Comprehensive Demonstration and Physical Origin of HfO2 Gate Stacks: Band Alignment, VFB Shift and Fermi Level Pinning

Abstract

Band alignment of TiN/HfO2/SiO2/Si stack is systematically investigated by X-ray photoelectron spectroscopy. The differences of binding energies of Si 2p core level between SiO2 and Si substrate are experimentally found to decrease with the sequence of 5 nm SiO2/Si, 4 nm HfO2/5 nm SiO2/Si and 2 nm HfO2/5 nm SiO2/Si stacks. The p-type Schottky barrier heights at TiN/HfO2 interface of TiN/HfO2/SiO2/Si stack are experimentally estimated to increase with thicker HfO2 thickness. A physical model based on band alignment of TiN/HfO2/SiO2/Si stack is employed to successfully explain these experimental results. The flatband voltage (VFB) of TiN/HfO2/SiO2/Si stack is demonstrated by the proposed model based on band alignment of entire gate stack. The positive VFB shift of TiN/HfO2/SiO2/Si stack and Fermi level pinning are also physically demonstrated by this model and attributed to interface induced gap states at TiN/HfO2 and HfO2/SiO2 interfaces.