The deposition of suitable hard protective coatings onto organic substrates for ophthalmic applications faces several challenges, such as proper surface preparation to ensure the adhesion to the rigid substrate and a delicate balance between hardness and flexibility. In this work it is shown that SiOxCy:H-based protective coatings grown by plasma enhanced chemical vapor deposition (PECVD) from mixtures of hexamethy1disiloxane and oxygen, can be used as protective buffer coatings between the soft and easily scratchable substrate and the antireflection stack that might be applied on top of it. These coatings must show absence of optical absorption and require index matching with the substrate. To meet these conditions, a three-phase multifunctional coating PECVD deposition method has been developed, in which a progressive decrease towards the surface in the carbon content of the SiOxCy: H hard coat has been implemented. Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy and Rutherford backscattering spectroscopy characterization of the individual layers that compose the multilayer functional structure has been performed. The comparison of the results obtained from each spectroscopy shows the complementarity of these techniques and allows optimizing the protective coating performance from the optical and mechanical points of view. (C) 2004 American Vacuum Society.