The Relationship between the Oxygen Vacancies Density with the Electronic and Optical Properties of Hafnium Oxide

Hafnia-based high- κ dielectrics are widely used in modern MOS devices, perspective RRAM and FRAM cells, dopand of ceramics in teeth prosthetic. The electronic properties of HfO 2 , such as leakage currents and luminescence, are defined by traps and defects. The presence of traps increases the conductance of dielectric. Electron or hole localization on traps shifts the voltage threshold and leads to device degradation. In active layers of RRAM, traps act as precursors of a filament during the HRS/LRS switch. The trap density ≲10 22 cm -3 is a huge for degeneration of devices, but is very low for detecting within chemical analytical techniques. Previously, it was reported that comparison measured J-V dependencies with multiphonon transport models allows extracting the density of oxygen vacancies (VO), which acts as traps, in the HfO 2 . In the study, we try to get correlations between the trap density and optical properties of hafnia films. Variation of the trap density in HfO 2 was supported by different conditions of film synthesis using ALD technique and different precursors: TEMAH+H 2 O and Hf(thd) 4 +O 2 . The series of samples was annealed in N 2 -flow for 1 hour at different temperatures. Annealing was performed directly in the reaction chamber at T ann = 440, 550 and 700 °C for TEMAH+H 2 O samples and T ann = 550 and 700 °C for samples deposited from Hf(thd) 4 +O 2 precursor system. Dispersion dependencies of refractive index were measured by spectral and laser ellipsometry. It was found that the refractive index grows as films are depleted by oxygen. The results offer a new in situ technique for quality evaluation of synthesized HfO 2 films, namely evaluation of oxygen vacancy density. The work was supported by the Russian Science Foundation, grant #16-19-00002.