JP2555000B2 - Polishing method for hard and brittle materials - Google Patents

Description

The present invention relates to a double-sided simultaneous polishing method for hard and brittle materials such as silicon wafers and compound semiconductor wafers. More specifically, the present invention relates to
The present invention relates to a polishing method for accurately processing a hard and brittle material with a synthetic grindstone.

(Prior Art) A semiconductor wafer such as a silicon wafer is a so-called hard and brittle material that is extremely brittle as a mechanical property, and can be said to be a material that is difficult to process. Nevertheless, when processing a semiconductor wafer, extremely high accuracy of surface flatness and thickness uniformity is required. These semiconductor wafers are conventionally processed by the following method. That is, the semiconductor single crystal ingot is first sliced into thin pieces using a diamond saw, then rough polishing is performed by a double-sided lapping machine using alumina-based free abrasive grains, polishing spots generated on the wafer surface during cutting, saw marks and The unevenness on the surface is removed to obtain a wrapped wafer having a uniform thickness to some extent. Next, the wrapped wafer is subjected to chemical etching using an acid or alkali chemical solution to remove the surface strain layer, and subsequently polished to obtain a mirror wafer.

In recent years, the processing accuracy is required to be much higher than before, and it is said that, for example, in a general 5-inch wafer, it is necessary to suppress the variation in thickness to 1 μm or less. The processing accuracy is mainly determined by the rough polishing process. The rough polishing process is conventionally carried out by lapping polishing in which a semiconductor wafer sliced in the gap between upper and lower surface plates equipped with cast iron surface plates is held and polished while quantitatively supplying a slurry of alumina-based free abrasive grains of about 5 to 50 μm. Was there.

However, the method described above can remove the polishing unevenness and saw marks of the sliced wafer and achieve the original purpose of obtaining preferable flatness, but consumes a large amount of expensive loose abrasive grains and is discharged in the rough polishing step. There is a problem that a large amount of equipment, labor, etc. are required for processing the slurry drainage liquid containing the abrasive grains with high precision, and that the working environment is significantly polluted.

(Problems to be solved by the invention) In view of the above-mentioned problems, the inventors of the present invention have conducted extensive studies, and as a result, in a double-sided lapping device, a cast iron surface plate which is usually used is replaced with a specific one. By polishing under a specific condition using a synthetic grindstone, it has been found that the problems in the above existing method can be significantly reduced, and the present invention has been completed. The purpose of the invention is to harden semiconductor wafers and the like. It is to provide a method of polishing a brittle material with high accuracy and efficiency.

(Means for Solving the Problems) The above-mentioned object is to hold a workpiece to be ground on a carrier that makes planetary motion, and to polish both surfaces of the workpiece at the same time with a grindstone attached to a rotating upper and lower surface plate, and 15 to 40 weight of at least one abrasive selected from the group consisting of silicon carbide, aluminum oxide, silicon dioxide, alumina emery, cerium oxide and chromium oxide in a synthetic resin porous body consisting of acetal resin and thermosetting resin. % Using a synthetic grindstone containing, while supplying 0.002 to 0.10 ml / min · cm ² of a polishing liquid with respect to the total area of the polishing surface of the synthetic grindstone,
This is achieved by a method for polishing a hard and brittle material, which comprises polishing an object to be polished with a pressing force of 300 g / cm ² or less.

In the present invention, a synthetic grindstone in which abrasive grains are mixed with a synthetic resin porous body is used. Abrasive grains applied to the synthetic grindstone include silicon carbide, aluminum oxide, alumina emery, silicon dioxide, cerium oxide, and chromium oxide, with silicon carbide and aluminum oxide being preferred.
Ultra-hard abrasive grains such as diamond are not suitable for the purpose of the present invention.

In the present invention, the above-mentioned abrasive grains are mixed in a synthetic grindstone matrix resin in an amount of 15 to 40% by volume. If the content of the abrasive grains is less than 15% by volume, the polishing effect is insufficient, and if it exceeds 40% by volume, the synthetic grindstone becomes brittle and the flatness of the polishing surface tends to change.

The synthetic grindstone of the present invention is required to have a three-dimensional network structure having continuous fine pores, and the proportion of pores in the entire constitution is preferably about 40 to 60% to obtain preferable results. . And, such fine pores bring about the effect of preventing clogging by the polishing layer and effectively preventing temperature rise due to storage of polishing heat.

As the matrix resin of the synthetic grindstone applied to the present invention, it is preferable to use a polyvinyl acetal resin and a thermosetting resin such as melamine resin, phenol resin, epoxy resin and urethane resin in combination. .

The synthetic grindstone according to the present invention is manufactured, for example, by the following method.

An average degree of polymerization of 300 to 2,000, a saponification degree of 80 mol% or more, the fine powder of the above abrasive grains is added to an aqueous solution of polyvinyl alcohol,
An aqueous formaldehyde solution as a cross-linking agent, acids as a catalyst, starches as a pore-forming agent, and, if necessary, a thermosetting resin such as a phenolic resin are added and stirred to prepare a uniform viscous slurry.

The viscous slurry is cast into a mold to solidify the reaction, and then washed with water to remove excess formaldehyde, acid, and starch, and if necessary, next dissolved or emulsified and dispersed in water or an organic solvent, such as a melamine resin. After being impregnated with the thermosetting resin liquid of, it is cured. The amount of resin impregnated should not appear to fill the already obtained continuous fine pores, nor should it cover the part corresponding to the skeleton of the network structure.

The synthetic whetstone thus obtained is washed with water and dried, and then formed into a desired shape.

In the present invention, fitted with the specific synthetic grinding stone in the polishing plates, polished body gripping a carrier of 300 g / cm ² or less, preferably 50 to 200 g / cm ^2, more preferably 100 to 150
Grind with a pressing force of g / cm ² . When the pressing force exceeds 300 g / cm ² , the hard and brittle material to be polished is cracked, the finish is deteriorated, and the abrasion of the synthetic grindstone is accelerated, which is not preferable.

As the polishing liquid of the present invention, lapping oil is preferably used, and more preferably water is used. These may be used alone or in combination. If necessary, a surfactant having a concentration of about 2% or less may be added to the polishing liquid. At the time of polishing, the polishing liquid is 0.002 to 0.10 ml / min · cm ^{2 with} respect to the total area of the polishing surface of the grindstone, preferably 0.005 to 0.0
Supply ² ml / min ・ cm ² . If the supply amount of the polishing liquid deviates from the above specified range and is too small, the object to be polished is damaged, while if the supply amount is too large, the polishing rate is lowered and the synthetic grindstone is easily worn, and the shape accuracy and flatness are Deteriorate.

(Effects of the Invention) The synthetic grindstone according to the present invention does not require any particular adjustment in the degree of bonding between the grindstone and the matrix resin during its production.
It can be manufactured relatively easily.

According to the method of the present invention, it is not necessary to use a slurry in which free abrasive grains are dispersed in a polishing liquid, and it is possible to perform extremely efficient polishing with little loss of a grindstone. In addition, the concentration of abrasive grains in the drainage is significantly reduced, which has an economic effect of reducing the cost including drainage treatment.

Since the synthetic grindstone used in the present invention is not as hard as the conventional cast iron, the flatness and parallelism of the polishing surface, that is, so-called dressing work can be performed in a short time and easily.

As described above, according to the method of the present invention, double-sided simultaneous polishing with excellent surface accuracy can be efficiently performed on hard and brittle materials such as silicon wafers and compound semiconductor wafers without damaging the object to be polished.

Hereinafter, the present invention will be described in detail with reference to examples. The polishing accuracy in the examples was measured and evaluated by the following method. Method of measuring and evaluating polishing accuracy: The center line flatness Ra and the maximum value roughness Rmax of the polished surface of the 3-inch silicon wafer after polishing were measured by Surfcom 553A (manufactured by Tokyo Seimitsu Co., Ltd.) and used as the evaluation standard of the surface state. Also, chuck the sample wafer and set the thickness of the entire surface excluding the peripheral edge of 3 mm to A
It was measured by DE Microscan 8100 and the maximum value was taken as TTV.

(Example 1) Polyvinyl alcohol 2.7 k having a degree of assembly of 1700 and completely saponified
g in water to make an approximately 15 wt% aqueous solution, 50% sulfuric acid 3.0,
65% polyphenol resin aqueous solution 5.5 kg, silicon carbide fine powder No. 800 abrasive grain 45.0 kg, potato starch 3.5 kg, 37% formalin 5.0 were added in this order, and finally water was added to bring the total amount to 50.0, and then a stirrer The mixture was stirred uniformly with to obtain a homogeneous slurry-like mixed liquid. This mixed solution was poured into a predetermined mold, immersed in a water bath at 60 ° C. and solidified for 20 hours to obtain an intermediate. After 20 hours, the solidified intermediate was taken out of the mold, and while excess water of sulfuric acid, formalin, and potato starch was removed by washing with water in a shower shape, it was cut to a thickness of about 60 mm. The cut pieces were placed in a ventilation dryer to remove water and dry.

As water-soluble melamine resin, SM- manufactured by Showa Highpolymer Co., Ltd.
A 50% aqueous solution of 700 (12.0) was prepared, and the dried product of the intermediate was completely impregnated, air-dried, and then placed in a heat treatment machine, heat-treated at a temperature of 140 ° C. for 10 hours, and molded to obtain a synthetic grindstone.

Other synthetic grindstones were prepared by the same method except that the silicon carbide fine powder blended by the above method was used instead of the No. 800 abrasive grains and No. 2000 abrasive grains.

The physical properties of the obtained two kinds of synthetic whetstones are as shown in Table 1.

The above-mentioned synthetic grindstone was attached to the lower surface plate of the 2300 type double-sided polishing machine manufactured by Hoffman, USA
After gripping an inch silicon wafer and setting it on the polishing machine, while supplying 0.01 ml / min · cm ² of water as a polishing liquid,
The carrier was ground at a revolution speed of 30 rpm and a rotation speed of 25 rpm with a pressing force as shown in Table 2. The results are shown in Table 2, and it was found that the polishing rate increases as the pressing force increases, but if the pressing force exceeds 300 g / cm ² , the silicon wafer is damaged, which is not preferable.

(Example 2) The same synthetic grindstone as that used in Example 1 was used, the pressing force was set to 150 g / cm ² , and water as a polishing liquid was used in Tables 3 and 4.
Polishing was performed in the same manner as in Example 1 except that the supply amount was as shown in the table. The results are shown in Tables 3 and 4. When the polishing liquid supply rate is as small as 0.001 ml / min · cm ² , the silicon wafer is easily damaged and the supply rate is 0.15 ml / min · cm 2.
When it was as large as ² , the polishing rate was remarkably reduced, and mirror polishing was performed instead of polishing.

Claims (1)

(57) [Claims] 1. A polyvinyl acetal-based resin and a thermosetting resin are used as grindstones when a grindstone attached to a rotating upper and lower platen is used to simultaneously grind a grindstone on a carrier that moves in a planetary motion. A synthetic grindstone containing 15 to 40% by volume of at least one abrasive grain selected from the group consisting of silicon carbide, aluminum oxide, silicon dioxide, alumina-based emery, cerium oxide and chromium oxide in a synthetic resin porous body consisting of , With respect to the total area of the polishing surface of the synthetic grindstone
A method for polishing a hard and brittle material, which comprises polishing an object to be polished with a pressing force of 300 g / cm ² or less while supplying a polishing liquid of 0.002 to 0.10 ml / min · cm ² .