Mechanism of bias-dependent contrast in scanning-capacitance-microscopy images

In this work, the physical processes leading to contrast in scanning capacitance microscopy (SCM) are investigated both experimentally and theoretically. Using a p-type epitaxial doping staircase on silicon, we show that a monotonic dependence of the SCM signal on the doping level is only obtained, if the tip bias is adjusted in a way that the sample is either in accumulation or depletion. In the transition region, the SCM signal is nonmonotonic as a function of doping and depends on the bias. Therefore, any doping concentration can yield a maximum SCM signal size. We also show that this behavior is in agreement with the conventional model of a metal-oxide-semiconductor junction. (C) 2001 American Institute of Physics.