Roles of SiH₃ and SiH₂ radicals in particle growth in rf silane plasmas

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 Si_nH_2n+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.