Effects of nitrogen composition on the resistivity of reactively sputtered TaN thin films

Nanocrystalline tantalum nitride (TaN) thin films have been deposited by reactive direct current magnetron sputtering technique on Si/SiO2 (100) substrate with nitrogen flow rate ranging from 0, 3, 5, 7, 9 to 11 standard cubic centimeter per minute (sccm). Structural properties, surface morphology, chemical composition and and resistivity of the TaN films were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy, X-ray photoemission spectroscopy (XPS) and four-point probe measurements, respectively. In the XRD spectra, a classical formation sequence of tantalum nitride phases in the order of Ta-Ta2N-TaN-Ta4N5 and decreasing amount of metallic Ta were observed with increasing nitrogen flow. The electrical resistivity of the TaN film was found to increase with increasing N/Ta ratio as a result of the increased electron scattering from interstitial N atoms. In the XPS analysis, two groups of Ta4f doublets relating to different TaN phases were observed in the core level spectra of TaN films. No strong coupling was observed between the Ta4f doublets and the Ta4p and the N1s groups. The appropriate nitrogen flow was believed to be helpful in the bonding and formation of stoichiometric TaN. Copyright © 2014 John Wiley & Sons, Ltd.