INVESTIGATION OF RELIABILITY MEASUREMENTS WITH RAMPED AND CONSTANT VOLTAGE STRESS ON MOS GATE OXIDES

摘要

MOS gate oxide capacitors over a wide range of oxide thicknesses (10.9-28nm) were stressed using constant voltage, ramped voltage stress and combined ramped/constant voltage stress measurements. The reliability measurements were performed with different bias conditions in order to assess the effect of the measurement conditions on the gate oxide lifetimes. A unipolar pulsed ramp was applied during the ramped voltage stress. It will be verified that this ramp yields identical breakdown distributions to the commonly used staircase ramp. Times to breakdown from ramped and constant voltage stress were directly compared. It was found that for thick oxides the times to breakdown of the ramped stress were greater than those of the constant stress. The measurement results of the combined ramped/constant voltage stress indicate that it is a valuable tool for monitoring extrinsic and intrinsic breakdown properties. The observations made in this work imply that the time to breakdown at a constant voltage is strongly dependent on the peak current injected into the oxide and, therefore, on a pre-stress before the constant stress voltage.