MICROSCOPY Vol.43▶No.3 2008
â– Feature Articles: Image formation and detection of signal in SEM

Illumination Effects and Image Contrasts Due to Various Electron Detectors in SEM

Akishige Ono and Masateru Shibata

Abstract: A position of a secondary electron detector or a backscattered electron detector gives large influence on image contrast and illumination effect. Strong illumination effect brought by an out-lens detector used in a conventional SEM gives topographic image contrast with directional shadow. A TTL detector used in an ultrahigh resolution SEM gives weak illumination effect and shadow-less topographic contrast. Morphological information and compositional information can be distinguished by selecting energies of detected electrons at a low accelerating voltage. Stronger illumination effect can be obtained with a lower detector combined with a snorkel objective lens, but an apparent detector position changes according to the change of working distance. Compositional information and topographical information can be separated by calculating output signals obtained from backscattered electron detectors placed symmetrically with respect to the optical axis.

Key words: out-lens detector, TTL detector, lower detector, backscattered electron detector, illumination effect