Radiofrequency reactive magnetron sputtering was used to deposit hydrogenated amorphous silicon carbonitride (a-SiCxNy: H) at 400 degrees C by sputtering a silicon target under CH4 and N-2 reactive gas mixture. Rutherford backscattering spectrometry revealed that the change of reactive gases flow rate (the ratio R = F-N2/(F-N2+ F-CH4)) induced a smooth chemical composition tunability from a silicon carbide-like film for R = 0 to a silicon nitride-like one at R = 1 with a large area of silicon carbonitrides between the two regions. The deconvolution of Fourier Transform InfraRed and X-ray photoelectron spectroscopy spectrum highlighted a shift of the chemical environment of the deposited films corresponding to the changes seen by RBS. The consequence of these observations is that a control of refractive index in the range of [1.9-2.5] at lambda = 633 nm and optical bandgap in the range [2 eV-3.8 eV] have been obtained which induces that these coatings can be used as antireflective coatings in silicon photovoltaic cells. (C) 2018 Elsevier B.V. All rights reserved.