A molecular dynamics study of deposition rate dependence of film morphology in the sputtering process

Abstract

The morphology of thin films grown by the sputtering process is studied by the two-dimensional molecular dynamics (MD) simulation. The numerical model uses the Lennard–Jones potential to model the atomic interaction between atoms. Impact energy transferred from incident atoms to the substrate is modeled by rescaling the upper layer atoms of the substrate. Deposition process parameters, incident energy and deposition rate, are investigated in terms of their effect on film morphology. It is found that deposition rate has a significant effect on thin film morphology for higher energy incident atoms (sputtering), but an effect not found at lower energy (evaporation). In addition, it is found that for a specific incident energy there exists an optimal deposition rate region for best film quality. Furthermore, the influence of deposition rate is mainly on the interaction frequency occurring between incident atoms on the surface of the deposited film. Increased deposition rate is beneficial to momentum transfer among the incident atoms during migration. However, too large a deposition rate loses this advantage. When the number of migrating atoms on the film surfaces reaches a critical number, long-distance migration is replaced by short-distance collision. Thus, momentum transfer and migration become confined to small local areas, creating isolated islands of growth and finally, higher numbers of voids in the finished film.