Effective work-function tuning of TiN/HfO2/SiO2 gate-stack; a density functional tight binding study

In this work, density functional tight binding (DFTB) calculations are used to study the characteristics of full gate stack TiN/HfO2/SiO2/Si and possible effective work-function (EWF) tuning options. First, the DFTB parameterization method to produce both electronic and repulsion information for all atom pairs is introduced briefly. Since the simulated gate-stack structure has thousands of atoms, conventional relaxation methods are computationally intensive. Hence a method to relax and passivate the material interfaces is introduced. Next, the impact of aluminum substitution is studied. It is shown that the change in EWF strongly depends on the atom which is substituting Aluminum; e.g. Aluminum substitutions of Hf and Ti show opposite impact on EWF. Finally, the origin of this different behavior is discussed.