Contributions to computer-aided interpretation of ion sputtering depth profiling

Abstract

To evade some of the problems that restrict the quantification of sputtering depth profiling, i.e. the conversion of measured signal intensity vs sputtering time profiles into the concentration vs depth scale in the case of changing sputtering rate with depth, algorithms and computer programs are presented for modelling the intensity vs time profile by computer simulation of the measuring process. Required are only rough a priori information on the sample type under investigation, e.g. implanted material or layer systems, some knowledge of the actual sputtering conditions and basic assumptions on origin, transmission and registration of the analytical signals. The modelled profile may be adapted to the measured one by interactive, stepwise variation of parameters assumed to be important. For scanned ion beams, procedures for efficient estimation of the actual ion current density and of the changing sputtering rate with depth are given too. All calculations can be performed at a desk using any IBM compatible personal computer. Owing to its modular structure, the program may be easily extended and completed according to model refinements by users. Agreement between computed and measured profiles indicates that the a priori assumptions on the true depth profile were correct in all probability. Otherwise, in most cases, further experiments have to be performed in order to decide between experimental artefacts and material-inherent deviations considering also atomic mixing, radiation enhanced diffusion, preferential sputtering and similar effects. Moreover, the quantitative relations between sputtering conditions and crater shape obtainable by the model can support optimization of the measuring conditions particularly with respect to depth resolution. At last, the procedures and algorithms given here are a contribution to the final aim of direct quantification of the results of sputtering depth profiling. This article is an electronic publication in Spectrochimica Acta Electronica (SAE), the electronic section of Spectrochimica Acta Part B (SAB). The hard copy text is accompanied by three disks with executable programs, source code files, data files and text files. The manual and tutorial text files include material that is useful for learning the effective handling of the program and for program extension by user-written program parts.