Composite structure for microlithography and optical arrangement
View Patent ↗A composite structure for microlithography, in particular a holding device for a wafer, has two or more components, the surfaces of which are bonded together at least at one bond. At least one of the components consists of cordierite (Mg 2 Al 4 Si 5 O 18 ) or of silicon carbide (SiC). Also disclosed is an optical arrangement, in particular a projection illumination apparatus for microlithography, having at least one such composite structure, preferably a wafer stage.
1. A composite structure for microlithography, comprising a first component having a first coefficient of thermal expansion, and a second component having a second coefficient of thermal expansion, each component having a surface, the surfaces being bonded together by at least one bond, wherein the first component comprises cordierite, and the second component comprises silicon carbide.
2. The composite structure according to claim 1 , wherein the second coefficient of thermal expansion is substantially similar to a coefficient of thermal expansion of a wafer; and
wherein the first coefficient of thermal expansion is substantially smaller than the second coefficient of thermal expansion.
3. The composite structure according to claim 2 , wherein the cordierite has a thermal conductivity of at least 4.3 W/mK.
4. The composite structure according to claim 1 , wherein the cordierite is crystalline.
5. The composite structure according to claim 1 , wherein the cordierite has at least one of: a density of at least 2.4 g/cm 3 and a porosity of at most 1%.
6. The composite structure according to claim 1 , wherein the cordierite has a coefficient of thermal expansion of less than |2.2×10 −6 |1/K in a range of 20° C. to 300° C.
7. The composite structure according to claim 1 , wherein a layer of silicon carbide (SiC) is deposited on a surface of the second component, and wherein the surface is at least one of: activated with oxygen and sputtered with silicon dioxide (SiO 2 ).
8. The composite structure according to claim 1 , further comprising a further component consisting of a glass or a glass ceramic having a coefficient of thermal expansion of at most |0.5×10 −7 |1/K in a range of 0° C. to 50° C.
9. The composite structure according to claim 1 , wherein the bond is produced by an inorganic joining agent cured at a temperature of less than 600° C.
10. The composite structure according to claim 9 , wherein the joining agent contains at least one substance selected from the group consisting of alkali hydroxides, alkaline earth hydroxides and ammonium hydroxide (NH 4 OH).
11. The composite structure according to claim 9 , wherein the joining agent contains at least one substance selected from the group consisting of alkali silicates, alkaline earth silicates, silicic acid, polysilicic acids, halogen-containing silicic acid and halogen-containing polysilicic acids.
12. The composite structure according to claim 1 , wherein respectively one first metallic layer is applied to the surfaces, and the bond is produced by pressing the components.
13. The composite structure according to claim 12 , wherein the first metallic layer has a maximum melting point of 700° C. and a maximum modulus of elasticity of 100 GPa.
14. The composite structure according to claim 12 , wherein the first metallic layer is formed by a metal selected from the group consisting of aluminium (Al), indium (In), zinc (Zn) and tin (Sn).
15. The composite structure according to claim 12 , wherein a second metallic layer is applied to the first metallic layer.
16. The composite structure according to claim 15 , wherein the second metallic layer is formed of a non-oxidizable metal.
17. The composite structure according to claim 12 , wherein the first metallic layer is applied in a vacuum process.
18. The composite structure according to claim 12 , wherein the components are pressed at a pressure of more than 1 bar and at a temperature of less than 250° C.
19. The composite structure according to claim 1 , wherein respectively one metal layer is applied to the surfaces, and the bond is produced by soldering the components.
20. The composite structure according to claim 19 , wherein the metal layer is formed from a metal which is selected from the group consisting of chromium (Cr), gold (Au), nickel (Ni) and titanium (Ti).
21. The composite structure according to claim 19 , wherein the solder has a maximum melting point of 400° C.
22. The composite structure according to claim 19 , wherein at least one of the metal layer and the solder is applied in a vacuum process.
23. The composite structure according to claim 1 , wherein the bond is formed by a glass frit or by a glass paste or glass solder paste.
24. The composite structure according to claim 23 , wherein the glass frit or the glass paste or the glass solder paste has a maximum sealing temperature of 350° C.
25. The composite structure according to claim 1 , wherein the bond is formed by an adhesive.
26. The composite structure according to claim 25 , wherein the adhesive is a two-component adhesive.
27. The composite structure according to claim 1 , wherein the bond is produced by anodic bonding.
28. The composite structure according to claim 1 , wherein the bond is produced by a spin-on-glass process, by a spin-on-dielectric process, or by a sol-gel process.
29. The composite structure according to claim 1 , wherein the bond has an adhesive strength of more than 10 N/mm 2 .
30. The composite structure according to claim 1 , further comprising at least one closed cavity.
31. The composite structure according to claim 1 , wherein the components form a first plate and a second plate between which are located a plurality of supporting elements forming a ribbed structure.
32. The composite structure according to claim 1 , wherein the surfaces are polished before bonding to a surface quality of less than λ=632 nm.
33. The composite structure according to claim 1 , which is configured as a wafer stage.
34. The composite structure according to claim 33 , wherein at least one cavity is formed between the at least two components.
35. The composite structure according to claim 33 , wherein the components are comprised in a base body and a supporting structure for a wafer.
36. The composite structure according to claim 1 , which is configured as a holding device for a wafer.
37. The composite structure according to claim 1 , which is configured as a wafer chuck.
38. The composite structure according to claim 1 , which is configured as a wafer table.
39. The composite structure according to claim 1 , wherein the first component is comprised in a base body, and the second component is comprised in a wafer supporting structure.