Optical element
In order to make possible both good laser resistance and good antireflection properties, an optical element, in particular for UV lithography, comprising a substrate and a coating on the substrate having at least four layers, is proposed, wherein a first layer comprising a low refractive index inorganic fluoride compound is arranged on the substrate, a layer comprising an inorganic oxide-containing compound is arranged as a layer the most distant from the substrate, and at least two further layers each comprising an inorganic fluoride compound or an inorganic oxide-containing compound are arranged alternately between the first and the most distant layers.
1. An optical element, comprising:
a substrate comprising a fluoride; and
a coating supported by the substrate,
wherein:
the coating comprises, in order moving away from the substrate, a first layer, a second layer, a third layer, a fourth layer, and a fifth layer;
the first layer comprises an inorganic oxide;
the coating does not include two consecutive oxide layers;
the second layer comprises an inorganic fluoride having a refractive index at a wavelength in the ultraviolet range that is less than a refractive index of calcium fluoride at the wavelength in the ultraviolet range;
the third layer comprises the inorganic oxide;
the fourth layer comprises an inorganic fluoride;
the fifth layer comprises the inorganic oxide;
the first layer is in contact with the substrate;
the fifth layer is in contact with the surroundings of the optical element;
the second layer is in direct contact with the first layer; and
the second layer is in direct contact with the third layer.
2. The optical element of claim 1 , wherein the inorganic oxide of the fifth layer has a refractive index at the wavelength in the ultraviolet wavelength range that is greater than the refractive index of the inorganic fluoride of the second layer at the wavelength in the ultraviolet range.
3. The optical element of claim 2 , wherein the inorganic oxide of the fifth layer has a refractive index at the wavelength in the ultraviolet range that is greater than a refractive index of the inorganic fluoride of the fourth layer at the wavelength in the ultraviolet range.
4. The optical element of claim 1 , wherein the inorganic oxide of the third layer has a refractive index at the wavelength in the ultraviolet range that is greater than the refractive index of the inorganic fluoride of the second layer at the wavelength in the ultraviolet range.
5. The optical element of claim 1 , wherein the inorganic oxide of the fifth layer has a refractive index at the wavelength in the ultraviolet range that is greater than the refractive index of calcium fluoride at the wavelength in the ultraviolet range.
6. The optical element of claim 5 , wherein the inorganic oxide of the third layer has a refractive index at the wavelength in the ultraviolet range that is greater than the refractive index of calcium fluoride at the wavelength in the ultraviolet range.
7. The optical element of claim 1 , wherein the inorganic oxide of the third layer has a refractive index at the wavelength in the ultraviolet range that is greater than the refractive index of calcium fluoride at the wavelength in the ultraviolet range.
8. The optical element of claim 1 , wherein the inorganic fluoride of the second layer comprises an inorganic metal fluoride.
9. The optical element of claim 1 , wherein the inorganic fluoride of the second layer comprises at least one material selected from the group consisting of aluminum fluoride, magnesium fluoride, lithium fluoride, sodium fluoride, yttrium fluoride, strontium fluoride, and barium fluoride.
10. The optical element of claim 1 , wherein the inorganic oxide of the fifth layer comprises at least one material selected from the group consisting of an oxyfluoride and an oxynitride.
11. The optical element of claim 1 , wherein the inorganic oxide of the fifth layer comprises at least one material selected from the group consisting of silicon dioxide, aluminum oxide, fluorine-doped silicon dioxide, and nitrogen-doped silicon dioxide.
12. The optical element of claim 1 , wherein the substrate comprises a metal fluoride.
13. The optical element of claim 1 , wherein the substrate comprises at least one material selected from the group consisting of magnesium fluoride, strontium fluoride, barium fluoride, lithium fluoride, and calcium fluoride.
14. The optical element of claim 1 , wherein the inorganic fluoride of the second layer is the same as the inorganic fluoride of the fourth layer.
15. The optical element of claim 1 , wherein the first layer comprises an inorganic oxide having a refractive index at the wavelength in the ultraviolet range that is higher than the refractive index of the inorganic fluoride of the second layer at the wavelength in the ultraviolet range.
16. The optical element of claim 1 , wherein the first layer comprises at least one material selected from the group consisting of silicon dioxide, aluminum oxide, fluorine-doped silicon dioxide, and nitrogen-doped silicon dioxide.
17. The optical element of claim 1 , wherein the coating is configured so that, when exposed to ultraviolet radiation, a maximum transmission is achieved at angles of incidence between 20° and 40°.
18. The optical element of claim 1 , wherein the coating is configured so that, when exposed to ultraviolet radiation, a maximum transmission is achieved at angles of incidence between 60° and 80°.
19. A system, comprising:
an optical element according to claim 1 ,
wherein the system is selected from the group consisting of an ultraviolet lithography illumination system and an ultraviolet projection system.
20. An apparatus, comprising:
an illumination system; and
a projection system,
wherein the apparatus is an ultraviolet lithography apparatus, a system comprises an optical element according to claim 1 , and the system is selected from the group consisting of the illumination system and the projection system.
21. The optical element of claim 1 , wherein the fourth layer is in direct contact with the third layer, and the fourth layer is in direct contact with the fifth layer.
22. An optical element, comprising:
a substrate comprising a fluoride; and
a coating supported by the substrate,
wherein:
the coating comprises an inner most layer, an outer most layer, and a multi-layer stack between the inner most layer and the outer most layer;
the inner most layer is the layer of the coating that is closest to the substrate;
the outer most layer is the layer of the coating that is furthest from the substrate;
the inner most layer comprises an inorganic oxide;
the outer most layer comprises the inorganic oxide;
the multi-layer stack comprises alternating layers of an inorganic fluoride and the inorganic oxide;
the inner most layer is in contact with the substrate;
the outer most layer is in contact with the surroundings of the optical element; and
the alternating layers of an inorganic fluoride and the inorganic oxide are in contact with each other.
23. An optical element, comprising:
a substrate comprising a fluoride; and
a coating supported by the substrate,
wherein:
the coating comprises at least five layers;
the at least five layers comprise alternating layers of the same inorganic oxide and the same inorganic fluoride;
the layer of the coating that is closest to the substrate comprises the inorganic oxide;
the layer of the coating that is furthest from the substrate comprises the inorganic oxide;
a refractive index of the inorganic oxide at a wavelength in the ultraviolet range is greater than a refractive index of the inorganic fluoride at the wavelength in the ultraviolet range;
the layer of the coating that is closest to the substrate is in contact with the substrate;
the layer of the coating that is furthest from the substrate is in contact with the surroundings of the optical element; and
the alternating layers of the same inorganic oxide and the same inorganic fluoride are in contact with each other.
24. An optical element, comprising:
a substrate comprising a fluoride; and
a coating supported by the substrate,
wherein:
the coating comprises, in order moving away from the substrate, a first layer, a second layer, a third layer, a fourth layer, and a fifth layer;
the first layer comprises an inorganic oxide;
the coating does not include two consecutive oxide layers;
the second layer comprises an inorganic fluoride having a refractive index at a wavelength in the ultraviolet range that is less than a refractive index of calcium fluoride at the wavelength in the ultraviolet range;
the third layer comprises the inorganic oxide;
the fourth layer comprises an inorganic fluoride;
the fifth layer comprises the inorganic oxide;
the first layer is in contact with the substrate;
the fifth layer is in contact with the surroundings of the optical element;
the fourth layer is in direct contact with the third layer; and
the fourth layer is in direct contact with the fifth layer.