Passivation of multi-layer mirror for extreme ultraviolet lithography

Abstract

A reflector structure suitable for extreme ultraviolet lithography (EUVL) is provided. The structure comprises a substrate having a multi-layer reflector. A capping layer is formed over the multi-layer reflector to prevent oxidation. In an embodiment, the capping layer is formed of an inert oxide, such as Al 2 O 3 , HfO 2 , ZrO 2 , Ta 2 O 5 , Y 2 O 3 -stabilized ZrO 2 , or the like. The capping layer may be formed by reactive sputtering in an oxygen environment, by non-reactive sputtering wherein the materials are sputtered directly from the respective oxide targets, by non-reactive sputtering of the metallic layer followed by full or partial oxidation (e.g., by natural oxidation, by oxidation in oxygen-containing plasmas, by oxidation in ozone (O 3 ), or the like), by atomic level deposition (e.g., ALCVD), or the like.

1 . A reflective device suitable for use in extreme ultraviolet or soft x-ray applications, the reflective device comprising: 
 a substrate;    a multi-layer reflector formed on the substrate; and    a capping layer formed on the multi-layer reflector, the capping layer comprising an oxide that is chemically inert in an oxidizing environment.    
     
     
         2 . The reflective device of  claim 1 , wherein the substrate comprises a low-thermal expansion material (LTEM).  
     
     
         3 . The reflective device of  claim 2 , wherein the substrate comprises ultra-low expansion (ULE) glass.  
     
     
         4 . The reflective device of  claim 2 , wherein the substrate comprises Zerodur®.  
     
     
         5 . The reflective device of  claim 1 , wherein the multi-layer reflector comprises alternating layers of a high atomic number Z material and a low atomic number Z material.  
     
     
         6 . The reflective device of  claim 5 , wherein the high atomic number Z material comprises molybdenum.  
     
     
         7 . The reflective device of  claim 5 , wherein the low atomic number Z material comprises silicon.  
     
     
         8 . The reflective device of  claim 5 , wherein each pair of the high atomic number Z material and the low atomic number Z material is about 6.8 nm in thickness.  
     
     
         9 . The reflective device of  claim 1 , wherein the capping layer comprises Al 2 O 3 , HfO 2 , ZrO 2 , Ta 2 O 5 , Y 2 O 3 -stabilized ZrO 2 , or a combination thereof.  
     
     
         10 . The reflective device of  claim 1 , wherein the capping layer comprises a plurality of layers.  
     
     
         11 . The reflective device of  claim 1 , wherein the capping layer is about 1 nm to about 5 nm in thickness.  
     
     
         12 . A method of forming a reflective device suitable for use in extreme ultraviolet or soft x-ray applications, the method comprising: 
 providing a substrate having a multi-layer reflector formed thereon; and    forming a capping layer over the multi-layer reflector, the capping layer comprising an oxide that is chemically inert in an oxidizing environment.    
     
     
         13 . The method of  claim 12 , wherein the substrate comprises a low-thermal expansion material (LTEM).  
     
     
         14 . The method of  claim 13 , wherein the substrate comprises ultra-low expansion (ULE) glass.  
     
     
         15 . The method of  claim 13 , wherein the substrate comprises Zerodur®.  
     
     
         16 . The method of  claim 12 , wherein the multi-layer reflector comprises alternating layers of a high atomic number Z material and a low atomic number Z material.  
     
     
         17 . The method of  claim 16 , wherein the high atomic number Z material comprises molybdenum.  
     
     
         18 . The method of  claim 16 , wherein the low atomic number Z material comprises silicon.  
     
     
         19 . The method of  claim 16 , wherein each pair of the high atomic number Z material and the low atomic number Z material is about 6.8 nm in thickness.  
     
     
         20 . The method of  claim 16 , wherein the capping layer comprises Al 2 O 3 , HfO 2 , ZrO 2 , Ta 2 O 5 , Y 2 O 3 -stabilized ZrO 2 , or a combination thereof.  
     
     
         21 . The method of  claim 12 , wherein the capping layer comprises a plurality of layers.  
     
     
         22 . The method of  claim 12 , wherein the capping layer is about 1 nm to about 5 nm in thickness.  
     
     
         23 . The method of  claim 12 , wherein the forming comprises performing a reactive sputter process in an oxygen atmosphere using metallic sputter targets.  
     
     
         24 . The method of  claim 12 , wherein the forming comprises performing a non-reactive sputter process wherein the inert oxide is sputtered directly from a respective oxide target.  
     
     
         25 . The method of  claim 12 , wherein the forming comprises performing a non-reactive sputter process of a metallic layer and fully or partially oxidizing the metallic layer.  
     
     
         26 . The method of  claim 12 , wherein the forming comprises performing an atomic layer deposition process.  
     
     
         27 . A method of patterning a semiconductor device, the method comprising: 
 providing a semiconductor wafer;    applying a photoresist material; and    exposing a portion of the photoresist material, the exposing using a reflective device suitable for use in extreme ultraviolet or soft x-ray applications, the reflective device having a capping layer over a multi-layer reflector, the capping layer comprising an oxide that is chemically inert in an oxidizing environment.    
     
     
         28 . The method of  claim 27 , wherein the reflective device further comprises a substrate formed of a low-thermal expansion material (LTEM).  
     
     
         29 . The method of  claim 28 , wherein the substrate comprises ultra-low expansion (ULE) glass.  
     
     
         30 . The method of  claim 28 , wherein the substrate comprises Zerodur®.  
     
     
         31 . The method of  claim 27 , wherein the multi-layer reflector comprises alternating layers of a high atomic number Z material and a low atomic number Z material.  
     
     
         32 . The method of  claim 31 , wherein the high atomic number Z material comprises molybdenum.  
     
     
         33 . The method of  claim 31 , wherein the low atomic number material comprises silicon.  
     
     
         34 . The method of  claim 31 , wherein each pair of the high atomic number Z material and the low atomic number Z material is about 6.8 nm in thickness.  
     
     
         35 . The method of  claim 27 , wherein the capping layer comprises Al 2 O 3 , HfO 2 , ZrO 2 , Ta 2 O 5 , Y 2 O 3 -stabilized ZrO 2 , or a combination thereof.  
     
     
         36 . The method of  claim 27 , wherein the capping layer comprises a plurality of layers.  
     
     
         37 . The method of  claim 27 , wherein the capping layer is about 1 nm to about 5 nm in thickness.