Accurate ray tracing through finite element solved potential distributions in charged particle optics

Abstract

This paper investigates the accuracy of direct ray tracing on finite element solved potential distributions in charged particle optics. The results show that while the conventional approach of first-order element solutions on region block meshes gives inaccurate results, reliable results are produced by the use of second-order elements and structured mesh refinement. Direct rays are plot on a test objective lens to calculate third and fifth-order spherical aberration coefficients. Either through using second-order elements or structured mesh refinement, variations in the aberration coefficients can be kept below 1%. For the direct ray tracing of secondary electrons, a single pole objective test example is used to demonstrate that field interpolation may limit the final accuracy, and that in this case, structured mesh refinement is the most effective means for improving the accuracy.