In-situ Electrothermal TEM Investigation of Electromigration in fully Embedded Cu/Co Interconnects

A novel in-situ electro-thermal TEM method is presented to observe EM Cu interconnects on Co capping and Co liner/TaN barriers. In order to suppress the surface diffusion induced by metallic contamination during sample preparation, a new sampling methodology based on embedded micro electro mechanical system was developed successfully using an additional ex-situ cleaning recipe with low energy ion beam. We observed that the void was initially nucleated at the top of Cu metal line between Co capping and low-k in upstream EM direction and then evolved along the Cu/low-k interface toward anode side, activated by increasing temperature with high current density. The in-situ observation was not only in good agreement with post-mortem analysis of a conventional package level EM reliability test but also allowed to investigate the initial void formation and growth of Cu interconnects in TEM level for the improvement of EM performance. This result provides good insights into the degradation mechanism of Cu interconnects on Co capping and liners for sub-nano technology.