Low-energy ion scattering spectroscopy (ISS) and X-ray photoelectron spectroscopy (XPS) have been used to determine the nature of Br atoms on very thin thermal silicon dioxide (approximately 5 nm) after HBr reactive ion etching (RIE). The result of ISS clarified that the etched surface was covered with 1 monolayer Br. The Br atoms on the etched SiO2 surface were found, from the result of XPS analysis, to have two chemical adsorption states. The experiment of atomic Br exposure showed that one adsorption state was on the as-grown SiO2 surface and the other state was at the damaged sites induced by ion bombardment.