Slurry and method for chemical mechanical polishing of copper

Abstract

A copper polish slurry, useful in the manufacture of integrated circuits generally, and for chemical mechanical polishing of copper and copper diffusion barriers particularly, may be formed by combining a chelating, organic acid buffer system such as citric acid and potassium citrate; and an to abrasive, such as for example colloidal silica. Alternative copper polish slurries, in accordance with the present invention, may be formed by further combining an oxidizer, such as hydrogen peroxide, and/or a corrosion inhibitor such as benzotriazole. Advantageous properties of slurries in accordance with the present invention include the enhancement of Cu removal rates to >3000 angstroms per minute. This high polish rate is achieved while maintaining local pH stability and substantially reducing global and local corrosion as compared to prior art copper polish slurries. Local pH stability provides for reduced within-wafer non-uniformity and reduced corrosion defects. Furthermore, copper diffusion barriers such as tantalum or tantalum nitride may also be polished with such slurries wherein the oxidizer is not included.

What is claimed is:  
     
         1 . A method of forming copper interconnect, comprising: 
 forming a copper diffusion barrier layer in at least a damascene structure;    forming a copper layer over the barrier layer;    removing a portion of the copper layer by chemical mechanical polishing with a slurry comprising a chelating organic acid buffer system, colloidal silica, and an oxidizer.    
     
     
         2 . The method of  claim 1 , wherein the oxidizer comprises hydrogen peroxide.  
     
     
         3 . The method of  claim 2 , wherein the chelating organic acid buffer system comprises citric acid and potassium citrate.  
     
     
         4 . The method of  claim 3 , wherein the slurry further comprises a corrosion inhibitor.  
     
     
         5 . The method of  claim 4 , wherein the corrosion inhibitor comprises benzotriazole.  
     
     
         6 . A method of forming copper interconnect, comprising: 
 forming a barrier layer over a substrate having at least one trench therein;    forming a copper seed layer on the surface of the barrier layer;    forming a copper layer over the barrier and seed layers;    removing a portion of the copper layer by chemical mechanical polishing with a first slurry comprising a chelating organic acid buffer system, colloidal silica, and an oxidizer; and    removing at least a portion of the barrier layer by chemical mechanical polishing with a second slurry comprising a chelating organic acid buffer system, and colloidal silica;    wherein the second slurry is formed without the oxidizer.    
     
     
         7 . The method of  claim 6 , wherein the barrier layer comprises tantalum.  
     
     
         8 . The method of  claim 7 , wherein the chelating organic acid buffer system comprises citric acid and potassium citrate.  
     
     
         9 . The method of  claim 8 , wherein the oxidizer comprises hydrogen peroxide.  
     
     
         10 . The method of  claim 9 , wherein the first slurry further comprises a corrosion inhibitor.  
     
     
         11 . The method of  claim 10 , wherein the first slurry has a pH in the range of 3 to 6, and the corrosion inhibitor comprises benzotriazole.  
     
     
         12 . A slurry produced by the process comprising: 
 combining citric acid, potassium citrate, silica, hydrogen peroxide, and benzotriazole.    
     
     
         13 . The slurry produced by the process of  claim 12 , wherein a concentration of citric acid is approximately 3 g/l, a concentration of potassium citrate is approximately 3 g/l, a concentration of silica is approximately 5 wt. %, a concentration of hydrogen peroxide is approximately 3 wt. %, and a concentration of benzotriazole is approximately 0.015 molar.  
     
     
         14 . The slurry produced by the process of  claim 13 , further comprising combining the citric acid, potassium citrate, silica, hydrogen peroxide, and benzotriazole with water.  
     
     
         15 . A slurry, comprising: 
 approximately 3 grams/liter of citric acid;    approximately 3 grams/liter of potassium citrate;    approximately 5 wt. % silica;    approximately 3 wt. % hydrogen peroxide;    approximately 0.015 molar benzotriazole; and    the mixture and reaction products thereof.    
     
     
         16 . The slurry of  claim 15 , wherein the slurry has a pH in the range of 3 to 6.  
     
     
         17 . A slurry formed by the process of combining a organic acid, an organic acid salt; approximately 5 wt. % silica; approximately 3 wt. % hydrogen peroxide; and approximately 0.015 molar benzotriazole.  
     
     
         18 . The slurry of  claim 17 , wherein the organic acid comprises acetic acid.  
     
     
         19 . The slurry of  claim 18 , wherein the organic acid salt comprises potassium acetate.  
     
     
         20 . The slurry of  claim 17 , wherein the organic acid comprises 3 grams/liter of citric acid, and the organic acid salt comprises 3 grams/liter of potassium citrate.  
     
     
         21 . A slurry for polishing copper diffusion barriers, comprising: 
 approximately 3 grams/liter of citric acid;    approximately 3 grams/liter of potassium citrate;    approximately 5 wt. % silica;    approximately 0.015 molar benzotriazole; and    the mixture and reaction products thereof.    
     
     
         22 . The slurry of  claim 21 , wherein the copper diffusion barriers comprise tantalum.  
     
     
         23 . The slurry of  claim 21 , wherein the slurry has a pH in the range of 3 to 6.  
     
     
         24 . A slurry for polishing barriers comprised of tantalum, comprising: 
 organic acid, an organic acid salt, an abrasive, a corrosion inhibitor, and the mixture and reaction products thereof, and wherein no oxidizer is included.    
     
     
         25 . The slurry of  claim 24 , wherein the organic acid comprise citric acid.  
     
     
         26 . The slurry of  claim 24 , wherein the corrosion inhibitor comprises benzotriazole, and wherein the slurry has a pH in the range of 3 to 6.  
     
     
         27 . The slurry of  claim 25 , wherein the organic acid salt comprises potassium citrate.