Polysilicon etch with high selectivity

Abstract

Provided are methods and systems for removing polysilicon on a wafer. A wafer can include a polysilicon layer and an exposed nitride and/or oxide structure. An etchant with a hydrogen-based species, such as hydrogen gas, and a fluorine-based species, such as nitrogen trifluoride, can be introduced. The hydrogen-based species and the fluorine-based species can be activated with a remote plasma source. The layer of polysilicon on the wafer can be removed at a selectivity over the exposed nitride and/or oxide structure that is greater than about 500:1.

What is claimed is: 
     
         1 . An apparatus for removing polysilicon from a wafer, the apparatus comprising:
 a reaction chamber comprising the wafer, wherein the wafer includes:
 a polysilicon layer; and 
 an exposed nitride and/or oxide structure 
   a plasma source coupled to the reaction chamber and configured to generate a plasma outside the reaction chamber; and   a controller with instructions for performing the following operations:
 (a) flowing an etchant including a hydrogen-based species and a fluorine-based species towards the wafer, wherein a concentration of the fluorine-based species is between about 0.7% and about 10% by volume and a concentration of the hydrogen-based species is greater than the concentration of the fluorine-based species; 
 (b) exposing the etchant to the plasma to activate the hydrogen-based species and the fluorine-based species; and 
 (c) removing the polysilicon layer at a selectivity over the exposed nitride and/or oxide structure of greater than about 500:1. 
   
     
     
         2 . The apparatus of  claim 1 , wherein the plasma source comprises a remote downstream plasma reactor. 
     
     
         3 . The apparatus of  claim 1 , wherein the hydrogen-based species includes hydrogen or ammonia. 
     
     
         4 . The apparatus of  claim 1 , wherein the fluorine-based species includes nitrogen trifluoride or carbon tetrafluoride. 
     
     
         5 . The apparatus of  claim 1 , wherein the exposed nitride structure includes silicon nitride or titanium nitride. 
     
     
         6 . The apparatus of  claim 1 , wherein the exposed oxide structure includes silicon dioxide. 
     
     
         7 . The apparatus of  claim 1 , wherein an etch rate of the polysilicon layer is greater than about 1000 Å per minute and an etch rate of the exposed nitride and/or oxide structure is less than about 5 Å per minute during removal of the polysilicon layer. 
     
     
         8 . The apparatus of  claim 1 , wherein the temperature of the wafer is between about 60° C. and about 100° C. 
     
     
         9 . The apparatus of  claim 1 , wherein the hydrogen-based species is hydrogen. 
     
     
         10 . The apparatus of  claim 9 , wherein the flow rate of hydrogen is about equal to or greater than 2 standard liters per minute.