Resistivity mapping of SiC wafers by quantified Raman spectroscopy†

Abstract

μRaman spectroscopy measurements were used to study the resistivity in 4H-SiC samples by intercalibrating with Eddy current measurements (eddy-current probe that accurately measures bulk resistivity of wafers). The position and line width associated with the Raman longitudinal optical phonon-plasmon coupled (LOPC) mode were used since their variation from the reference values of a material in the absence of dopant-generated defects is proportional to the amount of the free carrier concentration in the conduction band present in the semiconductor. Using wafers of known resistivity to calibrate the model and deconvolving the individual recorded spectra, a multi-variable model was created to predict the resistivity of individual map points. Resistivity was thus predicted in a pointwise manner resulting in maps of 92 points over a 6-inch diameter area of a wafer, from which false-colour images were created showing the spatial distribution along the X and Y axes, and in the bulk, along the Z axis of the resistivity. The analysis procedure was automated by creating suitable R-language codes that extract the necessary information on the individual aspects of the analysis and create the images described above from a single dataset.