The interaction of XeF 2 with sapphire

Abstract

The interaction of xenon difluoride (XeF 2) with the sapphire {0001} surface has been investigated using X-ray photoelectron spectroscopy. Exposure to XeF 2 etches off submonolayer amounts of carbonaceous residue present on the surface. The exposure leaves a surface of stoichiometry Al 2O 3F 3.6 with fluorine atoms bonded to both aluminum and oxygen atoms. Annealing of the fluorinated alumina surface to 100°C or above results in the slow desorption of fluorine in a variety of species. The interaction of XeF 2 with sapphire is similar to that of XeF 2 with silica (SiO 2), with the exception that fluorination of silica results in the preferential removal of oxygen to form SiOF 2. The greater resistance of the sapphire surface to room temperature etching of oxygen by XeF 2 may be associated with the bonding of oxygen atoms in bulk sapphire to four aluminum atoms, whereas in bulk silica each oxygen atom bridges only two silicon atoms. Based upon the saturation coverages of fluorine on silica and alumina at room temperature, and the subsequent rates of fluorine desorption from SiOF 2 and Al 2O 3F 3.6 at elevated temperatures, the fluorinated alumina is roughly as thermally stable as the fluorinated silica surface.