Modeling electromagnetic fields for the excitation of microwave discharges used for materials processing

Abstract
Low-pressure/high-density and moderate-pressure microwave plasma sources are finding increased use in a variety of materials processing applications. Several design variations have been developed using microwave excitation of the plasma discharges including permanent magnet and electromagnet ECR (electron cyclotron resonant) sources, resonant cavity sources, waveguide-excited sources, and surface wave sources. A central issue to understanding and modeling these sources is obtaining a self-consistent solution of the electromagnetic fields and plasma discharge behavior. A variety of numerical techniques have been applied to this problem by researchers including the finite difference time domain (FDTD) method, ray tracing calculations, finite element solutions of the wave equation, and other wave propagation-absorption solutions. In each of these solution methods, plasma parameters including electron density and electron collision frequencies must be known or solved self-consistent to determine the electromagnetic fields. This paper reviews the status and presents examples of electromagnetic field modeling solutions for microwave plasma sources used in materials processing.