Importance of control of oxidant partial pressure on structural and electrical properties of Pr-oxide films

For formation of gate dielectrics with higher permittivity (higher-k) using rare-earth oxide thin film, we have investigated the effect of H2O partial pressure (PH2O) during the Pr-oxide film formation and annealing on the Pr valence states and the amorphous and crystalline phase structures of the Pr-oxide films. The amorphous structure of Pr-oxide is dominantly formed in the film formed by metal-organic chemical vapor deposition (MOCVD) at a low temperature of 300 °C. The decrease in PH2O during MOCVD leads to the formation of Pr2O3 (Pr3 +) composition compared with PrO2 (Pr4 +) composition. It achieves the increase in the permittivity of the Pr-oxide films. The PH2O value drastically changes the grain size of crystal Pr-oxide in the amorphous film, and the crystalline structure is identified to be hexagonal Pr2O3 without depending on the Pr-oxide composition in the amorphous region. The annealing of the Pr2O3 film in vacuum at 500 °C promotes the crystallization of the hexagonal Pr2O3 phase, although the annealing in N2 ambient forms cubic Pr2O3 phase.