Structural and electrical characteristics of W-N thin films prepared by reactive rf sputtering

The crystal structure, chemical bonding state, composition, and electrical resistivity of W-N films deposited by reactive rf sputtering are investigated by x-ray diffraction, x-ray photoelectron spectroscopy, Auger electron spectroscopy, Rutherford backscattering spectrometry, and four-point probe. Using 150 W of sputtering power and 25% of N2 partial flow rate, the deposition rate and resistivity of W-N films decrease with increasing negative substrate bias. When the substrate bias is set at -100 V, resistivity of W-N films increases while the deposition rate decreases with increasing N2 partial flow rate. W+W2N mix phase, W2N phase, and W2N+WN mix phase are obtained at 10%, 15%-25%, and 40% of N2 partial flow rate, respectively. When the N2 partial flow rate is greater than 40%, the films become amorphous like. Nitrogen concentration in the W-N films increases continuously with increasing N2 partial flow rate, and the W 4f core-level electrons change gradually from metallic W bondings to WN bondings. By reducing the sputtering power to 50 W, we have found that film resistivity also rises with increasing N2 partial flow rate but crystalline W2N phase can be obtained with 10%-50% of N2 partial flow rate. The connection between the process conditions, structural change and electrical resistivity of the sputtered W-N thin films is discussed