Method and apparatus for measuring erosion and calibrating position for a moving process kit

1. A method of calibrating a processing chamber, comprising:

placing a sensor wafer onto a support surface in the processing chamber, wherein a process kit that is displaceable in a Z-direction is positioned around the support surface;

measuring a first gap distance between the sensor wafer and the process kit with a sensor on an edge surface of the sensor wafer;

displacing the process kit in the Z-direction; and

measuring an additional gap distance between the sensor wafer and the process kit.

2. The method of claim 1 , further comprising:

comparing the additional gap distance to the first gap distance.

3. The method of claim 2 , further comprising:

removing the sensor wafer from the support surface when the first gap distance is equal to the additional gap distance.

4. The method of claim 2 , further comprising:

repeating the operations of displacing the process kit in the Z-direction and measuring the additional gap distance until successive measurements of the additional gap distance are equal to each other.

5. The method of claim 1 , wherein the sensor is a capacitive sensor.

6. The method of claim 5 , wherein the capacitive sensor is a self-referencing capacitive sensor.

7. The method of claim 6 , wherein the capacitive sensor comprises a first pad and a second pad, and wherein current supplied to the first pad has an output phase that is 180 degrees from an output phase of current supplied to the second pad.

8. The method of claim 5 , wherein the capacitive sensor extends above a top surface of the sensor wafer.

9. A method for measuring erosion of a process kit, comprising:

placing a sensor wafer on a support surface in a processing tool;

aligning a top surface of the process kit surrounding the support surface to a top surface of sensor wafer using sensors on the sensor wafer;

removing the sensor wafer from the support surface;

processing one or more device substrates in the processing tool;

placing a sensor wafer on the support surface;

measuring a gap distance between the sensor wafer and the process kit with a sensor on an edge surface of the sensor wafer;

displacing the process kit in a Z-direction; and

measuring the gap distance between the sensor wafer and the process kit a second time; and

repeating the operations of displacing the process kit and measuring the gap distance until successive measurements of the gap distance are equal to each other.

10. The method of claim 9 , further comprising:

calculating a total displacement in the Z-direction of the process kit.

11. The method of claim 10 , further comprising:

calculating an erosion rate from the total displacement in the Z-direction of the process kit and a number of device substrates that were processed.

12. The method of claim 11 , further comprising:

storing the erosion rate in a database.

13. The method of claim 9 , wherein the sensor is a capacitive sensor.

14. The method of claim 13 , wherein the capacitive sensor is a self-referencing capacitive sensor.

15. The method of claim 14 , wherein the capacitive sensor comprises a first pad and a second pad, and wherein current supplied to the first pad has an output phase that is 180 degrees from an output phase of current supplied to the second pad.

16. The method of claim 13 , wherein the capacitive sensor extends above the top surface of the sensor wafer.