The physics and effects of nitrogen incorporation into HfO2 films were studied in detail. The authors found that only a trace amount (similar to 5%) of nitrogen can be introduced into the HfO2 films using plasma immersion ion-implantation technique, regardless of implantation dose. They proposed that the nitrogen incorporation is due to the filling of O vacancies (V-O) and replacement of V-O O neighbors in the bulk with nitrogen atoms. At the interface, the nitrogen atoms exist in the form of Hf-N and Si-N bonding, which significantly improve the interface properties of the HfO2/Si structure. Temperature-dependent capacitance-voltage characteristics measurements indicate that both interface and oxide trap densities were greatly reduced with the incorporation of trace amount of nitrogen atoms. (C) 2007 American Vacuum Society.