Fluoride-containing solutions are widely used to etch silicon dioxide-based films. A critical issue in integrated circuit and microelectromechanical system device fabrication is the achievement of adequate selectivity during the etching of different film materials when they are present in different areas on a device or in a stack. The use of organic fluoride-based salts in aqueous/organic solvent solutions can yield etch selectivities <1.9 for thermally grown silicon dioxide relative to borophosphosilicate glass films and thus may also obviate the need to add surfactants to the etch solutions to realize uniform etching. Etch studies with aqueous-organic fluoride salt-based solutions also offer insight into the etch mechanism of these materials. Specifically, the importance of water content in the solutions and of ion solvation in controlling the etch chemistry is described. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3374176] All rights reserved.