Nucleation and growth of clusters in the process of vapor deposition

A model for thin film formation and cluster growth was proposed to simulate the vapor deposition process onto solid substrate. The nucleation and grow th rates of clusters were computed based on an adatom concentration distrib ution that is obtained by solving an adatom diffusion equation on the subst rate. A sequence of time stages was proposed in order to solve the time-dep endent problem. By using of this computation procedure, the cluster density , surface coverage ratio, cluster size distribution and growth rate of a si ngle cluster during the deposition process can be obtained. The effects of operation conditions and interfacial parameters on the nucleation and growt h of cluster and film structure are discussed. The results show that a powe r law variation of cluster density with time was obtained. Higher values of J and E-a, and lower values of T, E-d and theta lead to a higher nucleatio n 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 c lusters grow slowly at the later stages and a smaller cluster results. In t he early stage of vapor deposition, when the coalescence of clusters is ins ignificant, the clusters are distributed with the most popular size of clus ters occurring near the right-hand end of the distribution curves. At an el evated substrate temperature, the cluster size distribution is much narrowe r and smaller than that for a lower substrate temperature. The results also show that to obtain a him structure of large grains or single crystal, the operation conditions of elevated temperature and low vapor impinging rate are required. (C) 1999 Elsevier Science B.V. All rights reserved.