OPTICAL ELEMENT FOR REFLECTION OF UV RADIATION, METHOD FOR MANUFACTURING THE SAME AND PROJECTION EXPOSURE APPARATUS COMPRISING THE SAME

• US 20100290021A1
• Filed: 05/14/2010
• Published: 11/18/2010
• Est. Priority Date: 11/14/2007
• Status: Active Grant

• Current Assignee: CARL Zeiss SMT GmbH (Carl-Zeiss-Stiftung)
• Original Assignee: Carl Zeiss AG (Carl-Zeiss-Stiftung)
• Inventors: Huber, Peter, PAZIDIS, Alexandra, Feldermann, Horst, Zaczek, Christoph
• Granted Patent: US 8,488,103 B2
• Time in Patent Office: Days
• US Class Current: 355/67
• 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: G03F 7/70316 Details of optical elements, e.g. of Bragg reflectors, extreme ultraviolet [EUV] multilayer or bilayer mirrors or diffractive optical elements
• CPC Class Codes: G03F 7/70958 Optical materials or coatings, e.g. with particular transmittance, reflectance or anti-reflection properties

Abstract

An optical element (1a, 1b) for reflecting UV radiation at an operating wavelength below 250 nm, preferably at 193 nm, which has a substrate (2a, 2b), a reflective layer (3a, 3b) made of aluminum superimposed on the substrate (2a, 2b). The reflective aluminum layer (3a, 3b) is not transparent to UV radiation and is (111)-plane oriented. The reflective optical element (1a, 1b) has a reflectivity of more than 85%, preferably of more than 88%, and even more preferably of more than 92%, in a range of incident angles of at least 10°, preferably of at least 15°, at the operating wavelength. Also disclosed is an optical element having a reflective layer made from a material having a melting point higher than that of aluminum, as well as methods for producing such optical elements, and optical arrangements incorporating such optical elements.

Claims

1. An optical element configured to reflect ultraviolet radiation at an operating wavelength (λ

₀) below 250 nm, comprising;

a substrate,

a reflective aluminum layer superimposed on the substrate, the reflective aluminum layer not being transparent to the ultraviolet radiation,

wherein;

the reflective aluminum layer is (111)-plane oriented, and

the reflective optical element has a reflectivity of more than 85% in a range of incident angles of at least 10°

at the operating wavelength.

2. The optical element according to claim 1, wherein the reflective aluminum layer is superimposed on a base material having a hexagonal surface structure.

3. The optical element according to claim 2, wherein a ratio between two integer multiples of the lattice constants (d_111Al;

d_111Si, d_111CaF2, d_002LaF3) of the reflective aluminum layer in the (111)-plane and of the hexagonal surface structure of the base material differs by less than 10% from unity, the integer multiples of the lattice constants (d_111Al;

d_111Si, d_111CaF2, d_002LaF3) being selected from a range of values between one and ten.

4. The optical element according to claim 2, wherein the base material is selected from the group consisting of:

calcium fluoride (CaF₂), silicon (Si), and lanthanum fluoride (LaF₃).

5. The optical element according to claim 2, wherein the substrate is made of the base material.

6. The optical element according to claim 2, wherein an interlayer (between the substrate and the reflective aluminum layer is made of the base material.

7. The optical element according to claim 1, wherein a dielectric multi-layer system is superimposed on the reflective aluminum layer.

8. The optical element according to claim 1, wherein a protective layer of chiolite (Na₅Al₃F₁₄) is superimposed on the reflective aluminum layer.

9. The optical element according to claim 1, wherein the substrate has a thermal conductivity of at least 12 W/(K m).

21. A microlithographic arrangement comprising the optical element according to claim 1 and configured as at least one of:

a projection exposure apparatus, an optical beam delivery system, an illumination system, and a projection lens.

10. An optical element configured to reflect ultraviolet radiation at an operating wavelength (λ

₀) below 250 nm, comprising;

a substrate,

a reflective layer superimposed on the substrate and made from a basic material that is not transparent to the ultraviolet radiation, and

a dielectric multi-layer system superimposed on the reflective layer,

wherein the reflective optical element has a reflectivity of more than 85%, over a range of incident angles of at least 10°

,

wherein

the basic material has a higher melting point than aluminum.

11. The optical element according to claim 10, wherein the basic material has a melting point of at least 900°

C.

12. The optical element according to claim 10, wherein the basic material has a real part of the refractive index of 1.4 or less at the operating wavelength (λ

₀).

13. The optical element according to claim 10, wherein the basic material has an imaginary part of the refractive index of more than 1.5, at the operating wavelength (λ

₀).

14. The optical element according to claim 10, wherein the real and imaginary part of the refractive index is at least 3.0 at the operating wavelength (λ

₀).

15. The optical element according to claim 10, wherein the basic material is selected from the group consisting of:

amorphous silicon, crystalline silicon, chromium, iridium, molybdenum, palladium, ruthenium, tantalum, tungsten, rhodium, rhenium, germanium and mixtures thereof.

16. The optical element according to claim 10, wherein the multi-layer system has between ten and fifty single layers.

17. The optical element according to claim 10, wherein at least one of:

the difference in the polarization-dependent reflectivity is at 5% or less and the polarization-dependent phase difference is less than 20°

over a range of incident angles of at least 10°

.

18. The optical element according to claim 10, wherein the layer materials of the multi-layer system are selected from the group consisting of:

oxides and fluorides.

19. The optical element according to claim 10, wherein at least one single layer of the multi-layer system has a package density of at least 0.98.

20. The optical element according to claim 10, wherein the reflective layer of the optical element is curved.

22. A method of forming a reflective optical element according to claim 10, comprising:

applying at least a single layer of the multi-layer system and, in is coating process, generating an energy input of more than 0.1 mJ/cm².

23. The method according to claim 22, wherein less than six further single layers are positioned between the single layer and the reflective layer.

24. The method according to claim 22, wherein the coating process is selected from the group consisting of:

sputtering, magnetron sputtering, ion beam sputtering, an ion supported coating process, and a plasma supported coating process.