Circular polariscopic measurement of a semi-insulating SiC wafer for evaluating strains and its relation with Raman spectra: Superiority to monochromatic Lang X-ray topography

Abstract

We have explored the effectiveness of applying the circular polariscopic measurement to the mapping of the strains in a semi-insulating 6H-SiC wafer. Initially, monochromatic Lang X-ray topography, which is regarded as a fundamental evaluation technique for wafers, is applied. In the monochromatic Lang X-ray topograph, the disappearance of the images is found in various areas, which suggests that the monochromatic Lang X-ray topographic measurement is not almighty. Next, we apply the circular polariscopic measurement, which is sensitive to strains through the photoelastic effect. The brightness of the circular polariscopic wafer map reveals that the inhomogeneous distribution of the strains. The observed phenomenon indicates that the magnitude of the crystal-plane distortion is too strong to apply monochromatic Lang X-ray topography. The presence of the relatively large strains is confirmed from the fact that the forbidden reflection lines are observed in the θ -2θ X-ray diffraction pattern. We also measure the Raman spectra of the several region of the wafer to evaluate the stress from the phonon frequency shift. The maximum stress is estimated to be ~490 MPa. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.