Method for producing glass body and method for producing optical member for EUV lithography

1. A method for producing a glass body, the method comprising:

feeding a raw material mixed gas through a central nozzle (A) positioned in a central portion of a burner, the raw material mixed gas comprising a gas of a silicon compound, a gas of a compound comprising a metal dopant, and a combustible gas;

feeding a combustible gas through a first nozzle directly adjacent to the central nozzle (A);

feeding a combustible gas or a combustion supporting gas through a second nozzle (B) different from the first nozzle and the central nozzle (A) of the burner;

optionally feeding a combustible gas, a combustion supporting gas, a mixed gas comprising a combustible gas, or a mixed gas comprising a combustion supporting gas through at least one nozzle (C) different from the central nozzle (A), the first nozzle, and the second nozzle (B);

hydrolyzing the silicon compound and the compound comprising the metal dopant, in a flame projected from the burner, to form glass fine particles; and

growing the glass fine particles on a base material,

wherein a flow rate of the raw material mixed gas is 50% or more and not more than 90% of a largest flow rate among flow rate(s) of the combustible gas(es) and the combustion supporting gas(es) fed through a nozzle or nozzles other than the central nozzle (A), and

the largest flow rate is provided in the first nozzle.

2. The method for producing a glass body according to claim 1 , further comprising:

feeding a noncombustible gas through a nozzle provided between a nozzle through which a combustible gas or a mixed gas comprising a combustible gas is fed and a nozzle through which a combustion supporting gas or a mixed gas comprising a combustion supporting gas is fed.

3. The method for producing a glass body according to claim 1 ,

wherein the burner comprises the at least one nozzle (C) through which a combustible gas, a combustion supporting gas, a mixed gas comprising a combustible gas, or a mixed gas comprising a combustion supporting gas is fed, and

a flow rate of a gas fed through a nozzle spatially farthest from the central nozzle (A) is not more than 95% of the flow rate of the raw material mixed gas.

4. The method for producing a glass body according to claim 1 , wherein the burner has a multitubular structure.

5. The method for producing a glass body according to claim 4 ,

wherein the burner comprises the central nozzle (A), a first peripheral nozzle which is the first nozzle directly adjacent to the central nozzle (A) and surrounding the central nozzle (A), a second peripheral nozzle surrounding the first peripheral nozzle, and a third peripheral nozzle which is the second nozzle (B) surrounding the second peripheral nozzle;

a noncombustible gas is fed through the second peripheral nozzle; and

a combustion supporting gas is fed through the third peripheral nozzle.

6. The method for producing a glass body according to claim 1 , wherein the metal dopant is Ti.

7. The method for producing a glass body according to claim 1 , wherein the raw material mixed gas is fed such that a mass of a finally obtained glass body is 50 kg or more.

8. A method for producing an optical member for EUV lithography, comprising:

forming a member from a glass body produced by the method according to claim 1 .

9. The method for producing a glass body according to claim 1 , wherein the flow rate of the raw material mixed gas is 60% or more and not more than 80% of the largest flow rate among flow rate(s) of the combustible gas(es) and the combustion supporting gas(es) fed through a nozzle or nozzles other than the central nozzle (A).

10. The method for producing a glass body according to claim 2 , wherein the noncombusible gas is fed at a flow rate which is smaller than the flow rate of the raw material mixed gas, a flow rate of the combustible gas, and a flow rate of the combustion supporting gas.

11. The method for producing a glass body according to claim 3 , wherein the flow rate of the gas fed through the nozzle spatially farthest from the central nozzle (A) is more than 30% of the flow rate of the raw material mixed gas.

12. A method for producing a glass body, the method comprising:

feeding a raw material mixed gas through a central nozzle (A) positioned in a central portion of a burner, the raw material mixed gas comprising a gas of a silicon compound, a gas of a compound comprising a metal dopant, and a combustible gas;

feeding a noncombustible gas through a first nozzle directly adjacent to the central nozzle (A);

feeding a combustion supporting gas through a second nozzle (B) directly adjacent to the first nozzle;

optionally feeding a combustible gas, a combustion supporting gas, a mixed gas comprising a combustible gas, or a mixed gas comprising a combustion supporting gas through at least one nozzle (C) different from the central nozzle (A), the first nozzle, and the second nozzle (B);

hydrolyzing the silicon compound and the compound comprising the metal dopant, in a flame projected from the burner, to form glass fine particles; and

growing the glass fine particles on a base material,

wherein a flow rate of the raw material mixed gas is 50% or more and not more than 90% of a largest flow rate among flow rate(s) of the combustible gas(es) and the combustion supporting gas(es) fed through a nozzle or nozzles other than the central nozzle (A), and

the largest flow rate is provided in the second nozzle (B).

13. The method for producing a glass body according to claim 12 , wherein the burner has a multitubular structure.

14. The method for producing a glass body according to claim 13 ,

wherein the burner comprises the central nozzle (A), a first peripheral nozzle which is the first nozzle directly adjacent to the central nozzle (A) and surrounding the central nozzle (A), and a second peripheral nozzle which is the second nozzle (B) and surrounds the first peripheral nozzle.

15. The method for producing a glass body according to claim 12 ,

wherein the burner comprises the at least one nozzle (C) through which a combustible gas, a combustion supporting gas, a mixed gas comprising a combustible gas, or a mixed gas comprising a combustion supporting gas is fed, and

a flow rate of a gas fed through a nozzle spatially farthest from the central nozzle (A) is not more than 95% of the flow rate of the raw material mixed gas.

16. The method for producing a glass body according to claim 12 , wherein the metal dopant is Ti.

17. The method for producing a glass body according to claim 12 , wherein the raw material mixed gas is fed such that a mass of a finally obtained glass body is 50 kg or more.

18. A method for producing an optical member for EUV lithography, comprising:

forming a member from a glass body produced by the method according to claim 12 .

19. The method for producing a glass body according to claim 12 , wherein the flow rate of the raw material mixed gas is 60% or more and not more than 80% of the largest flow rate among flow rate(s) of the combustible gas(es) and the combustion supporting gas(es) fed through a nozzle or nozzles other than the central nozzle (A).

20. The method for producing a glass body according to claim 12 , wherein the noncombusible gas is fed at a flow rate which is smaller than the flow rate of the raw material mixed gas, a flow rate of the combustible gas, and a flow rate of the combustion supporting gas.