Gold diffusion and intermetallic formation in Au/Al2O3/Al film

Diffusion across the Al2O3 film in the Au/Al2O3/Al film system (the Al film with 1 mu m 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 degrees and 500 degrees C 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 degrees 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 Bu 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 O-18 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 O-2 to the Al2O3 film through Au film.