Photoemission study of energy band alignment and gap state density distribution for high-k gate dielectrics

Abstract

The energy band gaps of thin high-dielectric-constant (high-k) insulators such as Ta2O5, Si3N4 and Al2O3 have been determined by measuring the energy loss spectra of O1s or N1s photoelectrons. From the analysis of the valence band spectra for thin high-k dielectrics prepared on metals and Si(100), the energy band profiles for metal/high-k dielectric/Si(100) systems have been determined in consideration for the measured energy bandgaps and metal work functions. Intrinsic tunneling leakage currents for TiN/Ta2O5/SiO2/Si(100) and Al/Al2O3/Si(100) systems were calculated by applying a transfer matrix method to their energy band profiles so determined. The results show that, for the TiN/Ta2O5/SiO2/Si(100) structure, the interfacial SiO2 layer is a crucial factor to suppress the electron tunneling rate, while for the Al/Al2O3/Si(100) structure the tunneling current is sufficiently low even in an SiO2-equivalent thickness of 1.2 nm compared with conventional n+-poly Si/SiO2/Si(100). It is also demonstrated that total photoelectron yield spectroscopy is a useful and high-sensitive technique to evaluate the energy distribution of defect states in the high-k dielectrics and at the interfaces.