METHOD FOR PRODUCING TITANIUM-DOPED SILICA GLASS FOR USE IN EUV LITHOGRAPHY AND BLANK PRODUCED IN ACCORDANCE THEREWITH

摘要

The Ti ³⁺ ions present in the Ti-doped silica glass cause browning of the glass, making inspection of the lens more difficult. Ti is performed by a sufficiently high proportion of OH groups causing internal oxidation due to external diffusion of hydrogen, or by carrying out costly pre-vitalization oxygen treatment by requiring a high treatment temperature and a special preservative furnace when the proportion of OH groups is low. It is known to ensure reduction of Ti ³⁺ ions for Ti ⁴⁺ ions in doped silica glass. A cost-effective method for producing Ti-doped silica glass having an internal transmittance (sample thickness of 10 mm) of 70% or more in a wavelength range of 400 nm to 1000 nm at a hydroxyl group content of less than 120 ppm, based on a flame hydrolysis soot deposition method In order to provide the present invention, it is proposed that the TiO ₂ -SiO ₂ soot body is subjected to a conditioning treatment including nitrogen oxide treatment prior to vitrification. The blanks prepared in this way from Ti-doped silica glass are characterized by a Ti ³⁺ /Ti ⁴⁺ ratio of 5 x 10 ^-4 or less.