Confocal Subsurface Backscattering Microscopy for Optical Identification of Nanoscale Threading Dislocations in SiC Substrates

High density threading dislocations in SiC wafers facilitate reverse leakage and degradation, yet commercial defect inspection systems based on surface profiling and PL dark-contrast miss nanoscale TDs because they lack resolvable surface signatures and band-edge PL is uniformly quenched by background dopants or compensating defects. Here, we develop confocal subsurface backscattering microscopy to nondestructively detect TDs, based on the synergy of confocal filtering induced dark field configuration and strain induced photoelastic mechanism. By simultaneously suppressing specular reflection while enhancing optical scattering from TD induced refractive index perturbation, CSBM enables high contrast, high resolution TD imaging. Moreover, TD types can be distinguished by their distinct photoelastic scattering patterns. Our work establishes a simple but effective optical approach for direct TD identification that is more tolerant of surface imperfections, providing a practical route toward industrial in line inspection.