Back-end dielectrics reliability under unipolar and bipolar AC-stress

The present paper compares the effects of AC and DC electrical stress on low-κ SiOCH and high-κ ZrO2 and Ta2O5 back-end dielectrics. A wide panel of stress conditions has been assessed, mixing DC, unipolar/bipolar and relaxation times. The DC-stress being the reference stress condition, no enhancement of the time-to-breakdown (TBD) has been found with pure bipolar stress. On the contrary unipolar stress showed a strong improvement of this characteristic. We propose that the lifetime enhancement is due to a charge detrapping mechanism within the dielectric that affects the defect density. Under unipolar- and relax-bipolar-stress the time-to-breakdown has been corrected by the duty cycle in order to consider the effective duration of the stress. In this study no impact of copper has been found on the breakdown behaviour.