Modeling of the formation of cationic silicon clusters in a remote Ar/H-2/SiH4 plasma

Cationic silicon clusters, containing up to ten silicon atoms, have been me asured by mass spectrometry in an argon/hydrogen/silane expanding thermal p lasma. A quasi-one-dimensional model, based on the idea that the clustering process initiated by argon or hydrogen ions depends on the path length of the plasma in the deposition chamber and on silane density, is presented. T he chemistry is described by ion-molecule reactions between the formed clus ters and silane and by dissociative recombination. The model is able to rep roduce fairly well the experimental data for various plasma conditions. It is shown that reaction rates for the clustering process do not strongly dep end on the number of silicon atoms in the cluster. This result is in contra st with rates published in the previous literature. For the conditions inve stigated, the consumption of silane by cationic cluster formation is not si gnificant. The contribution of neutral clusters is investigated and recombi nation proves to be an important process. (C) 2000 American Institute of Ph ysics. [S0021-8979(00)03808-1].