Comparative studies on oxygen diffusion coefficients for amorphous and γ-Al2O3 films using 18O isotope

We systematically investigated the oxygen diffusion in both amorphous and gamma-Al2O3 films using 180 as a tracer and observing depth profiles by secondary ion mass spectroscopy. The oxygen diffusion coefficients for amorphous Al2O3 films were two or three orders of magnitude larger than those of the gamma-Al2O3 films. The activation energies of about 1.2 eV for both films were considerably lower than those for bulk alpha-Al2O3. These results could be explained by the difference in Al2O3 structure: alpha-Al2O3 has a dense corundum structure while gamma-Al2O3 has a defective spinel structure with cation site vacancies. We found that the amorphous Al2O3 films prepared by atomic layer deposition could function as a barrier layer against oxygen diffusion only within a limited range of heat treatment conditions.