Method to improve palanarity of electroplated copper

Abstract

Narrow trenches in a substrate tend to fill more rapidly than wide trenches This results in a non-planar surface once all trenches have been filled. The present invention solves this problem by performing the electro-deposition in two steps. The plating bath used during the first step, is optimized for filling narrow trenches while the plating bath used during the second step, is optimized for filling wide trenches. The net result is a final layer having a planar surface, with all trenches being properly filled.

1 . A process for filling trenches with copper, comprising: 
 providing a silicon wafer having an upper surface in which are a plurality of trenches that have at least two different widths, all trenches being lined with a conductive barrier layer;    providing an aqueous solution that comprises at least one copper salt;    forming a first plating solution that contains a first concentration, in said aqueous solution, of a first accelerator additive;    forming a second plating solution that contains a second concentration, in said aqueous solution, of a second accelerator additive, said second concentration being greater than said first concentration;    filling a container with said first plating solution and immersing said wafer therein, then electroplating onto said upper surface a first thickness of copper that is sufficient to overfill all trenches whose width is less than an amount while under-filling all trenches whose width is greater than said amount;    while leaving said wafer in container, replacing said first plating solution with said second plating solution; and    then electroplating on said wafer a second thickness of copper that is sufficient to overfill all trenches.    
   
   
       2 . The process described in  claim 1  wherein the step, of replacing said first plating solution with said second plating solution, further comprises a continuous change in accelerator concentration without interruption of electroplating.  
   
   
       3 . The process described in  claim 1  wherein said aqueous solution further comprises 10-50 g/L copper salts, 5-300 g/L H 2 SO 4 , and 20-100 ppm HCI.  
   
   
       4 . The process described in  claim 1  wherein said first accelerator additive is 3-mercapto-1propanesulfonate at a concentration that is between about 10 and 100 ppm.  
   
   
       5 . The process described in  claim 1  wherein said second accelerator additive is 3sulfopropyl disulfide.  
   
   
       6 . The process described in  claim 5  wherein said second accelerator additive concentration is between about 10-100 ppm.  
   
   
       7 . The process described in  claim 1  wherein said accelerator additive is sulfonated sulfonated acetylthiourea, 3-mercapto-1propanesulfonate, dibenzyl-dithio-carbammat, 2-mercaptoethanesulfonate, or n,n-dimethyl-dithiocabamic acid-(3-sulfopropyl)ester.  
   
   
       8 . A process for filling trenches with copper, comprising: 
 providing a silicon wafer having an upper surface in which are a plurality of trenches that have at least two different widths, all trenches being lined with a seed layer;    providing an aqueous solution that comprises at least one copper salt;    forming a first plating solution that contains a first concentration, in said aqueous solution, of a first accelerator additive;    forming a second plating solution that contains a second concentration, in said aqueous solution, of a second accelerator additive, said second concentration being greater than said first concentration;    filling a plating bath with said first plating solution and immersing said wafer therein, then electroplating onto said seed layer a first thickness of copper that is sufficient to overfill all trenches whose width is less than an amount while under-filling all trenches whose width is greater than said amount;    while leaving said wafer in said plating bath, replacing said first plating solution with said second plating solution; and    then electroplating on said wafer a second thickness of copper that is sufficient to overfill all trenches.    
   
   
       9 . The process described in  claim 8  wherein the step, of replacing said first plating solution with said second plating solution, further comprises a continuous change in accelerator concentration without interruption of electroplating.  
   
   
       10 . The process described in  claim 9  wherein said aqueous solution further comprises 10-50 g/L copper salts, 5-300 g/L H.sub.2SO.sub.4, and 20-100 ppm HCl.  
   
   
       11 . The process described in  claim 9  wherein said first accelerator additive is (3-sulfopropyl) disulfide, 3-mercapto-propylsulfonic at a concentration that is between about 10-100 ppm.  
   
   
       12 . The process described in  claim 9  wherein said second accelerator additive is 3sulfopropyl disulfide.  
   
   
       13 . The process described in  claim 12  wherein said second accelerator additive concentration is between about 10-100 ppm.  
   
   
       14 . The process described in  claim 9  wherein said second accelerator additive is sulfonated acetylthiourea, 3-mercapto-1propanesulfonate, dibenzyl-dithio-carbammat, 2-mercaptoethanesulfonate, or n,n-dimethyl-dithiocabamic acid-(3-sulfopropyl)ester.  
   
   
       15 . The process described in  claim 8  wherein said seed layer is copper, or copper doped with titanium, magnesium, zirconium, tin, or zinc.