Simulation of the effect of bulk vacancy diffusion on the shape of sputtered films deposited onto trenches and vias

We present a model for the shape evolution of a thin metal film due to the bulk diffusion of vacancies. High-temperature Al sputter deposition and postdeposition annealing are currently becoming significant (very large scale integrated circuit metallization processes. The attractiveness of these processes lies in the ability to fill and planarize high-aspect-ratio vias and contacts with very few process steps. Previous attempts to model these processes have not fully emphasized the role played by bulk diffusion and three-dimensional curvature. We present the differential equation and boundary conditions that describe the flow of vacancies in metal films. An approximate method of solution for this equation system is presented and incorporated into the thin-film deposition simulator SIMBAD (simulation of ballistic deposition). This simulator is then used to present results pertaining to both postdeposition annealing and high-temperature sputter deposition. Particular emphasis is placed upon determining the effects of via and contact geometries, wetting angles and deposition rate during sputtering.