Plasma control using dual cathode frequency mixing

Abstract

A method and apparatus for controlling characteristics of a plasma in a semiconductor substrate processing chamber using a dual frequency RF source is provided. The method comprises supplying a first RF signal to a first electrode disposed in a processing chamber, and supplying a second RF signal to the first electrode, wherein an interaction between the first and second RF signals is used to control at least one characteristic of a plasma formed in the processing chamber.

1 . Apparatus for controlling characteristics of a plasma in a semiconductor substrate processing system, comprising: 
 a first electrode disposed within a chamber;    a first RF source for providing a first RF signal coupled to the first electrode through a match network;    a second RF source for providing a second RF signal coupled to the first electrode through the match network, wherein the match network has a single feed to the first electrode; and    a controller for controlling the application of the first and second RF signals such that a manipulable interaction between the first and second RF signals controls at least one plasma characteristic.    
   
   
       2 . The apparatus of  claim 1 , further comprising: 
 a third RF source for providing a third RF signal coupled to a second electrode disposed in the chamber.    
   
   
       3 . The apparatus of  claim 2 , wherein the first electrode is disposed in a substrate support pedestal contained in the chamber and the second electrode is disposed proximate a roof of the chamber above the support pedestal.  
   
   
       4 . The apparatus of  claim 2 , wherein the third RF signal coupled to the second electrode is adapted to form a plasma in the chamber during operation thereof.  
   
   
       5 . The apparatus of  claim 1 , wherein the first electrode is disposed in a substrate support pedestal contained in the chamber.  
   
   
       6 . The apparatus of  claim 1 , wherein the chamber an etch reactor.  
   
   
       7 . The apparatus of  claim 1 , wherein the plasma characteristic is at least sheath modulation.  
   
   
       8 . The apparatus of  claim 7 , wherein the first and second RF sources are adapted to provide respective first and second RF signals of a low enough frequency to provide a strong self-biasing sheath in the plasma.  
   
   
       9 . The apparatus of  claim 7 , wherein the frequency of the first RF signal is selected to provide a broad ion energy distribution and the frequency of the second RF signal is selected to provide a peaked, well defined ion energy distribution during operation of the chamber.  
   
   
       10 . The apparatus of  claim 9 , wherein the first RF signal has a cycle time that is larger than the transit time of an ion in the sheath, and wherein the second RF signal has a period that is nearly equal to or greater than the transit time of an ion in the sheath.  
   
   
       11 . The apparatus of  claim 7 , wherein the combined applied voltage of the first and second RF signal is used to control a peak-to-peak sheath voltage and a self-biased DC potential.  
   
   
       12 . The apparatus of  claim 11 , wherein the controller further controls a desired ratio of the applied power of the first and second RF signals.  
   
   
       13 . The apparatus of  claim 12 , wherein the ratio is used to tune the energy distribution about an average acceleration generated by the DC potential.  
   
   
       14 . The apparatus of  claim 1 , wherein the plasma characteristic is at least a power distribution within the plasma.  
   
   
       15 . The apparatus of  claim 14 , wherein the first and second RF signals provide similar plasma excitation properties and different spatial uniformity profiles.  
   
   
       16 . The apparatus of  claim 15 , wherein the manipulable interaction between the first and second RF signals is a varying effect on the power distribution in the plasma.  
   
   
       17 . The apparatus of  claim 16 , wherein the first and the second RF signals are selected such that a combined effect of the first and second RF signals produces a substantially flat power distribution.  
   
   
       18 . The apparatus of  claim 16 , wherein the manipulable interaction between the first and second RF signals is used to control the uniformity of a plasma enhanced etch process.  
   
   
       19 . The apparatus of  claim 1 , wherein the controller is further configured to control the application of the first and second RF signals to provide a desired plasma energy distribution along a continuum of plasma energy distributions obtainable using individual low to high frequency RF sources.  
   
   
       20 . The apparatus of  claim 19 , wherein the controller is further configured to provide the desired plasma energy distribution by controlling a ratio of the power of the first and second RF signals.  
   
   
       21 . The apparatus of  claim 1 , wherein the controller is further configured to control the application of the first and second RF signals to provide a desired power distribution within the plasma.  
   
   
       22 . The apparatus of  claim 1 , wherein the first power supply is adapted to provide a first power distribution in the plasma and wherein the second  
   
   
       23 . Apparatus for controlling characteristics of a plasma in a semiconductor substrate processing system, comprising: 
 a first electrode disposed beneath a substrate support pedestal in a chamber;    a first RF bias source for providing a first RF bias signal and a second RF bias source for providing a second RF bias signal, the first and second RF bias signals coupled to the first electrode through a match network having a single feed to the first electrode;    an RF source for providing an RF signal to a second electrode disposed above the substrate support pedestal, the RF signal adapted to form a plasma during operation;    a controller for controlling the application of the first and second RF bias signals such that a manipulable interaction between the first and second RF signals controls at least one plasma characteristic.