Method for producing titanium-doped silica glass for use in EUV lithography and blank produced in accordance therewith

摘要

The Ti3+ ions present in Ti-doped silica glass cause a brown staining of the glass, causing inspection of the lens to become more difficult. Known methods for reducing Ti3+ ions in favor of Ti4+ ions in Ti-doped silica glass include a sufficiently high proportion of OH-groups and carrying out an oxygen treatment prior to vitrification, which both have disadvantages. In order to provide a cost-efficient production method for Ti-doped silica glass, which at a hydroxyl group content of less than 120 ppm shows an internal transmittance (sample thickness 10 mm) of at least 70% in the wavelength range of 400 nm to 1000 nm, the TiO2—SiO2 soot body is subjected to a conditioning treatment with a nitrogen oxide prior to vitrification. The blank produced in this way from Ti-doped silica glass has the ratio Ti3+/Ti4+≦5×10−4.

主权项

1. A method for producing a blank of titanium-doped glass having a high silicic-acid content with an internal transmission of at least 70% in the wavelength range of 400 nm to 1000 nm at a sample thickness of 10 mm for use in EUV lithography, comprising the following steps:
(a) producing a TiO2—SiO2 soot body by flame hydrolysis of silicon- and titanium-containing precursor substances, (b) drying the soot body to obtain a mean hydroxyl group content of less than 120 wt. ppm, and (c) vitrifying the soot body to form a blank of titanium-doped glass having a high silicic-acid content,wherein prior to step (c) the TiO2—SiO2 soot body is subjected to a conditioning treatment which comprises a treatment with a nitrogen oxide at a treatment temperature in the range of 20° C. to 600° C. for a period of at least one hour.