layer 100 in the first step, the second step forms second modified layers 102 and 104 adjacent to the first modified layer 100 at a relatively shallow depth that does not reach the interface 20. This makes it possible to perform an external force application process that applies an external force to bend the chamfered portion 17A from the interface 20 in the direction indicated by arrow R4, as shown in Figure 6(b), starting from the first modified layer 100. As a result, the bonding force in the bonding force reduction region 21 formed at the interface 20 can be reduced more reliably, and cracks originating from the first modified layer 100 can be further extended when the first modified layer 100 is formed.

[0036] The modified layer formation process is thus completed. In the above embodiment, the second modified layers 102 and 104 were formed on the outside adjacent to the first modified layer 100, but the present invention is not limited thereto, and they may also be formed on the inside adjacent to the first modified layer 100. In the same way as when they are formed on the outside as described above, an external force can be applied in the direction indicated by arrow R4, which bends the chamfered portion 17A away from the interface 20, starting from the first modified layer 100.

[0037] Furthermore, when forming the second modified layer in the second step described above, it is not limited to forming three ring-shaped modified layers as described above, but may be two or fewer, or four or more.

[0038] The laser processing conditions used when carrying out the above-mentioned modified layer formation process are set to, for example, laser processing condition 1 or laser processing condition 2 as follows. (Laser processing conditions 1) Wavelength: 1099nm Repetition frequency: 80kHz Average output: 2.0W Machining feed rate: 450 mm / s or (Laser processing conditions 2) Wavelength: 1342nm Repetition frequency: 90kHz Average output: 1.9W Machining feed rate: 400 mm / s

[0039] When the first and second steps described above are performed using the laser processing conditions 2 described above, it is preferable to set the depth position for forming the modified layer to be slightly deeper than the depth positions of the modified layers 100 and 102, 104 described above. More specifically, when performing the first step, the focal point of the laser beam LB is positioned at a depth of 183 μm from the back surface 10Ab, which is close to the interface 20, in the inner interior adjacent to the chamfered portion 17A of the first wafer 10A, and the chuck table 34 is rotated to form the 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 side (upwards), for example, so that the depth from the back surface 10Ab becomes 173 μm → 163 μm → 153 μm, thereby forming a total of four ring-shaped modified layers along the chamfered portion 17A. Furthermore, when performing the second step to form the modified layers 102 and 104, the depth can be determined based on the depths of the third and fourth layers described above, i.e., 163 μm and 153 μm from the back surface 10Ab.

[0040] In the modified layer formation process described above, for example, as shown in Figure 7, a radial modified layer 110 may be formed extending outwards from the region where the first modified layer 100 is formed, toward the area where the chamfered portion 17A is formed. The modified layer 110 shown in the figure is a modified layer that serves to further divide the chamfered portion 17A into smaller pieces when removing the ring-shaped chamfered portion 17A. For example, it is formed by irradiating a laser beam LB under the same laser processing conditions as when forming 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 circumference of the first wafer 10A. By forming this modified layer 110, when removing the chamfered portion 17A from the first wafer 10A in the grinding process described later, the chamfered portion 17A is divided into multiple fragments 17A', and the removal of the chamfered portion 17A is successfully achieved.

[0041] In the above embodiment, a chamfer removal acceleration step was performed before the modified layer formation step. As a result, a bonding force reduction region 21 is formed on the outer periphery of the area where the interface 20 on the outer periphery side of the bonded wafer W is formed, reducing adhesion and forming a minute gap. As a result, even when the focusing point is positioned inside the first wafer 10A and the laser beam LB is irradiated at a relatively deep position during the modified layer formation step, the laser beam is blocked by the gap, preventing the second wafer 10B from being affected by the laser beam LB and thus preventing damage to the second wafer 10B. Furthermore, the chamfered portion 17A can be reliably removed without cutting using a cutting blade, and the problem of damaging the second wafer 10B, which occurs when a cutting blade is used, does not occur.

[0042] Furthermore, in the embodiments described above, a chamfer removal acceleration step is performed, followed by a modified layer formation step. However, when the modified layer formation step is performed in a form that includes the first and second steps described based on Figures 6(a) and (b), it is also effective to perform a chamfer removal acceleration step after the modified layer formation step, which involves supplying a fluid L that weakens the bonding force toward the interface 20. That is, before performing the chamfer removal acceleration step, the modified layer formation step including the first and second steps described above is performed, and the action of the second modified layers 102 and 104 formed in the second step generates an external force that bends the chamfer 17A away from the interface 20, starting from the first modified layer 100. Subsequently, by performing the chamfer removal acceleration step described above, a fluid L that weakens the bonding force is supplied from the outer periphery toward the interface 20 where the first wafer 10A and the second wafer 10B are joined. This, combined with the external force generated in a direction that bends the chamfered portion 17A created by the modified layer formation process away from the interface 20, makes it possible to efficiently weaken the bonding force on the outer circumference of the interface 20.

[0043] Furthermore, the present invention may also be used to perform the chamfer removal acceleration step simultaneously with the modified layer formation step. In particular, in the laser processing apparatus 1 described above, since the fluid supply means 8 is arranged adjacent to the chuck table 34 of the holding means 3, it is possible to perform the chamfer removal acceleration step simultaneously with the modified layer formation step, and it is also possible to perform an external force application step in which an external force is applied to the interface 20 by the fluid L supplied from the fluid supply means 8.

[0044] (Grinding process) In the present invention, after performing the modified layer formation step and the chamfer removal acceleration step described above, a grinding step is performed in which the back surface 10Ab of the first wafer 10A of the bonded wafer W is ground to thin it, and the chamfer portion 17A of the first wafer 10A is removed.

[0045] The bonded wafer W, which has undergone the above-described modified layer formation process and chamfer removal acceleration process, is transported to the grinding apparatus 50 (partially shown) shown in Figure 8. As shown in the figure, the grinding apparatus 50 is equipped with a grinding means 52 for grinding and thinning the bonded wafer W, which is held by suction on a chuck table 51. The grinding means 52 includes a rotating spindle 52a that is rotated by a rotational drive mechanism (not shown), a wheel mount 52b attached to the lower end of the rotating spindle 52a, and a grinding wheel 52c attached to the lower surface of the wheel mount 52b, with a plurality of grinding wheels 52d arranged in an annular pattern on the lower surface of the grinding wheel 52c.

[0046] Once the bonded wafer W is transported to the grinding apparatus 50, it is placed on the chuck table 51 with the second wafer 10B side facing downwards, and a suction means (not shown) is activated to hold it in place. Next, the rotating spindle 52a of the grinding means 52 is rotated at, for example, 6000 rpm in the direction indicated by arrow R5 in Figure 8, while the chuck table 51 is rotated at, for example, 300 rpm in the direction indicated by arrow R6. Then, grinding water is supplied onto the back surface 10Ab of the first wafer 10A by a grinding water supply means (not shown), and a grinding feed means (not shown) is activated to bring the grinding wheel 52d into contact with the back surface 10Ab of the first wafer 10A, and the grinding wheel 52c is fed downwards at, for example, a grinding feed speed of 0.1 μm / second, in the direction indicated by arrow R7. In this process, the thickness of the bonded wafer W can be measured using a contact-type or non-contact-type measuring gauge (not shown) while grinding is performed, allowing the wafer to be thinned until the desired thickness is reached.

[0047] Although not shown in the diagram, the grinding process described above can be carried out in two steps. For example, the grinding apparatus 50 may be equipped with a grinding means including a rough grinding wheel fitted with a coarse grinding wheel for rough grinding, and a grinding means including a finishing grinding wheel fitted with a fine grinding wheel for finishing grinding, and the rough grinding step of roughly grinding the back surface 10Ab of the first wafer 10A with the rough grinding wheel and the finishing grinding step of finishing grinding the back surface 10Ab with the finishing grinding wheel may be carried out in succession.

[0048] Then, by performing the grinding process described above, as shown in Figure 8, the first wafer 10A of the bonded wafer W is thinned, and an external force is applied to the first wafer 10A to remove the chamfered portion 17A, so that the chamfered portion 17A is removed as fragments 17A' starting from the modified layer 100. In this embodiment, since a radial modified layer 110 is also formed in the modified layer formation process described above, when the chamfered portion 17A is removed from the first wafer 10A in the grinding process described above, the chamfered portion 17A is divided into multiple fragments 17A' starting from the radial modified layer 110, so that the removal of the chamfered portion 17A is successfully achieved.

[0049] After grinding the back surface 10Ab of the first wafer 10A by a predetermined amount to remove the chamfered portion 17A and to achieve the desired thickness of the bonded wafer W, the grinding means 52 is stopped and retracted upward, completing the grinding process. Once the grinding process is complete, the bonded wafer W from which the chamfered portion 17A has been removed is subjected to appropriate cleaning, drying, and other processes, the details of which are omitted.

[0050] The bonded wafer W described above is an example in which a first wafer 10A and a second wafer 10B are bonded by siloxane bonding. However, the bonded wafer W processed by the present invention is not limited to being bonded by siloxane bonding. For example, the bonded wafer W may be formed by bonding the first wafer 10A and the second wafer 10B by SiCN bonding through nitride bonding, TEOS bonding which changes tetraethyl orthosilicate molecules into a solid with Si-O-Si bonding, or ThOx bonding which forms a thermal oxide film by heating the silicon surface in an oxidizing atmosphere. In any case, the bonding force can be weakened by the fluid L supplied by the chamfer removal acceleration step described above, and the chamfered portion 17A can be removed by the wafer processing method described above. Furthermore, the present invention can also be applied to bonded wafer W which is bonded after applying O2 plasma treatment or N2 plasma treatment as a pretreatment to the bonding surface forming the interface 20. Furthermore, as mentioned above, the fluid L is not limited to pure water; the present invention can also be applied to a mixed fluid that is a mixture of water molecules and other fluids. [Explanation of Symbols]

[0051] 1: Laser processing equipment 2: Base 3: Holding means 31:X-axis movable plate 32: Y-axis movable plate 34: Chuck Table 35: Suction Chuck 4: Means of transportation 43:X-axis movement means 46: Y-axis movement means 5:Frame body 6: Alignment Methods 7: Laser beam irradiation means 71: Light concentrator 8: Fluid supply means 8a: Nozzle 10A: First wafer 10Aa: Surface 10Ab: Reverse side 12A: Device 14A: Planned division line 16A: Effective area 17A: Chamfered section 18A: Outer perimeter surplus area 10B: Second wafer 10Ba: Surface 10Bb: Back side 20: Interface 21: Bonding force decrease area 50: Grinding equipment 51: Chuck Table 52: Grinding methods 52a: Rotating spindle 52b: Wheel mount 52c: Grinding Wheel 52d: Grinding wheel 100: First Modified Layer 102, 104: Second modified layer 110: Radial modified layer L: Fluid (pure water) W: Bonded wafer

Claims

1. A wafer processing method for a bonded wafer obtained by joining a first wafer and a second wafer, wherein the first wafer is processed. A modification layer formation step involves positioning the focal point of a laser beam on the inner side adjacent to the chamfered portion formed on the outer circumference of the first wafer and irradiating it to form a ring-shaped modification layer, A chamfer removal accelerating step involves supplying a fluid that weakens the bonding force to the interface of the chamfered portion where the first wafer and the second wafer are joined, and allowing the fluid to penetrate to an area where the chamfered portion can be removed. A wafer processing method comprising: a grinding step of holding the second wafer in a chuck table constituting a grinding apparatus, grinding the first wafer to thin it, and removing the chamfered portion.

2. A wafer processing method according to claim 1, comprising an external force application step of applying an external force to the interface, wherein in the chamfer removal promotion step, the bonding force of the interface is weakened in combination with the external force.

3. In the modified layer formation process, The first step involves positioning the focal point of the laser beam near the interface and irradiating it, thereby forming a relatively deep first modified layer where the crack reaches the interface, The process includes a second step of forming a relatively shallow second modified layer adjacent to the first modified layer, either on the outside or inside, that does not reach the interface, The wafer processing method according to claim 2, wherein the external force application step is performed to apply an external force that causes the chamfered portion to bend away from the interface, starting from the first modified layer.

4. The wafer processing method according to claim 1, wherein in the modified layer formation step, a radial modified layer is formed from the ring-shaped modified layer toward the outside.

5. The wafer processing method according to claim 1, wherein the chamfer removal acceleration step is performed before the modified layer formation step, after the modified layer formation step, or simultaneously with the modified layer formation step.

6. The first wafer and the second wafer are joined by a Si-O-Si siloxane bond, and the fluid that weakens the bonding force includes water, water vapor, or mist. The wafer processing method according to claim 1, wherein in the chamfer removal acceleration step, the Si-O-Si bond is changed to a Si-OH-OH-Si bond, thereby weakening the bonding force at the interface.

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