Kinetic modeling of tungsten silicide chemical vapor deposition from WF6 and Si2H6: Determination of the reaction scheme and the gas-phase reaction rates

Kinetic studies were carried out on tungsten silicide (WSix)(WSix) chemical vapor deposition from WF6/Si2H6 in a hot-wall type tubular reactor, focusing on the axial distributions of step coverage and composition ratio. The growth-rate profile within the tubular reactor showed exponential decay, which suggests first-order reaction kinetics. The silicon content of the film increased downstream in the reactor, but the step coverage quality was independent of axial position. The reactive sticking probabilities obtained from the step coverage profile were about 0.33. Two reaction models were investigated to explain these experimental results. The first model is a parallel deposition model, in which W-containing species and Si-containing species are depositing separately. The other model is a consecutive reaction model, in which W-species and Si-species react in the gas phase to form intermediate species containing W and Si. Considering these plausible kinetic mechanisms, consecutive reactions in the gas phase to form W and Si containing species were found to be the controlling factor in the WF6/Si2H6 process. These gas-phase homogeneous reaction-rate constants of the WF6/Si2H6 process were obtained from axial distribution of film composition ratio based on this kinetic model, and the activation energy is about 25 kJ/mol.