Process for providing a surface acoustic wave device

Abstract

This invention relates to a surface acoustic wave device and a production process thereof. An electrode is formed by alternately laminating a film of an aluminum alloy containing at least copper added thereto and a copper film on a piezoelectric substrate. While the particle size of the multi-layered electrode materials is kept small, the occurrence of voids in the film is prevented and life time of the surface acoustic wave device is elongated.

We claim:  
     
       1. A process for producing a surface acoustic wave device having a piezoelectric substrate and an electrode disposed on said substrate, comprising the steps of: 
       alternately laminating an aluminum copper alloy film and a copper film on said piezoelectric substrate at a temperature not higher than 200° C. to thereby form a laminate structure having at least three layers, with two aluminum-copper alloy films sandwiching one copper film the aluminum- copper alloy films being polycrystalline films having aluminum crystal grains and CuAl   2    segregated at a boundary of the aluminum crystal grains;    
       patterning the resultant laminate structure to form an electrode; and  
       carrying out subsequent processings while maintaining the temperature of not higher than 200° C.  
     
     
       2. A process for producing a surface acoustic wave device according to  claim 1 , wherein the laminate structure consists of two aluminum-copper alloy films sandwiching one copper film. 
     
     
       3. A process for producing a surface acoustic wave device according to  claim 1 , wherein the piezoelectric substrate is made of a piezoelectric material selected from the group consisting of LiTaO 3  and LiNbO 3 . 
     
     
       4. A process for producing a surface acoustic wave device according to  claim 1 , wherein: 
       the aluminum-copper alloy films have one of a tensile internal stress and a compressive internal stress,  
       the copper film has the other of a tensile internal stress and a compressive internal stress, such that the internal stresses of the aluminum copper alloy films and the cooper film have mutually opposite directions, and  
       the sum of the internal stresses is either zero or compressive.  
     
     
       5. A process for producing a surface acoustic wave device according to  claim 1 , wherein the aluminum-copper alloy films are polycrystalline films having aluminum crystal grains and CuAl 2  segregated at a grain boundary thereof. 
     
     
       6. A process for producing a surface acoustic wave device according to  claim 1 , wherein the aluminum-copper alloy films are formed by sputtering or electron beam deposition. 
     
     
       7. A process for producing a surface acoustic wave device having a piezoelectric substrate and an electrode disposed on said substrate, comprising the steps of: 
         alternately laminating an aluminum - copper alloy film and a copper film on said piezoelectric substrate at a temperature not higher than  200 ° C. to thereby form a laminate structure having at least three layers, with two aluminum - copper alloy films sandwiching one copper film, the laminate having CuAl   2    formed at the interfaces between said aluminum - copper alloy films and said copper film;    
       
         patterning the resultant laminate structure to form an electrode; and  
       
       
         carrying out subsequent processings while maintaining the temperature of not higher than  200 ° C.  
       
     
     
       8. A process for producing a surface acoustic wave device according to  claim 7 , wherein the piezoelectric substrate is made of a piezoelectric material selected from the group consisting of LiTaO 3    and LiNbO   3 .  
     
     
       9. A process for producing a surface acoustic wave device according to  claim 7 , wherein 
         the aluminum - copper alloy films have one of a tensile internal stress and a compressive internal stress,    
         the copper film has the other of a tensile internal stress and a compressive internal stress, such that the internal stresses of the aluminum - copper alloy films and the copper film have mutually opposite directions, and    
       
         the sum of the internal stresses is either zero or compressive.  
       
     
     
       10. A process for producing a surface acoustic wave device according to  claim 7 , wherein the aluminum- copper alloy films are formed by sputtering or electron beam deposition.    
     
     
       11. A process for producing a surface acoustic wave device according to  claim 7 , wherein 
         the aluminum - copper alloy films are polycrystalline having aluminum crystal grains and CuAl   2    segregated at a boundary of the aluminum crystal grains, and    
         the CuAl   2    segregated at the boundary of the aluminum crystal grains is mutually bonded with the CuAl   2    formed at the interfaces between the aluminum - copper alloy films and the copper film.    
     
     
       12. A process for producing a surface acoustic wave device having a piezoelectric substrate and an electrode disposed on said substrate, comprising the steps of: 
         alternately laminating an aluminum - copper alloy film and a copper film on said piezoelectric substrate at a temperature sufficient to produce CuAl   2   , to thereby form a laminate structure having at least three layers, with two aluminum - copper alloy films sandwiching one copper film, the laminate having CuAl   2    formed at the interfaces between said aluminum - copper alloy films and said copper film;    
       
         patterning the resultant laminate structure to form an electrode; and  
       
       
         carrying out subsequent processing while maintaining the temperature at a temperature not higher than  200 ° C.  
       
     
     
       13. A process for producing a surface acoustic wave device according to  claim 12 , wherein the temperature sufficient to produce CuAl 2    is not higher than  200 ° C.    
     
     
       14. A process for producing a surface acoustic wave device according to  claim 12 , wherein the piezoelectric substrate is made of a piezoelectric material selected from the group consisting of LiTaO 3    and LiNbO   3 .  
     
     
       15. A process for producing a surface acoustic wave device according to  claim 12 , wherein 
         the aluminum - copper alloy films have one of a tensile internal stress and a compressive internal stress,    
         the copper film has the other of a tensile internal stress and a compressive internal stress, such that the internal stresses of the aluminum - copper alloy films and the copper film have mutually opposite directions, and    
       
         the sum of the internal stresses is either zero or compressive.  
       
     
     
       16. A process for producing a surface acoustic wave device according to  claim 12 , wherein the aluminum- copper alloy films are formed by sputtering or electron beam deposition.    
     
     
       17. A process for producing a surface acoustic wave device according to  claim 12 , wherein 
         the aluminum - copper alloy films are polycrystalline having aluminum crystal grains and CuAl   2    segregated at a boundary of the aluminum crystal grains, and    
         the CuAl   2    segregated at the boundary of the aluminum crystal grains is mutually bonded with the CuAl   2    formed at the interfaces between the aluminum - copper alloy films and the copper film.    
     
     
       18. A process for producing a surface acoustic wave device having a piezoelectric substrate and an electrode disposed on said substrate, comprising the steps of: 
         alternately laminating an aluminum - copper alloy film and a copper film on said piezoelectric substrate to thereby form a laminate structure having at least three layers, with two aluminum - copper alloy films sandwiching one copper film;    
         producing a CuAl   2    layer from copper contained in said copper film at a temperature sufficient to produce CuAl   2 ;  
       
         patterning the resultant laminate structure to form an electrode; and  
       
       
         carrying out subsequent processing while maintaining the temperature at a temperature not higher than  200 ° C.  
       
     
     
       19. A process for producing a surface acoustic wave device according to  claim 18 , wherein the temperature sufficient to produce CuAl 2    is not higher than  200 ° C.    
     
     
       20. A process for producing a surface acoustic wave device according to  claim 18 , wherein the piezoelectric substrate is made of a piezoelectric material selected from the group consisting of LiTaO 3    and LiNbO   3 .  
     
     
       21. A process for producing a surface acoustic wave device according to  claim 18 , wherein 
         the aluminum - copper alloy films have one of a tensile internal stress and a compressive internal stress,    
         the copper film has the other of a tensile internal stress and a compressive internal stress, such that the internal stresses of the aluminum - copper alloy films and the copper film have mutually opposite directions, and    
       
         the sum of the internal stresses is either zero or compressive.  
       
     
     
       22. A process for producing a surface acoustic wave device according to  claim 18 , wherein the aluminum- copper alloy films are formed by sputtering or electron beam deposition.    
     
     
       23. A process for producing a surface acoustic wave device according to  claim 18 , wherein 
         the aluminum - copper alloy films are polycrystalline having aluminum crystal grains and AuCl   2    segregated at a boundary of aluminum crystal grains, and    
       
         the CuAl 
         2  
         segregated at the boundary of the aluminum crystal grains is mutually bonded with the CuAl 
         2  
         layer.  
       
     
     
       24. A process for producing a surface acoustic wave device having a piezoelectric substrate and an electrode disposed on said substrate, comprising the steps of: 
         producing a laminate structure at a temperature sufficient to produce CuAl   2   , the laminate structure having at least three layers, with two aluminum - copper alloy films sandwiching one CuAl   2    layer;    
       
         patterning the resultant laminate structure to form an electrode; and  
       
       
         carrying out subsequent processing while maintaining the temperature at a temperature not higher than  200   
         ° C.  
       
     
     
       25. A process for producing a surface acoustic wave device according to  claim 24 , wherein the piezoelectric substrate is made of a piezoelectric material selected from the group consisting of LiTaO 3    and LiNbO   3 .  
     
     
       26. A process for producing a surface acoustic wave device according to  claim 24 , wherein the aluminum- copper alloy films are formed by sputtering or electron beam deposition.    
     
     
       27. A process for producing a surface acoustic wave device according to  claim 24 , wherein 
         the aluminum - copper alloy films are polycrystalline having aluminum crystal grains and CuAl   2    segregated at a boundary of the aluminum crystal grains, and    
       
         the CuAl 
         2  
         segregated at the boundary of the aluminum crystal grains is mutually bonded with the CuAl 
         2  
         layer.  
       
     
     
       28. A process for producing a surface acoustic wave device having a piezoelectric substrate and an electrode disposed on said substrate, comprising the steps of: 
         producing a laminate structure at a temperature sufficient to produce CuAl   2   , the laminate structure having at least three layers, with two aluminum - copper alloy films sandwiching one CuAl   2    layer;    
       
         patterning the resultant laminate structure to form an electrode; and  
       
         carrying out subsequent processing while maintaining the temperature at the temperature sufficient to produce CuAl   2 .  
     
     
       29. A process for producing a surface acoustic wave device according to  claim 28 , wherein the piezoelectric substrate is made of a piezoelectric material selected from the group consisting of LiTaO 3    and LiNbO   3 .  
     
     
       30. A process for producing a surface acoustic wave device according to  claim 28 , wherein the aluminum- copper alloy films are formed by sputtering or electron beam deposition.    
     
     
       31. A process for producing a surface acoustic wave device according to  claim 28 , 
         wherein the aluminum - copper alloy films are polycrystalline having aluminum crystal grains and CuAl   2    segregated at a boundary of the aluminum crystal grains, and    
       
         the CuAl 
         2  
         segregated at the boundary of the aluminum crystal grains is mutually bonded with the CuAl 
         2  
         layer.  
       
     
     
       32. A process for producing a surface acoustic wave device having a piezoelectric substrate and an electrode disposed on said substrate, comprising the steps of: 
         alternately laminating an aluminum - copper alloy film and a copper film on said piezoelectric substrate at a temperature within the range of from  120 ° C. to  200 ° C. to thereby form a laminate structure having at least three layers, with two aluminum - copper alloy films sandwiching one copper film, the laminate having CuAl   2    formed at the interfaces between said aluminum - copper alloy films and said copper film;    
       
         patterning the resultant laminate structure to form an electrode; and  
       
       
         carrying out subsequent processing while maintaining the temperature at a temperature not higher than  200 ° C.  
       
     
     
       33. A process for producing a surface acoustic wave device according to  claim 32 , wherein the piezoelectric substrate is made of a piezoelectric material selected from the group consisting of LiTaO 3    and LiNbO   3 .  
     
     
       34. A process for producing a surface acoustic wave device according to  claim 32 , wherein 
         the aluminum - copper alloy films have one of a tensile internal stress and a compressive internal stress,    
         the copper film has the other of a tensile internal stress and a compressive internal stress, such that the internal stresses of the aluminum - copper alloy films and the copper film have mutually opposite directions, and    
       
         the sum of the internal stresses is either zero or compressive.  
       
     
     
       35. A process for producing a surface acoustic wave device according to  claim 32 , 
         wherein the aluminum - copper alloy films are polycrystalline having aluminum crystal grains and CuAl   2    segregated at a boundary of the aluminum crystal grains, and    
         the CuAl   2    segregated at the boundary of the aluminum crystal grains is mutually bonded with the CuAl   2    formed at the interfaces between the aluminum - copper alloy films and the copper film.    
     
     
       36. A process for producing a surface acoustic wave device having a piezoelectric substrate and an electrode disposed on said substrate, comprising the steps of: 
         producing a laminate structure having at least three layers with two aluminum - copper alloy films sandwiching one CuAl   2    layer, the CuAl   2   layer being formed by alternately laminating an aluminum - copper alloy film and a copper film at a temperature sufficient to produce CuAl   2   ; and    
       
         patterning the laminate structure to form an electrode.  
       
     
     
       37. A process for producing a surface acoustic wave device according to  claim 36  wherein the temperature sufficient to produce CuAl 2    is not higher than  200 ° C.