Multiple-step electrodeposition process for direct copper plating on barrier metals

Abstract

Embodiments of the invention teach a method for depositing a copper seed layer to a substrate surface, generally to a barrier layer. The method includes placing the substrate surface into a copper solution, wherein the copper solution includes complexed copper ions. A current or bias is applied across the substrate surface and the complexed copper ions are reduced to deposit the copper seed layer onto the barrier layer.

1 . A method for depositing a copper-containing seed layer onto a barrier layer, comprising:
 providing a substrate comprising the barrier layer disposed on a substrate surface, wherein the barrier layer has a barrier surface selected from the group consisting of a tungsten surface, a tungsten nitride surface, a titanium surface, a titanium nitride surface, a cobalt surface, a ruthenium surface, a nickel surface, and a silver surface; and   exposing the substrate to a first electroplating solution comprising complexed copper ions that have more negative deposition potential relative to free copper ions to deposit a copper seed layer directly on the barrier layer.   
   
   
       2 . The method of  claim 1 , wherein the electroplating solution has a pH value of less than 7. 
   
   
       3 . The method of  claim 1 , wherein exposing the substrate further comprises:
 applying a first electrical bias across the substrate surface to deposit the copper seed layer on the barrier layer.   
   
   
       4 . The method of  claim 1 , wherein the complexed copper ions are derived from a copper source selected from the group consisting of copper citrate, copper borate, copper tartrate, copper oxalate, derivates thereof, and combinations thereof. 
   
   
       5 . The method of  claim 1  further comprising:
 applying a second electrical bias across the substrate surface to deposit a copper gap-fill layer onto the copper seed layer.   
   
   
       6 . The method of  claim 5 , further comprising depositing a copper bulk-fill layer by:
 applying a third electrical bias across the substrate surface to deposit the copper bulk-fill layer onto the copper gap-fill layer.   
   
   
       7 . The method of  claim 3 , wherein the first electrical bias has a current density of less than about 10 mA/cm 2  across the substrate surface. 
   
   
       8 . The method of  claim 1 , wherein the copper source is copper citrate. 
   
   
       9 . The method of  claim 1 , wherein the first electroplating solution contains a copper concentration within a range from about 0.02 M to about 0.8 M. 
   
   
       10 . The method of  claim 1 , wherein the copper seed layer has a thickness of less than about 200 Å. 
   
   
       11 . The method of  claim 1 , wherein the barrier layer consists essentially of cobalt, ruthenium, nickel, or tungsten. 
   
   
       12 . The method of  claim 3 , wherein the complexed copper ions in the electroplating solution chemically reduce complexed copper ions with the first electrical bias to form the copper seed layer on the barrier surface. 
   
   
       13 . The method of  claim 1 , wherein the barrier layer is a ruthenium barrier layer. 
   
   
       14 . The method of  claim 1 , wherein the copper seed layer is directly formed on the barrier surface without intervening layer disposed therebetween. 
   
   
       15 . The method of  claim 6 , further comprising:
 annealing the copper gap-fill layer.   
   
   
       16 . The method of  claim 1 , wherein the complexed copper solution has a pH value within a range from about 4.5 to about 6.5. 
   
   
       17 . The method of  claim 1 , wherein the first electrical bias has a current density within a range from about 0.5 mA/cm 2  to about 3 mA/cm 2  across the substrate surface. 
   
   
       18 . The method of  claim 15 , further comprising:
 annealing the copper gap-fill layer in an oxygen free environment.