Improved utility of microwave energy for semiconductor plasmaprocessing through RF system stability analysis

摘要

Summary form only given. One of the major drawbacks of usingmicrowaves for plasma processing is the inherent instability of typicalmicrowave powered plasma systems. Any RF/microwave powered plasma systemcomprised of a nonlinear plasma, launched by a resonant antenna system,impedance matched by a resonant circuit or cavity, and powered by anRF/microwave generator with a complex source impedance is invariablyunstable over some operating conditions. For microwave systems, thisinstability typically manifests itself as a propensity for the plasma toextinguish or rapidly change to an undesired intensity as the impedancematching device is brought to best tune or a process transitschemistries. This paper shows through modeling and control analysis whythis instability exists, leading to knowledge of how a system can bedesigned to achieve a higher degree of stabilization in a preferredoperating regime. This paper: (1) defines stability as it applies to anRF/microwave driven plasma-processing system; (2) defines a method ofquantifying stability; (3) gives a brief background via a summary ofpast stability studies; (4) establishes a new set of variables andcriterion for stability; (5) introduces a Matlab Simulink model tosimulate a typical microwave driven plasma system and (6) shows howmodifying an RF/microwave generator's source impedance can modify plasmasystem stability