SPHERICAL-ABERRATION CORRECTOR USING SPACE-CHARGE

We have investigated the use of space charge for the correction of sph erical aberration in focused ion beam systems. A negative space charge cloud can be formed to reduce the spherical aberration of a lens for ions or for electrons, depending on the details of the space charge di stribution. Spherical aberration is important in focused ion beam appl ications where large aperture angles are needed to obtain high beam cu rrents used for milling or deposition, because it results in large tai ls on the current density distribution. A space charge distribution (c loud) can be produced with a small electron gun inside an electrostati c lens that can reduce this problem. We report on the properties of on e such design. (C) 1997 American Vacuum Society.