Wafer processing method
The use of resin sheets to form a cavity on the wafer absorbs the step difference, enabling efficient separation of the ring-shaped reinforcement portion, addressing inefficiencies in existing methods and simplifying the process.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- DISCO CORP
- Filing Date
- 2022-11-04
- Publication Date
- 2026-06-23
AI Technical Summary
Existing methods for removing the ring-shaped reinforcement portion from a thinned wafer require time-consuming adjustments of spacers and are inefficient due to the step difference between the circular recess and the reinforcement portion, complicating the formation of a separation groove.
A method involving the use of two resin sheets to form a cavity that absorbs the step difference, allowing the wafer to be held on a simple chuck table without spacers, and enabling efficient formation of a separation groove for separating the circular recess and ring-shaped reinforcement portion.
The method allows for rapid and efficient separation of the ring-shaped reinforcement portion from the wafer by forming a separation groove, eliminating the need for complex chuck table configurations and spacer adjustments.
Smart Images
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Abstract
Description
Technical Field
[0001] The present invention relates to a method for processing a wafer having a circular recess on the back surface and a ring-shaped reinforcing portion formed around the circular recess.
Background Art
[0002] In the manufacturing process of semiconductor devices such as ICs and LSIs used in electronic devices, in order to miniaturize and lighten the semiconductor devices, the back surface of the wafer is ground and the wafer is thinned to a predetermined thickness. In particular, in recent years, in order to meet the requirements for thinning and miniaturization of electronic devices such as mobile phones and personal computers, it has been required to form semiconductor devices thinly. However, when the wafer is ground until its thickness becomes, for example, 50 μm or less, there is a problem that the flexural strength of the wafer decreases and it becomes easily damaged, and subsequent handling becomes difficult.
[0003] Therefore, for example, in Patent Documents 1 and 2, only the back side of the region where the device of the wafer is formed is ground to form a circular recess in the central portion, and a ring-shaped reinforcing portion having the same thickness as before grinding is left on the outer peripheral side of the circular recess, whereby a grinding method for increasing the rigidity of the wafer after grinding has been proposed. By such a grinding method, breakage during handling of the wafer can be prevented by the ring-shaped reinforcing portion formed on the back surface of the wafer.
[0004] On the other hand, when dividing a wafer into individual chips after grinding, the ring-shaped reinforcement portion hinders the division, so it is necessary to remove the ring-shaped reinforcement portion beforehand. For this reason, a convex-shaped chuck table corresponding to the step difference between the circular recess of the wafer and the surrounding ring-shaped reinforcement portion is used to form a circular separation groove on the outer circumference of the wafer, and the ring-shaped reinforcement portion is removed by detaching it at this separation groove. In this case, when using a convex-shaped chuck table, it is necessary to support both the circular recess of the wafer and the ring-shaped reinforcement portion with high precision in order to prevent chipping and cracking when forming the separation groove. For this reason, Patent Document 3 proposes a method of adjusting the convex step difference between the circular recess of the wafer and the ring-shaped reinforcement portion by using annular spacers of different thicknesses according to the step difference between the circular recess of the wafer and the ring-shaped reinforcement portion. [Prior art documents] [Patent Documents]
[0005] [Patent Document 1] Japanese Patent Publication No. 2007-019461 [Patent Document 2] Japanese Patent Publication No. 2008-042081 [Patent Document 3] Japanese Patent Publication No. 2013-098248 [Overview of the project] [Problems that the invention aims to solve]
[0006] However, the method proposed in Patent Document 3 requires changing the spacer according to the step difference between the circular recess of the wafer and the ring-shaped reinforcement portion used to separate the ring-shaped reinforcement portion from the wafer, which is time-consuming and inefficient.
[0007] The present invention has been made in view of the above problems, and its object is to provide a wafer processing method that enables the efficient and rapid formation of a separation groove for separating the circular recess and the ring-shaped reinforcing portion of the wafer, regardless of the step difference between the two, and allows for the easy removal of the ring-shaped reinforcing portion. [Means for solving the problem]
[0008] To achieve the above objective, the present invention provides a method for processing a wafer having a device region on its surface in which devices are formed in a plurality of regions partitioned by grid-like division lines and an outer peripheral excess region surrounding the device region, and having a circular recess on the back side corresponding to the device region, and a ring-shaped reinforcing portion along the outer circumference of the circular recess, comprising: a first fixing step of fixing the back side of the wafer to a first resin sheet so that the first resin sheet conforms to the circular recess and the ring-shaped reinforcing portion; a second fixing step after the first fixing step of fixing a second resin sheet to the first resin sheet fixed to the ring-shaped reinforcing portion, thereby forming a cavity between the first resin sheet and the second resin sheet corresponding to the circular recess; a holding step after the second fixing step of holding the second resin sheet of the wafer on a chuck table; and a groove forming step of forming a separation groove that separates the circular recess and the ring-shaped reinforcing portion. [Effects of the Invention]
[0009] According to the present invention, in the first fixing step, the second resin sheet is fixed to the portion of the first resin sheet fixed to the ring-shaped reinforcement portion of the first resin sheet, which is fixed in accordance with the circular recess and ring-shaped reinforcement portion on the back surface of the wafer, in the second fixing step, thereby forming a cavity between the first resin sheet and the second resin sheet corresponding to the circular recess of the wafer. Therefore, in the next holding step, when the second resin sheet surface of the wafer is held on the chuck table, the step difference between the circular recess and the ring-shaped reinforcement portion of the wafer is absorbed by the cavity formed between the first resin sheet and the second resin sheet. As a result, a convex chuck table is not required, nor are spacers corresponding to the step difference between the circular recess and the ring-shaped reinforcement portion of the wafer, and the wafer can be held on the chuck table with a simple configuration.
[0010] Then, in the next groove formation step, by forming a separation groove on the surface of the wafer held on the chuck table, the ring-shaped reinforcement portion can be separated and removed from the wafer using this separation groove as a boundary. Therefore, according to the present invention, regardless of the step difference between the circular recess of the wafer and the ring-shaped reinforcement portion, the separation groove for separating the two can be formed efficiently in a short time, and the ring-shaped reinforcement portion can be easily removed. [Brief explanation of the drawing]
[0011] [Figure 1] This is a flowchart showing the method of the present invention in step order. [Figure 2] This figure shows the first fixing step in the method of the present invention, where (a) is a perspective view of the workpiece set and (b) is a longitudinal cross-sectional view of the same workpiece set. [Figure 3] This figure shows the second fixing step in the method of the present invention, where (a) is a longitudinal cross-sectional view showing the state before fixing the second resin sheet to the first resin sheet, and (b) is a longitudinal cross-sectional view showing the state after fixing the second resin sheet to the first resin sheet. [Figure 4]This figure shows the holding step in the method of the present invention, where (a) is a longitudinal cross-sectional view showing the state before the work set is held on the chuck table, and (b) is a longitudinal cross-sectional view showing the state after the work set is held on the chuck table. [Figure 5] This figure shows the groove forming step in the method of the present invention, where (a) is a perspective view of the cutting unit and workpiece set, and (b) is a longitudinal cross-sectional view showing groove processing by the cutting unit on a wafer held in a chuck table. [Figure 6] This figure shows the step of removing the ring-shaped reinforcement in the method of the present invention, where (a) is a perspective view showing the state during removal of the ring-shaped reinforcement, (b) is a longitudinal cross-sectional view thereof, and (c) is a longitudinal cross-sectional view showing the state after removal of the ring-shaped reinforcement. [Figure 7] This figure shows the peeling step in the method of the present invention, where (a) is a longitudinal cross-sectional view showing the state before peeling the second resin sheet, and (b) is a longitudinal cross-sectional view showing the state after peeling the second resin sheet. [Figure 8] This figure shows the chip splitting step in the method of the present invention, where (a) is a perspective view of the cutting unit and workpiece set, and (b) is a longitudinal cross-sectional view showing the cutting process of the wafer. [Modes for carrying out the invention]
[0012] Embodiments of the present invention will be described below with reference to the accompanying drawings.
[0013] The wafer processing method according to the present invention is, as shown in FIG. 2(b), a method of removing the ring-shaped reinforcing portion W2 before dividing the wafer W, in which a circular recess W1 is formed in the central portion of the back surface (the lower surface in FIG. 2(b)) and a ring-shaped reinforcing portion W2 is formed around the circular recess W1, into individual device chips, and then cutting the wafer W from which the ring-shaped reinforcing portion W2 has been removed to divide it into individual device chips. As shown in FIG. 1, it is a method of sequentially performing 1) a first fixing step, 2) a second fixing step, 3) a holding step, 4) a groove forming step, 5) a ring-shaped reinforcing portion removing step, 6) a peeling step, and 7) a chip dividing step to finally divide the wafer W into individual device chips. Hereinafter, each step will be described separately.
[0014] 1) First fixing step: As shown in FIG. 2(b), the first fixing step is a step of fixing the circular first resin sheet S1 so as to follow the circular recess W1 formed in the back surface (the lower surface in FIG. 2(b)) of the wafer W and the ring-shaped reinforcing portion W2 around it. Here, the thin disk-shaped wafer W is composed of a single-crystal silicon base material. As shown in FIG. 2(a), on its surface (the upper surface in FIG. 2(a)), it has a device region partitioned into a number of rectangular regions by a plurality of mutually orthogonal division planned lines L1, L2 called streets arranged in a lattice pattern, and an outer peripheral surplus region surrounding the device region.
[0015] Also, as shown in Fig. 2(b), on the wafer W, a circular recess W1 is formed at the central portion on the back side corresponding to the device region, and a ring-shaped reinforcing portion W2 is formed along the periphery of the circular recess W1. Here, as shown in Fig. 2(a), devices D such as ICs and LSIs are respectively formed in a plurality of rectangular regions partitioned by the division lines L1 and L2 of the wafer W. Then, a work set WS in which the wafer W and the ring frame F arranged around it are integrated is formed by attaching a first resin sheet S1. Note that the first resin sheet S1 may be an adhesive tape with an adhesive layer or a sheet only of a base material without an adhesive layer. As the sheet only of the base material without an adhesive layer, the storage elastic modulus at a temperature of 10°C to 30°C is 10 6 ~10 9 (Pa), and the storage elastic modulus at a temperature of 80°C to 100°C during heating (adhesion) is 10 6 ~10 7 (Pa) is preferably used.
[0016] In this first fixing step, when the first resin sheet S1 is fixed so as to follow the circular recess W1 formed on the back surface of the wafer W and the ring-shaped reinforcing portion W2 around it, as shown in Fig. 2(b), the first resin sheet S1, in addition to the circular recess W1 and the ring-shaped reinforcing portion W2 of the wafer W, has its outer peripheral edge fixed to the lower surface of the ring frame F.
[0017] 2) Second fixing step: The second fixing step is a step of fixing a circular second resin sheet S2 to the first resin sheet S1 which was fixed to the back surface of the wafer W in the first step. Specifically, as shown in Figure 3(a), the second resin sheet S2 is applied to the first resin sheet S1 fixed to the back surface of the wafer W from the direction of the arrow shown, and as shown in Figure 3(b), the second resin sheet S2 is fixed to the lower surface of the portion of the first resin sheet S1 excluding the portion fixed to the circular recess W1 of the wafer W (the ring-shaped reinforcing portion W2 of the wafer W, the ring frame F arranged on its outer circumference, and the portion connecting the two). As a result, an air-filled cavity S is formed between the first resin sheet S1 and the second resin sheet S2, specifically between the portion of the first resin sheet S1 fixed to the circular recess W1 of the wafer W and the central portion of the second resin sheet S2 corresponding to this portion. The second resin sheet S2 may be an adhesive tape with an adhesive layer formed on it, similar to the first resin sheet S1, or a sheet consisting only of a substrate without an adhesive layer. Here, the sheet consisting only of the substrate without an adhesive layer has a storage modulus of 10 at temperatures between 10°C and 30°C, similar to the one used in the first resin sheet S1. 6 ~10 9 (Pa), and the storage modulus at a temperature of 80°C to 100°C during heating (adhesion) is 10 6 ~10 7 (Pa) is preferably used.
[0018] 3) Holding step: The holding step involves holding a workset WS, which includes a wafer W in which a cavity S is formed between a first resin sheet S1 and a second resin sheet S2 in the second fixing step, on the holding surface of a chuck table 1. In this holding step, as shown in Figure 4(a), the workset WS is lowered from above the chuck table 1 in the direction of the arrow in the figure, with the second resin sheet S2 facing downwards, and placed on the holding surface of the chuck table 1. Here, the chuck table 1 is a disc-shaped member, and a disc-shaped porous member 2 made of porous ceramic or the like is incorporated in the upper central part thereof, with its upper surface forming the holding surface. The porous member 2 is selectively connected to a suction source, not shown, such as a vacuum pump. The chuck table 1 can also be rotated around a vertical axis by a rotation mechanism, not shown.
[0019] Furthermore, four clamps 3 (only two are shown in Figure 4) are arranged around the outer circumference of the chuck table 1 at equal angular pitches (90° pitches). Each clamp 3 is provided with an L-shaped gripping member 3a that can rotate around an axis 3b in the direction of the arrow in Figure 4(b). Before the workpiece set WS is fixed to the chuck table 1, the gripping members 3a of each clamp 3 are in the open position, as shown in Figure 4(a).
[0020] Then, when the workset WS is placed on the holding surface of the chuck table 1 with the second resin sheet S2 facing downwards, as shown in Figure 4(b), the gripping members 3a of each clamp 3 rotate in the direction of the arrows to fix the ring frame F of the workset WS together with the first resin sheet S1 and the second resin sheet S2 on the chuck table 1. Furthermore, when the porous member 2 is evacuated by a suction source (not shown), negative pressure is generated in the porous member 2, and the second resin sheet S2 is attracted by this negative pressure and adheres tightly to the holding surface on the upper surface of the porous member 2, so that the workset WS is securely held on the holding surface of the chuck table 1.
[0021] In this embodiment, in the first fixing step, the second resin sheet S2 is fixed to the portion of the first resin sheet S1 that is fixed to the ring-shaped reinforcing portion W2, following the circular recess W1 and ring-shaped reinforcing portion W2 on the back surface of the wafer W. In the second fixing step, the second resin sheet S2 is fixed to the portion of the first resin sheet S1 that is fixed to the ring-shaped reinforcing portion W2, and a cavity S is formed between the first resin sheet S1 and the second resin sheet S2 corresponding to the circular recess W1 of the wafer W. Therefore, in the next holding step, as described above, when the second resin sheet S2 of the wafer W is held on the chuck table 1, the step difference between the circular recess W1 and the ring-shaped reinforcing portion W2 of the wafer W is absorbed by the cavity S formed between the first resin sheet S1 and the second resin sheet S2. For this reason, the conventional convex chuck table is not required, and a spacer corresponding to the step difference between the circular recess W1 and the ring-shaped reinforcing portion W2 of the wafer W is also not required, and the wafer W can be held on the chuck table 1 with a simple configuration.
[0022] 4) Groove forming step: The groove formation step is a step in which a circular separation groove Wa (see Figure 5) is formed to separate the circular recess W1 and the ring-shaped reinforcing portion W2 of the wafer W, which is held together with the work set WS on the holding surface of the chuck table 1 in the holding step. In this separation step, as shown in Figure 5, the cutting blade 12 is rotated in the direction of the arrow by the spindle motor 11 of the cutting unit 10, and the chuck table 1 and the work set WS held thereon are rotated in the direction of the arrow in Figure 5(a) by a rotation axis (not shown), and as shown in Figure 5(b), the portion of the wafer W surface (top surface in Figure 5(b)) corresponding to the boundary between the circular recess W1 and the ring-shaped reinforcing portion W2 is cut by the cutting blade 12, and as shown in Figure 5(a), a circular separation groove Wa is formed on the outer periphery of the wafer W surface (the portion corresponding to the boundary between the circular recess W1 and the ring-shaped reinforcing portion W2).
[0023] 5) Step to remove the ring-shaped reinforcement: The ring-shaped reinforcement removal step is a step in which the ring-shaped reinforcement W2 of the wafer W is separated from the circular recess W1 and the first resin sheet S1 and removed, using the separation groove Wa (see Figure 5) formed on the surface of the wafer W in the groove forming step as the boundary. Specifically, in this ring-shaped reinforcement removal step, the removal unit 20 shown in Figure 6 is used. This removal unit 20 is provided with removal tools 23 fixed to shafts 22 that hang down from three locations in the circumferential direction of a horizontal plate 21 that can rotate and move up and down. Here, each shaft 22 and a total of three removal tools 23 fixed to the lower ends of these shafts 22 (only two are shown in Figures 6(b) and (c)) are provided at equal angular pitches (120° pitch) in the circumferential direction, and each removal tool 23 is constructed by connecting two upper and lower discs 23a and 23b parallel to each other at a distance wider than the thickness of the ring-shaped reinforcement W2 of the wafer W.
[0024] To remove the ring-shaped reinforcement portion W2 from the wafer W held on the chuck table 1 together with the workset WS, as shown in Figure 6(b), the outer circumference of the lower disc 23b of each removal tool 23 is inserted into the gap between the ring-shaped reinforcement portion W2 of the wafer W and the first resin sheet S1, and these removal tools 23 are lifted upward while rotating in the direction of the arrow in Figure 6(a). Then, as shown in Figure 6(c), the ring-shaped reinforcement portion W2 of the wafer W is lifted by the three removal tools 23 (only two are shown in Figure 6(c)), and this ring-shaped reinforcement portion W2 is separated from the circular recess W1 and the first resin sheet S1 with the separation groove Wa as the boundary, leaving only the thin portion on the wafer W.
[0025] 6) Peeling step: The peeling step is a step of peeling the second resin sheet S2 from the first resin sheet S1 which is fixed to the thin wafer W from which the ring-shaped reinforcement W2 was removed in the ring-shaped reinforcement removal step. That is, in this peeling step, as shown in Figure 7(a), the second resin sheet S2 is pulled in the direction of the arrow (downward) as shown in Figure 7(b) relative to the first resin sheet S1 which is fixed to the wafer (thin wafer from which the ring-shaped reinforcement W2 was removed) W and the ring frame F of the workset WS removed from the chuck table 1, thereby peeling the second resin sheet S2 from the first resin sheet S1. As a result, only the thin wafer W from which the ring-shaped reinforcement W2 was removed, the ring frame F and the first resin sheet S1 remain in the workset WS.
[0026] 7) Chip splitting step: The chip splitting step involves cutting the surface of the thin wafer W from which the ring-shaped reinforcing portion W2 has been removed along grid-like planned splitting lines L1 and L2 to form splitting grooves (not shown) in a grid pattern, and then splitting the wafer W along the splitting grooves to divide it into individual device chips.
[0027] In other words, in this splitting step, the workpiece set WS from which the second resin sheet S2 was peeled off in the peeling step is held on the holding surface of the chuck table 1, as shown in Figure 8(b), in the same manner as in the holding step. The cutting blade 12 is rotated in the direction of the arrow by the spindle motor 11 of the cutting unit 10, and the chuck table 1 and the workpiece set WS held thereon are moved in the X-axis direction (cutting direction) to cut the surface of the wafer W along, for example, one of the planned splitting lines L1.
[0028] More specifically, once an image is obtained by imaging the surface of the wafer W using an imaging unit (not shown), a pattern matching process based on that image detects the division line L1 to be cut, the position of the cutting blade 12 in the Y-axis direction (indexing direction) is determined, and the position of the cutting blade 12 in the Y-axis direction is aligned with the position of the division line L1 to be cut.
[0029] Then, from the above state, the cutting blade 12 of the cutting unit 10 is driven to rotate at high speed and descends by a predetermined amount of cutting, while the chuck table 1 and the work set WS (wafer W) held therein move in the X-axis direction. As a result, the wafer W is cut along the division line L1 by the cutting blade 12, and a division groove is formed along this division line L1. When this operation is performed for all division lines L1 in one direction, the chuck table 1 and the work set WS held therein are rotated by 90° by a rotation mechanism (not shown), and cutting is similarly performed on the wafer W along the division line L2 in the other direction, which is perpendicular to the division line L1 that has been cut, and a division groove is formed on the wafer W along the division line L2. When cutting along all division lines L1 and L2 of the wafer W is completed, the wafer W can be divided along the division groove by, for example, pulling and expanding the wafer W, thereby obtaining multiple device chips on which individual devices D (see Figure 1) are mounted.
[0030] In the processing method according to this embodiment, which obtains multiple device chips from a wafer W through the above series of steps, in the first fixing step, the second resin sheet S2 is fixed to the portion of the first resin sheet S1 fixed to the ring-shaped reinforcing portion W2, which is fixed to the circular recess W1 and ring-shaped reinforcing portion W2 on the back surface of the wafer W, in the second fixing step, and a cavity S is formed between the first resin sheet S1 and the second resin sheet S2 corresponding to the circular recess W1 of the wafer W. Therefore, in the next holding step, when the surface of the second resin sheet S2 of the wafer W is held on the chuck table 1, the step difference between the circular recess W1 and the ring-shaped reinforcing portion W2 of the wafer W is absorbed by the cavity S formed between the first resin sheet S1 and the second resin sheet S2. For this reason, a convex chuck table is not required, nor is a spacer corresponding to the step difference between the circular recess W1 and the ring-shaped reinforcing portion W2 of the wafer W, and the wafer W can be held on the chuck table 1 with a simple configuration.
[0031] Then, in the next groove formation step, by forming a separation groove Wa on the surface of the wafer W held by the chuck table 1, the ring-shaped reinforcement portion W2 can be separated and removed from the wafer W at the boundary of this separation groove Wa. Therefore, according to the method of the present invention, regardless of the step difference between the circular recess W1 of the wafer W and the ring-shaped reinforcement portion W2, the separation groove Wa for separating the two can be formed efficiently in a short time and the ring-shaped reinforcement portion W2 can be easily removed.
[0032] It should be noted that the present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the technical idea described in the claims, specification, and drawings. [Explanation of symbols]
[0033] 1: Chuck table, 2: Porous member, 3: Clamp, 3a: Gripping member, 3b: shaft, 10: cutting unit, 11: spindle motor, 12: cutting blade, 20: Removal unit, 21: Plate, 23: Removal tool, 23a, 23b: Disks, D: Device, F: Ring frame, L1, L2: Planned division lines, S: Cavity S1: First resin sheet, S2: Second resin sheet, WS: Workset, W: Wafer W1: Circular recess, W2: Ring-shaped reinforcement, Wa: Separation groove
Claims
1. A wafer processing method comprising a device region having devices formed in multiple regions demarcated by grid-like division lines, and an outer peripheral excess region surrounding the device region on its surface, having a circular recess on the back side corresponding to the device region, and having a ring-shaped reinforcing portion along the outer periphery of the circular recess, A first fixing step involves fixing the back surface of the wafer to the first resin sheet, thereby causing the first resin sheet to conform to the circular recess and the ring-shaped reinforcing portion. Following the first fixing step, the second fixing step involves fixing the second resin sheet to the first resin sheet fixed to the ring-shaped reinforcing portion, thereby forming a cavity between the first resin sheet and the second resin sheet corresponding to the circular recess. Following the second fixing step, a holding step is performed to hold the second resin sheet of the wafer on a chuck table, A groove forming step to form a separation groove that separates the circular recess and the ring-shaped reinforcing portion, A method for processing wafers, characterized by including [a certain element].
2. After the groove forming step, A ring-shaped reinforcing part removal step, which involves removing the ring-shaped reinforcing part from the first resin sheet, A peeling step of separating the second resin sheet from the first resin sheet, The wafer processing method according to claim 1, further comprising the above.
3. After the peeling step, The wafer processing method according to claim 2, further comprising a chip splitting step of forming separation grooves along the planned splitting line and dividing the wafer into individual device chips.