Role of Postdeposition Annealing and Doping with Si and Al Impurities in the Formation of Hf _x Si_1-x O₂ at the SiO₂/FE:HfO₂ Interface in a Ferroelectric Field-Effect Transistor

Characterization of the composition and extension ofthe SiO2/HfO2 interface in the model systemsSi-sub./SiO2 (7.5 nm)/FE:HfO2 (9.5 nm)/TiN (9nm) for standardimpurity concentrations and annealing temperatures (Si 3.6%, 1000 degrees C; Al 5.5%, 850 degrees C) were carried out using X-ray photoelectronspectroscopy with high kinetic energies. In addition, the crystallineproperties of HfO2 were characterized by transmission electronmicroscopy and grazing incidence X-ray diffraction depending on thetype of impurity. Formation of Hf (x) Si1-x O2 at the SiO2/HfO2 interface was revealed, and the dependence of itsthickness d (silicate) and stoichiometry X on the formation of the tetragonal phase P4(2)/nmc of HfO2 was established.It is shown that doping with aluminum followed by annealing preventsthe formation of a tetragonal phase and reduces both d (silicate) and X by about 20% (with respectto undoped HfO2 annealed at the same temperature), in contrastto doping with Si followed by annealing, which practically does notaffect d (silicate) and X. The results obtained are important for the problem of imbalancein the voltage drop across the gate oxides stack in a ferroelectricfield-effect transistor and improvement of its endurance and retentioncharacteristics.