GB980173A - Process for the manufacture of very pure silicon - Google Patents

Abstract

Very pure Si is manufactured by reduction decomposition of a halogeno-silano with H2 at 800-1400 DEG C. in contact with directly or indirectly heated carrier bodies; the reaction gases from the decomposition zone are passed through a heated static or fluidized bed of particulate Al which reacts with the HCl to form AlCl3 which is precipitated by cooling the gases, the residual gases after addition of fresh halogeno-silane, and if desired H2, are returned to the decomposition zone. The halogeno-silane may be SiCl4 or mono-, di- or tri-chlorosilane. In stage 1, Fig. 1, Si is produced by reductive decomposition at e.g. superatmospheric pressure. In stage 2 the reaction vessel is e.g. of steel or quartz and the Al bed is at 50-500 DEG C., preferably below 300 DEG C. for SiCl4 and above 300 DEG C. for SiHCl3. <PICT:0980173/C1/1> In stage 3 the vessel is at 20-80 DEG C., contains members of large surface area, e.g. metal plates, wire netting, fibres or finely divided filter material, and may be divided into 2 parts through which the gases flow successively, in the first part the greater part of the AlCl3 is precipitated and the second part, in which the gases are clean, contains very fine filter material, e.g. quartz wool. In an optional stage 4, the SiCl4 is condensed, e.g. fractionally, and then returned to storage vessel 9 or in Fig. 2 (not shown) to the gases resulting from the reaction of SiHCl3 and H2. The Si may be repeatedly zone-refined to give a high specific resistance and can be used as a semi-conductor.