RF voltage-current probes mounted between the matching network and the plasma can detect plasma impedance changes at the fundamental and harmonic RF frequencies. The plasma impedance is very sensitive to any electrical, chemical, mechanical and/or geometrical changes that may occur in the reactor. The nonlinear nature of the plasma impedance generates a rich harmonic spectrum, accurate measurement of which can be used to precisely detect faults that affect the workpiece being processed, often leading to a scrappage event. In addition to fault detection, endpoint detection is also achieved with plasma impedance monitoring and harmonic monitoring.
Since plasma impedance changes can be monitored indirectly via the plasma harmonic emission, this opens a new area of non-invasive diagnostics. In this application note, Impedans introduces its product, the Moduli | RF Spectrometer, built on the Impedans’ Octiv VI probe platform. The applications demonstrated for this product so far include air leak detection, wafer misplacement detection, endpoint for deposition and etch processes, and general plasma performance monitoring. This note will explain how the RF Spectrometer operates and will focus on the Endpoint Detection application, for both chamber cleaning endpoint and small open area etch endpoint detection.