Photon Stimulated Desorption of Fluorine from Silicon Etched by XeF2
We have measured soft x-ray photoemission and photon stimulated desorption (PSD) from silicon surfaces which were etched by XeF2. These surfaces are covered with a layer approximately 20Å thick composed of a mixture of silicon fluoride reaction intermediates. The relative intensities of both photoemission and PSD spectral features arising from each of the various SiFx species depends strongly on the structure of the overlayer. Since photoemission measurements probe the entire reaction layer and PSD is sensitive to only the very outermost atomic layer, a comparison of these data can reveal structural details. The relative proportion of fluorides measured with photoemission varied slightly from run to run, but always showed a mixture of SiF, SiF2 and SiF3, along with a small amount of trapped SiF4. The species observed with PSD, however, varied considerably more than the corresponding photoemission spectra. Some surfaces showed only SiF3 spectral features while others showed features indicative of all three of the subfluorides. The implications of these results on the structure of the reaction layer are discussed.
KeywordsReaction Layer Conduction Band Minimum Photoemission Spectrum Kinetic Energy Distribution Monolayer Surface
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