Self-consistent modeling of low pressure microwave discharges including non-collisional heating processes

Abstract

Summary form only given. Low pressure microwave plasma sources used for materials processing generally operate as overdense plasmas with the plasma density greater than the critical density. These sources can be operated with a static magnetic field that provides for ECR heating or without a static magnetic field via ohmic, resonance and other non-ohmic and stochastic heating mechanisms. Even when ECR strength magnetic fields are present these other heating mechanisms that occur in unmagnetized plasmas can be important and may even dominate. This paper examines via a two-dimensional, self-consistent microwave field and plasma model the heating of low pressure, overdense, magnetized and unmagnetized plasma discharges. Low-pressure (collision frequency /spl Lt/ excitation frequency) microwave plasma simulations that model the spatial variation of the microwave heating fields and plasma discharge are difficult to use in the local regions where the plasma frequency is near the excitation frequency. In these regions resonance effects occur and the microwave electric field can become large. Because of the localized nature of the resonance (high microwave field strength) region, stochastic (non-collisional) heating can occur as the electrons are accelerated/heated in this region and/or transverse through this resonance region via their initial momentum. This paper explores the self-consistent modeling of microwave discharges including resonance effects and stochastic heating effects. Further the models are constructed to closely match an experimental system that has been extensively characterized. This experimental system is a 2.45 GHz resonant cavity plasma source that has been studied while running argon discharges at pressures of 4-60 mTorr using Langmuir probes to determine the plasma density and electron temperature and using microwave field probes and optical diagnostic techniques to measure the microwave field strength.