Effect of reactive gases flow ratios on the microstructure and electrical resistivity of Ta-N-O thin films by reactive co-sputtering

A combination of the beneficial properties of tantalum oxide and tantalum nitride may result in a new and functional tantalum oxynitride (Ta-O-N). In this paper, Ta-O-N thin films were fabricated by using reactive magnetron sputtering at different reactive gas ratios. The ratio of reactive gases to total flow gases was controlled from 6% to 30%. The microstructure, composition, chemical bonding, morphology and resistivity of the Ta-O-N thin films were characterized. Increasing reactive gas flow ratio will result in the increase of the O/(O + N) ratio in Ta-O-N from 0.22 to 0.79. All films were quasi-amorphous structures in this study. The higher reactive gas flow ratio led to more disorder or amorphous microstructure with a broader diffraction peak. The position of the highest intensity peak about 36 deg. shifts downward with increasing O/(O + N) ratio because of the sufficient Ta-O phase formation. The FTIR absorption bands at 500-800 cm-1 corresponding to Ta-O-Ta and Ta-O stretching vibration modes were observed. A weak absorption band at 800-1000 cm-1 was the tantalum suboxides. The resistivity increased from 288 μΩcm (conducting) to 11,540 Ωcm (semiconducting-insulating) with increasing O/(O + N) ratio. The oxygen content dominates the microstructure formation and resistivity of the Ta-O-N system compared to nitrogen.