Method for processing a wafer

Abstract

The present invention provides a method for processing a wafer. When processing a wafer having a two-layer structure, even if the back surface of the wafer is ground and thinned, no blade is formed on the outer periphery, and the problem that the notch indicating the crystal orientation disappears and causes an obstacle to the processing in subsequent processes can be solved. The method for processing the wafer processes a wafer having a two-layer structure formed by laminating a second wafer on the front surface of a first wafer. The method for processing the wafer includes the following steps: a step difference portion forming step of cutting from the second wafer side until reaching the outer peripheral remaining region of the first wafer and a depth corresponding to the finished thickness of the first wafer, removing the chamfered portion formed at the outer peripheral end of the second wafer, and forming an annular step difference portion in the outer peripheral remaining region of the first wafer; and a second wafer grinding step of grinding the exposed surface of the second wafer after the step difference portion forming step is performed to form the second wafer into a predetermined thickness.

Description

Technical Field

[0001] The present invention relates to a method for processing wafers, and processes wafers having a two-layer structure obtained by laminating a second wafer on the front surface of a first wafer. Background Art

[0002] On the front surface of a wafer, there are a device region in which a plurality of devices such as ICs and LSIs are formed by being divided by a plurality of intersecting division predetermined lines, and a peripheral remaining region surrounding the device region. After the wafer 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 the divided device chips are used in electronic devices such as mobile phones and personal computers.

[0003] In addition, for a wafer having a two-layer structure obtained by bonding the front surfaces on which devices are formed to each other, after the back surfaces of the respective wafers are similarly ground to a predetermined thickness, they are divided into individual device chips by a cutting device or a laser processing device (for example, refer to Patent Document 1).

[0004] Patent Document 1: Japanese Patent Laid-Open No. 2010-225976

[0005] When thinning by grinding the back surfaces of one wafer and the other wafer of the above two-layer structure wafer, the chamfered portion formed at the outer peripheral end of the wafer becomes as sharp as a blade and thins, and sometimes defects are generated during grinding. There is a problem that cracks reach the device region from the defect and damage the devices formed on the wafer. Therefore, it is considered to cut and remove the chamfered portion formed at the outer peripheral end of the wafer before grinding the back surface of the wafer, thereby solving the above problem.

[0006] However, when processing a two-layer structure wafer obtained by bonding the front surfaces to each other as described above, if the chamfered portions formed at the outer peripheral ends of the respective wafers are cut and removed before grinding the exposed surface (back surface) of the wafer, the notches formed as marks indicating the crystal orientation of the wafer will disappear, and from an appearance perspective, the crystal orientation is not clear. As a result, there is a problem of causing an obstacle to the processing in subsequent processes. Summary of the Invention

[0007] Accordingly, an object of the present invention is to provide a method for processing wafers, which can prevent the formation of a blade at the outer periphery even when the back surface of the wafer is ground and thinned during the processing of a two-layer structure wafer, and can solve the problem that the notch indicating the crystal orientation disappears and causes an obstacle to the processing in subsequent processes.

[0008] According to the present invention, there is provided a method for processing a wafer, which processes a wafer having a two-layer structure formed by laminating a second wafer on the front surface of a first wafer. The first wafer has a device region formed by dividing a plurality of intersecting division predetermined lines on the front surface to form a plurality of devices and an outer peripheral remaining region surrounding the device region. The method for processing the wafer has the following steps: a step difference portion forming step of cutting from the second wafer side until reaching the outer peripheral remaining region of the first wafer and a depth corresponding to the finished thickness of the first wafer, removing the chamfered portion formed at the outer peripheral end of the second wafer, and forming an annular step difference portion in the outer peripheral remaining region of the first wafer; a second wafer grinding step of grinding the exposed surface of the second wafer after the step difference portion forming step to make the second wafer have a prescribed thickness; an annular modified layer forming step of irradiating with a laser beam having a wavelength transmissive to the first wafer with the focal point positioned inside the root of the step difference portion formed in the outer peripheral remaining region of the first wafer after the second wafer grinding step to form an annular modified layer; a protective tape disposing step of disposing a protective tape having a size corresponding to the first wafer on the exposed surface of the second wafer after the annular modified layer forming step; and a first wafer grinding step of grinding the exposed surface of the first wafer after the protective tape disposing step to stimulate the modified layer, separating an annular region including the step difference portion from the first wafer along the modified layer and dropping it onto the protective tape, and grinding the first wafer to the finished thickness.

[0009] Preferably, it has a cutting groove forming step as follows: after the second wafer grinding step and before the protective tape disposing step, cutting from the second wafer side to form a cutting groove, the cutting groove reaching the division predetermined line of the first wafer and including a groove having a depth corresponding to the finished thickness of the first wafer, and in the first wafer grinding step, dividing the two-layer structure wafer into individual device chips.

[0010] Preferably, it has a division predetermined line modified layer forming step as follows: after the second wafer grinding step and before the protective tape disposing step, irradiating a laser beam having a wavelength transmissive to the first wafer and the second wafer from the second wafer side to form a modified layer reaching the division predetermined line of the first wafer, and in the first wafer grinding step, dividing the two-layer structure wafer into individual device chips.

[0011] According to the present invention, even when grinding a wafer having a two-layer structure to thin one of the wafers, no blade is formed on the outer periphery, thereby solving the problem that a defect is generated during grinding and a crack reaches the device region, resulting in device damage. In addition, even when grinding the back surface of the first wafer to make the first wafer have a predetermined thickness, since an annular region including a step difference portion formed at the outer peripheral end of the first wafer peels off and transfers to the protective tape, the notch indicating the crystal orientation is retained, thereby solving the problem of causing an obstacle to the processing in subsequent processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 FIG. is a perspective view showing a manner of forming a two-layer structure by bonding the front surfaces of the first wafer and the second wafer to each other and the wafer having the two-layer structure.

[0013] Figure 2 (a) of FIG. is a perspective view showing an embodiment of a step difference portion forming process, Figure 2 and (b) of FIG. is an enlarged cross-sectional view showing a part of the manner of implementing the step difference portion forming process. Figure 2 and (c) of FIG. is a perspective view of the wafer having the step difference portion formed thereon.

[0014] Figure 3 FIG. is a perspective view showing a manner of placing the wafer on the chuck table when implementing the second wafer grinding process.

[0015] Figure 4 (a) of FIG. is a perspective view showing an embodiment of the second wafer grinding process, Figure 4 and (b) of FIG. is an enlarged cross-sectional view showing a part of the wafer after implementing the second wafer grinding process.

[0016] Figure 5 FIG. is a perspective view showing an embodiment of the protective tape disposing process.

[0017] Figure 6 (a) of FIG. is a perspective view showing an embodiment of the annular modification layer forming process, Figure 6 and (b) of FIG. is an enlarged cross-sectional view showing a part of the embodiment shown in (a) of FIG. Figure 6 FIG. is a perspective view showing a manner of placing the wafer on the chuck table for implementing the first wafer grinding process.

[0018] Figure 7 FIG. is a perspective view showing an embodiment of the first wafer grinding process.

[0019] Figure 8 (a) of FIG. is a perspective view showing an embodiment of the first wafer grinding process, Figure 8 and (b) of FIG. is a partially enlarged cross-sectional view showing the grinding process of the first wafer grinding process.

[0020] Figure 9 FIG. (a) is a perspective view of a wafer processed according to this embodiment, Figure 9 and FIG. (b) is a perspective view of another wafer processed according to another embodiment.

[0021] Figure 10 FIG. (a) is a perspective view showing an embodiment of a cutting groove forming process and a partial enlarged cross-sectional view of a wafer having a cutting groove formed therein, Figure 10 and FIG. (b) is a perspective view showing an embodiment of a modified layer forming process for a dicing line and a cross-sectional view showing a part of a wafer having a modified layer formed therein enlarged.

[0022] Reference Numeral Explanation

[0023] 10: First wafer; 10a: Front surface; 10b: Back surface; 10c: Device region; 10d: Outer peripheral remaining region; 10e: Chamfered portion; 10f: Notch (cut portion); 10g: Finished thickness; 10h: Step difference portion; 12: Device; 14: Dicing line; 18: Device chip; 20: Second wafer; 20a: Front surface; 20b: Back surface; 20c: Device region; 20d: Outer peripheral remaining region; 20e: Chamfered portion; 20f: Notch; 22: Device; 24: Dicing line; 30: First cutting device; 31: Spindle housing; 32: Spindle; 33: Cutting tool; 40: Grinding device; 41: Chuck table; 41a: Holding surface; 42: Holding surface; 43: Spindle; 45: Grinding wheel; 46: Grinding tool; 50: Second cutting device; 51: Cutting unit; 52: Spindle housing; 53: Spindle; 54: Cutting tool; 70: First laser processing device; 72: Laser beam irradiation unit; 74: Condenser; 80: Second laser processing device; 82: Laser beam irradiation unit; 84: Condenser; 100: Modified layer; 110: Cutting groove; 120: Modified layer; W: Wafer; LB1, LB2: Laser beams. Detailed Embodiment

[0024] Hereinafter, a method for processing a wafer according to an embodiment of the present invention will be described in detail with reference to the drawings.

[0025] In Figure 1 FIG., a method of bonding the front surfaces of the first wafer 10 and the second wafer 20 to each other to form a two-layer structure and a perspective view of the wafer W formed into the two-layer structure are shown. The first wafer 10 is made of, for example, a silicon substrate, and a plurality of devices 12 are formed on the front surface 10a divided by dicing lines 14, and has a device region 10c in which a plurality of devices 12 are formed and an outer peripheral remaining region 10d surrounding the device region 10c. A chamfered portion 10e obtained by removing upper and lower corner portions is formed at the outer peripheral end of the outer peripheral remaining region 10d, and a notch (cut) 10f indicating the crystal orientation of the wafer 10 is formed.

[0026] The second wafer 20 has substantially the same structure as the first wafer 10, for example, is made of a silicon substrate. On the front surface 20a, a plurality of devices 22 are formed by being divided by dicing predetermined lines 24, and there are a device region 20c where a plurality of devices 22 are formed and an outer peripheral remaining region 20d surrounding the device region 20c. A chamfered portion 20e is formed at the outer peripheral end of the outer peripheral remaining region 20d, and a notch (cut) 20f showing the crystal orientation of the wafer 20 is formed.

[0027] In the case of forming a two-layer structure wafer W by the above-mentioned first wafer 10 and second wafer 20, as Figure 1 shown in the upper part, the second wafer 20 is turned over so that the back surface 20b faces upward, and while aligning using the notch 10f of the first wafer 10 and the notch 20f of the second wafer 20, the second wafer 20 is bonded to the front surface 10a of the first wafer 10. When bonding the second wafer 20 to the first wafer 10, an adhesive (not shown) can be applied to the front surface 10a of the first wafer 10 to become integrated. The dicing predetermined line 14 formed on the first wafer 10 and the dicing predetermined line 24 formed on the second wafer 20 are set in a completely coincident manner when the first wafer 10 and the second wafer 20 are bonded. Thus, when the wafer W is diced into individual device chips, the wafer W is diced along these dicing predetermined lines 14, 24. In this way, the first wafer 10 and the second wafer 20 are laminated to form the two-layer structure wafer W to be processed in the processing method of the present embodiment. In addition, as can be understood from the enlarged cross-sectional view of a part of the outer peripheral end of the wafer W shown in the lowermost part of Figure 1 , chamfered portions 10e and 20e are formed at the outer peripheral ends of the first wafer 10 and the second wafer 20 constituting the wafer W, and the chamfered portions 10e and 20e are chamfered by removing the upper and lower corner portions of the outer peripheral end.

[0028] If the above two-layer structure wafer W is prepared, the wafer W is carried into Figure 2 the first cutting device 30 (only a part is shown) shown in (a) of

[0029] The first cutting device 30 has, for example: a suction and holding table (not shown); a spindle housing 31 (shown by a double-dot chain line); a spindle 32 held by the spindle housing 31; a cutting tool 33 fixed to the front end of the spindle 32; and a drive motor (not shown) that rotates the spindle 32 at the rear end of the spindle housing 31. Figure 2As shown in (a) thereof, the cutting tool 33 is positioned at the outer peripheral end of the wafer W held by the suction holding table. More specifically, the cutting tool 33 is positioned above a region including the chamfered portion 20e formed at the outer peripheral end of the second wafer 20. Next, the cutting tool 33 is rotated in the direction shown by the arrow R1, and the wafer W is rotated in the direction shown by the arrow R2. As shown in Figure 2 (b) thereof, the cutting tool 33 is lowered to remove the region including the chamfered portion 20e of the second wafer 20 along the entire circumference, and cutting is performed until reaching the first wafer 10 and a depth corresponding to the finished thickness of the first wafer 10 (shown as 10g in the figure). Since the outer peripheral end face of the cutting tool 33 is formed as a flat surface as shown in the figure, as shown in Figure 2 (b) and Figure 2 (c) thereof, an annular stepped portion 10h is formed along the entire circumference on the first wafer 10 (stepped portion forming process). In addition, it can be understood from Figure 2 (c) that the notch 20f of the second wafer 20 is completely removed, but the notch 10f of the first wafer 10 is retained.

[0030] Next, a second wafer grinding process is performed in which the back surface 20b side, which is the exposed surface of the second wafer 20, is ground to a predetermined thickness. When performing the second wafer grinding process, the wafer W is transported to the Figure 3 , Figure 4 shown grinding device 40 (only a part is shown). The grinding device 40 has a chuck table 41. The chuck table 41 is configured to be rotatable by a rotation drive mechanism (not shown), and the holding surface 41a is made of a porous material having air permeability. The chuck table 41 is connected to a suction source (not shown), and a negative pressure is generated on the holding surface 41a of the chuck table 41 by operating the suction source. In addition, as shown in Figure 4 (a) thereof, the grinding device 40 has a grinding unit 42 for grinding and thinning the wafer W placed on the chuck table 41. The grinding unit 42 has: a main shaft 43 rotated by a rotation drive mechanism (not shown); a mounting base 44 mounted on the lower end of the main shaft 43; and a grinding wheel 45 mounted on the lower surface of the mounting base 44. A grinding abrasive 46 is arranged in a ring shape on the lower surface of the grinding wheel 45.

[0031] If the wafer W is transported to the grinding device 40, as shown in Figure 3 shown, it is placed on the holding surface 41a of the chuck table 41 with the first wafer 10 side of the wafer W facing downward and the second wafer 20 side facing upward, and the suction source is operated to perform suction holding. In addition, when holding the wafer W on the chuck table 41, a protective tape can be disposed between the first wafer 10 and the chuck table 41.

[0032] If the wafer W is attracted and held on the chuck table 41, while rotating the main shaft 43 of the grinding unit 42 in the direction indicated by the arrow R3 in (a) of Figure 4 at, for example, 6000 rpm, the chuck table 41 is rotated in the direction indicated by the arrow R4 at, for example, 300 rpm. Then, the grinding unit 42 is lowered so that the grinding tool 46 contacts the back surface 20b of the second wafer 20, and the grinding wheel 45 is fed in a direction perpendicular to the second wafer 20 at a grinding feed rate of, for example, 1 μm / sec. At this time, grinding can be performed while measuring the thickness of the wafer W with a contact-type measuring instrument (not shown). As shown in Figure 4 (b), the back surface 20b of the second wafer 20 is ground to make the second wafer 20 have a prescribed thickness, completing the second wafer grinding process. In the present embodiment, since the outer periphery including the chamfered portion 20e of the second wafer 20 is removed in advance, even if the back surface 20b of the second wafer 20 is ground and thinned, no blade is formed at the outer peripheral end of the second wafer 20, solving the problem that defects are generated during grinding and cracks reach the device region 20c of the second wafer 20, thereby damaging the device 22.

[0033] If the second wafer grinding process is completed, the following processes are performed: an annular modification layer forming process of forming an annular modification layer inside the root of the step portion 10h in the outer peripheral remaining region 10d formed on the first wafer 10; and a protective tape disposing process of disposing a protective tape T having a size corresponding to the first wafer 10 on the exposed surface (back surface 20b) side of the second wafer 20. In the present embodiment, first, as shown in Figure 5 , a protective tape T having a size corresponding to the first wafer 10 is disposed and adhered to the back surface 20b of the second wafer 20 (protective tape disposing process).

[0034] Next, the wafer W with the protective tape T adhered is transferred to the Figure 6 first laser processing apparatus 70 shown in (a) of

[0035] If as shown in Figure 6As shown in (a) of , the wafer W is transferred to the first laser processing device 70, and is placed and sucked and held on the chuck table in such a manner that the first wafer 10 constituting the wafer W is located above and the protective tape T is located below. Next, the condenser 74 of the laser beam irradiation unit 70 is positioned on the outer peripheral side of the first wafer 10. Then, as shown in (a) of Figure 6 and (b) of Figure 6 , the condensing point of the laser beam LB1 is positioned inside the root of the step portion 10h formed on the first wafer 10 and irradiated, and the wafer W is rotated in the direction indicated by the arrow R5 in Figure 6 (a). In addition, the condensing point of the laser beam LB1 is positioned at a plurality of positions different in the thickness direction of the wafer W, and the wafer W is rotated in the direction indicated by the arrow R5, thereby repeatedly performing laser processing. Thus, as shown in (b) of Figure 6 , an annular modified layer 100 is formed along the inside of the root of the step portion 10h (annular modified layer forming step). In addition, when forming the modified layer 100, the condensing point may be initially positioned near the root of the step portion 10h to start the irradiation of the laser beam LB1, and the modified layer 100 may be formed in such a manner that as the condensing point moves toward the back surface 10b side of the first wafer 10, the modified layer 100 gradually expands toward the outer peripheral end side of the wafer W, i.e., obliquely.

[0036] In addition, the laser processing conditions during the above-described annular modified layer forming step are set as follows, for example.

[0037]

[0038] In the above-described embodiment, after performing the protective tape disposition step, the annular modified layer forming step is performed by irradiating the laser beam LB1 from the back surface 10b side of the first wafer 10, but the present invention is not limited thereto. For example, the annular modified layer forming step may be performed by irradiating the laser beam LB1 from the back surface 20b side of the second wafer 20. In this case, before performing the protective tape disposition step on the wafer W after performing the above-described second wafer grinding step, the wafer W is transferred to the first laser processing device 70 shown in (a) of Figure 6 , and is placed on a chuck table (not shown) in such a manner that the back surface 10b of the first wafer 10 faces downward and the back surface 20b side of the second wafer 20 faces upward. And, the condensing point of the laser beam LB1 is positioned inside the root of the step portion 10h of the first wafer 10 from above and irradiated, and the wafer W is rotated in the direction indicated by the arrow R5 together with the chuck table to form a modified layer similar to the above-described modified layer 100. After performing this annular modified layer forming step, the protective tape disposition step described with reference to Figure 5 is performed.

[0039] If the above-described annular modification layer forming step and protective tape disposing step are carried out, the wafer W is transported to the grinding apparatus 40 for carrying out the first wafer grinding step on the wafer W provided with the protective tape T. Figure 7 and Figure 8 shown grinding apparatus 40. In addition, since the grinding apparatus 40 used for carrying out the second wafer grinding step described above is used, detailed description thereof is omitted.

[0040] If the wafer W is transported to the grinding apparatus 40, as Figure 7 shown, the transported wafer W is placed on the holding surface 41a of the chuck table 41 in such a manner that the protective tape T side faces downward and the back surface 10b of the first wafer 10 faces upward, and is sucked and held. If the wafer W is sucked and held on the chuck table 41, while rotating the main shaft 43 of the grinding unit 42 in the direction of the arrow R3 shown in (a) of Figure 8 at, for example, 6000 rpm, the chuck table 41 is rotated in the direction of the arrow R4 at, for example, 300 rpm. And, the grinding tool 46 is brought into contact with the back surface 10b of the first wafer 10, and the grinding wheel 45 is fed in the direction perpendicular to the first wafer 10 at a grinding feed rate of, for example, 1 μm / second. At this time, grinding can be carried out while measuring the thickness of the wafer W by a contact type measuring instrument (not shown). Here, with reference to Figure 8 the function of the modification layer 100 formed by the above-described annular modification layer forming step is described.

[0041] As Figure 8 (a) shown, when grinding the back surface 10b of the first wafer 10, Figure 8 the thickness of the first wafer 10 shown in the upper part of (b) of Figure 8 slowly decreases. At this time, a strong stimulus (external force) such as rotational vibration and pressing force is applied to the wafer W from the grinding tool 46 of the grinding unit 42. This stimulus acts on the annular modification layer 100 formed inside the first wafer 10, and slowly cracks extend from the modification layer 100 in the vertical direction, and an annular region including the chamfered portion 10e and the step portion 10h slowly separates from the first wafer 10 along the modification layer 100. And, the ring member 11 composed of the annular region including the step portion 10h is completely separated from the first wafer 10 as shown in the lower part of (b) of Figure 9 and falls onto the protective tape T in the direction of the arrow R6. Adhesive force is imparted to the protective tape T, and the ring member 11 falling from the first wafer 10 is strongly pressed from above by the grinding unit 42, so that the ring member 11 does not rotate but adheres to the protective tape T. And, the ring member 11 is ground together with the first wafer 10, and the wafer W having a two-layer structure in which the first wafer 10 and the second wafer 20 are laminated becomes a prescribed thickness and becomes the state shown in (a) of

[0042] As described above, the ring member 11 falls and adheres to the protective tape T without rotating relative to the state before being separated from the first wafer 10. Thus, even after the ring member 11 is separated from the first wafer 10 and falls, the position of the notch 10f of the first wafer 10 remaining in the ring member 11 not only shows the crystal orientation of the first wafer 10 but also shows the crystal orientation of the second wafer 20. In other processes such as the process of dividing the wafer W into individual device chips by a cutting device or a laser processing device after the above-mentioned first wafer grinding process, it can also be used as a notch showing the crystal orientation of the wafer W, solving the problem of obstacles caused by unclear crystal orientation in subsequent processes. In addition, by retaining the ring member 11, the outer diameter of the wafer W including the ring member 11 is maintained relative to the state before processing, and the problem that the outer diameter size of the wafer W becomes smaller and inconsistent with the size of the chuck table when the chamfered portions 10e and 20e are removed is also solved. In addition, when forming the modified layer 100 in the above-mentioned annular modified layer forming process, the laser beam LB1 is initially irradiated with the focus positioned near the root of the step difference portion 10h, and the modified layer 100 is formed in such a way that as the focus moves toward the back surface 10b side of the first wafer 10, the modified layer 100 slowly expands toward the outer peripheral end side of the wafer W, that is, obliquely. In this first wafer grinding process, the falling of the ring member 11 becomes easier.

[0043] According to the present invention, various modifications are provided without being limited to the above-described embodiments. For example, in the above-described embodiment, after the second wafer grinding process, the protective tape arranging process is then performed, but the present invention is not limited thereto, and the process of forming a division starting point for dividing the wafer W into individual device chips can be performed at any time between after the second wafer grinding process and before performing the protective tape arranging process. Hereinafter, with reference to Figure 10 Specific examples of the process of forming the above division starting point will be described. In addition, all the processes described below are described as processes performed after the above-mentioned second wafer grinding process and before performing the annular modified layer forming process, and can also be performed after the annular modified layer forming process and before performing the protective tape arranging process.

[0044] In Figure 10 (a) shows an embodiment of the following process (cutting groove forming process): after the second wafer grinding process, cutting is performed from the second wafer 20 side to form a cutting groove that reaches the first wafer 10 and includes a groove having a depth corresponding to the finished thickness of the first wafer 10, and this cutting groove is used as the division starting point for dividing the wafer W into individual device chips.

[0045] The wafer W after the second wafer grinding process is transported toFigure 10 The second cutting device 50 shown in (a) of the figure. The second cutting device 50 has: a chuck table (not shown) for sucking and holding the wafer W; a cutting unit 51; and a moving unit (not shown) for relatively moving the chuck table and the cutting unit 51 in the X-axis direction shown by arrow X, the Y-axis direction shown by arrow Y, and the rotation direction. The cutting unit 51 has: a cutting tool 54 fixed to the front end of a spindle 53 supported by a spindle housing 52 and having a cutting edge on its outer periphery; and a tool cover 55 for protecting the cutting tool 54. On the tool cover 55, a cutting water supply unit 56 is disposed at a position adjacent to the cutting tool 54 to supply cutting water introduced through the tool cover 55 toward the cutting position. A rotation drive source such as a motor (not shown) is disposed on the other end side of the spindle 53, and the spindle 53 is rotated by this rotation drive source so that the cutting tool 54 rotates in the direction shown by arrow R7.

[0046] When performing the cutting groove forming process by the above-described second cutting device 50, first, the wafer W held by the chuck table is photographed using an alignment photographing unit (not shown). The photographing unit includes an infrared irradiation unit and an infrared camera capable of detecting the division predetermination lines 14 and 24 on the front surface 10a of the first wafer 10 and the front surface 20a of the second wafer 20 through the wafer W, and detects the positions of the division predetermination lines 14 and 24 (refer to Figure 1 ) formed on the front surfaces 10a and 20a of the first wafer 10 and the second wafer 20 that constitute the wafer W. If the division predetermination lines 14 and 24 are detected and the position information is stored in an appropriate control unit (not shown), then based on this position information, the wafer W held by the chuck table and the cutting unit 51 are relatively moved in the X-axis direction for machining feed, and indexing feed is appropriately performed in the Y-axis direction, so that as shown in the lower part of (a) of Figure 10 , cutting is performed from the second wafer 20 side, and cutting grooves 110 are formed along the division predetermination lines 14 and 24. The cutting grooves 110 reach the first wafer 10 and include grooves 110a having a depth corresponding to the finished thickness of the first wafer 10. In addition, the chuck table is rotated by 90°, and cutting grooves 110 are similarly formed along the division predetermination lines 14 and 24 in a direction perpendicular to the previously formed cutting grooves 110. Thus, cutting grooves 110 are formed along all the division predetermination lines 14 and 24 of the wafer W.

[0047] When performing this cutting groove forming process at an arbitrary timing after the second wafer grinding process and before the protective tape disposition process based on the above-described wafer processing method, when performing the first wafer grinding process described with reference to Figure 8 and making the first wafer 10 reach the finished thickness, as shown in Figure 8As shown in (b) thereof, the ring member 11 including the stepped difference portion 10h separates along the modified layer 100 and falls in the direction shown by the arrow R6, and as Figure 9 shown in (b) thereof, the wafer W is divided into individual device chips 18 along the dicing grooves 110.

[0048] As a process for forming a dicing start point when dividing the wafer W into individual device chips, instead of the above-described dicing groove forming process, a dividing predetermined line modified layer forming process for forming a modified layer reaching the first wafer 10 from the second wafer 20 side may be performed. Refer to Figure 10 (b) thereof for a more specific description.

[0049] The wafer W that has undergone the second wafer grinding process is transferred to Figure 10 the second laser processing apparatus 80 shown in (b) thereof. The second laser processing apparatus 80 includes: a chuck table (not shown); a laser beam irradiation unit 82; and a moving unit (not shown) that relatively moves the chuck table and the laser beam irradiation unit 82. The laser beam irradiation unit 82 includes an optical system (both not shown) including a laser oscillator that oscillates a laser beam having a wavelength that is transmissive to the first wafer 10 and the second wafer 20, an output adjustment unit, etc., and has a function of irradiating the laser beam LB2 from a condenser 84 including a condenser lens.

[0050] When performing the dividing predetermined line modified layer forming process by the above-described second laser processing apparatus 80, first, the wafer W held by the chuck table is photographed using a photographing unit for alignment (not shown). The photographing unit includes an infrared irradiation unit and an infrared camera that can detect the dividing predetermined line 14 and the dividing predetermined line 24 on the front surface 10a of the first wafer 10 and the front surface 20a of the second wafer 20 through the wafer W, and photographs the regions to be processed, that is, the dividing predetermined lines 14, 24 (refer to Figure 1) The overlapping positions are detected. If the dividing predetermined lines 14 and 24 are detected and the position information is stored in an appropriate control unit (not shown), then based on this position information, the condenser 84 is positioned above the processing start positions of the dividing predetermined lines 14 and 24 of the wafer W held by the chuck table. Next, the vertical position of the condenser 84 is adjusted to position the focus point of the laser beam LB2 near the depth position that becomes the finished thickness of the first wafer 10. Further, based on this position information, the wafer W held by the chuck table and the laser beam irradiation unit 82 are relatively moved in the X-axis direction for processing feed, and appropriately indexed in the Y-axis direction, so as to form the modified layer 120 along all the dividing predetermined lines 14 and 24 of the wafer W. In addition, the chuck table is rotated by 90°, and the modified layer 120 is similarly formed along the dividing predetermined lines 14 and 24 in a direction perpendicular to the previously formed modified layer 120. In addition, the focus point of the laser beam LB2 is slowly raised from near the depth position that becomes the finished thickness of the first wafer 10 to near the back surface 20b of the second wafer 20, and the laser processing for forming the modified layer 120 is repeatedly performed. As shown in the lower part of (b) of Figure 10 , it is formed in a manner that straddles both the first wafer 10 and the second wafer 20. Thus, the modified layer 120 is formed along all the dividing predetermined lines 14 and 24 of the wafer W.

[0051] In addition, the laser processing conditions during the above-described dividing predetermined line modified layer forming process are set as follows, for example.

[0052]

[0053] Similarly, in the case where the dividing predetermined line modified layer forming process is performed after the second wafer grinding process and before the protective tape attaching process as described above, when the first wafer 10 becomes the finished thickness by performing the first wafer grinding process described with reference to Figure 7 , as shown in (b) of Figure 8 , the ring member 11 formed in the outer peripheral remaining area including the chamfered portion 10e is separated from the first wafer 10 and drops and adheres to the protective tape T, and the wafer W is divided into individual device chips 18 along the modified layer 120.

Claims

1. A method for processing a wafer, which processes a wafer having a two-layer structure formed by laminating a second wafer on the front surface of a first wafer. The first wafer has a device region formed by dividing a plurality of intersecting division predetermined lines into a plurality of devices and an outer peripheral remaining region surrounding the device region on the front surface. Among them, The method for processing the wafer has the following steps: Step difference portion forming step: Cut from the second wafer side until reaching the outer peripheral remaining region of the first wafer and a depth corresponding to the finished thickness of the first wafer, remove the chamfered portion formed at the outer peripheral end of the second wafer, and form an annular step difference portion in the outer peripheral remaining region of the first wafer; Second wafer grinding step: After implementing the step difference portion forming step, grind the exposed surface of the second wafer to make the second wafer a specified thickness; Annular modified layer forming step: After implementing the second wafer grinding step, position the focus of the laser beam with a wavelength that is transmissive to the first wafer inside the root of the step difference portion formed in the outer peripheral remaining region of the first wafer and irradiate it to form an annular modified layer; Protective tape arranging step: After implementing the annular modified layer forming step, arrange a protective tape with a size corresponding to the first wafer on the exposed surface of the second wafer; and First wafer grinding step: After implementing the protective tape arranging step, grind the exposed surface of the first wafer to stimulate the modified layer, separate the annular region including the step difference portion from the first wafer along the modified layer and drop it onto the protective tape, and grind the first wafer to the finished thickness.

2. The method for processing a wafer according to claim 1, Among them, The method for processing the wafer further has the following cutting groove forming step: After the second wafer grinding step and before the protective tape arranging step, perform cutting from the second wafer side to form a cutting groove that reaches the division predetermined line of the first wafer and includes a groove with a depth corresponding to the finished thickness of the first wafer. In the first wafer grinding step, the two-layer structure wafer is divided into individual device chips.

3. The method for processing a wafer according to claim 1, Among them, The method for processing the wafer further has the following division predetermined line modified layer forming step: After the second wafer grinding step and before the protective tape arranging step, irradiate a laser beam with a wavelength that is transmissive to the first wafer and the second wafer from the second wafer side to form a modified layer that reaches the division predetermined line of the first wafer. In the first wafer grinding step, the two-layer structure wafer is divided into individual device chips.

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