Amorphous silicon nitride films, 500 and 700nm thick, were deposited on Eurofer substrates by applying reactive radio-frequency magnetron sputtering from pure Si targets in an argon/nitrogen atmosphere. The hydrogen permeation through such double-layered, 40mm diameter membranes at 400C and 1bar upstream pressure involved the use of a conventional technique with enhanced sensitivity. The extremely high barrier efficiency for these films with respect to hydrogen, expressed as a permeation-reduction factor in excess of 2000, was only achieved with films containing 6 to 7at%H. The achieved permeation-reduction factor at 400C corresponds to the permeability of silicon nitride, which was as low as P = 10−17mol H2/msPa0.5. The hydrogen concentration was determined with an Elastic Recoil Detection Analysis, which indicated that this high concentration represents only the strongly bound hydrogen that was not mobile at this low temperature, but impedes the mobility of the diffusive hydrogen. A silicon nitride film with a low hydrogen content was a far less efficient barrier, which supports the role of the strongly bound hydrogen.

Hydrogen Permeation through Silicon Nitride Films. V.Nemanič, P.J.McGuiness, N.Daneu, B.Zajec, Z.Siketić, W.Waldhauser: Journal of Alloys and Compounds, 2012, 539,184-9