Spatial characterization of doped SiC wafers by Raman spectroscopy

Raman spectroscopy has been used to investigate wafers of both 4H–SiC and 6H–SiC. The wafers studied were semi-insulating and n-type (nitrogen) doped with concentrations between 2.1×1018 and 1.2×1019 cm−3. Significant coupling of the A1 longitudinal optical (LO) phonon to the plasmon mode was observed. The position of this peak shows a direct correlation with the carrier concentration. Examination of the Raman spectra from different positions on the wafer yielded a rudimentary spatial map of the carrier concentration. These data are compared with a resistivity map of the wafer. These results suggest that Raman spectroscopy of the LO phonon–plasmon mode can be used as a noninvasive, in situ diagnostic for SiC wafer production and substrate evaluation.