Method for processing a wafer

Abstract

The present invention provides a method for processing a wafer. By irradiating a laser beam to the inside of the outer peripheral remaining region including the chamfered portion, a ring-shaped region including the chamfered portion can be easily removed from the wafer. The method for processing a wafer includes the following steps: a protective member disposing step of disposing a protective member on the front surface of the wafer; a modified layer forming step of irradiating a laser beam having a wavelength transmissive to the wafer so that the focal point of the laser beam is positioned inside the outer peripheral remaining region to form a ring-shaped modified layer; a separating step of dividing the wafer starting from the ring-shaped modified layer to separate a part or all of the outer peripheral remaining region from the wafer; and a grinding step of grinding the back surface of the wafer to thin the wafer. In the modified layer forming step, the modified layer is formed in a frustum shape with a diameter decreasing from the front surface to the back surface of the wafer.

Description

Technical Field

[0001] The present invention relates to a method for processing a wafer, which includes a device region formed with a plurality of devices on the front surface and an outer peripheral remaining region surrounding the device region and formed with a chamfered portion. Background Art

[0002] After a wafer having a device region with a plurality of devices such as ICs and LSIs divided by division predetermined lines on the front surface and an outer peripheral remaining region surrounding the device region is ground on the back surface to a predetermined thickness, it is divided into individual device chips by a cutting device or a laser processing device and used in electronic devices such as mobile phones and personal computers.

[0003] Moreover, when the back surface of the wafer is ground and thinned, the chamfered portion formed at the outer peripheral end of the wafer becomes as thin and sharp as a blade, and notches are generated during grinding and cracks reach the device region, thus there is a problem of damaging the devices. Therefore, the present applicant proposed the following technique: before grinding the back surface of the wafer, a laser beam is irradiated onto the outer peripheral remaining region having the chamfered portion to remove the outer peripheral remaining region (see Patent Document 1).

[0004] Patent Document 1: Japanese Patent Laid-Open No. 2006-108532

[0005] However, in order to irradiate a laser beam onto the outer peripheral remaining region to remove the chamfered portion, even if one wants to form a modified layer by irradiating a laser beam having a wavelength transmissive to the wafer onto the inside of the outer peripheral remaining region including the chamfered portion as in the technique described in Patent Document 1, and thus remove the annular region including the chamfered portion from the wafer along the modified layer, it is not easy for the outside of the outer peripheral remaining region having the modified layer to separate from the wafer, and there is a problem that the operation takes time. Summary of the Invention

[0006] Therefore, an object of the present invention is to provide a method for processing a wafer, which can irradiate a laser beam onto the inside of the outer peripheral remaining region including the chamfered portion and easily remove the annular region including the chamfered portion from the wafer.

[0007] According to one aspect of the present invention, there is provided a method for processing a wafer, the wafer including a device region having a plurality of devices formed on a front surface and an outer peripheral remaining region surrounding the device region and having a chamfered portion formed thereon. The method for processing the wafer includes the following steps: a protective member disposing step of disposing a protective member on the front surface of the wafer; a modified layer forming step of irradiating the wafer with a laser beam having a wavelength transmissive to the wafer so that the focal point of the laser beam is positioned inside the outer peripheral remaining region to form an annular modified layer; a separating step of dividing the wafer starting from the annular modified layer to separate a part or all of the outer peripheral remaining region from the wafer; and a grinding step of grinding the back surface of the wafer to thin the wafer. In the modified layer forming step, the modified layer is formed in a frustum shape with a diameter decreasing from the front surface to the back surface of the wafer.

[0008] Preferably, in the modified layer forming step, the modified layer is formed not only in a frustum shape with a diameter decreasing from the front surface to the back surface of the wafer but also in an inverted frustum shape.

[0009] In the method for processing a wafer according to one aspect of the present invention, since the annular modified layer inside the outer peripheral remaining region is formed in a frustum shape with a diameter decreasing from the front surface to the back surface of the wafer, it is possible to easily separate and remove a part of the annular outer peripheral remaining region including the chamfered portion from the wafer. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is a perspective view showing the protective member disposing step of the present embodiment.

[0011] Figure 2 is a perspective view showing a state where the wafer is placed and held on a chuck table when the modified layer forming step is performed.

[0012] Figure 3 is a perspective view showing the modified layer forming step of the present embodiment.

[0013] Figure 4 (a) of is a partial enlarged cross-sectional view showing a state where a modified layer is formed inside the outer peripheral remaining region by performing the modified layer forming step shown in Figure 3 , and Figure 4 (b) of is a partial enlarged cross-sectional view showing a modified layer forming step in a manner different from (a) of Figure 4 .

[0014] Figure 5 (a) of is a side view showing a part of the wafer and the like when the separating step is performed after the modified layer forming step shown in (a) of Figure 4 is enlarged, and Figure 5 (b) of is a side view showing a part of the wafer and the like when the separating step is performed after the modified layer forming step shown in Figure 4A partial enlarged side view of a wafer or the like when the separation process is performed after the modified layer forming process shown in (b).

[0015] Figure 6 (a) is a perspective view showing a state where a wafer is placed on a chuck table of a grinding device. Figure 6 (b) is a perspective view showing the grinding process.

[0016] Reference numeral description

[0017] 10: Wafer; 10A: Device region; 10a: Front surface; 10B: Outer peripheral remaining region; 10b: Back surface; 10c: Chamfered portion; 12: Device; 14: Dicing predetermined line; 20: Adhesive tape; 30: Laser processing device; 32: Chuck table; 34: Laser beam irradiation unit; 34a: Condenser; 40: Grinding device; 42: Chuck table; 44: Grinding unit; 44c: Grinding wheel; 44d: Grinding tool; 100, 110: Modified layer; LB: Laser beam; M: Separation bar. Detailed description of the preferred embodiments

[0018] Hereinafter, a method for processing a wafer according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0019] In the method for processing a wafer according to the present embodiment, for example, a wafer 10 made of silicon (Si) is used as a processing object. As Figure 1 shown, the wafer 10 has a device region 10A in which a plurality of devices 12 such as ICs and LSIs are divided by a dicing predetermined line 14 on the front surface 10a, and an outer peripheral remaining region 10B surrounding the device region 10A. A chamfered portion 10c is formed at an end portion on the outer peripheral side of the wafer 10 forming the outer peripheral remaining region 10B. For example, the diameter of the wafer 10 is 300 mm and the thickness is 780 μm. The wafer 10 of the present embodiment is ground on the back surface 10b to a predetermined thickness and then diced into individual device chips. In addition, as Figure 1 shown, a ring-shaped line L indicated by a double-dot chain line for dividing the device region 10A and the outer peripheral remaining region 10B is described on the front surface 10a of the wafer 10, but the line L is an imaginary line given for convenience of explanation and is not actually given on the wafer 10.

[0020] When implementing the method for processing a wafer according to the present embodiment, first, as Figure 1 shown, an adhesive tape 20 that functions as a protective member is pasted on the front surface 10a of the wafer 10 (protective member disposition step). The adhesive tape 20 is, for example, a tape obtained by applying a paste to the surface of a base film such as PET or PVC, but is not particularly limited.

[0021] Next, the wafer 10 integrated with the adhesive tape 20 pasted thereon is transferred toFigure 2 and Figure 3 In the laser processing apparatus 30 (only a part is shown) shown in Figure 3 , the back surface 10b side of the wafer 10 is oriented upward and the adhesive tape 20 side is oriented downward, and the wafer 10 is placed and attracted and held on the holding surface 32a of the chuck table 32 (see Figure 2 ). After the wafer 10 is attracted and held on the chuck table 32, a predetermined alignment process is performed to detect the position (processing position) where the laser beam should be irradiated. As shown in Figure 3 , the processing position where the laser beam should be irradiated is positioned below the condenser 34a that constitutes the laser beam irradiation unit 34. At this time, the processing position where the laser beam should be irradiated is set inside the outer peripheral remaining area 10B slightly outside the line L that divides the device area 10A and the outer peripheral remaining area 10B, that is, at a position inside the wafer 10 in the radial direction and closer to the inside than the chamfered portion 10c.

[0022] After the wafer 10 is held on the chuck table 32 of the laser processing apparatus 30 and positioned below the condenser 34a as described above, the following modified layer forming process is performed: The laser beam LB is irradiated on the wafer 10 so that the focus (focal point) of the laser beam LB having a wavelength that is transmissive to the wafer 10 is positioned inside the outer peripheral remaining area 10B to form an annular modified layer. Regarding the modified layer forming process of this embodiment, refer to Figure 4 (a) for a more specific description.

[0023] In the modified layer forming process of this embodiment, a plurality of annular modified layers are formed. First, the focus of the laser beam LB is positioned at a position P1 at a depth of 750 μm close to the front surface 10a that constitutes the lower surface when viewed from the back surface 10b that constitutes the upper surface of the wafer 10 having a thickness of 780 μm. After the focus of the laser beam LB is positioned at this position P1, while irradiating the laser beam LB from the condenser 34a of the laser beam irradiation unit 34, as shown in Figure 3 , the chuck table 32 is rotated in the direction shown by the arrow R1 to form an annular modified layer inside the outer peripheral remaining area 10B.

[0024] In addition, the laser processing conditions during the above laser processing are set as follows, for example.

[0025] Wavelength: 1342 nm

[0026] Repetition frequency: 60 kHz

[0027] Average output: 1.6 W

[0028] Chuck table rotation speed: 0.5 times / second

[0029] As described above, after the focal point of the laser beam LB is positioned at the position P1 and an annular modified layer is formed inside the outer peripheral remaining region 10B of the wafer 10, the irradiation of the laser beam LB is temporarily stopped, and the position of the focal point is moved 4 μm inward (toward the device region 10A side) from this position P1 and 90 μm upward (toward the upper surface (back surface 10b) side), that is, moved to a depth position of 660 μm as observed from the back surface 10b. Thereafter, similarly to the above, the laser beam LB is irradiated to form a modified layer inside the outer peripheral remaining region 10B. Thereafter, similarly, along the Figure 4 arrow direction shown in (1) of (a) of Figure 4 , the position of the focal point is moved 4 μm inward and 90 μm upward each time (P1...P2...P3), and the laser beam LB is irradiated to form the modified layer 100. In addition, in the present embodiment, the position P3 closest to the back surface 10b is, for example, a position 28 μm inward from the initial position P1 and is a position at a depth of 120 μm from the back surface 10b.

[0030] That is, the plurality of modified layers 100 are formed in a frustum shape (frustum of a cone) whose diameter becomes smaller from the front surface 10a (lower surface) of the wafer 10 toward the back surface 10b (upper surface) and are arranged along a curved surface having an inclination angle θ of approximately 2.4 degrees with respect to the vertical direction. In addition, in Figure 4 Figure 4 , for ease of explanation, the inclination angle of the curved surface on which the modified layers 100 are arranged is described as being larger than the actual value. And the inclination angle of the curved surface on which the modified layers 100 are arranged with respect to the vertical direction is not limited to the above 2.4 degrees, and the interval when the position of the focal point is moved inward can be appropriately adjusted, and the inclination angle θ can be set, for example, in a range of about 2 degrees to 5 degrees. Thus, the modified layer forming step is completed.

[0031] Next, the following separation step is performed: The wafer 10 is divided starting from the annular modified layer 100, and the portion of the outer peripheral remaining region 10B outside the modified layer 100 is separated from the wafer 10. In this separation step, as Figure 5 shown in (a) of Figure 5 , in a state where the wafer 10 is sucked and held by the chuck table 32, for the front surface 10a forming the lower surface of the outer peripheral remaining region 10B outside the position where the modified layer 100 is formed, for example, the claw portion Ma of the separation rod M is positioned and pulled upward (in the direction shown by the arrow R2). Thereby, the annular outer peripheral remaining region 10B including the chamfered portion 10c is easily separated along the curved surface (inclination) on which the modified layers 100 are arranged, and the frustum-shaped (frustum of a cone) wafer 10 including the device region 10A remains on the chuck table 32. Although not shown, in the outer peripheral remaining region 10B of the wafer 10, it is preferable to position the claw portion Ma of the separation rod M at least at three equally spaced positions in the circumferential direction. The above is the completion of the separation step.

[0032] After performing the above-described separation process, the wafer 10 with the chamfered portion 10c removed is transported to Figure 6 the grinding device 40 (only a part is shown) shown in (a) of Figure 6 . The back surface 10b of the wafer 10 is oriented upward and the adhesive tape 20 side is oriented downward, and the wafer 10 is placed and attracted and held on the holding surface 42a of the chuck table 42.

[0033] As Figure 6 shown in (b) of Figure 6 , the grinding device 40 has a grinding unit 44. The grinding unit 44 has: a main shaft 44a that is rotatably disposed; and a servo motor (not shown) as a drive source that is used to rotationally drive the main shaft 44a. A disk-shaped mounting base 44b is disposed at the lower end of the main shaft 44a, and a grinding wheel 44c is disposed on the lower surface of the mounting base 44b. Moreover, a plurality of grinding tools 44d are annularly disposed on the lower surface of the grinding wheel 44c.

[0034] When performing the grinding process, as Figure 6 shown in (b) of Figure 6 , the wafer 10 attracted and held on the chuck table 42 is positioned below the grinding unit 44. Next, the chuck table 42 is rotated in the direction shown by the arrow R4, for example, at a rotational speed of 300 rpm, and the main shaft 44a is rotated in the direction shown by the arrow R5 at a rotational speed of 6000 rpm. Next, an unillustrated grinding feed mechanism is operated to lower the grinding unit 44 in the direction shown by the arrow R6 and bring it into contact with the back surface 10b of the wafer 10. By bringing the grinding tools 44d of the grinding unit 44 into contact with the back surface 10b of the wafer 10, the back surface 10b of the wafer 10 is ground. The grinding feed speed when grinding the back surface 10b of the wafer 10 is set to, for example, 0.1 μm / second. In this grinding process, after the wafer 10 is ground to a desired thickness, for example, 100 μm, the grinding process is completed.

[0035] As described above, according to the present embodiment, when performing the modified layer forming process, the modified layer 100 is formed in a frustum shape (frustum of a cone) whose diameter decreases from the front surface 10a to the back surface 10b of the wafer 10. By performing the separation process, the outer peripheral remaining region 10B including the chamfered portion 10c is separated. Therefore, even when performing the grinding process of thinning the back surface 10b of the wafer 10, no blade is formed. And when separating the outer peripheral remaining region 10B including the chamfered portion 10c from the wafer 10, since the modified layer 100 is formed in a frustum shape, the outer peripheral remaining region 10B is easily separated.

[0036] In addition, in the above-described embodiment, when forming the modified layer 100, as Figure 4As shown in (a) thereof, after the modified layer 100 is formed into a truncated cone shape whose diameter decreases from the front surface 10a to the back surface 10a of the wafer 10, the above-described separation process is performed. However, the present invention is not limited thereto. For example, as shown in Figure 4 (b) thereof, not only is the modified layer 100 formed into a truncated cone shape whose diameter decreases from the front surface 10a to the back surface 10b of the wafer 10, but also the modified layer 110 is formed into a truncated cone shape having the back surface 10b side as the bottom surface and the front surface 10a side as the upper surface, that is, a truncated cone shape (inverted truncated cone shape) opposite to the truncated cone shape of the above-described modified layer 100 (a truncated cone shape whose diameter increases from the front surface to the back surface of the wafer). Refer to Figure 4 (b) thereof for a more specific description of the modified layer 100 and other embodiments of forming the modified layer 110.

[0037] First, in the same manner as the modified layer forming process described above, the focal point of the laser beam LB is positioned at a position P4 (=P1) having a depth of 750 μm close to the front surface 10a as observed from the back surface 10b constituting the upper surface of the wafer 10, that is, at a position P4 (=P1) inside the outer peripheral remaining region 10B. After the focal point of the laser beam LB is positioned at this position P4, the laser beam LB is irradiated from the condenser 34a of the laser beam irradiation unit 34 under the same laser processing conditions as in the above-described modified layer forming process. As shown in Figure 3 the chuck table 32 is rotated in the direction shown by the arrow R1 to form an annular modified layer inside the outer peripheral remaining region 10B. Next, the laser processing is temporarily stopped, the position of the focal point is moved 4 μm inward (toward the device region 10A side) from this P4, and moved 90 μm upward (toward the upper surface (back surface 10b) side) (a depth position of 660 μm as observed from the back surface 10b), and the same processing is performed. Similarly to the above, the position of the focal point is sequentially moved in the direction shown by (2) to repeatedly perform the same processing, and a plurality of modified layers are formed inside the outer peripheral remaining region 10B until the position shown by P5.

[0038] As described above, after the modified layer is formed by positioning the condensing point at position P5, the irradiation of the laser beam LB is temporarily stopped. Then, the laser beam LB is irradiated in such a way that the condensing point is positioned at a position having the same depth as the above-mentioned position P4 when viewed from the back surface 10b, i.e., a position having a depth of 750 μm when viewed from the back surface 10b and 28 μm inward from the position P4, and the chuck table 32 is rotated to form an annular modified layer. Thus, after the modified layer is formed at position P6, the irradiation of the laser beam LB is temporarily stopped, and the position of the condensing point is moved 4 μm outward (toward the outer peripheral remaining region 10B side) and 90 μm upward (toward the upper surface (back surface 10b) side) from this P6 (i.e., moved to a depth position of 660 μm when viewed from the back surface 10b), and the same processing is performed. Similarly to the above, the position of the condensing point is sequentially moved in the direction shown in (3), and the same processing is repeatedly performed to form a plurality of modified layers inside the outer peripheral remaining region 10B until the position shown by P7. After the modified layer is formed up to the position shown by P7, the position of the condensing point is further moved 4 μm outward (toward the outer peripheral remaining region 10B side) from this P7 and moved to a position P8 that is 90 μm higher on the upper surface (back surface 10b) side, and the laser beam LB is irradiated while rotating the chuck table 32 to form a modified layer. In addition, position P8 is a position that overlaps with position P5 when viewed from above or below. After the modified layer is formed at position P8, the position of the condensing point is further sequentially moved in the direction shown in (4), i.e., to a position 4 μm outward (toward the outer peripheral remaining region 10B side) and 90 μm higher on the upper surface (back surface 10b) side, and the same processing is repeatedly performed to form a plurality of modified layers until the position shown by P9.

[0039] After an annular modified layer is formed at the position corresponding to position P9 as described above, the condensing point is then positioned at the position shown by P10. Position P10 is a position having the same depth as the above-mentioned position P8 and overlapping with position P7 when viewed from above or below. After the condensing point is positioned at such a position P9, the laser beam is irradiated under the same laser processing conditions as above, and a modified layer is formed while rotating the chuck table 32. Then, the position of the condensing point is sequentially moved in the direction shown in (5), i.e., 4 μm inward (toward the device region 10A side) and 90 μm higher on the upper surface (back surface 10b) side, and the same processing is repeatedly performed. When a plurality of modified layers are formed up to the position shown by P11, the modified layer forming process is completed.

[0040] According to the above-described other embodiments, by forming the modified layer 100 along the directions shown in (2) and (5) of (b) of Figure 4 , the modified layer 100 is formed in a frustum shape (frustum of a cone) whose diameter becomes smaller from the front surface 10a of the wafer 10 toward the back surface 10b. And by along Figure 4The modified layer 110 is formed in the directions shown in (3) and (4) of (b) thereof, and the modified layer 110 is formed in an inverted truncated cone shape (inverted truncated conical shape) that is the upside-down of the truncated cone shape of the modified layer 100. Further, by performing the modified layer forming process in this way, even when the modified layer is formed at a position that overlaps when viewed from above or below, the modified layer on the lower side is necessarily formed first. Therefore, the modified layer 100 and the modified layer 110 are formed well.

[0041] Even when the modified layers 100 and 110 are formed by the above-described other embodiments, as Figure 5 shown in (b) thereof, by performing the same separation process as the above-described embodiment, the wafer can be divided starting from the modified layers 100 and 110 formed in a ring shape, and the annular outer peripheral remaining region 10B including the chamfered portion 10c can be easily separated. After performing the modified layer forming process as described above, the above-described grinding process is performed to thin the wafer 10 to a desired thickness.

[0042] After the modified layers 100 and 110 are formed by the above-described other embodiments, when the outer peripheral remaining region 10B is separated from the wafer 10, since the region 10d surrounded by the modified layer 100 and the modified layer 110 is further separated, the outer peripheral remaining region 10B is more easily separated, and the outer peripheral end of the wafer 10 becomes a good shape that does not form a blade even when the back surface 10b is ground.

Claims

1. A method for processing a wafer, the wafer including a device region having a plurality of devices formed on a front surface and an outer peripheral remaining region surrounding the device region and having a chamfered portion formed thereon, wherein, the method for processing the wafer includes the following steps: a protective member disposing step of disposing a protective member on the front surface of the wafer; a modified layer forming step of irradiating the wafer with a laser beam having a wavelength transmissive to the wafer so that the focal point of the laser beam is positioned inside the outer peripheral remaining region to form an annular modified layer; a separating step of dividing the wafer starting from the annular modified layer to separate a part or all of the outer peripheral remaining region from the wafer; and a grinding step of grinding the back surface of the wafer to thin the wafer, in this modified layer forming step, the modified layer is formed in a frustum of a cone shape whose diameter decreases from the front surface to the back surface of the wafer, in this modified layer forming step, the modified layer is formed not only in a frustum of a cone shape whose diameter decreases from the front surface to the back surface of the wafer, but also in an inverted frustum of a cone shape.

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