16 June 2003 Improved materials meeting the demands for EUV substrates
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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.
© (2003) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Ina Mitra, Ina Mitra, Jochen Alkemper, Jochen Alkemper, Uwe Nolte, Uwe Nolte, Axel Engel, Axel Engel, Rolf Mueller, Rolf Mueller, Simone Ritter, Simone Ritter, Hrabanus Hack, Hrabanus Hack, Klaus Megges, Klaus Megges, Heiko Kohlmann, Heiko Kohlmann, Wolfgang Pannhorst, Wolfgang Pannhorst, Mark J. Davis, Mark J. Davis, Lutz Aschke, Lutz Aschke, Konrad Knapp, Konrad Knapp, } "Improved materials meeting the demands for EUV substrates", Proc. SPIE 5037, Emerging Lithographic Technologies VII, (16 June 2003); doi: 10.1117/12.484728; https://doi.org/10.1117/12.484728

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