Apparatus and method for substrate clamping in a plasma chamber
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 monitoring a substrate during a plasma process, comprising:
positioning a substrate on an electrostatic chuck in a process chamber;
applying an RF power between 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;
monitoring slope variation of impedance of the electrostatic chuck over a time duration; and
correlating slope variation of the impedance of the electrostatic chuck to a flatness of the substrate.
2. The method of claim 1 , wherein the monitoring variation of impedance of the electrostatic chuck comprises monitoring variation of imaginary impedance of the electrostatic chuck.
3. The method of claim 2 , further comprising adjusting the DC bias applied to the electrode in the electrostatic chuck according to the variation of imaginary impedance of the electrostatic chuck.
4. The method of claim 1 , further comprising correlating an overall negative slope variation of the impedance of the electrostatic chuck to a decrease in the flatness of the substrate.
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 the monitoring variation of 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. The method of claim 1 , wherein the monitoring variation of impedance of the process chamber is performed without measuring capacitances associated with the process chamber.
9. A method for monitoring a substrate during a plasma process, comprising:
positioning a 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;
applying a DC bias to the first parallel electrode to secure the substrate directly or indirectly on the first parallel electrode; and
monitoring flatness of the substrate by determining slope variation of imaginary impedance of the plasma generator over a time duration, wherein a negative slope indicates a decrease in the flatness of the substrate.
10. The method of claim 9 , wherein the imaginary impedance is determined using a sensor connected to one of parallel electrodes of the plasma generator.
11. The method of claim 9 , further comprising adjusting the DC bias to the first parallel electrode according to the slope variation of the imaginary impedance.
12. The method of claim 9 , wherein the determining the slope variation of imaginary impedance of the plasma generator is performed without measuring capacitances associated with the plasma generator.