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

The effects of annealing in N₂ and N₂O gas environments on the thin tantalum pentoxide (Ta₂O₅) films have been comparatively studied in this research. Annealing in N₂O 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 N₂O 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.