Improvements on surface carrier mobility and electrical stability of MOSFETs using HfTaO gate dielectric

Physical and electrical characteristics of HfTaO gate dielectric have been systematically investigated for the first time. Based on the X-ray diffraction spectra and high-resolution transmission electron microscope pictures, the crystallization temperature of HfO₂ film is significantly increased with incorporating Ta, and the HfTaO with 43% Ta film remains amorphous after annealing at 950°C for 30 s. X-ray photoelectron spectroscopy results show that the formation of Si-O bonds in interfacial layer is increased with Ta concentration. The high atomic percentage of Si-O bonds may result in the HfTaO-Si interface inclining to SiO₂-Si interface, as well as good interface properties. Hence, the interface states density (D_it) in HfTaO film is reduced by one order of magnitude compared with HfO₂. In addition, charge trapping induced threshold voltage (V_th) instability in HfO₂ and HfTaO films is compared using a pulsed I_d--V_g measurement technique, and the V_th shift in HfTaO film is much lower than HfO₂. This indicates that charge trapping in HfO₂ film is significantly suppressed by incorporating Ta. Since both of the interface traps and charged traps in HfTaO film are less than in HfO₂, more than twice higher peak mobility is achieved in HfTaO nMOSFETs, which is due to the suppression of Coulomb scattering caused by the interface traps and charged traps.