Simulation of the microstructure of chemical vapor deposited refractory thin films

Abstract

A ballistic deposition model (SIMBAD) has been extended to provide qualitative cross-sectional depictions of the microstructure present in chemical vapor deposited (CVD) films. The model qualitatively depicts the pronounced columnar structure typical of refractory metal, nitride, and silicide films−especially when deposited over integrated circuit topography. The important factors affecting thin film microstructure are seen to be flux shadowing, precursor surface diffusion, and a nonunity sticking coefficient. While the conformal step coverage typical of refractory CVD films is primarily due to a low sticking coefficient, the detailed columnar structure is the result of all three of these mechanisms. The angular distribution of the incident precursor flux is important to the shadowing mechanism, and a sticking coefficient-dependent angular distribution relevant to CVD is presented. Variations of the model to represent selective deposition (including selectivity loss) are also shown.