DE1767667B2 - METHOD FOR CLEANING UP CHLOROSILANES - Google Patents

Description

The invention relates to a method for purifying chlorosilanes, which is characterized is that the chlorosilanes cyclic and / or polymeric acetals, in amounts of 0.05-5.0% by weight, preferably 0.01-2.0% by weight, based on the amount of chlorosilane, and that resulting mixture then separates by distillation.

Silicon for semiconductor purposes must be particularly pure. Traces of accompanying substances affect the Semiconductor properties of silicon are considerable. Such troublesome trace impurities are for example the elements boron, aluminum, titanium, phosphorus, arsenic, iron etc. They come mainly from the for Production of pure silicon commonly used chlorosilanes, from which they are commonly used Reduction processes with hydrogen are also deposited at elevated temperature.

While most of the disruptive elements can be removed by zone melting, this measure does not achieve the goal ^{with some impurities, such as with Bo r.} The boron is soluble in both phases of silicon during zone melting. There is therefore great interest in removing the boron from the chlorosilanes using suitable cleaning methods.

It is well known that the degrees of purity required for semiconductor production could not be achieved by a Extraction or distillation method can be achieved. Therefore, methods have been developed that the To achieve separation of the accompanying substances by chemical means. For example, it is known to some to convert the accompanying substances into volatile hydrides with hydrogen silanes. However, it won't all elements are included and the hydrogenation is not complete either. In addition, the systems of contaminated the hydrides. The cleaning effect is therefore not sufficient. A particular disadvantage of this Process is the mostly high toxicity of the hydrides in question.

According to another method, additives such. B. salts of ethylenediaminetetraacetic acid and pyrrolidinodithiocarbamic acid used and, using longer reaction times, partially reacted under pressure and elevated temperature. These Additives cause precipitates which, in the case of continuous operation, are only removed before the distillation must be in order to prevent the distillation column from being relocated.

Furthermore, a method has become known, according to which water vapor together with a carrier gas in the chlorosilanes to be cleaned is passed. However, this process leads to silicification. In addition, fts Substance losses occur because of the recovery of the chlorosilane entrained with the gas flow is laborious and usually only partially succeeds.

Compared to simple distillation, all known methods require considerably more effort in terms of time and resources.

It has now been found that chlorosilanes can be obtained in a simple manner without the disadvantages described can clean by adding cyclic and / or polymeric acetals to the chlorosilanes in amounts of 0.005-5.0% by weight, preferably 0.01-2.0% by weight, based on the amount of chlorosilane, added and the resulting mixture then by distillation separates. In addition to all other inorganic foreign substances of the chlorosilanes, especially boron compounds, up to analytically no longer detectable concentrations, removed.

The process according to the present invention makes it possible to obtain technical grade chlorosilane to clean semiconductor quality. Suitable chlorosilanes are, for example, tetrachlorosilane, trichlorosilane, Dichlorosilane, hexachlorodisilane and similar compounds. These connections can also be through the following general formula can be circumscribed:

Cl-Si-Cl

wherein X can be chlorine or hydrogen and Y can be X or -Si- (Cl) ₃ . The following cyclic acetals, for example, can be used as cleaning additives: trioxane, tetroxane, metaldehyde, paraldehyde, etc.

Suitable polymeric acetals are: polyoxymethylene, polyglyoxa! i.a. The molecular weight of the polyacetals is not critical. The polymeric acetals used can be end-group-capped or also end-group-unlocked be. Appropriately, low molecular weight polyacetals are used with the Impurities form soluble complexes.

The cleaning according to the invention is carried out by adding the complexing agent together with the Crude silanes either in the still or in the column inlet. Temperature and pressure conditions can be chosen at will. Work-up by distillation can then be carried out without further treatment be connected. The inorganic accompanying substances go with the cleaning additives in non-volatile Form in the distillation sump, which is expediently not completely distilled off. It can be used in both Batch operation as well as continuously can be worked. As a particular advantage of the procedure would be It should also be mentioned that technical chlorosilanes with high concentrations of contaminating foreign substances used without pretreatment and according to the process according to the invention to the required high level Purity can be brought.

The following examples are intended to illustrate the invention.

example 1

A 10-liter flask made of appliance glass was placed under 5 kg Trichlorosilane, 10 g of trioxane and a further 5 kg of trichlorosilane are introduced and the mixture is passed through a 30-tray column distilled with the reflux ratio 10. It became technical grade trichlorosilane with a boron content of 90 ppm and an iron content of 0.02% by weight. There was neither iron nor boron in the distillate

verifiable. On the other hand, the reactions to iron and boron in the still residue, which weighed 340 g, were very strong strong.

Example 2
Analogous to the example above! became technical

Paraldehyde treated In the clear distillate was none Boron more detectable. The distillation residue of 510 g contained a high proportion of boron.

Example 3
Example 2 is repeated with 1 g of metaldehyde

Analogous to the example above! became technical wieaernoiung ac * οαιμ. ^. ... »; & ■ · ■ - · - ■ ·

Trichlorosilane of the same composition with 2 g instead of the paraldehyde brought the same result

Claims (1)

Claim: Process for the purification of chlorosilanes by distillation, characterized in that the chlorosilanes: cyclic and / or polymeric acetals in amounts of 0.005-5.0% by weight, preferably 0.01-2.0% by weight, based on the amount of chlorosilane, is added and the resulting mixture then separates by distillation