The Ar/O2/hexamethyldisiloxane-fed expanding thermal plasma setup is employed for the deposition of scratch-resistant silicone films on polycarbonate with the purpose of replacing glass by polymers in the architectural and transportation industry. It is shown that the versatile control of parameters in the ETP setup (i.e. arc current, gas flow rates and working pressure) enables specific tuning of the film properties (i.e. chemical composition, optical and mechanical properties). The gas phase is monitored by means of mass spectrometry and cavity ringdown spectroscopy. In situ/ex situ ellipsometry is applied for the optical characterisation of the film. The film composition is determined by means of X-ray photoelectron spectroscopy and the mechanical properties are obtained using nano-indentation measurements. The control parameters are tuned such that the final scratch-resistant films are carbon-deficient and have a strong SiOSi network: stoichiometry SiC0.6HyO1. The low refractive index of 1.42 is due to the presence of residual voids in the film network. The hardness and Young's modulus of the film is 1.2 GPa and 12 GPa, respectively.