Characterization of Semiconductor Surface Conductivity by Using Microscopic Four-Point Probe Technique

Four-point probe characterization is a standard method for studying the electrical properties of solids and thin films. The probe spacing in four-point probe technique has to be reduced to micro-scale to obtain expected surface sensitivity and spatial resolution. Therefore, microscopic four-point probes (M4PPs) need to be combined with some microscopy techniques. Two types of M4PPs systems have been developed in the past few years, which are monolithic micro-four-point probe and four-point scanning tunneling microscopy probe approaches. This paper reviews the latest development of M4PPs including probe structure and principle measuring theories. The probe fabrication approaches are discussed in detail. It is shown that focused ion beam lithography is a promising method to fabricate probes with sub-50 nm spacing. This approach has advantages of high precision and maskless nanoscale fabrication. Probe life and sample surface damage are the other two main challenges for microscopic four-point probe technique. To deal with such problems, we can use flexible cantilevers as the probe and keep a certain angle between the probe and the sample surface.