The Degradation Process of High- $k~{rm SiO}_{2}/{rm HfO}_{2}$ Gate-Stacks: A Combined Experimental and First Principles Investigation

摘要

Theoretical and experimental methods are applied to investigate the degradation of ${rm SiO}_{2}/{rm O}_{2}$ gate-stacks in state-of-the-art MOSFETs. A combination of density functional theory and nonequilibrium Green's function formalism has been applied to the atomic scale calculation of the leakage current through ${rm SiO}_{2}/{rm O}_{2}$ dielectrics. Samples with different dielectric stacks have been taken into account to study the thickness dependence of ${rm SiO}_{2}$ and ${rm HfO}_{2}$ on the leakage current. The calculated results show a good agreement with the leakage current and constant voltage stress measurements. The current influenced by oxygen vacancies, particularly in the High- $k$ dielectric close to the ${rm SiO}_{2}/{rm O}_{2}$ interface has been analyzed. Comparison between the measurement and simulation results show that oxygen vacancy defects in the ${rm HfO}_{2}$ are a likely cause for progressive stress-induced leakage current in MOSFETs with ultrathin High- $k$ gate-stack.