A fWLR test structure and method for device reliability monitoring using product relevant circuits

The measurement of device degradation in product relevant circuits during production monitoring is described. Ring oscillators with local on-chip heaters are introduced for quick characterization of the voltage and temperature dependence and for fast wafer level reliability (fWLR) monitoring. The suitability of the structures, the equipment and the stress/measurement algorithm is demonstrated. Results for optimizing the stress and readout conditions are shown as well as the relation to standard device stress measurements. The dominating degradation mechanism in this work turned out to be NBTI (negative bias temperature instability).