A model was presented for shape changes in thin metal films, due to the bulk diffusion of vacancies. It was recalled that high-temperature Al sputter deposition and post-deposition annealing were increasingly used in very large-scale integrated circuit metallization. These processes could fill and planarize high aspect-ratio vias and contacts, using a few processing steps. It was noted that previous attempts to model these processes had not fully considered the role which was played by bulk diffusion and 3-dimensional curvature. Here, differential equations and boundary conditions were derived which described the flow of vacancies in metal films. An approximate method of solution for this system of equations was presented and was incorporated into a thin-film deposition simulation of ballistic deposition. This simulation was then used to analyze data on post-deposition annealing and high-temperature sputter deposition. Particular emphasis was placed upon determining the effects of via and contact geometries, wetting angles and the deposition rate during sputtering.

S.S.Winterton, T.Smy, S.K.Dew, M.J.Brett: Journal of Applied Physics, 1995, 78[6], 3572-9