9 - Nucleation in Plasmas

Summary

Particle nucleation in plasmas occurs under a wide range of conditions. In some cases, such as thermal plasma synthesis of metal nanoparticles, nucleation may follow the conventional scenarios of single-component homogeneous or ion-induced nucleation. In other cases, such as dust formation in nonthermal plasmas of the type used in semiconductor processing, the paths to nucleation are specific to the chemistry of the gases introduced into the processing chamber. In such cases, nucleation typically involves a mix of phenomena that combine chemical nucleation with plasma physics, with the chemistry being driven by electron impact, and the charging of small clusters by free electrons and ions playing an important role in cluster growth. The charging and transport of clusters and particles affect the electric field profile, causing the plasma and the aerosol phase to be strongly coupled. An example is considered of silicon particle nucleation in silane-containing plasmas, the most studied system because of its importance in semiconductor processing. Cluster growth in this system is dominated by reactions between anion clusters and neutral molecules.