Exploring the influence of Al content on the optical and interface properties of HfAlO_x mixed gate dielectric thin films and their applications in MOS devices

HfAlO_x gate dielectric films with different aluminum contents were prepared on silicon substrates by sol-gel method. Determine the actual Hf: Al ratio for each sample through EDS. The effect of aluminum addition on the microstructure of HfO₂ was studied through XRD. The interface structure and bonding structure of HfAlO_x/Si stacked layers were studied using FT-IR and XPS as a function of Al content. The band arrangement of HfAlO_x/Si gate stack layers with varying Al content was studied through UV-Vis. Introducing a certain amount of aluminum can effectively reduce the oxygen vacancies in the film and the content of silicates in the interface layer. The valence band offset and conduction band offset of all samples are above the minimum requirement of 1 eV, with sufficient barrier height to suppress leakage current. Especially for Hf: Al = 5:2 (i.e. H5A2) samples, their conduction band offset reaches 2.20 eV. Au/HfAlO_x/n Si/Au structured MOS devices were prepared by magnetron sputtering and their electrical characteristics were tested and analyzed. The results show that H5A2 has the best performance, with the highest dielectric constant (17.7), the smallest flat band voltage (-0.04 V) and flat band voltage offset (0.23 V), a smaller oxide charge density, and the smallest boundary trap oxide charge density.