Band offset and leakage current in fluorine doped Si/HfO2/SiO2 gate stack of metal oxide semiconductor field effect transistors: An ab initio investigation

Ab initio calculations were employed to investigate the influence of Fluorine doping in the gate dielectric stacks of state-of-the-art metal-oxide-semiconductor field-effect transistors. Different configurations of F dopants as well as their interactions with O vacancies at different layers of a Si/SiO2/HfO2 gate stack were considered. The calculated formation energies reveal that F atoms prefer to occupy O vacancy sites, particularly at the SiO2/HfO2 interface. It is shown that the instability of the threshold voltage due to the high concentration of O vacancies can be compensated by F doping in the HfO2 layer. Moreover, non-equilibrium Green's function formalism was employed for the ab initio calculations of the gate leakage current. For applied gate voltages between 0.8 V and 1.0 V, F-doped gate stacks show a lower gate leakage current compared to the stacks with O vacancies. In general, F doping seems to be an effective way to improve the quality of Si/SiO2/HfO2 gate stacks.