Retarded growth of sputtered HfO₂ films on germanium

HfO₂ films were deposited by reactive sputtering on Ge and Si substrates simultaneously, and we found not only the interface layer but the HfO₂ film was thinner on Ge substrate compared with that on Si substrate. A metallic Hf layer has a crucial role for the thickness differences of both interface layer and HfO₂ film, since those thickness differences were observed only when an ultrathin metallic Hf layer was predeposited before HfO₂ film deposition. The role of metallic Hf is understandable by assuming a formation of volatile Hf-Ge-O ternary compounds at the early stage of film growth. These results show an advantage of HfO ₂/Ge over HfO₂/Si systems from the viewpoint of further scaling of electrical equivalent thickness of the gate oxide films.