Wire bonding on a novel immersion gold capped copper metallized integrated circuit

The objective of this research work is to investigate alternative cap metallization, compatible with wire bonding interconnection, for dual damascene Cu metallized ICs. Several selective cap metallization methods, such as immersion Ag, electroless Ni immersion Au (ENIG), and immersion Au plating are evaluated in this study. This paper reports a novel approach to cap dual damascene back end of line (BEOL) Cu metallization by a direct immersion Au (DIG) plating method and its investigation on the Au wire bondability. The Cu-Au thin film metallization is qualified by theoretical and experimental diffusion characterization methods. A fine pitch (60 μm) Au wire bonding process is established for immersion Au capped test vehicles. The wire bond interconnects are characterized by ball shear test, wire pull test and a high temperature storage (HTS) reliability study using analytical tools such as optical microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). This paper also compares and reports the Au wire bonding on immersion Au cap metallization with the classical Au-aluminum (Al) system.