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Proceedings Paper

Improved materials meeting the demands for EUV substrates
Author(s): Ina Mitra; Jochen Alkemper; Uwe Nolte; Axel Engel; Rolf Mueller; Simone Ritter; Hrabanus Hack; Klaus Megges; Heiko Kohlmann; Wolfgang Pannhorst; Mark J. Davis; Lutz Aschke; Konrad Knapp
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Paper Abstract

The enhanced demands for substrate materials for next-generation optics and masks have initiated detailed investigations on Zerodur as a proposed EUVL substrate material with focus on thermal expansion behavior and surface roughness. As a result of specifically adjusted process parameters, the coefficient of thermal expansion (CTE) was tailored to be a minimum at 22.5°C. Laboratory samples of Zerodur exhibit a CTE < 5 ppb/K corresponding to the lowest expasnion class of the SEMI standard P37 (19 to 25°C) for EUV mask blanks. By further variation of process parameters, the position of zero crossing, e.g. at 30°C, can be varied, revealing an attractive attribute feature of Zerodur. A new dilatometer type was mounted in 2002 with first operatinoal results revealing an improved reproducibility of ~1ppb/K in the temperature range of 0 to 50°C. A series of CTE measurements with a small block of Zerodur provides information on CTE homogeneity on a cm-scale: No CTE variation was observed within the error of measurements for a block exhibiting ± 3.5*10-6 vairtion in refractinve index. CTE variation can cause surface deformations during changing temperature conditions. A first setup of Fizeau-Interferometer with a current resolution of 0.3 nm rms was used to record surface deformation of Zerodur due to elevated temperature was determined to be lower than the current resolution. Both methods to analyze the CTE homogeneity of Zerodur lead to the result of CTE variation below 1 ppb/K, still identifying today's need to improve metrology further. Final finishing of EUV substrates may increase roughness of super-polished surfaces significantly. Using appropriate processes a to surface roughness < 0.25 nm rms under production conditions can be achieved after final finishing of Zerodur. As an improved Zerodur-type material, recent achievements of material development demonstrate the optimization of glass-ceramic composition to nearly meeting the specification of surface roughness after a standard finishing process. These results are regarded as a promising milestone to develop an optimized glass-ceramic material providnig adjusted thermal expansion behavior and surface processability according to the specific demands of EUV technology.

Paper Details

Date Published: 16 June 2003
PDF: 8 pages
Proc. SPIE 5037, Emerging Lithographic Technologies VII, (16 June 2003); doi: 10.1117/12.484728
Show Author Affiliations
Ina Mitra, Schott Glas (Germany)
Jochen Alkemper, Schott Glas (Germany)
Uwe Nolte, Schott Glas (Germany)
Axel Engel, Schott Glas (Germany)
Rolf Mueller, Schott Glas (Germany)
Simone Ritter, Schott Glas (Germany)
Hrabanus Hack, Schott Glas (Germany)
Klaus Megges, Schott Glas (Germany)
Heiko Kohlmann, Schott Glas (Germany)
Wolfgang Pannhorst, Schott Glas (Germany)
Mark J. Davis, Schott Glass Technologies Inc. (United States)
Lutz Aschke, Schott Lithotec AG (Germany)
Konrad Knapp, Schott Lithotec AG (Germany)

Published in SPIE Proceedings Vol. 5037:
Emerging Lithographic Technologies VII
Roxann L. Engelstad, Editor(s)

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