Ceric-ion slurry for use in chemical-mechanical polishing

Abstract

The invention provides a chemical-mechanical polishing slurry comprising a liquid, cerium ions as an oxidizer, an abrasive, and a pH increasing substance. The cerium ions are in the liquid in a quantity equal to the inclusion of at least 0.02 molar ammonium cerium nitrate in the liquid. The abrasive is also included in the liquid. The liquid, the cerium ions and the abrasive jointly have a first pH value. The pH increasing substance increases the first pH value to a second pH value above 1.5.

What is claimed:  
     
         1 . A chemical-mechanical polishing slurry comprising: 
 a liquid;    cerium ions as an oxidizer in the liquid, the cerium ions being in a quantity equal to the inclusion of at least 0.02 molar ammonium cerium nitrate in the liquid;    an abrasive in the liquid, the liquid, the cerium ions and the abrasive together having a first pH value; and    a pH increasing substance in the liquid that increases the first pH value to a second pH value above 1.5.    
     
     
         2 . The slurry of  claim 1  comprising cerium ions in quantity equal to the inclusion of between 0.05 molar and 0.1 molar of ammonium cerium nitrate.  
     
     
         3 . The slurry of  claim 1  comprising between 1 percent and 30 percent abrasive by weight.  
     
     
         4 . The slurry of  claim 1  wherein the abrasive is silica.  
     
     
         5 . The slurry of  claim 1  wherein the second pH value is at least between 2.5 and 4.  
     
     
         6 . The slurry of  claim 1  wherein the substance is glycine.  
     
     
         7 . The slurry of  claim 1  which is environmentally green.  
     
     
         8 . The slurry of  claim 1  further comprising a complexing agent.  
     
     
         9 . The slurry of  claim 8  wherein the complexing agent is glycine.  
     
     
         10 . The slurry of  claim 1  further comprising an anti-oxidizing agent.  
     
     
         11 . The slurry of  claim 10  wherein the anti-oxidant is BTA.  
     
     
         12 . The slurry of  claim 11  comprising between 0.00200 molar and 0.00500 molar BTA.  
     
     
         13 . The slurry of  claim 1  comprising cerium ions in quantity equal to between 0.02 molar and 0.1 molar ammonium cerium nitrate and BTA comprising between 0.00200 and 0.00500 molar BTA.  
     
     
         14 . The slurry of  claim 13  wherein the second pH value is at least 2.5.  
     
     
         15 . A method of preparing a chemical-mechanical polishing slurry, comprising: 
 adding together an abrasive and a complex cerium double salt as a source of cerium ions.    
     
     
         16 . The method of  claim 15 , wherein the double salt is selected from the group consisting of ammonium cerium nitrate, and ammonium cerium sulfate.  
     
     
         17 . The method of  claim 15  wherein the double salt is ammonium cerium nitrate.  
     
     
         18 . The method of  claim 15  wherein the abrasive and the source of cerium ions, in solution, has a first pH value, the method further comprising adding a substance which increases the first pH value to a second pH value above 1.5.  
     
     
         19 . The method of  claim 18  wherein the substance is glycine.  
     
     
         20 . The method of  claim 18  further comprising adding a complexing agent.  
     
     
         21 . A method of forming a metal line, comprising: 
 forming a first layer, with an opening therein, over a semiconductor substrate;    depositing a metal layer which fills the opening and covers the first layer;    applying a chemical-mechanical polishing slurry onto the metal layer, the slurry comprising cerium ions as an oxidizer, and an abrasive;    contacting a polishing surface against the metal layer; and    moving the polishing surface over the metal layer.    
     
     
         22 . The method of  claim 21  wherein the slurry comprises cerium ions in quantity sufficient to oxidize a portion of the metal layer, and the abrasive in quantity sufficient to assist in removal of the oxidized portion when the polishing surface is moved over the metal layer.  
     
     
         23 . The method of  claim 21  wherein the metal layer is of a metal selected from the group consisting of copper and tungsten.  
     
     
         24 . The method of  claim 21  further comprising: 
 depositing a barrier layer over the first layer and before depositing the metal layer, the cerium ions selectively oxidizing the material of the metal layer over the material of the barrier layer.  
 
     
     
         25 . The method of  claim 21  wherein the metal layer is removed at a rate of at least 1000 angstroms per minute.  
     
     
         15 . A method of preparing a chemical-mechanical polishing slurry, comprising: 
 adding together an abrasive and a complex cerium double salt as a source of cerium ions.    
     
     
         16 . The method of  claim 15 , wherein the double salt is selected from the group consisting of ammonium cerium nitrate, and ammonium cerium sulfate.  
     
     
         17 . The method of  claim 15  wherein the double salt is ammonium cerium nitrate.  
     
     
         18 . The method of  claim 15  wherein the abrasive and the source of cerium ions, in solution, has a first pH value, the method further comprising adding a substance which increases the first pH value to a second pH value above 1.5.  
     
     
         19 . The method of  claim 18  wherein the substance is glycine.  
     
     
         20 . The method of  claim 18  further comprising adding a complexing agent.