Interferometer sensor for determination of plasma enhanced chemical vapor deposition characteristics

This article addresses the use of an interferometer to study the plasma characteristics of the Florida Institute of Technology's low temperature, low frequency, Plasma Enhanced Chemical Vapor Deposition (PECVD) system. The main body of this work consists of the design, construction, and interface of an interferometer with the PECVD system to act as a sensor for the monitoring and eventual control of some silicon nitride film characteristics. Design considerations of major components and interface requirements are discussed as well as interferometer and plasma mathematics. It was found that the interferometer performed well in the study of plasma density in a pure nitrogen plasma. The density could be easily monitored and controlled, however the addition of silane to the nitrogen gas resulted in an interferometer readout that indicated a constant non-controllable plasma density.