Extreme high resolution scanning electron microscopy (XHR SEM) and beyond

Abstract

For decades, high resolution scanning electron microscopes (SEM) have strived to offer improved performance in the high and low energy regimes. High energies have always been attractive, because they lead to sub-nanometer resolution without complex electron optics, especially when using a scanning transmission electron microscopy (STEM) mode in the SEM. Lower energies have caught the attention of microscopists, due to their increased surface sensitivity, minimized charging effects or reduced depth of radiation damage. While going to very low beam landing energies was demonstrated more than 20 years ago, keeping a nanometric spot-size below 1 keV proved to be a technological challenge. Only a few years ago did the first commercial SEM succeed in delivering sub-nanometer resolution at 1 kV, but with some restrictions. Recently, the introduction of the extreme high resolution (XHR) SEM has demonstrated subnanometer resolution in the entire 1 to 30 kV range, thanks to a monochromatized Schottky electron source that reduces the effects of chromatic aberrations at lower energies. Of at least equal interest is the fact that the same XHR SEM can take advantage of its optics, modularity, platform stability and cleanliness developments to explore new avenues, such as high resolution imaging at very low beam energies or up to 30 kV STEM-in-SEM. For the first time, complementary information from the very surface and internal structure at the true nanometer level is obtained in the same SEM.