Control of Oxygen and Carbon Related Crystal Defects in Silicon Processing

In the production of silicon articles at an elevated temperature, a stream comprising a controlled mixture of an oxygen-containing first gas and a second gas is admitted to the processing chamber. The first gas is one which partially dissociates under the conditions in the chamber to form both oxygen and the second gas. The second gas is one which is not harmful to silicon at the conditions in the chamber. Substantially equilibrium conditions are established in the chamber so that the dissociation of the first gas to oxygen occurs reversibly. The partial pressure of oxygen (P _O2 ) is sensed in the chamber during processing of the article. In response to the P _O2 level, the ratio of the rates of flow of the oxygen-containing gas and the second gas is adjusted so as to maintain the P _O2 at a level less than about 10-6 atmosphere, and usually no greater than about 10-10 atmosphere, at which the density of oxygen-related defects in the processed silicon article is acceptably low. Oxygen-related defects in the silicon are thereby reduced. If graphite structures are present in the hot zone of the processing chamber, they are preferably coated with an impervious coating which will stand the high temperature and will prevent the gas stream from coming into contact with the hot graphite. Carbon-related defects in the silicon are thereby also reduced.