Low energy dual beam depth profiling:: influence of sputter and analysis beam parameters on profile performance using TOF-Sims

In the dual beam mode for TOF-SIMS depth profiling, the high energy analysis beam performs the analysis in the center of the sputter crater. Usually, the depth resolution is determined only by the parameters of the low energy sputter beam eroding the sample given that its sputter rate-and therefore, its contribution to the atomic mixing-is large compared to the sputter rate of the analysis beam. Typically, in shallow depth profiling the ratio of the sputter rates R is larger than 100. In microarea depth profiling however, the area to be analyzed is comparatively small. If the analysis current is kept high in order to get a good dynamic range, the sputter rate of the analysis beam is increased and its contribution to the atomic mixing becomes significant. We have investigated the dependence of the depth resolution on the sputter rate ratio for different sputter and analysis beam energies, using delta layer samples of B and Ge in Si. From these results, the value of R, below which the mixing of the analysis beam can degrade the depth resolution, can be estimated. On the other hand, the amount of additional mixing in applications that require low values of R like 3D microanalysis can be derived as well. (C) 2002 Elsevier Science B.V. All rights reserved.