Ion Sources for Focused Ion Beams – Present Status and Prospective Developments

Focused Ion Beam (FIB) processing has been developed into a well-established, irreplaceable and still promising technique in nearly all fields of nano-technology in particular for direct patterning and proto-typing on the μm scale and well below as well as sample preparation for further investigations, using SEM or TEM.
At the moment nearly exclusively gallium Liquid Metal Ion Sources (LMIS) are used for ion beam generation. Therefore, the Liquid Metal Alloy Ion Sources (LMAIS) represent a promising new alternative research area to expand the global FIB application fields. Here, especially, IBL (Ion Beam Lithography) - a direct, resistless and threedimensional patterning - enables a simultaneous in-situ process control by crosssectioning and inspection. Thanks to this, nearly half of the elements of the periodic table are made available in the FIB technology as a result of continuous research in this area during the last forty years [1]. Key features of a LMAIS are long life-time, high brightness and stable ion current. Recent developments could make these sources as an alternative technology feasible for nano patterning challenges e.g. to tune electrical, optical, magnetic or mechanic properties. In this contribution the operation principle, the preparation and testing
technology as well as prospective domains for modern FIB applications will be presented. As an example we will introduce a Ga35Bi60Li5 LMAIS in detail. It enables high resolution imaging with light Li ions, obtained with a VELION FIB/SEM system (Raith GmbH), as well as heavy Bi ions or polyatomic clusters, all coming from one ion source [2]. Additionally, also new ion source developments based on gas field emission (GFIS), on ionic liquids (ILIS), on magneto-optical traps (MOTIS) or on ICP or ECR high current sources for Xe-FIB are presented. Combined with an optimized FIB optics design they can open a bright field of new employments. These alternative ion sources will be introduced and briefly described.
[1] L. Bischoff, P. Mazarov, L. Bruchhaus, and J. Gierak, Liquid Metal Alloy Ion Sources - An Alternative
for Focused Ion Beam Technology, Appl. Phys. Rev. 3 (2016) 021101.
[2] W. Pilz, N. Klingner, L. Bischoff, P. Mazarov, and S. Bauerdick, Lithium Ion Beams from Liquid Metal
Alloy Ion Sources, J. Vac. Sci. Technol. B 37 (2019) 021802-1.