Identification of the atomic-scale defects involved in the negative bias temperature instability in plasma-nitrided p-channel metal-oxide-silicon field-effect transistors

Abstract

We utilize a combination of DC gate-controlled diode recombination current measurements as well as two very sensitive electrically detected magnetic resonance techniques, spin-dependent recombination and spin-dependent tunneling, to identify atomic-scale defects involved in the negative bias temperature instability (NBTI) in 2.3nm plasma-nitrided SiO2-based p-channel metal-oxide-silicon field-effect transistors. We demonstrate that the dominating NBTI-induced defect in the plasma-nitrided devices is fundamentally different than those observed in pure SiO2-based devices. (In pure SiO2 devices, we observe NBTI-induced Pb0 and Pb1 defects.) Our measurements indicate that the NBTI-induced defect in the plasma-nitrided devices extends into the gate dielectric. The defect participates in both spin-dependent recombination and spin-dependent tunneling. The defect also has a density of states which is more narrowly peaked than that of Pb centers near the middle of the band gap. The high sensitivity of our spin-dependent tunneling measurements allow for an identification of the physical and chemical nature of this defect through observations of Si29 hyperfine interactions. We identify these defects as silicon dangling bond defects in which the central silicon is back bonded to nitrogen atoms. We assign these NBTI-induced defects as KN centers because of their similarity to K centers observed in silicon nitride. (The silicon nitride K centers are also silicon dangling bond defects in which the silicon atom is back-bonded to nitrogen atoms.) The defect identification in plasma-nitrided devices helps to explain (1) why NBTI is exacerbated in nitrided devices, (2) conflicting reports of NBTI-induced interface states and/or bulk traps, and (3) fluorine’s ineffectiveness in reducing NBTI in nitrided devices.