Identifying the weakest interface in BEOL structures

This study investigates the interfacial adhesion between thin films in back-end-of-line (BEOL) structures, including Cu electrodes, capping (Cap) layers, and inter-metal dielectric (IMD) layers. The adhesion energies of the Cu–Cap, Cu–IMD, and IMD–Cap interfaces are measured using a double cantilever beam (DCB) fracture mechanics test. Specifically, various process and material parameters affecting interfacial adhesion are investigated by categorizing them into the following: (1) surface treatments for the Cu–Cap interfaces with two different Cap materials, (2) the dielectric constants of IMD materials for the Cu–IMD interfaces, and (3) deposition sequences for the IMD–Cap interfaces. Moreover, the mechanisms underlying the measured adhesion are thoroughly explored by analyzing the chemical and physical bonding characteristics at each interface. Finally, the weakest interface in BEOL structures is identified based on the experimentally measured adhesion energies and numerical simulation results. We believe that these findings will provide critical insights into enhancing the interfacial reliability of BEOL structures through optimized material selection and process refinement.