Thin film microstructures: Simulation and theory

The nature of the microstructure of physical vapor-deposited films depends sensitively on the substrate temperature during deposition. At low temperatures the microstructure is porous and ballistic aggregation-like, at intermediate temperatures the microstructure is columnar, and at elevated temperatures the grains are three dimensional. These different microstructural regimes are known as Zone I, II, and III, respectively. A theoretical analysis is presented in which the temporal evolution of the columnar micro-structure (Zone II) is studied. The columnar microstructure is shown to be a balance between shadowing (which results in Zone I microstructures) and surface diffusion (which tends to smooth the surface). In addition to predicting the proper microstructure, this analysis properly predicts the temperature at which the Zone II to Zone I microstructural transition occurs. Since bulk diffusion is negligible and surface diffusion controls the microstructure in Zone II, the microstructure in the bulk of the film, may be viewed as frozen and all microstructural evolution occurs at the current, or active, surface. A Monte Carlo computer simulation technique which models the microstructural evolution of the surface is presented. The simulation follows the temporal evolution of realistic three dimensional Zone II microstructures and accounts for growth competition between adjacent grains and the formation of film texture.