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25 June 1999 Thermal management of EUV lithography masks using low-expansion glass substrates
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Lithographic masks must maintain dimensional stability during exposure in a wafer stepper. In extreme UV lithography, multilayer coatings are deposited on a flat mask, substrate to make the mask surface reflective at EUV wavelengths. About 40 percent of the incident EUV radiation is absorbed by the multilayer coatings causing a temperature rise. The choice of mask substrate material affects dimensional stability due to thermal expansion and/or deformation. Finite element modeling has ben used to investigate the proper choice of mask substrate material and to explore the efficacy of various thermal management strategies. This modeling indicates that significant machine design and engineering challenges are necessary in order to employ Si as a mask substrate. Even if these challenges can be met, the thermal expansion of Si is likely to be too large to meet overlay error budgets for lithography at ground rules beyond the 100 nm technology node. ULE - a single phase, fused silica glass doped with titania - has near zero thermal expansion at the temperatures where EUV lithography is performed. Due to its small coefficient of thermal expansion, ULE does not undergo appreciable instantaneous or transient thermal expansion that results in image placement error.
© (1999) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Steven E. Gianoulakis, Avijit K. Ray-Chaudhuri, and Scott Daniel Hector "Thermal management of EUV lithography masks using low-expansion glass substrates", Proc. SPIE 3676, Emerging Lithographic Technologies III, (25 June 1999);

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