Electromigration in Aluminum to Tantalum Silicide Contacts

The use of silicide interconnects in VLSI circuits is becoming common. However, little has been published on the aluminum to tantalum silicide contact window reliability. We report life test results for two geometries of Al-Si-Cu to TaSi2 contact windows. High activation energies, moderate sigmas and large current density exponents are observed. Detailed EMA using standard and novel SEM techniques shows aluminum void formation on the window sidewalls and at the Al/TaSi2 interface as one of the failure modes. Transition of the contact to a high resistance nonohmic state is another. We show these two modes of failure to occur within different temperature ranges and propose that this is due to differing activation energies. We conclude that the nonohmic failure mode will be dominant at typical operating temperatures but operating lifetimes of such structures can be hundreds of years.