Growth mechanism difference of sputtered HfO2 on Ge and on Si

${\mathrm{HfO}}_2$ films were deposited by the reactive sputtering on $\mathrm{Ge}$ and $\mathrm{Si}$ substrates simultaneously, and we found both the interface layer and the ${\mathrm{HfO}}_2$ film were thinner on $\mathrm{Ge}$ substrate than those on $\mathrm{Si}$ substrate. A metallic $\mathrm{Hf}$ layer has a crucial role for the thickness differences of both interface layer and ${\mathrm{HfO}}_2$ film, since those thickness differences were observed only when an ultrathin metallic $\mathrm{Hf}$ layer was predeposited before the reactive sputtering process. The role of metallic $\mathrm{Hf}$ in these phenomena is understandable by assuming the formation of a volatile $\mathrm{Hf}–\mathrm{Ge}–\mathrm{O}$ ternary compound at the early stage of the film growth. This result shows that the ${\mathrm{HfO}}_2∕\mathrm{Ge}$ system has an advantage over the ${\mathrm{HfO}}_2\mathrm{∕Si}$ system from the viewpoint of further reduction of the gate oxide film thickness.