Internal photoemission of electrons at interfaces of metals with low-κ insulators

Abstract

Energy barriers for electrons at interfaces of several low-permittivity insulators with metals (Ta, TaNx, TiNx, Au, and Al) are characterized using internal photoemission spectroscopy. In sharp contrast to thermal SiO2, the barriers show little sensitivity to the Fermi energy of the metal, suggesting that the uppermost occupied electron revels at the interface are states localized in the near-interfacial insulator layer. Moreover, despite large differences in the defect spectrum of the studied low-κ materials as revealed by electron spin resonance, all the measured energy barriers are found to be close to 4.5eV. The latter indicates an extrinsic nature of the corresponding common electron state, which is tentatively ascribed to traces of moisture at the interface.