Comprehensive Demonstration and Physical Origin of HfO_2 Gate Stacks: Band Alignment, V_(FB) Shift and Fermi Level Pinning

摘要

Band alignment of TiN/HfO_2/SiO_2/Si stack is systematically investigated by X-ray photoelectron spectroscopy. The differences of binding energies of Si 2p core level between SiO_2 and Si substrate are experimentally found to decrease with the sequence of 5 run SiO_2/Si, 4 nm HfO_2/5 nm SiO_2/Si and 2 nm HfO_2/5 nm SiO_2/Si stacks. The p-type Schottky barrier heights at TiN/HfO_2 interface of TiN/HfO_2/SiO_2/Si stack are experimentally estimated to increase with thicker HfO_2 thickness. A physical model based on band alignment of TiN/HfO_2/SiO_2/Si stack is employed to successfully explain these experimental results. The flatband voltage (V_(FB)) of TiN/HfO_2/SiO_2/Si stack is demonstrated by the proposed model based on band alignment of entire gate stack. The positive V_(FB) shift of TiN/HfO_2/SiO_2/Si stack and Fermi level pinning are also physically demonstrated by this model and attributed to interface induced gap states at TiN/HfO_2 and HfO_2/SiO_2 interfaces.