Migration across the oxide film of a Au/Al2O3/Al film system, at temperatures of between 25 and 500C, was studied by means of Auger electron spectroscopy, X-ray photo-electron spectroscopy and electrical resistivity measurements. An Al film, with a thickness of 1, was vapor-deposited onto a SiO2/Si substrate and was exposed to the atmosphere so as to form a natural oxide layer. The Au film was then deposited onto it. The temperature at which Al was detected on the surface of the Au/Al2O3/Al system was 100C higher than that for a Au/Al system without the oxide film. The activation energies for intermetallic layer growth of the Au/Al2O3/Al and Au/Al systems were 110 and 72kJ/mol, respectively. The oxide film that was formed by exposure in air (about 3.2nm thick) acted as a barrier to diffusion in Au/Al. The Au-Al intermetallic layer formed in the Al layer during the initial stages of Au/Al2O3/Al diffusion, via Au diffusion through the oxide film and into the Al layer. The effect of the annealing environment upon diffusion in the Au/Al2O3/Al system was also studied by using 18O as a tracer for secondary ion mass spectrometric analysis. The Au-Al intermetallic layer grew in island form in the Au/Al2O3/Al system and, when annealed in air, the number of islands decreased. This was because, during heat treatment in air, the oxide film formed continuously via the supply of O through the Au film.

A.Tsuge, K.Mizuno, T.Uno, K.Tatsumi: Journal of the Japan Institute of Metals, 1995, 59[11], 1095-102

Table 5

Diffusion of Al in Doped Alumina at 1180C