EUV reticle substrates with high thermal conductivity
A reflective reticle substantially reduces or eliminates pattern distortion that results from the absorption of EUV radiation while maintaining a reticle thickness consistent with industry standards. The reflective reticle includes a layer of ultra-low expansion (ULE) glass and a substrate of Cordierite having a thermal conductivity substantially larger than that of ULE glass. An aluminum layer is disposed onto a first surface of the ULE glass and a second surface of the ULE glass is polished to be substantially flat and defect-free. The Cordierite substrate can be directly bonded to the aluminum layer using anodic bonding to form the reflective reticle. Alternatively, a first surface of an intermediate Zerodur layer can be bonded to the aluminum layer, and a second aluminum layer can be used to anodically bond the Cordierite substrate to a second surface of the Zerodur layer, thereby forming the reflective reticle.
1. A reticle, comprising:
an optical layer having a first surface and a second surface;
a cordierite substrate; and
a conductive layer disposed between the optical layer and the cordierite substrate, the conductive layer being bonded to one or more of (i) a surface of the cordierite substrate and (ii) the first surface of the optical layer.
2. The reticle of claim 1 , wherein:
the optical layer comprises a material having a substantially-zero coefficient of thermal expansion; and
the cordierite substrate has a substantially-zero coefficient of thermal expansion.
3. The reticle of claim 1 , wherein:
a thermal conductivity of the cordierite substrate is larger than a thermal conductivity of the optical layer; and
the conductive layer comprises aluminum.
4. The reticle of claim 1 , wherein the conductive layer is disposed on the first surface of the optical layer.
5. The reticle of claim 4 , further comprising:
a second conductive layer disposed on the surface of the cordierite substrate; and
an intermediate layer disposed between the conductive layer and the second conductive layer,
wherein:
the conductive layer is bonded to a first surface of the intermediate layer; and
the second conductive layer is bonded to a second surface of the intermediate layer.
6. The reticle of claim 1 , wherein the second surface of the optical layer is substantially flat and substantially free of defects.
7. The reticle of claim 6 , further comprising a reflective layer disposed on the second surface of the optical layer.
8. The reticle of claim 1 , wherein a thickness of the cordierite substrate is larger than a thickness of the optical layer.
9. A lithographic apparatus, comprising:
an illumination system configured to produce a beam of radiation for a reticle that is configured to pattern the beam of radiation; and
a projection system configured to project the patterned beam onto a target portion of a substrate,
wherein the reticle comprises:
an optical layer having a first surface and a second surface;
a cordierite substrate; and
a conductive layer disposed between the optical layer and the substrate, the conductive layer being bonded to one or more of (i) a surface of the substrate and (ii) the first surface of the optical layer.
10. The lithographic apparatus of claim 9 , wherein:
the optical layer comprises a material having a substantially-zero coefficient of thermal expansion; and
the cordierite substrate has a substantially-zero coefficient of thermal expansion.
11. The lithographic apparatus of claim 9 , wherein:
a thermal conductivity of the cordierite substrate is larger than a thermal conductivity of the optical layer; and
the conductive layer comprises aluminum.
12. The lithographic apparatus of claim 9 , wherein the conductive layer is disposed onto the first surface of the optical layer.
13. The lithographic apparatus of claim 12 , further comprising:
a second conductive layer disposed on the surface of the cordierite substrate; and
an intermediate layer disposed between the conductive layer and the second conductive layer,
wherein:
the conductive layer is bonded to a first surface of the intermediate layer; and
the second conductive layer is bonded to a second surface of the intermediate layer.
14. A method for making a reticle, comprising:
disposing a layer of conductive material onto a first surface of an optical layer; and
bonding the layer of conductive material to one of (i) a first surface of an intermediate layer comprising a glass-ceramic material or (ii) a surface of a cordierite substrate having a thermal conductivity larger than a thermal conductivity of the optical layer.
15. The method of claim 14 , wherein the disposing step comprises:
disposing a layer of aluminum onto the first surface of the optical layer.
16. The method of claim 14 , wherein the bonding step comprises:
anodically bonding the layer of conductive material to one of (i) the surface of the intermediate layer or (ii) the surface of the cordierite substrate.
17. The method of claim 14 , wherein the bonding step comprises:
bonding the layer of conductive material to the first surface of the intermediate layer;
disposing a second layer of a conductive material onto the surface of the cordierite substrate; and
bonding the second layer of conductive material to a second surface of the intermediate layer.
18. The method of claim 14 , wherein the bonding step comprises bonding the layer of conductive material to the surface of the cordierite substrate.
19. The method of claim 14 , further comprising:
processing a second surface of the optical layer to be substantially flat and substantially free of defects.
20. The method of claim 14 , further comprising:
applying a reflective coating to a second surface of the optical layer; and
forming a pattern on the reflective coating.