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.