In this paper, we present a novel broadband radio frequency (RF) sensor technology, which can be used for plasma process control, including Fault Detection and Classification (FDC). Plasma is a non-linear complex electrical load, therefore generates harmonics of the driving frequency in the electrical circuit. Plasma etch processes have dependencies on chamber pressure, delivered power, wall and substrate temperatures, gas phase and surface chemistry, chamber geometry and particles, and many other second order contributions. Any changes, which affect the plasma complex impedance, will be reflected in the Fourier spectrum of the driving RF power source.
We have found that high-resolution broadband sensing, up to 1GHz or more than 50 harmonics (for a fundamental frequency of 13.56MHz), greatly increases the effectiveness of RF sensing for process-state monitoring. This paper describes the measurement sampling technique; the broadband RF sensor and presents data from commercial plasma etch tool monitoring.