Demonstration of defect free EUV mask for 22nm NAND flash contact layer using electron beam inspection system

Abstract

Fabrication of defect free EUV masks including their inspection is the most critical challenge for implementing EUV lithography into semiconductor high volume manufacturing (HVM) beyond 22nm half-pitch (HP) node. The contact to bit-line (CB) layers of NAND flash devices are the most likely the first lithography layers that EUV will be employed for manufacturing due to the aggressive scaling and the difficulty for making the pattern with the current ArF lithography. To assure the defect free EUV mask, we have evaluated electron beam inspection (EBI) system eXplore™ 5200 developed by Hermes Microvision, Inc. (HMI) [1]. As one knows, the main issue of EBI system is the low throughput. To solve this challenge, a function called Lightning Scan™ mode has been recently developed and installed in the system, which allows the system to only inspect the pattern areas while ignoring blanket areas, thus dramatically reduced the overhead time and enable us to inspect CB layers of NAND Flash device with much higher throughput. In this present work, we compared the Lightning scan mode with Normal scan mode on sensitivity and throughput. We found out the Lightning scan mode can improve throughput by a factor of 10 without any sacrifices of sensitivity. Furthermore, using the Lightning scan mode, we demonstrated the possibility to fabricate the defect free EUV masks with moderate inspection time.