Far-field deep sub-wavelength defect sensing using conjugate structured illumination microscopy (c-SIM)

Defects in deep subwavelength nanopatterns are difficult to inspect using a visible light probe due to the limitation of the diffraction barrier and weak signal-to-noise ratio. In this work, we show a defect inspection method capable of locating and classifying defects in a large background nanopattern using structured light field illumination. This method replaces the planewave illumination in a traditional bright field microscope with a structured light field. We demonstrate the inspection of killer defects with 38nm critical dimensions, which precisely pinpoint the defect twin nanowires unit. The underlying physics is that the customized structured light field, which mimics the geometrical features of the background pattern on the wafer, induces a position-dependent breakdown of geometrical symmetry when defects are present. We believe this work develops a common standard method that can be easily combined with the bright field microscope to detect a nanoscale object and has the potential to extend to many other requirements, such as bioimaging, lithographic mask inspection, and nanoscale metrology.