WIDE-ANGLE HIGHLY REFLECTIVE MIRRORS AT 193NM

• US 20100215932A1
• Filed: 02/26/2009
• Published: 08/26/2010
• Est. Priority Date: 02/26/2009
• Status: Active Grant

• Current Assignee: Corning Incorporated
• Original Assignee: Corning Incorporated
• Inventors: Smith, Charlene Marie, Schreiber, Horst, Wang, Jue
• Granted Patent: US 8,153,241 B2
• Time in Patent Office: Days
• US Class Current: 428/216
• CPC Class Codes: G02B 5/0833 comprising inorganic materials only
• CPC Class Codes: G02B 5/0891 Ultraviolet [UV] mirrors apparatus for microlithography exposure G03F7/70; X-ray multilayer structures G21K1/06
• CPC Class Codes: Y10T 428/24942 including components having same physical characteristic in differing degree
• CPC Class Codes: Y10T 428/24975 No layer or component greater than 5 mils thick
• CPC Class Codes: Y10T 428/265 1 mil or less

Abstract

The invention is directed to highly reflective optical elements having an amorphous MgAl₂O₄₋SiO₂ coating with fluoride enhancements inserted and sealed by dense smooth SiO₂ layers, and to a method for preparing such elements using energetic deposition techniques and the spinel crystalline form of MgAl₂O₄ as the source of the amorphous MgAl₂O₄ coating, The coating and the method described herein can be used to make highly reflective mirrors, and can also be applied to beamsplitters, prisms, lenses, output couplers and similar elements used in <200 nm laser systems.

Claims

1. An optical element comprising a selected substrate and an amorphous coating of formula (H_oL_o)ⁱH_o on said substrate,

wherein

(H_oL_o)ⁱ is a stack of a plurality i of coating periods consisting of a H_o layer and a L_o layer on said substrate,

i is in the range of 14-20,

H_o is amorphous MgAl₂O₄ and

L_o is amorphous SiO₂,

to thereby form an amorphous MgAl₂O₄—

SiO₂ coating on said substrate, the H_o layer of the first period being in contact with the substrate.

2. The coating according to claim 1, wherein i is in the range of 14-20 and the thickness is in the range of 600 nm to 1200 nm.

3. The coating according to claim 1, wherein i is in the range of 14-20 and the thickness is in the range of 860 nm to 1200 nm

4. The optical element according to claim 1, wherein:

said element is a mirror;

i has a value in the range of 14-20;

said amorphous coating of formula (H_oL_o)ⁱH_o has a thickness in the range of 860 nm to 1200 nm; and

said substrate is selected from the group consisting of

(a) alkaline earth metal fluoride single crystals,

(b) silica, fused silica, and F-doped fused silica

(c) aluminum, titanium, Si and Si₃N₄, and

(d) silica, fused silica, and F-doped fused silica, each of which has a metallic coating thereon.

5. The optical element according to claim 4, wherein said element further comprises a capping coating of an amorphous material selected from the group consisting of amorphous SiO₂, F-doped SiO₂ and fused silica, said capping coating being on top of said (H_oL_o)ⁱH_o coating.

6. The optical element according to claim 1, wherein the substrate is an alkaline earth metal fluoride single crystal substrate, i has a value in the range of 14-20, the thickness of the amorphous (H_oL_o)ⁱH_o coating is in the range of 860 nm to 1200 nm, and a capping coating of an amorphous material selected from the group consisting of amorphous SiO₂, F-doped SiO₂ and fused silica is placed on top of said amorphous (H_oL_o)ⁱH_o.

7. The optical element according to claim 6, wherein said substrate is CaF₂.

9. The optical element according to claim 7, wherein:

said element is a mirror;

said substrate is selected from the group consisting of alkaline earth metal fluoride single crystals, silica, fused silica, and F-doped fused silica aluminum, titanium, Si and Si₃N₄, and

silica, fused silica, and F-doped fused silica having a metallic coating thereon; and

said amorphous coating of formula (H_oL_o)ⁱH_o has a thickness in the range of 860 nm to 1200 m.

8. An optical element consisting of:

a selected substrate having a first coating having a formula (H_oL_o)ⁱH_o, a second coating of formula (L_fH_f)^j2M_o on top of said first coating, and a third coating of formula (L_fH_f)^k2M_o on top of said second coating;

wherein (H_oL_o)ⁱ is a stack consisting of a plurality i of periods H_oL_o on said substrate, i is in the range of 14-20, H_o is amorphous MgAl₂O₄, L_o is amorphous SiO₂ and the H_o layer of the first period is in contact with the substrate; and

(L_fH_f)^j is a stack formed on top of (H_oL_o)ⁱH_o and is a plurality j of periods L_fH_f formed by alternating layers where L_f is the first layer and H_f is the second layer, j is an integer in the range of 2 to 6, and 2M_o is a coating on top of said (L_fH_f)^j stack; and

(L_fH_f)^k is a stack formed on top of (L_fH_f)^j2M_o and is a plurality k of periods L_fH_f formed by alternating layers where L_f is the first layer and H_f is the second layer, k is an integer in the range of 2 to 6 on top of said (L_fH_f)^k coating, and a 2M_o is a coating on top of said (L_fH_f)^k stack; and

L_f is a low refractive index metal fluoride and H_f is a high refractive index metal fluoride, and 2M_o is an oxide material selected from the group consisting of silica, fused silica and F-doped fused silica.

10. The optical element according to claim 8, wherein:

the substrate is an alkaline earth metal fluoride single crystal substrate,

i has a value in the range of 14-20 and the thickness of the amorphous (H_oL_o)ⁱH_o coating is in the range of 860 nm to 1200 nm;

j has a value in the range of 2-6;

k has a value in the range of 2-6; and

in each layer of stacks (L_fH_f)^j and (L_fH_f)^k, the thickness of L_f is in the range of 30 nm to 50 nm and the thickness of H_f is in the range of 20-40 nm, and the thickness of the stacks is in the rage of 140 nm to 420 nm.

11. The optical element according to claim 10, wherein the optical element is a mirror and the substrate is CaF₂.

12. An optical element comprising of:

a selected substrate having a first coating of formula (H_oL_o)ⁱH_o, a second coating of formula (L_fH_f)^k2M_o on top of said first coating, and a third coating of formula H_f(L_fH_f)^k2M_o on top of said second coating;

wherein (H_oL_o)ⁱ is a stack consisting of a plurality i of coating periods H_oL_o on said substrate, i is in the range of 14-20, H_o is amorphous MgAl₂O₄, L_o is amorphous SiO₂ and the H_o layer of the first period is in contact with the substrate; and

(L_fH_f)^j is a stack formed on top of (H_oL_o)ⁱH_o and is a plurality j of periods L_fH_f formed by alternating layers where L_f is the first layer and H_f is the second layer, j is an integer in the range of 2 to 6, and 2M_o is a coating on top of said (L_fH_f)^j stack;

H_f is a first high refractive index metal fluoride layer formed on top of the second coating, and

(L_fH_f)^k is a stack, formed on top of said first high refractive index layer H_f, of a plurality k of periods L_fH_f formed by alternating layers where L_f is the first layer and H_f is the second layer, k is an integer in the range of 2 to 6, and a 2M_o is a coating on top of said (L_fH_f)^k stack; and

wherein L_f is a low refractive index metal fluoride and H_f is a high refractive index metal fluoride, and 2M_o is an oxide material selected from the group consisting of silica, fused silica and F-doped fused silica.

13. The optical element according to claim 12, wherein:

said element is a mirror;

said substrate is selected from the group consisting of

alkaline earth metal fluoride single crystals,

silica, fused silica, and F-doped fused silica

aluminum, titanium, Si and Si₃N₄, and

silica, fused silica, and F-doped fused silica having a metallic coating thereon; and

said amorphous coating of formula (H_oL_o)ⁱH_o has a thickness in the range of 860 nm to 1200 m.

14. The optical element according to claim 12, wherein the substrate is an alkaline earth metal fluoride single crystal substrate,

i has a value in the range of 14-20 and the thickness of the amorphous (H_oL_o)ⁱH_o coating is in the range of 860 nm to 1200 nm;

j has a value in the range of 2-6;

k has a value in the range of 2-6; and

in each period of stacks (L_fH_f)^j and (L_fH_f)^k, the thickness of L_f is in the range of 30 nm to 50 nm and the thickness of H_f is in the range of 20-40 nm, and the thickness of stacks is in the rage of 140 nm to 420 nm.

15. The optical element according to claim 14, wherein the optical element is a mirror and the substrate is CaF₂.

16. A method of making a highly reflective optical element, said method having the steps of;

providing a vacuum chamber and within said vacuum chamber;

providing a substrate on which one or a plurality of coating are to be deposited;

providing at least one selected coating material source, or a mixture of coating materials source, and vaporizing said material(s) to provide a coating material vapor flux, said flux passing from said material source through a selected mask to said substrate;

providing plasma ions from a plasma source;

rotating said substrate at a selected rotation frequency f;

depositing said coating material(s) on said substrate as one or a plurality of coating layers and bombarding said substrate and said film with said plasma ions before and during said material deposition process for thereby form a substrate have one or a plurality of coating thereon;

wherein coating said substrate means coating said substrate with a first coating of formula (H_oL_o)ⁱH_o, a second coating of formula (L_fH_f)^j2M_o on top of said first coating, and a third coating of formula (L_fH_f)^k2M_o on top of said second coating to provide an optical element having a highly reflective coating thereon; and

wherein;

(H_fL_f)ⁱ is a stack consisting of a plurality i of coating periods H_fL_f on said substrate, i is in the range of 10-25, Ho is amorphous MgAl₃O₄, L_f is amorphous SiO₂ and the H_o layer of the first period is in contact with the substrate;

(L_fH_f)^j is a stack formed on top of (H_oL_o)ⁱH_o and is a plurality j of periods L_fH_f formed by alternating layers where Lf is the first layer and H_f is the second layer, j is an integer in the range of 2 to 6, and 2Mo is a coating on top of said (L_fH_f)^j stack;

(L_fH_f)^k is a stack, formed on top of said first high refractive index layer H_f, of a plurality k of periods L_fH_f formed by alternating layers where Lf is the first layer and H_f is the second layer, k is an integer in the range of 2 to 6, and a 2M_o is a coating on top of said (L_fH_f)^k stack; and

L_f is a low refractive index metal fluoride and H_f is a high refractive index metal fluoride, and 2M_o is an oxide material selected from the group consisting of silica, fused silica and F doped fused silica.

17. The method according to claim 16, wherein said fluoride stacks are deposited with a set of partial or reversed masks from electron beam or thermal resistance heated evaporation sources.

18. The method according to claim 16, wherein said fluoride stacks are deposited with a set of partial or reversed masks from electron beam or thermal resistance heated evaporation sources with a fluorine containing inert gas.

19. The method according to claim 16, wherein L_f is selected from the group consisting of AlF₃ and MgF₂.

20. The method according to claim 16, wherein H_f is selected from the group consisting of LaF₃ and GdF₃.

21. A method of making a highly reflective optical element, said method having the steps of;

providing a vacuum chamber and within said vacuum chamber;

providing a substrate on which one or a plurality of coating are to be deposited;

providing at least one selected coating material source, or a mixture of coating materials source, and vaporizing said material(s) using an e-beam to provide a coating material vapor flux, said flux passing from said material source through a selected mask to said substrate;

providing plasma ions from a plasma source;

rotating said substrate at a selected rotation frequency f;

depositing said coating material(s) on said substrate as one or a plurality of coating layers and bombarding said substrate and said film with said plasma ions before and during said material deposition process for thereby form a substrate have one or a plurality of coating thereon;

wherein coating said substrate means coating said substrate with a first coating of formula (H_oL_o)ⁱH_o, a second coating of formula (L_fH_f)^j2Mo on top of said first coating, and a third coating of formula H_f(L_fH_f)^k2Mo on top of said second coating to provide an optical element having a highly reflective coating thereon;

wherein;

(H_oL_o)i is a stack consisting of a plurality i of coating periods H_oL_o on said substrate, i is in the range of 14-20, H_o is amorphous MgAl₂O₄, Lo is amorphous SiO₂ and the H_o layer of the first period is in contact with the substrate; and

(L_fH_f)^j is a stack formed on top of (H_oL_o)ⁱH_o and is a plurality j of periods L_fH_f formed by alternating layers where L_f is the first layer and H_f is the second layer, j is an integer in the range of 2 to 6, and 2Mo is a coating on top of said (L_fH_f)j stack;

H_f is a first high refractive index metal fluoride layer formed on top of the second coating, and

(L_fH_f)^k is a stack, formed on top of said first high refractive index layer H_f, of a plurality k of periods L_fH_f formed by alternating layers where L_f is the first layer and H_o is the second layer, k is an integer in the range of 2 to 6, and a 2M_o is a coating on top of said (L_fH_f)k stack; and

wherein Lf is a low refractive index metal fluoride and H_f is a high refractive index metal fluoride, and 2Mo is an oxide material selected from the group consisting of silica, fused silica and F doped fused silica.

22. The method according to claim 21, wherein said fluoride stacks are deposited with a set of partial or reversed masks from electron beam or thermal resistance heated evaporation sources.

23. The method according to claim 21, wherein said fluoride stacks are deposited with a set of partial or reversed masks from electron beam or thermal resistance heated evaporation sources with a fluorine containing inert gas.

24. The method according to claim 21, wherein Lf is selected from the group consisting of AlF₃ and MgF₂.

25. The method according to claim 21, wherein H_f is selected from the group consisting of LaF₃ and GdF₃.