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

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 O-1s or N-1s 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 1.2nm 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.