DE1044781B - Process for the production of the purest silicon or germanium - Google Patents

Description

Process for the production of the purest silicon or germanium It is known to produce the purest silicon, which can be used for semiconductor purposes, by thermal cleavage of SiH4. The S i H4 required for this can, for. B. be prepared by hydrolysis of magnesium silicide, by hydrogenation of Sic14 with LiA1H4 and other known methods. But even after this process, some elements present as impurities are very difficult to remove because they, such as. B. the boron, are converted into their hydrogen compounds and accompany the Si114. It is therefore necessary in the previously known processes to subject the Si114 or the starting products to lengthy and yield-reducing purification or distillation processes, if it was at all possible to achieve the required high degree of purity.

It has now been found that the purest can be used directly for semiconductor purposes Silicon or Geri-nanium by thermal decomposition of their hydrides in the way can be produced that still boron, arsenic, antimony or similar '#,' impurities containing Si H 4 or GeH 4 produced in any way by a suspension of an alkali metal, which is also an organic compound, an element of III. Group of the periodic table contains, is directed and the discharged SH4 or GeH4 is subjected to a known thermal decomposition.

For the organic compounds of the elements of III. Group of the Periodic Table, in particular organoaluminum compounds come into question, of these in particular the aluminum trialkyls, z. B. aluminum trimethyl, triethyl or tributyl. It is also possible to use aluminum alkyl hydrides, aluminum alkyl alcoholates or aluminum alcoholates (less favorable, due to their lower reactivity, boron alkyls, boric acid esters, alkyl boric acid esters, gallium alkyls, etc. These compounds have the property of being effective even in small amounts 5 to 10 mol percent, based on the alkali hydride used, to carry out the reaction, but larger amounts of organic compounds of group 111 of the Periodic Table can also be used, for example 10 to 30 or 30 to 100 mol percent or more, based on the alkali hydride used In particular when using the stoichiometric amount of the organic compound of group III, the reaction temperature can be greatly reduced, and it has been found that even temperatures as low as -50 ° C. and below can be used it however v One advantage of working with practically catalytic amounts and using a reaction temperature of more than about +60 ° C.

The organic compound of an element of III. Group of the periodic system need not be added as such but can be produced only by the reaction according to any known processes in the suspension itself.

Sodium hydride, in particular, is by far the cheapest alkali hydride in question, but Li H, K H or mixtures thereof can also be used.

For faster and better implementation of the reaction, it is advisable to to use the alkali hydride in finely divided form, although in larger batches coarser-grained alkali hydride can also be used. Good stirring makes it easier general implementation. The process is expediently carried out in the presence of or suspending agents carried out, as such the most varied organic Compounds can be used provided they are compatible with the starting and end products not react.

For example, aliphatic and aromatic hydrocarbons are suitable, Alkylsilanes, mineral oils and many more.

The reaction temperature can be varied within wide limits and is, for example, between -50 and + 150 ° C.

The decomposition temperature of the hydride is generally 500 to about 1400 ° C for si H4; for GeH4 it is lower, about 500 to 1200 ° C. The Si or Ge is expediently deposited on the purest Si or Ge.

It is expedient to carry out the reaction according to the invention in several series-connected Carry out reaction vessels, the rear one not being charged with catalyst are. What is achieved here is that, if the catalyst is highly volatile, it in the next vessel, which only contains alkali hydride, is dragged along. Of course several of these units can be connected in series.

According to the claimed new process, it is achieved that in particular the very unpleasant boron impurities which are difficult to remove in the purest silicon and which are very undesirable. It has now been found that, for example, the volatile boron compounds still contained in the SiH4 are either converted to NaBH4 with the catalysed NaH, reacting with the formation of or with the catalyst (AIR, BR, which immediately reacts with the alkali hydride present to form the NaHBR complex and deposited. Similar conditions exist for the production of pure germanium from germanium tetrachloride before. example a 0.5 mole percent B, H "containing Si H4 was passed through a 20% suspension of NaH in mineral oil, bp.,. 200 ' C at 100 to 140 ° C , which contained 15 mol percent Al (C2 H5)., Based on the NaH used. The emerging SiH4 was passed through a second reactor, which is the same, and two more, which are like the first and the second, but without Al (C, H "), are fed. After thermal decomposition at 800 to 1000 ° C., no more boron could be detected in the purest silicon obtained.

Claims (3)

PATENT CLAIMS: 1. A process for the production of the purest silicon or germanium by the thermal decomposition of their hydrides, characterized in that the SiH4 or GeH4, which still contains boron and / or other impurities and is produced in any manner, is replaced by a suspension of an alk-alihydride, which also contains an organic compound of an element of III. Group of the periodic system contains as a catalyst, passed and the discharged SiH4 or GeH4 is subjected to a known thermal decomposition. 2. The method according to claim 1, characterized in that the organic compounds of an element of III. Group of the periodic table z. B. Al (C2 H, 5), 9, Al (C2 H.5) 2 H, Al (0 R) s. Al R " (0 R) 3, (R = alkyl, n = 1 or 2) or 3. Process according to Claims 1 and 2, characterized in that several reaction vessels are connected in series, the rear vessels not being charged with catalyst.