Observation of DC currents induced in MOS capacitors during NBTS aging

Abstract

A current which is directly related to build-up of positive charge in thermal oxide due to negative bias temperature stress (NBTS) aging in the temperature range from 25°C to 350°C has been observed in MOS capacitors. The current was very noticeable in the MOS capacitors which had been exposed to plasma in a magnetron sputtering system or in a reactive ion etching system. Two extreme situations were observed. One was that most of the holes injected in oxide move a short distance before being captured. Another was that most of the injected holes transport through the entire oxide, arriving at the metal interface and recombining with electrons there. It was found that, during negative weak field thermal stimulation current (TSC) measurement performed on a heavily charged capacitor, the observed current in the external circuit flows in the direction opposite to the external bias field. A mechanism which is responsible for the slow-trapping related current is proposed.