[en] The morphology of single crystal silicon and SiO₂ surfaces etched in CF₄ or CF₄ + 5% O₂ plasma as well as properties of MOS structures obtained by thermal oxidation of plasma etched Si are studied. The etched surfaces are rough and the shape and the size of the roughnesses depend mainly on the thickness of the removed layer and are different for Si and SiO₂. The electrical properties of MOS structures fabricated on plasma etched Si surfaces can not be distinguished from those of reference samples, prepared on standard cleaned Si wafers. (author)