PROBLEMS IN THE DECONVOLUTION OF SIMS DEPTH PROFILES USING DELTA-DOPED TEST STRUCTURES

The notion that the experimentally observed sputter depth profile can be corrected for the distortions introduced by ion mixing, through a d econvolution process using the as-measured result for a delta-function like impurity distribution, is examined critically. Starting point is an existing simple, but conceptually transparent and basically not in correct, model to describe ion mixing effects. First it is shown that the characteristic exponential rise and decay lengths can be expressed as the fourth power sum of intrinsic and mixing contributions. Then i t is demonstrated that the observed variation of the full-width at hal f-maximum with primary beam parameters (ion type, impact energy and an gle of incidence) for delta-like impurity distributions is incompatibl e with the notion that the mixing efficiency may be estimated from the slopes of the profile. Consequently, the outcome of a deconvolution s tep does not result in a unique solution, but depends (strongly) on th e measurement conditions chosen.