Interfacial oxygen and nitrogen induced dipole formation and vacancy passivation for increased effective work functions in TiN/HfO₂ gate stacks

Effective work function (EWF) changes of TiN/HfO₂ annealed at low temperatures in different ambient environments are correlated with the atomic concentration of oxygen in the TiN near the metal/dielectric interface. EWF increases of 550 meV are achieved with anneals that incorporate oxygen throughout the TiN with [O] = 2.8×1021 cm⁻³ near the TiN/HfO₂ interface. However, further increasing the oxygen concentration via more aggressive anneals results in a relative decrease of the EWF and increase in electrical thickness. First-principles calculations indicate the exchange of O and N atoms near the TiN/HfO2 interface cause the formation of dipoles that increase the EWF.