Impact of EUV Pellicle Transmittance on Imaging Performance Analyzed by Coherent Scattering Microscopy

Abstract

We investigated the impact of the transmittance of EUV pellicles on imaging performance using coherent scattering microscopy (CSM). Although the pellicle has no effect on the optical path of diffracted light, it deteriorates the imaging performance owing to EUV photon loss. The results showed that the line critical dimension (CD) increased by 20.7% and that the normalized image log slope (NILS) decreased by 7.4% upon using a pellicle with 80% transmittance. Since the local transmittance variation due to pellicle non-uniformity or contamination can cause local CD variation, it is important to ensure uniform transmittance throughout the active pellicle area.