Oxidation of non-equilibrium hafnium-adsorbed silicon (111) surface/interface induced by supersonic oxygen molecule beam irradiation

Kakiuchi, Takuhiro*; Anai, Ryota*; Saiki, Taiju*; Tsuda, Yasutaka   ; Yoshigoe, Akitaka 

Initial oxidation mechanism of hafnium adsorbed Si(111)-77 [Hf-Si(111), the thickness of Hf:0.5 monolayer] was studied by synchrotron radiation X-ray photoelectron spectroscopy. The individual Hf atoms were associated with the back bonds of Si rest atoms or Si adatoms on Si(111)-77, and the Hf monosilicide HfSi) unit was formed on the outermost surface. Following the HfSi units immediately reacted with the thermal O molecules [translational energy (Et=0.03eV], Hf silicates (Hf-O-Si) were produced. In addition, some dissociated O atoms were inserted between the adsorbed Hf atoms. As a result, Hf sub-oxides/silicates up to 3+ states were formed. When a non-equilibrium condition was induced by irradiation of the supersonic O molecular beam of Et = 0.39 eV, the Hf4+ state was confirmed along with and the oxidation of Si bulk. This indicates that there is an activation energy to oxidize the Hf-Si bonds of the bulk side.