The reaction of a silicon-containing vapor with a photoresist layer, as used in some dry developable lithographic processes, was studied with Rutherford backscattering spectrometry. Degradation of the polymer layer under ion beam irradiation was observed, but it was found that this had no influence on the shape of the Si-depth profile and the total areal density. The RBS measurements were also verified with secondary ion mass spectrometry measurements. To describe the degradation process that occurs in polymeric layers upon ion beam exposure, elastic recoil detection measurements were carried out on polystyrene layers. Only one dose-independent cross section for carbon and only one for hydrogen were needed to describe the degradation behavior.