Method for processing wafer and apparatus for removing chamfered portion

Abstract

To provide a method for processing a wafer, the method enabling complete removal of a chamfered portion from the outer peripheral edge of the wafer.SOLUTION: The method for processing a wafer includes: a modified layer forming step of irradiating the wafer with a laser beam having a wavelength transmissive to the wafer, with the focal point of the laser beam positioned inside the boundary portion between an effective region and a chamfered portion, so as to form a modified layer into a ring shape along the boundary portion; a chamfered portion removing step of detecting a position where the modified layer has been formed, inserting a sharp tool (54) into the detected position, and relatively rotating the wafer and the tool (54) along the modified layer to remove the chamfered portion; and a processing step of grinding the back surface of the wafer to process the wafer to a desired thickness.SELECTED DRAWING: Figure 8

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 surrounding the outer periphery of the effective area, and to a chamfered portion removing device for removing the chamfered portion from a wafer on which a ring-shaped modified layer is formed. [Background technology]

[0002] Wafers have device regions (effective regions) formed on their surface, where multiple devices such as ICs and LSIs are partitioned by planned division lines.The back surface is ground to thin the wafer to the desired thickness, and then the wafer is divided into individual device chips using a cutting device and a laser processing device.Each of the divided device chips is used in electrical equipment such as mobile phones and personal computers.

[0003] Because the wafer has a chamfered edge on its outer periphery, grinding the backside of the wafer to thin it creates a sharp knife-edge. This requires operators to handle the wafer with extra care. Furthermore, the sharp knife-edge chamfer makes it more likely for cracks to form from the outer periphery of the wafer to the inside, increasing the risk of device damage.

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

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-88187 Summary of the Invention [Problem to be solved by the invention]

[0006] However, there are cases where the chamfered portion is not completely removed from the outer periphery of the wafer and a small portion remains, which can cause problems such as the remaining portion falling off in a later process and becoming a source of contamination, or causing chipping of device chips when the wafer is divided into individual device chips, etc. The above-mentioned problems can occur not only with a single wafer but also with a bonded wafer in which two wafers are stacked.

[0007] An object of the present invention is to provide a wafer processing method and a chamfer removing device that can completely remove a chamfer from the outer periphery of a wafer. [Means for solving the problem]

[0008] According to the present invention, there is provided the following wafer processing method that solves the above-mentioned problems. "A method for processing a wafer having an effective area formed on the surface and a chamfered portion surrounding the periphery of the effective area, a modified layer forming step of irradiating the wafer with a laser beam having a wavelength that is transparent to the wafer, with the focused point positioned within the boundary between the effective area and the chamfered portion, to form a ring-shaped modified layer along the boundary; a chamfer removing step of detecting the position where the modified layer is formed, inserting a sharp tool into the detected position, and rotating the wafer and the tool relatively along the modified layer to remove the chamfer; and a processing step of grinding the back surface of the wafer to a desired thickness.

[0009] Preferably, in the modified layer forming step, a modified layer is further formed from the boundary portion toward the outer periphery of the chamfered portion. The wafer is a bonded wafer in which the effective region of a first wafer and the effective region of a second wafer are bonded together, and it is desirable to perform the modified layer forming step, the chamfered portion removing step, and the processing step on the first wafer.

[0010] Furthermore, according to the present invention, there is provided the following chamfer removal device that solves the above-mentioned problems. "A chamfering portion removing device for performing the chamfering portion removing step as described above, a holding means having a rotatable holding table for holding the wafer; an imaging means disposed opposite the holding table for imaging the wafer held on the holding table; and tool means for inserting the tool into the position of the modified layer detected by the imaging means.

[0011] The imaging means is preferably an infrared camera and is adapted to image the interior of the wafer. The tool means can be adapted to follow the tool in the radial direction in accordance with the eccentricity of the wafer. The tool means is preferably equipped with a nozzle for spraying air, and is adapted to spray air onto the wafer from which the chamfered portion has been removed to remove processing debris. [Effects of the Invention]

[0012] The wafer processing method of the present invention includes: A method for processing a wafer having an effective area formed on a surface and a chamfered portion surrounding an outer periphery of the effective area, comprising: a modified layer forming step of irradiating the wafer with a laser beam having a wavelength that is transparent to the wafer, with the focused point positioned within the boundary between the effective area and the chamfered portion, to form a ring-shaped modified layer along the boundary; a chamfer removing step of detecting the position where the modified layer is formed, inserting a sharp tool into the detected position, and rotating the wafer and the tool relatively along the modified layer to remove the chamfer; Since the process includes a processing step of grinding the back surface of the wafer to the desired thickness, the chamfered portion can be completely removed from the outer periphery of the wafer, thereby eliminating problems such as the remaining portion falling off and becoming a source of contamination in subsequent processes, or causing chipping of device chips when the wafer is divided into individual device chips.

[0013] The chamfer removing device of the present invention comprises: A chamfering portion removing device for performing the chamfering portion removing step as described above, a holding means having a rotatable holding table for holding the wafer; an imaging means disposed opposite the holding table for imaging the wafer held on the holding table; and tool means for inserting the tool into the position of the modified layer detected by the imaging means, so that the chamfered portion can be completely removed from the outer periphery of the wafer, thereby eliminating problems such as the remaining portion falling off in a later process and becoming a source of contamination, or causing chipping of device chips when the wafer is divided into individual device chips. [Brief explanation of the drawings]

[0014] [Figure 1] (a) Perspective view of a single wafer, (b) Partial cross-sectional view of the wafer shown in (a). [Figure 2] (a) A perspective view of the bonded wafer, (b) A partial cross-sectional view of the bonded wafer shown in (a). [Figure 3] FIG. 2 is a schematic diagram showing a state in which a bonded wafer is held on a chuck table of a laser processing apparatus. [Figure 4] FIG. 4 is a schematic diagram showing a state in which a modified layer is being formed. [Figure 5] (a) Partial cross-sectional view of a bonded wafer on which a Type 1 modified layer is formed, (b) Partial cross-sectional view of a bonded wafer on which a Type 2 modified layer is formed, (c) Partial cross-sectional view of a bonded wafer on which a Type 3 modified layer is formed, (d) Partial cross-sectional view of a bonded wafer on which a Type 4 modified layer is formed. [Figure 6] FIG. 10 is a plan view of a wafer on which a ring-shaped modified layer and a radial modified layer are formed. [Figure 7] FIG. [Figure 8] FIG. [Figure 9] FIG. 10 is a perspective view of the bonded wafers with the chamfer removed from the first wafer. [Figure 10] Schematic diagram showing the processing steps. DETAILED DESCRIPTION OF THE INVENTION

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a wafer processing method and a chamfer removing apparatus according to the present invention will now be described with reference to the drawings.

[0016] (single wafer 2) 1(a) and 1(b) show a single, disc-shaped wafer 2 that can be processed using the method and apparatus of the present invention. The wafer 2 can be formed from a suitable semiconductor material, such as silicon. The wafer 2 has dimensions, for example, a diameter of 300 mm and a thickness of approximately 750 μm. The surface 2a of the wafer 2 has an effective area 8 in which multiple devices 4, such as ICs and LSIs, are defined by lattice-like dividing lines 6, and a chamfered portion 10 surrounding the periphery of the effective area 8. For convenience, the ring-shaped boundary 12 between the effective area 8 and the chamfered portion 10 is shown by a two-dot chain line in FIG. 1(a), but in reality, no line indicating the boundary 12 exists. The outer periphery of the chamfered portion 10 is chamfered to a curved surface, and a notch 14 indicating the crystal orientation is formed. When the single wafer 2 is processed, a circular protective tape 16 is attached to the surface 2a of the wafer 2.

[0017] (Bonded wafer 18) Not only a single wafer 2 can be processed by the method and apparatus according to the present invention, but also a bonded wafer 18 shown in FIGS. 2(a) and 2(b) can be processed. The bonded wafer 18 is formed by stacking and integrating a first wafer 2' and a second wafer 2" together. The configuration of the first and second wafers 2', 2" (for example, the devices 4 and the planned dividing lines 6) may be the same as that of the single wafer 2, and therefore the same reference numerals are used and a description thereof will be omitted.

[0018] When forming the bonded wafer 18, the effective region 8 of the first wafer 2' and the effective region 8 of the second wafer 2" are bonded together. At this time, the notch 14 of the first wafer 2' and the notch 14 of the second wafer 2" are aligned, and the first and second wafers 2' and 2" are bonded together with the crystal orientations of the first and second wafers 2' and 2" being the same. After the first and second wafers 2' and 2" are bonded together, they are preferably heat-treated to bond the first and second wafers 2' and 2" together by siloxane bonding.

[0019] (Modified layer forming process) In this embodiment, first, a modified layer formation process is carried out in which the focal point of a laser beam having a wavelength that is transparent to the wafer is positioned inside the boundary 12 between the effective area 8 and the chamfered portion 10, and the laser beam is irradiated onto the wafer to form a ring-shaped modified layer along the boundary 12.

[0020] The modified layer forming step can be performed using, for example, a laser processing apparatus 20 shown in Figures 3 and 4. The laser processing apparatus 20 includes a chuck table 22 that suction-holds the wafer, an oscillator (not shown) that oscillates a pulsed laser beam LB having a wavelength that is transparent to the wafer, and a condenser 24 (see Figure 4) that condenses the laser beam LB oscillated by the oscillator and irradiates the wafer with it.

[0021] As shown in Fig. 3, a circular suction chuck 26 is disposed on the upper end of the chuck table 22. The suction chuck 26 is formed from a porous material such as porous ceramics, and is connected to a suction means (not shown). The chuck table 22 is rotated by a motor (not shown) in the direction indicated by arrow R1 in Fig. 4.

[0022] An example of processing the first wafer 2' of the bonded wafers 18 will be mainly described below. In the modified layer forming step, the bonded wafer 18 is first held on the upper surface of the chuck table 22. At this time, the bonded wafer 18 is placed on the upper surface of the chuck table 22 with the center of rotation of the chuck table 22 aligned with the center of the first wafer 2'. At this time, the first wafer 2' from which the chamfered portion 10 is to be removed is positioned on top. Then, a suction force is generated on the upper surface of the suction chuck 26 by the suction means, and the second wafer 2'' side is suction-held on the upper surface of the suction chuck 26.

[0023] Once the bonded wafer 18 is suction-held on the chuck table 22, the ring-shaped boundary 12 to be irradiated with the laser beam LB is detected. At this time, the first wafer 2' is imaged from above using an imaging means (not shown) of the laser processing device 20, and the outer periphery and center position of the first wafer 2' are determined based on the image of the first wafer 2' captured by the imaging means. Next, the boundary 12 between the effective area 8 and the chamfered portion 10 is detected based on the outer periphery and center position of the first wafer 2'.

[0024] Once the boundary 12 to be irradiated with the laser beam LB has been detected, the focal point of the laser beam LB is positioned at a required position on the boundary 12. At this time, the height of the back surface 2b' of the first wafer 2' is detected by a height detection means (not shown) of the laser processing device 20. Then, using the detected height of the back surface 2b' as a reference, the focal point of the laser beam LB is positioned at a required position on the boundary 12 inside the first wafer 2'.

[0025] Once the focal point of the laser beam LB is positioned at the required position, the first wafer 2' is irradiated with the laser beam LB having a wavelength that is transparent to the first wafer 2' to form a ring-shaped modified layer along the boundary 12. That is, by irradiating the first wafer 2' with the laser beam LB while rotating the chuck table 22 in the direction indicated by the arrow R1 in Figure 4, a ring-shaped modified layer 28 is formed around the entire circumference of the ring-shaped boundary 12.

[0026] After one ring-shaped modified layer 28 (one circumference) has been formed, the height position of the focal point of the laser beam LB is shifted to a shallower position, and the laser beam LB is irradiated onto the first wafer 2' in the same manner as above. By repeating this process of shifting the height position of the focal point and irradiating the laser beam LB, multiple ring-shaped modified layers 28 are formed at intervals in the vertical direction, as shown in Figure 5(a) (Type 1).

[0027] Furthermore, as shown in Figure 5(b), by repeatedly changing the height position and radial position of the focal point of the laser beam LB and irradiating the laser beam LB, multiple ring-shaped modified layers 28 may be formed at intervals in the vertical and radial directions (Type 2).

[0028] Alternatively, as shown in Figure 5(c), multiple ring-shaped modified layers 28 may be formed at intervals in the vertical direction, and multiple ring-shaped modified layers 28 may be formed at intervals in the radial direction on the surface 2a' side (bonding surface side) of the first wafer 2' (Type 3).

[0029] Alternatively, as shown in Figure 5(d), multiple ring-shaped modified layers 28 may be formed at intervals in the vertical direction, and multiple ring-shaped modified layers 28 may be formed at intervals in the radial direction on the back surface 2b' side (exposed surface side) of the first wafer 2' (Type 4).

[0030] In any of the above types 1 to 4, after forming the ring-shaped modified layer 28 along the ring-shaped boundary 12, a modified layer 30 may be further formed from the boundary 12 toward the outer periphery of the chamfered portion 10, as shown in Fig. 6. That is, a plurality of linear modified layers 30 (three in the illustrated embodiment) extending radially from the ring-shaped modified layer 28 to the outer periphery of the first wafer 2' may be formed at equal intervals in the circumferential direction inside the first wafer 2'. By forming such radial modified layers 30, the chamfered portion 10 can be finely divided and effectively removed in the chamfered portion removing step described below.

[0031] Such a modified layer forming step can be carried out, for example, under the following processing condition 1 or processing condition 2. Note that the defocus described below is the amount of movement of the condenser 24 when the condenser 24 is moved toward the bonded wafer 18 from a state in which the focal point of the laser beam LB is positioned on the back surface 2b' (exposed surface) of the first wafer 2'. <Processing conditions 1> Laser beam wavelength: 1099nm Repetition frequency: 80kHz Feed speed: 450mm / s Average output: 2W Defocus (ring-shaped modified layer): 180 μm, 160 μm, 140 μm, 120μm, 100μm Defocus (radial modified layer): 150 μm (3 pieces) <Processing conditions 2> Laser beam wavelength: 1342nm Repetition frequency: 90kHz Feed speed: 400mm / s Average power: 1.9W Defocus (ring-shaped modified layer): 180 μm, 160 μm, 140 μm, 120μm, 100μm Defocus (radial modified layer): 150 μm (3 pieces)

[0032] The modified layers 28, 30 can also be formed in the same manner as above on the single wafer 2 shown in Fig. 1. However, when forming the modified layers 28, 30 on the single wafer 2, the back surface 2b of the single wafer 2 is faced upward, and the protective tape 16 side is held by suction on the chuck table 22 of the laser processing device 20.

[0033] (chamfered portion removal process) After the modified layer formation process is performed, the position where the modified layer 28 is formed is detected, and a chamfer removal process is performed in which a sharp tool is inserted into the detected position and the wafer and the tool are rotated relative to each other along the modified layer 28 to remove the chamfer.

[0034] (chamfer removal device 32) The chamfer removing step can be performed using, for example, a chamfer removing device 32 shown in Fig. 7. The chamfer removing device 32 includes a holding means 34 that holds a wafer and has a rotatable holding table, an imaging means 36 that is disposed opposite the holding table and captures an image of the wafer held on the holding table, and a tool means 38 that inserts a sharp tool into the position of the modified layer 28 detected by the imaging means 36.

[0035] (Holding means 34) The holding means 34 includes a rotatable holding table 40 that holds a wafer, and a motor 42 that rotates the holding table 40. A circular suction chuck 44 is disposed on the upper end of the holding table 40. The suction chuck 44 is formed from a porous material such as porous ceramics. The suction chuck 44 is also connected to a suction means (not shown). The holding table 40 generates a suction force on the upper surface of the suction chuck 44 by the suction means, thereby suction-holding the wafer. A rotation shaft 42a of the motor 42 is connected to the lower center of the holding table 40, and the motor 42 rotates the holding table 40 in the direction indicated by arrow R2, with the vertical axis as its axis.

[0036] (imaging means 36) The imaging means 36 is disposed above the holding table 40 and facing the holding table 40. The imaging means 36 in this embodiment is an infrared camera, and is configured to capture an image of the inside of the wafer held on the holding table 40.

[0037] (Tool means 38) The tool means 38 includes a support wall 46 installed adjacent to the holding means 34, a lifting arm 48 supported by the support wall 46 and extending substantially horizontally so as to be movable in the vertical direction indicated by the arrow Z, a movable member 50 supported by the lifting arm 48 and movable in the substantially horizontal direction indicated by the arrow X, a holding piece 52 fixed to the lower surface of the movable member 50, and a sharp tool 54 held at the lower end of the holding piece 52. The tool 54 may be, for example, a needle-shaped member extending in the vertical direction. The tool means 38 of this embodiment further includes a nozzle 56 that sprays air toward the outer periphery of the wafer held on the holding table 40 of the holding means 34, and air supply means (not shown) that supplies air to the nozzle 56.

[0038] In the chamfer removal step of this embodiment, first, the bonded wafer 18 is held by the holding means 34. At this time, the bonded wafer 18 is placed on the upper surface of the holding table 40 with the first wafer 2′ on which the modified layer 28 has been formed facing upward. The center of rotation of the holding table 40 is aligned with the center of the first wafer 2′. Then, a suction force is generated on the upper surface of the suction chuck 44 by the suction means, and the second wafer 2″ side of the bonded wafer 18 is suction-held on the upper surface of the suction chuck 44.

[0039] Once the bonded wafer 18 is held by the holding means 34, the position on the first wafer 2' where the ring-shaped modified layer 28 is formed is detected. To do this, first, the imaging means 36 is positioned above the boundary portion 12 of the first wafer 2'. Then, while rotating the holding table 40 in the direction indicated by arrow R2 in FIG. 7, the infrared camera of the imaging means 36 captures an image of the inside of the first wafer 2'. In this way, the position on the first wafer 2' where the ring-shaped modified layer 28 is formed is detected.

[0040] Once the position on the first wafer 2' where the modified layer 28 has been formed has been detected, the chamfered portion 10 is removed from the first wafer 2' using a tool 54. To do this, first, the rotation of the holding table 40 is stopped. Next, as shown in FIG. 8, a sharp tool 54 is inserted into the detected position of the modified layer 28. Then, the holding table 40 is rotated in the direction indicated by arrow R2. This allows the chamfered portion 10 to be completely removed from the outer periphery of the first wafer 2' (see FIG. 9). Thereafter, it is desirable to spray air from a nozzle 56 onto the first wafer 2' from which the chamfered portion 10 has been removed to remove processing debris.

[0041] When removing the chamfered portion 10, the tool means 38 may be configured to move a sharp tool 54 radially in accordance with the eccentricity of the first wafer 2'. In the modified layer forming step described above, the ring-shaped modified layer 28 is formed so that the center of the first wafer 2' and the center of the ring-shaped modified layer 28 coincide with each other. However, the center of the first wafer 2' and the center of the ring-shaped modified layer 28 may be slightly misaligned. Even if the center of the first wafer 2' and the center of the ring-shaped modified layer 28 precisely coincide with each other, the center of the first wafer 2' and the center of rotation of the holding table 40 may be slightly misaligned when the bonded wafer 18 is held on the holding table 40 in the chamfered portion removing step.

[0042] Therefore, when removing the chamfered portion 10, the tool means 38 preferably moves the movable member 50 appropriately in accordance with the eccentricity of the first wafer 2' relative to the center of rotation of the holding table 40, based on the position of the ring-shaped modified layer 28 detected by the infrared camera of the imaging means 36, and moves the sharp tool 54 radially so as to coincide with the position of the ring-shaped modified layer 28. This makes it possible to completely remove the chamfered portion 10 from the outer periphery of the first wafer 2' along the ring-shaped modified layer 28, even if the above-mentioned misalignment occurs.

[0043] (Processing process) After the chamfered portion removing step is performed, a processing step is performed in which the back surface of the wafer is ground to a desired thickness.

[0044] (Grinding equipment 58) The processing step can be performed using, for example, a grinding device 58 shown in Fig. 10. The grinding device 58 includes a chuck table 60 that holds a wafer by suction, and grinding means 62 that grinds the wafer held by suction on the chuck table 60. The grinding means 62 includes a spindle 64 that extends in the vertical direction, and a disk-shaped wheel mount 66 fixed to the lower end of the spindle 64. An annular grinding wheel 70 is fastened to the lower surface of the wheel mount 66 by bolts 68. A plurality of grinding stones 72 are fixed to the outer periphery of the lower surface of the grinding wheel 70, and are arranged in an annular shape at intervals in the circumferential direction.

[0045] In the processing steps of this embodiment, first, the back surface 2b' of the first wafer 2' is faced upward, and the second wafer 2" side is suction-held on the upper surface of the chuck table 60. Next, the chuck table 60 is rotated in the direction indicated by arrow R3 at a predetermined rotational speed (e.g., 300 rpm). Also, the spindle 64 is rotated in the direction indicated by arrow R4 at a predetermined rotational speed (e.g., 6000 rpm). Next, the spindle 64 is lowered to bring the grinding wheel 72 into contact with the back surface 2b' of the first wafer 2', and grinding water is supplied to the portion of the back surface 2b' of the first wafer 2' where the grinding wheel 72 is in contact. Thereafter, the spindle 64 is lowered at a predetermined grinding feed rate (e.g., 1.0 μm / s). This allows the back surface 2b' of the first wafer 2' to be ground to process the first wafer 2' to a desired thickness.

[0046] As described above, in this embodiment, the chamfered portion 10 can be completely removed from the outer periphery of the wafer, which eliminates problems such as the remaining portion falling off in a later process and becoming a source of contamination, or causing chipping of device chips when the wafer is divided into individual device chips. [Explanation of symbols]

[0047] 2: Single wafer 2a: Surface of wafer 2b: Backside of wafer 2': First wafer 2a': Surface of the first wafer 2b': Back surface of the first wafer 2": Second wafer 2a″: Surface of the second wafer 2b": Backside of the second wafer 8: Effective area 10: Chamfered part 12: Boundary 18: Bonded wafer 28: Ring-shaped modified layer 32: Chamfer removal device 34: Holding means 36: Imaging means 38: Tool means 40: Holding table 54: Tools 56: Nozzle LB: Laser beam

Claims

1. A method for processing a wafer having an effective area formed on a surface and a chamfered portion surrounding an outer periphery of the effective area, comprising: a modified layer forming step of irradiating the wafer with a laser beam having a wavelength that is transparent to the wafer, with the focused point positioned within the boundary between the effective area and the chamfered portion, to form a ring-shaped modified layer along the boundary; a chamfer removing step of detecting the position where the modified layer is formed, inserting a sharp tool into the detected position, and rotating the wafer and the tool relatively along the modified layer to remove the chamfer; and a processing step of grinding the back surface of the wafer to a desired thickness.

2. 2. The wafer processing method according to claim 1, wherein in the modified layer forming step, a modified layer is further formed from the boundary portion toward the outer periphery of the chamfered portion.

3. the wafer is a bonded wafer in which an effective region of a first wafer and an effective region of a second wafer are bonded together; 3. The wafer processing method according to claim 1, wherein the modified layer forming step, the chamfer removing step, and the processing step are carried out on a first wafer.

4. A chamfer removing device for performing the chamfer removing step according to claim 1, a holding means having a rotatable holding table for holding the wafer; an imaging means disposed opposite the holding table for imaging the wafer held on the holding table; and tool means for inserting the tool into the position of the modified layer detected by the imaging means.

5. 5. The chamfer removing apparatus according to claim 4, wherein said imaging means is an infrared camera for imaging the inside of the wafer.

6. 5. The chamfer removing apparatus according to claim 4, wherein said tool means moves said tool in a radial direction in accordance with the eccentricity of the wafer.

7. 5. The chamfer removing apparatus according to claim 4, wherein said tool means comprises a nozzle for ejecting air, and ejects air onto the wafer from which said chamfer has been removed to remove processing debris.

Images