Electron optics of microlenses with inclined beams

Abstract

For multielectron beam systems with a single electron source, the outside beams need to be collimated before entering the individual microcolumns. As an alternative of the traditional multibeam source design where the broad beam from the source is collimated by a single lens, the broad beam can be first split in subbeams that are focused by a microlens array and subsequently collimated by a deflector array. This configuration avoids the large angular error due to spherical and chromatic aberration of the collimator lens. The electron optics of the microlenses that are focusing skewed beams is investigated for different lens types and geometries. A two-electrode immersion microlens array with offset apertures is a good candidate due to its small off-axial aberrations. A 100-beam source unit, comprising a Schottky emitter, an immersion microlens array, and a deflector array, is capable of generating 100 parallel beamlets with beamlet current of 2?nA.