The transport of Al into Cu was studied by annealing Cu/Al/SiO2 layers. The samples were prepared and annealed in all-metal ultra-high vacuum systems. The in situ resistivity was used to monitor continuously the transport of Al into the bulk of the Cu films. It was observed that Al began to move into the Cu at 100 to 150C and that, during isothermal annealing, there was an initially rapid increase in the Al concentration in the Cu. This was followed by a very slow increase. Some Al remained bound at the silica interface, or at the Cu surface, and was not free to dissolve in the Cu. The data were not consistent with simple 1-dimensional bulk diffusion, but were in good agreement with a 3-dimensional model for Cu grains in which there was rapid transport to saturate grain boundaries, followed by the diffusion of Al from the grain boundaries and into the Cu grains. An important observation was that, because of the role played by grain boundaries, it was possible to transport Al through Cu films without any significant increase in the resistivity of the Cu films.

Low-Temperature Transport of Al into and through Copper Starting with Cu/Al/SiO2 Bilayers. W.A.Lanford, S.Bedell, P.Isberg, B.Hjorvarsson, S.K.Lakshmanan, W.N.Gill: Journal of Applied Physics, 1999, 85[3], 1487-95