Sample processing by Bi-FIB for in situ TOF-SIMS imaging of buried interfaces

Focused ion beam (FIB) is commonly used as a standard machining technique in failure analysis, quality control, reverse engineering, material research, and so on, for the samples having microstructures and nanostructures. FIB combined with time-of-flight secondary ion mass spectrometry (TOF-SIMS), so-called FIB-TOF, has attracted attention as a method to determine the three-dimensional (3D) chemical distributions of complex samples. In general, a highly focused Ga+ ion beam is used for FIB, however, the FIB-milled area is limited and it was difficult to expand the Ga-FIB to hundreds of micron length scale for sample fabrication. In order to overcome the drawback, we proposed the Bi-FIB approach for large scale sample cross-sectioning. Although the possibility of Bi-FIB has been reported, there were almost no performance examinations as well as practical applications. In this study, therefore, the authors summarize the comparison of milling rate and milling damage between Ga-FIB and Bi-FIB. As a result, it was found that Bi-FIB can provide a higher milling rate with thinner milling damage. Finally, the Bi-FIB approach was applied to the interfacial analysis of all-solid-state battery (ASSB) material. With this approach, the detailed chemical distributions at the interface were discovered, leading to the better understanding of battery behaviors.