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

Abstract

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