Systematical investigation and physical mechanism of HfO2 gate stacks band alignment, VFB shift and Fermi level pinning

Band alignment of TiN/HfO
2
/SiO
2
/Si stack is systematically investigated by X-ray photoelectron spectroscopy. The differences of Si 2p binding energies between SiO
2
and Si substrate are experimentally found to decrease with the sequence of SiO
2
/Si, 4 nm HfO
2
/SiO
2
/Si and 2 nm HfO
2
/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 positive VFB 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.