Ti-thickness dependent electromigration resistance of the Al-Cu-Si/TiN/sub x//TiSi/sub y/ barrier contact system

The electromigration resistance for the Al-Cu-Si alloy/titanium nitride/titanium silicide barrier contact system was evaluated as a function of the deposited Ti thickness (0-1000 AA). Both the conventional constant current stress and current ramping stress were applied. It was found that the electromigration resistance of the contact structure increases with the Ti thickness monotonically, although the rate of increase reduces drastically once the Ti thickness exceeds 400 AA. At a Ti thickness of 1000 AA, the mean time to failure is more than an order of magnitude longer than that of contacts without the titanium nitride barrier. There is an excellent correlation between the result derived from conventional constant current stress and that from the current ramping stress. The current ramp method, therefore, can be used as a relative reliability indicator for contact structures on wafer-level tests. Thermal stress data show that an adequate margin of thermal stability exists for contact structures at all Ti thicknesses (>or=200 AA). Accordingly, a process window for the Ti thickness in this technology can be defined depending on the requirement of electromigration resistance for contacts.<>