Improvements in performance of focused ion beam cross-sectioning: aspects of ion-sample interaction

TLDR

A gallium focused ion beam is increasingly used for site‑specific preparation of cross‑sectional samples for TEM, STEM, SEM, and SIM. The paper seeks to clarify the parameters that limit FIB cross‑sectioning performance, including milling rate, right‑angle cross‑section, curtain structures, ion implantation, and damage. The authors analyze these limitations through the lens of ion‑sample interaction. They show that reducing limiting factors or correcting their effects improves performance, notably that higher scanning speed boosts milling rate and that a microsampling approach with sideward or upward incidence minimizes curtain structures.

Abstract

A gallium (Ga) focused ion beam (FIB) has been applied increasingly to 'site-specific' preparation of cross-sectional samples for transmission electron microscopy (TEM), scanning TEM, scanning electron microscopy and scanning ion microscopy. It is absolutely required for FIB cross-sectioning to prepare higher-quality samples in a shorter time without sacrificing the site specificity. The present paper clarifies the parameters that impose limitation on the following performances of the FIB cross-sectioning: milling rate, cross-sectioning at a right angle with respect to the sample surface, curtain structures formed on the cross sections, ion implantation and ion damage. All of these are discussed from the viewpoint of ion-sample interaction. Improvements for these performances achieved by diminishing their limiting origins or by correcting the resultants are described. Especially, the FIB scanning speed is significantly utilizable to improve the milling rate. A microsampling method, which allows the FIB incidence in a sidewards or upwards direction as well as downwards with respect to the microsample surface, is very effective to minimize the curtain structures.