Enhancement in thermal stability of atomic layer deposited HfO2 films by using top Hf metal layer

A thin (∼ 0.5 nm) layer of Hf metal was deposited on an atomic layer deposited (ALD) HfO2 film by the DC sputtering method. X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy analyses showed that the Hf metal layer transformed into HfO2 during the post-deposition annealing process. It appears that the HfO2 layer formed by the oxidation of Hf metal provided the underlying ALD HfO2 layer with the nucleation sites necessary to decrease the grain-boundary density of the crystallized HfO2 film. The decrease in the grain-boundary density resulted in a reduction in the Hf-silicate formation and interfacial layer growth during post deposition annealing. This eventually resulted in a smaller increase in the capacitance equivalent thickness (CET) and high-k characteristics in the CET vs. leakage current density curve even after post deposition annealing at 1000 °C.