Effects of postannealing on the electrical properties of Ta2O5 thin films deposited on TiN/T

Abstract

The effects of postannealing on the structural and leakage current characteristics of Ta2O5 thin films deposited on a TiN/Ti bottom electrode by chemical-vapor deposition at 350 °C were investigated. The Ta2O5 film of 50 nm thickness shows an amorphous phase and smooth surface morphology after annealing in N2O plasma at 350 °C, but the film treated with rapid thermal annealing in nitrogen (RTN) at 750 °C prior to N2O plasma annealing at 350 °C has an orthorhombic structure and rugged surface morphology. In addition, the TiSi phase also appears in the specimen of RTN-treated Ta2O5 film. Moreover, the residual carbon can be effectively eliminated and the oxygen deficiency can be well compensated by the N2O plasma annealing for both amorphous and crystalline Ta2O5 films. The I–V relation of the amorphous Ta2O5 films is asymmetric with respect to the biasing polarity, which indicates that the leakage current is primarily dominated by the Schottky emission. On the other hand, the crystalline Ta2O5 film has a symmetrical I–V relation, suggesting that the non-Ohmic leakage in the crystalline Ta2O5 film is related to the Poole–Frenkel effect. The barrier heights φB for the non-Ohmic leakage in the amorphous and crystalline Ta2O5 films, as evaluated from the temperature dependence of the I–V relation, are 0.52 and 0.82 eV, respectively.