Identification of Polytype and Estimation of Carrier Concentration of Silicon Carbide Wafers by Analysis of Apparent Color using Image Processing Software

Abstract

n-type SiC wafers with localized 4H, 6H, and 15R polytype grains were photographed and their colors were analyzed to find correlations among polytypes, carrier concentration, and apparent color. The SiC wafers were photographed and the color information of different colored regions from the photographs was extracted, both for RGB (red, green, and blue) and HSV (hue, saturation, and value) color space formats using image processing software (PicMan). Polytype and carrier concentration of n-type SiC wafers were identified from Raman spectra for correlation with the color analysis results. The carrier concentration of SiC wafers was estimated to be in the range of 2 × 1017 cm-3 to 1 × 1019 cm-3 from a line-shape analysis of measured Raman spectra. The color analysis revealed that there is very strong correlation between polytype and hue value. The carrier concentration strongly affects saturation and value of apparent color. SiC wafers with lower carrier concentration showed higher clarity (lower saturation (or colorless) and higher value (higher transparency)). As the carrier concentration is increased, the wafer becomes translucent (high saturation or colored) and dark or opaque (low value). The polytype and carrier concentration of SiC wafers can conveniently be estimated from their apparent color.