Morphology of films and nanostructures grown on trenched substrates by Monte Carlo simulations

Abstract

We performed numerical simulations of two-dimensional models of film deposition on a substrate with a square trench. The particle flux mixes convection and diffusion in a broad range of the Peclet number (Pe). Two models, formerly termed SARM (Standard Adherence Rule Model) and PARM (Potential Adherence Rule Model), are considered. SARM considers aggregation of the incident particle at the first contact with the deposit, while PARM considers aggregation if a potential barrier is overcome during the particle motion. Both models represent a broad range of growth conditions in which effects of adsorbate diffusion can be neglected. The surface roughness converges to values similar to those for growth on flat substrates when the deposit is up to 5 times thicker than the trench depth. In some growth conditions, we observe the formation of funnel-like structures on the trench bottom, with dimension similar to those of the trench. This can be anticipated by an initial large aggregation rate at the upper corners of the trench. In SARM, the funnels are observed with Pe~1 (balanced diffusion and convection) and Pe> > 1 (dominant convection). In PARM, it occurs only with Pe~1, and the substrate coverage is larger in comparison with SARM deposits. Thus, a larger adsorption barrier may improve the adherence of the funnels to the substrate, with the cost of a more careful control of the properties of the incoming flux.