Scanning Helium Ion Microscope

Abstract

Scanning helium ion microscope (SHIM) is based on the similar principle with field emission scanning electron microscope (FE-SEM) (Guo in Scanning Helium Ion Microscopy, Characterization of Materials. Wiley, pp. 1–9, 2012 [1]). The difference between them is that scanning beam of SHIM is a positively charged helium ion (He+) beam from a gas field ion source (GFIS), but not a negatively charged electron beam. An enlarged image of the sample surface is obtained like FE-SEM. Helium gas is field-ionized almost only from the top-most atoms by applying a high voltage to a sharp tip made of monocrystalline refractory metals in a diluted helium gas. Only the He+ beam emitted from a single atom is focused by the ion optical system and is scanned over the sample surfaces. If a backscattered ion detector is equipped, the secondary electrons (SE) and backscattered ions (BSI) can be acquired simultaneously. SHIM can observe the sample image with less current than FE-SEM. If the neutralizing flood gun is equipped, it is easier to observe insulating materials than FE-SEM. SHIM can also be used for direct nanofabrication like focused ion beam (FIB) systems. Since He+ beam does not have such a sputtering capability as a gallium ion beam, it cannot process on the micron-scale, but nanoscale ultrafine modification utilizing the nanoscale-focused He+ beam is possible. If a gas introduction system is installed, deposition of gas-decomposition microstructures by a precisely controlled He+ beam is possible