Effects of the illumination NA on EUV mask inspection with coherent diffraction imaging

RESCAN is a lensless APMI tool that is based on coherent diffraction imaging (CDI). A complex-amplitude image of the EUV reticle is reconstructed from diffraction patterns using a phase-retrieval algorithm. To keep up with future semiconductor technology nodes, we are upgrading RESCAN with a Fourier synthesis illuminator, which will enhance the resolution down to 20 nm on mask [3]. The new system will have a higher illumination NA. To understand how this influences the mask inspection procedure, we present here a simulation study on how the illumination NA affects the reconstructed EUV mask image quality and defect detection sensitivity.