Preparation of W-C:H coatings by reactive magnetron sputtering

Abstract

The reactive d.c.-magnetron sputter technique in conventional and unbalanced modes was used to prepare tungsten-containing hydrodcarbon (W-C:H) coatings which have low friction coefficients and high wear resistances. Reproducible deposition processes stable over a long time without poisoning could be realized using a plasma emission monitor (PEM) control unit. From investgigation of light emission spectra of the magnetron discharge the intensive tungsten line at 401 nm was selected as most suitable for process control. The dependences of characteristic process parameters such as target voltage, optical emission intensity or deposition rate on the reactive gas flow were quite different from those known for the reactive sputter deposition of TiN or other nitrides and oxides. For both tungsten and WC targets the PEM intensity decreased monotonically with increasing acetylene flow. However, the deposition rates on substrates with floating potential increased. An additional r.f. excitation of the substrate electrode caused only slight changes in rate and metal content in the coatings. It can be concluded that the sputter process is dominant for W-C:H growth. The contribution of direct plasma polymetrization at the substrate is small. From-X-ray diffraction investigations it was concluded that the W-C:H coatings contain microcrystallites of the metastable cubic tungsten carbide WC 1 − x . The Vickers hardness and Young's modulus depend on the atomic ratio of tungsten to carbon.