Development of a fountain detector for spectroscopy of secondary electrons in scanning electron microscopy

Abstract

The low-pass secondary electron (SE) detector, the so-called “fountain detector (FD)”, for scanning electron microscopy has high potential for application to the imaging of low-energy SEs. Low-energy SE imaging may be used for detecting the surface potential variations of a specimen. However, the detected SEs include a certain fraction of tertiary electrons (SE3s) because some of the high-energy backscattered electrons hit the grid to yield SE3s. We have overcome this difficulty by increasing the aperture ratio of the bias and ground grids and using the lock-in technique, in which the AC field with the DC offset was applied on the bias grid. The energy-filtered SE images of a 4H-SiC p–n junction show complex behavior according to the grid bias. These observations are clearly explained by the variations of Auger spectra across the p–n junction. The filtered SE images taken with the FD can be applied to observing the surface potential variation of specimens.