An Investigation of Fixed Charge Buildup in Nitrided Oxides

Abstract

Fixed charge buildup has been studied in nitrided oxides. Oxides were grown at 1000°C in dry, wet, and containing ambients. Nitridation was carried out in pure at temperatures from 950° to 1150°C for 10, 30, 90, and 240 min. In many cases, thermal nitridation was found to cause fixed positive charge buildup in the films, resulting in negative shifts in flatband voltage. Under appropriate conditions, however, the charge buildup reverses, and approaches prenitridation values as nitridation proceeds. The rates of charge buildup and subsequent relaxation are highly dependent on nitridation conditions and initial oxide thickness, with no significant dependence on oxide growth conditions. The current model for positive charge buildup in nitrided oxides, based on dissociation of Si‐O bonds caused by hydrogen gas, is found to be incomplete and probably incorrect. Irradiation experiments were performed at doses of 104–105rad. Thermal nitridation was found to be capable of providing improved resistance to radiation‐induced positive charge buildup in some cases.