Process for depositing elemental silicon semiconductor material from a gas phase

Claim 1

In a process for depositing elemental silicon from a reactive gas comprised of a mixture of a halogen silane and hydrogen whereby the reactive gas flows through a reaction housing containing a heated mandrel on which silicon is deposited from such gas and wherein the deposition rate of silicon onto the mandrel surface varies during the course of the deposition process, the improvement comprising: chronologically maintaining a relatively constant temperature at the mandrel surface and maintaining a relatively constant composition within the reactive gas; varying the reactive gas through-put past the mandrel in such a manner that the deposition rate of silicon onto the mandrel surface remains substantially constant throughout the deposition process, said deposition rate being selected at the beginning of the deposition process in relation to a surface unit area of the mandrel and in relation to a unit of time, so that the deposition rate of silicon per unit area of mandrel surface and per unit time is maintained so as to be at least about 0.1 gram per square centimeter per hour and less than about 0.5 gram per square centimeter per hour; and increasing the reactive gas through-put past said mandrel proportionately to the diameter of said mandrel which increases during the course of the deposition process.