The H-content dependence of 22Na diffusion in amorphous hydrogenated films was studied at 350, 375 and 400C. It was found that the diffusion profiles of Na in SiN films exhibited a short Gaussian region and a shallow linear region. The results were explained in terms of a structural model which treated the material as a 2-phase mixture of a highly-ordered Si3N4-like phase and a highly disordered phase. The Gaussian region of the profile was attributed to bulk diffusion through the Si3N4-like phase and the shallow linear region was attributed to fast diffusion through the interfacial region. At 400C, the fast diffusion was some 1000 times greater than bulk diffusion. At 80C, the fast diffusion was some 105 times slower than bulk diffusion. The large change in the ratio of the diffusion coefficients was attributed to the large difference in the activation energies for the 2 mechanisms. That is, the activation energy for bulk diffusion was about 1.8eV, and the activation energy for fast diffusion was about 2.6eV. The latter value was due to the association of diffusing Na+ ions with (N-Si-N)- groups to form a Na-N-Si-N complex. This interaction required about 1.2eV. Only one region was found in the case of O diffusion profiles, and this was attributed to bulk diffusion. The magnitude of, and activation energy for, O diffusion was markedly dependent upon the O content; such that:

Do (cm2/s) = 3.8 x 10-18exp[0.15 O(%)]

E (eV) = 1.8 + 0.01[O(%)]

Thus, the activation energy decreased from about 1.8 to 1.3eV when the O content of the film was increased from 0 to 25%.

J.W.Osenbach, S.S.Voris: Journal of Applied Physics, 1988, 63[9], 4494-500