Effect of Recycling on the Axial Distribution of Coating Thickness in a Low Pressure CVD Reactor

Abstract

It has been proposed that a recycle loop would increase the uniformity of the coating thickness in a low pressure chemical vapor deposition reactor. Research was conducted to analytically and experimentally evaluate the effects of recycling on the axial coating thickness uniformity during the deposition of polycrystalline silicon. This research shows that considerable improvement in the uniformity can be obtained through the use of a recycle loop. The amount of improvement depends upon a variety of factors, including pressure, temperature, gas velocity through the reactor, and the recycle ratio. Furthermore, these improvements can increase the uniformity of the wafers while decreasing the amount of reactants required to produce an acceptably thick coating. This is accomplished primarily by operating the reactor at a high conversion so that the amount of reactants lost in the outlet gas is minimized.