Numerical studies of synthesis of silicon nanoparticles in capacitively-coupled radiofrequency plasmas

Abstract

The formation and growth of silicon nanoparticles (SiNPs) (diameter < 5 nm) in plasmas is being investigated due to many potential applications, including biomedical devices, renewable energy, and photovoltaics. Although experimental synthesis of SiNPs has had success in optimizing the process, the formation mechanisms are not yet fully understood. We have developed a two dimensional numerical model for synthesis of SiNPs in a capacitively-coupled radio frequency (RF) plasma which we have used to investigate mechanisms for particle growth and charging in Ar/He/SiH4 gas mixtures. Algorithms for the kinetics of nanoparticle formation were self-consistently embedded in a plasma hydrodynamics simulation to account for SiNP nucleation, growth, charging, and transport. A silicon hydride reaction mechanism was used to self-consistently calculate rates of nucleation and radical deposition on nanoparticle surfaces. Coagulation was calculated, along with nanoparticle charge distribution and transport. The electron current to particles was self-consistently calculated with rate coefficients provided by solutions of Boltzmann's equation for the electron energy distribution, which accounts for collisions with nanoparticles.