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17 October 2008 Development status of EUVL mask blanks
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Abstract
Extreme ultraviolet lithography (EUVL) is the most promising lithographic technology to fabricate the next generation devices with a 20~30 nm feature size or smaller. The production of the EUVL mask blank is one of the critical issues to realize the EUVL because of various kinds of stringent requirements. For instance, a <+/-5 ppb/K thermal expansion coefficient (CTE) and a <30 nm surface flatness of the polished substrate, a high and uniform reflectivity at the 13~14 nm wavelength of the reflective multilayer film, and a low defect density as small as 30nm of the blank. Most of these requirements are different from the optical lithography mask blank and some are specific to the EUVL blank. We have continuously been developing all of key materials and processes essential to prepare the EUVL mask blank, and we showed a good progress in its performance improvement. Our low thermal expansion material (LTEM) showed the CTE properties requirements defined in SEMI P37, which were 0 +/- 5 ppb/K mean CTE at 22°C and < +/-3 ppb/K CTE spatial variation across 6 inch square substrate. ~30nm flatness was demonstrated on both front and back surfaces of the LTEM polished substrate, which was very close to the most stringent flatness requirement of SEMI P37. Ta-based absorber film and anti-reflective film were also developed. Their film properties almost met SEMI P38 class A, and the absorbers showed good etching and patterning performances with the inductively coupled plasma etching process. In addition, the thinner resist coating process was developed. As a consequence, Asahi Glass has a capability to deliver the ready-to-write EUVL blank which is the most suitable for the EUVL process developments by using the full field exposure tools.
© (2008) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Kazuaki Shiromo "Development status of EUVL mask blanks", Proc. SPIE 7122, Photomask Technology 2008, 712225 (17 October 2008); https://doi.org/10.1117/12.801427
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