Diffusion across the Al₂O₃ film in the Au/Al₂O₃/Al film system (the Al film with 1 μm thickness was vapor-deposited on a SiO₂/Si substrate and exposed to the atmosphere to form a natural oxide layer, then the Au film was deposited on it.) at temperatures between 25° and 500° has been studied by using Auger Electron Spectroscopy, X-ray Photoelectron Spectroscopy and electrical resistivity measurement. The temperature where Al is detected on the surface of the Au/Al₂O₃/Al system is 100°C higher than that on the surface of the regular Au/Al system without the Al₂O₃ film. The activation energies for the intermetallic layer growth of the Au/Al₂O₃/Al system and the Au/Al system are 110 and 72 kJ/mol, respectively. The Al₂O₃ film formed by the exposure in air (ca. 3.2 nm in thickness) acts as a barrier for diffusion in Au/Al. In addition, we observed the SEM image of cross section of the Au/Al₂O₃/Al system. The Au-Al intermetallic layer is formed in the Al layer in the initial stage of Au/Al₂O₃/Al diffusion by Au diffusion through the Al₂O₃ film into the Al layer.
On the other hand, we studied the effect of annealing environment on the diffusion for the Au/Al₂O₃/Al system by using ¹⁸O as tracer for SIMS analysis. The Au-Al intermetallic layer grows in an island formation for the Au/Al₂O₃/Al system and when annealed in air, the number of islands decreases. Because, during heat treatment in air, the Al₂O₃ film is formed continuously by supply of O₂ to the Al₂O₃ film through Au film.