The HfO 2 /Si interface stability has been investigated by using a rapid thermal annealing (RTA), an inductively coupled plasma (ICP) and a reactive sputtering, as a comparison of thermal and plasma oxidations of the Hf/Si interface. Reduction in both capacitance equivalent thickness (CET) and leakage current density (J g ) was difficult to be attained by the thermal oxidation since it accompanies the crystalline HfO 2 with SiO 2 -like interface. Advantage is found for the plasma oxidation technique to oxidize Hf metal at low temperatures remaining the HfO 2 in an amorphous phase with silicate interface. Reduction in both CET and J g was attained by the plasma oxidation and a Hf metal pre-deposition technique.