Nucleation and growth of clusters in the process of vapor deposition

Abstract

A model for thin film formation and cluster growth was proposed to simulate the vapor deposition process onto solid substrate. The nucleation and growth rates of clusters were computed based on an adatom concentration distribution that is obtained by solving an adatom diffusion equation on the substrate. A sequence of time stages was proposed in order to solve the time-dependent problem. By using of this computation procedure, the cluster density, surface coverage ratio, cluster size distribution and growth rate of a single cluster during the deposition process can be obtained. The effects of operation conditions and interfacial parameters on the nucleation and growth of cluster and film structure are discussed. The results show that a power law variation of cluster density with time was obtained. Higher values of J and E a, and lower values of T, E d and θ lead to a higher nucleation rate and higher cluster density. However, for a system of high nucleation rate, owing to the depletion of the adatom by the existing clusters, the clusters grow slowly at the later stages and a smaller cluster results. In the early stage of vapor deposition, when the coalescence of clusters is insignificant, the clusters are distributed with the most popular size of clusters occurring near the right-hand end of the distribution curves. At an elevated substrate temperature, the cluster size distribution is much narrower and smaller than that for a lower substrate temperature. The results also show that to obtain a film structure of large grains or single crystal, the operation conditions of elevated temperature and low vapor impinging rate are required.