Effectiveness of extreme ultraviolet actinic blank inspection prototype for 16-nm half-pitch for mitigation of multilayered defects

Abstract

A major challenge for extreme ultraviolet (EUV) lithography is avoiding defects in the fabrication of multilayered (ML) mask blanks. Substrate defects and adders during ML coating are responsible for ML defects, which cause changes on phase and amplitude of EUV light. The ML defects must be identified by inspection prior to absorber patterning in order to reduce the effects of ML defects via covering them with patterns to permit the use of fewer ML defect blanks. Fiducial marks (FMs) on ML blanks can be used for mask alignment and to accurately and precisely determine the locations of ML defects. In this study, we fabricated an FM mask by resist exposure using an e-beam writer and etching. Then, we inspected FMs and ML defects with an EUV actinic full-field mask blank inspection tool developed by EIDEC-LaserTec (LT ABI; EIDEC, Tsukuba, Japan and LaserTec, Yokohama, Japan). Next, we evaluated the ML defect location accuracy on the mask based on FMs of several line depths. Here, we explain the estimation of defect location accuracy using FMs and the LT ABI and discuss the defect numbers which can be covered by absorber patterns. Fewer than 19 defects per blank should be required for EUV blanks to cover the ML defects with patterns.