Plasma enhanced chemical vapour deposition of hydrogenated amorphous silicon at atmospheric pressure

Amorphous hydrogenated silicon films were grown using an atmospheric pressure helium and hydrogen plasma with silane added downstream of the source. A maximum deposition rate of 120±12 A min−1 was recorded at a substrate temperature of 450°C, 6.3 Torr H2, 0.3 Torr SiH4, 778 Torr He, 32.8 W cm−3, and an electrode-to-substrate spacing of 6.0 mm. The deposition rate increased rapidly with the silane and hydrogen partial pressures, up to 0.1 and 7.0 Torr, respectively, then remained constant thereafter. By contrast, the deposition rate decreased exponentially as the electrode-to-substrate distance was increased from 5.0 to 10.5 mm. The total hydrogen content of the films ranged from 2.5 to 8.0± 1.0 at%. These results together with a model of the plasma chemistry indicate that H atoms and SiH3 radicals play an important role in the deposition process.