Modeling study of scanning capacitance microscopy measurement for p-n junction dopant profile extraction

In this paper we present a numerical simulation study of the scanning capacitance microscopy (SCM) measurement of p-n junctions. A 2-D numerical solver of the Poisson and carrier continuity equations is used to model the measurement and to study the effects of dc offset bias, ac bias and interface charges on SCM output. The results show that SCM capacitance over the junction space charge region approaches a low frequency C-V plot due to the supply of minority carriers from across the junction. The position of the zero cross point of the SCM signal, often taken as the location of the junction, is dependent on the bias conditions. Interface fixed charge and traps change the C-V plot over the space charge region of the p-n junction in a complex fashion. It is concluded that to obtain a quantitative dopant profile from SCM data, it is necessary to account for the above effects.