Formation of a Polar Ferroelectric Phase in HFO₂ Films Depending on Annealing Conditions and Chemical Properties of Impurities

The Rietveld quantitative phase analysis of the HfO₂ active layer in the Si-sub./SiO₂/HfO₂/TiN layered structures has been carried out at different annealing temperatures and dopant types. The HfO₂ crystal structure has been additionally examined by transmission electron microscopy. A relationship between the dopant valence and crystalline phases forming in the HfO₂ film has been found. It is shown that the Al doping followed by high-temperature annealing prevents the formation of the tetragonal phase (sp. gr. P42/nmc) in favor of the formation of the polar orthorhombic phase (sp. gr. Pca2₁). The results obtained can be used in the synthesis of HfO₂-based ferroelectric films for non-volatile memory systems.