DE1105397B - Process for the production of high purity silicon - Google Patents

Description

In the known reductive production of silicon from silicon halides at elevated temperature When using hydrogen as a reducing agent, hydrogen chloride is formed in addition to silicon. There the conversion of the silicon halides is carried out below 1400 ° C, is a complete reduction of the silicon halides used is not possible. This would be due to the thermochemical Data much higher temperatures necessary. However, since silicon melts at 1420 ° C, it can be used as a carrier material for the deposition of silicon from the gas phase practically only at temperatures between 800 to 1400 ° C can be used.

In the known procedures for the production of high-purity silicon, high-purity hydrogen must always be used are used, of which only a very small part is consumed in the reduction. That The gas mixture withdrawn still contains more than 90 percent by volume even under the most favorable reaction conditions Hydrogen. This high-purity hydrogen was previously unable to use its hydrogen chloride content can be used again, although cleaning occurs during the reduction. There is therefore a need to use this hydrogen, which occurs with increased purity, for silicon production.

Are hydrogen-containing halosilanes such as silicon chloroform, Dichlorosilane and monochlorosilane are processed, this is how the reduction with hydrogen results always compounds that contain more chlorine than the starting materials, mainly silicon tetrahalides. These compounds are more difficult to reduce than the corresponding hydrogen-containing compounds Silicon halides and inhibit further silicon production. It is therefore also necessary before the further processing of the exhaust gases to reduce their silicon tetrahalide content, respectively to reduce so far that the further processing of the hydrogen-free he en chlorosilanes is not disturbed.

It has now been found that the aforementioned difficulties in the production of high-purity silicon can be eliminated in a simple manner by a cycle process in which the halosilanes on directly or indirectly heated deposition bodies at 800 to 1400 ° C reductively decomposed and the reaction gases are then implemented with metals, as well as the residual gas mixture after completing the Used halosilanes is fed back into the separation chamber. The procedure is characterized by that the gas mixture leaving the separation chamber by a heated solid or Fluidized bed made of grained aluminum that conducts

sublimed, entrained aluminum chloride under-

cools and deposits on large surfaces.

In the literature, there is indeed a method of manufacturing
of high purity silicon

Applicant:

Wacker-Chemie GmbH,
Munich 22, Prinzregentenstr. 22nd

Dr. Eduard Enk, Dr. Julius Nicki

and Horst Teich, Burghausen (Obb.),

have been named as inventors

position of silicon described, in which the gas mixture escaping from the reaction zone under Addition of new starting gas is circulated. This becomes more incurred in the implementation Hydrogen chloride was removed from the mixture by treatment with evaporated zinc.

In the process according to the invention, on the other hand, the hydrogen chloride contained in the exhaust gas is added increased temperature of aluminum with the formation of aluminum chloride and hydrogen in known Way tied. Silicon tetrachloride can be hydrogenated to form hydrogen-containing silicon halides will. At the same time, the aluminum cMorid formed binds disturbing impurities. This method therefore not only offers the possibility of to process the resulting gas mixture practically completely on silicon, it also leads to purer ones Starting products and thus back to purer semiconductor silicon. Besides, the one at the beginning has to be The hydrogen used must only be supplemented if losses occur in the circuit.

In Fig. 1 the substance is nut for example Processing of silicon tetrachloride shown. Contains the exhaust gas flowing out of process stage 1 Hydrogen chloride, unreacted silicon tetrachloride and unused hydrogen. In process stage 2, at a temperature up to about 350 ° C bound by aluminum hydrogen chloride and aluminum chloride and hydrogen are formed.

The exhaust gas comes from process stage 2, which Contains aluminum chloride, silicon tetrachloride and hydrogen, in process stage S, where through Cool and.Filter aluminum chloride is deposited in solid form. Silicon tetrachloride and Hydrogen continue to flow, supplemented with fresh silicon tetrachloride via line 5 again Process stage 1 to be fed.

t09578 / 3S3

If desired, the gas mixture obtained from process stage 3 can be fed to a condensation stage 4 and silicon tetrachloride is condensed and fed separately via line 6 to the storage container.

Is used as the starting material for the production silicon halides containing hydrogen from hyperpure silicon, for example silicon chloroform and hydrogen, as shown in Scheme 2, procedure.

The exhaust gas emerging from process stage 1 contains excess, unconverted hydrogen, unreacted silicon chloroform, silicon tetrachloride and hydrogen chloride formed.

In process stage 2, the gas mixture is used at temperatures from over 350 ° to about 500 ° C Treated aluminum, whereby not only the hydrogen chloride with the formation of aluminum chloride and Hydrogen is removed, but also the silicon tetrachloride formed in 1 is hydrogenated. In the Hydrogenation is formed from silicon tetrachloride, preferably silicon chloroform. But it is also possible to control the hydrogenation so that preferably di- or monochlorosilane is formed. These substances can are also fed to the silicon deposition circuit.

The gas mixture from process stage 2 is, as described in scheme 1, in process stage 3 freed from aluminum chloride.

After process stage 3, the remaining components can be fed back to the reduction (process stage 1) via lines 6 and 5, after having been supplemented with fresh starting material, possibly also hydrogen.

If the starting product free of silicon tetrachloride is to be used, the product emerging from 3 becomes Gas mixture fully or partially condensed in process stage 4, advantageously fractionated condenses, with silicon tetrachloride being precipitated. The residual gases: unreacted silicon chloroform, Silicon chloroform formed by hydrogenation and chlorosilanes richer in hydrogen and not converted hydrogen are returned via lines 7 and 5 after being replenished with fresh starting product fed to the reduction (process stage 1). With this arrangement, the process stage becomes at the same time 4 exiting liquid silicon tetrachloride via line 8 for hydrogenation of the cycle gas before Process stage 2 added continuously.

In this way, it is also possible to use silicon chloroform as the starting material for the components used practically completely consumed for the deposition of hyperpure silicon. It is observed that the hydrogen flowing off at 4 is purer than the hydrogen originally used. Silicon that is obtained using hydrogen from the process stage, is deposited, gives with less zone trains a high-purity silicon with higher resistance values.

The individual process steps work as follows:

In process stage 1, silicon is produced according to the known process, possibly using an increased Pressure produced by reductive decomposition.

In process stage 2, aluminum is used in the solid or fluidized bed at temperatures of worked approx. 50 to approx. 500 ° C. At temperatures up to approx. 300 ° C, practically only hydrogen chloride is produced implemented from the exhaust gas. The hydrogenation of silicon tetrachloride and those containing hydrogen Chlorosilane increases with increasing temperature.

In the case of silicon tetrachloride and hydrogen as the starting product for silicon production, therefore preferably worked at temperatures below approx. 300 ° C.

In the case of silicon chloroform and hydrogen as the starting product, process stage 2 is not only used Hydrogen chloride is removed, but at the same time the silicon tetrachloride formed in stage 1 at temperatures Hydrogenated above approx. 300 ° C.

Used as reaction vessels for process stage 2 mild steel, stainless steel or glass-like materials, e.g. B. Quartz glass.

In process stage 3, the deposition of the Aluminum chloride carried out by cooling the reaction gas to about 80 to 20 ° C. It will observed that this freshly deposited aluminum chloride is disturbing, even in traces Binds impurities.

Process stage 3 is advantageously designed in such a way that large surfaces are arranged in a hollow body, on which the aluminum chloride can precipitate without the flow being impeded. Cooled inserts made of metal plates, webs made of metal wires and fibers or other known fine-particle filter materials that are not attacked by the exhaust gas are preferably suitable for this purpose. Process stage 3 is advantageously divided into two areas. In area 1, the largest part is deposited, and in area 2, the ultra-pure filter materials, e.g. B. quartz wool contains, a complete cleaning of the withdrawing gas flow is achieved.

In process stage 4, the incoming gas mixture freed from hydrogen chloride is converted into silicon tetrachloride severed.

The silicon chlorides carried in the circuit are very pure and, together with that in the circuit, they produce Led hydrogen is a silicon that has a higher specific resistance with fewer zones having.

Claims (2)

Patent claims: 1. A process for the production of high-purity silicon by the reductive decomposition of halosilanes on directly or indirectly heated separation bodies at 800 to 1400 ° C and subsequent conversion of the reaction gases with metals and renewed supply of the residual gas mixture after adding the used halosilanes to the separation space, characterized in that the gas mixture leaving the separation chamber is passed through a heated solid or fluidized bed of grained aluminum; the sublimed, entrained aluminum chloride is supercooled and separated on large surfaces. 2. The method according to claim 1, characterized in that in a temperature range of about 50 to about 500 ° C is worked. Considered publications:
German interpretative document No. 1 053 478. 1 sheet of drawings © 109 578/383 4.61