We have used x-ray photoelectron spectroscopy (XPS) to analyze resist patterned silicon surfaces etched in a commercial 200 mm high density plasma etcher. After anisotropic etching using gate etching chemistries based on HBr/Cl2/O2 gas mixtures with or without CF4 addition, wafers are transferred under vacuum to perform chemical topography analysis using XPS in order to measure the element concentration on the silicon surfaces at the bottom of the trenches as well as the silicon sidewalls. Composition of the layers formed on the silicon sidewalls as a function of the plasma operating conditions is reported and discussed. The sidewall layer formation is mainly attributed to the oxidation of silicon etching by-products and the deposition of fluorocarbon species. Depending on the O2 and CF4 amount during a silicon gate main etch step, composition of the layer can be either SiOx-like or fluorocarbon rich. In all cases, the sidewall layer is transformed into a SiOx material during the subsequent fluorine free soft-landing step, as a result of the direct oxidation of silicon combined with the fluorocarbon species removal by oxygen in the plasma. © 2003 American Vacuum Society.