Selective deposition of tungsten—prediction of selectivity

Abstract

Preferential or selective chemical vapor deposition to a substrate region is based on a difference in thermochemical stability between different substrate regions. The higher this difference is, the higher selectivity is expected. In this paper a thermodynamic analysis of selective deposition of tungsten from H2 and WF6 on silicon regions in the presence of silicon dioxide is presented. At the initial stages of growth—silicon present in the vapor—the selectivity is favored by a low temperature, a low total pressure and a high WF6 concentration in the vapor. For the continuation—growth on the deposited tungsten—a low total pressure, a low WF6 concentration in the vapor and a higher temperature than that used initially should be chosen for highest selectivity. From the analysis it is also seen that simultaneous etching and tungsten oxide/tungsten deposition may occur on the silicon dioxide. The technique used to analyze the selective tungsten deposition process seems to be a useful tool for optimizing the selectivity in a given system and for reducing or eliminating undesired side reactions.