Self-activated electroless metal deposition

Abstract

A method of plating metal, such as to form a metal interconnect on a semiconductor assembly is described. The metal plating process is a one-step, self-activating (self-initiating) electroless process utilized to deposit metal, such as nickel on varying types of metal substrates, such as tungsten and copper substrates, by adjusting the pH and temperature of a metal based liquid bath solution.

1 . A method of forming a self-initiating bath for the forming of a metal connection to a metal substrate comprising: 
 forming a bath solution comprising a complexed metal solution, a complexing agent solution and a reducing agent solution;    adjusting the pH of the bath solution such that an oxidation potential of the reducing agent (E O   reducing agent ) is greater than the net oxidation potential sum (|E O |) of the oxidation potential of the substrate metal (E O   substrate metal ) plus the reduction potential of the complexed metal (E O   complexed Metal ); and    maintaining a bath solution temperature and the pH at sufficient levels to cause the bath solution to operate as the self-initiating bath.    
     
     
         2 . The method of  claim 1 , wherein the metal substrate comprises Copper or Tungsten.  
     
     
         3 . The method of  claim 1 , wherein the complexed metal comprises complexed nickel (Ni).  
     
     
         4 . The method of  claim 1 , wherein the complexing agent comprises Potassium salt of Ethylene di-amine tetra-acetic acid (EDTA).  
     
     
         5 . The method of  claim 1 , wherein the reducing agent comprises Ammonium Hypophosphite.  
     
     
         6 . The method of  claim 1 , wherein the reducing agent comprises Dimethylaminoborane (DMAB).  
     
     
         7 . The method of  claim 1 , wherein the bath solution comprises: 
 26 g/l of NiSO 4 6H 2 O;    26 g/l of Ammonium Hypophosphite; and    23 g/ of Potassium salt of Ethylene di-amine tetra-acetic acid (EDTA).    
     
     
         8 . The method of  claim 7 , wherein the pH of the bath solution is greater than 7.0 and the bath solution temperature is greater than 85° C.  
     
     
         9 . The method of  claim 1 , wherein the bath solution comprises: 
 26 g/l of NiSO 4 6H 2 O;    4 g/l of Dimethylaminoborane (DMAB); and    23 g/ of Potassium salt of Ethylene di-amine tetra-acetic acid (EDTA).    
     
     
         10 . The method of  claim 9 , wherein the pH of the bath solution is greater than 7.0 and the bath solution temperature is greater than 55° C.  
     
     
         11 . A method of forming a metal interconnect on a semiconductor assembly comprising: 
 subjecting a metal substrate to a metal deposition bath solution with a pH level and an operating temperature level, the metal deposition bath solution comprising comprising a complexed metal solution, a complexing agent solution and a reducing agent solution;    adjusting the pH level of the bath solution such that an oxidation potential of the reducing agent (E O   reducing agent ) is greater than the net oxidation potential sum (|E O |) of the oxidation potential of the substrate metal (E O   substrate metal ) plus the reduction potential of the complexed metal (E O   complexed Metal ); and    maintaining the operating temperature level and the pH at sufficient levels to cause the bath solution to operate as the self-initiating bath.    
     
     
         12 . The method of  claim 11 , wherein the metal substrate comprises Copper or Tungsten.  
     
     
         13 . The method of  claim 11 , wherein the complexed metal comprises complexed nickel (Ni).  
     
     
         14 . The method of  claim 11 , wherein the complexing agent comprises Potassium salt of Ethylene di-amine tetra-acetic acid (EDTA).  
     
     
         15 . The method of  claim 11 , wherein the reducing agent comprises Ammonium Hypophosphite.  
     
     
         16 . The method of  claim 11 , wherein the reducing agent comprises Dimethylaminoborane (DMAB).  
     
     
         17 . The method of  claim 11 , wherein the bath solution comprises: 
 26 g/l of NiSO 4 6H 2 O;    26 g/l of Ammonium Hypophosphite; and    23 g/ of Potassium salt of Ethylene di-amine tetra-acetic acid (EDTA).    
     
     
         18 . The method of  claim 17 , wherein the pH of the bath solution is greater than 7.0 and the bath solution temperature is greater than 85° C.  
     
     
         19 . The method of  claim 11 , wherein the bath solution comprises: 
 26 g/l of NiSO 40.6 H 2 O;    4 g/l of Dimethylaminoborane (DMAB); and    23 g/ of Potassium salt of Ethylene di-amine tetra-acetic acid (EDTA).    
     
     
         20 . The method of  claim 9 , wherein the pH of the bath solution is greater than 7.0 and the bath solution temperature is greater than 55° C.  
     
     
         21 . A method of depositing a first metal on a second metal by a one step self-initiating bath comprising: 
 forming a bath solution comprising a complexed metal solution, a complexing agent solution and a reducing agent solution;    adjusting the pH of the bath solution such that an oxidation potential of the reducing agent (E O   reducing agent ) is greater than the net oxidation potential sum (|E O |) of the oxidation potential of the substrate metal (E O   substrate metal ) plus the reduction potential of the complexed metal (E O   complexed Metal ); and    maintaining a bath solution temperature and the pH at sufficient levels such that oxidation potential sum (|E O |) is great enough to reduce the first metal and thus displace the second metal with the first metal.    
     
     
         22 . The method of  claim 21 , wherein the second metal comprises Copper or Tungsten.  
     
     
         23 . The method of  claim 21 , wherein the first metal comprises Nickel.  
     
     
         24 . The method of  claim 21 , wherein the complexed metal comprises complexed nickel (Ni).  
     
     
         25 . The method of  claim 21 , wherein the complexing agent comprises Ethylene di-amine tetra-acetic acid (EDTA).  
     
     
         26 . The method of  claim 21 , wherein the reducing agent comprises Hypophosphite.  
     
     
         27 . The method of  claim 21 , wherein the reducing agent comprises Dimethylaminoborane (DMAB).  
     
     
         28 . The method of  claim 21 , wherein the bath solution comprises: 
 26 g/l of NiSO 4 6H 2 O;    26 g/l of Ammonium Hypophosphite; and    23 g/ of Potassium salt of Ethylene di-amine tetra-acetic acid (EDTA).    
     
     
         29 . The method of  claim 28 , wherein the pH of the bath solution is greater than 7.0 and the bath solution temperature is greater than 85° C.  
     
     
         30 . The method of  claim 21 , wherein the bath solution comprises: 
 26 g/l of NiSO 4 6H 2 O;    4 g/l of Dimethylaminoborane (DMAB); and    23 g/ of Potassium salt of Ethylene di-amine tetra-acetic acid (EDTA).    
     
     
         31 . The method of  claim 9 , wherein the pH of the bath solution is greater than 7.0 and the bath solution temperature is greater than 55° C.  
     
     
         32 . A method of depositing Nickel by a one step self-initiating bath comprising: 
 presenting a Copper or Tungsten substrate to a bath solution comprising a complexed metal solution, a complexing agent solution and a reducing agent solution;    adjusting the pH of the bath solution such that an oxidation potential of the reducing agent (E O   reducing agent ) is greater than the net oxidation potential sum (|E O |) of the oxidation potential of the substrate metal (E O   substrate metal ) plus the reduction potential of the complexed metal (E O   complexed Metal );    maintaining a bath solution temperature and the pH at sufficient levels such that oxidation potential sum (|E O |) is great enough to reduce the nickel and thus displace the Copper of Tungsten substrate with a Nickel nucleation layer; and    continuing the self-activating bath to deposit Nickel on the Nickel nucleation layer.    
     
     
         33 . The method of  claim 32 , wherein the complexed metal comprises complexed nickel (Ni).  
     
     
         34 . The method of  claim 32 , wherein the bath solution comprises: 
 26 g/l of NiSO 4 6H 2 O;    26 g/l of Ammonium Hypophosphite; and    23 g/ of Potassium salt of Ethylene di-amine tetra-acetic acid (EDTA).    
     
     
         35 . The method of  claim 34 , wherein the pH of the bath solution is greater than 7.0 and the bath solution temperature is greater than 85° C.  
     
     
         36 . The method of  claim 32 , wherein the bath solution comprises: 
 26 g/l of NiSO 4 6H 2 O;    4 g/l of Dimethylaminoborane (DMAB); and    23 g/ of Potassium salt of Ethylene di-amine tetra-acetic acid (EDTA).    
     
     
         37 . The method of  claim 36 , wherein the pH of the bath solution is greater than 7.0 and the bath solution temperature is greater than 55° C.