Origin of flat band voltage shift in HfO2 gate dielectric with La2O3 insertion

The origin of flat band voltage (VFB) shift with La2O3 insertion for HfO2 gate dielectrics has been carefully examined. By separating the effect of the fixed charges located at each interface by thickness-dependent VFB evolution, total voltage shifts (dipole) at metal/high-k and high-k/SiO2 interfaces have been estimated. Using stacked capacitors of La2O3 and HfO2, it can be concluded that VFB is mainly determined by the high-k on SiO2. Therefore, the dipole at La2O3 and the interface has an additional dipole of 0.36 eV compared with that of HfO2/SiO2. The same trend has also been obtained with a high-k on a Si substrate without a SiO2 layer. A simple model using electronegativity has been proposed to explain the VFB shift.