Claims
- 1. A method of evaluating a light-transmitting optical component for transmitting light of a wavelength of less than about 200 nm, the method comprising the steps of:
(a) measuring a transmissivity of the optical component; (b) thereafter irradiating the optical component with light of a wavelength less than about 200 nm for a predetermined time period; (c) measuring a transmissivity of the optical component that was irradiated in step (b) to determine an amount of a transmissivity decrease due to the irradiation; and (d) comparing the amount of transmissivity decrease with a predetermined value to determine whether the light transmitting component is usable in an optical lithography apparatus.
- 2. The method according to claim 1, wherein step (b) includes irradiating the optical component until an instantaneous rate of change in the transmissivity of the optical component becomes substantially zero.
- 3. The method according to claim 1, wherein step (b) includes irradiating the optical component until the transmissivity of the optical component substantially reaches a constant minimum value.
- 4. The method according to claim 1, wherein step (d) includes determining that the optical component is usable when the amount of transmissivity decrease is less than about 5% of the measured transmissivity of the optical component prior to irradiation.
- 5. The method according to claim 1, wherein step (b) includes irradiating the optical component with 10,000 pulses of an F2 laser light having a wavelength of about 157 nm and an energy density of about 10 mJ/(cm2·pulse)
- 6. The method according to claim 5, wherein the predetermined value of the amount of transmissivity decrease in step (d) is less than about 5%/inch.
- 7. An optical member for transmitting light of a wavelength less than about 200 nm comprising:
crystalline calcium fluoride with a potassium content less than about 0.5 ppm, wherein a degradation in a transmissivity of the optical member after an irradiation for a fixed period of time with the light of the wavelength of less than about 200 nm is less than about 5% of a transmissivity of the optical member before the irradiation.
- 8. The optical member according to claim 7, wherein the potassium content is at most about 0.1 ppm.
- 9. The optical member according to claim 7, wherein the fixed time period for the irradiation is a time period ending when an instantaneous rate of change of a transmissivity of the optical member becomes substantially zero.
- 10. The optical member according to claim 7, wherein the fixed time period for the irradiation is a time period ending when a transmissivity of the optical member reaches a substantially constant minimum value.
- 11. The optical member according to claim 7, wherein the wavelength of less than about 200 nm is a wavelength of about 157 nm of an F2 laser light.
- 12. The optical member according to claim 11, wherein the potassium content is at most about 0.1 ppm.
- 13. The optical member according to claim 7, wherein the wavelength of less than about 200 nm is a wavelength of about 157 nm of an F2 laser light with an energy density of 10 mJ/(cm2 ·pulse) and the fixed time period for the irradiation is such that the optical member is irradiated with 10,000 pulses of the F2 laser light.
- 14. The optical member according to claim 13, wherein the degradation in the transmissivity is about less than 5%/inch.
- 15. A method for manufacturing a light-transmitting optical member that transmits light of a wavelength less than about 200 nm, the method comprising the steps of:
(a) melting a calcium fluoride raw material; and (b) gradually cooling the melted raw material with a temperature gradient at a solid-melt interface to crystallize calcium fluoride in a pulling-down scheme, wherein a potassium content in the raw material and the temperature gradient in step (b) are adapted to provide for the potassium content of the resulting crystal to be less than about 0.5 ppm.
- 16. The method according to claim 15, wherein the raw material has a potassium content of at most about 0.1 ppm.
- 17. The method according to claim 15, further comprising before step (a) the step of:
(c) heat treating the raw material at a temperature below the melting point of the calcium fluoride raw material.
- 18. The method according to claim 17, wherein step (c) includes heating the raw material at a temperature between about 800° C. and about 1300° C.
- 19. The method according to claim 17, wherein step (c) includes heating the raw material at a temperature of more than about 1000° C.
- 20. The method according to claim 17, wherein step (c) includes heat treating the raw material for a time period of at least about 1 hour.
- 21. The method according to claim 17, wherein the heat treatment in step (c) is carried out inside a vacuum atmosphere.
- 22. The method according to claim 17, wherein step (b) includes maintaining a temperature gradient of at least about 8° C./cm at a solid melt interface.
- 23. The method according to claim 15, wherein step (b) includes maintaining the temperature gradient of at least about 8° C./cm at the solid-melt interface.
- 24. The method according to claim 15, wherein step (b) includes maintaining the temperature gradient of between about 8° C./cm to about 20° C./cm at the solid-melt interface.
- 25. The method according to claim 15, further comprising after step (b) the steps of:
(d) heating and maintaining the crystallized calcium fluoride at a temperature; and (e) thereafter gradually cooling the crystallized calcium fluoride.
- 26. The method according to claim 25, wherein step (d) includes maintaining the temperature of the crystallized calcium fluoride substantially constant at 1000° C.
- 27. The method according to claim 25, wherein step (e) includes gradually cooling the crystallized calcium fluoride at a rate of about 5° C./hr.
- 28. An optical lithography apparatus comprising:
an illumination optical system that emits exposure light of a wavelength less than about 200 nm towards a mask having a pattern; and a projection optical system that projects an image of the pattern on the mask onto a substrate via the exposure light, wherein at least one of the illumination optical system and the projection optical system includes a light-transmitting optical member formed of crystalline calcium fluoride with a potassium content of less than about 0.5 ppm.
- 29. An optical member for transmitting light of a wavelength less than about 200 nm comprising:
crystalline calcium fluoride with a potassium content less than about 0.5 ppm, wherein a degradation in a transmissivity of the optical member after an irradiation for a fixed period of time with the light of the wavelength of less than about 200 nm is less than about 5%/inch.
Priority Claims (1)
Number |
Date |
Country |
Kind |
10-252554 |
Sep 1998 |
JP |
|
Parent Case Info
[0001] This application claims the benefit of Japanese Application No. 10-252554, filed in Japan on Sep. 7, 1998, which is hereby incorporated by reference.
Divisions (1)
|
Number |
Date |
Country |
Parent |
09389462 |
Sep 1999 |
US |
Child |
09791892 |
Feb 2001 |
US |