Interface microstructure effects in Au thermosonic ball bonding contacts by high reliability wire materials

Palladium-doped and (Cu, Pt)-doped high reliability gold wires were used to form wire bond interconnects on aluminum IC metallization. By isothermal annealing of wire bond samples the formation of intermetallic Au-Al phases was stimulated. SEM/EBSD investigations of the phase regions exhibited significantly slower isothermal growth rates compared to a reference gold wire. Correlated TEM, STEM-EDXS and nanobeam diffraction analyses revealed that Pd is preferentially incorporated into the Au8Al3 intermetallic forming a new stable phase but additionally can obviously form a new Pd-rich ternary intermetallic. In comparison, Cu dopants are also accumulated into a new Al-Au-Cu phase while Pt is rather found agglomerating within grain boundaries and interfaces. These results suggest a diffusion barrier model that allows discussing how wire doping can affect the bond contact microstructure, thus increasing the lifetime of bond contacts.