The Reduction of Au-Al Intermetallic Formation and Electromigration in Hydrogen Environments

A series of experiments to determine the effect of the environment on gold-aluminum intermetallic compound formation have been carried out. The results of these experiments led to an investigation of the effect of the envirorment on electromigration in aluminum. Bond pull tests as well as SEM examination were done on commercial IC packages. After removing the lid, the packages were heated (350 or 400°C) in hydrogen or argon (0.5 atm) for 1 to 150 hours. The results of the bond pull tests (150 bonds per test) show a drastic deterioration in bond strength for the specimens heat treated in argon. Failure for the hydrogen treated specimens occurred almost entirely at the wire span. The SEM examination showed the formation of Au-Al intermetallics in the specimens treated in argon. The specimens treated in hydrogen showed little or no compound formation. In order to confirm the results of these experiments substrates of silicon, thermally oxidized silicon, nitrided silicon and sapphire were coated with aluminum films (4200 Å thick) across one half the surface. Gold films (8200 Å thick) were deposited on these same substrates such that there was a 2 mm gold overlap on the aluminum. These specimens were then heated (350 or 400°C) for 1-3 hours in half atmospheres of H2, Ar, O2, N2, He or air and examined in an SEM.