Enhanced extreme ultraviolet mask imaging with Fourier ptychographic microscopy

Extreme ultraviolet (EUV) imaging for photomask metrology requires quantitative phase imaging, accurate control of the pupil-fill and wafer-side through-focus behavior. We explore Fourier Ptychographic Microscopy (FPM) as a solution, addressing challenges such as field-dependent aberrations outside of the microscope’s designed field-of-view (FOV). Using binary pseudorandom mask patterns, we achieve 1.8× resolution enhancement beyond the 0.5 λ/NA diffraction limit, improving the resolved feature size from 82 to 46 nm across a 30 μm×30 μm FOV. We investigate various reconstruction algorithms for their robustness under spatially varying aberrations from the zoneplate imaging system. FPM’s phase reconstruction also enables arbitrary illumination synthesis, allowing for the computational emulation of diverse illumination patterns from a single FPM dataset. These results demonstrate FPM’s potential as a powerful computational imaging tool for high-NA EUV mask imaging and metrology.