Systematic study of the effect of La_2O_3 incorporation on the flatband voltage and Si band bending in the TiN/HfO_2/SiO_2/p-Si stack

摘要

Recent studies have shown that La_2O_3 films can be used to adjust the threshold voltage (V_t) of NMOS Hf-based high-k/metal gate devices to desirable values, and a dipole at the high-k/SiO_2 interface has been proposed to explain the V_t shifts. In order to investigate the mechanism of the V, shift further, we have measured the flatband voltage (V_(fb)) and Si band bending of technologically relevant TiN/HfO_2/La_2O_3/SiO_2/p-Si stacks where the thickness and position of the La_2O_3 layer have been systematically varied. We observed systematic changes in V_(fb), Si band bending and the HfO_2-Si valence band offset as a function of La_2O_3 layer thickness and position. These changes can be explained by a band alignment model that includes a dipole at the high-k/SiO_2 interface, thus supporting the work of previous authors. In addition, we have derived the theoretical relationship between V_(fb) and Si band bending, which agrees well with our experimental measurements.