Microstructural and electrical characteristics of reactively sputtered Ta-N thin films

Ta-N thin films were prepared by RF magnetron sputtering a Ta target in an Ar+N₂ atmosphere, with the nitrogen gas flow ratio varying from 0 to 15%. The resistivity and deposition rate were measured and the microstructure of the films was characterized using glancing-angle X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Auger electron spectroscopy and X-ray photoelectron spectroscopy. The resistivity of the Ta-N films increases, while the deposition rate decreases, with increasing N₂ flow. The N/Ta ratio of the Ta-N films sputtered with 1% of N₂ is 1:2, while those of the films sputtered with 2.5-15% of N₂ are all approximately 1. X-Ray diffraction reveals that the zero-N₂ film shows a b.c.c. Ta structure, and the films with 1, 2.5-10 and 15% of N₂ are amorphous, f.c.c. TaN and amorphous, respectively. However, electron diffraction shows that, in addition to the amorphous phase, the Ta-N film sputtered with 1% of N₂ also contains nanocrystalline β-Ta and Ta₂N phases. X-Ray photoelectron spectroscopy indicates that the 1% N₂ Ta-N film shows an intermediate bonding state between metallic Ta and TaN, while the films with 2.5-15% N₂ exhibit TaN bonding. Correlation between the film resistivity and the microstructral characteristics of sputtered Ta-N films is discussed.