Low-frequency noise characterization of gate oxide trap depth distribution of MOSFETs

Abstract

To accurately obtain the depth distribution of the gate oxide traps that cause low-frequency noises, this study developed a discrete form of the low-frequency noise model in MOSFETs based on McWhorter's theory. The non-negative least squares (NNLS) method is employed to numerically solve the designed model. The low-frequency noises of planar Ge nMOSFETs with a gate stack match the prerequisite of the proposed form, which is dominated by carrier number fluctuations and is consistent with the McWhorter model. These transistors are used as the object of analysis in this study. By introducing a La2O3 cap layer to the gate stack, the gate oxide trap profiles calculated by the discrete model and the NNLS method showed obvious suppression of the traps in the HfO2 body and concentration of the traps in and near the SiO2/HfO2 interface. The research on both energy-dispersive x-ray spectroscopy and electron energy-loss spectroscopy has shown during annealing the diffusion of La into HfO2 and the appearance of La-rich layer at the SiO2/HfO2 interface in the Ge nMOSFET with a La2O3 cap. According to the existing first-principles calculations, the substitution of Hf in HfO2 by La increases the formation energy of oxygen vacancies, and the formation energy of oxygen vacancies in the HfnLamSixOy layer formed near the SiO2/HfO2 interface is lower than that of HfO2. The experimental and theoretical results support the physical connotation of the calculations and validate the solution proposed by this study.