Scanning Electron Microscopy of Dopants in Semiconductors

Extract

It has been demonstrated that doped regions in semiconductors yield contrast in secondary electron images taken under appropriate imaging conditions. Perovic et al. attributed this "electronic" contrast to surface potentials arising from the bending of the energy bands at the surface of the semiconductor. This band-bending results from the presence of surface states which pin the Fermi level. These effects have found application to an important problem in the electronics industry -- the profiling of dopant distributions in two-dimensions. However, such dopant distributions are rarely uniform, i.e., the dopant concentration may change over many orders of magnitude within distances of only a few tens to hundreds of nanometers. Therefore, it is necessary to understand how the observed contrast from the doped regions varies for non-uniform dopant distributions to apply the technique to real electronic devices.