Invited Paper PS-ThA8
Microwave Plasma Source Technologies: A Fifty Year Evolution from Unwanted Discharges to Free Radical Sources, to Low Pressure and Temperature Plasma Processing, to Gem Quality Diamond Synthesis

Thursday, October 22, 2015, 4:40 pm, Room 210A

Opportunities to create, to experiment with and to apply microwave plasmas occurred after world war II when high power microwave sources became commercially available. The first applications of microwave plasmas used a small, micro plasma - like discharge as a harmonic generator, i.e. these plasmas were used to generate even higher frequency electromagnetic radiation. As the understanding of how to efficiently create and maintain a discharge improved, microwave plasma sources, as they were identified at that time, were applied to numerous high and low pressure applications such as down stream and in - plasma free radical sources for thin film deposition, etching and more generally to a large variety of plasma surface treatments. Under the influence of these applications, microwave applicator and plasma source technologies rapidly evolved and became more application specialized. Initially a plasma discharge scale up was identified as a challenge, but the ability to produce large, high density microwave discharges was demonstrated. Completely new subclasses of microwave discharges, such as electron cyclotron resonance (ECR) discharges, were identified. Eventually applications, such as microwave plasma - assisted synthesis of diamond, created important new microwave plasma technologies. Certainly over the past fifty years microwave plasma sources have evolved into an important and diverse group of technologies that have broad range of material processing applications.

In this presentation, the historical evolution of microwave plasma source technologies will be briefly reviewed. The current diverse group of the technologies now known as microwave plasma source technologies will be organized into subclasses. The physics and the methods of efficiently coupling microwave energy to both high and low pressure discharges will be identified and compared. The state - of - the - art applications such as single crystal diamond synthesis and ECR discharges will be reviewed. Finally the current microwave plasma source technologies will be compared with the more common, lower frequency excited capacitive and inductive plasma sources.