Surface composition and micromasking effect during the etching of amorphous Ge-Sb-Se thin films in SF6 and SF6/Ar plasmas

Abstract A functional waveguide for photonic applications must fulfil some specific requirements in terms of dimension, shape, etch rate and roughness. In this study, Ge-Sb-Se thin films were etched using an Inductively Coupled Plasma reactor via fluorine-based chemistry. In a SF6 plasma, etch rate and roughness highlight a micro masking effect which originates from the formation of SbF3, (Se)-Sb-Fx and (Sb)-Se-F environments. The latter have been identified with in situ XPS. Systematically, a SF6 plasma is associated with a quasi-isotropic profile and a rough surface. In a SF6/Ar plasma, the impact of pressure and the argon content has been investigated. The addition of argon affects directly the fluorine atom flux and the argon atom flux which were calculated using a global model. It was found that there is a strong coherence between the fluorine atom flux, the proportion of fluorine at the surface and the RMS roughness. A synergistic effect, between ion bombardment and reactive neutral species, is observed when varying both parameters. Surface is free of fluorinated products for a high percentage of argon (95%) and low-pressures ( 4mTorr). A smooth surface and a quasi-vertical profile were achieved in a SF6/Ar with a gas mixture ratio 5/95 and at a pressure of 1.5 mTorr.