Secondary electron imaging of SiC-based structures in secondary electron microscope

Abstract

Secondary electron imaging plays an important role in surface science, not only in imaging of surface topography and in the ability to resolve, for example, surface defects, but also in revealing the local variations in surface barrier height or work function, e.g. p–n junctions in semiconductor devices/materials. In our study, high resolution FESEM is used to qualitatively investigate the secondary electron contrast associated with band-structure variations in the semiconductor heterostructure formed by two adjacent hexagonal (4H) and (6H) silicon carbide polytype layers. In such heteropolytipic structure, effects due to different chemical constituents, defects, incoherent interfaces, and lattice mismatching can be avoided. The study of the 4H/6H heterostructure has revealed that the 6H polytype region, with a band-gap energy of 3.05 eV, exhibits higher secondary emission than the 4H region, with a larger band-gap of 3.26 eV. Reasons for the observed contrast will be discussed, with regard to the effects of the electronic structure and the theory of secondary electron emission with its stages of generation, transport to the surface and escape. Our measurements reveal that the operating “window” for maximizing SE contrast is very sensitive to the operating conditions, particularly incident electron energy. The observed secondary electron contrast can be useful in revealing electronic structure variation between different components of silicon carbide semiconductor devices.