Method of forming si tip by single etching process and its application for forming floating gate

Abstract

The invention provides a method of forming a silicon tip by a single etching process, as well as a method of forming a tip floating gate to increase erase speed. Etching gases comprising (1) chlorine and/or (2) oxygen/helium are performed to form a silicon tip without bottom dimple. The invention may further control the tip angle by adjusting the etching parameters of gas compositions and ratios, chamber pressures, and radio frequency powers.

1 . A method of forming a Si tip by a single etching process, comprising: 
 providing a substrate having a silicon layer;    putting the substrate into an etching chamber of an etching process tool; and    etching portions of the silicon layer to form a tip edge by an etching process comprising hydrogen bromide as a major etching gas with suitable amounts of gases (1) chlorine and/or (2) oxygen/helium.    
     
     
         2 . The method as claimed in  claim 1 , comprising: 
 controlling the tip edge angles by adjusting the etching parameters of the etching gas compositions and ratios, the etching chamber pressures, and the etching process tool radio frequency powers.    
     
     
         3 . The method as claimed in  claim 1 , wherein the silicon layer comprises polysilicon, epitaxial silicon, single crystal silicon, or doped silicon.  
     
     
         4 . The method as claimed in  claim 2 , wherein the etching chamber pressures are less than 8 mTorr.  
     
     
         5 . The method as claimed in  claim 4 , wherein the tip edge angles are between 15˜45 degrees.  
     
     
         6 . The method as claimed in  claim 5 , wherein the etching gas comprises 65˜80% of hydrogen bromide, 15˜25% of chlorine, as well as 5˜8% of oxygen/helium, wherein the ratio of oxygen to helium is about 3:7; and the flow rate of the etching gas is about 132˜166 sccm.  
     
     
         7 . The method as claimed in  claim 6 , wherein the etching process tool radio frequency powers comprise a top radio frequency power of about 300˜600 watts, and a bottom radio frequency power of about 15˜35 watts.  
     
     
         8 . The method as claimed in  claim 4 , wherein the tip edge angles are between 45˜65 degrees.  
     
     
         9 . The method as claimed in  claim 8 , wherein the etching gas comprises 61˜71% of hydrogen bromide, 14˜24% of chlorine, as well as 12˜16% of oxygen/helium, wherein the ratio of oxygen to helium is about 3:7; and the flow rate of the etching gas is about 91˜116 sccm.  
     
     
         10 . The method as claimed in  claim 9 , wherein the etching process tool radio frequency powers comprise a top radio frequency power of about 225˜275 watts, and a bottom radio frequency power of about 15˜35 watts.  
     
     
         11 . The method as claimed in  claim 4 , wherein the tip edge angles are between 65˜85 degrees.  
     
     
         12 . The method as claimed in  claim 11 , wherein the etching gas comprises 65˜80% of hydrogen bromide, 15˜25% of chlorine, as well as 5˜8% of oxygen/helium, wherein the ratio of oxygen to helium is about 3:7; and the flow rate of the etching gas is about 132˜166 sccm.  
     
     
         13 . The method as claimed in  claim 12 , wherein the etching process tool radio frequency powers comprise a top radio frequency power of about 225˜275 watts, and a bottom radio frequency power of about 25˜35 watts.