Highly accelerated electromigration lifetime test (HALT) of copper

The reliability of copper interconnects is an important aspect in ULSI technology. The test time of the standard electromigration test is rising with improving interconnect systems. At moderate current densities, lifetime test could last more than 500 h. In this paper, lifetime tests on via-line test structures in a copper dual-damascene technology at extremely high temperatures have been investigated. This method is an alternative solution to the well-known SWEAT method where high current densities are used to accelerate the lifetime test. The used test system was a modified Suss probe station with a self-made reactor. The results have been compared with standard tests performed in commercial oven test equipment. Bimodal behavior was observed above 425°C. Only one of the two observed failure types shows the expected thermal dependency and can be extrapolated to the standard test temperatures with Black´s equation. The estimated activation energy E_A=0.81 eV is comparable to the activation energy determined by standard tests below 350°C. The benefit of this method is a reduction in test time of more than a decade at 425°C in comparison to the standard test at 300°C and a moderate current density.