Effect of nitrogen plasma conditions on the electrical properties of silicon oxynitrided thin films for flash memory applications

Si[100] substrates were oxynitrided with nitrogen plasma, at different exposure times, followed by thermal oxidation in dry O₂ without using any harmful or global warming gas. Secondary ion mass spectroscopy (SIMS) measurements confirm that nitrogen is confined to the immediate vicinity of the surface. The damage induced in the thin SiO₂-Si system after an exposure to nitrogen plasma at different exposure times ranged from 10 to 60 s was estimated from the analysis of C-V and I-V measurements. A generation of different densities of positive oxide charge has been observed. Correlation between the local bonding structures in the oxynitride films and the electrically active defective states at the Si-SiO₂ interface are also discussed. It is proposed that improved electrical characteristics for positive charge trapping, interface state density, leakage current, and stress immunity of the oxynitride films could be obtained by using an optimal plasma exposure time of about 30 s. The preliminary results obtained indicate that these oxynitride films can be considered as potential candidates for ultra thin gate oxide and flash memory applications.