Investigation of the mechanical characteristics of the Cu/low-k BEOL under wire bonding process loading

Wire bonding is a key integrated circuit (IC) interconnect technology, and it adheres metal wires to the IC pad and substrate by applying significant compression and energic loading. On the other hand, the Cu/low-k technology of the advanced IC industry is driven by the market demands of small size, and low resistance-capacitance delay applications. Because material properties of Cu/low-k back end of line (BEOL) exhibit significant differences from the conventional Al-based system, 3 new reliability failure modes are introduced after the wire bonding process, including the Al pad lift, Cu pad lift and the nanoscaled Cu diffusion barrier crack. To study the mechanical characteristics of the Cu/low-k BEOL under the wire bonding process loading, this research establishes a set of transient numerical models with mesh control and computation acceleration techniques. The mechanical characteristics of the wire bonding process and the differences between the conventional and Cu/low-k BEOLs are analyzed via the detailed analysis of the historical stress plots over the wire bonding process time. Moreover, the risks of wire bonding induced the failure modes against different Cu/low-k designs are studied by the proper mechanical indices, and optimized design trends are suggested.