Optical emission spectroscopy study of r.f. magnetron sputtering discharge used for multilayers thin film deposition

An investigation by Optical Emission Spectroscopy (OES) was performed on RF (13.56 MHz) magnetron sputtering discharge used for Tungsten Carbide/Diamond-Like Carbon (W-C/DLC) multilayer thin film deposition. The multilayer deposition is obtained from a single tungsten (99.99%) and carbon (99.99%) binary compound target by gradual variation of methane (CH4) concentration in the argon/methane (ArCH4) gas mixture. The optical emission spectra supply information about the chemical species present in the plasma, and the densities of these species can be correlated with the structure and composition of the deposited layers. The electron temperature dependence on gas pressure and methane concentration in ArCH4 gas mixture by using some Ar, W and H emission line intensities, are studied in the center of the discharge. A simple model for the excitation process of the Ar, W and H atoms allows us to calculate the density of sputtered atoms in the plasma. At high methane concentrations for deposition of DLC layers, OES shows that besides the atomic hydrogen peaks Hα (656.3 nm) and Hβ (486.1 nm) of Balmer series, emission spectra are dominated by neutral CH species and the most intense peak in the spectra corresponds to CH-band head at 431.5 nm, which is supposed to be the precursor species in the diamond-like films. Owing to the transport regime of the W and C sputtered species across the discharge, the existence of correlation between the target composition, tungsten density in the plasma, multilayer thin film composition, and microstructure determined by XPS, XRD, IR and Raman spectroscopy are studied.