COMPARISON BETWEEN DIFFERENT IMAGING MODES IN FOCUSED ION-BEAM INSTRUMENTS

In a two-lens focussed ion beam instrument, one can choose to either h ave a crossover in between the lenses or not. For a representative ins trument, it is shown that the optimized probe size of the non-crossove r mode is smaller than that of the crossover mode. Both the lens aberr ations and the statistical Coulomb effects are responsible for this ef fect. We analyzed the differences for a large range of beam currents a nd found that in the absence of statistical Coulomb interactions, the difference can be as much as a factor 1.6. In the presence of Coulomb interactions, the difference increases to a factor 1.8.