Endpoint control for small open area by RF source parameter Vdc

Abstract

A method of detecting endpoint of a plasma etching system that measures the DC voltage drop across both the sheath and the film being etched. When the film is nearly removed, a drop in voltage indicates thinning of the film which detects endpoint for etching before optical emission techniques. The voltage drop is measured across resistors within the matching network.

What is claimed is:  
     
         1 . A wafer fabrication system, comprising: 
 a power source coupled to a plasma system by circuitry;    wherein the endpoint for plasma etching is determined by measuring the voltage across an element of said circuitry.    
     
     
         2 . The system of  claim 1 , wherein said element is a resistor.  
     
     
         3 . The system of  claim 1 , wherein said circuitry includes impedance matching circuitry.  
     
     
         4 . The system of  claim 1 , wherein said voltage is a DC voltage corresponding to a DC voltage within the plasma system where said plasma etching occurs.  
     
     
         5 . A wafer fabrication system, comprising: 
 a plasma system for etching a material within said plasma system;    circuitry coupled to said plasma system;    wherein said etching ends when a voltage across an element external to said plasma system undergoes a predetermined change.    
     
     
         6 . The system of  claim 5 , wherein said element is a resistor.  
     
     
         7 . The system of  claim 5 , wherein said voltage is a DC voltage corresponding to a DC voltage within the plasma system.  
     
     
         8 . A method of endpoint detection in a plasma etching system, said system having an RF power source coupled to a plasma chamber by a matching network, comprising the actions of: 
 monitoring a voltage across an element in said matching network; and    changing etching parameters when said voltage undergoes a predetermined change.    
     
     
         9 . The method of  claim 8 , wherein said voltage is a DC voltage corresponding to a DC voltage in said plasma chamber.  
     
     
         10 . The method of  claim 8 , wherein said element is a resistor.  
     
     
         11 . The method of  claim 8 , wherein said predetermined change is a voltage drop of not less than 5%.  
     
     
         12 . A method of endpoint detection in plasma etching, comprising the actions of: 
 measuring voltage across a plasma system by measuring a voltage difference across an element that is external to said plasma system; and    stopping etch when said voltage decreases a predetermined amount within a predetermined time.    
     
     
         13 . The method of  claim 12 , wherein said element is a resistor.  
     
     
         14 . The method of  claim 12 , wherein said voltage is a DC voltage.  
     
     
         15 . The method of  claim 12 , wherein said predetermined amount is a voltage drop of not less than 5% and said predetermined time is not less than 3 seconds.  
     
     
         16 . A method of endpoint detection in plasma etching, comprising the actions of: 
 measuring the voltage across a resistor, said voltage sensitive to changes within the plasma system where said plasma etching occurs;    halting said etching based on a change in said voltage.    
     
     
         17 . The method of  claim 16 , wherein said resistor is part of impedance matching circuitry between said plasma system and a power source.  
     
     
         18 . The method of  claim 16 , wherein said voltage is a DC voltage.