Silica glass containing TiO

1. A silica glass comprising TiO2, which has a fictive temperature of at most 1,000° C., a F concentration of at least 100 ppm and a coefficient of thermal expansion of 0±200 ppb/° C., from 0 to 100° C., and produced by one of the following processes:

(a) forming a porous glass body by depositing and growing on a target quartz glass particles obtained by flame hydrolysis of glass-forming materials;

(b) holding the porous glass body in a fluorine-containing atmosphere to obtain a fluorine-containing porous glass body;

(c) heating the fluorine-containing porous glass body to a vitrification temperature to obtain a fluorine-containing vitrified glass body;

(d) heating the fluorine-containing vitrified glass body to a temperature of at least the softening temperature and forming it in a shape to obtain a fluorine-containing formed glass body; and

(e) carrying out annealing treatment wherein the formed glass body is held at a temperature exceeding 500° C., for at least 5 hours, and then, the temperature is lowered to 500° C., at an average cooling rate of at most 10° C./hr, or a step of carrying out annealing treatment wherein the formed glass body at a temperature of at least 1,200° C., is cooled to 500° C., at an average cooling rate of at most 10° C./hr, or

(a) forming a porous glass body by depositing and growing on a target quartz glass particles obtained by flame hydrolysis of glass-forming materials;

(b) holding the porous glass body in a fluorine-containing atmosphere to obtain a fluorine-containing porous glass body;

(c) holding the fluorine-containing porous glass body in an atmosphere containing oxygen at from 300 to 1,300° C., for at least 5 hours, and then heating it to a vitrification temperature to obtain a fluorine-containing vitrified glass body;

(d) heating the fluorine-containing vitrified glass body to a temperature of at least the softening temperature and forming it in a shape to obtain a fluorine-containing formed glass body; and

(e) carrying out annealing treatment wherein the formed glass body is held at a temperature exceeding 500° C., for at least 5 hours, and then, the temperature is lowered to 500° C., at an average cooling rate of at most 10° C./hr, or a step of carrying out annealing treatment wherein the formed glass body at a temperature of at least 1,200° C., is cooled to 500° C., at an average cooling rate of at most 10° C./hr.

2. The silica glass comprising TiO2 according to claim 1 , which has a F concentration of at least 500 ppm.

3. The silica glass comprising TiO2 according to claim 1 , which has a coefficient of thermal expansion of 0±150 ppb/° C., from 0 to 100° C.

4. The silica glass comprising TiO2 according to claim 1 , which has a F concentration of at least 1,000 ppm.

5. The silica glass comprising TiO2 according to claim 1 , which exhibits a fluctuation of the refractive index (Δn) of at most 2×10−4 within an area of 30 mm×30 mm in at least one plane.

6. The silica glass comprising TiO2 according to claim 2 , which has a coefficient of thermal expansion of 0±150 ppb/° C., from 0 to 100° C.

7. The silica glass comprising TiO2 according to claim 2 , which has a F concentration of at least 1,000 ppm.

8. The silica glass comprising TiO2 according to claim 2 , which exhibits a fluctuation of the refractive index (Δn) of at most 2×10−4 within an area of 30 mm×30 mm in at least one plane.

9. The silica glass according to claim 1 , which exhibits a temperature width wherein the coefficient of thermal expansion becomes 0±5 ppb/° C., of at least 4.50° C.

10. The silica glass according to claim 9 , which exhibits a temperature width wherein the coefficient of thermal expansion becomes 0±5 ppb/° C., of at least 5.0° C.

11. The silica glass according to claim 9 , which exhibits a temperature width wherein the coefficient of thermal expansion becomes 0±5 ppb/° C., of at least 6.0° C.

12. An EUVL exposure device comprising the silica glass according to claim 9 , wherein said glass is an optical material.

13. An EUVL exposure device comprising the silica glass according to claim 10 , wherein said glass is an optical material.

14. An EUVL exposure device comprising the silica glass according to claim 11 , wherein said glass is an optical material.

15. A process for producing a silica glass comprising TiO2, which has a fictive temperature of at most 1000° C., a F concentration of at least 100 ppm and a coefficient of thermal expansion of 0±200 ppb/° C., from 0 to 100° C., which comprises:

(a) forming a porous glass body by depositing and growing on a target quartz glass particles obtained by flame hydrolysis of glass-forming materials;

(b) holding the porous glass body in a fluorine-containing atmosphere to obtain a fluorine-containing porous glass body;

(c) heating the fluorine-containing porous glass body to a vitrification temperature to obtain a fluorine-containing vitrified glass body;

(d) heating the fluorine-containing vitrified glass body to a temperature of at least the softening temperature and forming it in a shape to obtain a fluorine-containing formed glass body; and

(e) carrying out annealing treatment wherein the formed glass body is held at a temperature exceeding 500° C., for at least 5 hours, and then, the temperature is lowered to 500° C., at an average cooling rate of at most 10° C./hr, or a step of carrying out annealing treatment wherein the formed glass body at a temperature of at least 1,200° C., is cooled to 500° C., at an average cooling rate of at most 10° C./hr.

16. A process for producing a silica glass comprising TiO2, which has a fictive temperature of at most 1000° C., a F concentration of at least 100 ppm and a coefficient of thermal expansion of 0±200 ppb/° C. from 0 to 100° C., which comprises:

(a) forming a porous glass body by depositing and growing on a target quartz glass particles obtained by flame hydrolysis of glass-forming materials;

(b) holding the porous glass body in a fluorine-containing atmosphere to obtain a fluorine-containing porous glass body;

(c) holding the fluorine-containing porous glass body in an atmosphere containing oxygen at from 300 to 1,300° C., for at least 5 hours and then heating it to a vitrification temperature to obtain a fluorine-containing vitrified glass body;

(d) heating the fluorine-containing vitrified glass body to a temperature of at least the softening temperature and forming it in a shape to obtain a fluorine-containing formed glass body; and

(e) carrying out annealing treatment wherein the formed glass body is held at a temperature exceeding 500° C., for at least 5 hours, and then, the temperature is lowered to 500° C., at an average cooling rate of at most 10° C./hr, or a step of carrying out annealing treatment wherein the formed glass body at a temperature of at least 1,200° C., is cooled to 500° C., at an average cooling rate of at most 10° C./hr.

17. A silica glass comprising TiO2, doped with halogen, and which has a fictive temperature of at most 1,000° C., and which exhibits a temperature width wherein the coefficient of thermal expansion becomes 0±5 ppb/° C., of at least 4.5° C.

18. The silica glass according to claim 17 , which exhibits a temperature width wherein the coefficient of thermal expansion becomes 0±5 ppb/° C., of at least 5.0° C.

19. The silica glass according to claim 17 , which exhibits a temperature width wherein the coefficient of thermal expansion becomes 0±5 ppb/° C., of at least 6.0° C.

20. An EUVL exposure device comprising the silica glass according to claim 17 , wherein said glass is an optical material.