Surface planarization of high temperature superconductors

Abstract

Planarizing High Temperature Superconductor (HTS) surfaces, especially HTS thin film surfaces is crucial for HTS thin film device processing. Disclosed is a method of surface planarization for HTS film. The method includes first smoothing the HTS surface by Gas Cluster Ion Beam bombardment, followed by annealing in partial pressure of oxygen to regrow the damaged surface layer. A rough HTS surface can be planarized down to a smoothness with a standard deviation of one nanometer or better.

What is claimed is:  
     
         1 . A method of processing a substrate comprising a high temperature crystalline superconductor surface, having a surface roughness R 0 , the method comprising: 
 (a) contacting the surface of the substrate with gas cluster ions to reduce both the surface roughness and the crystallinity of the surface; and    (b) processing the surface of the substrate to restore the crystallinity of the surface.    
     
     
         2 . The method of  claim 1 , wherein said processing step comprises thermally annealing the surface to restore crystallinity.  
     
     
         3 . The method of  claim 1 , wherein said processing step comprises removing a shall ow layer of the surface to expose underlying material having higher crystallinity.  
     
     
         4 . The method of  claim 1 , wherein the superconductor surface comprises a YBCO type of superconductor.  
     
     
         5 . The method of  claim 1 , wherein the contacting in step (a) comprises bombarding with gas cluster ions of high energy.  
     
     
         6 . The method of  claim 1  further comprising: 
 (c) depositing a single crystal layer on the surface.  
 
     
     
         7 . The method of  claim 1 , wherein said contacting step comprises bombarding said surface with gas cluster ions comprising a cluster in a range between 10 and 30 KeV with a total dose of 10 14  to 2×10 16  clusters/cm 2 .  
     
     
         8 . The method of  claim 1 , wherein said annealing step comprises annealing the surface under a partial oxygen atmosphere.  
     
     
         9 . The method of  claim 8 , wherein said annealing is carried out at approximately 800° C. under oxygen partial pressure of approximately 100 mTorr for approximately 30 minutes followed by an approximately 450° C. and 200 mTorr oxygen pressure for approximately 30 minutes.  
     
     
         10 . The method of  claim 8 , wherein said annealing is carried out at approximately 870° C., 660° C., and 450° C. consecutively for approximately 35 minutes, each under flowing oxygen gas.  
     
     
         11 . The method of  claim 6  further comprising: 
 (d) processing said single crystal layer to configure structures thereon.  
 
     
     
         12 . The method of  claim 11 , wherein said second processing step comprises smoothing said single crystal layer, and annealing the smoothed single crystal layer.  
     
     
         13 . A method of processing a substrate comprising: 
 (a) depositing a crystalline high temperature superconductor surface layer on said substrate, said layer having a surface roughness RO;    (b) bombarding said surface layer with gas cluster ions to reduce the surface roughness to R 1 , wherein R 1  is less than R 0 , and to reduce the crystallinity of the surface layer; and    (c) processing the surface layer of the substrate to restore the crystallinity of the surface layer.    
     
     
         14 . The method of  claim 13 , wherein said processing step comprises thermally annealing the surface to restore crystallinity.  
     
     
         15 . The method of  claim 13 , wherein said processing step comprises removing a shallow layer of the surface to expose underlying material having higher crystallinity.  
     
     
         16 . The method of  claim 13 , wherein said surface layer comprises a YBCO type of superconductor.  
     
     
         17 . The method of  claim 13  further comprising: 
 (d) depositing a single crystal layer on the surface.  
 
     
     
         18 . The method of  claim 17 , wherein said single crystal layer comprises an insulating layer.  
     
     
         19 . The method of  claim 17 , wherein said single crystal layer comprises a superconducting layer.  
     
     
         20 . The method of  claim 13 , wherein said contacting step comprises bombarding said surface with gas cluster ions comprising a cluster in a range between 10 and 30 KeV with a total dose of 10 14  to 2×10 16  clusters/cm 2 .  
     
     
         21 . The method of  claim 14 , wherein said annealing step comprises annealing the surface in partial oxygen.  
     
     
         22 . The method of  claim 21 , wherein said annealing is carried out at approximately 800° C. under oxygen partial pressure of approximately 100 mTorr for approximately 30 minutes followed by an approximately 450° C. and 200 mTorr oxygen pressure for approximately 30 minutes.  
     
     
         23 . The method of  claim 21 , wherein said annealing is carried out at approximately 870° C., 660° C., and 450° C. consecutively for approximately 35 minutes, each under flowing oxygen gas.  
     
     
         24 . The method of  claim 17  further comprising: 
 (e) processing said single crystal layer to configure structures thereon.