Visible and infrared ellipsometry applied to the study of metal-containing diamond-like carbon coatings

Abstract

Metal-containing diamond-like carbon (Me-DLC) films were deposited by combining r.f. plasma-enhanced chemical vapour deposition (PECVD) and pulsed d.c. magnetron sputtering of several target materials (Mo, Nb, Ti and W) at different gas mixtures of methane and argon (relative methane flow ratios varying from 0 to 25%). Spectroscopic ellipsometric measurements from 1.5 to 4.1 eV were performed by a multichannel rotating analyser ellipsometer. It can detect a full spectrum in 20 ms at fixed positions of the analyser. IR ellipsometric spectra of the Me-DLC thin films as well as of the bare substrates were obtained from 900 to 3500 cm −1 with a FTIR phase-modulated ellipsometer that takes advantage of an optimized calibration method. The optical properties (refractive index and absorption) showed a clear dependence on concentration and type of metal on the film. When methane flow ratio increases, the size and concentration of nanocrystalline particles determine the variation from pure metal optical properties to typical DLC values. Optical results are discussed along with X-ray diffraction data and ellipsometry allows for a high sensitive analysis of Me-DLC films.