Analysis of multipole fields for a practical wire lens of an aberration corrector

Abstract

A new type of aberration corrector with a “wire lens” instead of conventional magnetic material pole pieces has been developed in order to avoid magnetic hysteresis and inhomogeneity. The wire lens consists of symmetric parallel lines alongside the optical axis and contains no magnetic materials. Multipole fields as means of aberration correction are generated by the currents running through the parallel lines. Previous studies have proved the possibility of aberration correction by parallel lines (wire lens) under a hypothetical condition. In particular, the wire lens is assumed to have an ideal shape (infinite lines) and generate rectangular multipole field distributions. In this study, more practical configurations, i.e., closed loops for the current flows and the finite length of the lines, are presumed. Furthermore, analytical equations of multipole fields for the practical wire lens are derived to verify the aberration correction.

Correcting an Aberration with a Wire Corrector for SEM

“…The wire corrector uses symmetric parallel lines (a wire lens) which allow the current to generate multipole fields without using any magnetic materials. Optical simulations have previously suggested the wire corrector can correct spherical aberration [3][4]. In this study, a demonstration of the aberration correction using a prototype wire corrector installed in a conventional scanning electron microscope (SEM) reveals the wire corrector is a practical possibility.…”