Mechanism for secondary electron dopant contrast in the SEM

The growing use of secondary electron imaging in the scanning electron micr oscope (SEM) to map dopant distributions has stimulated an increasing inter est in the mechanism that gives rise to so-called dopant contrast. In this paper a range of experimental results are used to demonstrate the wide appl icability of the technique. These results are then incorporated into a mode l where, in particular, the effect of the surface barrier and the vacuum le vel are considered. It is found that the dominant contribution to the contr ast mechanism is due to the three-dimensional variation of the vacuum level outside the semiconductor.