Electron-impact silane dissociation and deposition rate relationship in the PECVD of microcrystalline silicon thin films

摘要

An investigation of the relation between silane electron impact dissociation and deposition rates of microcrystalline silicon thin films, has been performed in highly diluted SiH_4 in H_2 discharges, by applying a combination of experimental measurements and modeling of the process. A wide range of frequencies (13.56 MHz - 50 MHz), power densities (11 mW/cm~2 - 162 mW/cm~2) and silane partial pressures (2%-6%) at two total SiH_4/H_2 pressures of 0.5 Torr and 1 Torr has been studied.In the lower pressure, independent of all other discharge parameters, SiH_4 primary dissociation has been found to be responsible for about 70% of the total silane consumption in the discharge, while a fraction of 12% of the initially produced silicon hydrides are incorporated into the growing film. The increase of pressure leads to a drop of the contribution of the SiH_4 primary dissociation to the total silane consumption and to an increase of the deposition efficiency of the initially produced radicals to a value of 26%. This result is attributed to the production of additional, two silicon atom precursors via secondary gas-phase reactions.