Low energy focused ion beam system design

Abstract

Focused ion beam (FIB) systems operated at typically 30keV energy have now reached a remarkable level of sophistication in terms of optical performance. Not unlike the much earlier developments in scanning electron microscopy, there now seems to be a fairly recent trend towards also enhancing the low energy performance of these systems—mainly driven by their possible utilization in transmission electron microscopy sample preparation. However, low energy operation indeed appears to have already been an issue in the very early days of FIB development—although then against the background of potential applications in direct semiconductor device fabrication. In this study, different approaches for generating low energy ion probes are discussed on the basis of previous and existing FIB systems for which experimental data have been made available. Subsequently, a dedicated low energy focused ion beam column design is introduced, which operates similarly to many modern field emission scanning electron microscopes. The performance of the system is assessed by means of standard aberration-optical calculations as well as by using data from direct ray tracing. The latter also allows the consideration of the impact of mutual Coulomb interactions.