Selective effect of ion/surface interaction in low frequency PACVD of SiC:H films: Part A. Gas phase considerations

Abstract

Hard silicon carbide based films (a-SiC:H) are obtained in a capacitively coupled low frequency PACVD device from the decomposition of tetramethylsilane (TMS) diluted in argon (ν=50 KHz, DC bias: ∣Vdc∣=0–400 V). To get a better understanding of the effect of ion bombardment occurring during growth, optical emission spectroscopy was performed near film surfaces to identify energies and relative densities of Si+ and H emitting species, and underline their etching or sputtering from the film surface as it corresponds to strong microstructural modifications of the material. Concurrently, simulation of the effect of ion bombardment onto a film surface has been performed by the use of ©SRIM 2003 to estimate sputtering yields of its different constituting elements. As a general manner, carbon in C–Csp3 form presents the lower sputtering yield relatively to C–Csp2 and Si–C. Ion sputtering can then lead to a relative increase of C–Csp3 at the extreme surface of the target. Such an increase is observed both in experiments, through post-treatments of a film in Ar plasmas (results are exposed in Ref. [A., Soum-Glaude, L., Thomas, E., Tomasella, J.M., Badie, R., Berjoan, Selective effect of ion/surface interaction in low frequency PACVD of SiC:H films: Part B: Microstructural study. Submitted for publication Surf.Coat.Technol.]), and in simulations where this phenomena occurs when ions energy ranges 100–250 eV. For higher energies, sputtering of the surface is no more selective: the simulated sputtering yield ratio [γ(Si–C)/γ(C–Csp3)] is constant versus EAr+ and equals the relative content (%(Si–C)/%(C–Csp3) in the material. Similar results are obtained for C–Csp2 bonds. Such a phenomenon is employed to enhance hardness of films.