Modeling complex chemistry using a 0-D kinetic model

Many problems in plasma processing involve complex chemistries with neutral and multiply charged species. Furthermore, these complex chemistries may involve hundreds of reactions. For low pressures ( 40 mTorr), a kinetic model provides advantages over other modeling methods (e.g. fluid models). The first advantage is that at low pressures, the plasma distribution functions are often non-Maxwellian, which can be modeled correctly with kinetic models. The second advantage is that collisions are modeled correctly with kinetic models. Lastly, kinetic models correctly model sheaths at plasma-surface boundaries. Therefore, kinetic models can correctly provide diagnostics such as the angular-energy distribution function at plasma-surface boundaries. The most common kinetic approach to modeling low pressure plasma processing problems is with the Particle-in-Cell (PIC) method with Monte-Carlo collisions (MCC). However, including hundreds of reactions in a kinetic model requires intensive computation both for the computation of the reactions and because more particles are needed to correctly model the reactions using MCC. This presentation discusses a kinetic global model that uses Monte-Carlo collisions to determine the reaction rates. The global kinetic model imposes a sheath boundary condition that allows modeling conditions similar to multi-dimensional PIC-MCC models of plasma chambers. A constant-power, out-of-plane source term allows the simulations to reach steady state in several milliseconds. We present steady state reaction rates and densities of all fluid and kinetic species of Ar and Ar/Cl₂ plasmas. We also compare results between the kinetic 0-D model and a fluid-based global model. This capability allows for reduction of the complete reaction set to include only the dominant reactions.