Effect of deposition conditions and buffer layers on amorphous or polytype phase formation in Al₂O₃ thin films by chemical vapor deposition using tri-methyl aluminum

抄録

Al₂O₃ thin films were deposited on (001)Si substrate through Cr₂O₃/yttria-stabilized-zirconia (YSZ) buffer layer by cold-wall type chemical vapor deposition method with tri-methyl aluminum as a raw material. By changing the deposition temperature, different polytypes of Al₂O₃ thin films were formed. At lower temperatures (1123–1173 K), η-Al₂O₃ and amorphous Al₂O₃ were found in mixture. With increasing the deposition temperature, the series of Al₂O₃ polytypes (γ, κ and α) appeared in the order of decreasing the unit cell volume per Al atom. At 1323 K, single-phase α-Al₂O₃ thin film was obtained in success. On (00l)Cr₂O₃/YSZ/Si substrate, epitaxial (00l)α-Al₂O₃ thin-film was grown, however, on (00l)YSZ/Si substrate, epitaxial (00l)κ-Al₂O₃ thin film was formed. It shows that buffer layer also has much influence on polytype of Al₂O₃ thin film. On the other hand, there exist the polycrystalline α-Al₂O₃ and Cr₂O₃ have the same Miller index (h k l), therefore, polycrystalline α-Al₂O₃ thin film was deposited on the polycrystalline Cr₂O₃ buffer layer in which each Al₂O₃ and Cr₂O₃ grain has an epitaxial relation. This epitaxial growth can be explained by both the similarity in crystal structure between Al₂O₃ film and Cr₂O₃ buffer layer, and also their moderate lattice mismatch.