Scanning capacitance microscopy applied to two-dimensional dopant profiling of semiconductors

Scanning capacitance microscope (SCM) images of a semiconductor have contrast that is sensitive to variations in dopant density and spatial resolution on the order of the tip radius, approximately 10 nm. SCMs can be operated in a direct-capacitance, a constant-voltage-difference (open loop), or a constant-capacitance-difference (closed loop) mode. A fast and accurate formalism to convert SCM images to quantitative two-dimensional (2-D) dopant profiles, using either a 1-D model extended to 2-D (quasi-2-D model) or a full 2-D, finite element, numerical solution of Poissonʹs equation, has been developed. Measurements on silicon junctions are used to illustrate the effect of the SCM operating conditions on the quality of the image. For the first time with the SCM, dopant variations of GaAs pn-junctions have been imaged.