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

Theoretical and experimental methods are applied to investigate the degradation of SiO
₂
/HfO
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 SiO
₂
/HfO
₂
dielectrics. Samples with different dielectric stacks have been taken into account to study the thickness dependence of SiO
₂
and 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 SiO
₂
/HfO
₂
interface has been analyzed. Comparison between the measurement and simulation results show that oxygen vacancy defects in the HfO
₂
are a likely cause for progressive stress-induced leakage current in MOSFETs with ultrathin high-k gate-stack.