JPS6330782B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a semiconductor wafer characterized in that a removable conductive adhesive sheet is used to prevent electrostatic damage to circuits when the semiconductor wafer is divided into single devices (hereinafter referred to as chips). This article relates to a method for converting into chips. In general, in the manufacturing process of semiconductor products, chips such as integrated circuits (hereinafter abbreviated as IC) are manufactured by cutting a wafer, which has a large number of lattice-shaped circuit patterns simultaneously formed on a disk made of silicon single crystal, into individual patterns. It has been obtained. Conventionally, when cutting wafers, chips are fixed on a general-purpose adhesive sheet and cut with a dimming saw to prevent chips from scattering after cutting, but the rotation speed of the rotary blade is high, ranging from several thousand to tens of thousands of RPM. Therefore, a large amount of static electricity tends to be generated and accumulated within the wafer. Therefore, it has a fine circuit pattern.
In the case of ICs, etc., dielectric breakdown is likely to occur between conductors, and this risk is particularly great in MOS type semiconductors. Therefore, in the case of such semiconductors, the wafer is fixed on a grounded semiconductor without using an adhesive sheet, and the cutting is limited to a portion of the surface layer of the wafer (referred to as half-cutting) to prevent scattering. Currently, they are attached to adhesive sheets, bent and broken, and turned into chips. However, in this method, the bending fracture does not proceed linearly in the thickness direction, and the fracture line on the end face of the chip extends into the circuit, resulting in poor precision in chip dimensions. As a method to improve chip dimensional accuracy and prevent electrostatic damage to ICs, attempts have been made to cut the entire thickness of the wafer (referred to as full cut) while imparting conductivity to the wafer. One method is to fully cut the wafer by fixing it on a general insulating adhesive sheet and spraying ionized water made conductive by adding a surfactant, but impurity ions are extremely For semiconductor wafers that are sensitive to water, there are limits to the selection of surfactants that impart ionicity to water, and sufficient conductivity cannot be obtained, so no significant effects have been obtained. Another attempt is to fix the wafer with a conductive base material such as a conductive adhesive or a conductive pressure-sensitive adhesive sheet and then perform full cutting. However, conventional conductive adhesives and conductive adhesive sheets are intended for permanent adhesion;
When applied to this purpose, it has the following drawbacks. That is, the chips cannot be peeled off from the conductive adhesive and adhesive sheet surface after the wafer cutting process is completed. Furthermore, even if it can be forcibly removed, the adhesive and pressure-sensitive adhesive will transfer to the chip surface, making it impossible to apply it to semiconductor applications where contamination is extremely averse. In general conductive adhesive sheets, in order to provide both conductivity and adhesiveness, the cohesive force of the adhesive is reduced to make it as soft as possible, and re-peeling after application is not considered. In addition, if there is contamination on the chip surface after peeling, the adhesion may be insufficient when fixing the chip on the substrate in the next process.
In the case of Au-Si eutectic bonding, contamination can penetrate into the chip and cause circuit failure. The present invention has been made in view of such circumstances. That is, the present invention relates to a wafer chipping method characterized in that a conductive adhesive sheet having removability to the chips is used as a wafer support when the wafer is cut into chips. More specifically, it takes advantage of the characteristics of a removable conductive adhesive sheet, and by attaching a wafer to the conductive adhesive sheet and cutting it, the conductivity of the sheet removes the static electricity generated on the wafer during cutting. In addition, the removability of the conductive adhesive sheet enables a chipping method that does not cause chip contamination after cutting, making it possible to significantly reduce the defective rate when chipping wafers. It is something. The conductive adhesive sheet used in the present invention is an adhesive in which a conductive filler such as carbon or fine metal powder is dispersed, and can ground static electricity generated on a wafer during cutting into a metal foil or plastic film. Although it is advantageous to have a structure that allows grounding in the shortest distance in the vertical direction along the thickness direction of the wafer, it may also be a structure that allows grounding in the longitudinal direction of the wafer. Electrical resistance in the thicker direction of the adhesive layer (hereinafter referred to as translayer resistance)
is preferably 10 ⁴ Ω/cm ² or less, preferably 10 ² Ω/cm ² or less, and the adhesion property is preferably one having removability as described below. In other words, removability in the present invention means that the wafer can be attached to the adhesive sheet by some method, the wafer adheres tightly to the adhesive surface even during cutting, and the chip can be removed from the adhesive surface by an appropriate means after cutting. It has adhesive strength that allows it to be peeled off and does not leave any contamination such as adhesive transfer on the chip surface. Appropriate adhesive strength cannot be unconditionally defined because it varies depending on the chip size, but usually about 30 to 600 g/19 mm (adhesive strength according to JIS C-2107) can be used. If it is less than 30 g/19 mm, the adhesion during cutting will not be sufficient and the wafer or chips will easily scatter, and if it is more than 600 g/19 mm, it will be difficult to separate the chips after cutting. The means to impart removability is achieved by crosslinking the adhesive, and the crosslinking means for this purpose is to add a monomer having a carboxyl group, hydroxyl group, amino group, acid amide group, etc. as a functional group to the adhesive. be copolymerized singly or in combination,
Alternatively, it is common to blend polyester resins, phenol resins, etc., which have these functional groups, and crosslink them with a crosslinking agent having an isocyanate group, a methylol group, an alkyl etherified methylol group, or the like. In addition, in the case of natural rubber, well-known sulfur crosslinking, resin crosslinking, etc. may be used. When using these crosslinking means, it is effective to use catalysts such as metal soaps, acids, and tin chloride in combination because the reaction rate increases. In these pressure-sensitive adhesives, it is also possible to use tackiness modifiers such as tackifiers and plasticizers, if necessary. At the time of pasting, as a method of obtaining the necessary adhesive strength, for example, means such as applying pressure, heating, activating the pasting surface with a solvent, etc. can be used alone or in combination. To remove static electricity during cutting, for example, as shown in FIG. Wafer 6 by suction
The conductive adhesive sheet 3 to which is pasted is fixed. Alternatively, there is a method of covering the base material 2 of the conductive adhesive sheet or the adhesive 1 alone or both with a grounded conductive frame. Typical examples of this case are shown schematically in FIGS. 2 to 4. FIG. 2 shows a conductive frame 7 surrounding a conductive adhesive sheet 3 on which a wafer 6 is attached on an insulating base material 8.
The conductive frame 7 is grounded via a metal fixed plate 5 which is grounded by a ground wire 4.
In FIG. 3, the conductive frame 7 is grounded directly from the conductive base material 2 by a ground wire 4. In FIG. Fourth
The figure shows a case in which a conductive frame 7 grounded by a ground wire 4 is attached to a conductive adhesive 1 to establish a ground. In FIGS. 2 to 4, the ground wire 4 is directly connected to the conductive base material 2 without using the conductive frame 7.
Alternatively, it is also possible to take it out from the conductive adhesive 1, and the conductive frame 7 is typically made of metal, but care must be taken to ensure that the conductive adhesive sheet 3 is grounded to the fixed plate 5 as shown in FIG. You can also paste it. As for the wafer cutting method, devices and methods commonly used for cutting semiconductor wafers can be used, including a method using a dicing saw in which a very thin blade made of diamond or the like is rotated at high speed to cut the wafer. Although the present invention is particularly advantageous for full cuts, it can also be effectively applied to half cuts. A detailed explanation will be given below using Examples. Example 1 100 parts of 1st grade natural rubber (30 minute masticated product) based on solid content,
Polyterpene resin (melting point 100℃) as tackifier
A conductive adhesive composition consisting of 30 parts by weight of 30 parts of sulfur powder as a crosslinking agent and 70% by weight of silver powder (manufactured by Tokuriki Co., Ltd., trade name: Silvest TCG-1) was diluted with toluene. An adhesive solution with a solid content of 30% was obtained. This adhesive solution was applied to a 50 μm thick aluminum foil using a roll coater and dried to obtain a pressure sensitive adhesive sheet having a 20 μm thick adhesive layer. The through-layer resistance of this adhesive sheet in the thickness direction was 10 ^-2 Ω/cm ² . This adhesive sheet was used to form a bipolar integrated circuit.
A 75φ wafer was attached using a rubber roll under a pressure of 2 kg/cm ² so that the element surface was exposed. At this time, the adhesive force to the wafer was 80 g/19 mm. (JIS
Adhesive force of C-2107 to the wafer surface) As shown in FIG. At the same time, the conductive adhesive sheet 3 obtained in this example was used to secure the wafer 6 around the wafer 6 so that it was in contact with the adhesive 1 of the conductive adhesive sheet. In other words, the static electricity generated on the wafer 6 is absorbed by the conductive adhesive 1.
The structure is such that it is connected to the metal fixed platen 5 via the base material 2 and is grounded. The wafer was fully cut in the thickness direction using a dicing saw at a rotational speed of 30,000 RPM to obtain bipolar IC chips of 5 mm square. At this time, it was possible to successfully form the wafer into chips without scattering chips during cutting. The obtained chips could be easily peeled off from the conductive adhesive sheet, and when the surface of the chip peeled from the adhesive sheet was observed under a microscope, no adhesive transfer was observed. Further, as a result of testing this chip, the defect rate due to electrostatic damage was 0%, and there were no defects in chip size because full cutting was possible. Examples 2 to 4 and Comparative Examples 1 to 2 Conductive carbon black (manufactured by Denki Kagaku Kogyo Co., Ltd.)
Dispersion amount of Denka Black (product name: Denka Black) from 0 to 40% by weight
The mixture was dispersed in an acrylic adhesive (manufactured by Toagosei Co., Ltd., trade name: Aron S-1511) using a kneader. These several types of adhesives have different electrical resistances depending on the carbon black content. A conductive PVC adhesive containing 100 parts by weight of the above adhesive and 3 parts by weight of a crosslinking agent (manufactured by Nippon Polyurethane Industries Co., Ltd., trade name Coronate L) in a solid content ratio.
Sheet (manufactured by Riken Vinyl Co., Ltd., product name: Super Ohm)
100μ) using a roll coater, then 120μ
It was dried for 2 minutes at -20° C. to obtain a pressure-sensitive adhesive sheet with a thickness of 10 μm. Comparative Example 1 had no carbon black filling and the adhesive was non-conductive, and Comparative Example 2 had the same adhesive formulation as Example 3 but without using a crosslinking agent. A 100φ C-MOS circuit with a chip size of 3 mm square was formed on the surface of the conductive adhesive sheet made of the above.
The wafers were attached using a rubber roll. In this case, since the adhesiveness was insufficient in Example 4, the wafer was heated to 100° C. to enable attachment. Vacuum the adhesive sheet to which the wafer is attached from the bottom of the conductive sheet, connect the conductive base material and a grounded metal plate to make a ground connection, and fully cut the wafer in the thickness direction using a dicing saw at a rotation speed of 10,000 RPM. As a result, a 3 mm square C-MOS chip was obtained. Regarding this chip, as in Example 1, the peelability of the chip from the adhesive sheet, the contamination of the chip surface, and the failure rate due to electrostatic discharge were measured. These results are shown in Table 1.

[Table] As a result, it was found that in the adhesives subjected to the conductive treatment of Examples 2 to 4, the electrostatic breakdown failure rate was extremely reduced or completely eliminated. In addition, by using a crosslinking agent in the adhesive,
It was also found that the adhesive had removability and could be easily peeled off without any adhesive transfer to the chip surface. As in Example 1, the above results are due to the fact that the static electricity generated during cutting was grounded to the grounded metal panel via the conductive adhesive sheet, which is why C-MOS circuits are particularly susceptible to electrostatic damage. It appears that there was no electrostatic breakdown phenomenon as there was no electrostatic charge. In all of Examples 2 to 4, as in Example 1, no defect in chip size or chip scattering during cutting was observed. In Comparative Example 1, the electrostatic breakdown failure rate was as high as 10% because the adhesive was non-conductive. In addition, in the case of Comparative Example 2, the pasting and cutting were good and no electrostatic damage occurred, but since the adhesive did not have removability, the adhesive was transferred to the chip surface and the chip was cleaned. required. As described above, the conventional problem of electrostatic discharge damage during cutting of wafers can be drastically reduced or even eliminated by making chips using removable conductive adhesive sheets. It became. Furthermore, since the conductive adhesive sheet has removability, the obtained chip can be easily peeled off from the conductive adhesive sheet, and no adhesive or the like is transferred to the chip surface. Therefore, a highly reliable chip can be obtained. Accordingly, the present invention provides the semiconductor industry with a significant reduction in defective rate and provides highly reliable IC chips.

[Brief explanation of the drawing]

1 to 5 are schematic cross-sectional views showing how to provide grounding for the method of the present invention. Explanation of symbols, 1... Conductive adhesive, 2... Conductive base material, 3... Conductive adhesive sheet, 4... Ground wire, 5... Metal fixing plate, 6... Wafer, 7...
conductive frame.

Claims (1)

[Claims] 1 In a method of chipping a semiconductor wafer stuck on an adhesive sheet by dicing, the adhesive sheet is a recyclable material having an adhesive strength of 30 to 600 g/19 mm (JIS C2107) and an electrical resistance of 10 ⁴ Ω/cm ² or less. A method for converting semiconductor wafers into chips, characterized by using a removable adhesive sheet.