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Pupil shaping and coherence control in an EUV mask-imaging microscope

We are investigating the effect of pupil-fill patterns and partial coherence settings on EUV reticle images on the new SEMATECH High-NA Actinic Reticle review Project (SHARP), to deepen our understanding of its performance, and improve the emulation of image formation in arbitrary printing tools. SHARP is an EUV mask microscope developed as the successor of the SEMATECH Berkeley Actinic Inspection Tool (AIT). It is equipped with a unique, MEMS-based Fourier synthesis illuminator that generates arbitrary, customized pupil fill patterns to control the illumination partial coherence. The high-magnification objective lenses are an array of interchangeable Fresnel zoneplates with 4×NA values ranging from 0.25 to 0.625. We have used SHARP to inspect isolated and dense features with half pitch as low as 55 nm using lenses with a range of NA values, and common illumination patterns, such as annular, dipole and QUASAR™. We will show the effect of illumination on important, measured pattern parameters, including contrast, normalized image log-slope, and depth of focus. We have also studied the effect of partial coherence on the imaging of on multilayer roughness observed in bright mask regions, a topic important for expanding our understanding of the causes of LER.