Deposition uniformities on a wafer and in a trench for tungsten silicide LPCVD in a single-wafer reactor

Abstract

A transient model of a single-wafer reactor in axisymmetric, stagnation point flow is used to study the effects of operating conditions on film thickness uniformity and composition uniformity across the wafer during low pressure chemical vapor deposition of tungsten silicide. Orthogonal collocation on finite elements is used to solve the transient model equations; continuity, momentum, energy and chemical species balances. A feature scale model for simultaneous Knudsen transport and heterogeneous reactions is used to predict film thickness in infinite trenches. Boundary conditions for the feature scale model are established using the reactor scale model. The use of a combined reactor scale and feature scale model is demonstrated to select deposition conditions which provide both good interwafer uniformity and good intrafeature uniformity. Film thickness and composition uniformity on a wafer are predicted using a model for a single-wafer reactor. Significant differences in step coverage predicted using partial pressures in the feed stream and partial pressures at the wafer surface were observed. Step coverage differences between the wafer center and the wafer edge were also significant under the operating conditions used in this study. Uniformities of interwafer and intrafeature step coverages inceased as either the wafer temperature or the partial pressure ratio of dichlorosilane to tungsten silicide in the feed was decreased.