Voltage contrast imaging with energy filtered signal in a field-emission scanning electron microscope.

A new band-pass energy filter (BPF) technique of secondary electron (SE) detection using scanning electron microscope (SEM) was developed to enhance voltage contrast (VC) in SEM images. The energy filtering condition was optimized to enhance VC of dopant distribution using Si p-n structure. The relation between VC and SE energy was investigated by BPF as well as a conventional high-pass filter (HPF). Whereas the p-type regions were always brighter than the n-type region in the case of HPF, the contrast reversal between p region and n region occurred at the low SE energy range in the case of BPF. The variation of signal intensity of BPF against specimen bias voltage can be considered as SE spectrum analysis, and the peak split of the spectra between n-type and p-type regions was obtained. The peak split can be explained with a model with metal-semiconductor contact. This peak split causes the contrast reversal.