Gold-Aluminum Intermetallics: Ball Bond Shear Testing and Thin Film Reaction Couples

The gold-aluminum intermetallic phases are known to contribute to the long term degradation of gold wire ball bonds to aluminum metallization on semiconductor devices. The properties of these intermetallics were investigated through two techniques: 1) ball bond shear testing and 2) preparation of known intermetallic compositions by using thin film Au-Al diffusion couples. The influence of thermal aging on gold ball bonds attached to aluminum metallization (on both Si and SiO2) was determined through ball shear measurements. The strength of gold wire bonds made to films of Au-Al intermetallics was similarly measured. Failure mode analyses of the sheared bonds for the various systems examined are presented. The effect of a nondestructive ball shear test on the ultimate ball shear strength is given. Ultraviolet (UV)-ozone cleaning of the aluminum prior to gold wire bonding is discussed in light of Auger spectroscopy of the aluminum oxide formed on the surface. The effect of shearing direction relative to the direction of the ultrasonic scrubbing was also examined.