Effects of heat treating Au/Ni thin film composites in various ambients

Morphology changes and oxide formation for 100 nm gold films over 60 nm nickel films deposited on SiO 2 (300 nm of SiO 2 on silicon wafers) have been studied in ambients of H 2, O 2, air, N 2, helium and argon temperatures between 250 and 500°C and times of 5 min-4 h. Composition rearrangement was analyzed using Rutherford backscattering spectroscopy and sputter profilling Auguer electron spectroscopy, and changes in film morphology were observed using scanning electron microscopy. The data show that NiO formed very thick layers on the surface in O 2, air or inert ambients (N 2 and Ar), but not in H 2. This was explained on the basis of the heat of formation of NiO and the kinetic theory of gases. It was shown that NiO passivates the gold surface and diffusion within the oxide, rather than diffusion in the gold film, limited the oxide thickness. In addition, porosity has been observed to develop in the gold film under all oxidizing conditions. This porosity interfered with the analysis of interdiffusion and therefore prevented the determination of the mechanism and coefficients describing diffusion between nickel and gold thin films.