Lawrence Berkeley National Laboratory

Fourier ptychography is a computational imaging techniques that combines various full-field coherent images acquired under varied illumination angles and combined to yield a angular spectrum with a large synthetic numerical aperture and non-interferometric phase information. We present here the implementation of this technique in a full-field soft x-ray microscope designed to emulate modern EUV lithography tools imaging conditions, and we show that this technique can be used for the study of EUV photomasks. The technique allows us to quantitatively characterize phase defects (predominant in EUV lithography), to study new mask designs made of phase structures, to study sub-resolution assist features and extend the resolution of the microscope down to 26-nm, correspond to the N1 technology node.