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

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.

Surface damage induced by FIB milling and imaging of biological samples is controllable

“…Strategies to Minimize the Damage of FIB-Sample Interaction Our experimental results and those published in the literature suggest that the side wall damage can be largely reduced by using low ion current polishing mill termed also ''clean-up cut'' (Cairney and Munroe, 2003;Chaiwan et al, 2002;Ishitani et al, 2004;Rubanov and Munroe, 2004). Milling at low currents can remove the layer of damage left by high-energy ions.…”

“…Milling at low currents can remove the layer of damage left by high-energy ions. The reduction of sidewall damage can be achieved also by low-kV FIB polishing at the final step (Barna et al, 1999;Boxleitner et al, 2001;Ishitani et al, 2004;Kato, 2004; Lipp et al, 1995;Nebiker et al, 1997;Wang et al, 2005).…”

“…The FIB induced artifacts are described as morphological defects, crystal damage, uncontrolled Ga + implantation, amorphization, material redeposition, mixing of material, radiation damage, changes in surface geometry, and its electronic properties, etc. (Adams, 2006;Barber, 1993;Barna et al, 1999;Bever et al, 1992;Boxleitner et al, 2001;Brezna et al, 2003;Cairney and Munroe, 2003;Frey et al, 2003;Huang, 2004;Inkson et al, 2006;Ishitani et al, 1998Ishitani et al, , 2004McCaffrey et al, 2001;Nord et al, 2002;Perrey et al, 2004;Rajsiri et al, 2002;Reiner et al, 2004;Rubanov and Munroe, 2003Stanishevsky et al, 2002;Vetterli et al, 1995;Wang et al, 2005;Yabuuchi et al, 2004;Yu et al, 2006).…”

Nano-Tomography of Porous Geological Materials Using Focused Ion Beam-Scanning Electron Microscopy

“…Once the preparation of the isolated cube is complete, the free face of the cube perpendicular to the sample surface is gently 'polished' using a low ion current [4,59,60]. Polishing produces a smooth, flat surface for imaging and, along with the presence of the protective Pt surface layer, reduces the curtaining effect, producing the most accurate electron image of the material [61,62].…”

“…This results in a roughness within the slice plane and thus slice milling with inconsistent thickness. This is particularly the case when the sample surface has a rough topography or the material contains phases with different densities [60,63]. This effect is greatly reduced by depositing a thick Pt layer on the top surface above the ROI by in situ FIB assisted deposition, followed by gentle ion milling (polishing using a relatively low ion beam).…”