Prediction of Step Coverage during Blanket CVD Tungsten Deposition in Cylindrical Pores

Abstract

A mathematical model has been developed for predicting radius profiles in cylindrical pores during tungsten deposition from silane, tungsten hexafluoride, and hydrogen. The model is based on an unsteady‐state mass balance over a differential element of the pore, from which a system of partial differential equations has been derived. The conformality of deposition is measured by the parameter step coverage. Step coverage is found to be highly sensitive to deposition rate, decreasing with increasing temperature, silane and hydrogen reactant concentration, and aspect ratio of the pores. However, it is found to increase with increasing tungsten hexafluoride concentration even though the deposition rate is zero order in this variable. Experimentally derived step coverage measurements were also compared to simulations run under comparable reactor conditions. The agreement between the experimental and simulated results is good.