Light-transmitting optical member, manufacturing method thereof, evaluation method therefor, and optical lithography apparatus using the optical member
AssigneeNikon Corporation
InventorMasaki Shiozawa
Life of this patent
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Abstract
An optical member for transmitting light of a wavelength less than about 200 nm including 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.
Claims29
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.
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.
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.
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.
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.
Dependencies are inferred from the claim text.