A comparison of Al2O3/HfO2 and Al2O3/ZrO2 bilayers deposited by the atomic layer deposition method for potential gate dielectric applications

Abstract

Thin films of Al2O3/HfO2 and Al2O3/ZrO2 bilayers were investigated as potential replacements for traditional SiO2 gate dielectrics. The Al2O3 film exhibited an amorphous structure without an interfacial layer, while the HfO2 and ZrO2 films had randomly oriented polycrystalline structures with a silicate interlayer. The two gate oxides, Al2O3 and HfO2, have characteristics that are complementary to each other, and it was possible to achieve a high-k gate oxide with a low leakage current as well as large band gap characteristics using a composite of these two oxides. Leakage currents of the Al2O3, HfO2, ZrO2, Al2O3/HfO2, and Al2O3/ZrO2 films were about 4.2 x 10(-8), 8.2 x 10(-4), 7.5 x 10(-5), 2.4 x 10(-6), and 1.2 x 10(-6) A/cm(2), respectively, at a gate bias voltage of vertical bar V-G-V-FB vertical bar = 2 V. The corresponding calculated equivalent oxide thickness (EOT) values for the Al2O3, HfO2, ZrO2, Al2O3/HfO2, and Al2O3/ZrO2 films were about 2.3, 1.8, 1.9, 1.3, and 1.4 nm, respectively. The Al2O3/HfO2 and Al2O3/ZrO2 bilayers had improved gate oxide characteristics compared to those that were composed of only Al2O3, ZrO2 or HfO2 alone.