Investigation of tip-depletion-induced fail in scanning capacitance microscopy for the determination of carrier type

Scanning capacitance microscopy (SCM) was performed on an n-type Si multilayer structure doped by phosphorus whose concentration ranges from 2×10¹⁷ to 2×10¹⁹cm^-3. Three types of tips were used, i.e. fresh Pt/Ir coated tip, worn Pt/Ir coated tip and non-coated commercial Si tip. The use of fresh Pt/Ir coated tips produces SCM result in good agreement with the doping profile including the correct identification of the carrier type. In contrast, a worn Pt/Ir coated tip which has lost its metal coating and a non-coated tip will fail to recognize successfully the carrier type for phosphorus dopant concentration above 8×10¹⁸cm^-3 (identifying as p instead of n) due to the tip depletion effect. These results alert us to carefully interpret the SCM results, especially in the case for identification of carrier type inside the sample of interest which is unknown.