Factors influencing the capacitance–voltage characteristics measured by the scanning capacitance microscope

Abstract

A scanning capacitance microscope (SCM) can measure the local capacitance–voltage (C–V) characteristics of a metal-oxide-semiconductor structure formed by the SCM probe tip and a doped semiconductor sample. A common realization of the SCM depends on a parallel atomic force microscope, which includes a laser focused on the end of the cantilever to monitor the position of the probe tip. In this configuration, it is found that the stray light from the laser can dramatically affect the measured C–V curve. The difference between the SCM C–V curves measured in this high stray light condition and those measured in the true dark condition are shown and discussed. Also discussed is the distortion of the measured C–V curves caused by the SCM method of measuring the differential capacitance using a capacitance-modulating ac voltage and a lock-in amplifier. After reducing and accounting for these effects, the SCM C–V curves show markedly different behavior from that of conventional one-dimensional C–V curves. The measured C–V curves are stretched out in voltage and have a larger |dC/dV| signal in the depletion and the inversion regions, as compared to the conventional one-dimensional C–V curve. The measured C–V curves are compared with the results of three-dimensional calculations for different values of the probe-tip size.