Oxide etch with nh4-nf3 chemistry

Abstract

The present invention generally provides apparatus and methods for selectively removing various oxides on a semiconductor substrate. One embodiment of the invention provides a method for selectively removing an oxide on a substrate at a desired removal rate using an etching gas mixture. The etching gas mixture comprises a first gas and a second gas, and a ratio of the first gas and a second gas is determined by the desired removal rate.

1 . A method for selectively removing an oxide on a substrate at a desired removal rate, comprising: 
 positioning the substrate in a vacuum chamber, wherein a surface of the substrate has a structure comprises the oxide;    cooling the substrate to a first temperature;    generating active species of an etching gas mixture within the vacuum chamber, wherein the etching gas mixture comprises a first gas and a second gas, and a ratio of the first gas and a second gas is determined by the desired removal rate;    exposing the structure on the surface of the substrate to the active species to form a film on the structure;    heating the substrate to vaporize the film formed on the structure; and    removing the vaporized film from the vacuum chamber.    
   
   
       2 . The method of  claim 1 , wherein the active species comprise nitrogen and fluorine atoms.  
   
   
       3 . The method of  claim 1 , wherein the structure comprises another oxide.  
   
   
       4 . The method of  claim 3 , wherein the etching gas mixture removes the another oxide at a second removal rate.  
   
   
       5 . The method of  claim 4 , wherein the second removal rate is substantially equal to the desired removal rate.  
   
   
       6 . The method of  claim 1 , wherein the first gas is ammonia (NH 4 ) and the second gas is nitrogen trifluoride (NF 3 ).  
   
   
       7 . The method of  claim 6 , wherein the ratio of ammonia and nitrogen trifluoride is about at least 3:1.  
   
   
       8 . The method of  claim 6 , wherein the ratio of ammonia and nitrogen trifluoride is between about 10:1 to about 20:1.  
   
   
       9 . The method of  claim 1 , wherein the etching gas mixture further comprises a carrier gas.  
   
   
       10 . The method of  claim 1 , further comprising introducing a carrier gas to the vacuum chamber prior to generating the active species.  
   
   
       11 . A method for processing a substrate having an oxide structure comprising a first oxide and a second oxide, comprising: 
 positioning the substrate in a vacuum chamber;    cooling the substrate to a first temperature;    introducing an etching gas mixture into the vacuum chamber, wherein the etching gas mixture is adjusted to reduce the first oxide at a first rate and the second oxide at a second rate;    generating a plasma of the etching gas mixture within the vacuum chamber;    exposing the oxide structure to the plasma to form a film on the structure;    heating the substrate to vaporize the film formed on the oxide structure; and    removing the vaporized film from the vacuum chamber.    
   
   
       12 . The method of  claim 11 , wherein the first oxide a thermal grown oxide and the second oxide is a deposited oxide.  
   
   
       13 . The method of  claim 11 , wherein the oxide structure further comprises a native oxide.  
   
   
       14 . The method of  claim 11 , wherein the first rate is substantially equal to the second rate.  
   
   
       15 . The method of  claim 11 , the etching gas mixture comprises ammonia (NH 4 ) and nitrogen trifluoride (NF 3 ).  
   
   
       16 . The method of  claim 15 , wherein a molar ratio of ammonia and nitrogen trifluoride is about at least 3:1.  
   
   
       17 . A method for processing a substrate, comprising: 
 positioning the substrate in a vacuum chamber, wherein the substrate having a surface feature comprising a first oxide and a second oxide;    introducing an etching gas mixture to the vacuum chamber;    generating active species from the etching gas mixture;    at least partially reducing the first oxide by exposing the surface feature to the plasma of the etching gas mixture; and    reducing the second oxide by an aqueous etch process.    
   
   
       18 . The method of  claim 17 , wherein the etching gas mixture comprises comprises ammonia (NH 4 ) and nitrogen trifluoride (NF 3 ).  
   
   
       19 . The method of  claim 18 , further comprising adjusting a molar ratio of ammonia and nitrogen trifluoride to selectively remove the first oxide.  
   
   
       20 . The method of  claim 17 , wherein reducing the second oxide comprises providing a diluted hydrofluoric acid solution.