Abstract text (incl. figure legends and references)

Liquid Metal Alloy Ion Source (LMAIS) is an emerging Focused Ion Beam (FIB) source technology. It has been established for nanofabrication over the last years [1]. Most recently, ion imaging with Lithium ions from GaBiLi eutectic alloy has become feasible [2]. Multiple ion species such as Lithium and Bismuth are emitted simultaneously from a single source and are separated in a subsequent Wien filter. Different ion species, light or heavy and fast or slow, can be selected quickly without any mechanical sample or column adjustment [3].

Lithium is the lightest ion available from LMAIS. It features the smallest virtual source diameter and lowest energy spread [4]. Hence Lithium offers the smallest probe size of all ions emitted from eutectic alloys, resulting in sub 2nm image resolution

Besides Lithium, also Gallium and Bismuth ions as well as Bi clusters are available from the same source. Bismuth ions and in particular Bi clusters have an excellent depth resolution for sample delayering. The combination of Bi and provides outstanding ion beam imaging capabilities.

Switching between Li and Bi can be accomplished within a few seconds and enables access to different ion beams within the same FIB column. This setup allows stable imaging of 3D structures and sample reconstruction. With the FIB system presented (here), Ion beams are always perpendicular to the sample and no stage movement or sample tilt is needed resulting in a stable and reliable process for tomography and 3D sample reconstruction.

In this contribution we describe the working principle and capabilities of LMAIS with a focus on GaBiLi. Results of 2D Lithium-ion microscopy and workflows for stable 3D tomography by Bismuth milling and Li imaging will be presented.

Figure 1: Li ion image of Sn/C

Figure 2: Li ion image of graphite

Figure 3: Region of interest (RIO) for tomography. Box created by 80 Bi+ milling steps and in between Li+ ion imaging

Figure 4: 3D reconstruction of semiconductor chip Stack of Li images from RIO (Figures 3)

[1] J. Gierak et al, Journal of Vacuum Science & Technology B 36, 06J101 (2018)

[2] N. Klinger et al, Beilstein J. Nanotechnology, 11, 1742–1749 (2020)

[3] W. Pilz et al, Journal of Vacuum Science & Technology B 37, 021802 (2019)

[4] L. Bischoff et al, Appl. Phys. Rev. 3, 021101 (2016)