Mechanical characterization of a-C:H:SiOx coatings synthesized using radio-frequency plasma-assisted chemical vapor deposition method

A series of SiOx containing a-C:H films was deposited on polished silicon substrates by RF PACVD (Radio Frequency Plasma Assisted Chemical Vapour Deposition) method using methane and hexamethyldisiloxane (HMDSO). Three CH4/HMDSO flow ratios and four self-bias voltages were applied for the synthesis of 12 different a-C:H:SiOx coatings having different properties and silicon/oxygen concentrations. The chemical structure of the deposited films was determined by Fourier transform infrared spectroscopy. Detailed characterization of the mechanical properties of SiOx incorporated carbon coatings was made using the nanoindentation (hardness and modulus) and profilometry (residual stress) methods. Hardness and elastic modulus were used for the evaluation of the endurance capability (H/E) and resistance to plastic deformation (H3/E2). The elastic recovery was calculated based on loading and unloading curves. The residual stress of diamond-like carbon coatings can be effectively reduced by the incorporation of SiOx. The mechanism of reducing the residual stress depending on the applied self-bias voltage is proposed. In the case of all of the examined coatings the addition of SiOx reduces the hardness, while for high self-bias voltages an increase of endurance capability and resistance to plastic deformation is observed.