Interface trap and oxide charge generation in p-MOSFETs by direct/Fowler-Nordheim tunneling under negative bias temperature stress

In this study, we characterized the interface and oxide charge generation in p-MOSFETs under negative bias temperature stress (NBTS). Thin (2.5 nm) and thick (6 nm) gate oxide MOSFETs were utilized to induce direct and Fowler-Nordheim (FN) tunneling, respectively. The threshold voltage and subthreshold swing in the thick oxide MOSFET was more significantly affected by NBTS than that of the thin oxide MOSFETs. The direct-current current-voltage (DCIV) method was implemented to investigate changes in trapped charges at the SiO₂/Si interface. The change in oxide charges in the SiO₂ bulk was obtained from the midgap voltage shift. The interface and oxide charges are predominantly affected by FN tunneling with less impact from direct tunneling, because of not only the hole-induced impact ionization at the SiO₂/Si interface, but also the larger number of broken hydrogen atoms from the Si-H bonds, which are induced by the high applied gate bias. We conclude that devices' electrical performance can be significantly degraded when the MOSFETs are predominantly affected by FN tunneling rather than by direct tunneling under NBTS.