Roles of SiH3 and SiH2 Radicals in Particle Growth in rf Silane Plasmas

Abstract

Temporal evolutions of spatial profiles of SiH3 radicals, radical production rates, short-lifetime radicals and particle amount in rf silane plasmas are studied using various methods including infrared-diode-laser-spectroscopic and laser-light-scattering methods. Based on the results, contributions of SiH3 and SiH2 radicals to particle growth are discussed. Particles nucleate and grow, from beginning of their growth, principally around the plasma/sheath boundary near the powered electrode. The spatial profile of the particle amount is very similar to those of the densities and production rate of short-lifetime radicals. A density of SiH3 radicals amounts to about 1012 cm-3, and its spatial profile is fairly flat between the electrodes from the discharge initiation. These results suggest that the particle species responsible for the nucleation of particles is not SiH3 but radicals such as SiH2, which is highly reactive and produced at a high rate. The SiH2 radicals react quickly with Sin H2n +2 (n=1, 2,…) to form polymerized species. Among them, the higher-order polymerized species absorb the lower-order ones produced later, and consequently suppress further nucleation of particles. While the contribution of SiH3 radicals to particle nucleation and subsequent initial growth is not so important, they may affect the deposition rate of film on the substrate when the particle radius increases to about 10 nm.