Tribological properties of sputtered tungsten and tungsten nitride thin films

The surface roughness, hardness and tribological properties of tungsten (W) and tungsten nitride (WNx) thin films prepared by dc magnetron sputtering and reactive magnetron sputtering in Ar-N-2 gas mixtures have been studied using atomic force microscopy (AFM), nanoindentation measurements and ball-on-disc wear testing. A pronounced surface roughness was observed only for films under compressive strains. The surface was flat under tension but rough under compression. Similar hardness with value about 20 GPa were observed in the W and WNx (x=0.3) films. This is thought to be due to the fact the grains are restricted to a very small size in the coatings. The higher coefficients of friction (0.4 for W and 0.9 for WN0.3) suggest that WN0.3 is not the optimum phase. Finally, discussions are made with tribological test results.