Optimized ion beam raster for SIMS sputter depth profiling

A computer‐driven ion beam deflection system is described. This system allows custom tailoring of the ion beam raster to optimize SIMS depth profile performance. The ion beam is deflected to produce an approximately elliptical crater, which better matches the acceptance geometry of the ion extraction optics. A crater with a larger and more evenly flat bottom is produced by varying the resident time of the ion beam within the raster area, thus allowing for the collection of more signal with better depth resolution. This is accomplished by creating an array of equally spaced sputter points on the sample, taking into account the orientation of the ion gun and the SIMS optics with respect to the sample normal. The resident time of the ion beam along the crater perimeter is extended and the raster and mass spectrometer are synchronized. The improvement in performance is shown using a strain layer superlattice test sample 720 nm thick, consisting of 40 double layers of Si/Si–30% Ge.