Initial growth kinetics of positive and negative hydrogenated Si cluster ions under the presence of silane radicals

We investigated the time evolution of SinHx +/- ion populations in an ion trap filled with SiH4 and He buffer gas to elucidate the roles of silane ions and radicals generated by an electron shower. The initial growth of SinHx +/- ions is accelerated by SiH2 until n = 3 for cations and n = 2 for anions, where the radical effect diminishes because further Si-addition is inhibited by reverse reactions. Through reactions with SiH4, the cations reach lessreactive n = 5 with large H contents and further growth significantly slows, while the anion growth completely stops at n = 2 because SinHx- is not reactive with SiH4. This anion inertness is attributed to instability of the hydrogen-bonded reaction intermediates based on ab initio calculations. Hence the ionization is not a promoting factor but the SiH2 insertion into neutral SinHx is the major pathway for cluster growth in silane plasmas. (C) 2019 The Japan Society of Applied Physics