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

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Abstract
The energy band gaps of thin high-dielectric-constant (high-k) insulators such as Ta 2 O 5 , Si 3 N 4 and Al 2 O 3 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/Ta 2 O 5 /SiO 2 /Si (100) and Al/Al 2 O 3 /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/Ta 2 O 5 /SiO 2 /Si (100) structure, the interfacial SiO 2 layer is a crucial factor to suppress the electron tunneling rate, while for the Al/Al 2 O 3 /Si (100) structure the tunneling current is sufficiently low even in an SiO 2 -equivalent thickness of 1.2 nm compared with conventional n + -poly Si/SiO 2 /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.

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