Interface studies of tungsten nitride and titanium nitride composite metal gate electrodes with thin dielectric layers

Interface formation between reactively sputtered tungsten nitride $(WNx)$ or titanium nitride $(TiNx)$ metallic films and thermally grown silicon dioxide $(SiO2)$ layers is studied by interrupted growth with on-line Auger electron spectroscopy. For both composite metals, growth proceeds directly without a metal precursor layer. The chemical stability of these $WNx/SiO2$ and $TiNx/SiO2$ interfaces is investigated by rapid thermal annealing up to 850 °C. The $WNx/SiO2$ interface is stable up to 650 °C while $TiNx/SiO2$ is stable below 850 °C. Metal–oxide–semiconductor capacitors have been fabricated with $WNx$ and $TiNx$ gates and 7.5 nm thick thermal oxide gate dielectrics with interface trap densities, $Dit<2×1011$ $cm−2 eV−1.$ Capacitance–voltage and current–voltage measurements indicate the Fermi level for $TiNx$ lies near midgap in Si, while for $WNx$ it lies closer to the valence band.