Roughness conformality during thin films deposition onto rough substrates: A quantitative study

This work aims to develop a tool to quantitatively connect the surfaces of a thin film and the substrate underneath during growth. To this purpose, it is suggested that at microscopic scales the surface of a rough substrate can be conveniently treated as a set of spatial wavelengths, whose periodicities undergo a gradual modification upon arrival of the depositing species and consequent formation of the front roughness. This enables the implementation of approximate models based on local roughening of surfaces to follow the evolution of morphology during growth. Focused primarily on situations in which growth models based on idealized deposition conditions are no longer valid, as typically happens under shadowing instability, the methodology detailed here is potentially capable to cover a broad class of thin-film processes with impact on many technological and industrial applications. As an example, two different batches of thin films, namely a ceramic (zirconia) and a metal (silver) deposited by pulsed electron ablation on rough substrates, are investigated. Our results agree well with expectations related to the different response to ablation of the used materials and, at the same time, match with the previously observed kinetic of formation of the surfaces under mainly nonideal conditions.