Spherical aberration corrector using space charge

We have investigated the use of space charge for the correction of spherical 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 distribution. Spherical aberration is important in focused ion beam applications where large aperture angles are needed to obtain high beam currents used for milling or deposition, because it results in large tails on the current density distribution. A space charge distribution (cloud) can be produced with a small electron gun inside an electrostatic lens that can reduce this problem. We report on the properties of one such design. (C) 1997 American Vacuum Society.