DE1064486B - Process for cleaning silicon - Google Patents

Description

33 / 02-

P 195911 Va / 12 i

ANM ELDETAG: NOVEMBER 4, 1957

NOTICE
THE REGISTRATION
AND ISSUE OF THE
EDITORIAL: SEPTEMBER 3, 1959

Silicon with a purity of more than 95% is produced by reducing silica using coal in an electric furnace. With regard to certain technical application possibilities, for which a silicon of particularly high purity is required, one has recently been forced to start from very pure raw materials that are not always available.

On the other hand, in silicon production, the transition to three-phase furnaces instead of those previously used Single phase furnace with conductive sole at a lower cost and a noticeable Decrease in silicon losses due to volatilization. However, this also increases the amount of im Raw silicon still present volatile impurities, especially the aluminum and calcium content.

If, for example, the same starting materials are treated in different types of ovens, one arrives at following results:

Single phase furnace
with senior
sole Three phase furnace Insoluble 0.10%
0.05%
0.60%
0.40%
0.20%
98.65% 0.12%
0.06%
0.50%
0.65%
0.65%
98.02% titanium iron aluminum Calcium Silicon

In the case of certain light metal alloys, however, the calcium content of the added silicon must not be 0.30% and in the case of silicon sheets, too, the combined Ti, Ci and Al content must not exceed 0.5% amount, which is why the silicon produced in the three-phase furnace not without prior purification for such Purposes is usable.

The invention relates to a novel cleaning method for raw silicon, which is then in particular of The advantage is if you start from relatively impure starting materials and use them for the purpose of lowering them of the prime costs in the three-phase high-performance furnace.

According to the invention, the crude silicon obtained from the furnace is subjected to the action in the liquid state an oxidizing gas, whereby most of the calcium and aluminum in the melt is converted into the oxides, which rise to the surface of the bath and pull off as slag permit.

Solid silicon or contaminated ferrosilicon can also be used for the process using any Si process for cleaning silicon

Applicant:

PECHINEY Company de Produits

Chimiques et Electrometallurgiques,

Paris

Representative: Dr.-Ing. F. Wuesthoff, Dipl.-Ing. G. Pulse

and Dipl.-Chem. Dr. rer. nat. E. Frhr. v. Bad luck man,

Patent Attorneys, Munich 9, Schweigerstr. 2

Claimed priority:
France 5 November 1956

Andre Castex, Edea (Cameroon),
and Henri Schmitt, Sabart, Tarascon-sur-Ariege

(France),
have been named as inventors

Melt down the salary beforehand, but for economic reasons it is preferable to stop this immediately to use the crude silicon obtained in the furnace in the liquid state.

It is already known to treat molten silicon with oxidizing or oxygen-containing gases, however, these processes differ insofar as silicon oxide is not obtained at all is, in essential points of the method according to the invention.

Thus, according to a known method, the electrical properties of germanium or Existing silicon semiconductor bodies can be improved by the fact that this is already done at a very high level Degree of purity (0.001% impurities) of the semiconductor material present in a simultaneous oxidation and reducing agent-containing environment melts and the influence of these agents so controls that a certain balance is established between acceptor and donor additives. These For this reason alone, the method is obviously unsuitable for the purposes pursued by the invention requires a starting material that has already been purified far beyond the intended degree of purity is. A transfer to the starting materials for the process according to the invention would be uneconomical and, moreover, would not definitely lead to the desired success.

909 610/362

Claims (3)

According to another known method, silicon intended for use as a semiconductor is purified by heating it in the form of a rod in an oxidizing atmosphere, a short section of the rod being temporarily melted. The oxidizing atmosphere only serves to form a thin oxide layer on the rod surface, which is desirable for certain reasons, and which in turn protects the vast majority of the molten silicon from the effects of the oxidizing gases. The cleaning itself takes place in a manner known per se without converting the impurities into their oxides. It is clear that there are no parallels here with the method according to the invention. When carrying out the method according to the invention, one works as follows: The raw silicon is continuously withdrawn from the furnace into a spacious pouring ladle, where it collects. Immediately above the ladle, a burner with an oxidizing flame is arranged in such a way that the jet of liquid silicon passes through the oxidizing flame after exiting the furnace. The flame remains in contact with the molten metal contained in the ladle until the moment when the cleaned silicon is poured into bars. In the drawing, a ladle consisting of the metal jacket 1 and the refractory lining 2 is shown, which is closed in the upper part by a cover 3. The burner 4 is introduced through an opening in the latter in such a way that its flame 5, which is fed through the supply lines 6 and 7 for fuel and air, extends downward. The continuous jet of liquid raw silicon 8, which emerges from the production furnace (not shown), now passes through the flame 5 as it enters the ladle at 9. When the ladle is full, the slag is drawn off the surface of the melt and it is poured purified silicon in ingots. The following example illustrates the practical implementation of the method according to the invention. EXAMPLE The liquid raw silicon is continuously tapped from a furnace designed to obtain about 650 kg of silicon per hour into a pouring ladle which is lined with tamped silica and holds 700 kg of liquid metal. The burner, through whose downward directed flame the melt jet passes, is an oil burner that burns around 150 m3 of combustion air and 45 kg of heating oil per hour. The raw silicon exits the production furnace at a temperature of around 1800 ° C. The method leads to the following result: Crude silicon Purified silicon Insoluble 0.12% 0.06% 0.08% 0.06% / »0.47 ° / o TitaniumV« & 5 ° / p0.31% 0.12% Iron 97 ^% 0.06% 98.90% Aluminum Calcium CarbonSilicon The above analysis values are mean values from several analyzes, whereby the samples were taken from the raw silicon when it exited the furnace and from the cleaned silicon when it overflowed the ladle when it was poured into bars. As can be seen, the calcium content of the silicon purified according to the invention is well below 0.30%, and the total content of Ti, Al and Ca together of 0.49% allows the purified metal to be used for the production of silicon sheets. The carbon content is also greatly reduced. The iron, calcium and aluminum content can be further reduced by using fluxes containing alkali salts. P \ TENTA "PROBLEMS 1. Process for the purification of silicon, in particular that in the reduction of silica accruing raw silicon, or contaminated ferrosilicon by treating with oxidizing Gases, characterized in that the liquid contaminated silicon or ferrosilicon an oxidizing flame can be passed through in a thin beam and the surface of the cleaned Keeps the melt in contact with the flame until it is poured. 2. The method according to claim 1, characterized in that the one from a three-phase electric furnace raw silicon tapped for silica reduction a protruding into the ladle Fuel oil or gas flame can be crossed out with which the surface of the accumulating Melt until the slag layer formed is tapped and the subsequently poured obtained pure silicon remains in contact. 3. The method according to claim 1 or 2, characterized in that the liquid silicon or ferrosilicon adds flux containing alkali salts. Considered publications:
German Patent No. 944 571; British Patent Nos. 690 243, 749 423;
French patent specification No. 1,131,796. 1 sheet of drawings ® 909 610/362 8. 59