The present invention provides a TiO 2 -containing silica glass from which a transparent extremely low thermal expansion glass having excellent transparency and having a temperature region in which the coefficient of thermal expansion is substantially zero can be obtained. The present invention relates to a TiO 2 -containing silica glass for optical member for EUV lithography, having a TiO 2 concentration of from 3 to 14% by mass; an internal transmittance per 1-mm thickness in a wavelength region of from 400 to 700 nm, T 400-700 , of 97% or more; and an internal transmittance per 1-mm thickness in a wavelength region of from 400 to 3,000 nm, T 400-3,000 , of 70% or more.
1. A TiO 2 -containing silica glass for optical member for EUV lithography, having a TiO 2 concentration of from 3 to 14% by mass; containing Sn, in terms of SnO 2 , in an amount of from 0.01 to 10% by mass; having an internal transmittance per 1-mm thickness in a wavelength region of from 400 to 700nm, T 400-700 , of 98% or more; having a fluctuation width ΔSnO 2 of SnO 2 concentration of 0.1% by mass or less within an area of 10 mmx10 mm; and having an internal transmittance per 1-mm thickness in a wavelength region of from 400 to 3,000 nm, T 400-3000 , of 70% or more.
2. The silica glass for optical member for EUV lithography according to claim 1 , having a Ti 3+ concentration, in terms of TiO 2 , of 100 ppm by mass or less.
3. The silica glass for optical member for EUV lithography according to claim 1 , having Sn 2+ /(Sn 2+ +Sn 4+ ) of 0.5 or less.
4. The silica glass for optical member for EUV lithography according to claim 1 , having a fluctuation width (Δn) of a refractive index of 2x 10 −3 or less within an area of 10 mm x 10 mm in at least one plane.
5. The silica glass for optical member for EUV lithography according to claim 1 , having a fluctuation width (Δn) of a refractive index of 2 x 10 −3 or less within an area of 10 mm x 10 mm in each of two planes orthogonal to each other.
6. The silica glass for optical member for EUV lithography according to claim 1 , having a coefficient of thermal expansion in a temperature range of from 0 to 100° C., CTE 0-100 , of from −150 ppb/° C.
7. The silica glass for optical member for EUV lithography according to claim 1 , having a temperature width, in which the coefficient of thermal expansion is from −5 ppb/° C. to 5 ppb/° C., of 4.0° C. or greater.
8. The silica glass for optical member for EUV lithography according to claim 1 , having a fictive temperature of 1,200° C. or lower.
9. The silica glass for optical member for EUV lithography according to claim 1 , having an OH concentration of 600 ppm by mass or less.
10. The TiO 2 -containing silica glass according to claim 1 , having a TiO 2 concentration of from 4 to 10% by mass.
11. The silica glass of claim 10 , having a SnO 2 concentration of from 0.1 to 2% by mass.
12. The silica glass according to claim 10 , having a coefficient of thermal expansion in a temperature range of from −50 to 150° C. of from −234 to 163 ppb/° C.
13. The silica glass according to claim 10 having a fictive temperature of 1,000° C. or lower.
14. The silica glass according to claim 10 having a T 400-3,000 of from 92.1 to 97.0%.
15. The silica glass according to claim 1 , having a maximum CTE 0-100 of 100 ppb/° C.
16. The silica glass according to claim 1 , having a SnO 2 content of from 0.1 to 0.5% by mass.