AVS 47th International Symposium
    Surface Science Tuesday Sessions
       Session SS2-TuA

Paper SS2-TuA4
Surface Modification of CaF@sub 2@ for Improved Heteroepitaxy

Tuesday, October 3, 2000, 3:00 pm, Room 209

Session: Stimulated Processes and Excitations
Presenter: A. Bostwick, University of Washington
Authors: A. Bostwick, University of Washington
B.R. Schroeder, University of Washington
S. Meng, University of Washington
E. Rotenberg, Lawrence Berkeley National Laboratory
M.A. Olmstead, University of Washington
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Fluorite (CaF@sub 2@) is a candidate epitaxial insulator for three dimensional circuits. However, heteroepitaxial growth of semiconductors and metals on CaF@sub 2@(111) surfaces is inhibited by CaF@sub 2@s low surface energy. We have investigated use of electron irradiation and surfactant incorporation to alter the surface energy balance and promote laminar growth of silicon and related materials on CaF@sub 2@(111). We report here photoelectron diffraction studies of the interaction of electrons and arsenic with CaF@sub 2@(111) surfaces. Irradiation of CaF@sub 2@ with 40 eV electrons creates fluorine vacancies in the film, raising the fluorite surface energy. The resultant defects are extremely reactive. Exposure of this surface to arsenic passivates the surface to oxygen and water contamination. We find As@sub 4@ does not stick to pristine CaF@sub 2@(111) between room temperature and 600C, but sticks only in the presence of surface defects. Room temperature exposure results in As on the fluorite surface. At elevated temperature, however, arsenic diffuses into CaF@sub 2@. It occupies two ordered sites, neither of which is a bulk fluorine site. As-stabilized, irradiated CaF@sub 2@ is more stable than either pristine or irradiated CaF@sub 2@ with regard to photon-stimulated desorption of fluorine. Deposition of Si on unirradiated CaF@sub 2@ results in an amorphous film at room temperature, but sticking is inhibited at high temperature. Si deposition on As-terminated CaF@sub 2@, on the other hand, leads to laminar growth of Si at 550C. The As acts as a surfactant, floating to the top of the Si film.