There have been some researches which describe that the thermal stability and the dielectric constant of the high-k dielectrics could be improved by the nitridation process. In this study, we examined the effect of different ICP plasma nitridation process to the reliability of HfO2 thin films. The capacitance-voltage and current-voltage characteristics of nitrided samples were observed to decide the most suitable process time. The hysteresis, stress induced leakage current (SILC) and constant voltage stress (CVS) characteristics of the nitrided samples were preformed to verify the improvement effect of the plasma nitridation. According to this study, the ICP plasma nitridation process would be an effective technology to improve the reliability of pure HfO 2 thin films.