Multiple frequency pulsing of multiple coil source to control plasma ion density radial distribution

Abstract

A method is provided for processing a workpiece supported on a support surface in a chamber of a plasma reactor. A process gas is introduced into the chamber and a plasma is generated with pulse-modulated RF power. The method comprises successively repeating the following cycle: (a) concentrating the plasma in the chamber in a center-high plasma ion distribution for a first on-time duration; (b) permitting plasma to drift during a first off-time duration away from the center-high plasma ion distribution; (c) concentrating the plasma in the chamber in an edge-high plasma ion distribution for a second on-time duration; and (d) permitting plasma to drift during a second off-time duration away from the edge-high plasma ion distribution. The method further comprises adjusting a plasma process rate near a center of the workpiece by adjusting a duty cycle of the first on-time and first off-time. The method also comprises adjusting a plasma process rate near a periphery of the workpiece by adjusting a duty cycle of the second on-time and second off-time.

1 . A method of processing a workpiece supported on a support surface in a chamber of a plasma reactor, comprising:
 supplying a process gas into said chamber, said chamber comprising a concentric inner and outer coil antennas over the chamber and facing the support surface and said chamber comprises a first and second pulse-modulated RF power sources of first and second RF frequencies for respective ones of said inner and outer coil antennas;   applying pulse-modulated RF power to said inner and outer coil antennas by successively repeating the following cycle:
 (a) applying RF power from said first source to said inner coil antenna for a first on-time duration corresponding to a first duty cycle, and at the end of said first on-time duration refraining from applying RF power to said inner coil antenna; 
 (b) applying RF power from said second source to said outer coil antenna for a second on-time duration corresponding to a second duty cycle, and at the end of said second on-time duration refraining from applying RF power to said outer coil antenna; 
   adjusting a plasma process rate near a center of said workpiece by adjusting said first duty cycle; and   adjusting a plasma process rate near a periphery of said workpiece by adjusting said second duty cycle.   
   
   
       2 . The method of  claim 1  wherein adjusting the plasma process rate near the center of said workpiece comprises reducing the plasma process rate near the center of the workpiece and said adjusting said first duty cycle comprises reducing said first duty cycle. 
   
   
       3 . The method of  claim 2  wherein adjusting the plasma process rate near the periphery of said workpiece comprises reducing the plasma process rate near the periphery of the workpiece and said adjusting said second duty cycle comprises reducing said second duty cycle. 
   
   
       4 . The method of  claim 3  wherein said reducing the plasma process rate near said center of said workpiece and said reducing of the plasma process rate near said periphery of said workpiece reduces non-uniformity in distribution of process rate across said workpiece. 
   
   
       5 . The method of  claim 1  wherein said first and second frequencies are offset from one another. 
   
   
       6 . The method of  claim 1  further comprising coupling RF bias power to said workpiece. 
   
   
       7 . The method of  claim 6  wherein said RF bias power has a frequency different from said first and second frequencies. 
   
   
       8 . The method of  claim 1  wherein said process gas comprises an etchant precursor and the plasma process rate an etch rate. 
   
   
       9 . The method of  claim 1  wherein said cycle has a period of about 0.01-100 milliseconds. 
   
   
       10 . The method of  claim 1  wherein the durations of said first and second on-time durations are one the order to 0.01-100 milliseconds. 
   
   
       11 . A method of processing a workpiece supported on a support surface in a chamber of a plasma reactor, comprising:
 introducing a process gas into the chamber and generating a plasma in said chamber with pulse-modulated RF power;   successively repeating the following cycle:
 (a) concentrating the plasma in said chamber in a center-high plasma ion distribution for a first on-time duration; 
 (b) permitting plasma to drift during a first off-time duration away from said center-high plasma ion distribution; 
 (c) concentrating the plasma in said chamber in an edge-high plasma ion distribution for a second on-time duration; 
 (d) permitting plasma to drift during a second off-time duration away from said edge-high plasma ion distribution; 
   adjusting a plasma process rate near a center of said workpiece by adjusting a duty cycle of said first on-time and first off-time; and   adjusting a plasma process rate near a periphery of said workpiece by adjusting a duty cycle of said second on-time and second off-time.   
   
   
       12 . The method of  claim 11  wherein adjusting the plasma process rate near the center of said workpiece comprises reducing the plasma process rate near the center of the workpiece and said adjusting said first duty cycle comprises reducing said first duty cycle. 
   
   
       13 . The method of  claim 12  wherein adjusting the plasma process rate near the periphery of said workpiece comprises reducing the plasma process rate near the periphery of the workpiece and said adjusting said second duty cycle comprises reducing said second duty cycle. 
   
   
       14 . The method of  claim 13  wherein said reducing the plasma process rate near said center of said workpiece and said reducing of the plasma process rate near said periphery of said workpiece reduces non-uniformity in distribution of process rate across said workpiece. 
   
   
       15 . The method of  claim 11  wherein said first and second frequencies are offset from one another. 
   
   
       16 . The method of  claim 11  further comprising coupling RF bias power to said workpiece. 
   
   
       17 . The method of  claim 16  wherein said RF bias power has a frequency different from said first and second frequencies. 
   
   
       18 . The method of  claim 11  wherein said process gas comprises an etchant precursor and the plasma process rate an etch rate. 
   
   
       19 . The method of  claim 11  wherein said cycle has a period of about 0.01-100 milliseconds. 
   
   
       20 . The method of  claim 11  wherein the durations of said first and second on-time durations are one the order to 0.01-100 milliseconds. 
   
   
       21 . The method of  claim 1  or  11  further comprising holding one of said first and second duty cycles at 100%. 
   
   
       22 . A method of processing a workpiece supported on a support surface in a chamber of a plasma reactor, comprising:
 supplying a process gas into said chamber, said chamber comprising concentric inner and outer coil antennas over the chamber and facing the support surface;   continuously applying RF power to one of said inner and outer coil antennas;   applying pulse-modulated RF power to the other one of said inner and outer coil antennas by successively repeating the following cycle:
 (a) applying RF power to said other coil antenna for an on-time duration corresponding to a duty cycle, 
 (b) at the end of said on-time duration refraining from applying RF power to said other coil antenna; and 
   adjusting radial distribution of a plasma process rate over said workpiece by adjusting said duty cycle.   
   
   
       23 . A method of processing a workpiece supported on a support surface in a chamber of a plasma reactor, comprising:
 supplying a process gas into said chamber, said chamber comprising concentric inner and outer coil antennas over the chamber and facing the support surface, and said chamber configured to receive RF power provided from a common RF power source to said inner and outer coil antennas;   apportioning RF power from said common RF power source to said inner and outer coil antennas;   pulse-modulating the RF power applied to said inner and outer coil antennas by successively repeating the following cycle of (a) followed by (b):
 (a) applying RF power from said common source to said inner coil antenna for a first on-time duration corresponding to a first duty cycle, and at the end of said first on-time duration refraining from applying RF power to said inner coil antenna; 
 (b) applying RF power from said common source to said outer coil antenna for a second on-time duration corresponding to a second duty cycle, and at the end of said second on-time duration refraining from applying RF power to said outer coil; 
   adjusting a plasma process rate near a center of said workpiece by adjusting said first duty cycle; and   adjusting a plasma process rate near a periphery of said workpiece by adjusting said second duty cycle.   
   
   
       24 . A method of processing a workpiece supported on a support surface in a chamber of a plasma reactor, comprising:
 supplying a process gas into said chamber, said chamber comprising a coil antenna;   applying pulse-modulated RF power to said coil antenna by successively repeating the following cycle:
 (a) applying RF power to said coil antenna for a first on-time duration corresponding to a duty cycle, 
 (b) at the end of said on-time duration refraining from applying RF power to said coil antenna; and 
   adjusting radial distribution of a plasma process rate by adjusting said duty cycle.