Development of scanning capacitance force microscopy using the dissipative force modulation method

We have developed scanning capacitance force microscopy (SCFM) using the dissipative force in frequency-modulation atomic force microscopy. An SCFM signal depends on the dopant density and polarity of semiconductors, whose evaluation is important for developing electronic devices. Thus, improving the force sensitivity of SCFM can prove effective for investigating these devices. In a previous report, the dissipative force modulation method was developed to increase the force sensitivity for Kelvin probe force microscopy. Thus, the force sensitivity of SCFM can be increased using this method. In this study, we determined the theoretical formula for SCFM by using dissipative force. Because this force was modulated using a multiplication signal with the same phase as that of a cantilever excitation signal, the SCFM signal was detected from the deflection of the cantilever by using a demodulation circuit. In the conventional method, the SCFM signal is detected using the second resonance frequency of the cantilever with a high-quality factor. The minimum detectable force of SCFM was calculated to be 0.74 fN from the Brownian motion of the cantilever, which is smaller than that obtained using the conventional method. The differential capacitance of a patterned silicon sample was measured using the proposed method and conventional one. The modulation signal amplitude was reduced from 3.0 V to 1.5 V in increments of 0.5 V. Using the proposed method, the differential dopant regions could be distinguished under a modulation signal amplitude of 1.5 V. However, using the conventional method, the regions could not be observed under the modulation signal amplitude of 2.0 V. Therefore, the proposed method could reduce the modulation signal amplitude from 2.5 V to 1.5 V. In addition, the signal-to-noise ratio and the spatial resolution of the proposed method were found to be higher than that of the conventional one.