Scanning capacitance microscopy and the role of localized charges in dielectric films: Infering or challenging?

Scanning capacitance microscopy (SCM) is considered a suitable technique to examine dopant profiles and to provide images of the charge carrier distribution in real device structures. A drawback of the application is the sensitivity of the method to different kinds of charges in the surface passivation layer. For a systematic study silicon structures with stripe patterns of different doping concentrations, covered either by a native oxide or by a thermally grown silicondioxide layer, were examined. The dependence of the dC/dV characteristic on the sweep rate of the tip bias and on the bias sweep direction was analyzed. Local charge trapping in the passivation layer was estimated from shifts of the peak position of the dC/dV versus V curves. It is demonstrated as to how features related to the charge trapping in the passivation layer and induced by a certain dc bias at the tip superimpose the dopant related features in the SCM image.