Characteristics of Copper-to-Silicon diffusion in copper wire bonding

The replacement of Au and Al wires with Cu wires in wire bonding has become an emerging trend in IC packaging nowadays. Although some research works have been carried out for the applications of Cu wire bonding, they are mainly focused on the processing and material issues of Cu wire bonds. However, the Cu in the wire bonds may diffuse into the Si chip and impose reliability threats to the silicon devices. There is no study yet on the Cu-to-Si diffusion in Cu wire bonding. In the present study, Cu-to-Si diffusion in the wire bond is studied in real diode devices. The effect of Cu source supply and Al pad deformation on Cu-to-Si diffusion is investigated with the aid of lab made multilayer structure. The samples with and without titanium-tungsten (TiW) barrier layer is adopted to study the barrier layer effect. Au wire bond samples are prepared for parallel comparison with Cu wire bond samples. Secondary ion mass spectrometry (SIMS) depth profiling is implemented for diffusion characterization.