The Effect of Oxygen and Argon on the Interdiffusion of Au-Al Thin Film Couples

Thin film diffusion couples were prepared by a sequential deposition of Al and Au on clean glass substrates in an ultra-high vacuum system. Aluminum was deposited at a rate of 1 nm sec¿1 to a thickness of 0.6 ¿m and then 0.12 ¿m of Au, which was shuttered to cover half of the Al film, at a rate of 0.1 nm sec¿1. Diffusion annealing of the couples was carried out at 250°C for 45 minutes in 0.5 atm. of either oxygen or argon gas. Optical and SEM examination of the couples annealed in argon showed ball-like intermetallic compound formation across the entire film, that is, even on that part of the Al film which was not covered with Au. Those films which had been annealed in oxygen showed dendritic intermetallic formation only in the region where the Au covered the Al; the uncovered Al region of the film was clean. These observations are explained on the basis of adsorbed gas and its effect on surface diffusion.