Peak-tracking scanning capacitance force microscopy with multibias modulation technique

Abstract

Scanning capacitance force microscopy (SCFM) is a good method for capacitance measurements using electrostatic force detection. However, to obtain an entire capacitance–voltage (C–V) curve by SCFM, a sweep of a direct current (DC) bias voltage is required at a certain fixed point on a sample surface during scan suspension, and thus the measurements become very time-consuming when we want to observe some types of image related with C–V characteristics. In this paper, we propose peak-tracking scanning capacitance force microscopy (PTSCFM) for the purpose of extracting the main feature of the C–V curve without DC voltage sweep. In PT-SCFM, alternating current voltages at three different angular frequencies, ω 1, ω 2, and , are applied together with DC voltage, , to generate an electrostatic force, and high-order components at the angular frequencies of and , which represent a voltage derivative of a capacitance () and a second-order derivative of the capacitance (), respectively, are extracted from the electrostatic force. Then, a DC voltage, , giving the peak of is determined from to be adjusted to nullify the component using a feedback controller. From the obtained values of and at , the C–V curve can be outlined. In PT-SCFM, the distributions of those values are simultaneously imaged together with a topography without sweep, and when we operate PT-SCFM under various modulation frequency conditions, analyses similar to those based on the frequency dependence of the C–V property are realized. We have applied the PT-SCFM to a microcrystalline material to discuss the effects of surface depletion and deep-level states, from which the validity of PT-SCFM has been examined.