Thermal and dielectric breakdown for metal insulator metal capacitors (MIMCAP) with tantalum pentoxide dielectric

Wafer level constant voltage stress of metal insulator metal capacitors, with Ta/sub 2/O/sub 5/ dielectric show a bimodal time to failure distributions. The two regimes of times to breakdown are separated by 2 orders of magnitude in time and this gap cannot be accessed with any constant voltage stress condition. The early failure mode is explained by thermal runaway model based on positive feedback loop: the high power dissipation in the MIM capacitors leads to an temperature increase, which in turn increases the leakage current of the dielectric and thus increases the power dissipation. This simple model explains a thermally unstable stress mode at high voltages and a thermally stable mode at lower voltages. The predicted critical current density at the beginning of the stress is consistent with experimental results. The temperature activation of the leakage current mechanism is shown to be 0.7eV. Other potential explanations for the early failure mode are discussed.