ON THE USE OF CSX+ CLUSTER IONS FOR MAJOR ELEMENT DEPTH PROFILING IN SECONDARY ION MASS-SPECTROMETRY

The use of Cs bombardment secondary ion mass spectrometry (SIMS) in conjunction with the detection of positively charged Cs-cluster ions, CsX+, is described. This methodology is shown to be useful for the quantitative analysis of matrix-level elements in III-V compounds such as AlGaAs, and atom fractions in mixed Group IV semiconductors such as Si: Ge alloys. The technique obtains this quantitative accuracy while not sacrificing the beneficial characteristics of SIMS such as excellent depth resolution, high dynamic range, and ability to analyze small areas. Data are shown which demonstrate the ability to detect dopant profiles (Zn) while simultaneously obtaining quantitative depth profiles for the major constituents of the sample (AlGaAs). In addition, descriptions are given of this technique's use in quantitative analysis of a sample directly from the CsX+ mass spectrum. A mechanism is also put forth which explains the surprising uniformity of sensitivities for elements detected as CsX+ cluster ions. The mechanism involves a recombination above the sample surface of the leaving flux of resputtered Cs ions and the leaving sputtered neutral atoms of the sample material. This mechanism separates the ionization process from the sputtering process much like electron gas or electron beam sputtered neutral mass spectrometry (SNMS). The result can be though of as cesium-ion SNMS.