Multi-scale Simulations of Ion Energy Effects on Amorphous Silicon (a-Si:H) Film Deposition

Research into the synthesis of amorphous silicon (a-Si:H) films aims to elucidate the physicochemical processes occurring during plasma discharge and to identify methods for improving film quality. In this work, a complex multi-scale model based on a self-consistent two-dimensional fluid model is developed, including a one-dimensional ion MC model and a two-dimensional deposition profile evolution model, to simulate the growth process of amorphous silicon thin films in silane and hydrogen mixture gas sustained in a RF CCP discharge, in which the impacts of various parameters, including electrode spacing, electrode material, gas pressure, gas ratio, the flux of neutral and ion, and ion energy on film quality and deposition rate is comprehensively considered. From our simulation, neutral particle fluxes and ion energy demonstrate sensitivity to variations in discharge parameters(e.g. pressure, gas ratio), thereby resulting in different film quality and deposition rate. At higher gas pressures (>1 Torr), the ion energy remains low, and the dominant factor on the deposition rate is the fluxes of neutral species arriving at the electrode. At lower pressures (<0.5 Torr), the ion energy increases significantly, and the bombardment of the surface by ions within the sputtering threshold range will appropriately slow down the deposition rate and simultaneously enhance the densification of the film. However, excessively high ion energy can induce excessive vacancies via film bombardment, creating defects.