Double nitridation of crystalline ZrO ₂ /Al ₂ O ₃ buffer gate stack with high capacitance, low leakage and improved thermal stability

The gate dielectric stack composed of crystalline ZrO ₂ and Al ₂ O ₃ buffer layer treated with double nitridation was developed to reduce the capacitance equivalent thickness (CET), leakage current density (J _g ), interfacial state density (D _it ), and enhance thermal stability as well. A high dielectric constant of the gate stack was provided by the crystalline ZrO ₂ with tetragonal/cubic phase. The J _g and D _it were suppressed by the insertion of the Al ₂ O ₃ buffer layer treated with remote NH ₃ plasma nitridation because of the deactivation of the oxygen vacancies and the well passivation of the Si dangling bonds. A further nitridation using remote N ₂ plasma on ZrO ₂ was carried out to reduce the CET and J _g by the enhancement of the dielectric constant and the deactivation of the grain boundaries and oxygen vacancies. Accordingly, a low CET of 1.09 nm, J _g of 3.43 × 10 ^-5 A/cm ² , and D _it of 3.35 × 10 ¹¹ cm ^-2 eV ^-1 were achieved in the crystalline ZrO ₂ /Al ₂ O ₃ buffer gate stack treated with the double nitridation. The hysteresis was also minimized significantly by the post-deposition annealing at 800 °C, which is attributed to the enhanced thermal stability. The results indicate that the crystalline high-K dielectrics/buffer layer with double nitridation treatments is a promising gate stack structure beneficial to the sub-nanometer CET scaling in the future.