Formation of large positive silicon-cluster ions in a remote silane plasma

The formation of hydrogen poor cationic silicon clusters SinHm+ with up to ten silicon atoms in an expanding argon-hydyogen-silane plasma has been stu died by mass spectrometry and Langmuir probe measurements. Sequential clust ering reactions with silane, initiated by silane ions, cause their size to depend on the product of silane density and geometrical path length having possible implications for a-Si:H films deposited by remote plasmas. Reactio n rates, estimated by a one-dimensional model, show no strong dependence on the number of silicon and hydrogen atoms present in the ions in contrast w ith rates determined by ion-cyclotron resonance mass spectrometry studies. Possible causes of the discrepandy are discussed as well as the hydrogen po verty of the clusters. The maximum contribution of the cationic clusters to the growth flux is about 6% for the conditions investigated. (C) 1999 Amer ican Vacuum Society. [S0734-2101(99)10304-X].