Thermal and Si-beam assisted desorption of SiO2 from silicon in ultrahigh vacuum

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Abstract
We have measured the kinetic parameters for the removal of SiO2 films from silicon in ultrahigh vacuum using Auger electron spectroscopy and low‐energy electron diffraction, both with and without a beam of atomic silicon incident on the surface. Due to the very low vapor pressure of SiO2, it is removed only through reduction to SiO by excess silicon. We find that the activation energy for the rate limiting step in the thermal desorption of SiO2 is 3.54±0.2 eV, so that at temperatures below ∼900 °C, thick films (∼25 Å) can scarcely be removed by thermal desorption alone, in agreement with earlier work. Very thin oxide films (∼5Å) can be readily removed at lower temperatures, since SiO formed at the Si‐SiO2 interface encounters a negligible diffusion barrier and sublimes directly into vacuum. With a beam of silicon incident, SiO forms at the oxide surface and desorbs with an activation energy of only 0.84±0.2 eV. Oxide films on silicon can be removed at temperatures as low as 700 °C using an incident silicon beam flux of 3×1013 cm−2 s−1.