Reduction of Electrical Defects in Atomic Layer Deposited HfO₂ Films by Al Doping

Abstract

The gate leakage current density (Jg) of ultrathin (∼3 nm) Al-doped HfO2 (Al:HfO2) films with an Al concentration of ∼11% was lower than that of the control HfO2 film by 2 orders of magnitude at an equivalent oxide thickness of ∼1 nm. The permittivity of the Al:HfO2 film was similar to that of the control HfO2 film. Al doping of HfO2 films reduced the concentration of the oxygen vacancies and carbon in the film, which act as electrical defects (traps). It also increased the band gap of the film, resulting in a reduced Jg. Although the crystalline structure of a ∼ 12 nm-thick Al:HfO2 film contained both tetragonal and monoclinic phases after high temperature annealing, the ∼3 nm thick Al:HfO2 film showed a monoclinic structure, which is the same as the control HfO2 film. Therefore, there was no modification of the crystalline structure of the Al:HfO2 film in the ultrathin film case that would increase the permittivity. However, Si diffusion into the film and interfacial layer growth during annealing were suppressed significantly, which improved the thermal stability of the Al:HfO2 films.