Multi-Ion Plasma FIB for Advanced TEM Lamella Preparation: A Comparative Study Toward (SE)EBIC-Enabled Analysis

Ga-based Focused Ion Beam (FIB) systems are widely used for TEM lamella preparation, but undesired Ga incorporation can modify critical properties of the specimen (e.g., electrical behavior) [1]. Consequently, alternative plasma-FIB (PFIB) sources, such as Xe+ or Ar+, have become attractive for producing high-quality, electron-transparent lamellae [2]. A critical yet sometimes overlooked step in the in situ lift-out process is the protective-layer deposition. Here the thickness, uniformity, and composition can affect the subsequent FIB processing steps, including curtaining and beam-induced damage [3]. Furthermore, emerging Scanning Transmission Electron Microscopy (STEM) techniques such as (Secondary Electron) Electron Beam-Induced Current ((SE)EBIC) [4–6] demand carefully optimized lamella preparation to minimize artifacts and accurately probe conduction pathways at high spatial resolution. We aim to develop an optimized PFIB in situ lift-out protocol balancing protective layer quality, minimal ion-induced artifacts, and overall throughput by comparing Xe+- and Ar+-assisted protective deposition. By establishing reproducible and damage-minimized lamella preparation, conduction and sample uniformity can be directly visualized in future (SE)EBIC experiments. The integration of operando two-terminal (S)TEM devices, which rely on van der Waals contacts for local electrical measurements [7], also presents an opportunity for more reliable in situ conduction analyses and streamlined device integration—further enhancing the capabilities of (SE)EBIC-based studies. A functional oxide device stack (metal–insulator–metal on sapphire) was employed as the test structure. All FIB procedures were performed in a Thermo Fisher Helios Hydra UX PFIB system equipped with Xe+, Ar+, N+, and O+ plasma sources. Protective layers were deposited using GIS precursors (C, Pt, W, and co-deposited Pt + C) with either Xe+ or Ar+ as the assisting ion species with varying ion currents and deposition rates. After the protective deposition, thinning to electron transparency was conducted under different ion species and current regimes. Figure 1 compares mixed Pt+C protective layers deposited using Xe+ and Ar+ ions. The Xe+-based layer appears denser and more uniform, whereas the Ar+-based layer appears rougher and more prone to early-stage curtaining. Figure 2 shows final lamella cross-sections for Ar+ deposition, and Xe+ deposition both milled with Ar+. When milled with the lighter-ion (Ar+), the Xe+-deposited lamella exhibits a smoother surface, highlighting how a denser, Xe+-deposited protective layer combined with lighter-ion thinning offers a promising route for high-quality lamella production. Future implementation of SEEBIC will allow a direct correlation between the structural quality of these lamellae and their localized conduction behavior. Our results highlight that an optimal PFIB in situ lift-out approach can exploit the advantages of both Xe+ and Ar+. A heavier ion (Xe+) is advantageous for forming robust, uniform protective deposits—critical for high-quality electron-transparent lamellae—while a lighter ion (Ar+) provides superior surface finish during the final thinning stage. This improved methodology, combined with forthcoming SEEBIC studies, will enable new insights into the interplay between PFIB preparation, local electrical properties, and device performance [8]. SEM images of a) Xe+ assisted Pt+C deposition layer. b) Ar+ assisted Pt+C deposition layer. Note that the image colour was inverted using the invert gray LUT for more visible pores seen as white dots. Both depositions were milled with Ar+. Scale bar is 1 µm. STEM HAADF images of a) Ar+ assisted Pt+C deposition layer. b) Xe+ assisted Pt+C deposition layer. Both layers were milled with Ar+. Scale bar is 1 µm.