Effects of Al Pad Deformation and TiW Barrier Layer on Copper-to-Silicon Diffusion and Intermetallic Compound Formation in Copper Wire Bonding

Abstract

Cu wire bonding attracts great attention in recent years due to its many advantages over Au and Al wire bonding. However, Cu is a fast diffuser in Si compared with Au and Al and may impose more threats to Si devices. Therefore, Cu-to-Si diffusion and its correlation with intermetallic compound (IMC) formation in wire bonding should be investigated. In this study, Cu-to-Si diffusion and IMC formation are studied in real diode devices. The effect of Al pad deformation to Cu 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. Secondary ion mass spectrometry depth profiling is carried out for diffusion characterization and cross sections of the wire bonded samples are made for IMC observation and measurement.