Interface Study in a "Metal/High-k" Gate Stack: Tantalum Nitride on Hafnium Oxide

In this work, we investigate the crystalline structure and the chemical properties of a "metal / high-k" gate stack with TaN as the gate electrode and HfO2 as the dielectric. We show that a 3nm-thick layer of HfO2 is crystallized when it is integrated whereas it is amorphous as deposited. Increasing the TaN thickness increases the amount of the TaN crystalline FCC phase. Concerning the gate stack chemistry, oxygen and nitrogen diffusion between the layers is shown. This occurs during the gate electrode deposition for all TaN thicknesses. We show that the gate stacks which use thick TaN layers are not chemically stable under the spike anneal used for dopant activation, since oxygen and nitrogen diffusion is increased by this thermal treatment. Gate stacks with a thin TaN layer exhibit a high chemical stability under annealing.