Wafer processing method

Abstract

A wafer processing method is provided, which can process the back side of the wafer without reducing the quality of the device. The wafer processing method processes the back side (10b) of a wafer (10) divided by a predetermined dividing line (12) and having a plurality of devices (11) formed on the front side (10a), wherein the method comprises at least the following steps: a wafer arranging step, wherein a sheet (14) of a polyolefin sheet or a polyester sheet having a size larger than the shape of the wafer is laid on the upper surface of a support table (20) whose upper surface (22) is formed flat, and a peeling layer (16) having a diameter smaller than the wafer is laid on the upper surface of the sheet, and the front side of the wafer is positioned on the upper surface of the sheet for arrangement; a sheet hot pressing step, wherein the wafer arranged on the support table with the sheet and the peeling layer interposed therebetween is decompressed and the sheet is heated, and the wafer is pressed to hot press the outer periphery of the wafer onto the sheet; a processing step, wherein the back side of the wafer is processed; and a peeling step, wherein the sheet is peeled off from the wafer.

Description

Technical Field

[0001] The invention relates to a method for processing a wafer, which processes the back side of the wafer. Background Art

[0002] A wafer having multiple devices such as IC and LSI formed on the front side divided by predetermined dividing lines is ground on the back side by a grinding device to a specified thickness, and then divided into individual device chips by a dicing device for use in electronic devices such as mobile phones and personal computers.

[0003] The grinding device includes at least: a chuck table having a holding surface for holding a wafer; a grinding unit having a rotatable grinding wheel for grinding the upper surface of the wafer held by the chuck table; and a feed unit for grinding and feeding the grinding tool. The grinding device can process the wafer to a desired thickness (for example, refer to Patent Document 1).

[0004] In the above-mentioned grinding device, when grinding the wafer, a protective tape with an adhesive layer is pasted on the front side of the wafer to prevent multiple devices formed on the front side of the wafer from being damaged by the contact between the holding surface of the chuck table and the front side of the wafer.

[0005] Patent Document 1: Japanese Patent Application Publication No. 2005-246491

[0006] Although, as described above, by sticking a protective tape with an adhesive layer on the front side of the wafer, problems such as damage to the front side of the wafer when grinding the back side of the wafer can be avoided, when the protective tape is peeled off from the front side of the wafer after grinding, a portion of the adhesive layer (adhesive chips) remains attached, and there is a problem of reduced quality of the device after the wafer is divided into individual chips. Summary of the invention

[0007] The present invention has been accomplished in view of the above-mentioned circumstances, and a main technical problem thereof is to provide a wafer processing method that does not degrade the quality of the device even when the back side of the wafer is processed.

[0008] In order to solve the above-mentioned main technical problems, according to the present invention, a method for processing a chip is provided, wherein the back side of a chip divided by a predetermined dividing line and having a plurality of devices formed on the front side is processed, wherein the method for processing the chip includes at least the following steps: a chip arrangement step, wherein any sheet selected from a polyolefin sheet or a polyester sheet having a size larger than the shape of the chip is laid on the upper surface of a supporting workbench having a flat upper surface, and a peeling layer having a diameter smaller than the chip is laid on the upper surface of the sheet, and the front side of the chip is positioned on the upper surface of the sheet for arrangement; a sheet hot pressing step, wherein the chip arranged on the supporting workbench with the sheet and the peeling layer interposed therebetween is decompressed and heated in a closed environment, and the chip is pressed to hot-press the outer periphery of the chip onto the sheet; a processing step, wherein the back side of the chip is processed; and a peeling step, wherein the sheet is peeled off from the chip.

[0009] The release layer may include at least any one of paper, cloth, rice paper, and a polyimide sheet.

[0010] Preferably, the support table includes a heating unit, and the support table is heated by the heating unit during the sheet thermal compression bonding process. In addition, the upper surface of the support table is preferably coated with fluororesin. In addition, during the processing step, a grinding process can be performed to grind the back side of the wafer.

[0011] The polyolefin sheet is preferably composed of any sheet selected from polyethylene sheet, polypropylene sheet, and polystyrene sheet. In the sheet heat pressing step, the heating temperature is preferably 120°C to 140°C when the polyethylene sheet is selected, 160°C to 180°C when the polypropylene sheet is selected, and 220°C to 240°C when the polystyrene sheet is selected.

[0012] The polyester sheet is preferably made of any sheet selected from polyethylene terephthalate sheets and polyethylene naphthalate sheets. In the sheet heat pressing step, the heating temperature is preferably 250°C to 270°C when the polyethylene terephthalate sheet is selected, and the heating temperature is preferably 160°C to 180°C when the polyethylene naphthalate sheet is selected.

[0013] Preferably, in the sheet thermocompression bonding step, the wafer is pressed so that the sheet bulges around the wafer.

[0014] The wafer processing method of the present invention includes at least the following steps: a wafer placement step, in which a sheet of a polyolefin sheet or a polyester sheet having a size larger than the shape of a wafer is laid on the upper surface of a support table whose upper surface is formed flat, and a peeling layer having a diameter smaller than that of the wafer is laid on the upper surface of the sheet, and the front side of the wafer is positioned on the upper surface of the sheet for placement; a sheet thermal compression step, in which the wafer arranged on the support table with the sheet and the peeling layer interposed therebetween is depressurized and heated, and the wafer is pressed to thermally press the periphery of the wafer onto the sheet; a processing step, in which the back side of the wafer is processed; and a peeling step, in which the wafer is peeled off from the sheet. Thus, even if the processing step of processing the back side is completed and the sheet is peeled off from the front side of the wafer, the problem that a part of the adhesive layer adheres to the protruding electrode and reduces the quality of the device can be solved. In addition, a peeling layer is sandwiched between the sheet and the wafer, so that the thermally compressed sheet can be easily peeled off from the front side of the wafer. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 (a) and (b) are perspective views showing an embodiment of a wafer placement process.

[0016] Figure 2 (a) is a side view of a heat pressing device for performing a sheet heat pressing process. Figure 2 (b) is a cross-sectional view of an integrated chip formed by the sheet thermal compression bonding process.

[0017] Figure 3 This is a perspective view showing a manner in which an integrated wafer is placed on a chuck table of a grinding device for performing a processing step.

[0018] Figure 4 It is a perspective view showing an embodiment of grinding processing using a grinding device.

[0019] Figure 5 (a) is a perspective view showing a method of placing an integrated wafer on a holding unit for peeling. Figure 5 (b) is a perspective view showing an embodiment of a peeling step of peeling the sheet from the wafer.

[0020] Description of symbols

[0021] 10: wafer; 11: device; 12: predetermined dividing line; 14: sheet; 16: peeling layer; 20: supporting table; 22: upper surface; 24: electric heater (heating unit); 30: hot pressing device; 32: supporting base; 34: suction hole; 36: sealing cover part; 38: pressing part; 38b: pressing plate; 50: grinding device; 52: chuck table; 60: grinding unit; 66: grinding wheel; 68: grinding tool; 70: holding unit. DETAILED DESCRIPTION

[0022] Hereinafter, embodiments of a wafer processing method according to the present invention will be described in detail with reference to the accompanying drawings.

[0023] exist Figure 1 (a) shows a wafer 10 divided by planned dividing lines 12 and having a plurality of devices 11 formed on a front surface 10a. In this embodiment, a back surface 10b of the wafer 10 is processed.

[0024] When executing the wafer processing method of this embodiment, first prepare the above-mentioned wafer 10, sheet 14, and peeling layer 16 disposed between wafer 10 and sheet 14. Sheet 14 has a diameter larger than the diameter of wafer 10, and is selected from any sheet of polyolefin-based sheets or polyester-based sheets. In this embodiment, polyethylene (PE) sheet is selected. Peeling layer 16 is a circular sheet with a diameter smaller than wafer 10, and is selected from a non-adhesive film material such as paper. In addition, peeling layer 16 is not limited to paper, and can be selected from cloth, rice paper, and polyimide sheet.

[0025] (Wafer placement process)

[0026] When the wafer placement process is performed, the sheet 14 is first laid on the center of the upper surface 22 of the support table 20, and the support table 20 is a thermocompression bonding device 30 (see FIG. 1 ) for performing the thermocompression bonding process described later. Figure 2 The upper surface 22 of the support table 20 is coated with fluororesin and formed flat. Figure 2 As shown in FIG. 2( a ), an electric heater 24 including a temperature sensor (not shown) as a heating means is built in the support table 20 .

[0027] return Figure 1 Continuing with (a), the peeling layer 16 is laid on the upper surface of the sheet 14 laid on the upper surface 22 of the support table 20. When laying the peeling layer 16 on the sheet 14, it is preferred that the center of the sheet 14 and the center of the peeling layer 16 coincide with each other. As described above, the sheet 14 is formed to have a diameter greater than or equal to the diameter of the wafer 10, and the peeling layer 16 is formed to have a diameter smaller than the diameter of the wafer 10, so that the outer periphery of the sheet 14 is exposed outside the peeling layer 16.

[0028] After the peeling layer 16 is laid on the sheet 14, the front surface 10a of the wafer 10 is positioned on the upper surface of the sheet 14 on which the peeling layer 16 is laid and arranged so that the back surface 10b is exposed upward. The wafer arrangement process is completed as described above (see Figure 1 (b)).

[0029] (Sheet thermal compression bonding process)

[0030] After the wafer placement process is completed, the sheet thermal compression bonding process is performed. The sheet thermal compression bonding process is a process in which the wafer 10 placed on the support table 20 with the sheet 14 and the peeling layer 16 interposed therebetween is depressurized in a closed environment, the sheet 14 is heated, and the wafer 10 is pressed to thermally compress the outer periphery of the wafer 10 onto the sheet 14. Figure 2 , the functions and effects of the heat pressing device 30 for implementing the sheet heat pressing step will be described.

[0031] The heat press bonding device 30 includes: a support table 20 having the above-mentioned electric heater 24 built therein; a support base 32 on which the support table 20 is placed and fixed; a suction hole 34 formed in the support base 32; and a sealing cover member 36 for making a space S on the support base 32 including the support table 20 a sealed space. The sealing cover member 36 is a box-shaped member that covers the entire upper surface of the support base 32, but in the side view of the heat press bonding device 30, the suction hole 34 is formed in the support base 32. Figure 2 In (a), in order to facilitate the description of the internal structure, only the cross section of the sealing cover part 36 is shown.

[0032] An opening 36b is formed in the center of the upper wall 36a of the sealed cover 36, and the opening 36b is used for the support shaft 38a of the pressing part 38 to pass through and move forward and backward in the up and down directions indicated by the arrow Z. In order to make the space S of the sealed cover part 36 isolated from the outside and form a closed environment while making the support shaft 38a move forward and backward up and down, a sealing structure 36c is formed around the opening 36b. A pressing plate 38b is provided at the lower end of the supporting shaft 38a. The pressing plate 38b is formed in a disc shape with a diameter at least larger than the wafer 10, and is preferably set to a size with a diameter that is the same as that of the supporting workbench 20. An elastic sealing component (not shown in the figure) can be appropriately provided on the lower end surface of the sealed cover part 36 along the entire circumference. In addition, a driving unit (not shown in the figure) for making the pressing part 38 move forward and backward in the up and down directions is provided above the pressing part 38.

[0033] The sealing cover member 36 is lowered onto the support base 32 including the support table 20 on which the wafer 10 is placed in the wafer placement step, so that the space S becomes a sealed environment. Figure 2 As shown in FIG. 1 (a), the pressing plate 38 b is lifted to an upper position where it does not contact the upper surface of the wafer 10 .

[0034] After the space S formed inside the sealed cover part 36 becomes a closed environment, the suction unit (not shown) is operated to suck the air in the space S through the suction hole 34, and the area containing the chip 10 is depressurized to a state close to vacuum. At the same time, the electric heater 24 built into the support workbench 20 is operated to control the temperature of the upper surface 22 of the support workbench 20. Specifically, the polyethylene sheet constituting the sheet 14 is heated to 120°C to 140°C near the melting temperature. In addition, the driving unit (not shown) is operated to lower the pressing plate 38b in the direction indicated by the arrow Z, so that the entire upper surface of the chip 10 is pressed with uniform force. The space S containing the chip 10 is depressurized to a state close to vacuum, and air is appropriately sucked and removed from each bonding surface of the chip 10, the peeling layer 16 and the sheet 14. Then, the sheet 14 is heated to a temperature near the melting temperature of the sheet 14 (120°C to 140°C) to soften and exert adhesiveness, and the wafer 10, the peeling layer 16 and the sheet 14 are bonded together. Figure 2 The wafer 10 and the sheet 14 are heat-pressed in the state shown in the cross-sectional view of (b). The peeling layer 16 is made of a material (paper) that does not exhibit adhesiveness even when heated, and the peeling layer 16 is arranged in a substantially vacuum state. The wafer 10 and the sheet 14 are heat-pressed in the peripheral area. In addition, at this time, the wafer 10 is pressed by the pressing plate 38b, so that Figure 2 As shown in (b), the outer periphery of the softened sheet 14 disposed directly below the wafer 10 bulges to form a bulging portion 14a surrounding the outer periphery of the wafer 10. In this way, the thermal compression bonding process is completed to form an integrated wafer W in which the wafer 10, the sheet 14, and the peeling layer 16 are integrated.

[0035] (Processing steps)

[0036] After the above-mentioned thermal compression bonding process is completed to form an integrated wafer W, a processing step of processing the back side of the wafer 10 is performed. The processing step of this embodiment is to grind the back side 10b. Figure 3 , Figure 4 A more specific description will be given.

[0037] exist Figure 3 1 shows a chuck table 52 of a grinding device 50 (only a part is shown), and the upper surface of the chuck table 52 is composed of a suction chuck 54, which is composed of porous ceramics with air permeability. The integrated wafer W is placed on the suction chuck 54 with the sheet 14 side facing downward. After the integrated wafer W is placed on the suction chuck 54, a suction unit (not shown) connected to the chuck table 52 is operated to suck and hold the integrated wafer W.

[0038] like Figure 4As shown, the grinding device 50 has a grinding unit 60 for grinding and thinning the back surface 10b of the wafer 10 held by suction on the chuck table 52. The grinding unit 60 has a rotating spindle 62 that is rotated by a rotation drive mechanism (not shown); a mounting seat 64 that is mounted on the lower end of the rotating spindle 62; and a grinding wheel 66 that is mounted on the lower surface of the mounting seat 64. A plurality of grinding tools 68 are provided in an annular shape on the lower surface of the grinding wheel 66.

[0039] After the integrated wafer W is sucked and held on the chuck table 52, the rotating spindle 62 of the grinding unit 60 is moved in a Figure 4 The chuck table 52 is rotated in the direction indicated by the arrow R1 at, for example, 6000 rpm, while Figure 4 The wafer 10 is rotated at, for example, 300 rpm in the direction indicated by the arrow R2. Furthermore, while the grinding water is supplied to the wafer 10 exposed on the upper surface of the integrated wafer W by a grinding water supply unit (not shown), the grinding tool 68 is brought into contact with the back side 10b of the wafer 10, and the grinding wheel 66 supporting the grinding tool 68 is fed downward for grinding at a grinding feed speed of, for example, 1 μm / second. At this time, the thickness of the wafer 10 can be measured by a thickness detection device (not shown) while grinding, and the back side 10b of the wafer 10 is ground by a predetermined amount so that the wafer 10 becomes a predetermined thickness (for example, 50 μm), and then the grinding unit 60 is stopped. In this way, the processing step of grinding the back side 10b of the wafer 10 is completed. As described above, in the present embodiment, the wafer 10 is supported by being hot-pressed on the sheet 14. Thus, the sheet 14 plays the role of a protective tape to prevent the front side 10b of the wafer 10 from being damaged. In addition, the sheet 14 can exert sufficient holding force on the wafer 10, and the wafer 10 will not move even if the back surface 10b of the wafer 10 is ground.

[0040] After the above-mentioned processing step of processing the back surface 10 b of the wafer 10 is completed, the integrated wafer W is unloaded from the grinding device 50 .

[0041] (Peeling process)

[0042] After the integrated wafer W is unloaded from the grinding device 50, it is transported to a Figure 5 The holding unit 70 in the peeling step shown in (a) of FIG. The upper surface of the holding unit 70 is formed of an air-permeable adsorption chuck 72 similarly to the above-mentioned chuck table 52, and is connected to a suction unit (not shown).

[0043] The integrated wafer W transported to the holding unit 70 is placed on the suction chuck 72 of the holding unit 70 with the back side 10b of the wafer 10 facing downward (i.e., with the sheet 14 facing upward). After the integrated wafer W is placed on the suction chuck 72, the suction unit (not shown) is operated to suck and hold the integrated wafer W.

[0044] After the integrated wafer W is attracted and held in the holding unit 70, as shown in FIG. Figure 5 As shown in (b), the sheet 14 and the peeling layer 16 are peeled off from the wafer 10 in the integrated wafer W while the wafer 10 remains on the suction unit 70. At this time, the integrated wafer W is preferably heated or cooled. The sheet 14 is softened by heating as described above, so it is easy to peel off from the wafer 10 even if it has adhesive force. In addition, the sheet 14 is hardened by cooling and the adhesive force is reduced, so it can also be easily peeled off by cooling. When performing the peeling process, whether to perform heating or cooling can be selected in consideration of the material constituting the sheet 14 or the adhesive force of the sheet 14. The above is the completion of the peeling process.

[0045] In the present embodiment, the sheet 14 that exerts adhesive force by heating is attached to the wafer 10 without using liquid resin, wax, double-sided tape, etc. Therefore, even if the sheet 14 is peeled off from the wafer 10, there is no problem that adhesive scraps of liquid resin, wax, double-sided tape, etc. adhere to and remain around the bumps constituting the protruding electrodes, and the quality of the device will not be reduced. In addition, a peeling layer 16 having a diameter smaller than that of the wafer 10 is sandwiched between the wafer 10 and the sheet 14 in a vacuum state, and thermocompression bonding is performed only on the periphery. Therefore, in the process of peeling the sheet 14 from the wafer 10, air enters the area of ​​the peeling layer 16, and the thermocompression-bonded sheet 14 can be easily peeled off from the wafer 10, thereby improving workability.

[0046] In the above-mentioned embodiment, the sheet 14 is composed of a polyethylene sheet, but the present invention is not limited thereto. As the sheet 14 that can be thermally pressed onto the wafer 10 without using liquid resin, double-sided tape, wax, etc., it can be appropriately selected from polyolefin-based sheets and polyester-based sheets. As the polyolefin-based sheet, in addition to the above-mentioned polyethylene sheet, for example, a polypropylene (PP) sheet and a polystyrene (PS) sheet can be selected. In addition, as the polyester-based sheet, for example, a polyethylene terephthalate (PET) sheet and a polyethylene naphthalate (PEN) sheet can be selected.

[0047] In the above-mentioned embodiment, the temperature at which the sheet 14 is heated in the sheet heat pressing step is set to a temperature near the melting point of the polyethylene sheet (120°C to 140°C), but when other sheets are selected to constitute the sheet 14 as described above, it is preferred to heat to a temperature near the melting point of the material of the selected sheet. For example, when the sheet 14 is composed of a polypropylene sheet, it is preferred to set the temperature at the time of heating to 160°C to 180°C, and when the sheet 14 is composed of a polystyrene sheet, it is preferred to set the temperature at the time of heating to 220°C to 240°C. In addition, when the sheet 14 is composed of a polyethylene terephthalate sheet, it is preferred to set the temperature at the time of heating to 250°C to 270°C, and when the sheet 14 is composed of a polyethylene naphthalate sheet, it is preferred to set the temperature at the time of heating to 160°C to 180°C.

[0048] In the above embodiment, the peeling layer 16 is formed into a circular shape, but it does not necessarily need to be circular, and any shape may be used as long as the diameter is smaller than the wafer 10 and the wafer 10 and the sheet 14 can be bonded to each other in the peripheral region.

[0049] In the above-mentioned embodiment, the case where the grinding process of grinding the back side 10b of the chip 10 is performed as the processing step of processing the back side 10b of the chip 10 is described, but the present invention is not limited to this and can also be applied to the case where the grinding process of grinding the back side 10b of the chip 10 is performed.

[0050] In addition, in the above-mentioned embodiment, by Figure 2 The apparatus shown implements thermal compression bonding, but the present invention is not limited thereto, and the following sheet thermal compression bonding process may be implemented: the sheet 14 is heated to a desired temperature while pressing the entire surface of the wafer 10 side with a roller having a heating unit (not shown), and the sheet 14 is thermally compressed and bonded to the wafer 10. In addition, at this time, it is preferable to coat the surface of the roller with a fluororesin.

Claims

1. A method for processing a wafer, wherein the back side of the wafer is processed by a predetermined dividing line and a plurality of devices are formed on the front side, wherein: The wafer processing method comprises at least the following steps: A wafer placement step, comprising laying a polyolefin sheet or a polyester sheet larger than the wafer on the upper surface of a flat support table formed on the upper surface, laying a release layer of a circular sheet having a smaller diameter than the wafer and having no adhesiveness on the upper surface of the sheet, and placing the wafer with the outer periphery of the front side of the wafer directly positioned on the upper surface of the sheet; a sheet thermal compression bonding step, in which the wafer disposed on the support table with the sheet and the peeling layer interposed therebetween is depressurized in a closed environment, the sheet is heated to a temperature near a melting temperature at which it softens and exhibits adhesiveness, and the wafer is pressed to thermally compress the periphery of the wafer onto the sheet; A processing step is performed on the back side of the wafer; as well as The peeling step is to peel the sheet from the wafer. In the sheet thermocompression bonding step, the wafer is pressed so that the sheet bulges around the wafer.

2. The wafer processing method according to claim 1, wherein: The release layer includes at least one of paper, cloth, rice paper, and a polyimide sheet.

3. The wafer processing method according to claim 1 or 2, wherein: The support table includes a heating unit, and the support table is heated by the heating unit during the sheet thermal compression bonding step.

4. The wafer processing method according to claim 3, wherein: The upper surface of the support table is covered with fluororesin.

5. The wafer processing method according to claim 1 or 2, wherein: In this processing step, a grinding process is performed to grind the back surface of the wafer.

6. The wafer processing method according to claim 1 or 2, wherein: The polyolefin-based sheet is composed of any sheet of a polyethylene sheet, a polypropylene sheet, or a polystyrene sheet.

7. The wafer processing method according to claim 6, wherein: In the sheet thermal compression bonding step, the polyethylene sheet is heated to a temperature of 120°C to 140°C, the polypropylene sheet is heated to a temperature of 160°C to 180°C, and the polystyrene sheet is heated to a temperature of 220°C to 240°C.

8. The wafer processing method according to claim 1 or 2, wherein: The polyester-based sheet is composed of any sheet of a polyethylene terephthalate sheet or a polyethylene naphthalate sheet.

9. The wafer processing method according to claim 8, wherein: In the sheet thermal compression bonding step, the heating temperature of the polyethylene terephthalate sheet is 250°C to 270°C, and the heating temperature of the polyethylene naphthalate sheet is 160°C to 180°C.

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