Characterization of WC x/B 4C multilayers sputtered in reactive argon/methane atmospheres

Abstract

Two series of WC x /B 4C thin film multilayers were produced by d.c. magnetron sputtering in reactive atmospheres of argon with methane additions (up to 18%). Thin films of boron carbide and tungsten were also deposited separately to provide information about the composition of individual layers. The microstructure and chemistry of the sputtered films were characterized using transmission/high resolution electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, secondary ion mass spectroscopy, and ion beam analysis with MeV helium beams. High-resolution imaging showed that the structure of the individual layers was completely amorphous, although diffraction (electron and X-ray) indicated well-defined layer ordering. Chemical analysis revealed that, in addition to carbon incorporation, the multilayers contained significant levels of hydrogen. As the methane percentage was increased, the amounts of hydrogen and carbon present increased, and oxygen (which was present in all samples) and hydrogen were preferentially incorporated into the boron carbide layer. The peak reflectivity for Mg Kα radiation depended on the methane concentration, with the sample sputtered in a 12% methane atmosphere showing the highest reflectivity of 30%. Annealing of a representative multilayer caused substantial hydrogen loss, and a decrease of the bilayer spacing.