Method for attaching protective sheet and method for processing wafer

Abstract

To provide a novel adhering method for a protective sheet for reducing the risk that the protective sheet is peeled from a wafer while cutting a top face of the protective sheet, and a processing method for the wafer.SOLUTION: The present invention relates to an adhering method for adhering a protective sheet 20 which does not comprise a paste layer on a surface 10a of a wafer 10. The adhering method for the protective sheet 20 includes: a pressing plate preparing step of preparing a pressing plate 30 including a projection 32 corresponding to an outer peripheral part of the wafer 10; a thermal crimping step of disposing the protective sheet 20 on the surface of the wafer 10, heating the protective sheet 20 and crimping the protective sheet 20 to the wafer 10; and a step forming step of pressing the protective sheet 20 in a region corresponding to the outer peripheral part of the wafer 10 using the projection 32 of the pressing plate 30 after implementing the thermal crimping step, and forming a step 20d in the protective sheet 20.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a method for adhering a protective sheet having no adhesive layer to the surface of a wafer, and a method for processing a wafer having a protective sheet having no adhesive layer adhered to its surface. [Background technology]

[0002] In the backside grinding of wafers in the manufacturing process of semiconductor devices, a protective sheet such as pressure-sensitive tape or UV tape is attached to the front side of the wafer in advance, and the front side of the wafer is held on the holding table of the grinding equipment via the protective sheet, and the backside of the wafer is ground.

[0003] When a protective sheet is attached to the surface of a wafer on which protruding electrodes called bumps are formed, the surface of the protective sheet may become uneven in the shape of the bumps. If the front surface of the wafer is held on a holding table via the protective sheet in this state, the height of the back surface of the wafer will vary, making it impossible to thin the wafer to a uniform thickness.

[0004] Therefore, as disclosed in Patent Document 1, for example, a method has been proposed in which a protective sheet (protective tape) is attached to the surface of the wafer, and then the upper surface of the protective sheet is cut with a cutting tool to flatten it. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-021017 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when cutting with a cutting tool to flatten the top surface of a protective sheet, the protective sheet may peel off during cutting. Peeling is particularly likely to occur with protective sheets that have low fixing strength to the wafer. The applicant discovered that when cutting begins, the cutting tool, which hits the outer edge of the protective sheet from outside the outer periphery, moves further inward, inducing peeling of the protective sheet starting from the outer periphery.

[0007] On the other hand, protective sheets that have a low fixing strength to the wafer have the advantage of being easy to peel off from the wafer, and therefore their use is desirable.

[0008] In view of the above, the present invention provides a novel method for attaching a protective sheet and a novel method for processing a wafer, which reduces the risk of the protective sheet peeling off from the wafer during cutting of the upper surface of the protective sheet. [Means for solving the problem]

[0009] The problem to be solved by the present invention is as described above, and the means for solving this problem will now be described.

[0010] According to one aspect of the present invention, there is provided a method for adhering a protective sheet having no adhesive layer to the surface of a wafer, the method comprising: a pressure plate preparation step for preparing a pressure plate having a convex portion corresponding to the outer periphery of the wafer; a thermocompression bonding step for disposing the protective sheet on the surface of the wafer, heating the protective sheet, and pressing the protective sheet to the wafer; and a step formation step for, after the thermocompression bonding step, pressing the protective sheet in an area corresponding to the outer periphery of the wafer with the convex portion of the pressure plate to form a step in the protective sheet.

[0011] According to another aspect of the present invention, the step forming step is performed while heating the protection sheet.

[0012] According to one aspect of the present invention, the wafer processing method includes a planarization step in which the cutting edge of the cutting tool is positioned so as not to be below the step portion and the upper surface of the protective sheet is cut with the cutting tool. [Effects of the Invention]

[0013] According to the configuration of the present invention, a step portion is formed on the outer periphery of the protective sheet, so that when cutting begins, the bit does not hit the outer edge of the protective sheet from outside the outer periphery of the protective sheet, preventing peeling of the protective sheet from starting from the outer periphery. Furthermore, a step portion can be formed in the protective sheet simply by pressing it with a pressure plate, which is a simpler process than, for example, cutting the protective sheet to remove a portion to form a step portion, and processing can be completed in a short time. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a diagram showing a wafer as an example of a workpiece. [Figure 2] 1 is a flowchart of an embodiment of a method for attaching a protective sheet. [Figure 3] (A) is a diagram showing the configuration of the pressure plate, and (B) is a diagram showing the wafer with a protective sheet attached and the pressure plate. [Figure 4] 1A is a diagram showing a state in which a wafer is placed on a heating table in a thermocompression bonding step, and FIG. 1B is a diagram showing how a protective sheet is pressed onto a wafer by a roller in a thermocompression bonding step. [Figure 5] 10A and 10B are diagrams illustrating a state in which the pressing plate is held by a pressing unit in the step forming step, and a state in which the protection sheet is pressed by the pressing plate in the step forming step. [Figure 6] FIG. 10 is a diagram showing a state in which a step portion is formed on the outer periphery of the protective sheet. [Figure 7] 1A is a diagram showing how the protective sheet is cut in the planarization step, and FIG. 1B is a diagram showing the protective sheet after being planarized. [Figure 8]10A to 10C are diagrams illustrating a back grinding step. DETAILED DESCRIPTION OF THE INVENTION

[0015] The method for attaching a protective sheet according to the present invention will now be described with reference to the drawings. 1 shows a wafer 10, which is an example of a workpiece. The wafer 10 is a semiconductor wafer made of silicon as a base material, and on the surface 10a of the disk-shaped wafer 10, devices 14 such as ICs and LSIs are formed in a plurality of areas partitioned in a grid pattern by a plurality of streets 12.

[0016] 1, a plurality of bumps 16 (electrodes) protruding from the surface 10a of the wafer 10 are formed on the periphery of each device 14, and these bumps 16 form irregularities on the surface 10a of the wafer 10. If a TEG (Test Element Group) is formed on the street 12, this TEG also forms irregularities on the surface 10a of the wafer 10.

[0017] The workpieces to be processed in the present invention include various types other than those shown in Fig. 1, and include not only semiconductor wafers but also optical device wafers, resin substrates, glass, ceramics, etc., but are not limited to these.

[0018] For wafer 10 having the above-described unevenness formed on front surface 10a by bumps 16, protective sheet 20 is attached to front surface 10a in order to grind back surface 10b of wafer 10. In the following example, the steps of the flowchart shown in FIG. 2 are carried out in order.

[0019] <Pressure plate preparation step> As shown in FIGS. 3(A) and 3(B), this is a step of preparing a pressing plate 30 having a protrusion 32 corresponding to the outer periphery of the wafer 10.

[0020] The pressure plate 30 can be constructed by, for example, grinding (so-called TAIKO grinding) the outer periphery of one side of a disk-shaped plate material so that a protrusion 32 remains in the circumferential direction.

[0021] The pressing plate 30 can be constructed by forming a protrusion 32 on the outer periphery of a semiconductor wafer having the same diameter as the wafer 10 or a semiconductor wafer having a larger diameter, for example.

[0022] The pressing plate 30 is not limited to a semiconductor wafer, but may be made of glass, ceramics, metal, etc. The width and height of the protrusions 32 are set based on the width and depth of the step to be formed, as will be described in detail later. The area inside the protrusions 32 is configured as a gap 34 that does not press against the protective sheet 20.

[0023] As will be described later, as shown in Fig. 3(B), the pressing plate 30 presses the outer peripheral portion 20c of the protective sheet 20 attached to the wafer 10 with the protrusions 32, thereby forming a step portion in the outer peripheral portion 20c. Note that the outer peripheral portion 20c can be, for example, a region corresponding to an outer peripheral excess region on the front surface 10a of the wafer 10 where no devices 14 are formed.

[0024] <Thermocompression bonding step> As shown in FIGS. 1 and 4(A) and (B), this is a step in which a protective sheet 20 is placed on the surface 10a of the wafer 10, and the protective sheet 20 is heated and pressed onto the wafer 10.

[0025] 1, the protective sheet 20 can be made of, for example, a polyolefin-based sheet (such as a polyethylene sheet, a polypropylene sheet, or a polystyrene sheet) or a polyester-based sheet (such as a polyethylene terephthalate sheet or a polyethylene naphthalate sheet). The protective sheet 20 is pre-cut into a circle having a diameter equal to or larger than the diameter of the wafer 10 so as to cover the area where the devices 14 are formed on the front surface 10a of the wafer 10 (the device formation area). After being attached to the wafer 10, the protective sheet 20 may be cut into a circle along the outer periphery of the wafer 10.

[0026] 1 and 4(A), one side of the protective sheet 20 serves as an adhered surface 20b that is adhered to the surface 10a of the wafer 10, and the opposite side serves as a pressed surface 20a that is pressed. No adhesive layer is formed on the adhered surface 20b, so that when the protective sheet 20 is later peeled off, no adhesive will remain on the surface 10a of the wafer 10.

[0027] 4(A), for example, the wafer 10 is placed on the suction holding unit 52 of the heating table 50 to hold the back surface 10b by suction, and then the surface 20b to be adhered of the protective sheet 20 is placed on the front surface 10a of the wafer 10. The suction holding unit 52 is connected to a suction source 56.

[0028] Next, as shown in Figure 4(B), the protective sheet 20 is heated to a predetermined temperature via the wafer 10 using a heater 54 built into the heating table 50, and then a roller 58 is rolled over the protective sheet 20 to thermocompress the protective sheet 20 to the wafer 10.

[0029] The predetermined temperature during heating is a temperature at which the protective sheet 20 does not melt excessively, but softens and becomes adhesive. Specific preferred temperatures for sheets of each material are as follows: Polyethylene sheet: 120 to 140°C Polypropylene sheet: 160~180℃ Polystyrene sheet: 220~240℃ Polyethylene terephthalate sheet: 250-270°C Polyethylene naphthalate sheet: 160 to 180°C

[0030] 4(B), the space in which the heating table 50 and rollers 58 are disposed may be closed and depressurized, and the protective sheet 20 may be thermocompression-bonded in a vacuum state. By thermocompression-bonding the protective sheet 20 in a vacuum state in this manner, it is possible to prevent air from remaining between the front surface 10a of the wafer 10 and the protective sheet 20, which would otherwise cause bubbles to form. Alternatively, the wafer 10 may be held by the heating table 50 having a suction-holding surface with an outer diameter larger than that of the wafer 10, while the wafer 10 and the suction-holding surface are covered with a protective sheet with an outer diameter larger than that of the wafer 10, and a negative pressure may be applied to the suction-holding surface to perform thermocompression bonding.

[0031] Furthermore, instead of the heating table 50, the wafer 10 may be held by a holding table without a heater, and a heater may be built into the roller 58 to form a heating roller, which heats the protective sheet 20 to a predetermined temperature while pressing it, thereby thermocompressing the protective sheet 20 onto the wafer 10. Alternatively, the protective sheet 20 may be heated by both the heating table 50 and the heating roller.

[0032] <Step formation step> As shown in Figures 5(A)(B) and 6, after performing the thermocompression bonding step, the protective sheet 20 in the area corresponding to the outer peripheral portion 10c (Figure 6) of the wafer 10 is pressed with the convex portion 32 of the pressing plate 30 to form a step portion 20d in the protective sheet 20.

[0033] 5(A), the rear surface 30b of the pressure plate 30 is held by a pressure unit 60 so that the protrusion 32 of the pressure plate 30 faces downward. The pressure unit 60 is configured to have a suction holding part 62 that suction-holds the pressure plate 30, and a heater 64 that heats the pressure plate 30 via the suction holding part 62, and is raised and lowered by a lifting mechanism (not shown). The suction holding part 62 is connected to a suction source 66.

[0034] As shown in FIG. 5(B), the pressing unit 60 holding the pressing plate 30 is lowered to press the pressing plate 30 against the pressing surface 20a of the protective sheet 20 attached to the wafer 10. At this time, the protrusion 32 of the pressing plate 30 first contacts the outer peripheral portion 20c of the protective sheet 20, forming a step 20d in the outer peripheral portion 20c of the protective sheet 20, as shown in FIG. 6. Note that, as shown in FIG. 2(B), if the pressing plate 30 is made of a semiconductor wafer and has a notch 30c, it is preferable to configure the pressing unit 60 to be rotatable, and after pressing once, rotate the pressing plate 30 appropriately to change the position of the notch 30c and press again to prevent the occurrence of areas not pressed by the notch 30c.

[0035] When pressing the protective sheet 20 with the pressing plate 30, it is preferable to heat the protective sheet 20. The heating temperature can be, for example, the same as the temperature in the thermocompression bonding step described above. The protective sheet 20 can be heated, for example, by the heater 54 of the heating table 50 or the heater 64 of the pressing unit 60. If the protective sheet 20 has been heated to a predetermined temperature, heating by these heaters may be omitted.

[0036] 6, the width 20n of the step 20d to be formed in the protective sheet 20 can be, for example, 0.5 to 2 mm, and the depth 20m can be, for example, 0.05 to 0.1 mm. To achieve these dimensions of the step 20d, the amount of lowering by the pressing unit 60 and the dimensions of the protrusion 32 are appropriately set. Specifically, the height of the protrusion 32 is set to a value equal to or greater than the depth of the step 20d to be formed, and the width is set to a value equal to or greater than the width of the step 20d to be formed.

[0037] <Planarization step> As shown in FIG. 7(A), this is a step in which the cutting edge of the cutting tool 78 is positioned at a position that does not go below the step portion 20d, and the upper surface of the protective sheet 20 is cut with the cutting tool 78.

[0038] The wafer 10 is held by suction on a holding table 72 of a cutting tool device 70, with the protective sheet 20 exposed. A cutting tool holder 76 is provided on a cutting tool wheel 74 of the cutting tool device 70, and a cutting tool 78 is attached to the cutting tool holder 76. The height position H of the cutting edge of the cutting tool 78 is set by an elevation mechanism that positions the cutting tool holder 76 at a predetermined height.

[0039] The height position H of the cutting edge of the cutting tool 78 is set to a position not lower than the step portion 20d, that is, a position higher than the bottom surface 20f of the step portion 20d.

[0040] Then, the bite wheel 74 is rotated at a predetermined rotation speed, and the holding table 72 is processed and fed in the horizontal direction, whereby the upper surface of the protection sheet 20 is ground and flattened.

[0041] At this time, the cutting edge of the cutting tool 78 does not reach the bottom surface 20f of the step portion 20d and does not cut the bottom surface 20f, thereby preventing the bottom surface 20f of the step portion 20d from peeling off from the wafer 10. The protective sheet 20 is likely to peel off starting from the outer periphery 20c, but by forming the step portion 20d in advance, cutting by the cutting tool 78 at the outer periphery 20c can be eliminated, preventing the problem of peeling off of the protective sheet 20. Note that the bumps 16 (FIG. 1) may also be cut when the protective sheet 20 is cut. In this way, the top surface of the wafer 10 with the protective sheet 20 attached thereto is flattened as a whole.

[0042] Furthermore, in the flattening step, instead of using a cutting tool, a grinding wheel equipped with a grinding stone may be used to flatten the top surface of protective sheet 20. Even in this case, outer periphery 20c of protective sheet 20 is not ground, so that peeling of protective sheet 20 starting from outer periphery 20c, which is prone to peeling, can be prevented.

[0043] As described above, as shown in Figure 7(B), by forming a step portion 20d on the outer peripheral portion 20c of the protective sheet 20, when cutting begins, the cutting tool 78 does not come into contact with the outer peripheral edge of the protective sheet 20 from outside the outer peripheral portion 20c of the protective sheet 20, and peeling of the protective sheet 20 starting from the outer peripheral portion 20c can be prevented.

[0044] Furthermore, as shown in Figures 5(A) and (B), a step portion 20d can be formed in the protective sheet 20 simply by pressing it with a pressure plate 30. This is a simpler process than, for example, cutting the protective sheet 20 and removing a portion to form the step portion 20d, and processing can be completed in a short time.

[0045] <Back grinding step> As shown in Figure 8, this is a step in which the protective sheet 20 is held by suction on the holding table 82 of the grinding device 80, leaving the back surface 10b of the wafer 10 exposed, and the back surface 10b of the wafer 10 is ground using a grinding stone 86 attached to a grinding wheel 84 of the grinding device 80.

[0046] The grinding wheel 84 is driven to rotate by a motor (not shown) and lowered by a lifting unit (not shown). The holding table 82 is rotated at a predetermined rotation speed, and the grinding wheel 84 is lowered while rotating at the predetermined rotation speed, so that the grinding stone 86 comes into contact with the back surface 10b of the wafer 10 to perform grinding. In this way, the wafer 10 is thinned to a predetermined thickness.

[0047] In this back grinding step, the wafer 10 can be held on the holding table 82 via the protective sheet 20, and the devices 14 (FIG. 1) formed on the front surface of the wafer 10 can be protected from damage.

[0048] After the back grinding step is completed, the wafer 10 is transported to another device, and then the protective sheet 20 is peeled off from the wafer 10. As shown in Fig. 1, no adhesive layer is formed on the adhesion surface 20b of the protective sheet 20, so that no adhesive remains on the front surface 10a of the wafer 10 when the protective sheet 20 is peeled off. [Explanation of symbols]

[0049] 10 wafers 10a surface 10b back side 10c outer periphery 12th Street 14 devices 16 Bump 20 Protective Sheet 20a Pressed surface 20b Surface to be pasted 20c outer periphery 20d Step 20f bottom 20n width 30 Pressure plate 30b back side 32 Convex part 34 Cavity 50 Heating Table 52 Suction holding part 54 Heater 56 Suction source 58 Roller 60 Pressing unit 62 Suction holding part 64 Heater 66 Suction source 70 Bit Cutting Device 72 Holding table 74 Bite Wheel 76 Byte Holder 78 bytes 80 Grinding equipment 82 Holding table 84 Grinding Wheel 86 Grinding Wheel

Claims

1. A method for adhering a protective sheet having no adhesive layer to a surface of a wafer, comprising: a presser plate preparation step of preparing a presser plate having a protrusion corresponding to the outer periphery of the wafer; a thermocompression bonding step of placing the protective sheet on the surface of the wafer, heating the protective sheet, and compressing the protective sheet to the wafer; a step forming step of, after carrying out the thermocompression bonding step, pressing the protective sheet in an area corresponding to the outer periphery of the wafer with the convex portion of the pressing plate to form a step in the protective sheet further inward than the outer periphery of the wafer.

2. The step of forming the stepped portion is carried out while heating the protective sheet.

2. The method for attaching a protective sheet according to claim 1.

3. A method for processing a wafer to which a protective sheet has been attached using the attachment method according to claim 1 or 2, comprising the steps of: The wafer processing method includes a flattening step in which the cutting edge of the cutting tool is positioned at a height not lower than the step portion and the cutting tool is used to cut the upper surface of the protective sheet that is located inside the outer periphery of the wafer.

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