High-Sensitivity Optical Scattering Inspection Method for Nanoscale Morphological Defects on SiC Wafers

Silicon carbide (SiC) has emerged as a critical wide-bandgap semiconductor for power electronics. However, its high optical transmittance and relatively low dielectric contrast impose fundamental limitations on nanoscale defect detection compared with conventional silicon (Si) wafers. In this work, a numerical framework combining the finite-difference time-domain (FDTD) method with vectorial Debye–Wolf theory is developed. Comparison of the optical responses of Si and 4H-SiC identifies a dual degradation mechanism in 4H-SiC darkfield inspection: roughness-induced background enhancement associated with high transmittance and defect signal attenuation caused by the lower dielectric contrast. To improve the signal-to-noise ratio (SNR) and defect intensity, the effects of incidence angle and polarization state on defect scattering are investigated, and the illumination configuration is optimized accordingly. A 405 nm polarization-tunable laser scattering darkfield imaging system is developed for 4H-SiC wafer inspection, enabling high-SNR detection of 100 nm-diameter polystyrene latex (PSL) particles and effective identification of practical morphological defects. The experimental results agree with the numerical predictions, validating the effectiveness of system optimization guided by defect scattering characteristics. This work elucidates the material-dependent mechanisms limiting darkfield inspection sensitivity in SiC wafers and provides a viable pathway toward high-sensitivity detection of nanoscale morphological defects.