In order to submit surface analysis database, we have studied how to measure AES and XPS spectra of thermal silicon dioxide (SiO₂) films which is one of the most popular materials in silicon ULSI devices. We investigated damages induced by an electron beam probe and by inert gas ion for surface cleaning. It was found that low energy electrons cause heavier damages than high energy electrons in AES measurements. In XPS measurements it was revealed that a peak width (FWHM) is broadened by inert gas ion irradiation, and that SiO₂ surfaces are reduced by ion irradiation. Carbon-free surfaces on SiO₂ were obtained by the anneal (400°C, 2h) in air. We are certain that the annealing process can be used as a more practical cleaning method than inert gas ion cleaning.