Elimination of cluster interferences in secondary ion mass spectrometry using extreme energy filtering

A Cameca IMS-3f secondary ion microanalyzer has been modified to allow analysis using secondary ions emitted with initial kinetic energies as high as 4500 eV. Cluster ion signals including hydrides are essentially absent when ions with initial energies < 400 eV are rejected, while atomic ion signals are sufficiently intense to allow trace element analysis. The useful ion yield for ³¹P^- sputtered from a phosphorus-implanted silicon wafer is comparable under these conditions to the useful ion yield in a depth profile obtained at high mass resolution. Because the mass spectrometer is operated at low mass resolution, peak switching is possible to monitor several ion signals in the course of a single depth profile, and the energy acceptance of the mass spectrometer can also be adjusted for individual species so that interference-free ions can be sampled at low initial energy and consequently high sensitivity.