Surface loss probabilities of hydrocarbon radicals on amorphous hydrogenated carbon film surfaces

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Abstract
The surface loss probabilities of hydrocarbon radicals on the surface of amorphous hydrogenated carbon (C:H) films are investigated by depositing films inside a cavity with walls made from silicon substrates. This cavity is exposed to a discharge using different hydrocarbon source gases. Particles from the plasma can enter the cavity through a slit. The surface loss probability β is determined by analysis of the deposition profile inside the cavity. This surface loss probability corresponds to the sum of the probabilities of effective sticking on the surface and formation of a nonreactive volatile product via surface reactions. By comparing the deposition profiles measured in CH4, C2H2, C2H4, C2H6 discharges one obtains for C2H radicals β=0.80±0.05, for C2H3 radicals β=0.35±0.1, and for C2H5 radicals β<10−3. The growth rate of C:H films is, therefore, very sensitive to any contribution of undersaturated C2Hx species in the impinging flux from a hydrocarbon discharge.