SYSTEM AND PROCESS FOR DEPOSITION OF POLYCRYSTALLINE SILICON WITH SILANE IN VACUUM

摘要

SYSTEM AND PROCESS FOR DEPOSITION OF POLYCRYSTALLINE SILICON WITH SILANE IN VACUUM The present invention is directed to the method and means for depositing polycrystalline silicon from silane in a vacuum. This process contemplates the use of a gas source and a means for assuring a uniform flow of gas into the deposition chamber. The deposition chamber is a hot wall furnace. The deposition zone is kept at as uniform a temperature as possible. The preferred temperature is 600.degree.C with a workable range extending from 600.degree.C to 700.degree.C. While the deposition zone is profiled flat from a temperature point of view, the deposition rate over the length of the tube appears as a flattened curve. This means that at the source and exhaust portions of the tube, the deposition rates are different from that rate in the central flattened portion. The boat upon which the wafers are placed is centered within the center portion of the curve along its flattest portion. Wafers are placed perpendicular to the gas flow with a preferred spacing approximately 50 mils on center when using wafers 20 mils thick. The wafers are placed in the tube from the source input end. At the gas exhaust end, intermediate the tube and the vacuum pump, is an optical baffle. The function of the optical baffle is to collect the undeposited silane material and silicon byproducts which pass through the tube. The undeposited silane material appears in the form of a brown dust which is granular silicon and silicon monoxide. This granular material forms around the exit end of the tube and in the baffle.