Wafer processing method

Abstract

This invention provides a wafer processing method that enables the realization of high-precision metal stacks. [Solution] The wafer processing method includes a reinforcement forming step of thinning the back surface of the wafer 2 corresponding to the device region to form a ring-shaped reinforcement portion 34 on the back surface of the wafer 2 corresponding to the outer peripheral excess region; a metal film coating step of coating the back surface of the wafer 2 corresponding to the device region with a metal film 38; and a protective member attachment step of attaching a protective member 40 to the ring-shaped reinforcement portion 34 formed on the back surface of the wafer 2 so as not to come into contact with the metal film 38 in order to protect the metal film 38.

Description

Technical Field

[0001] The present invention relates to a method for processing a wafer on which a device region partitioned by a division planned line and an outer peripheral surplus region surrounding the device region are formed on the surface.

Background Art

[0002] A wafer on which a device region partitioned by a division planned line and an outer peripheral surplus region surrounding the device region are formed on the surface is thinned by grinding the back surface and then divided into individual device chips by a dicing device, a laser processing device, etc. Each of the divided device chips is used in electrical devices such as mobile phones and personal computers.

[0003] Also, a technique for coating a metal film on the back surface of a wafer is used in a wide semiconductor device for forming a die attach metal stack. That is, power devices such as high-brightness LEDs (HB-LEDs) require a metal film for improving thermal conductivity and reliability, and RF sputtering, DC sputtering, or electron beam evaporation technology is used (for example, see Patent Document 1).

[0004] A general metal stack is composed of sputter-deposited titanium (film thickness 500 Å), nickel thereon (film thickness 3000 Å), and finally gold (film thickness 200 Å). Also, copper, chromium, palladium, and silver are used as needed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Since metal stacking is performed in a cleanroom (e.g., Class 100), the metal film requires a high degree of cleanliness. However, if wafers coated with the metal film are left for extended periods due to factory equipment or other reasons, the metal film may oxidize or contaminants may adhere to it, making it impossible to produce high-precision metal stacks.

[0007] The object of the present invention is to provide a wafer processing method that can realize a high-precision metal stack. [Means for solving the problem]

[0008] According to the present invention, the following wafer processing method is provided that solves the above problems. That is, A method for processing a wafer in which a device region is formed on the surface, partitioned by lines indicating multiple devices, and an outer peripheral surplus region surrounding the device region, A reinforcing portion forming step involves thinning the back surface corresponding to the device region and forming a ring-shaped reinforcing portion on the back surface corresponding to the excess outer peripheral region, A metal film coating step is performed to coat the back surface corresponding to the device region with a metal film, A wafer processing method is provided, which includes a step of attaching a protective member to a ring-shaped reinforcing portion formed on the back surface so as not to come into contact with the metal film, thereby protecting the metal film.

[0009] Preferably, the protective member to be attached in the protective member attachment process is an adhesive sheet with an adhesive layer attached to the area corresponding to the excess outer periphery. Alternatively, the protective member to be attached in the protective member attachment process may be a heat-sealable sheet, and the area corresponding to the excess outer periphery may be heated to attach the heat-sealable sheet to the ring-shaped reinforcement portion. In the protective member attachment process, it is desirable to seal an inert gas in the space between the metal film and the protective member. It is preferable that pores are formed in the sheet so that the pressure in the space between the metal film and the protective member follows atmospheric pressure. [Effects of the Invention]

[0010] The wafer processing method of the present invention is A method for processing a wafer having a device region formed on its surface, which is demarcated by dividing lines, and an outer peripheral surplus region surrounding the device region, A reinforcing portion forming step involves thinning the back surface corresponding to the device region and forming a ring-shaped reinforcing portion on the back surface corresponding to the excess outer peripheral region, A metal film coating step is performed to coat the back surface corresponding to the device region with a metal film, The present invention includes a step of attaching a protective member to a ring-shaped reinforcing portion formed on the back surface so as not to come into contact with the metal film, thereby protecting the metal film. Therefore, even if the wafer coated with the metal film is left for a long time due to factory equipment or other reasons after the metal film has been applied to the back surface corresponding to the device area, the protective member prevents the metal film from oxidizing or dust from adhering to it. Accordingly, the present invention enables the realization of a high-precision metal stack. [Brief explanation of the drawing]

[0011] [Figure 1] (a) Perspective view of the wafer and backgrind sheet, (b) Perspective view of the wafer with the backgrind sheet attached to the surface. [Figure 2] (a) Perspective view showing the reinforcement formation process, (b) Schematic cross-sectional view of a wafer with a ring-shaped reinforcement formed on it. [Figure 3] A schematic diagram illustrating the metal film coating process. [Figure 4] (a) A schematic diagram showing the protective member attachment process, (b) A perspective view of a wafer with a protective member attached to a ring-shaped reinforcing portion. [Figure 5] (a) Perspective view of an adhesive sheet with an adhesive layer attached to the area corresponding to the excess outer perimeter, (b) Perspective view of an adhesive sheet with pores formed therein, (c) Perspective view of a heat-sealable sheet, (d) Perspective view of a heat-sealable sheet with pores formed therein. [Modes for carrying out the invention]

[0012] Hereinafter, preferred embodiments of the wafer processing method according to the present invention will be described with reference to the drawings.

[0013] (Waha 2) Figure 1(a) shows a disc-shaped wafer 2 that can be processed by the method according to the present invention. The wafer 2 can be formed from a suitable semiconductor material such as silicon. The dimensions of the wafer 2 are, for example, a diameter of 200 mm and a thickness of approximately 700 μm. On the surface 2a of the wafer 2, a device region 8 is formed, in which multiple devices 4 such as ICs and LSIs are demarcated by grid-like division lines 6, and an outer peripheral surplus region 10 surrounds the device region 8. In Figure 1, the ring-shaped boundary 12 between the device region 8 and the outer peripheral surplus region 10 is shown by a dashed line for convenience, but in reality, there is no line indicating the boundary 12.

[0014] (Reinforcement part forming process) In this embodiment, a reinforcement forming step is performed in which the back surface 2b corresponding to the device region 8 is thinned to form a ring-shaped reinforcement on the back surface 2b corresponding to the outer peripheral excess region 10. When performing the reinforcement forming step, as shown in Figures 1(a) and 1(b), a backgrind sheet 14 for protecting the device 4 is first attached to the surface 2a of the wafer 2. The backgrind sheet 14 is a circular sheet having a diameter approximately the same as the diameter of the wafer 2. As the backgrind sheet 14, an adhesive sheet with an adhesive layer attached, or a thermocompression sheet without an adhesive layer can be used. The adhesive layer of the adhesive sheet may be attached to the entire surface of one side of the adhesive sheet, or to the annular region on the outer peripheral side corresponding to the outer peripheral excess region 10 of the wafer 2. The thermocompression sheet is a sheet of thermoplastic synthetic resin (for example, polyolefin resin, polyester resin), which softens or melts and exhibits adhesive force when heated to a temperature near its melting point. Examples of polyolefin resins used as materials for heat-sealable sheets include polyethylene (PE), polypropylene (PP), and polystyrene (PS). Examples of polyester resins used as materials for heat-sealable sheets include polyethylene terephthalate (PET) and polyethylene naphthalate (PEN).

[0015] The reinforcing portion forming step can be carried out, for example, using the grinding device 16 shown in Fig. 2(a). The grinding device 16 includes a chuck table 18 for sucking and holding the wafer 2, and grinding means 20 for grinding the wafer 2 sucked and held by the chuck table 18. The grinding means 20 includes a spindle housing 22, a spindle 24 rotatably supported about an axis extending in the vertical direction in the spindle housing 22, a motor (not shown) for rotating the spindle 24, and a disk-shaped wheel mount 26 fixed to the lower end of the spindle 24. An annular grinding wheel 30 is fastened to the lower surface of the wheel mount 26 by bolts 28. A plurality of grinding wheels 32 arranged annularly at intervals in the circumferential direction are fixed to the outer peripheral edge portion of the lower surface of the grinding wheel 30. The diameter of the grinding wheel 32 is substantially the same as the radius of the wafer 2.

[0016] In the reinforcing portion forming step, first, the back surface 2b of the wafer 2 is turned upward, and the surface 2a side of the wafer 2 is sucked and held on the upper surface of the chuck table 18. Next, the positional relationship between the wafer 2 and the grinding means 20 is adjusted such that the grinding wheel 32 is located radially inward of the region corresponding to the outer peripheral surplus region 10 and passes through the center of the wafer 2. Next, the spindle 24 is rotated at a predetermined rotational speed (for example, 6000 rpm) in the direction indicated by the arrow R1. Also, the chuck table 18 is rotated at a predetermined rotational speed (for example, 300 rpm) in the direction indicated by the arrow R2. Next, the spindle 24 is lowered to bring the grinding wheel 32 into contact with the back surface 2b of the wafer 2, and grinding water is supplied to the portion where the grinding wheel 32 contacts the back surface 2b of the wafer 2. Then, the spindle 24 is lowered at a predetermined feed rate (for example, 1.0 μm / s). As a result, as shown in Fig. 2(b), the back surface 2b corresponding to the device region 8 can be ground and thinned, and a ring-shaped reinforcing portion 34 can be formed on the back surface 2b corresponding to the outer peripheral surplus region 10. The thickness of the thinned device region 8 is, for example, about 30 μm.

[0017] After performing the reinforcing portion forming step, a metal film coating step of coating the back surface 2b corresponding to the device region 8 with a metal film is performed. The metal film coating step can be performed using, for example, the RF sputtering apparatus 36 shown in FIG. 3. Since the configuration of the RF sputtering apparatus 36 may be a well-known configuration, detailed description thereof will be omitted.

[0018] During the metal film coating step, an appropriate mask is applied in advance to the ring-shaped reinforcing portion 34 so that the metal film is not coated on the reinforcing portion 34. Then, using the RF sputtering apparatus 36, the back surface 2b corresponding to the device region 8 is coated with the metal film 38. The metal film 38 to be coated may contain titanium, nickel, gold, copper, chromium, palladium, silver, etc. Note that the coating of the metal film 38 is not limited to RF sputtering, and other coating methods such as DC sputtering and electron beam evaporation technology may be used. Also, in FIG. 3, the metal film 38 is coated with the back grind sheet 14 adhered to the front surface 2a of the wafer 2, but the metal film 38 may be coated after removing the back grind sheet 14 from the front surface 2a of the wafer 2.

[0019] After performing the metal film coating step, a protective member attaching step of attaching a protective member 40 to the ring-shaped reinforcing portion 34 formed on the back surface 2b to protect the metal film 38 so as not to contact the metal film 38 is performed (see FIGS. 4(a) and 4(b)). The protective member 40 is a circular sheet having a diameter substantially the same as the diameter of the wafer 2. Note that before attaching the protective member 40, the mask applied during the metal film coating step is removed from the ring-shaped reinforcing portion 34. Also, regarding the back grind sheet 14, similar to the metal film coating step, the protective member attaching step may be performed with the back grind sheet 14 adhered to the front surface 2a of the wafer 2, or the protective member attaching step may be performed after removing the back grind sheet 14 from the front surface 2a of the wafer 2.

[0020] As the protective member 40, as shown in Figure 5(a), an adhesive sheet 40a can be used, in which an adhesive layer 42 is attached to the area corresponding to the outer peripheral excess area 10. In Figure 5(a), the area of ​​the adhesive sheet 40a where the adhesive layer 42 is not attached (the area corresponding to the device area 8) is indicated by reference numeral 44. Alternatively, as shown in Figure 5(b), an adhesive sheet 40b in which pores (reference numeral omitted) are formed in the area 44 where the adhesive layer 42 is not attached can also be used as the protective member 40. This allows the pressure in the space between the metal film 38 and the protective member 40 to follow atmospheric pressure. The size of the pores is such that foreign matter such as dust does not enter the space between the metal film 38 and the protective member 40 (for example, 10 μm to 20 μm).

[0021] Alternatively, a thermocompression sheet 40c shown in Figure 5(c) may be used as the protective member 40. As described above, the thermocompression sheet is a sheet of thermoplastic synthetic resin that softens or melts and exhibits adhesive properties when heated to a temperature near its melting point. When using the thermocompression sheet 40c as the protective member 40, the thermocompression sheet 40c can be attached to the ring-shaped reinforcement part 34 by placing the thermocompression sheet 40c on the reinforcement part 34 and then heating the area corresponding to the outer peripheral excess area 10 to cause the thermocompression sheet 40c to exhibit adhesive properties. When heating the area corresponding to the outer peripheral excess area 10, for example, the wafer 2 may be placed on a heated table (not shown), or the thermocompression sheet 40c may be pressed against the reinforcement part 34 with a heated roller (not shown). Note that, as shown in Figure 5(d), a thermocompression sheet 40d with pores (reference numerals omitted) can also be used as the protective member 40.

[0022] In the protective member attachment process, an inert gas may be sealed in the space between the metal film 38 and the protective member 40. This makes it possible to more effectively prevent oxidation of the metal film 38. When an inert gas is sealed in the space between the metal film 38 and the protective member 40, a protective member 40 without pores (the adhesive sheet 40a or the heat-sealed sheet 40c) is used.

[0023] As described above, the wafer processing method of this embodiment includes a reinforcement forming step of thinning the back surface 2b corresponding to the device area 8 to form a ring-shaped reinforcement portion 34 on the back surface 2b corresponding to the outer peripheral excess area 10, a metal film coating step of coating the back surface 2b corresponding to the device area 8 with a metal film 38, and a protective member attachment step of attaching a protective member 40 to the ring-shaped reinforcement portion 34 formed on the back surface 2b so as not to come into contact with the metal film 38 in order to protect the metal film 38. Therefore, even if the wafer 2 coated with the metal film 38 is left for a long time due to factory equipment or other reasons after the back surface 2b corresponding to the device area 8 has been coated with the metal film 38, the protective member 40 prevents the metal film 38 from oxidizing or dust from adhering to the metal film 38. Accordingly, the wafer processing method of this embodiment makes it possible to realize a high-precision metal stack. [Explanation of Symbols]

[0024] 2: Wafer 2a: Wafer surface 2b: Back side of the wafer 4: Device 6: Planned division line 8: Device area 10: Peripheral surplus area 34: Ring-shaped reinforcement 38: Metal film 40: Protective component 40a: Adhesive sheet 40b: Adhesive sheet with formed pores 40c: Heat-sealable sheet 40d: Heat-sealable sheet with formed pores 42: Glue layer

Claims

1. A method for processing a wafer having a device region formed on its surface, which is demarcated by dividing lines, and an outer peripheral surplus region surrounding the device region, A reinforcing portion forming step involves thinning the back surface corresponding to the device region and forming a ring-shaped reinforcing portion on the back surface corresponding to the excess outer peripheral region, A metal film coating step is performed to coat the back surface corresponding to the device region with a metal film, A wafer processing method comprising a step of attaching a protective member to a ring-shaped reinforcing portion formed on the back surface so as not to come into contact with the metal film, thereby protecting the metal film.

2. The wafer processing method according to claim 1, wherein the protective member to be attached in the protective member attachment step is an adhesive sheet in which an adhesive layer is attached to the area corresponding to the excess area on the outer periphery.

3. The wafer processing method according to claim 1, wherein the protective member to be attached in the protective member attachment step is a heat-sealable sheet, and the region corresponding to the excess outer peripheral region is heated to attach the heat-sealable sheet to the ring-shaped reinforcing portion.

4. A wafer processing method according to any one of claims 1 to 3, wherein in the protective member attachment step, an inert gas is sealed in the space between the metal film and the protective member.

5. The wafer processing method according to claim 2 or 3, wherein pores are formed in the sheet, and the pressure in the space between the metal film and the protective member follows atmospheric pressure.

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