The surface properties of SiO2/Si structures after different steps of contact etching processes have been studied by using normal and angular x-ray photoelectron spectroscopy (XPS). Patterned samples have been successfully analyzed. After the SiO2 etching treatments, the silicon of the trench bottom of patterned samples presents the same modifications as an unpatterned SiO2/Si samples. These modifications are well described by a two-layer model involving a fluorocarbon overlayer and an interface layer. The thickness and the composition of these two layers have been studied after the etching of SiO2 in CHF3/CF4/Ar plasmas, postetching in CF4, CF4/O-2 or SF6/O-2 plasmas, and stripping treatments. Depending on the treatment, the overlayer thickness varies from 7 to 60 Angstrom, and its relative composition of F-C bonds and C-C bonds changes. The interface layer is composed of Si-F, Si-C, and Si-O bonds. CF4/O-2 postetching has been revealed to be ineffective for the removal of the SiC residues. XPS analyses performed with a monochromatized x-ray source have permitted the estimation of structural damage : the damaged silicon resulting from the etching step is removed by each of the three postetching treatments studied in this work. Finally, the sidewall surfaces of the structure have been characterized by using an angular analysis technique with a shadowing effect.