減圧CVDにより作製したFe₂O₃-Cr₂O₃薄膜の溶解過程のリアルタイム分光エリプソメトリー解析

抄録

Fe₂O₃-Cr₂O₃ thin films were formed on Pt substrates at 623K by low pressure CVD technique using Fe(O₂C₅H₇)₃ and Cr(O₂C₅H₇)₃ as precursors and O₂ as a reaction gas. The dissolution processes of the films under anodic and cathodic polarization in 1kmol·m^-3 H₂SO₄ were examined in-situ by real-time spectroscopic ellipsometry. Spectra of refractive index n_film and extinction coefficient k_film of the optical constant of the films, N_film (=n_film-ik_film), in a wavelength range 470-780nm were measured as a function of dissolution time. When the film with a Cr cationic fraction X_Cr=0.26 was polarized at a cathodic potential of 0.0V (vs. Ag/AgCl/3.33kmol·m^-3 KCl), the value of n_film in a wavelength range less than 700nm and that of k_film in the whole wavelength range decreased with time. This suggests that reductive dissolution of Fe₂O₃ gives rise to an enrichment of Cr₂O₃ in the film, which is followed by an increase in the void fraction of the film. When the film with X_Cr=0.61 was polarized at an anodic potential of 1.1V, the value of n_film first increased and then decreased with time, while that of k_film monotonously decreased with time. The change in n_film was prominent in a short wavelength range. These results show that the oxidative dissolution of Cr₂O₃ causes both an enrichment of Fe₂O₃ and an increase in a void fraction or surface roughness. The influence of the enrichment of Fe₂O₃ on n_film is ascendant in the initial stage of dissolution and that of the increased void fraction or surface roughness is predominant in the subsequent stage of dissolution.