Plasma Processing System with Synchronized Signal Modulation

Abstract

A system and method for using plasma to treat a substrate are described. A plasma processing system includes a substrate holder arranged to support a substrate, a first signal generator for coupling a first signal at a first frequency to plasma in the plasma processing system, and a second signal generator for coupling a second signal at a second frequency that is less than the first frequency to the plasma in the plasma processing system. The system further includes a waveform generator configured to dynamically adjust a duty cycle of the second signal while the first signal is coupled to the plasma to spatially and temporally control the plasma density.

What is claimed is: 
     
         1 . A plasma processing system, comprising:
 a substrate holder arranged to support a substrate;   a first signal generator for coupling a first signal at a first frequency to plasma in the plasma processing system;   a second signal generator for coupling a second signal at a second frequency that is less than the first frequency to the plasma in the plasma processing system; and   a waveform generator configured to dynamically adjust a duty cycle of the second signal while the first signal is coupled to the plasma to spatially and temporally control the plasma density.   
     
     
         2 . The plasma processing system of  claim 1 , wherein the first frequency is greater than about 50 MHz, and the second frequency is less than about 5 MHz. 
     
     
         3 . The plasma processing system of  claim 1 , wherein the waveform generator is further configured to adjust a waveform of the second signal, and wherein the waveform is a square wave. 
     
     
         4 . The plasma processing system of  claim 1 , wherein the waveform generator is further configured to adjust a waveform of the second signal, and wherein the waveform is a saw-tooth waveform. 
     
     
         5 . The plasma processing system of  claim 1 , wherein the first signal and the second signal are coupled to the substrate holder. 
     
     
         6 . The plasma processing system of  claim 1 , wherein the first signal is coupled to an electrode opposing the substrate holder, and the second signal is coupled to the substrate holder. 
     
     
         7 . A plasma processing system, comprising:
 a substrate holder disposed arranged to support a substrate;   a first signal generator for coupling a first signal at a first frequency to plasma in the plasma processing system;   a second signal generator for coupling a second signal at a second frequency that is less than the first frequency to the plasma in the plasma processing system;   a waveform generator configured to dynamically adjust a duty cycle of the second signal while the first signal is coupled to the plasma to spatially and temporally control the plasma density; and   a controller configured to receive data relating to a spatial and temporal distribution of the plasma density across the substrate, and instruct the waveform generator to adjust the duty cycle to achieve a target spatial distribution.   
     
     
         8 . The plasma processing system of  claim 7 , wherein the first frequency is greater than about 50 MHz, and the second frequency is less than about 5 MHz. 
     
     
         9 . The plasma processing system of  claim 7 , further comprising:
 an in-situ diagnostic coupled to the plasma processing system, and configured to measure data related to the spatial and temporal distribution of the plasma density.   
     
     
         10 . The plasma processing system of  claim 7 , wherein the waveform generator is further configured to adjust a waveform of the second signal, and wherein the waveform is a square wave. 
     
     
         11 . The plasma processing system of  claim 7 , wherein the waveform generator is further configured to adjust a waveform of the second signal, and wherein the waveform is a saw-tooth waveform. 
     
     
         12 . The plasma processing system of  claim 7 , wherein the first signal and the second signal are coupled to the substrate holder. 
     
     
         13 . The plasma processing system of  claim 7 , wherein the first signal is coupled to an electrode opposing the substrate holder, and the second signal is coupled to the substrate holder. 
     
     
         14 . A method for plasma processing, comprising:
 placing a substrate on a substrate holder disposed within a plasma processing system;   applying a first signal to plasma formed in the plasma processing system using a first signal generator at a first frequency;   applying a second signal at a second frequency that is less than the first frequency to the plasma formed in the plasma processing system using a second signal generator;   spatially and temporally controlling the plasma density by dynamically adjusting a duty cycle of the second signal while the first signal is coupled to the plasma.   
     
     
         15 . The method of  claim 14 , wherein the first frequency is greater than about 50 MHz, and the second frequency is less than about 5 MHz. 
     
     
         16 . The method of  claim 14 , wherein spatially and temporally controlling the plasma density comprises:
 using a waveform generator to adjust a waveform and the duty cycle of the second signal.   
     
     
         17 . The method of  claim 16 , wherein the waveform is a square wave. 
     
     
         18 . The method of  claim 16 , wherein the waveform is a saw-tooth waveform. 
     
     
         19 . The method of  claim 14 , wherein spatially and temporally controlling the plasma density comprises:
 increasing the duty cycle of the second signal to decrease the plasma density at an edge of the substrate relative to the center of the substrate; and   decreasing the duty cycle of the second signal to increase the plasma density at the center of the substrate relative to the edge of the substrate.   
     
     
         20 . The method of  claim 14 , further comprising:
 sensing the plasma density of the plasma using an in-situ diagnostic coupled to the plasma processing system;   generating data relating to a spatial and temporal distribution of the plasma density across the substrate according to the sensed plasma density; and   instructing a waveform generator to adjust the duty cycle to achieve a target spatial distribution.