The impact of embedded substrate defects on end-of-line die yield has become significant for advanced process technology nodes. Quality control and grading of wafers intended for leading-edge devices thus require effective detection and identification of embedded defects. In this paper, we present the results of a study on incoming prime-grade wafers using a new defect inspection system capable of dark field scattering and bright field differential interference contrast inspection. The wafers were scanned on a KLA-Tencor Surfscan SP2XP inspection tool, and the combined scan signal were real time analyzed to classify the defects of interest from particles. Inspection of the wafers both before and after a resist-coat process showed that all air pockets detected on the bare substrates resulted in coating defects. In the second part of the study, a set of epitaxial (epi) wafers was inspected using oblique- and normal- incidence dark field scattering as well as bright field differential interference contrast. The defects were classified by rules-based binning, and found to contain a large number of killer defects including epi stacking faults and bumps. Classification results were confirmed by SEM review, and showed that this multi-channel methodology successfully identified the killer defects with >95% accuracy and purity.