Beam-induced broadening effects in sputter depth profiling

Abstract

The broadening effects encountered in sputter depth profiling are reviewed in some detail. Discussion is restricted to cases where beam-induced microtopographical changes are of negligible importance. Qualitatively, the broadening effects are due to the fact that most of the energy of the incident beam is consumed for damage production in the bulk of the sample rather than for sputter ejection of surface atoms. Available models of collisional mixing are shown to describe some experimental results surprisingly well. However, experiment and theory are often not directly comparable. Analytical models predict only the smearing of a tracer atom distribution in the bulk of the sample. The sputter profile, on the other hand, constitutes a plot of an intensity, as seen by some surface analytical technique, vs the bombardment fluence. Accordingly, the sputter ejection characteristics of the sample constituents play a dominant role (selective sputtering). This feature appears to have been neglected in most of the previous studies. Rather detailed information about atomic mixing and selective sputtering can be derived from experiments involving very thin interfacial layers. The element-specific character of the broadening effects is demonstrated.