Oxygen vacancy defect engineering using atomic layer deposited HfAlO_x in multi-layered gate stack

This work evaluates the defects in high quality atomic layer deposited (ALD) HfAlO_x with extremely low Al (<3% Al/(Al + Hf)) incorporation in the Hf based high-k dielectrics. The defect activation energy estimated by the high temperature current voltage measurement shows that the charged oxygen vacancies, V⁺/V²⁺, are the primary source of defects in these dielectrics. When Al is added in HfO₂, the V⁺ type defects with a defect activation energy of E_a ∼ 0.2 eV modify to V²⁺ type to E_a ∼ 0.1 eV with reference to the Si conduction band. When devices were stressed in the gate injection mode for 1000 s, more V⁺ type defects are generated and E_a reverts back to ∼0.2 eV. Since Al has a less number of valence electrons than do Hf, the change in the co-ordination number due to Al incorporation seems to contribute to the defect level modifications. Additionally, the stress induced leakage current behavior observed at 20 °C and at 125 °C demonstrates that the addition of Al in HfO₂ contributed to suppressed trap generation process. This further supports the defect engineering model as reduced flat-band voltage shifts were observed at 20 °C and at 125 °C.