Modeling of rapid particle growth by coagulation in silane plasma reactor

초록

The rapid particle growth by coagulation of particles in silane plasma reactor was analyzed, considering the Gaussian distribution function for particle charges. The model equations for particle growth were based on the experimental observations that the large predator particles of a few hundred nms are quite monodisperse and are composed of many small, tiny protoparticles of a few nms. The effects of process conditions such as protoparticle size, residence time, and mass generation rates of predator and protoparticles on particle growth in plasma reactor were analyzed theoretically. Based on the Gaussian distribution function of particle charges, most of the large predator particles in plasma reactor are found to be charged negatively, but some fractions of small, tiny protoparticles are in neutral state or even charged positively. Significant amount of negative charges in plasma reactor exist on the protoparticles. The predator particles charged negatively are believed to coagulate very fast with the protoparticles charged positively. The predator particle size and average charge per predator particle increase with time. The protoparticle concentration increases at first by the faster generation rate than the disappearance rate by coagulation and decreases later by the faster coagulation rate with predator particles and reaches the steady state. The predator particle concentration increases with time in the beginning as predator particles are generated and reaches the steady state later by the balance of generation and disappearance rates. As the protoparticle size decreases, predator particle size increases more quickly by the faster coagulation with protoparticles of higher concentration. As the residence time increases, or as the mass generation rate of protoparticles increases, the protoparticle concentration and the predator particle size increase more quickly. As the mass generation rate of predator particles increases, the predator particle concentration increases and the number of protoparticles per predator particle decreases and the predator particle size becomes smaller. The model results of rapid particle growth by coagulation in this study are found to be in close agreement with the published experimental results. © 2000 American Institute of Physics.