Optimizing photon sieves to approach Fresnel diffraction limit via pixel-based inverse lithography

This article presents a novel, rigorous method to construct photonic sieves whose imaging resolution approaches the Fresnel diffraction limit. Photon sieves (PS), which use holes in place of Fresnel Zone Plate (FZP) as diffractive elements, offer many advantages, such as low fabrication cost, higher contrast, narrower main lobe and smaller side lobes. Particularly in EUV imaging, the minimum feature size for fabricating a FZP limits the achievable NA or, equivalently, outermost zone width. And PS allows for much higher NA than FZP, because its hole size can be much larger than the outermost zone width in a FZP without losing resolution. Thus it is of great interest to apply PS in EUV imaging or maskless lithography (ML2). When used in imaging, the Point Spread Function (PSF) on the focal plane should approximate a δ-function. To explore the optimal design of PS, we presented a technique from inverse lithography that treats the PS as a mask, uses Fresnel diffraction as the transfer function, and seeks to m...