Development of dual bias modulation electrostatic force microscopy for variable frequency measurements of capacitance

Abstract

We propose dual bias modulation electrostatic force microscopy (DEFM) for variable frequency measurements of surface depletion capacitance on a semiconductor. In DEFM, dual alternating current bias voltages at angular frequencies of ω1 and ω2 are applied to generate an electrostatic force, and we detect the high order term at an angular frequency of ω2 - 2ω1 in the electrostatic force from which a derivative of surface depletion capacitance by voltage (∂C/∂V) can be evaluated. Even with a fixed value of ω2 - 2ω1 at a specific resonant frequency of the cantilever, to ensure sufficient sensitivity of the electrostatic force, a pair of ω1 and ω2 can be varied; this enables variable frequency measurements of ∂C/∂V by DEFM. The validity of the quantitation and spatial resolution of DEFM were assessed through the analysis of metal-oxide-silicon and Zn(O, S)/Cu(In,Ga)(Se,S)2 samples.