On the lateral resolution of scanning capacitance microscope based C–V measurements

摘要

The effect of stray electrostatic field of a pointed probe, placed over the semiconductor surface, on the probe/substrate capacitance has been analysed using the finite element method. Whereas on conducting surfaces the contribution to the capacitance at the probe axis peaks relatively sharply, in semiconductors the applied-voltage-determined increase of depletion depth flattens this dependence. The lateral resolution is limited by the depletion depth rather than by the radius of curvature of the probe. The high-frequency C–V dependence does not saturate above the voltage of inversion threshold, and it would be hardly distinguishable from the case of deep depletion. The stray capacitance increases the dC/dV dependence and affects its relation to dopant concentration. The error is negligible at low doping levels but may attain the multiple of the value expected on high-doped materials. The stray field of a tip-on-cantilever probe is orders of magnitude larger than that of a pointed thin wire perpendicular to the surface. It has unexpected consequences—the local sensitivity achieved with the cantilever is less affected by the radius of curvature on the one hand and the calibration accuracy of the wire probe is less sensitive to the pitch of test structure used, on the other.