Method and apparatus for etching material layers with high uniformity of a lateral etch rate across a substrate

Abstract

A method and apparatus for etching material layers with high uniformity of a lateral etch rate across a substrate using a gas mixture that includes a passivation gas. The passivation gas is provided to a peripheral region of the substrate to passivate sidewalls of the structures being etched.

1 . A method of etching a material layer on a substrate, comprising: 
 (a) providing a substrate in a process chamber;    (b) supplying an etchant gas into the process chamber through a first gas inlet; and    (c) supplying a passivation gas having a greater concentration proximate a peripheral region of the substrate relative to the center region of the substrate.    
   
   
       2 . The method of  claim 1  wherein the step (c) further comprises: 
 selectively adjusting a flow rate of the passivation gas.    
   
   
       3 . The method of  claim 1  further comprising: 
 energizing the etchant gas and the passivation gas to form a plasma.    
   
   
       4 . The method of  claim 3  further comprising: 
 selectively adjusting a degree of dissociation of the passivation gas in the peripheral region of the substrate.    
   
   
       5 . The method of  claim 3  further comprising: 
 selectively adjusting a density of the plasma of the passivation gas in the peripheral region of the substrate.    
   
   
       6 . The method of  claim 5  further comprising: 
 controlling a power level applied an element of an inductively coupled antenna to adjust the plasma density.    
   
   
       7 . The method of  claim 1  wherein the etchant gas removes a polysilicon from the substrate to form a gate structure of a transistor.  
   
   
       8 . The method of  claim 1  wherein the passivation gas is at least one gas selected from the group consisting of SiF 4  and SiH 4 .  
   
   
       9 . The method of  claim 7  wherein the etchant gas comprises at least one of HBr, Cl 2 , and O 2 .  
   
   
       10 . The method of  claim 9  further comprising: 
 providing HBr and Cl 2  at a flow ratio HBr:Cl 2  in a range from 1:15 to 15:1.    
   
   
       11 . The method of  claim 10  wherein the passivation gas comprises at least one of SiF 4  and SiH 4 .  
   
   
       12 . The method of  claim 11  further comprising: 
 providing one of SiF 4  and SiH 4  at a flow rate of about 1 to 100 sccm.    
   
   
       13 . The method of  claim 3 , wherein the step of selecting the process condition further comprises: 
 dissociating a greater amount of ions of the passivation gas in the peripheral region relative to the central region.    
   
   
       14 . The method of  claim 3 , further comprising: 
 selecting an inner to outer coil power ratio that produces a higher degree of dissociation of the passivation gas at the peripheral region of the substrate relative to the center region.    
   
   
       15 . The method of  claim 3  further comprising: 
 energizing the passivation gas to produce a higher plasma density of the passivation gas in the peripheral region of the substrate.    
   
   
       16 . The method of  claim 1 , wherein the step of supplying the passivation gas further comprises: 
 injecting the passivation gas from a nozzle coupled to a chamber sidewall.    
   
   
       17 . The method of  claim 1 , wherein the step pf supplying the passivation gas further comprises: 
 reacting the passivation gas with an etched material on the periphery region of the substrate; and    forming a passivation film on sidewall of the etched polysilicon material.    
   
   
       18 . The method of  claim 17 , wherein the step of forming a passivation film on sidewall of the etched polysilicon material further comprises: 
 reducing the lateral etch rate in the peripheral region of the substrate.    
   
   
       19 . The method of  claim 17 , wherein the step of forming a passivation film on sidewall of the etched polysilicon material further comprises: 
 preferentially etching polysilicon in the center region of the substrate relative to the peripheral region.    
   
   
       20 . The method of  claim 1 , wherein the step of supplying the passivation gas further comprises: 
 selecting a process condition to establish an edge to center ratio of passivation gas sufficiently high enough to maintain lateral polysilicon etch rate uniformity across the substrate.    
   
   
       21 . The method of  claim 1 , wherein the step of supplying the passivation gas further comprises: 
 selectively adjusting the degree of dissociation of the passivation gas to compensate the depletion of the etched by-products in the center region of the substrate associated with the etchant gas.