Slow-trapping related current in MOS capacitors during NBTS aging

A current which is directly related to build-up of positive charge in thermal oxide due to negative bias temperature stress (NBTS) aging in a temperature range from 25°C to 350°C has been observed in MOS capacitors. The current was very noticeable in MOS capacitors which had been exposed to plasma in a magnetron sputtering system or in a reaction ion etching system. It was postulated that the carriers in the current flowing in the oxide consists mainly of holes. Two extreme situations were observed. One was that most of the holes injected in oxide moved a little distance and then were captured by hole traps in the oxide. Another was that most of the injected holes traveled through the whole oxide, arriving at the metal interface and recombing with electrons there. It was found that in negative weak field thermal stimulation current (TSC) measurements performed on a highly charged capacitor, the observed current in an external circuit may flow against the direction of the external bias field. A mechanism which is responsible for the build-up of positive oxide charge and resulting in the slow-trapping related current was proposed