Method and apparatus for plasma processing

Abstract

The invention provides a plasma processing apparatus capable of minimizing the non-uniformity of potential distribution around wafer circumference, and providing a uniform process across the wafer surface. The apparatus is equipped with a focus ring formed of a dielectric, a conductor or a semiconductor and having RF applied thereto, the design of which is optimized for processing based on a design technique clarifying physical conditions for flattening a sheath-plasma interface above a wafer and the sheath-plasma interface above the focus ring. A surface voltage of the focus ring is determined to be not less than a minimum voltage for preventing reaction products caused by wafer processing from depositing thereon. The surface height, surface voltage, material and structure of the focus ring are optimized so that the height of an ion sheath formed on the focus ring surface is either equal or has a height difference within an appropriate tolerance range to the height of the ion sheath formed on the wafer surface. Optimization of the structure is realized by setting up an appropriate tolerance range taking into consideration the variation caused by consumption of the focus ring.

1 . A plasma processing method for processing an object to be processed using plasma, the method comprising: 
 placing the object to be processed on a process stage;    disposing a focus ring on the process stage surrounding the object to be processed; and    applying an RF bias to the focus ring and the object to be processed;    wherein a structure of the focus ring and the process stage is optimized through an optimization design technique using equivalent circuit analysis.    
   
   
       2 . The plasma processing method according to  claim 1 , wherein the optimization design technique includes an equivalent circuit modeling of plasma and ion sheath based on a plasma-sheath model.  
   
   
       3 . The plasma processing method according to  claim 1 , wherein the optimization design technique optimizes a focus ring surface potential so as to prevent wafer process reaction products from depositing on the focus ring.  
   
   
       4 . The plasma processing method according to  claim 1 , wherein the optimization design technique optimizes a focus ring surface height, a focus ring surface voltage, a focus ring material and a focus ring structure so that a height of an ion sheath formed on the focus ring surface is either equal or has a height difference within an appropriate tolerance range to a height of an ion sheath formed on the wafer surface.  
   
   
       5 . The plasma processing method according to  claim 1 , wherein the optimization design technique optimizes the structure by setting up an appropriate tolerance taking into consideration a variation by time caused by consumption of the focus ring.  
   
   
       6 . The plasma processing method according to  claim 1 , wherein the optimization design technique aims at flattening as much as possible an equi-potential surface within an ion sheath through the equivalent circuit analysis and, when necessary, a sequential coupling analysis of two dimensional plasma analysis and two dimensional electric field analysis.  
   
   
       7 . The plasma processing method according to  claim 1 , wherein the optimization design technique comprises two plasma-sheath interface flattening conditions, one of which is that a voltage drop of an RF voltage from an electrode in the process stage to the plasma-sheath interface above the object to be processed must be equal to the voltage drop of the RF voltage from the electrode in the processing stage to the plasma-sheath interface above the focus ring.  
   
   
       8 . The plasma processing method according to  claim 1 , wherein the other plasma-sheath interface flattening condition is that a sum of a surface height of the object to be processed measured from a certain height reference point and a sheath thickness above the object to be processed must be equal to a sum of a surface height of the focus ring measured from the height reference point and the sheath thickness above the focus ring.