DE1138746B - Process for purifying silicon tetrachloride - Google Patents

Description

Process for Purifying Silicon Tetrachloride The invention relates to refer to a process for the purification of silicon tetrachloride, which is used to manufacture of very pure silicon for electrical semiconductor devices by thermal Decomposition of silicon hydrogen produced from silicon tetrachloride is determined is.

The silicon hydride is produced, for example, by the known reaction made of lithium aluminum hydride with purified silicon tetrachloride. It however, calcium-aluminum hydride, magnesium-aluminum hydride or aluminum hydride can also be used instead of lithium aluminum hydride reacted with silicon tetrachloride will.

Since even the smallest amounts of impurities, e.g. B. arsenic, phosphorus and boron, which severely affect the properties of silicon, must be strictly followed care must be taken that no hydrides of the elements mentioned are present in the for decomposition provided hydrogen silicon arrive.

For example, it is necessary that the silicon tetrachloride used is specially cleaned. Arsenic, phosphorus and boron can to some extent can be removed by fractional distillation, but small amounts of it can be removed lag behind.

The invention is based on the knowledge that boron compounds are faster are hydrolyzed as silicon compounds. The invention relates to a method for the purification of silicon tetrachloride by partial hydrolysis for production pure boron-free silicon for electric semiconductor devices, which thereby is characterized in that the silicon tetrachloride for hydrolysis of the boron halides an amount of water of about 1 part of water to 1000 parts of silicon tetrachloride in fine Distribution in a solvent for the silicon tetrachloride or an inert one Gas is added.

This amount of water is so small that there are no visible traces of gel form. The silicon tetrachloride is then subjected to fractional distillation subject.

Although it is already known to use silicon tetrachloride as a starting material for the production of very pure silicon in such a way that the silicon tetrachloride a small amount of water is added in as evenly a distribution as possible and thereby the silicon tetrachloride is partially hydrolyzed. In the hydrolysis of silicon tetrachloride It is known that silica is formed, which to some extent absorb impurities able.

In the known method, the water is in the form of a water of crystallization Salt or in the form of water vapor-saturated filter paper or cellulose powder added.

However, the known method is different from the invention Disadvantage.

When adding very small amounts of water, it is essential that the concentration of water in silicon tetrachloride is the same everywhere because at discontinuous distribution of the water at the points of higher water concentration the water is mainly used for hydrolysis of the surrounding silicon tetrachloride and in other places the water concentration is too low to remove the boron halides to hydrate completely.

Such a discontinuous distribution of the water is achieved if, as in the known method, the water is in the form of powdered substances is bound by water of crystallization or in pieces of filter paper or cellulose powder is included. That in a relatively high concentration in the individual solid Water containing particles not only hydrolyzes in the vicinity of these particles the boron halides, but also part of the silicon tetrachloride. This is at the known method is desirable because the resulting gel removes the impurities to remove the silicon tetrachloride. In the method according to the invention is but the formation of gel undesirable, since it was recognized that this is a not inconsiderable one Part of the silicon tetrachloride that has been pre-cleaned with great effort get lost and, moreover, the resulting gel does not contain the boron halides in the desired manner removed from the silicon tetrachloride. _ That is why the procedure according to Invention the water to be added in the form of a moist solvent or a wet inert gas added. The small amount of water in the solvent is ideal evenly distributed, and the solvent mixes completely with the silicon tetrachloride. When using a moist gas, the even mixing is with Silicon tetrachloride is not so simple, but the moisture content can of the gas dimensioned very small and for it an arbitrarily large volume in the course of the cleaning process on the silicon tetrachloride are brought into action, by passing the gas through the silicon tetrachloride or over its surface is blown.

In the known method, no arbitrarily large amount of Carrier substance can be used for the water, since it is a solid matter. In addition, solid carrier substances cannot readily be used in the required form Establish purity so that there is a risk of contamination by the carrier substance consists. In the known method, the solid substances must also be in one additional process step separated from the purified silicon tetrachloride will. This is not necessary in the method according to the invention. That used Solvent is used in the further process steps for the production of silicon needed anyway, and the carrier gas escapes from the silicon tetrachloride. aside from that gases and liquids can be cleaned much easier and better than solid substances.

The extremely small amount of added water, for example a Part of water to a few 1000 parts of silicon tetrachloride is completely sufficient to to completely hydrolyze the boron halide contained in silicon tetrachloride.

You can z. B. the silicon tetrachloride a moist solvent, z. B. diethyl ether or tetrahydrofuran add. The boron trichloride that acts as an impurity contained in silicon tetrachloride is hydrolyzed faster than silicon tetrachloride. A non-volatile hydrolysis product is formed, namely boric acid. After heating with the moist solvent on the reflux condenser and fractional distillation a silicon tetrachloride is obtained which is free from all traces of boron. The fractional Distillation to purify the silicon tetrachloride is always necessary, however, all traces of boron trichloride can only be removed if the process is applied according to the invention.

After the distillation, traces of the solvent can still be found in the silicon tetrachloride be included, which depends on the efficiency of the fractionation. You play but in the subsequent reaction of the silicon tetrachloride to produce Silicon does not matter as it is the same solvent in this reaction can and normally is used.

The method according to the invention can also be carried out so that moist nitrogen or an inert gas through silicon tetrachloride or blown over its surface while stirring the silicon tetrachloride.

In this way you can a solution of silicon tetrachloride add the appropriate amount of water.

After adding water and fractional distillation, the purified silicon tetrachloride reacted with a suitable hydride, so that pure silicon hydride is obtained. This is then pure for extraction Thermally decomposed silicon.

Claims (3)

PATENT CLAIMS: 1. Process for purifying silicon tetrachloride by partial hydrolysis to produce pure, boron-free silicon for electrical Semiconductor devices, characterized in that silicon tetrachloride contains a Amount of water from about 1 part of water to a few 1000 parts of silicon tetrachloride in finely divided in a solvent for the silicon tetrachloride or a inert gas is added. 2. The method according to claim 1, characterized in that that the silicon tetrachloride in a moist solvent such as diethyl ether or Tetrahydrofuran, is dissolved. 3. The method according to claim 1, characterized in that that either moist nitrogen or another inert gas containing water vapor through the silicon tetrachloride or a solution thereof or over its surface blown and the liquid is stirred. Considered publications: French patent specification No. 1125 207.