Silica glass and optical material

摘要

It is to obtain a silica glass suitable as a material for an optical material constituting an optical system to be used for EUVL, which has a low coefficient of thermal expansion from 0 to 100° C., and on which formation of concave defects is suppressed in a polishing step to achieve a high level of flatness. A silica glass containing from 0.1 to 10 mass % of Sn calculated as SnO2 and from 3 to 10 mass % of Ti calculated as TiO2, which has a homogeneity of the coefficient of thermal expansion from 0 to 100° C. to the temperature of from 50 to 200 ppb/° C., a coefficient of thermal expansion from 0 to 100° C. of 0±250 ppb/° C., and a Vickers hardness of at most 650.