Hafnium-doped tantalum oxide high-k gate dielectric films for future CMOS technology

摘要

A novel high-k gate dielectric material, i.e., hafnium-doped tantalum oxide (Hf-dopedTaOx), has been studied for the application of the future generation metal-oxidesemiconductorfield effect transistor (MOSFET). The film's electrical, chemical, andstructural properties were investigated experimentally. The incorporation of Hf into TaOximpacted the electrical properties. The doping process improved the effective dielectricconstant, reduced the fixed charge density, and increased the dielectric strength. Theleakage current density also decreased with the Hf doping concentration. MOS capacitorswith sub-2.0 nm equivalent oxide thickness (EOT) have been achieved with the lightlyHf-doped TaOx. The low leakage currents and high dielectric constants of the doped filmswere explained by their compositions and bond structures. The Hf-doped TaOx film is apotential high-k gate dielectric for future MOS transistors.A 5 ???? tantalum nitride (TaNx) interface layer has been inserted between the Hf-dopedTaOx films and the Si substrate to engineer the high-k/Si interface layer formation andproperties. The electrical characterization result shows that the insertion of a 5 ???? TaNxbetween the doped TaOx films and the Si substrate decreased the film's leakage current density and improved the effective dielectric constant (keffective) value. The improvementof these dielectric properties can be attributed to the formation of the TaOxNy interfaciallayer after high temperature O2 annealing. The main drawback of the TaNx interface layeris the high interface density of states and hysteresis, which needs to be decreased.Advanced metal nitride gate electrodes, e.g., tantalum nitride, molybdenum nitride,and tungsten nitride, were investigated as the gate electrodes for atomic layer deposition(ALD) HfO2 high-k dielectric material. Their physical and electrical properties wereaffected by the post metallization annealing (PMA) treatment conditions. Work functionsof these three gate electrodes are suitable for NMOS applications after 800????C PMA.Metal nitrides can be used as the gate electrode materials for the HfO2 high-k film.The novel high-k gate stack structures studied in this study are promising candidatesto replace the traditional poly-Si-SiO2 gate stack structure for the future CMOStechnology node.