Nonmonotonic behavior of the scanning capacitance microscope for large dynamic range samples

The phenomenon of contrast reversal in scanning capacitance microscopy (SCM) imaging will be discussed, taking into account the implications for samples which contain both p-type and n-type dopants. Experiments show that a monotonic change in SCM output versus dopant concentration for large dynamic range samples ${\text{(10}}^{14}{\text{–10}}^{20}\hspace{0.5em}{\mathrm{cm}}^{\mathrm{-3}})$ is dependent on the applied dc bias. Incorrect adjustment of this parameter can lead to contrast reversal in the SCM images causing a problem for conversion algorithms and dopant quantification. Simulation results demonstrating this feature will be presented. In addition, the appearance of shifting bands which are common in voltage-dependent measurements of $\mathrm{p-n}$ junctions complicates the data interpretation and extraction of length measurements within an image, such as the effective electrical channel length in the case of transistor characterization. The significance of these problems with respect to the SCM response curve will be discussed.