This study is dedicated to an analysis of the etch mechanisms of SiOCH, SiO2 and SiCH in fluorocarbon plasmas. The etching of these materials is performed on blanket wafers in a magnetically enhanced reactive ion etcher reactor using. fluorocarbon based chemistry (CF4/N-2/Ar). After partial etching, the Fourier transform infrared spectroscopy and mercury probe measurement indicate that the remaining substrate of SiOCH is not altered by the reactive plasma. A decrease in the etch rate of SiOCH, SiO2 and SiCH is observed either with increasing Ar dilution, or polymerizing gas addition as CH2F2 and C4F6. X-ray photoelectron spectroscopy analysis of the surface after partial etching shows that the thickness of the fluorocarbon layer formed at the film surface and its composition play a key role in controlling etch rate and selectivity of SiOCH, SiO2 and SiCH. The etch rate of these materials is getting lower when the fluorocarbon layer thickness increases and also when its fluorine concentration decreases. The fluorocarbon layer thickness and composition depend on the plasma chemistry but also on the concentration and nature of impurities (C and H) in the etched materials. Etch rates are presented and discussed with respect to plasma parameters and material composition in terms of etching mechanisms. (C) 2003 American Vacuum Society.