Non-linear dielectric constant increase with Ti composition in high-k ALD-HfTiO_x films after O₂ crystallization annealing

HfTiO_x films deposited on TiN, Pt and Al₂O₃/Si bottom electrodes (BE) by Atomic Layer Deposition (ALD) method were investigated in terms of the crystallization temperature, dielectric constant and leakage current. The as-deposited films show a linear increase of dielectric constant from 20 (HfO₂) to 40 (TiO₂) as a function of Ti content in the film. On the other hands, the dielectric constant of HfTiO_x films with 64% – 30% Hf content increases up to 60 after crystallization annealing, which strongly correlates with the appearance of the orthorhombic HfTiO₄ structure. Furthermore, the thermal treatment in O₂ ambient is found to have a drastic effect to decrease the leakage current density (J_g). As a result, 10⁻⁸ A/cm² at V_g = +1V with 0.8nm EOT is achieved with 30%-Hf contained film.