A CONTINUUM MODEL OF LOW PRESSURE GAS DISCHARGES

In order to understand the behavior of gas discharge or plasma chemical reactors used extensively in the microelectronics materials processing industry, it is necessary to have a model of the discharge physics. The discharge physics, in this context, consists of the charged particle (electrons, positive and negative ions) densities and energies and the self-consistent electric field. This information is required as a function of space and time in the discharge reactors. Knowledge of the discharge physics is not sufficient for a complete understanding of discharge reactor performance; neutral species chemistry and transport must also be included.; A model of discharge physics is presented in this thesis which is based on the continuum conservation equations. These equations are solved numerically for a variety of conditions: steady state dc discharges and time-dependent radiofrequency discharges at 13.56 MHz and 55 KHz. A Galerkin finite element technique for spatial variation was used in all simulations, and a variety of techniques to solve for the time dependence were used. For the 13.56 MHz simulation, a spectral method was used based on a Fourier series expansion in time. At 55 KHz, a predictor-corrector scheme was employed. The choice of time integration scheme depends upon the characteristic times of the electrons and ions and the frequency of the applied field.; Two simpler discharge models which appear to be promising in the analysis of 13.56 MHz discharges are ambipolar theory and equivalent circuit theory. Ambipolar theory appears to work well in the plasma or quasineutral region and equivalent circuit theory appears to represent the electrical characteristics of the discharge fairly well.