Composition Dependence of Work Function in Metal (Ni,Pt)–Germanide Gate Electrodes

Abstract

The composition ratio dependence of electrical (work function and resistivity) and structural properties in metal (Ni,Pt)–germanide gate electrodes was investigated for metal–oxide–semiconductor (MOS) devices. X-ray diffraction and cross-sectional transmission electron microscopy clearly revealed that metal–germanide MOS gate electrodes with a single Ni–germanide (Ni–Ge) or Pt–germanide (Pt–Ge) phase can be formed by controlling the thicknesses of the deposited metal and Ge. The resistivities of both Ni–Ge and Pt–Ge were lower than that of conventional polycrystalline silicon (poly-Si) gate electrodes. From the capacitance-voltage characteristics, the work functions of the Ni–Ge gate electrodes were measured to be from 4.6 to 4.9 eV, and those of the Pt–Ge gate electrodes were from 4.9 to 5.3 eV. With increasing metal (Ni,Pt) content, the work function of Ni–Ge decreased, while that of Pt–Ge increased. This composition dependence of the work function of the metal–germanide can be explained by considering the electronegativity of the pure metals that are often used.