Band offsets of metal–oxide–semiconductor capacitor with HfLaTaO/HfSiO stacked high-k dielectric

Abstract

Band offsets of the metal–oxide–semiconductor (MOS) capacitor with HfLaTaO/HfSiO stacked dielectric were investigated and determined in this work. First, equivalent-oxide-thickness (EOT) of HfLaTaO/HfSiO stacked dielectric was demonstrated to be around 1.0 nm. Then, a typical flatband voltage (Vfb) versus EOT plot was used to extract the work function (Φm) of Ta deposited on HfLaTaO/HfSiO stacked structure. Furthermore, the Φm of the Ta gate electrode deposited on HfLaTaO/interfacial layer stacked dielectric was estimated to be 4.25 eV. Since the optical energy bandgap (Egopt) is one of the most important physical parameters, the Egopt of HfLaTaO dielectric was extracted from the HfLaTaO/quartz substrate structure by optical absorption measurements. The results suggest that the Egopt of 5.5 eV for HfLaTaO dielectric was determined by extrapolating a linear part of the curve to the intercept on the energy axis. Moreover, the Schottky barrier height (ΦB) was extracted from the analysis of the temperature dependence of the gate leakage current from 298 to 398 K. The result shows that the estimated ΦB during gate injection in Ta/HfLaTaO interface is around 1.0 eV. Through the extracted values of Φm, Egopt, and ΦB, band offsets of MOS capacitor with a Ta/HfLaTaO/HfSiO/P-Si(100) stacked structure were obtained. Finally, the related degradation mechanisms of the HfLaTaO/HfSiO stacked dielectrics under constant voltage stress are presented. The interface trap density and oxide positive charges increase with increasing the injected charges and are not constant during negative bias stress.