Investigation of vacancy diffusion path for stress migration failure mode in highly scaled Cu/low-k interconnects

Recently, a Stress Migration (SM) failure mode in the metal line was explored and the failure was found to associate with unstable Cu microstructure in the narrow line and fast surface drift velocity at weak interface adhesion. In this work, we further investigate SM behavior in different material and process at Cu/barrier and Cu/ESL interfaces. We observed that vacancies from the wide metal plate initially migrate through Cu grains to Cu/barrier interface, they then move to Cu/ESL interface, and eventually voiding is formed in the narrow metal line. This SM failure mode can be eliminated through a new nose structure with special narrow metal line design consisting of two branch widths (BW). In addition, we successfully demonstrated that, by process optimization at Cu/barrier and Cu/ESL interfaces, migration path of vacancies can be effectively suppressed and thus SM effect can be dramatically eliminated.