Reliability study of La₂ O₃ capped HfSiON high-permittivity n -type metal-oxide-semiconductor field-effect transistor devices with tantalum-rich electrodes

A significant difference in the magnitude of the threshold voltage (Vt) reduction achieved by lanthanum oxide (La2 O3) incorporation in ultra-thin dielectrics is observed for TaCx and TaCx Ny electrodes. This is explained by dielectric consumption resulting from the thermodynamically unstable TaCx electrode, which gives rise to electrically active oxygen vacancies in the high-permittivity dielectric. We report extensively on the presence and origins of an aberrant negative Vt shift during positive bias temperature instability stressing and, conversely, a positive shift during negative bias temperature instability stressing for La2 O3 capped HfSiON dielectrics observed for TaCx electroded films, not seen for the TaCx Ny case. Although, oxygen vacancies are inherent due to the differences in electronic configuration between lanthanum and hafnium, this effect is exacerbated by the electrode instability, which is reflected in the Vt dependence.