Chemical topography analyses of silicon gates etched in HBr/Cl₂/O₂ and HBr/Cl₂/O₂/CF₄ high density plasmas

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 SiO_x-like or fluorocarbon rich. In all cases, the sidewall layer is transformed into a SiO_x 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.