A Synchrotron‐Based Fourier‐Synthesis Custom‐Coherence Illuminator

Scanning illumination systems provide for a powerful and flexible means for controlling illumination coherence properties. Here we present a synchrotron‐based scanning‐mirror Fourier synthesis illuminator that enables sources with intrinsically high spatial coherence, such as undulators, to be used in situations demanding less coherence. The application considered here involves microfield extreme ultraviolet (EUV) lithography, however, the same methods are applicable to conventional microscopy as well as coherence‐imaging techniques. This flexible illuminator allows the coherence to be tuned in situ enabling the illumination to be tailored to the specific pattern being imaged. The effectiveness of the system is demonstrated through a variety of lithographic print experiments. These include the use of resolution enhancing coherence functions, which enable the printing of 50‐nm line‐space features using a lithographic optic with a NA of 0.1 and an operational wavelength of 13.4 nm.