TiO₂-SiO₂ glass is one of the leading candidates for optical elements of extreme ultraviolet lithography. TiO₂-SiO₂ glass synthesized by the soot method has shown striae related to inhomogeneity of TiO₂ concentration formed in the planes perpendicular to soot growth direction in the synthesis process. It can induce CTE variation and localized surface roughness. Striae were characterized in three modes by polarization microscope. Such striae were improved with an improved gas condition and developing a modified material gas supply system. Specimen prepared from the improved TiO₂-SiO₂ glass was evaluated by a line-focus-beam ultrasonic material characterization system, using a surface-acoustic-wave mode. Improved glass had 43% striae level compared to conventional glass by birefringence measurement, 31% compared to conventional glass by the ultrasonic measurement. It was found that improved glass had good homogeneity to both directions perpendicular and parallel to striae plane.

Date Published: 1 April 2013
PDF: 7 pages
Proc. SPIE 8679, Extreme Ultraviolet (EUV) Lithography IV, 86791N (1 April 2013); doi: 10.1117/12.2011655

Published in SPIE Proceedings Vol. 8679:
Extreme Ultraviolet (EUV) Lithography IV
Patrick P. Naulleau, Editor(s)