Problems in elemental concentration depth profiling with an ion microprobe

Abstract

The results of depth profiling with an ion microprobe mass analyser can be obscured by problems in the experimental conditions. When layered systems are analysed the signals of the sputtered ions from a top layer do not decay to a level below background after the penetration of such a layer. Results appear to indicate a higher concentration of the elements of the top layer much deeper in the sample. This behaviour could be attributed to ions sputtered from the surface by a non-focused component of the incident ion beam. This component of the beam, acting on the crater rim, prevents the ion signals of the top layer from decaying to below the anticipated background. The routine techniques to improve depth profiling such as rastering the incident ion beam, electronic aperturing and coating of the sample, do not overcome the influence of this phenomenon. Measuring the elemental concentrations in different depths of the sample after recoating of previously made burnrasters is shown to result in good depth profiles.