Wafer processing method

Abstract

To provide a wafer processing method for completely removing a chamfered portion from the outer periphery of a wafer without deteriorating the quality of a chip.SOLUTION: A method performs irradiation with a laser beam having a wavelength transparent to a wafer from the back surface 10Ab of a wafer 10A while positioning the focal point of the laser beam LB at the inside of a boundary 18A between an effective area and a chamfered portion 17A to form a modified layer along the chamfered portion, applies an external force to the outer periphery of the wafer to remove the chamfered portion, and grinds the back surface of the wafer to a desired thickness. In forming the modified layer, irradiation with the laser beam is performed while positioning the focal point of the laser beam at the inside of the boundary between the effective area and the chamfered portion to form a relatively deep first modified layer 100 with a crack 101 reaching the front surface 10Aa of the wafer, and form relatively shallow second modified layers 102 to 106 adjacent to the first modified layer with no crack reaching the front surface of the wafer on the outside or inside, so that the chamfered portion is warped from the front surface to the back surface with the warp starting from the first modified layer.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a method for processing a wafer having an effective area and a chamfered portion on the outer periphery surrounding the effective area. [Background technology]

[0002] A wafer has a device area on its front surface, with multiple devices such as ICs and LSIs separated by planned division lines.The back surface is ground to the desired thickness, and then the wafer is divided into individual device chips using a cutting device and laser processing device.These chips are then used in electrical equipment such as mobile phones and personal computers.

[0003] In addition, a chamfer is formed on the outer periphery of the wafer, and when the back surface of the wafer is ground to thin it, the chamfer becomes as sharp as a knife edge, which can injure an operator or cause cracks to form from the outer periphery of the wafer, damaging the device.

[0004] Therefore, the present applicant has proposed a technology in which, before grinding the back surface of the wafer, a focal point of a laser beam having a wavelength that is transparent to the wafer is positioned inside the chamfer and the beam is irradiated to form a ring-shaped modified layer inside the wafer, thereby removing the chamfer when performing the grinding process (see Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2020-088187 A Summary of the Invention [Problem to be solved by the invention]

[0006] According to the technology described in Patent Document 1, the chamfered portion is removed by the external force applied during grinding, but there are cases where the chamfered portion is not completely removed from the outer periphery of the wafer and a small portion remains. This causes problems such as the remaining portion falling off in a later process and becoming a source of contamination, or causing chipping of the device chips when the wafer is divided into individual device chips.

[0007] The present invention has been made in view of the above-mentioned circumstances, and its main technical object is to provide a wafer processing method capable of completely removing a chamfered portion from the outer periphery of a wafer, which can solve the problems that the remaining portion falls off in a subsequent process and becomes a source of contamination, or that the remaining portion causes chipping of device chips when the wafer is divided into individual device chips, thereby reducing quality. [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 method for processing a wafer having an effective area formed on its front surface and a chamfered portion on its outer periphery surrounding the effective area, the method comprising the steps of: forming a modified layer along the chamfered portion by irradiating the back surface of the wafer with a laser beam having a wavelength that is transparent to the wafer, the focused point of the beam being positioned inside the boundary between the effective area and the chamfered portion; applying an external force to the outer periphery of the wafer to remove the chamfered portion; and grinding the back surface of the wafer to a desired thickness. a processing step of processing a wafer, the processing step including a first step of irradiating the wafer with a focused point of the laser beam within the boundary between the effective area and the chamfered portion to form a relatively deep first modified layer with cracks reaching the surface of the wafer, and a second step of forming a relatively shallow second modified layer adjacent to the first modified layer on the outside or inside and with cracks not reaching the surface of the wafer, and the chamfered portion is warped from the front surface to the back surface starting from the first modified layer.

[0009] In the chamfer removing step, the external force applied to the outer periphery of the wafer is preferably any one of high pressure air, high pressure water, a mixed fluid of high pressure air and high pressure water, and a picker. The chamfer removing step may be performed by applying an external force by a grinding action when grinding the back surface of the wafer in the processing step. Furthermore, the wafer may be a stacked wafer in which a first wafer and a second wafer are stacked, and the modified layer forming step, the chamfer removing step, and the processing step may be performed on the first wafer. In the second step, the second modified layer is preferably formed at a position where it is ground and removed in the processing step. Effect of the Invention

[0010] The wafer processing method of the present invention is a method for processing a wafer having an effective area formed on its front surface and a chamfered portion on its outer periphery surrounding the effective area, and includes a modified layer forming step of irradiating a laser beam having a wavelength that is transparent to the wafer from the back surface of the wafer with a focal point positioned inside the boundary between the effective area and the chamfered portion to form a modified layer along the chamfered portion, a chamfer removing step of applying an external force to the outer periphery of the wafer to remove the chamfered portion, and a processing step of grinding the back surface of the wafer to a desired thickness, wherein in the modified layer forming step, the focal point of the laser beam is positioned inside the boundary between the effective area and the chamfered portion to irradiate the laser beam, The method includes a first step of forming a relatively deep first modified layer, with cracks reaching the surface of the wafer, and a second step of forming a relatively shallow second modified layer adjacent to the first modified layer on the outside or inside, with cracks not reaching the surface of the wafer, and is configured to warp the chamfered portion from the front surface to the back surface starting from the first modified layer. This makes it possible to effectively remove the chamfered portion from the outer periphery of the wafer, eliminating problems such as the chamfered portion remaining on the outer periphery edge of the wafer falling off in subsequent processes and becoming a source of contamination or causing chipping of devices when the wafer is divided into individual device chips. [Brief description of the drawings]

[0011] [Figure 1] FIG. 2A is a perspective view of a single wafer which is a workpiece in this embodiment, and FIG. 2B is a perspective view of a stacked wafer which is a workpiece in this embodiment. [Diagram 2] FIG. 2A is a perspective view showing a manner in which a wafer is placed on a chuck table in a modified layer forming step, and FIG. 2B is a perspective view showing a manner in which a modified layer is formed in the modified layer forming step. [Diagram 3] FIG. 1A is a schematic cross-sectional view showing the configuration of a first modified layer; FIG. 1B is a schematic cross-sectional view showing the configuration of a second modified layer; and FIG. 1C is a schematic cross-sectional view showing another configuration of the second modified layer. [Figure 4] FIG. 2A is a perspective view showing a manner in which a wafer is held by a holding means in a chamfered portion removing step, and FIG. 2B is a perspective view showing a configuration of a fluid ejecting means. [Diagram 5] FIG. 1A is a side view showing how a fluid is sprayed onto the outer periphery of a wafer by a fluid spraying means; FIG. 1B is an enlarged side view of a portion of a wafer from which a chamfer has been removed from its outer periphery; and FIG. 1C is an overall oblique view of a wafer from which a chamfer has been removed from its outer periphery. [Figure 6] FIG. 2 is a perspective view showing the overall configuration of a picker. [Figure 7] 7A is a side view showing how the movable plate of the picker shown in FIG. 6 is operated; (b) is a side view showing how the movable plate of the picker shown in (a) is inserted into the mating surfaces of stacked wafers; and (c) is a side view showing how the picker shown in (b) is tilted to remove the chamfered portion from the wafer. [Figure 8] FIG. 13 is a perspective view showing an embodiment in which a processing step that also serves as a chamfered portion removing step is performed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a wafer processing method according to the present invention will be described in detail with reference to the accompanying drawings.

[0013] FIG. 1(a) shows a single wafer 10A to be processed by the wafer processing method of this embodiment, and a protective tape T to be attached to the wafer 10A. The illustrated wafer 10A is, for example, a silicon wafer having a diameter of 300 mm and a thickness of 300 μm, and a plurality of devices 12A are formed on the front surface 10Aa, partitioned by a division line 14A. The wafer 10A has a front surface 10Aa and a back surface 10Ab, and includes an effective area 16A near the center where the devices 12A to be used as products are formed, a chamfered portion 17A formed at the edge of the periphery surrounding the effective area 16A, and a boundary portion 18A between the effective area 16A and the chamfered portion 17A where the devices 12A to be products are not formed. When processed by the wafer processing method of this embodiment, as shown in the figure, a protective tape T is attached to the front surface 10Aa side to be integrated.

[0014] FIG. 1(b) shows another wafer W to be processed by the wafer processing method according to the present invention. The wafer W is a laminated wafer in which a first wafer 10B and a second wafer 10C are laminated and integrated. The first wafer 10B has the same configuration as the above-mentioned wafer 10A, and is a silicon wafer having a front surface 10Ba and a back surface 10Bb, a diameter of 300 mm, and a thickness of 300 μm. A plurality of devices 12B are formed on the front surface 10Ba, partitioned by a division line 14B. The first wafer 10B has an effective area 16B near the center where the devices 12B to be used as products are formed, a chamfered portion 17B formed at the edge of the outer periphery surrounding the effective area 16B, and a boundary portion 18B between the effective area 16B and the chamfered portion 17B where the devices 12B to be products are not formed. The second wafer 10C has a similar structure to the first wafer 10B, and although not shown in the figure, is a silicon wafer having a surface 10Ca facing the lower side in the figure, on which a plurality of devices are formed by dividing the surface 10Ca along predetermined dividing lines. The first wafer 10B and the second wafer 10C are integrated together by, for example, siloxane bonding, which is achieved by bonding the surface 10Ba of the first wafer 10B and the surface 10Ca of the second wafer 10C together and subjecting them to a heat treatment.

[0015] The wafer processed by the wafer processing method of the present embodiment described below is not limited to the single silicon wafer 10A and the wafer W in which two silicon wafers are stacked, but includes various wafers having an effective area and a chamfered portion at the edge of the outer periphery surrounding the effective area. For example, a wafer of gallium nitride (GaN), a wafer of gallium arsenide (GaAs), a wafer of lithium tantalate (LiTaO 3 ) wafers, lithium niobate (LiNbO 3 ), or it may be a wafer (e.g., a glass wafer) in which no device is formed in the central region but the central region is processed later and used as a product. In the embodiment described below, the wafer processing method of this embodiment will be described using the above-mentioned wafer 10A or the wafer W which is a laminated wafer as an example.

[0016] (Modified layer forming process) When the wafer processing method of this embodiment is performed on wafer 10A, a modified layer formation process is performed in which a laser beam having a wavelength that is transparent to wafer 10A is irradiated from back surface 10Ab of wafer 10A to a focal point positioned within boundary 18A between effective area 16A and chamfered portion 17A, thereby forming a modified layer along chamfered portion 17A.

[0017] In the substance layer forming step, first, the wafer 10A is transferred to a laser processing device 20 (only a part of which is shown) shown in Figures 2(a) and (b). The laser processing device 20 includes at least a chuck table 21 shown in Figure 2(a) and a laser beam application means 22 shown in Figure 2(b). The chuck table 21 includes an adsorption chuck 21a formed of a breathable material constituting a holding surface on the upper side, and a frame body 21b surrounding the adsorption chuck 21a. The laser beam application means 22 includes a laser oscillator (not shown) that oscillates a laser beam having a wavelength that is transparent to the silicon that constitutes the wafer 10A, and a condenser 23 that condenses and irradiates the laser beam LB oscillated by the laser oscillator. The laser processing apparatus 20 further includes a moving means for moving the chuck table 21, a rotary drive means for rotating the chuck table 21, a suction means for generating negative pressure on the upper surface of the suction chuck 21a, and the like (all of which are omitted from the illustration).

[0018] 2(a), the wafer 10A is placed on the chuck table 21 with the protective tape T facing downward and the back surface 10Ab of the wafer 10A facing upward, and the wafer 10A is held by suction using an suction means (not shown). The wafer 10A held by suction on the chuck table 21 is aligned using an alignment means and a height detection means (not shown) provided in the laser processing device 20 to detect the position of the outer circumferential edge where the chamfered portion 17A of the wafer 10A is formed and the center position of the wafer 10A, as well as the height of the upper surface of the back surface 10Ab of the wafer 10A, and to detect the processing position at the boundary portion 18A where the laser beam LB should be irradiated.

[0019] The modified layer forming process carried out in the present invention includes at least a first step and a second step which will be described below.

[0020] (First step) By detecting the position of the edge of the outer periphery where the chamfered portion 17A of the wafer 10A is formed and the center position of the wafer 10A, for example, a position that is inside the region where the chamfered portion 17A is formed from the edge of the outer periphery of the wafer 10A (for example, a region 0.5 mm from the edge of the outer periphery) and is set in a ring shape corresponding to the above-mentioned boundary portion 18A, for example, a position with a radius of 147 mm from the center point of the wafer 10A is detected as a predetermined processing position where the laser processing is performed in the first step to form a modified layer. The position information of the processing position detected in this way is stored in a control means (not shown).

[0021] Based on the information of the processing position related to the first step detected by the above-mentioned alignment, the chuck table 21 is moved to position the condenser 23 of the laser beam application means 22 on the above-mentioned predetermined processing position as shown in FIG. 2(b). Next, the laser beam LB is irradiated from the back surface 10Ab side of the wafer 10A by positioning the condensing point inside the boundary portion 18A, and the chuck table 21 is rotated in the direction indicated by the arrow R1 to form a first modified layer 100 over the entire circumference along the chamfered portion 17A of the wafer 10A. In the first modified layer 100 formed by this first step, as shown in FIG. 3(a), cracks 101 are generated by forming the first modified layer 100, and the cracks 101 are formed at a relatively deep position reaching the front surface 10Aa side of the wafer 10A. Furthermore, it is preferable that the first modified layer 100 is formed in a plurality of layers in the vertical direction. For example, the first modified layer 100 shown in Fig. 3(a) is composed of four modified layers in the vertical direction. When forming such a first modified layer 100, first, the focal point of the laser beam LB is positioned at a position set at the deepest part inside the boundary portion 18A of the wafer 10A (for example, at a depth of 180 μm from the back surface 10Ab) and the laser beam LB is irradiated while the chuck table 21 is rotated as described above to form a first annular modified layer along the chamfered portion 17A, and then, while rotating the chuck table 21, the focal point is raised toward the back surface 10Ab side (upward) three times, for example, from the back surface 10Ab to a depth of 170 μm → 160 μm → 150 μm, forming a total of four annular modified layers along the chamfered portion 17A and generating cracks 101 reaching the front surface 10Aa side of the wafer 10A. This completes the first step.

[0022] (Second step) As described above, after the first modified layer 100 is formed by the first step, a second step is performed to form a second modified layer at a relatively shallow position close to the back surface 10Ab of the wafer 10A, which does not reach the front surface 10Aa of the wafer 10A even if a crack is generated on the outside or inside of the first modified layer 100. More specifically, for example, as shown in Fig. 3(b), a focused point of a laser beam LB is positioned and irradiated at a position adjacent to the outside of the top modified layer (150 µm deep from the back surface 10Ab) of the first modified layer 100, and the chuck table 21 is rotated to form an annular modified layer 102. The second modified layer formed by the second step is preferably formed of a plurality of modified layers as shown in FIG. 3(b). In this embodiment, the focal point of the laser beam LB is positioned at a position adjacent to the outside of the annular modified layer 102 and irradiated to form annular modified layers 104 and 106 in addition to the above-mentioned annular modified layer 102. The depth at which the second modified layer consisting of the plurality of modified layers 102, 104, and 106 is formed is shallower than that of the first modified layer 100, and is set to a position that will be removed when the back surface 10Ab of the wafer 10A is ground to a desired thickness in a later processing step. This completes the second step and the process of forming the modified layer.

[0023] The first step described above is performed to form the first modified layer 100 and generate the crack 101 reaching the front surface 10Aa of the wafer 10A, and the second step is further performed to form the second modified layers 102, 104, and 106 as described above, thereby applying stress to the first modified layer 100. As a result, as shown in Fig. 3(b), the crack 101 further extends in the vertical direction along the first modified layer 100, and the chamfered portion 17A can be warped from the first modified layer 100 as a starting point in the direction indicated by the arrow R2 in the figure, i.e., toward the back surface 10Ab.

[0024] The laser processing conditions when carrying out the modified layer forming step are set, for example, as follows. Wavelength: 1099nm Repetition frequency: 80kHz Average power output: 2.0W Machining feed speed: 450mm / s or Wavelength: 1342nm Repetition frequency: 90kHz Average power output: 1.9W Machining feed speed: 400mm / s

[0025] The second modified layer formed by the second step performed in the modified layer forming process of the present invention is not limited to the form shown in Fig. 3(b). For example, as shown in Fig. 3(c), the focal point of the laser beam LB may be positioned at a relatively shallow position adjacent to the above-mentioned first modified layer 100 and not reaching the surface 10Aa of the wafer 10A even if a crack occurs inside (on the effective area side) of the boundary portion 18A, and a second modified layer (modified layers 107, 108, 109) may be formed by irradiating the laser beam LB. 3(b), the second modified layer (modified layers 107, 108, 109) shown in Fig. 3(c) can also apply stress to the first modified layer 100, so that the crack 101 can be extended in the vertical direction along the first modified layer 100, and the chamfered portion 17A can be warped in the direction indicated by the arrow R2 in the figure, i.e., toward the back surface 10Ab, starting from the first modified layer 100. The second modified layers (modified layers 107, 108, 109) in this form are also set to a depth position to be removed when the back surface 10Ab of the wafer 10A is ground to a desired thickness in a later processing step.

[0026] In addition, when the modified layer forming process according to the present invention is performed on the wafer W in which the first wafer 10B and the second wafer 10C are stacked, the above-mentioned first step and second step are performed to form the first modified layer and the second modified layer described based on Fig. 3(a)-(c). When the modified layer forming process is performed on the wafer W, the modified layer forming process is performed in the same procedure as the modified layer forming process on the wafer 10A described above, except that the back surface 10Bb of the first wafer 10B faces upward and is held by suction on the chuck table 21 of the laser processing device 20, so a detailed description will be omitted. In the following description, the description will be continued assuming that the first modified layer 100 and the second modified layer (modified layers 102, 104, 106) described based on Fig. 3(a) and (b) are formed on the wafer 10A and the first wafer 10B of the wafer W by the modified layer forming process described above.

[0027] A chamfer removing step is carried out on the outer periphery of the wafer on which the first modified layer and the second modified layer have been formed by the modified layer forming step described above, in which an external force is applied to remove the chamfer.

[0028] 4(a) and (b) show a chamfer removing device 30 suitable for performing the chamfer removing step on the wafer 10A that has been subjected to the modified layer forming step (only a part of the device is shown). The chamfer removing device 30 of this embodiment includes a holding means 32 for holding the effective area 16A of the wafer 10A, and a fluid injection means 34 arranged as a chamfer removing means for removing the chamfer 17A from the effective area 16A of the wafer 10A. The holding means 32 includes a disk-shaped suction section 32b having a holding surface 32a on the lower side, and a support shaft 32c connected to the center of the suction section 32b and having a rotation drive means (not shown). The holding surface 32a is made of a breathable material, and a communication passage 33 is formed in the support shaft 32c, which connects the suction means (not shown) to the holding surface 32a, and a negative pressure V is generated on the holding surface 32a through the communication passage 33. The suction portion 32b is formed to have a size smaller than the wafer 10A and corresponding to the effective area 16A of the wafer 10A.

[0029] 4(b) is a means for removing the chamfered portion 17A by applying an external force of a fluid to the outer periphery of the wafer 10A, the effective area 16A of which is held by the holding means 32 and which protrudes outward from the holding surface 32a. The fluid injection means 34 includes a fluid injection nozzle 36, a water source 37 for supplying high-pressure water L to the fluid injection nozzle 36, and an air supply source 38 for supplying high-pressure air P to the fluid injection nozzle 36. The fluid injection nozzle 36 is a two-fluid nozzle, and the water source 37 is connected to a high-pressure water inlet 36b formed in a nozzle body 36a of the fluid injection nozzle 36 by a communication passage 37a including a metering valve 37b, and the air supply source 38 is connected to a high-pressure air inlet 36c formed in the nozzle body 36a by a communication passage 38a including a metering valve 38b. The high-pressure water L introduced into the nozzle body 36a from the above-mentioned high-pressure water inlet 36b and the high-pressure air P introduced into the nozzle body 36a from the high-pressure air inlet 36c are mixed inside the nozzle body 36a, and the mixed fluid L+P of the high-pressure water L and the high-pressure air P is sprayed from the nozzle 36d.

[0030] In this embodiment, the chamfer removing device 30 is installed in parallel with the laser processing device 20. Therefore, when performing the chamfer removing step, as shown in FIG. 4(a), the holding means 32 is positioned on the chuck table 21 of the laser processing device 20 and lowered to abut against an area corresponding to the effective area 16A on the back surface 10Ab of the wafer 10A, and the suction means (not shown) is operated to suck the wafer 10A. Then, the negative pressure generated on the chuck table 21 is released to hold the wafer 10A on the holding means 32 side of the chamfer removing device 30. Next, the moving means (not shown) is operated to move the holding means 32, and as shown in FIG. 4(b), the chamfer 17A formed on the outer periphery of the wafer 10A is positioned near the injection port 36d of the fluid injection nozzle 36 of the fluid injection means 34.

[0031] Next, the metering valves 37b and 38b are opened, and high-pressure water L (e.g., 0.3 MPa) and high-pressure air P (e.g., 0.6 MPa) are introduced into the fluid injection nozzle 36 from the water source 37 and the air supply source 38, and the mixed fluid L+P is injected from the injection port 36d toward the outer periphery of the wafer 10A where the chamfered portion 17A is formed, as shown in Fig. 5(a). In the illustrated embodiment, the injection port 36a of the fluid injection nozzle 36 is positioned slightly below the back surface 10Ab of the wafer 10A, and the injection direction of the injected mixed fluid L+P is set to be slightly upward relative to the horizontal direction. As a result, an external force is applied by the mixed fluid L+P to the chamfered portion 17A on the outer periphery of the wafer 10A, and the mixed fluid L+P acts to separate the protective tape T from the outer periphery of the wafer 10A, so that the chamfered portion 17A is broken along the modified layer 100, and the chamfered portion 17A is removed from the outer periphery 10Ac of the wafer 10A, as shown in Fig. 5(b). Note that the area that is broken at this time is the area near where the mixed fluid L+P was sprayed.

[0032] Then, as described above, while the mixed fluid L+P is sprayed from the liquid spray nozzle 36 toward the outer periphery of the wafer 10A, the holding means 32 is rotated in the direction indicated by the arrow R3 in FIG. 4(b), and the chamfered portion 17A is removed over the entire outer periphery of the wafer 10A, as shown in FIG. 5(c). In this manner, the chamfered portion removing step is preferably performed. The above-described chamfered portion removing device 30 includes a closed space for performing the chamfered portion removing step, and the wafer 10A and the fluid spraying means 34 are positioned in the closed space to perform the chamfered portion removing step, so that the high-pressure water L sprayed from the fluid spraying means 34 and the fragments of the chamfered portion 17A scattered from the outer periphery of the wafer 10A can be efficiently collected.

[0033] 3(b) are formed in addition to the first modified layer 100, the chamfered portion 17A is warped from the front surface 10Aa toward the back surface 10Ab starting from the first modified layer 100. This allows the chamfered portion 17A to be efficiently removed by the action of the mixed fluid L+P sprayed from the nozzle 36a of the fluid spray nozzle 36, and solves the problem of the chamfered portion 17A remaining at the outer circumferential end 10Ac. Furthermore, even if the chamfered portion 17A is warped from the front surface 10Aa to the back surface 10Ab starting from the first modified layer 100 by forming the second modified layer (modified layers 107, 108, 109) shown in Figure 3(c) described above, the chamfered portion removal apparatus 30 can efficiently remove the chamfered portion 17A from the wafer 10A, thereby eliminating the problem of the chamfered portion 17A remaining at the outer circumferential edge 10Ac.

[0034] In the above embodiment, the external force applied to the outer periphery of the wafer 10A is applied by a mixed fluid L+P obtained by mixing high pressure air P and high pressure water L by the fluid injection nozzle 36 of the fluid injection means 34, but the present invention is not limited to this, and for example, it is also possible to use an external force that removes the chamfered portion 17A by injecting only high pressure air P, or an external force that removes the chamfered portion 17A by injecting only high pressure water L. In that case, it is not necessary for the fluid injection nozzle 36 to be capable of injecting the above-mentioned two fluids, and a fluid injection nozzle that injects a single fluid will suffice.

[0035] Furthermore, the chamfer removing means of the present invention is not limited to the chamfer removing means that uses a fluid as an external force, but may be a chamfer removing means that uses a picker 40 shown in Figures 6 and 7 arranged in place of the above-mentioned fluid ejection means 34.

[0036] As shown in Fig. 6, the picker 40 includes a main body 41 extending in the vertical direction and an external force acting part 42 formed at the lower end of the main body 41. The external force acting part 42 includes a fixed plate 42a, a movable plate 42b configured to be adjustable in distance to the fixed plate 42a, and a gap adjustment part 43 having a screw structure that adjusts the gap between the fixed plate 42a and the movable plate 42b by moving the movable plate 42b. The picker 40 is supported by the chamfer removing device 30 via a moving means (not shown), and is configured to be able to move the picker 40 up and down in the direction indicated by the arrow R4 and also in the direction indicated by the arrow R5 in the figure (horizontal direction) toward the holding means 32. In addition, the picker 40 can also tilt the external force acting part 42 of the picker 40 by tilting the main body 41 in the direction indicated by the arrow R6 in the figure where the holding means 32 is positioned.

[0037] The above-mentioned picker 40 is suitable for removing the chamfered portion 17B of the first wafer 10B in the wafer W described based on Fig. 1(b). Therefore, in the following description, a mode of carrying out the chamfered portion removing step using the above-mentioned picker 40 will be described assuming that the above-mentioned modified layer forming step is performed on the wafer W to form the above-mentioned first modified layer 100 and second modified layer (modified layers 102, 104, 106) along the chamfered portion 17B inside the boundary portion 18B between the effective area 16B and the chamfered portion 17B of the first wafer 10B of the wafer W.

[0038] When performing the chamfer removal process on the wafer W, the effective area 16B of the first wafer 10B constituting the wafer W is held by the holding means 32 in the same procedure as that described based on Figure 4(a), and the moving means (not shown) is operated to position the chamfered portion 17B of the first wafer 10B constituting the wafer W in the vicinity of the external force application portion 42 of the picker 40, as shown in Figures 6 and 7(a).

[0039] Next, by rotating the above-mentioned interval adjustment unit 43, the movable plate 42b is adjusted in the direction indicated by the arrow R7 as shown in FIG. 7(a), the interval between the fixed plate 42a and the movable plate 42b is adjusted to an interval capable of accepting the thickness of the outer periphery of the first wafer 10B, and the position of the movable plate 42b is positioned at the height of the mating surface where the first wafer 10B and the second wafer 10C are stacked. Next, as shown in FIG. 7(b), the moving means (not shown) is operated to move the picker 40 in the direction indicated by the arrow R8. The movable plate 42b is inserted into the boundary where the first wafer 10B and the second wafer 10C are stacked.

[0040] After the movable plate 42b is inserted as described above, the main body 41 is tilted in the direction indicated by the arrow R9 as shown in Fig. 7(c). This causes the movable plate 42b to act on the chamfered portion 17B of the first wafer 10B, breaking it along the modified layer 100 formed at the boundary portion 18B described above, and the chamfered portion 17B can be removed from the outer peripheral end 10Bc of the first wafer 10B. Note that, since the breaking occurs only in the region where the movable plate 42b is inserted and in its vicinity, the picker 40 is temporarily moved away from the first wafer 10B, and the main body 41 is returned to the vertical state as shown in Fig. 7(a).

[0041] During this time, the broken pieces of the chamfered portion 17B that was broken earlier fall off the picker 40. Next, the holding means 32 is rotated by a predetermined angle in the direction shown by the arrow R3 in FIG. 6 to position the outer peripheral end portion on which the chamfered portion 17B remains in the vicinity of the external force application portion 42 of the picker 40. Then, the above-mentioned operations shown in FIG. 7(b) and (c) are performed again to remove the chamfered portion 17B from the outer periphery. By repeating these operations multiple times, as shown in FIG. 7(d), a wafer W is obtained in which the chamfered portion 17B has been removed from the outer peripheral end 16Bc of the wafer 10B over the entire outer periphery of the first wafer 10B, and the chamfered portion removing process is completed.

[0042] Even when the above-described chamfered portion removal process is performed, a second modified layer (modified layers 102, 104, 106) is formed on the first wafer 10B in addition to the first modified layer 100, and the chamfered portion 17B is warped from the front surface 10Ba toward the back surface 10Bb starting from the first modified layer 100. This makes it possible to efficiently remove the chamfered portion 17B, thereby eliminating the problem of the chamfered portion 17B remaining at the outer circumferential edge 10Bc.

[0043] In the above-described embodiment, an example of removing the chamfered portion 17A of a single wafer 10A using the fluid ejection means 34 for ejecting a fluid and an example of removing the chamfered portion 17B of the first wafer 10B of a wafer W in which the first wafer 10B and the second wafer 10C are stacked together using the picker 40 are shown, but the present invention is not limited thereto. For example, it is also possible to use the above-described fluid ejection means 34 to remove the chamfered portion 17B of the first wafer 10B in the wafer W, which is a stacked wafer, or to use the picker 40 to remove the chamfered portion 17A of a single wafer 10A.

[0044] When the above-mentioned chamfered portion removing step is completed, the wafer from which the chamfered portion has been removed can be transported to a grinding device 50 shown in FIG. 8 to perform a processing step in which the back surface of the wafer is ground to a desired thickness. In this case, the wafer to be processed is the wafer that has been subjected to the chamfered portion removing step, but the present invention is not limited to processing the wafer after the above-mentioned chamfered portion removing step in the processing step. For example, the wafer W that has been subjected to the above-mentioned modified layer forming step can be subjected to a processing step that also serves as the chamfered portion removing step described below without performing the above-mentioned chamfered portion removing step.

[0045] In the following explanation, a form will be described in which the back surface 10Bb of the wafer W including the first wafer 10B on which the first modified layer 100 and the second modified layer (modified layers 102, 104, 106) have been formed by the modified layer formation process described above is ground to process the first wafer 10B to a desired thickness, while also performing a processing step that also serves as a chamfer removal step for removing the chamfered portion 17B.

[0046] The wafer W (without the chamfer removing step) on which the modified layer forming step has been performed and the first modified layer 100 and the second modified layer (modified layers 102, 104, 106) have been formed is transported to a grinding device 50 (only a part of which is shown) shown in the upper part of FIG. 8. As shown in the figure, the grinding device 50 includes a grinding means 52 for grinding and thinning the back surface 10Bb of the first wafer 10B of the wafer W held by suction on a chuck table 51. The grinding means 52 includes a rotating spindle 52a rotated by a rotation 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, and a plurality of grinding stones 52d are annularly arranged on the lower surface of the grinding wheel 52c.

[0047] The wafer W is transferred to the grinding device 50, placed on the chuck table 51 with the second wafer 10C side facing downward, and then the suction means (not shown) is operated to hold the wafer W by suction, and the rotating spindle 52a of the grinding means 52 is rotated in the direction indicated by the arrow R10 in the figure at, for example, 6000 rpm, while the chuck table 51 is rotated in the direction indicated by the arrow R11 at, for example, 300 rpm, as shown in the upper part of Fig. 8. Then, while grinding water is supplied onto the back surface 10Bb of the first wafer 10B by a grinding water supply means (not shown), the grinding stone 52d is brought into contact with the back surface 10Bb of the first wafer 10B, and the grinding wheel 52c is fed downward as indicated by the arrow R12 in the figure at a grinding feed speed of, for example, 1 µm / sec.

[0048] At this time, the grinding can be carried out while measuring the thickness of the wafer W by a contact or non-contact measuring gauge (not shown). As described above, the first modified layer 100 and the second modified layer (modified layers 102, 104, 106) are formed on the first wafer 10B, so that by carrying out the grinding process described above, an external force is applied to the chamfered portion 17B of the first wafer 10B, and the chamfered portion 17B of the first wafer 10B is removed from the outer peripheral end 10Bc of the first wafer 10B, as shown in the lower part of FIG. 8. In this way, when the back surface 10Bb of the first wafer 10B is ground by a predetermined amount and the wafer W has a desired thickness, the grinding means 52 is stopped and the processing process is completed.

[0049] According to the above-mentioned wafer processing method, a relatively deep first modified layer in which cracks reach the wafer surface and a relatively shallow second modified layer in which cracks do not reach the wafer surface are formed adjacent to the first modified layer on the outside or inside, so that the chamfered portion warps toward the back side starting from the first modified layer. This makes it possible to effectively remove the chamfered portion from the outer periphery of the wafer, and solves the problem that the chamfered portion remains on the outer periphery of the wafer and falls off in a later process to become a source of contamination or to cause chipping of devices when the wafer is divided into individual device chips.

[0050] In the above embodiment, an example in which the above-mentioned chamfer removing device 30 is provided in parallel with the laser processing device 20 has been shown, but the present invention is not limited to this, and an independent chamfer removing device 30 may be provided separately from the laser processing device 20. In that case, after the modified layer forming step is performed in the laser processing device 20, the wafer carried out from the laser processing device 20 may be carried into the chamfer removing device 30, and then the wafer may be held by the holding means 32 to carry out the above-mentioned chamfer removing step. [Explanation of symbols]

[0051] 10A: Wafer 10Aa: Surface 10Ab: Back 10Ac: Outer edge 12A: Device 14A: Planned division line 16A: Effective area 17A: Chamfered part 18A: Border 10B: First wafer 10Ba: Surface 10Bb: Back side 10Bc: Outer edge 12B: Device 14B: Planned division line 16B: Effective area 17B: Chamfered part 18B: Boundary part 10C: Second wafer 10Ca: surface 10Cb: Back side 20: Laser processing equipment 21: Chuck table 21a: Suction chuck 21b: Frame 22: Laser beam irradiation means 23: Concentrator 30: Chamfer removal device 32: Holding means 32a: Holding surface 32b: Suction part 32c: Support shaft 33:Communication path 34:Fluid injection means 36: Fluid injection nozzle 36a: Nozzle body 36b: High pressure water inlet 36c: High pressure air inlet 36d: Nozzle 37: Water source 37a: Communication path 37b: metering valve 38: Air supply source 38a: Communication path 38b: metering valve 40: Picker 41: Main body 42: External force acting part 42a: Fixing plate 42b: Movable plate 43: Spacing adjustment section 50: Grinding equipment 51: Chuck table 52: Grinding means 52a: Rotating spindle 52b: Wheel mount 52c: Grinding wheel 52d: Grinding wheel 100: First modified layer 101: Crack 102, 104, 106: second modified layer 107, 108, 109: Second modified layer

Claims

1. A method for processing a wafer having an effective area formed on a surface and a chamfered portion on an outer periphery surrounding the effective area, comprising the steps of: a modified layer forming step of irradiating a laser beam having a wavelength that is transparent to the wafer from the rear surface of the wafer with a focal point positioned within the boundary between the effective area and the chamfered portion to form a modified layer along the chamfered portion; a chamfer removing step of removing the chamfer by applying an external force to the outer periphery of the wafer; a processing step of grinding the back surface of the wafer to a desired thickness; Including, In the modified layer forming step, a first step of irradiating the laser beam with a focal point positioned inside the boundary between the effective area and the chamfered portion to form a relatively deep first modified layer with cracks reaching the surface of the wafer; a second step of forming a relatively shallow second modified layer adjacent to the first modified layer on the outer or inner side, the second modified layer having cracks that do not reach the surface of the wafer; The wafer processing method includes warping the chamfered portion from the front surface to the back surface, starting from the first modified layer.

2. 2. The wafer processing method according to claim 1, wherein the external force applied to the outer periphery of the wafer in the chamfer removing step is any one of high pressure air, high pressure water, a mixed fluid of high pressure air and high pressure water, and a picker.

3. 2. The wafer processing method according to claim 1, wherein the chamfer removing step is performed by applying an external force by a grinding action when grinding the back surface of the wafer in the processing step.

4. The wafer is a laminated wafer in which a first wafer and a second wafer are laminated, 2. The wafer processing method according to claim 1, wherein the modified layer forming step, the chamfered portion removing step, and the processing step are carried out on the first wafer.

5. 2. The wafer processing method according to claim 1, wherein in the second step, a second modified layer is formed at a position that is to be removed by grinding in the processing step.

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