Modelling of microwave plasma sources: potential and applications

Low-temperature, non-equilibrium plasmas form the basis of a growing variet y of plasma-related processes. The demand for high-density plasmas over a w ide pressure range has stimulated the development and use of microwave plas ma sources in the last few years. Depending on the specific application, qu ite different and specialized sources have emerged. Other than empirical tr ial and error methods, computer simulations drastically reduce the time and effort needed to optimize the power coupling and distribution into a given gas. The computation of electromagnetic fields in plasma sources, including the plasma as a lossy dielectric, is a practical (though not self-consistent) a pproach yielding valuable insight on a short time-scale. Finite integral me thods (FIMs) have proven to be powerful tools because they may be interpret ed as a discrete analogue representation of Maxwell's equations in the comp utational grid. We have already developed and optimized a whole family of slot antenna micr owave plasma sources (SLANs) based on such an approach. Our work included t hree-dimensional numerical simulations of the coupling structures and imped ance matching in the time and frequency domains. For the smallest source mu SLAN geometry-dependent resonances were also identified, suppressed or enh anced to improve plasma ignition and power coupling. In that case the drivi ng force was to use these sources more efficiently for time-modulated power flow, which is becoming very attractive for advanced plasma-based material s processing. The insight gained from our smallest source type mu SLAN has also been succ essfully applied to model larger plasma sources with diameters of up to mor e than 0.5 m and predict their performance at realistic working parameters before construction. Examples of these approaches as well as performance da ta will be given.