6 - Microwave Plasma Disk Processing Machines

Abstract

This chapter discusses the concepts of microwave high density plasma machine. The emphasizes the status of a microwave high density plasma machine concept that was invented and developed at Michigan State University (MSU), which is sometimes referred to as the microwave plasma disk reactor (MPDR). It briefly outlines the historical development of microwave discharge technology at MSU, and defines a generic microwave plasma processing machine, describing several specific realizations of microwave plasma machines It adopts a more engineering-oriented approach in summarizing the state-of-the-art microwave discharge technology. It recognizes that the microwave discharge itself is only a part of a larger microwave plasma/vacuum processing system which is identified as a microwave plasma processing machine. Microwave discharge itself is only a part of a larger microwave plasma/vacuum processing system, which is identified as a microwave plasma processing machine. This plasma machine that is sometimes referred to as the microwave plasma disk reactor, utilizes several design approaches that result in an electrically efficient, physically compact, and user-friendly plasma machine. One feature of this plasma machine is the use of a resonant cavity applicator with internal tuning. This type of applicator enables specific and pre-chosen electromagnetic modes to be impressed and efficiently focused into the discharge chamber. This allows simple discharge ignition, and by length and coupling probe tuning of the cavity, produces rapid automatic impedance matching of the plasma machine as the process variables are changed. Such a machine is capable of matching microwave power into disk or cylindrical discharge volumes over pressure regimes of several mtorr to over 300 torr. If lower pressure operation is required, it is useful to improve the coupling of microwave energy to the plasma by adding a static magnetic field to create electron cyclotron resonance zones inside the discharge volume. Then, at low pressures, microwave coupling efficiency and discharge stability are improved.