Analysing Imaging Signals of Negative-Charging Contrast in Scanning Electron Microscopy

Negative charging of a specimen may produce the image contrast of yielding the information under the insulating thin film in scanning electron microscopy. To clarify and make good use of the recently developed negative-charging contrast (NCC), we propose a simplified procedure for quantifying secondary electron (SE) imaging signals and report the calculated results. The theoretical considerations and calculations are validated by comparing the calculated relation between the SE signal and the surface potential with measured dynamic characteristics of the NCC images. The results show that in the region of weak negative charging the NCC formation is due to the SE redistribution. The intensity of SE signals decreases with the increase of the amount of the SEs returning to the negatively charged surface whose local electric field may attract electrons. This results in the NCC transient characteristics.