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.