Influence of substrate bombardment on sputtered a-Si:N thin film properties

Amorphous silicon nitride thin films (a-Si:N) were deposited using RF diode reactive sputtering method in a mixture of argon-nitrogen gas atmosphere. The deposition RF power was varied in order to investigate the influence of Ar ions' substrate bombardment on a-Si:N film properties. The deposition rate was found to be an increasing function of RF power, its variation follows the law: Rd∼(PRF)1/2. It is found that an increase in the RF power enhances the energy of striking Ar ions, which causes Si-Si and Si-N bonds' breaking, this yields an increase in Si and N dangling bonds concentrations. Infrared and UV-visible absorption results suggest that at low deposition RF power is nitrogen-rich material formed with a continuum network of Si-Nx bonds. However, films deposited at high RF power are formed with silicon-rich islands containing SiNx and characterized by a larger gap states density. The electrical conduction mechanism is governed by the ohmic regime in films elaborated with low RF power. However, with increasing the deposition power the Poole-Frenkel conduction mode became dominant with the possibility of Fowler-Nordheim tunneling contribution at high electrical fields. The amphoteric character of Si dangling bonds is revealed in films containing a large density of defect, the contribution of holes' conduction in current transport is also observed in these films.