Atomistic simulation study of high-?? oxide defects for understanding gate stack and RRAM reliability

Abstract

Bias temperature instability (BTI) is widely recognized as a critical reliability issue for the state-of-the-art complementary metal-oxide-semiconductor (CMOS) device. Generally, BTI is result from a progressive building up of the interface states and bulk oxide charges under the combining effect of the gate voltage and an elevated temperature. These charged defects will shift the threshold voltage (V t) of the metaloxide-semiconductor field-effect transistor (MOSFET) and degrade the inversion charge mobility, reducing the device driving current. Worse case, when the shift of V t exceeds the design tolerance, functional failure of integrated circuits may result. Previous studies of the NBTI on the SiON gated device show that the threshold voltage degradation is typically characterized by a much weaker dependence on the stress time and temperature as compared to that of the SiO 2 counterpart. Moreover, in a recent NBTI study, Ang et al. reveals the presence of deep-level hole traps (DLHTs) after negative-bias temperature stressing. Their experimental results show that the hole traps have energy states above the Si Fermi potential, which enable them have the ability to retain the positive charges for a very long time after the negative gate biasing. However an unambiguous understanding of the role of nitrogen on the DLHTs generation is still not available. Therefore, in this work, we investigate the impact of nitrogen on the trap level generation via first-principles modeling and simulation. Our results show that the coordination of the neighboring nitrogen atom plays a paramount role on the structural relaxation of V O following the capture of a hole. In particular, a twofold coordinated nitrogen atom is shown to induce very significant structural relaxation of V O. The resultant trapped-hole site has a very deep charge transition level Abstract VIII in the SiO 2 band gap (DLHTs). On the other hand, in the absence of the nitrogen atom or if the neighboring nitrogen atom is threefold coordinated (e.g., the dangling nitrogen bond is terminated by a hydrogen atom). The resultant trapped-hole site would have a much shallower charge transition level. This set of simulation results show a clear correlation between nitrogen in the gate oxide and the DLHT generation by negative-bias temperature stress. Besides, in Ang's work, a broad energy distribution of stress induced positive trap states across over the band gap were detected, whereas knowledge on how the neighboring nitrogen atoms affect the defect levels in the SiON is quite limited. Hence, in the subsequent modeling and simulation work, we modeled various oxide defects with different nitrogen configurations in the SiON gate stack. Our simulation results from these models show a widespread of the defects levels within the SiON gap due to the different dynamics of these defect morphors. Distinctive relaxation characteristics of deep-level hole traps, as compared to those of the interface states, are also observed. As the scaling of the transistors continuously moves ...