High quality oxide on an epitaxial layer

Abstract

Some embodiments of the invention improve the quality of gate oxide dielectric layers using a two-pronged approach, thus permitting the use of much thinner silicon dioxide gate dielectric layers required for lower-voltage, ultra-dense integrated circuits. In order to eliminate defects caused by imperfections in bulk silicon, an in-situ grown epitaxial layer is formed on active areas following a strip of the pad oxide layer used beneath the silicon nitride islands used for masking during the field oxidation process. By growing an epitaxial silicon layer prior to gate dielectric layer formation, defects in the bulk silicon substrate are covered over and, hence, isolated from the oxide growth step. In order to maintain the integrity of the selective epitaxial growth step, the wafers are maintained in a controlled, oxygen-free environment until the epitaxial growth step is accomplished. In order to eliminate defects caused by a native oxide layer, the wafers are maintained in a controlled, oxygen-free environment until being subjected to elevated temperature in a controlled, oxidizing environment. In one embodiment, the oxidizing environment comprises diatomic oxygen, while in another embodiment, the oxidizing environment comprises diatomic oxygen and ozone. Other embodiments of the invention are described and claimed.

1 . A method comprising: 
 forming a pad oxide layer on a silicon wafer;    forming a nitride island on the pad oxide layer and over a first area of the silicon wafer;    forming field oxide regions in a second area and a third area of the silicon wafer;    stripping the nitride island;    stripping the pad oxide layer in an oxygen-free environment, wherein the pad oxide layer being stripped in the oxygen-free environment is the pad oxide layer formed beneath the nitride island before the nitride island was stripped;    maintaining the silicon wafer in a controlled environment;    exposing the first area while the controlled environment is in a first state, wherein the first state is the oxygen-free environment;    growing an epitaxial silicon layer only on the surface of the first area while depositing substantially no silicon on the field oxide regions, and while the controlled environment is in the first state;    oxidizing at least a portion of the epitaxial silicon layer while the controlled environment is in a second state, wherein the second state is an oxidizing environment; and    maintaining the controlled environment in the first state continuously between growing the epitaxial silicon layer and oxidizing at least the portion of the epitaxial silicon layer.    
   
   
       2 . The method of  claim 1 , further comprising: 
 preventing a formation of a native oxide layer on the surface of the first area before growing the epitaxial silicon layer.    
   
   
       3 . The method of  claim 1 , wherein the oxidizing environment comprising diatomic oxygen.  
   
   
       4 . The method of  claim 1 , wherein the oxidizing environment comprising ozone and diatomic oxygen.  
   
   
       5 . The method of  claim 1 , wherein the oxygen free environment is a low pressure environment.  
   
   
       6 . A method comprising: 
 forming a pad oxide layer on a silicon wafer;    forming a nitride island on the pad oxide layer and over an active area of the silicon wafer;    forming field oxide regions in a first non-active area and a second non-active area of the silicon wafer;    stripping the nitride island;    stripping the pad oxide layer in an oxygen-free environment, wherein the pad oxide layer being stripped in the oxygen-free environment is the pad oxide layer formed beneath the nitride island before the nitride island was stripped;    maintaining the silicon wafer in a controlled environment;    exposing the first area while the controlled environment is in an active state, wherein the first state is the oxygen-free environment;    growing an epitaxial silicon layer only on the surface of the first area while depositing substantially no silicon on the field oxide regions, and while the controlled environment is in the first state;    forming a non-sacrificial oxide layer from at least a portion of the epitaxial silicon layer while the controlled environment is in a non-active state, wherein the second state is an oxidizing environment; and    maintaining the controlled environment in the first state continuously between growing the epitaxial silicon layer and oxidizing at least the portion of the epitaxial silicon layer.    
   
   
       7 . The method of  claim 6 , wherein forming the non-sacrificial oxide layer includes thermally oxidizing at least a portion of the epitaxial silicon layer.  
   
   
       8 . The method of  claim 7 , wherein the oxidizing environment comprising diatomic oxygen.  
   
   
       9 . The method of  claim 7 , wherein the oxidizing environment comprising ozone and diatomic oxygen.  
   
   
       10 . The method of  claim 7 , further comprising: 
 preventing a formation of a native oxide layer on the surface of the first area before growing the epitaxial silicon layer.    
   
   
       11 . A method comprising: 
 forming a pad oxide layer on a silicon wafer;    forming a mask on the pad oxide layer and over a first area of the silicon wafer;    forming field oxide regions in a second area and a third area of the silicon wafer;    removing the mask;    stripping the pad oxide layer in an oxygen-free environment, wherein the pad oxide layer being stripped in the oxygen-free environment is the pad oxide layer formed beneath the mask before the mask was removed;    maintaining the silicon wafer in a controlled environment;    exposing the first area while the controlled environment is in a first state, wherein the first state is the oxygen-free environment;    growing an epitaxial silicon layer only on the surface of the first area while depositing substantially no silicon on the field oxide regions, and while the controlled environment is in the first state;    forming a gate oxide dielectric layer from the epitaxial silicon layer while the controlled environment is in a second state, wherein the second state is an oxidizing environment; and    maintaining the controlled environment in the first state continuously between growing the epitaxial silicon layer and forming the non-sacrificial oxide layer.    
   
   
       12 . The method of  claim 11 , wherein the oxygen free environment is a low pressure environment.  
   
   
       13 . The method of  claim 12 , further comprising: 
 preventing a formation of a native oxide layer on the surface of the active area before growing the epitaxial silicon layer.    
   
   
       14 . The method of  claim 13 , wherein the oxidizing environment comprising diatomic oxygen.  
   
   
       15 . The method of  claim 13 , wherein the oxidizing environment comprising ozone and diatomic oxygen.  
   
   
       16 . A method comprising: 
 forming a pad oxide layer on a silicon wafer;    forming a nitride island on the pad oxide layer and over a first area of the silicon wafer;    forming field oxide regions in a second area and a third area of the silicon wafer;    stripping the nitride island;    stripping the pad oxide layer in an oxygen-free environment, wherein the pad oxide layer being stripped in the oxygen-free environment is the pad oxide layer formed beneath the nitride island before the nitride island was stripped;    maintaining the silicon wafer in a controlled environment;    exposing the first area while the controlled environment is in a first state, wherein the first state is the oxygen-free environment;    growing an epitaxial silicon layer only on the surface of the first area while depositing substantially no silicon on the field oxide regions, and while the controlled environment is in the first state;    thermally oxidizing at least a portion of the epitaxial silicon layer while the controlled environment is in a second state to form a gate oxide dielectric layer, wherein the second state is an oxidizing environment;    maintaining the controlled environment in the first state continuously between growing the epitaxial silicon layer and forming the non-sacrificial oxide layer;    forming a gate electrode layer over the gate oxide dielectric layer.    
   
   
       17 . The method of  claim 16 , wherein the oxygen free environment is a low pressure environment.  
   
   
       18 . The method of  claim 16 , further comprising: 
 preventing a formation of a native oxide layer on the surface of the active area before growing the epitaxial silicon layer.    
   
   
       19 . The method of  claim 16 , wherein the oxidizing environment comprising diatomic oxygen, and ozone and diatomic oxygen.  
   
   
       20 . The method of  claim 16 , wherein the oxidizing environment comprising ozone and diatomic oxygen.