Optical Properties and X-ray Photoelectron Spectroscopy Study\ ofReactive-sputtered Ta-N Thin Films

The optical properties and an X-ray photoelectron spectroscopy (XPS) analysis of amorphous TaN thin films were investigated. Ta-N thin films reactively sputtered at N2 partial pressures (P(N2)) < 0.2 mTorr had the [111]-axis preferred orientation with a cubic δ-TaN phase while amorphous TaN thin films were obtained for P(N2) = 0.2 mTorr. The band gap of the amorphous Ta-N thin films increased from 1.4 eV to 3.6 eV with increasing P(N2) from 0.3 mTorr to 5.0 mTorr. For P(N2) < 0.3 mTorr, the chemical binding states of Ta-N are predominant as the TaN compound. Otherwise, in the chemical states of Ta-N, N-rich metastable phases similar to those of Ta2O5 increase up to a 50% fraction of Ta-N bonding states with increasing P(N2) and are closely related to the optical transparency of amorphous Ta-N thin films.