Non-Invasive Measurement Of Ion Currents In Plasma Assisted Processes Using An Optical Fiber Faraday Ring Ammeter

The efficiency of plasma assisted deposition processes such as reactive ion plating, with regard to the densification of the deposited thin films, depends strongly on the arrival rate ratio of ionized species (atoms, molecules) to the total influx of vaporized coating material. While it is relatively easy to measure ion beam currents produced by an auxiliary ion beam source (for example a Kaufman gun), it is much more difficult to meausre ion currents in plasma processes. Typical probe measurements change the plasma conditions almost instantaneously. An optical fiber Faraday ring ammeter initially developed for space plasma research provides for a non-invasive measurement of ion currents present in plasma assisted deposition processes. We will be discussing the principles and the potential use of such a device in a high vacuum boc coater equipped for low voltage reactive ion plating deposition