Systematic study of the effect of La2O3 incorporation on the flatband voltage and Si band bending in the TiN/HfO2/SiO2/p-Si stack

Recent studies have shown that La2O3 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/SiO2 interface has been proposed to explain the V-t shifts. In order to investigate the mechanism of the V-t shift further, we have measured the flatband voltage (V-fb) and Si band bending of technologically relevant TiN/HfO2/La2O3/SiO2/p-Si stacks where the thickness and position of the La2O3 layer have been systematically varied. We observed systematic changes in V-fb, Si band bending and the HfO2-Si valence band offset as a function of La2O3 layer thickness and position. These changes can be explained by a band alignment model that includes a dipole at the high-k/SiO2 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. (c) 2010 American Institute of Physics. [doi:10.1063/1.3516483]