MICROSCOPY Vol.47▶No.1 2012
â– Reviews

Basics and Interpretation of Scanning-Ion-Microscope Images

Tohru Ishitani

Abstract: Secondary-electron (SE) image information in a scanning ion microscope (SIM) using gallium (Ga) and helium (He) ion species has been described comparing with a scanning electron microscope (SEM). Using the Monte Carlo (MC) simulation, the trajectories of all the collision partners (i.e., primary ions, recoiled target atoms, and excited electrons (electron cascade) have been simulated to excite SEs under the ion impacts. For Ga ion impact, the SE yields show a gradual decrease with increasing Z2, being superimposed with a periodic change. This general Z2-dependency is opposite to that for electron impact. The Z2-dependency for He ion impact is characterized to the middle position of Ga ion and electron impacts and is weak. The characteristics of SIM images have been compared with SEM images in material contrast, information depth, incident-angle dependency of SE yields dominating topography contrast, and energy distribution of SEs influencing voltage contrast.

Key words: focused ion beam (FIB), scanning ion microscope (SIM), scanning electron microscope (SEM), secondary electron emission, image resolution