Effects of annealing on tantalum pentoxide films in N2 and N2O gas environments

The effects of annealing in N-2 and N2O gas environments on the thin tantalum pentoxide (Ta2O5) films have been comparatively studied in this research. Annealing in NO favored the stoichiometric Ta2O5 film formation because the most significant decrease in the intensity signal of transmittance detected at 612 cm(-1) was obtained by Fourier transform infrared spectroscopy. Using X-ray photoelectron spectroscopy, the Ta 4f spectrum had a 1.9 eV spin-orbit splitting between the peak signal of Ta 4f(7/2) at 26.2 eV and that of Ta 4f(5/2) at 28.1 eV, Moreover, enhancement of the intensity signal corresponding to stoichiometric Ta2O5 at 530.7 eV was also clearly shown in O 1s spectrum. This implied that oxygen species released by NO reduce the amount of oxygen vacancies and interfacial defects to form a thermodynamically stable interface. Low leakage current density, nearly no hysteresis and low flat-band voltage in capacitance-voltage measurements also supported the above results. However, the deficiencies induced by annealing were out-diffusion of Si atoms into the Ta2O5 films and an increase in the interfacial thickness of silicon oxide that directly decreased the effective dielectric constant of Ta2O5.