IMPROVEMENT OF BEAM PROPERTIES BY OPTIMIZING ION OPTICS AND MINIMIZING BEAM INTERACTIONS

The beam quality of focused ion beam systems strongly depends on the aberrations of the optical elements and the Coulomb interactions between the beam particles. In order to optimize a system these have to be calculated and minimized. Methods for the optimization of electrostatic lenses and the calculation of beam interactions are discussed and some results are presented. The optimization method is used to improve an accelerator lens resulting in a new design with 35% smaller chromatic aberration. The Monte Carlo program for beam interactions is used for a simple one lens system, 105 mm long, which images a source of 1-mu-m with B(r) = 10(6) A/(m2srV) into a spot of 50 nm. Results show that for a 10 nA current the energy width has already increased 100% and the spot size 70% due to these Coulomb interactions.