Masaki Mikami

Development of EUVL mask blank in AGC

Recent rapid progress in the technologies of extreme ultraviolet lithography (EUVL) is ensuring that EUVL will be a primary candidate for the next generation lithography beyond 32-nm node. However, realization of defect-free reflective mask blank is still counted as one of the most critical issues for high volume production in EUVL. Asahi Glass Company (AGC) has developed comprehensive technologies for manufacturing EUVL mask blanks from figuring and polishing glass substrate to cleaning, multilayer coating, and evaluating its performances by making use of our long and wide experience in providing high quality processed glass substrates and coatings for electronic devices. In this paper, we will present the current status of each aspect of EUVL mask blank development in AGC toward the specifications required for high volume production. In the effort to meet the specifications, we have introduced a number of key technologies that can be divided into three regions, which are materials, glass processings, and evaluations. We have developed state-of-the-art processes and tools for manufacturing EUV mask blanks, such as a new polishing technique for extremely flat substrate, a new cleaning recipe and tool for low-defect substrate, and a newly developed deposition tool for ultra-low defect and higher EUV reflective coating with our new optical thin film materials for multilayer coating. Furthermore, in order to clarify their performances, we also introduced a wide variety of evaluation techniques such as flatness and roughness measurement of substrate, a defect inspection, and EUV reflectometry as well as defect analysis techniques which help us eliminate printable defects in EUVL mask blanks.