Apparatus and method for substrate clamping in a plasma chamber

Abstract

The present invention generally provides methods and apparatus for monitoring and maintaining flatness of a substrate in a plasma reactor. Certain embodiments of the present invention provide a method for processing a substrate comprising positioning the substrate on an electrostatic chuck, applying an RF power between the an electrode in the electrostatic chuck and a counter electrode positioned parallel to the electrostatic chuck, applying a DC bias to the electrode in the electrostatic chuck to clamp the substrate on the electrostatic chuck, and measuring an imaginary impedance of the electrostatic chuck.

1 . A method for processing a substrate, comprising: 
 positioning the substrate on an electrostatic chuck;    applying an RF power between the an electrode in the electrostatic chuck and a counter electrode positioned parallel to the electrostatic chuck;    applying a DC bias to the electrode in the electrostatic chuck to clamp the substrate on the electrostatic chuck; and    measuring an imaginary impedance of the electrostatic chuck.    
   
   
       2 . The method of  claim 1 , further comprising adjusting the DC bias applied to the electrode of the electrostatic chuck according to the measured imaginary impedance of the electrostatic chuck.  
   
   
       3 . The method of  claim 1 , further comprising correlating the imaginary impedance of the electrostatic chuck to a flatness of the substrate.  
   
   
       4 . The method of  claim 3 , further comprising calculating a slope of the imaginary impedance over a time period.  
   
   
       5 . The method of  claim 4 , further comprising increasing the DC bias applied to the electrostatic chuck when the slope of the imaginary impedance is negative.  
   
   
       6 . The method of  claim 1 , wherein measuring the imaginary impedance comprises measuring a voltage and a current of the electrostatic chuck.  
   
   
       7 . The method of  claim 6 , wherein the voltage and the current are measured using a VI probe connected to the counter electrode.  
   
   
       8 . A method for monitoring a substrate during a plasma process, comprising: 
 positioning the substrate in a plasma generator having first and second parallel electrodes, wherein the substrate is positioned between the first and second parallel electrodes and substantially parallel to the first and second parallel electrodes;    applying an RF power between the first and second electrodes of the plasma generator; and    monitoring the substrate by measuring a characteristic of the plasma generator.    
   
   
       9 . The method of  claim 8 , further comprising applying a DC bias to the first parallel electrode to secure the substrate directly or indirectly on the first parallel electrode.  
   
   
       10 . The method of  claim 8 , wherein the characteristic is impedance.  
   
   
       11 . The method of  claim 10 , wherein the impedance is measured using a VI probe connected to the plasma generator.  
   
   
       12 . The method of  claim 10 , further comprising correlating a measured imaginary impedance of the plasma generator to a flatness of the substrate.  
   
   
       13 . The method of  claim 12 , further comprising calculating a slope of the measured imaginary impedance over a time period, wherein a negative slope indicating a decrease in the flatness of the substrate.  
   
   
       14 . The method of  claim 13 , further comprising applying a sufficient chucking voltage to the first parallel electrode to obtain a desired flatness of the substrate.  
   
   
       15 . An apparatus for processing a substrate, comprising: 
 an electrostatic chuck comprising a first electrode connected with a DC power supply, wherein the electrostatic chuck has a supporting surface configured to support the substrate thereon;    a counter electrode positioned substantially parallel to the supporting surface of the electrostatic chuck, wherein the counter electrode is positioned a distance apart from the electrostatic chuck, the substrate is configured to be positioned between the electrostatic chuck and the counter electrode;    a RF power supply configured to apply a RF power between the first electrode and the counter electrode; and    a sensor configured to measure a characteristic of the electrostatic chuck.    
   
   
       16 . The apparatus of  claim 15 , further comprising: 
 a capacitor connected between the first electrode and the ground, wherein the RF power is connected to the counter electrode via a matching network, the first electrode and the capacitor provide a return path to the RF power; and    a filter connected between the first electrode and the DC power supply, wherein the filter is configured to remove noise and/or any RF current from the biasing voltage from the DC power supply.    
   
   
       17 . The apparatus of  claim 15 , wherein the sensor is a VI probe connected to the counter electrode.  
   
   
       18 . The apparatus of  claim 15 , further comprising a system controller configured to receive input from the sensor.  
   
   
       19 . The apparatus of  claim 18 , wherein the system controller is configured to correlating the measured characteristic of the electrostatic chuck to a flatness of the substrate.  
   
   
       20 . The apparatus of  claim 18 , wherein the system controller is configured to adjust the DC power supply according to a slope of an imaginary impedance of the electrostatic chuck.