Effects of O2/Ar ratio and annealing temperature on electrical properties of Ta2O5 film prepared by magnetron sputtering

The effects of the oxygen-argon ratio on electric properties of Ta2O5 film prepared by radio-frequency magnetron sputtering were investigated. The Ta2O5 partially transforms from the amorphous phase into the crystal phase when annealing temperatures are 800 degrees C or higher. The lattice constant of Ta2O5 decreases with the increase of the O-2/Ar ratio, which indicates that oxygen gas in the working gas mixture contributes to reducing the density of oxygen vacancies during the deposition process. For the films deposited in working gas mixtures with different O-2/Ar ratios and subsequently annealed at 700 degrees C, the effective dielectric constant is increased from 14.7 to 18.4 with the increase of the O-2/Ar ratio from 0 to 1. Considering the presence of an SiO2 layer between the film and the silicon substrate, the optimal dielectric constant of Ta2O5 film was estimated to be 31. Oxygen gas in the working gas mixture contributes to reducing the density of oxygen vacancies, and the oxygen vacancy density and leakage current of Ta2O5 film both decrease with the increase of the O-2/Ar ratio. The leakage current decreases after annealing treatment and it is minimized at 700 degrees C. However, when the annealing temperature is 800 degrees C or higher, it increases slightly, which results from the partially crystallized Ta2O5 layer containing defects such as grain boundaries and vacancies.