A numerical investigation of aerosol dynamics during silane pyrolysis

The growth of silicon thin films from silane, SiH4, by chemical vapor deposition (CVD) is a common process in which a gaseous mixture of reactive precursors flows over a heated substrate upon which deposition occurs. Process parameters are often selected to optimize characteristics of the deposited film, such as uniformity and morphology. The unintended consequence of optimizing this process at the growth interface is that significant chemical reactions can occur in the gas prior to reaching the substrate surface. Under conditions typical of epitaxial silicon deposition from silane, these homogeneous reactions can lead to the gas-phase formation of solid silicon particles. The objective of this research is to develop numerical models to describe the formation and subsequent dynamics of the aerosol population encountered during silane pyrolysis.; A one-dimensional aerosol model, intended for use with the Sandia SPIN code in a rotating disk CVD reactor, is constructed using a moment transport formulation. A detailed gas-phase chemical kinetic mechanism for the thermal decomposition of silane is utilized to simulate the formation of silicon particles and the depletion of intermediates through condensation, while the heterogeneous kinetics are simulated using a phenomenological mechanism involving sticking coefficients. This model is used to systematically investigate the gas-phase dynamics of the aerosol population and the subsequent impact on film deposition rate. Conditions which minimize the deleterious effect of the aerosol population on film deposition rate are identified.; A two-dimensional model is then used to investigate aerosol formation during silane pyrolysis in a wall-less reactor. The wall-less reactor is particularly amenable to numerical investigation because the homogeneous kinetics leading to aerosol formation are isolated from heterogeneous effects. The model for aerosol dynamics is based on a simplified sectional technique, modified to allow for the simulation of particle growth via condensation. The effects of process parameters on the dynamics of the aerosol population are investigated.; A more complete understanding of the aerosol dynamics encountered during silane decomposition has resulted from this research. The models' limitations are shown to be due to the kinetic mechanisms utilized to simulate particle formation and condensational growth.