| The microfailure of thin-film interconnect by electromigration phenomena is one of the primary causes to degrade the reliability of microelectronic circuits. Tn this study, we analyzed the electromigration-induced microfailure considering thermal stress effect in the interconnect. The thermal stress is generated by the difference of thermal expansion coefficient between metal interconnect and oxidized silicon substrate. This thermal stress, which is developed during fabrication, produces the defects such as microvoids which accelerate the electromigration. The effect of thermal stress on the electromigration-induced failure was analyzed via the kinetic considerations. For those, after applying different thermal cycles to develop various thermal stress in the test specimens, the MTF (mean time to failure) was evaluated by measuring the change of electrical resistance during the electromigration test. And then, the apparent activation energy for electromigration was calculated. The experimental results show that the apparent activation energy and MTF tend to decrease with increasing thermal stress. Microvoids due to thermal stress are the important factor to accelerate the electromigration-induced failure. And, the presence of stress-induced microvoids was ascertained by the fact that the initial resistance increases with increasing thermal stress. |
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