Probing growth precursor diffusion lengths by inter-surface diffusion

Understanding and optimizing thin-film synthesis requires measuring the diffusion length d α of adsorbed growth precursors. Despite technological advances, in-situ measurements of d α are often unachievable due to harsh deposition conditions, such as high temperatures or reactive environments. In this paper, we propose a fitting approach to determine d α from experimental data by leveraging inter-surface diffusion between a substrate and a strip obtained by, for example, processing a film. The substrate serves as a source or sink of precursors, which influences the growth dynamics and shapes the strip profile. By fitting simulated profiles to given profiles, we demonstrate that d α can be determined. To achieve this, we develop a theoretical growth model and a simulation strategy. The growth model incorporates inter-surface diffusion, adsorption, and desorption of growth precursors, with growth being proportional to the concentration of adsorbed precursors. In our simulations, a chain of nodes represents a profile, and growth is captured by the displacement of those nodes, while keeping the node density approximately constant. For strips significantly wider than d α , a dimensionless precursor concentration and d α are the fitting parameters that are determined by optimizing a suitably defined measure of the similarity between simulated and given profiles. We examine how variations in model parameters influence growth dynamics. We also evaluate the robustness of our procedure by analyzing the effect of profile resolution and noise on the fitted parameters. Our approach can offer valuable insights into thin-film growth processes, such as those occurring during plasma-enhanced chemical vapor deposition.