JPS5936821B2 - Silicon wafer manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved method of cutting an ingot of semiconductor material into wafers.

When cutting an ingot of a semiconductor material such as silicon to make a wafer, carbon or the like is conventionally used as a support material for the ingot. In recent years, silicon ingots have become larger in diameter, and demand for thinner wafers is increasing.

For this reason, chipping is likely to occur at the outer circumference of the wafer, especially at the cutting end of the ingot. One of the causes of this chipping is due to the hardness of the object to be cut.
Conventional carbon supports are too soft, causing changes in the behavior of the blade edge (specifically, the difference in hardness causes a difference in resistance, which causes fluctuations in the behavior of the blade edge). . In order to prevent this chipping from occurring, it is possible to use a support base with a certain degree of hardness.
A method is known in which a semiconductor is fixed with an adhesive that is easily soluble in a liquid that is harmless to the semiconductor, then cut, and the adhesive is later dissolved and removed (Japanese Patent Publication No. 48-10266). Shellac adhesives such as shellac and tan wax are used as adhesives that are easily soluble in solvents that are harmless to semiconductors, but such adhesives have limited adhesion retention ability. There is a limit to the thickness of the adhesive layer, and the thickness of the adhesive layer must be made considerably thick.

This means that chipping cannot be completely eliminated for reasons described later. In addition, when using a Sierra-based adhesive, the adhesive is dissolved with a solvent such as alcohol when separating the thin plate from the support after cutting, so the dissolved adhesive adheres to the wafer and stains it afterwards. This may cause problems in the process.

According to the present invention, there is provided a method in which a semiconductor material ingot is fixed to a support using an adhesive and the fixed ingot is cut into thin pieces using a cutter, and the support includes a mixture of silicon powder and epoxy resin. D. Use a hardened material with a surface that matches the surface shape of the ingot to be cut, and use a heat-swellable epoxy adhesive that is easy to peel off as an adhesive. A method is provided in which a silicon ingot is glued and cut into a plurality of thin plates, and then the adhesive is swollen in hot water to separate the thin plates from the support without contaminating them.

According to the present invention, there is provided the above-mentioned method, which further comprises applying a load to the entire ingot when bonding the ingot to the support base to make the thickness of the adhesive layer extremely thin and uniform. provided.

The silicon powder used in the present invention does not need to be highly pure. Its particle size is #5~#1500
, preferably #10 to #800, more preferably #
20 to #320. The mixing ratio of silicon powder and epoxy resin is 0.5 to 3, preferably 1 to 3, and more preferably 1.5 to 2.7, by weight, of the former to the latter. The Witzkars hardness of this cured mixture is Hv (5
) 100-4, preferably Hv(5) 70-10, and the resin is selected accordingly. The resin used is an epoxy resin adhesive represented by the product known under the trade name "Araldite", with a viscosity of 400-1
Use one with a low viscosity of 0,000 centipoise (25°C). If a material with a viscosity lower than this range is used, the silicon powder will not be able to maintain uniform distribution during curing, and
If a material with a viscosity higher than this range is used, the amount of powder that can be mixed will be small and hardness effective for preventing chipping will not be obtained. Suitable resins can be determined by one skilled in the art by simple experimentation. The support is made of the above-mentioned material and shaped to match the surface shape of the rod-shaped mass to be cut that is placed on it.

If the ingot is cylindrical, its upper surface will be formed into a cylindrical concave surface to accommodate it. The adhesive for bonding the support base and the ingot must be an epoxy-based adhesive with strong adhesive strength and swellable when heated (hot water at 60° C. or higher).

If the adhesive exhibits swelling properties when heated with hot water, it is easy to separate the wafer from the support after cutting, and the adhesive does not need to be dissolved with a solvent such as alcohol, unlike Sierra-based adhesives. There is no possibility that the wafer will be contaminated by the melted adhesive and cause problems in subsequent steps. Even if the silicon block to be cut is cut using a support base with similar hardness properties as described above, if the adhesive layer between the silicon block and the base is thick, the blade will break in the adhesive layer. The cutting edge is subject to resistance changes due to differences in hardness, and chipping cannot be sufficiently prevented.

According to research conducted by the present inventors, chipping can be almost completely prevented by setting the thickness of this adhesive layer within the following limits. That is, the thickness of the adhesive should be between 50 and 500 microns, preferably between 50 and 300 microns, and even more preferably between 50 and 150 microns in the cured state.

It has been found that in order to obtain a thickness of 50 to 500 microns, it is necessary to apply a load in the range of 0.01 to 0.5 k9/~ until solidification in the case of epoxy adhesive.

Appropriate adhesives and loads can be determined by one skilled in the art by simple experimentation. Since the adhesive strength of Sierra-based adhesives is weaker than that of epoxy-based adhesives, when they are made this thin, they must be made considerably thicker because they will cause the phenomenon of spacing during cutting. Next, the present invention will be explained by examples.

Example 1 Silicon powder with a particle size of #320 made from shavings of semiconductor silicon and araldite with an initial viscosity of 800 centipoise were mixed in a weight ratio of 2:1 (araldite was of course mixed with a curing agent and then silicone (mixed with powder)
The mixture was placed in a mold for making a support base and cured (by heating) to obtain a support base whose surface had a concave shape corresponding to a cylindrical silicon semiconductor having a diameter of 76.2 mm (3 inches).

The hardness of this support was Hv(5)60. The cylindrical silicon semiconductor ingot described above was adhered to this support with araldite, which exhibits heat-swelling property, and after solidifying, it was continuously cut into a thickness of about 400 μm using a cutter.

The cut surface is prone to chipping (1,0,
0), but the occurrence of chipping could be significantly prevented. After cutting, it was immersed in warm water (60° C. or higher) to peel off from the support. In this method, since the adhesive did not dissolve, the entire surface of the cut wafer was not contaminated. For comparison, when the ratio of silicon powder to araldite was made smaller than 0.5:1, the hardness of the support was too low and chipping could not be sufficiently prevented.

In addition, when the ratio was 3:1, the bonding properties of the mixture on the support base decreased and it became brittle9, and the support base part was easily broken during cutting, causing the wa...1 cracking phenomenon. Furthermore, when the ingot was glued to the support stand before it was cured and the ingot was cut after it had hardened, it was effective in preventing chipping, but it was difficult to separate the wafer from the support stand after cutting, which was not appropriate. .

Example 2 In the method of Example 1, the adhesive layer between the support base and the ingot was too thick, and the change in resistance in this area still caused changes in the behavior of the blade edge, and the chipping prevention effect was lower than that of the conventional method. It's better than the method, but it's not enough.

Therefore, in order to improve this point, the method of Example 1 was repeated nine times by applying a load over the entire length of the ingot so that the adhesive layer was extremely thin (50 to 500 μm) and uniform. Specifically, the same ingot and support as in Example 1 were used, and Araldite, which is swellable by heat, was applied as an adhesive at a rate of 0.39/d to adhere them together, and the entire length of the ingot was 0.3kg/Cfl over
A load of 1 was applied until the adhesive set.

This allowed the adhesive to solidify to a thickness of 70 microns. When cutting was carried out in this state in the same manner as in Example 1, chipping defects, which accounted for 56% of defects in the conventional method, could be reduced to 7%. At this time, the load is 0.
01kg/(If it is smaller than 71, the thickness of the adhesive layer is 500μ
The chipping prevention effect was not sufficient.

Also, the load is 0.5k9/CTi! However, the thickness of the adhesive layer was less than 30 μm, and it peeled off under the force of the wafer during cutting, making it easy to cause the phenomenon of chipping.

Claims (1)

[Claims] 1. An epoxy adhesive having heat-swelling properties that can be easily peeled off by heat on a support base formed by mixing and curing silicon powder and epoxy resin and forming the mixture to match the surface of the silicon ingot to be cut. A method for manufacturing a silicon wafer, which comprises gluing a silicon ingot to be cut with an adhesive and cutting it into a plurality of thin plates, and then swelling the adhesive in hot water and separating the thin plates from a support without contaminating them. 2. The method for manufacturing a silicon wafer according to claim 1, wherein the particle size of the silicon powder is #5 to #1500, and the mixing ratio of the epoxy resin and the silicon powder is 0.5:
1 to 3:1, and the thickness of the adhesive layer bonding the silicon ingot and the support is 50 to 500μ.