Assessment of the relative contribution of atomic mixing and selective sputtering to beam induced broadening in SIMS depth profiling.

A thin native silicon oxide layer, covered with hydrogen- and carbon-containing impurities, was sandwiched between a crystalline silicon substrate and an evaporated 35 nm layer of amorphous silicon. SIMS depth profiles of H-, C-, O- and Si- were measured under 4 to 12 keV Cs+ impact. The impurity profiles exhibit exponential slopes at the leading and the trailing edges. The characteristic widths describing the exponential tails increase with increasing probe energy. At the leading edges the characteristic widths for H, C and O are identical whereas at the trailing edges the decay lengths are strongly element-specific. The results are interpreted in terms of the relative importance of atomic mixing and selective sputtering. The oscillatory behaviour of the Si- and H- yields, observed in the vicinity of the interface, is also discussed