Extreme ultraviolet lithography (EUVL) is a leading candidate for lithographic technology to fabricate the next
generation devices with a 32 nm feature size or smaller. The production of the defect-free mask blanks is one of the key
technologies to realize the EUVL. The EUV mask blanks requires various kinds of properties such as a low thermal
expansion coefficient and an ultra-low flatness of the substrate, a high and uniform reflectivity at EUV wavelength and a
ultra-low defectivity down to 30 nm in the reflective multilayer film, and so on. Asahi Glass Company (AGC) has
employed its own high quality glass synthetic technology, the glass polishing technology, the glass cleaning technology
and film-coating technology acquired for electronic and optical devices to develop the EUV mask blanks. In this paper,
we report on the current status of the EUVL mask blank development in AGC. We demonstrated <50 nm flatness on both
sides and ~10 defects >60 nm on low thermal expansion material (LTEM) substrate. We also demonstrated a Mo/Si
multilayer and a Ru capping layer-coated mask blanks with ~10defects >83 nm and ~65% reflectivity at EUV
wavelength. New Ta-based absorber materials and antireflective layers were also developed. Their superior optical
properties at the wavelength of the mask pattern inspection light were shown in comparison with the current
conventional TaN absorber layer and TaON AR layer. AGC can provide full-stack EUVL mask with this new absorber
material for the process developments with the alpha-demo EUV exposure tools.
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.