Metrology methods to detect plasma in wafer cavity and use of the metrology for station-to-station and tool-to-tool matching

A process chamber for detecting formation of plasma during processing of a semiconductor wafer, the process chamber comprising,

• an upper electrode, the upper electrode including a plurality of inlets for supplying a gas chemistry to the process chamber, the upper electrode connected to a radio frequency (RF) power source through a match network to provide RF power to generate a plasma;
• a lower electrode for supporting the semiconductor wafer, the lower electrode is disposed within the process chamber so as to define a wafer cavity between a surface of the upper electrode and a top surface of the lower electrode, wherein the lower electrode is electrically grounded;
• and
• a coil sensor disposed at a base of the lower electrode that extends outside the process chamber, the coil sensor disposed to substantially surround the base of the lower electrode, the coil sensor configured to measure characteristics of RF current conducting through the wafer cavity and to exclude current due to parasitic plasma and parasitic capacitive coupling to ground, the characteristics of RF current used to confirm generation of the plasma within the wafer cavity.