Corning ULE glass can meet P-37 specifications

William Rosch; Lorrie Beall; John Maxon; Robert Sabia; Robert Sell

doi:10.1117/12.712160

15 March 2007 Corning ULE glass can meet P-37 specifications

William Rosch, Lorrie Beall, John Maxon, Robert Sabia, Robert Sell

Proceedings Volume 6517, Emerging Lithographic Technologies XI; 651724 (2007) https://doi.org/10.1117/12.712160
Event: SPIE Advanced Lithography, 2007, San Jose, California, United States

Abstract

Corning ULE® glass is a binary SiO₂ + TiO₂ composition formed directly using a flame hydrolysis process. ULE possesses a very low thermal expansion range that can also be accurately adjusted for various applications including EUV photolithography. For ULE to be used for mask blanks and optics applications, it is also necessary that the material be capable of meeting stringent flatness and roughness specifications. For ULE, small compositional striations have been shown to affect the surface quality by inducing mid-spatial frequency roughness during polishing. Therefore, the main challenge has been to reduce mid-spatial frequency roughness to an acceptably low level by diminishing compositional striations present in the glass. Recently, a combination of predictive modeling and experimentation has resulted in a process that reduces striae to the levels needed for EUV masks and optics. These models have enhanced the fundamental understanding of the glass forming process, leading to process adjustments both in oscillation patterns and additional thermal treatments producing glass with improved striae characteristics. ULE masks with reduced striae have been polished to mid-spatial frequency roughness peak-to-valley levels of less than 8 nm. This sub-8 nm topography accounts for less than 20% of the total 50 nm flatness error budget allowable for EUVL masks. These results indicate that Corning's ULE product can meet the P-37 surface finishing specifications, and combined with ULE's superior CTE performance is positioned as the material of choice for EUV mask blanks.

Citation Download Citation

William Rosch, Lorrie Beall, John Maxon, Robert Sabia, and Robert Sell "Corning ULE glass can meet P-37 specifications", Proc. SPIE 6517, Emerging Lithographic Technologies XI, 651724 (15 March 2007); https://doi.org/10.1117/12.712160

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