Optical Far-Field Detection of Sub-λ/14 Wide Defects by Conjugate Structured Light-Field Microscopy (c-SIM)

Optical far-field detection and imaging of deep-subwavelength objects in a large-area wafer is challenging because of the well-known diffraction barrier and weak Rayleigh scattering. Although the scattering signal of deep subwavelength defects can be enhanced by various methods, such as using a high full-well-capacity camera and increasing the exposure time, the accurate classification of various defects and the precise positioning of defects in a subwavelength domain is rather challenging. In this letter, we report a theoretical framework that the optical bright-field imaging microscopy, coupled with an optical proximity correction-based structured light-field illumination mode, could pinpoint and classify various sub-λ/14 wide defects in a subwavelength domain in a large-area wafer. The underlying physics is that the illuminated structured light field, which is customized to mimic the geometrical feature of the background pattern in the wafer, creates the defect-induced breakdown of geometrical and electromagnetic symmetry. We believe that this work not only paves the route for optical wafer defect inspection and classification at advanced technology nodes but also could potentially be extended to many other areas, such as biosensing, lithographic mask inspection, material characterization, and nanoscale metrology.