Investigations of Fermi Level Pinning and Dipole Formation in TiN/HfO2/SiO2/Si Stacks

Abstract

Fermi level pinning (FLP) and dipole formation in TiN/HfO2/SiO2/Si stacks are investigated. The magnitude of FLP at TiN/HfO2 interface is estimated to be ~0 V based on dipole theory using concepts of interfacial gap states and charge neutrality level (CNL). The dipole amount at HfO2/SiO2 interface is experimentally extracted to be +0.33 V. These results show that dipole formation at HfO2/SiO2 interface is important for tuning flatband voltage of the TiN/HfO2/SiO2/Si stacks. Possible origin of dipole formation is demonstrated and attributed to be lower CNL of HfO2 compared with that of SiO2/Si stacks.