Ion energy bias control with plasma-source pulsing

Abstract

This disclosure describes systems, methods, and apparatus for controlling ion energy in a plasma processing chamber. In particular, a system for plasma processing includes a plasma processing chamber, a plasma source coupled to the plasma processing chamber, a plasma power supply coupled to the plasma source that is configured to apply power to the plasma processing chamber in periodic pulse envelopes to control a density of a plasma in the plasma processing chamber, and a support within the plasma processing chamber to support a substrate. A bias supply is configured to provide a modified periodic voltage function to the substrate support within each of the periodic pulse envelopes to control an energy of ions impacting the substrate support in the plasma processing chamber.

What is claimed is: 
     
         1 . A system for plasma processing, the system comprising:
 a plasma processing chamber;   a plasma source coupled to the plasma processing chamber;   a plasma power supply coupled to the plasma source configured to apply power to the plasma processing chamber in periodic pulse envelopes to control a density of a plasma in the plasma processing chamber;   a support within the plasma processing chamber to support a substrate; and   a bias supply configured to provide a modified periodic voltage function to the substrate support within each of the periodic pulse envelopes to control an energy of ions impacting the substrate support in the plasma processing chamber.   
     
     
         2 . The system of  claim 1 , wherein the modified periodic voltage function is formed from a combination of a periodic voltage function and an ion current compensation, I C . 
     
     
         3 . The system of  claim 2 , wherein the modified periodic voltage function includes:
 a rapidly increasing voltage called a first portion;   a substantially constant voltage starting at an end of the first portion and called a second portion;   a voltage step, ΔV, below the substantially constant voltage starting at an end of the second portion and called a third portion; and   a sloped voltage starting ΔV below the substantially constant voltage, starting at an end of the third portion, and called a fourth portion, the sloped voltage having a slope dV 0 /dt controlled by the ion current compensation.   
     
     
         4 . The system of  claim 3 , wherein the plasma power supply is an RF power supply configured to apply sinusoidal power. 
     
     
         5 . The system of  claim 1 , wherein the bias supply is configured to provide the modified periodic voltage function to the substrate support within each of the periodic pulse envelopes to provide multiple ion energies. 
     
     
         6 . The system of  claim 1 , wherein the bias supply is configured to provide the modified periodic voltage function to change ion energy from cycle-to-cycle. 
     
     
         7 . The system of  claim 1 , wherein the bias supply is configured to measure a density of the plasma and the source supply is controlled, at least in part, by the measured plasma density. 
     
     
         8 . A method for plasma processing, the method comprising:
 placing a substrate on a substrate support in a plasma processing chamber;   sustaining a plasma within the plasma processing chamber with power applied to the plasma processing chamber in periodic pulse envelopes; and   providing a modified periodic voltage function to the substrate support within each of the periodic pulse envelopes to control an energy of ions impacting the substrate support in the plasma processing chamber.   
     
     
         9 . The method of  claim 8 , wherein the modified periodic voltage function is formed from a combination of a periodic voltage function and an ion current compensation, I C . 
     
     
         10 . The method of  claim 9 , wherein the modified periodic voltage function includes:
 a rapidly increasing voltage called a first portion;   a substantially constant voltage starting at an end of the first portion and called a second portion;   a voltage step, ΔV, below the substantially constant voltage starting at an end of the second portion and called a third portion; and   a sloped voltage starting ΔV below the substantially constant voltage, starting at an end of the third portion, and called a fourth portion, the sloped voltage having a slope dV 0 /dt controlled by the ion current compensation.   
     
     
         11 . The method of  claim 10 , wherein sustaining the plasma in the plasma processing chamber includes sustaining the plasma with sinusoidal RF power in the periodic pulse envelopes. 
     
     
         12 . The method of  claim 10 , including modifying the voltage step, ΔV, within each of the periodic pulse envelopes to provide multiple ion energies within each of the periodic pulse envelopes. 
     
     
         13 . The method of  claim 10 , including modifying the voltage step, ΔV, from cycle-to-cycle. 
     
     
         14 . The method of  claim 8 , including:
 measuring a density of the plasma with a bias supply that provides the modified periodic voltage function; and   controlling a plasma supply that applies the power to the plasma processing chamber in periodic pulse envelopes using, at least in part, the measured plasma density.   
     
     
         15 . A non-transitory processor-readable medium encoded with instructions, the instructions including instructions for:
 sustaining a plasma within the plasma processing chamber with power applied to the plasma processing chamber in periodic pulse envelopes; and   providing a modified periodic voltage function to the substrate support within each of the periodic pulse envelopes to control an energy of ions impacting the substrate support in the plasma processing chamber.   
     
     
         16 . The non-transitory processor-readable medium of  claim 15  encoded with instructions for forming the modified periodic voltage function from a combination of a periodic voltage function and an ion current compensation, I C . 
     
     
         17 . The non-transitory processor-readable medium of  claim 16  encoded with instructions for forming the modified periodic voltage function with:
 a rapidly increasing voltage called a first portion; 
 a substantially constant voltage starting at an end of the first portion and called a second portion; 
 a voltage step, ΔV, below the substantially constant voltage starting at an end of the second portion and called a third portion; and 
 a sloped voltage starting ΔV below the substantially constant voltage, starting at an end of the third portion, and called a fourth portion, the sloped voltage having a slope dV 0 /dt controlled by the ion current compensation. 
 
     
     
         18 . The non-transitory processor-readable medium of  claim 17  encoded with instructions for modifying the voltage step, ΔV, within each of the periodic pulse envelopes to provide multiple ion energies within each of the periodic pulse envelopes. 
     
     
         19 . The non-transitory processor-readable medium of claim of  claim 17  encoded with instructions for modifying the voltage step, ΔV, from cycle-to-cycle. 
     
     
         20 . The non-transitory processor-readable medium of  claim 15  encoded with instructions for:
 measuring a density of the plasma with a bias supply that provides the modified periodic voltage function; and 
 controlling a plasma supply that applies the power to the plasma processing chamber in periodic pulse envelopes using, at least in part, the measured plasma density.