Thermal annealing effect on electrical properties of metal nitride gate electrodes with hafnium oxide gate dielectrics in nano-metric MOS devices

Electrical properties of hafnium oxide (HfO2) gate dielectric with various metal nitride gate electrodes, i.e., tantalum nitride (TaN), molybdenum nitride (MoN), and tungsten nitride (WN), were studied over a range of HfO2 thicknesses, e.g., 2.5–10 nm, and post-metal annealing (PMA) temperatures, e.g., 600 °C to 800 °C. The work function of the nitride gate electrode was dependent on the material and the post-metal annealing (PMA) temperature. The scanning transmission electron microscopy technique is used to observe the effect of PMA on the interfacial gate dielectric thickness. After high-temperature annealing, the metal nitride gates were suitable for NMOS. At the same PMA temperature, the oxide-trapped charges increased and the interface state densities decreased with the increase of the HfO2 thickness for TaN and WN gate electrodes. However, for MoN gate electrode the interface state density is almost independent of film thickness. Therefore, dielectric properties of the HfO2 high-k film depend not only on the metal nitride gate electrode material but also the post-metal annealing condition as well as the film thickness. During constant voltage stress of the MOS capacitors, an increase in the time-dependent gate leakage current is also observed.