| Summary: | 碩士 === 國立東華大學 === 應用物理研究所 === 94 === Using atomic force microscopy (AFM) and scanning capacitance force microscopy (SCFM), the study is first to get the surface morphology and surface capacitance profiles of n-type and p-type silicon wafers which are doped in different concentrations. Then, the capacitance force spectra are acquired at a local surface point of each silicon wafer by using capacitance force spectroscopy (CFS) that is based on SCFM. There are two modes in CFS: one is to detect the force change in decreasing the distance between the tip and the sample, and the other one is detect the force change with varying the dc bias on the sample.
We find that the capacitance force increases with the decrease of the distance between tip and sample. This is because the spatial capacitance between tip and sample and the value of increase with the decrease of the distance. According to the capacitance force spectra, we can estimate the magnitudes of the surface capacitances that are about 10-11 F by the numerical simulation and calculation. In addition, the smaller the resistivity of the sample is, the larger the surface capacitance gets. When the dc voltage is applied to the sample, the capacitance force decreases. This is because the electric field force produced suppresses the capacitance force. The maximum capacitance force affected by the applied dc voltage is strongly related to the concentration of the n-type and p-type silicon wafers.
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