Formation of highly uniform silicon nanoparticles in high density silane plasmas

Abstract

We have investigated silicon particles formed in an inductively coupled plasma (ICP) system and have measured their structural properties by electron microscopy. ICP silane plasmas are shown to be an interesting and versatile source of nanoparticles. Three regimes are mapped out: a regime of no observable particle growth at the lowest pressures, a regime of polydisperse and agglomerated particles at the highest pressures, and a regime yielding highly monodisperse particles at intermediate pressures. Our results suggest that an ICP allows this unique production of monodisperse nanoparticles at high concentrations. The particle size can be controlled from 15 to 200 nm and is determined by the plasma on time. For short plasma times, particle growth appears to be due primarily to coagulation, while in the second phase particle growth is attributed primarily to surface deposition. For H2 dilutions less than 92%, the growth rate is almost independent of H2 partial pressure. Transmission electron micrographs, however, indicate that the addition of hydrogen decreases the particle density. At higher dilution ratios, polycrystalline particles are obtained. Under all other conditions the particles are amorphous.