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



Kwanseob Park, Yoon Sung Bae, Sang-Soo Choi, Martin Sohn


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. Optical image-based characterization of reflective nanoscale devices requires a reflection-mode optical system with nanoscale resolution to enable measurements on opaque samples with nanoscale target features, as state-of-the-art device sizes have become sub-wavelength. Adopting a deep ultraviolet (DUV) wavelength source for resolution enhancement, we first report a reflective DUV FPM using a 193 nm excimer laser and a high numerical aperture (NA) catadioptric objective. Epi-illumination optics designed for aperture scanning at a large conjugate back focal plane (CBF) enables robust angle-resolved illumination and collection of multiple images for synthesizing high-frequency components in the Fourier domain. Image reconstruction of multiline targets with a minimum line-width of 80 nm was achieved with an average contrast two times higher than traditional optical microscopy. The implemented reflective DUV FPM demonstrated enhanced resolution and contrast, which is anticipated to provide a practical approach for the realization of high-resolution reflective FPM for the characterization of nanoscale devices.
APL Photonics


Fourier ptychography, deep ultraviolet, reflection mode, nanoscale imaging, aperture scanning, modulation transfer function


Park, K. , Bae, Y. , Choi, S. and Sohn, M. (2022), High numerical aperture reflective deep ultraviolet Fourier ptychographic microscopy for nanofeature imaging, APL Photonics, [online],, (Accessed May 22, 2024)


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Created September 8, 2022, Updated November 29, 2022