Optimization of Object-Image Distance for Aberration and Space-Charge Effect in Symmetric Magnetic Doublet with Dynamically Compensated Field Aberrations

Abstract

Maximum beam currents are expected when the optimum object-image distances and beam semiangle are 840 mm and 0.53 mrad, 840 mm and 0.27 mrad, and 1008 mm and 0.16 mrad for the subfield sizes of 250, 500, and 1000 µ m squares, respectively, where main field size, beam energy, energy width, and beam blur specifications are assumed to be 20 mm, 100 keV, 3 eV, and 45 nm, respectively, and the space-charge effect is assumed to be proportional to the object-image distance, beam current and (beam semiangle)-1. The residual distortions after correction of the beam rotation and position are 5.2, 7.6, and 6.6 nm for the above respective object-image distance and field size conditions.