Modelling and computer simulation of ion-beam- and plasma-assisted film growth

Abstract

Computer simulations of the binary collision approximation type have been applied to problems of the ion-assisted deposition of thin films. Calculations can be performed using simplifying rate equation models, into which yields obtained from static Trim simulations are inserted. Alternatively, the dynamic-composition code Tridyn allows direct and complete simulations of the time-dependent processes. Results are shown for different processes of ion-beam-assisted deposition and plasma-enhanced chemical vapour deposition. Simulations of the formation of boron nitride films deposited from evaporated boron and energetic nitrogen show excellent agreement with experimental results for nitrogen concentrations below the stoichiometric limit. For high N-to-B flux ratios, non-collisional mechanisms (ion-induced outdiffusion and surface trapping of outdiffusing nitrogen) have been included in the simulations, again producing good agreement with the experimental results. Under appropriate conditions, the ion-assisted evaporation of titanium is subject to a delicate balance of deposition and erosion, which results in selective deposition on different substrates and a self-controlled stationary film thickness. Finally, a simple model is evaluated for the composition of hydrogenated carbon films grown in methane plasmas. The hydrogen content of the films decreases with increasing ion energy owing to ion-induced release of hydrogen.