Atomic-scale defects involved in the negative bias temperature instability in silicon dioxide and plasma-nitrided oxide based pMOSFETs

This study examines the atomic-scale defects involved in a metal-oxide-silicon field-effect-transistor reliability problem called the negative bias temperature instability (NBTI). NBTI has become the most important reliability problem in modern complementary-metal-oxide-silicon technology. Despite 40 years of research, the defects involved in this instability were still undetermined prior to this work. We combine DC gate-controlled diode measurements of interface state density with two very sensitive electrically detected magnetic resonance measurements called spin-dependent recombination and spin-dependent tunneling. An analysis of these measurements provides an identification of the dominating atomic-scale defects involved in NBTI in pure SiO2- and plasma-nitrided oxide-based devices. (The fundamental mechanism behind NBTI's enhancement due to the addition of nitrogen had previously been a mystery.); Our results in pure SiO2 devices indicate an NBTI mechanism which is dominated by the generation of Pb0 and Pb1 interface state defects. (Pb0 and Pb1 are both silicon dangling bond defects in which the central silicon is back bonded to three other silicon atoms precisely at the Si/SiO2 interface.) This observation is consistent with what most NBTI researchers have assumed. However, our observations in plasma-nitrided oxide devices contradict what most NBTI researchers had previously assumed.; We demonstrate that the dominating NBTI-induced defect in the plasma-nitrided devices is fundamentally different than those observed in pure SiO2-based devices. Our measurements indicate that the new plasma-nitride NBTI-induced defect's physical location extends into the gate dielectric. The defect participates in both spin-dependent recombination and spin-dependent tunneling. Our spin-dependent recombination results strongly indicate that the plasma-nitrided defect has a density of states which is more narrowly peaked than that of Pb centers and is 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 29Si hyperfine interactions. The defects are silicon dangling bonds in which the central silicon is back bonded to nitrogen atoms. We call these NBTI-induced defects KN centers because of the similarities to the K centers observed in silicon nitride. (The silicon nitride K center is also a silicon dangling bond in which the silicon atom is back bonded to nitrogen atoms.) The defect identification in plasma-nitrided devices helps to explain (1) NBTI's enhancement in plasma-nitrided devices, (2) conflicting reports of NBTI induced interface states and/or bulk traps, and (3) fluorine's ineffectiveness to reduce NBTI in plasma-nitrided devices. Our measurements also allow for observations of the atomic-scale defects involved in NBTI recovery.