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EUV lithography (EUVL) is the most promising solution for 16nm HP node semiconductor device manufacturing and
beyond. The fabrication of defect free EUV mask is one of the most challenging roadblocks to insert EUVL into high
volume manufacturing (HVM). To fabricate and assure the defect free EUV masks, electron beam inspection (EBI) tool
will be likely the necessary tool since optical mask inspection systems using 193nm and 199nm light are reaching a
practical resolution limit around 16nm HP node EUV mask. For production use of EBI, several challenges and potential
issues are expected. Firstly, required defect detection sensitivity is quite high. According to ITRS roadmap updated in
2011, the smallest defect size needed to detect is about 18nm for 15nm NAND Flash HP node EUV mask. Secondly,
small pixel size is likely required to obtain the high sensitivity. Thus, it might damage Ru capped Mo/Si multilayer due
to accumulated high density electron beam bombardments. It also has potential of elevation of nuisance defects and
reduction of throughput. These challenges must be solved before inserting EBI system into EUV mask HVM line.
In this paper, we share our initial inspection results for 16nm HP node EUV mask (64nm HP absorber pattern on the
EUV mask) using an EBI system eXplore® 5400 developed by Hermes Microvision, Inc. (HMI). In particularly, defect
detection sensitivity, inspectability and damage to EUV mask were assessed. As conclusions, we found that the EBI
system has capability to capture 16nm defects on 64nm absorber pattern EUV mask, satisfying the sensitivity
requirement of 15nm NAND Flash HP node EUV mask. Furthermore, we confirmed there is no significant damage to
susceptible Ru capped Mo/Si multilayer. We also identified that low throughput and high nuisance defect rate are critical
challenges needed to address for the 16nm HP node EUV mask inspection. The high nuisance defect rate could be
generated by poor LWR and stitching errors during EB writing of 64nm HP resist pattern. This result suggests we need
further improvements not only in the EBI inspection system but also the patterning processes for 16nm HP node EUV
masks.
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