Composition depth profiles of oxidized silicon and sputtered GaAs from angle-resolved x-ray photoelectron spectroscopy

Abstract

An inverse Laplace transform method has been used to extract composition depth profiles from angle-resolved x-ray photoelectron spectroscopy data from oxidized Si and Ar+ bombarded GaAs. An iterative procedure determines a least-squares curve fit of the data using the Laplace transforms of step functions, which are summed to yield the composition profiles. For a sample of native oxide on a Si wafer, the composition profile defines the thickness and chemical layering of the various silicon oxide states. For GaAs sputtered with 1.5-, 3.0-, and 5.0-keV Ar+, the composition depth profiles show a surface composition near the bulk ratio, a subsurface As depletion, the extent of which increases with increasing ion energy, then a return to the bulk composition at greater depth. These As composition profiles result from preferential sputtering caused by surface segregation enhanced by sputter-assisted diffusion in the near surface region.