ENERGY SPREAD OF A FOCUSED ION-BEAM SYSTEM WITH A SUPERTIP

Our focused ion beam system equipped with a supertip gas field ion source has been operated as a retarding field analyzer in order to measure the energy spread of charged particle beams field emitted from a supertip. This quantity is of major importance for lens aberrations and thus for the obtainable target current densities. For electrons, the energy spread DELTAE ranges between 0.3 and 1.0 eV (FWHM), depending on field and current density. For hydrogen and the lighter rare gas ions, however, the energy width amounts to about DELTAE approximately 1.0 eV under typical operation conditions, independent of ion species. At low fields an unexpected rise in DELTAE up to about 10 eV takes place, which is due to a specific supertip condensation effect. An ionographic application of the recently installed computer controlled beam writing system is presented.