Top surface imaging processes are considered as attractive schemes for future lithographic processes. A major issue associated with these schemes is the dry development step which implies the obtention of anisotropic resist profiles. This anisotropy is achieve by adding SO2 to O-2 gas mixtures. In this work, oxide-masked organic resist features are etched in high density plasma sources using SO2/O-2 gas mixtures. The chemical constituents present on the tops, sidewalls, and bottoms of the etched features are determined by quasi ira situ x-ray photoelectron spectroscopy (XPS). XPS analyses show that when using SO2/O-2 gas mixtures, a thin passivation layer is formed on the sidewalls of the polymer features. This layer is mainly formed by sulfur atoms present on the polymer surface in elemental state or bonded to carbon atoms. This film is thick enough to minimize the spontaneous etching reaction of oxygen atoms with the organic resist. Samples are also analyzed after air exposure in order to determine the air-induced modification of the reactive layers formed during the dry development step. XPS analyses show that the sulfur-based passivation layer formed during the etch process interact with water moisture to form sulfur-based acids.