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

Abstract

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: R d ∼ ( P RF ) 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–N x bonds. However, films deposited at high RF power are formed with silicon-rich islands containing SiN x 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.