THE EFFECT OF PARAMETER CHOICE ON PREDICTED DEPTH RESOLUTION IN SPUTTER PROFILING

The generalised balance equation for atom accumulation (or loss) is established for conditions of ion implantation and congruent surface sputtering together with atomic redistribution in the bulk resulting from ballistic collision processes alone. A diffusion and drift approximation to the atomic redistribution allows conditions to be specified in which changes in atomic depth profiles are mostly influenced by sputtering and depth distributed implant collection rather than by relocation processes. Under these conditions the balance equation relaxes to a first-order nonlinear partial differential equation which can be solved using the method of characteristics. These solutions allow, on the one hand, prediction of the fluence and depth evolution of concentration profiles of implanted species and, on the other hand, the fluence and depth evolution of marker species concentration. The relevance of the latter predictions to sputter etch depth profiling is explored in terms of marker shifts and broadenings. The effects of atomic mixing and preferential sputtering are also assessed in approximations to a second-order nonlinear differential equation description.