High numerical aperture reflective deep ultraviolet Fourier ptychographic microscopy for nanofeature imaging

Abstract

Pushing the resolution limit to the nanoscale is a critical challenge for applying the reflective Fourier ptychographic microscopy (FPM) to metrologies for characterization of nanoscale features. Characterization of opaque nanoscale samples using reflective FPM requires chiefly a light source with shorter wavelength to obtain nanoscale resolution, as state-of-the-art device sizes have become sub-100 nm or deep sub-wavelength. We report a reflective deep ultraviolet (DUV) FPM featured by an aperture scanning illumination based on the epi-illumination scheme for accommodating a 193 nm excimer laser source and a high numerical aperture (NA) catadioptric objective lens. The illumination system enables robust control of high-NA angular illumination and optimal energy fluence for FPM imaging and prevention of damage to the sample and optical components. The implemented reflective DUV FPM demonstrated image reconstruction of multiline targets with a minimum linewidth of 80 nm with an average contrast six times higher than conventional DUV microscopy.