Absolute density of precursor SiH₃ radicals and H atoms in H₂-diluted SiH₄ gas plasma for deposition of microcrystalline silicon films

Microcrystalline hydrogenated silicon films were produced at a high deposition rate of about 2 nm/s by using a capacitively coupled plasma under a practical pressure of around 1 kPa. The SiH₄ source gas was almost fully dissociated when highly diluted with H₂ gas, and the dominant species in the gas phase were found to be SiH₃ radicals, which are film-growth precursors, and H atoms. The absolute density of these species was measured as the partial pressure of SiH₄ gas was varied. With the increasing SiH₄ gas flow rate, the SiH₃ radical density, which was on the order of 10¹² cm⁻³, increased linearly, while the H-atom density remained constant at about 10¹² cm⁻³. The film growth mechanism was described in terms of precursors, based on the measured flux of SiH₃ radicals and H atoms, and the relative fraction of higher-order radicals.