Kinetic Monte Carlo simulation of the growth of polycrystalline Cu films

A kinetic Monte Carlo (KMC) technique has been developed for simulating the growth of polycrystalline thin Cu films on Cu. This method consists of an impact angle-based multiple-collision method for the deposition of incident atoms from an atomic beam and surface diffusion of the surface atoms, combined with a restriction of growth within identically oriented grains to simulate the surface morphology and porosity of a polycrystalline-like material. The effect of incident angle (measured from the substrate normal) on the growth morphology and characteristics was the main focus of the study here. This simulation scheme allowed us to observe both columnar growth, at incident angles below about 60°, and dendritic porous growth, at angles above this value. A comparison was made between results from the atomic-scale KMC simulation and existing macroscopic theories to relate the morphological features of the grown film to the angle of the incident beam. We observed that the relationship between the angle of growth and the angle of incidence depends sensitively on the rules governing the sticking probability. Comparison of the roughness of the films predicted by KMC to experimental atomic force microscopy and X-ray reflectance data shows similar behavior. The predicted density of the porous films was also in good agreement with experimental results. It was demonstrated that faceting phenomena is a function not only of temperature but also the angle of incidence of the incoming beam. At grazing angles of incidence, faceting can be observed at a temperature much lower than the minimum temperature necessary in experiments conducted at normal incidence.