EUV mask pattern inspection with an advanced electron beam inspection system

Readiness of defect-free mask is one of the biggest challenges to insert extreme ultraviolet (EUV) lithography into semiconductor high volume manufacturing for 22nm half pitch (HP) node and beyond. According to ITRS roadmap updated in 2008, minimum size of defect needed to be removed is 25nm for 22nm HP node in 2013 [1]. It is necessary, therefore, to develop EUV mask pattern inspection tool being capable of detecting 25nm defect. Electron beam inspection (EBI) is one of promising tools which will be able to meet such a tight defect requirement. In this paper, we evaluated defect detection sensitivity of electron beam inspection (EBI) system developed by Hermes Microvision, Inc. (HMI) using 88nm half-pitch (HP) line-and-space (L/S) pattern and 128nm HP contact-hole (C/H) pattern EUV mask. We found the EBI system can detect 25nm defects. We, furthermore, fabricated 4 types of EUV mask structures: 1) w/ anti-reflective (AR) layer and w/ buffer layer, 2) w/ AR layer and w/o buffer layer, 3) w/o AR layer and w/ buffer layer, 4) w/o AR layer and w/o buffer layer. And the sensitivity and inspectability for the EBI were compared. It was observed that w/o AR layer structure introduce higher image contrast and lead to better inspectability, although there is no significant different in sensitivity.