Wafer processing method

Abstract

To provide a wafer processing method which solves problems that a part remaining on the outer periphery of a wafer falls off in a post-process and becomes a source of contamination, and that the part becomes a cause of chipping of device chips when the wafer is divided into individual device chips, thereby deteriorating the quality.SOLUTION: A method includes a modified layer forming step for irradiating a wafer with a laser beam having a wavelength transparent to a wafer while positioning the focal point of the laser beam inside a boundary between an effective area and a chamfered portion, thereby forming a modified layer along the chamfered portion, a chamfered portion removing step for holding the wafer on a spinner table and rotating the wafer at high speed to scatter and remove the chamfered portion by centrifugal force; and a processing step for grinding the back surface of the wafer to achieve a desired thickness.SELECTED DRAWING: Figure 6

Description

[Technical field]

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

[0002] A wafer has a device area on its front surface, where a plurality of devices such as ICs and LSIs are partitioned by planned division lines. The back surface of the wafer is ground to thin it to the desired thickness, and then the wafer is divided into individual device chips using a cutting device or laser processing device. These chips are then used in electrical devices 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 problems, according to the present invention, there is provided a method for processing a wafer having an effective area formed on its surface and a chamfered portion on its outer periphery surrounding the effective area, comprising: a modified layer forming step of irradiating a laser beam having a wavelength that is transparent to 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 holding the wafer on a spinner table and rotating it at high speed to scatter and remove the chamfered portion by centrifugal force; and a processing step of grinding the back surface of the wafer to process it to a desired thickness.

[0009] In the modified layer forming step, the laser beam is irradiated by positioning the focal point of the laser beam 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, and a second step is preferably formed adjacent to the first modified layer and on the outside or inside to form a relatively shallow second modified layer that does not reach the surface, and the chamfered portion is warped from the effective area to the back side starting from the first modified layer. In addition, the wafer is a laminated wafer in which a first wafer and a second wafer are laminated, and the modified layer forming step, the chamfered portion removing step, and the processing step can be performed on the first wafer. Furthermore, in the second step, the second modified layer is preferably formed at a position where it is ground and removed in the processing step. In the chamfered portion removing step, the rotation speed of the spinner table is preferably 1000 to 3000 rpm. Effect of the Invention

[0010] The wafer processing method of the present invention includes a modified layer forming step of irradiating the wafer with a laser beam having a wavelength that is transparent to the wafer, 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 holding the wafer on a spinner table and rotating it at high speed to scatter and remove the chamfered portion by centrifugal force; and a processing step of grinding the back surface of the wafer to a desired thickness. Therefore, it is possible to completely remove the chamfered portion from the outer periphery of the wafer before carrying out the processing step of grinding the back surface of the wafer to a desired thickness, and this solves the problem that the chamfered portion remains on the outer periphery of the wafer and falls off in a later step to become a source of contamination, or causes chipping of device chips when the wafer is divided into individual device chips, thereby degrading the quality of the devices. [Brief description of the drawings]

[0011] [Figure 1] FIG. 2A is a perspective view of a stacked wafer serving as a workpiece in this embodiment, and FIG. 2B is a perspective view of a single wafer serving as 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] (a) A schematic cross-sectional view showing the shape of a first modified layer that is half-cut, (b) A schematic cross-sectional view showing the shape of a second modified layer adjacent to the first modified layer shown in (a), and (c) A schematic cross-sectional view showing another shape of the second modified layer. [Figure 4] (a) A schematic cross-sectional view showing the shape of a first modified layer resulting in a full cut; (b) A schematic cross-sectional view showing the shape of a second modified layer adjacent to the first modified layer shown in (a); (c) A schematic cross-sectional view showing another shape of the second modified layer. [Diagram 5] FIG. 2 is a plan view showing a state in which radially shaped modified layers for division are formed on the first wafer shown in FIG. 1(a). [Figure 6] FIG. 2 is an overall perspective view of a chamfer removing device equipped with a spinner table. [Figure 7] 7 is a side view showing an embodiment of a chamfer removing step with a part of the chamfer removing device shown in FIG. 6 in cross section. FIG. [Figure 8] 1 is a perspective view showing an embodiment of a processing step. 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 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 10A and a second wafer 10B are laminated and integrated. The first 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 a 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 outer 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. The second wafer 10B has a similar structure to the first wafer 10A, and although not shown, is a silicon wafer having a surface 10Ba facing the lower side in the figure, on which a plurality of devices are formed by dividing the surface 10Ba along predetermined dividing lines. The first wafer 10A and the second wafer 10B are integrated together by siloxane bonding, for example, by bonding the surface 10Aa of the first wafer 10A and the surface 10Ba of the second wafer 10B together and subjecting them to a heat treatment.

[0014] FIG. 1(b) shows another wafer 10C to be processed by the wafer processing method of the present embodiment. The wafer 10C is a single wafer, and a protective tape T attached to the surface 10Ca of the wafer 10C is also shown. The illustrated wafer 10C has the same configuration as the above-mentioned wafer 10A, for example, and is a silicon wafer with a diameter of 300 mm and a thickness of 300 μm, and a plurality of devices 12C are formed on the surface 10Ca by dividing the wafer by a division line 14C. The wafer 10C has a surface 10Ca and a back surface 10Cb, and includes an effective area 16C near the center where the devices 12C to be used as products are formed, a chamfered portion 17C formed at the edge of the outer periphery surrounding the effective area 16C, and a boundary portion 18C between the effective area 16C and the chamfered portion 17C where the devices 12C to be products are not formed. As described above, when processing the wafer by the processing method of the present embodiment, the protective tape T is attached to the front surface 10Ca side and integrated with the wafer, as shown in the figure.

[0015] The wafer processed by the wafer processing method of the present invention is not limited to the above-mentioned two silicon wafers stacked wafer W and single silicon wafer 10C, 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, it may be a gallium nitride (GaN) wafer, a gallium arsenide (GaAs) wafer, a lithium tantalate (LiTaO3) wafer, or a lithium niobate (LiNbO3) wafer, or it may be a wafer (e.g., a glass wafer) in which no device is formed in the central area, but the central area 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 stacked wafer wafer W as an example.

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

[0017] In the substance layer forming step, first, the wafer W is transferred to a laser processing device 20 (only a part of which is shown) shown in Fig. 2(a) and (b). The laser processing device 20 includes at least a chuck table 21 shown in Fig. 2(a) and a laser beam application means 22 shown in Fig. 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 first wafer 10A constituting the wafer W, and a condenser 23 that condenses and irradiates the laser beam LB oscillated by the laser oscillator. Furthermore, the laser processing apparatus 20 is equipped with 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, etc. (all of which are omitted from the illustration).

[0018] 2(a), the wafer W is placed on the chuck table 21 with the back surface 10Bb of the second wafer 10B facing downward and the back surface 10Ab of the first wafer 10A facing upward, and a suction means (not shown) is operated to hold the wafer W by suction. Alignment is performed on the wafer W held by the chuck table 21 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 first wafer 10A is formed and the center position of the first wafer 10A, as well as the height of the upper surface of the back surface 10Ab of the first 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 step carried out in the present invention can be carried out, for example, including a first step and a second step described below.

[0020] (First step) By detecting the position of the edge of the outer periphery where the chamfered portion 17A of the first wafer 10A is formed and the center position of the first 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 first 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 first 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 on the processing position for the first step detected by the above-mentioned alignment, the chuck table 21 is moved to position the above-mentioned predetermined processing position directly below the condenser 23 of the laser beam application means 22, as shown in Fig. 2(b). Next, the laser beam LB is irradiated from the back surface 10Ab side of the first wafer 10A with the condensing point positioned within 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 first wafer 10A.

[0022] As shown in Fig. 3(a), the first modified layer 100 formed by the above-mentioned first step has cracks 101 generated by forming the first modified layer 100, and the cracks 101 are formed at relatively deep positions reaching the front surface 10Aa side of the first wafer 10A. Furthermore, it is preferable that the first modified layer 100 is formed of multiple 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 set position in the deepest part inside the boundary portion 18A of the first wafer 10A (for example, 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 170 μm to 160 μm to 150 μm from the back surface 10Ab, to form a total of four annular modified layers along the chamfered portion 17A and generate cracks 101 reaching the front surface 10Aa side of the first wafer 10A. In addition, since the first modified layer 100 and the cracks 101 formed by the above-mentioned first step do not extend from the front surface 10Aa to the back surface 10Ab of the first wafer 10A, the first modified layer 100 shown in Fig. 3 is also referred to as a half cut in the following. With the above, the first step is completed.

[0023] (Second step) After the first modified layer 100 is formed by the first step as described above, a second step is performed to form a relatively shallow second modified layer that does not reach the front surface 10Aa of the first wafer 10A on the outside or inside of the first modified layer 100. More specifically, for example, as shown in FIG. 3(b), a focal point of a laser beam LB is positioned 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 this second step is preferably formed by a plurality of modified layers as shown in FIG. 3(b), and in this embodiment, the focal point of a laser beam LB is positioned adjacent to the outside of the annular modified layer 102 and at the same depth as the modified layer 102, and the laser beam LB is irradiated to form annular modified layers 104 and 106 in addition to the above-mentioned annular modified layer 102. This completes the second step, completing the plasma layer formation process.

[0024] By performing the first step described above to form the first modified layer 100, a crack 101 reaching the front surface 10Aa side of the first wafer 10A is generated, and by performing the second step to form the second modified layers 102, 104, 106 as described above, stress is applied 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, that is, toward the back surface 10Ab side, over the entire circumference. Note that, when forming the second modified layer, it is not limited to forming an annular modified layer by positioning the light focusing points at three locations as described above, but the light focusing points may be positioned at two or less locations, or at four or more locations to form an annular modified layer, and preferably, the light focusing points are positioned at three to six locations and irradiated to form an annular modified layer.

[0025] The laser processing conditions when carrying out the modified layer forming process including the above-mentioned first step and second 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: 1.9W Machining feed speed: 400mm / s

[0026] The position of 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 laser beam LB may be irradiated by positioning the focal point of the laser beam LB at a relatively shallow position adjacent to the above-mentioned first modified layer 100, inside the inner part (effective area side) of the boundary part 18A, and not reaching the surface 10Aa of the first wafer 10A, to form a second modified layer (modified layers 107, 108, 109). The second modified layer (modified layers 107, 108, 109) shown in Fig. 3(c) is also processed under the same laser processing conditions as the second modified layer (modified layers 102, 104, 106) shown in Fig. 3(b), and stress can be applied to the first modified layer 100, and 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, that is, 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 set to a depth position to be removed when the back surface 10Ab of the first wafer 10A is ground to a desired thickness in a later processing step.

[0027] The modified layer formed in the modified layer forming step of the present invention is not limited to the above-mentioned form. Fig. 4(a) shows a first modified layer 100' formed by another embodiment of the first step of the modified layer forming step described based on Fig. 3. In the first step shown in Fig. 4(a), the focal point of the laser beam LB is positioned inside the boundary 18A between the effective area 16A and the chamfered portion 17A and irradiated, forming a first modified layer 100' in which the crack 101 reaches the front surface 10Aa and the back surface 10Ab of the first wafer 10A. When forming such a first modified layer 100', for example, the focal point of the laser beam LB is first positioned at a position set at the deepest part inside the boundary portion 18A of the first wafer 10A (for example, at a depth of 175 μm from the back surface 10Ab) and the laser beam LB is irradiated while the chuck table 21 is rotated in the direction of R2 shown in FIG. 2(b) to form a first annular modified layer along the chamfered portion 17A. Thereafter, while rotating the chuck table 21, the focal point is raised toward the back surface 10Ab side (upward) many times, for example, from the back surface 10Ab to a depth of 165 μm→155 μm→135 μm→120 μm→105 μm→90 μm→70 μm→50 μm→35 μm→20 μm, to form a total of 11 annular modified layers along the chamfered portion 17A. The first step is thus completed. The first modified layer 100' and the cracks 101 formed in the first step described with reference to Fig. 4(a) are formed in the entire region from the front surface 10Aa to the back surface 10Ab of the first wafer 10A, and are therefore called full cuts, whereas the first modified layer 100 shown in Fig. 3 is called half cuts.

[0028] After the first step described above is performed, the second step is performed. The second step can be performed in the same procedure as the second step described based on Fig. 3(b) and (c). Specifically, a relatively shallow second modified layer that does not reach the front surface 10Aa of the first wafer 10A is formed outside or inside the first modified layer 100'. For example, as shown in Fig. 4(b), the focal point of the laser beam LB is positioned at a position adjacent to the outside of the modified layer formed at a depth of 150 μm from the back surface 10Ab in the first modified layer 100', and the chuck table 21 is rotated to form a ring-shaped modified layer 102. In this embodiment as well, the second modified layer formed by the second step is preferably formed of a plurality of modified layers as shown in Fig. 4(b), and 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. This completes the second step and the modified layer forming process.

[0029] By performing the first step described above to form the first modified layer 100', and then performing the second step to form the second modified layers 102, 104, and 106 as described above, stress is applied to the first modified layer 100'. As a result, similar to the embodiment described above, 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 FIG. 4(b), i.e., toward the back surface 10Ab.

[0030] The second modified layer formed by the second step in the modified layer forming process shown in Fig. 4 may be formed by irradiating the laser beam LB at a focal point adjacent to the first modified layer 100' at a shallow position inside the boundary portion 18A (effective area side) that does not reach the front surface 10Aa of the wafer 10A, as shown in Fig. 4(c), to form the second modified layer (modified layers 107, 108, 109). The second modified layer (modified layers 107, 108, 109) shown in Fig. 4(c) can be formed by the procedure described based on Fig. 3(c), and similarly to the second modified layer (modified layers 102, 104, 106) shown in Fig. 4(b), stress can be applied to the first modified layer 100', and the chamfered portion 17A can be warped from the first modified layer 100' in the direction indicated by the arrow R2 in the figure, that is, toward the back surface 10Ab side. The second modified layers (modified layers 107, 108, 109) in this embodiment are also set to a depth 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.

[0031] 4, the laser processing conditions for carrying out the modified layer forming process are set, for example, as follows: Note that DF is the defocus position of the focal point of the laser beam LB, and indicates the depth position from the back surface 10Ab of the first wafer 10A. Wavelength: 1099nm Repetition frequency: 80kHz Average output: DF(μm)≧135→2W If DF(μm)<135 → 1W Machining feed speed: 450mm / s or Wavelength: 1342nm Repetition frequency: 90kHz Average output: DF(μm)≧135→1.9W If DF(μm)<135 → 1W Machining feed speed: 400mm / s

[0032] In addition to the first modified layer and the second modified layer formed by the modified layer forming step, for example, as shown in FIG. 5, a radially dividing modified layer 110 extending from the first modified layer 100' toward the outer circumferential end direction where the chamfered portion 17A is formed may be formed. The dividing modified layer 110 shown in the figure is a modified layer for dividing the chamfered portion 17A more finely, and is formed, for example, by irradiating a laser beam LB under the same laser processing conditions as the above-mentioned first modified layers 100 and 100', and is formed at a plurality of locations (four locations in the illustrated embodiment) at equal intervals along the chamfered portion 17A of the first wafer 10A. By forming this dividing modified layer 110, when removing the chamfered portion 17A in the chamfered portion removing step described later, the chamfered portion 17A is divided into small portions, and the removal of the chamfered portion 17A is performed well.

[0033] When the modified layer forming step according to the present invention is performed on the single silicon wafer 10C described with reference to Fig. 1(b), the above-described first step and second step can be performed to form the first modified layer 100 or 100' and the second modified layer (modified layer 102, 104, 106 or modified layer 107, 108, 109) described with reference to Figs. 3 and 4. The procedure for performing the modified layer forming step on the wafer 10C is the same as the procedure for forming a modified layer on the stacked wafers W described above, except that the back surface 10Cb of the wafer 10C is turned upward and the protective tape T side is suction-held on the chuck table 21 of the laser processing device 20, and therefore a detailed description thereof will be omitted. In the following description, it is assumed that the first modified layer 100 and the second modified layer (modified layers 102, 104, 106) have been formed on the first wafer 10A of the wafer W by the modified layer forming step described above.

[0034] (Bevel removal process) After the modified layer forming step is performed as described above, a chamfer removing step is performed in which the wafer W is rotated at high speed to scatter and remove the chamfer 17A by centrifugal force. Fig. 6 shows a chamfer removing device 30 suitable for performing the chamfer removing step of the present invention.

[0035] As shown in FIG. 6, the chamfer removing device 30 includes a spinner table 32 and a cover section 31 that surrounds the entire side of the spinner table 32 and has a circular opening 31a at the top. For convenience of explanation, FIG. 6 shows a cutaway view of the front side of the cover section 31. The spinner table 32 is composed of an adsorption chuck 32a formed of a porous material having air permeability, and a frame section 32b that surrounds the adsorption chuck 32a. The adsorption chuck 32a is connected to a suction means (not shown) to generate a suction force on the upper surface of the adsorption chuck 32a. A rotating shaft 33 is connected to the spinner table 32, and the rotating shaft 33 is driven by a motor 34 to rotate the spinner table 32. A plurality of air pistons 35 are disposed on the outer periphery of the motor 34. The air pistons 35 move a rod 36 up and down to move the spinner table 32, the shaft section 33, and the motor 34 up and down as a unit. The above-mentioned rotating shaft 33 and motor 34 function as a base that supports the spinner table 32 .

[0036] As can be seen from Fig. 6, the cover part 31 includes an annular bottom wall 31c, an outer wall 31d erected on the outer periphery of the bottom wall 31c, an inner wall 31e erected on the inner periphery of the bottom wall 31c, and a plurality of legs 31b supporting the cover part 31. The outer wall 31d has a curved shape that gradually reduces in diameter as it goes upward, and the circular opening 31a is formed with dimensions slightly larger than the outer dimensions of the frame part 32b of the spinner table 32. A skirt part 37 is disposed on the rotating shaft 33 below the spinner table 32 and rotates together with the rotating shaft 33. The chamfer removing device 30 is generally configured as described above, and the procedure for performing the chamfer removing process using the chamfer removing device 30 will be described below with reference to Fig. 6 and Fig. 7. In FIG. 7, for convenience of explanation, the outer wall 31d and skirt portion 37 of the cover portion 31 are shown in cross section, and the leg portion 31b of the cover portion 31 and the air piston 35 are omitted.

[0037] 7(a), when performing the chamfered portion removing step, the air piston 35 is operated to raise the spinner table 32 within the internal space 38 of the cover part 31, and the spinner table 32 is positioned near the opening 31a of the cover part 31, which is the loading / unloading position for loading and unloading the wafer W. Then, the wafer W that has been subjected to the modified layer forming step is placed on the spinner table 32 with the first wafer 10A facing upward and the second wafer 10B facing downward, and the suction means (not shown) is operated to suction and hold the wafer W on the spinner table 32.

[0038] After the wafer W is suction-held on the spinner table 32, the air piston 35 is operated to lower the spinner table 32 and position it at the chamfer removing position shown in Fig. 7(b). At this time, the skirt portion 37 is in a state of covering the outside of the inner wall 31e of the cover portion 31.

[0039] Next, the motor 34 is operated to rotate the rotating shaft 33, which rotates the spinner table 32, at high speed for a predetermined time in the direction indicated by the arrow R3 in FIG. 7(b). The rotation speed of the rotating shaft 33 is preferably, for example, 1000 to 3000 rpm. By rotating the spinner table 32 at high speed in this manner, a strong centrifugal force acts on the chamfered portion 17A. As a result, the chamfered portion 17A is separated from the first modified layer 100 or the first modified layer 100' formed by the modified layer forming step described above as a starting point, and is scattered from the outer peripheral end 10Ac of the first wafer 10A into the internal space 38 of the cover portion 31, and the chamfered portion 17A is removed from the first wafer 10A, completing the chamfered portion removing step. At this time, since the outer wall 31d of the cover part 31 is formed so as to have a smaller diameter going upward as described above, the scattered chamfered portion 17A falls along the inner surface of the outer wall 31d of the cover part 31, and is prevented from scattering to the outside of the cover part 31. The chamfered portion 17A removed from the first wafer 10A accumulates on the bottom wall 31c of the cover part 31, and is periodically collected after this chamfered portion removing step is performed on a plurality of wafers W.

[0040] After the above-mentioned chamfered portion removing step is completed, a processing step is performed in which the back surface 10Ab of the first wafer 10A of the wafer W is ground to a desired thickness. In the following description, a form for performing the processing step in which the back surface 10Ab of the wafer W including the first wafer 10A from which the chamfered portion 17A has been removed by the above-mentioned chamfered portion removing step is ground to a desired thickness will be described.

[0041] The wafer W that has been subjected to the chamfer removing process is transported to a grinding device 50 (only a part of which is shown) shown on the right side of Fig. 8. As shown in the figure, the grinding device 50 is equipped with a grinding means 52 for grinding and thinning the workpiece that is suction-held on a chuck table 51. The grinding means 52 is equipped with a rotating spindle 52a that is rotated by a rotation drive mechanism (not shown), a wheel mount 52b that is attached to the lower end of the rotating spindle 52a, and a grinding wheel 52c that is 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.

[0042] As shown in the figure, the wafer W is transported to the grinding device 50, placed on the chuck table 51 with the second wafer 10B side facing downward, and the suction means (not shown) is operated to hold the wafer W by suction. Next, the rotating spindle 52a of the grinding means 52 is rotated in the direction indicated by the arrow R4 in FIG. 8 at, for example, 6000 rpm, while the chuck table 51 is rotated in the direction indicated by the arrow R5 at, for example, 300 rpm. Then, while supplying grinding water onto the back surface 10Ab of the first wafer 10A by the grinding water supply means (not shown), the grinding wheel 52d is brought into contact with the back surface 10Ab of the first wafer 10A, and the grinding wheel 52c is ground and fed downward as indicated by the arrow R6 at, for example, a grinding feed speed of 1.0 μm / sec. At this time, grinding can be carried out while measuring the thickness of the wafer W by a contact or non-contact measuring gauge (not shown). When the back surface 10Ab of the first wafer 10A is ground by a predetermined amount to make the wafer W have a desired thickness, the grinding means 52 is stopped and retreated, and the processing step is completed. After the processing step is completed, cleaning, drying steps, etc., the details of which are omitted, are appropriately performed. In the above processing step, the back surface 10Ab of the first wafer 10A in the wafer W in which the first wafer 10B and the second wafer 10C are stacked is ground to a desired thickness. However, when the back surface 10Cb of a single wafer 10C that has been subjected to the modified layer forming step and the chamfered portion removing step is ground to a desired thickness, the above-mentioned grinding device 50 can be used to process the wafer in the same manner. The above completes the wafer processing method of this embodiment.

[0043] According to the processing method of the above-described embodiment, it is possible to completely remove the chamfered portion from the outer circumferential edge of the wafer before carrying out the processing step of grinding the back surface of the wafer to a desired thickness, and this solves problems such as the chamfered portion remaining on the outer periphery of the wafer falling off in a later step to become a source of contamination or causing chipping of device chips when the wafer is divided into individual device chips, thereby degrading the quality of the devices.

[0044] The modified layer formed by the modified layer forming process in the present invention is not limited to the modified layer formed by the first step and the second step described above. For example, the second step may be omitted, and only the first step may be performed to form only the half-cut first modified layer 100 or the full-cut first modified layer 100'. In addition, after performing only the first step to form the above-mentioned first modified layer 100 or the first modified layer 100', the above-mentioned radial dividing modified layer 110 may be appropriately combined. [Explanation of symbols]

[0045] 10A: First wafer 10Aa: Surface 10Ab: Back 12A: Device 14A: Planned division line 16A: Effective area 17A: Chamfered part 18A: Border 10B: Second wafer 10Ba: Surface 10Bb: Back side 10C: Wafer (single wafer) 10Ca: surface 10Cb: Back side 12C:Device 14C: Planned division line 16C: Effective area 17C: Chamfered part 18C: Border 20: Laser processing equipment 21: Chuck table 22: Laser beam irradiation means 30: Chamfer removal device 31: Cover part 31a: Opening 31b: Legs 31c: Bottom wall 31d: Exterior wall 31e:Inner wall 32: Spinner table 33: Rotating shaft 34: Motor 35: Air piston 36: Rod 37: Interior space 50: Grinding equipment 51: Chuck table 52: Grinding means 52a: Rotating spindle 52b: Wheel mount 52c: Grinding wheel 52d: Grinding wheel 100, 100': first modified layer 101: Crack 102, 104, 106: second modified layer 107, 108, 109: Second modified layer 110: Modified layer for division W: Stacked wafer

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 with a focal point located within the boundary between the effective area and the chamfered portion to form a modified layer along the chamfered portion; a chamfer removing step in which the wafer is held on a spinner table and rotated at high speed to scatter and remove the chamfer by centrifugal force; a processing step of grinding the back surface of the wafer to a desired thickness; A wafer processing method comprising the steps of:

2. 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 not reaching the surface; 2. The method for processing a wafer according to claim 1, wherein the chamfered portion is warped from the effective area toward the back surface side, starting from the first modified layer.

3. 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 a first wafer.

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

5. 2. The wafer processing method according to claim 1, wherein in the chamfer removing step, the rotation speed of the spinner table is 1000 to 3000 rpm.

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