Study on Growth Processes of Subnanometer Particles in Early Phase of Silane RF Discharge

Growth processes of particles formed in an early phase of silane RF plasmas are investigated using the modified Langmuir probe, spectroscopic and photodetachment methods. From the probe measurements, the particles are estimated to be on the order of subnanometer size, and they are found to nucleate and grow principally around the plasma/sheath boundary near the RF electrode, where optical emission intensity of SiH radicals is high. These spatial profiles are different from those of positive and negative ion densities during discharging periods. These results suggest that many short-lifetime neutral radicals are necessary for the nucleation and subsequent growth of a particle. The photodetachment experiments and scanning electron microscope (SEM) observation also show that the particles are in the size ranges below about 200 atoms and about 1 nm. Spatial profile measurements of probe currents and negatively charged particle density obtained by the photodetachment method confirm that the mass of the particles around the plasma/sheath boundary near the RF electrode is large.