In the present study, diffusion phenomena in titanium/gold (Ti/Au) thin films occurring at temperatures ranging between 200 and 400C were investigated. The motivation was twofold: the first objective was to characterize Ti diffusion into Au layer as an effect of different heat-treatments. The second goal was to prove that the implementation of a thin titanium nitride layer between Ti and Au could remarkably reduce Ti diffusion. It was observed that Ti atoms could fully diffuse through polycrystalline Au thin films (260nm thick) already at temperatures as a low as 250C. Starting from secondary ion mass spectroscopy data, the overall diffusion activation energy ΔE = 0.66eV and the corresponding pre-exponential factor D0 = 5 x 10−11cm2/s were determined. As for the grain boundary diffusivity, both the activation energy range 0.54 < ΔEgb < 0.66eV and the pre-exponential factor s0Dgb0 = 1.14 x 10−8cm2/s were obtained. Finally, it was observed that the insertion of a thin TiN layer (40nm) between gold and titanium acts as an effective diffusion barrier up to 400C.

Titanium Diffusion in Gold Thin Films. W.E.Martinez, G.Gregori, T.Mates: Thin Solid Films, 2010, 518[10], 2585-91