Ionic species in a silane plasma

The abundances Aj of groups of higher silane ions Si jH+k were measured mass spectrometrically in an rf glow discharge in SiH4 under conditions used for preparation of hydrogenated amorphous silicon. The ratio Aj/Aj-1 is about 0.3 nearly independently of j, of pressure, of degree of ionization, and of rf power. The mean hydrogen to silicon ratio for j≥3 is 1.5±0.1 and pressure independent in the 0.017-0.100-Torr range. A mechanism postulating charge or hydride ion transfer and the addition of SiH4 as the most rapid reactions of silane ions is consistent with the observations.