Long range capacitive gap measurement in a wafer form sensor system

1. A sensor wafer, comprising:

a substrate, wherein the substrate comprises a first surface and a second surface opposite the first surface;

a first conductive pad with a first surface area, wherein the first conductive pad has a surface that is substantially coplanar with the first surface of the substrate, and wherein an edge of the first conductive pad that faces an edge of the substrate has a curvature that matches a curvature of the substrate; and

a second conductive pad with a second surface area that is smaller than the first surface area, wherein the second conductive pad has a surface that is substantially coplanar with the first surface of the substrate, and wherein an edge of the second conductive pad that faces an edge of the substrate has a curvature that matches the curvature of the substrate.

2. The sensor wafer of claim 1 , wherein the second surface area is at least 5% smaller than the first surface area.

3. The sensor wafer of claim 1 , further comprising:

a plurality of first conductive pads; and

a plurality of second conductive pads.

4. The sensor wafer of claim 3 , wherein the first conductive pads and the second conductive pads are arranged in an alternating pattern around a perimeter of the substrate.

5. The sensor wafer of claim 1 , further comprising:

an electric field guard around the perimeters of the first conductive pad and the second conductive pad.

6. The sensor wafer of claim 1 , wherein a shortest distance between an edge of the first conductive pad or an edge of the second conductive pad and an edge of the substrate is at least 1 inch.

7. The sensor wafer of claim 1 , further comprising:

a control module embedded in the substrate, wherein the control module comprises circuitry for sensing a distance between the first surface of the substrate and a surface external to the sensor wafer opposing the first surface using the first conductive pad and the second conductive pad.

8. The sensor wafer of claim 7 , wherein the circuitry provides an output phase of the first conductive pad that is 180 degrees offset from an output phase of the second conductive pad.

9. The sensor wafer of claim 7 , wherein the distance between the first surface of the substrate and a surface external to the sensor wafer is up to 1.5 inches.

10. The sensor wafer of claim 9 , wherein an accuracy of the measured distance is at least +/−0.0005 inches.

11. The sensor wafer of claim 7 , wherein the control module further comprises a wireless communication module, wherein the wireless communication module transmits measurement data to an external device.

12. A method for measuring a gap between a showerhead and a support surface in a processing chamber, comprising:

pumping down a processing chamber, wherein the processing chamber comprises a support surface and a showerhead opposing the support surface;

placing a sensor wafer on the support surface, wherein the sensor wafer comprises a first conductive pad with a first surface area and a second conductive pad with a second surface area that is smaller than the first surface area;

measuring a gap between the sensor wafer and the showerhead with the first conductive pad and the second conductive pad, wherein measuring the gap comprises providing an output phase to the first conductive pad that is 180 degrees offset from an output phase of the second conductive pad; and

removing the sensor wafer from the processing chamber without venting the processing chamber.

13. The method of claim 12 , wherein the gap between the sensor wafer and the showerhead is greater than 1 inch.

14. The method of claim 13 , wherein an accuracy of the measured gap between the sensor wafer and the showerhead is at least +/−0.0005 inches.

15. The method of claim 12 , wherein the sensor wafer comprises a plurality of first conductive pads and a plurality of second conductive pads.

16. The method of claim 15 , wherein the gap between the showerhead and the sensor wafer is measured in a plurality of locations to provide a parallelism measurement.

17. A sensor wafer, comprising:

a substrate, wherein the substrate comprises a first surface and a second surface opposite the first surface;

a plurality of first conductive pads with a first surface area, wherein the first conductive pads have surfaces that are substantially coplanar with the first surface of the substrate;

a plurality of second conductive pads with a second surface area that is smaller than the first surface area, wherein the second conductive pads have surfaces that are substantially coplanar with the first surface of the substrate, wherein the first conductive pads and second conductive pads are arranged radially around the substrate in an alternating pattern, and wherein outer edges of the first conductive pads and outer edges of the second conductive pads are equidistant from an edge of the substrate; and

a control module embedded in the substrate, wherein the control module comprises circuitry for sensing a distance between the first surface of the substrate and a surface external to the sensor wafer opposing the first surface using the first conductive pads and the second conductive pads.

18. The sensor wafer of claim 17 , wherein the circuitry provides an output phase of the first conductive pads that is 180 degrees offset from an output phase of the second conductive pads.

19. The sensor wafer of claim 17 , wherein the distance between the first surface of the substrate and a surface external to the sensor wafer is up to 1.5 inches.