Modeling of hole generation/trapping in ultrathin SiO₂ films during gate injection of electrons in direct tunneling regime

An experimental investigation on oxide positive charge buildup in sub 3-nm silicon dioxide (SiO₂) films is presented during direct tunneling (DT) of electrons at -1.8 V of gate bias. The measurement results can be best explained by hole generation via anode hole injection (AHI) mechanism and the subsequent trapping of holes in the as-fabricated neutral hole traps in the oxide. A comparative study of hole trapping characteristics and threshold voltage shift during constant voltage and current stress are also discussed. We demonstrate that constant voltage stress (CVS) is more vulnerable than constant current stress (CCS) in deteriorating device performances. Furthermore, our measurement results indicate generation of interface states due to interaction with holes and the subsequent release of proton which in turn generates neutral electron traps as the SiOH centers.