Thin-film growth dynamics with shadowing and re-emission effects

Abstract

Growth dynamics of thin-films involves both shadowing and re-emission effects. Shadowing can originate from obliquely incident atoms being preferentially deposited on hills of the surface, which leads to a long range geometrical effect, as well as from an atomic shadowing process that can occur even during normal angle deposition. Re-emission effect is a result of nonsticking atoms, which can bounce off from hills and deposit on valleys of the surface. In the case of an energetic incident flux, re-emission can also originate from a resputtering process that includes a surface atom being knocked off by an incident ion/atom followed by redeposition to another surface point. Due to their long-range nonlocal nature, both the shadowing effect (which tries to roughen the surface) and re-emission effect (which has a smoothening effect) have been shown to be more dominant over local effects such as surface diffusion, and have been proven to be critical processes in accurately determining the dynamic evolution of surface roughness. Recent Monte Carlo simulation methods that involve shadowing, re-emission, surface diffusion, and noise effects successfully predicted many experimentally relevant surface roughness evolution results reported in the literature. For example, root-mean-square surface roughness (ω) of Monte Carlo simulated thin-films have evolved with time t according to a power law behavior ω ∼ t^β, with β values ranging from about 0 to 1 for a growth with strong re-emission effects (i.e., low sticking coefficients) and a growth with dominant shadowing effects (i.e., with high sticking coefficients), respectively. Potential future thin-film growth modeling studies are also discussed. These include advanced simulation approaches that can incorporate atomistic details of physical and chemical processes and a recently developed network growth model that can potentially capture some universal aspects of thin-film growth dynamics independent of the details of growth process.