Investigation of oxygen-related defects and the electrical properties of atomic layer deposited HfO_2 films using electron energy-loss spectroscopy

摘要

The electrical properties of hafnium dioxide (HfO_2) thin films are often attributed to the oxygen composition and oxygen-related defects; however, there have been few systematic studies on the electronic structures of such oxygen atoms. In this study, we used electron energy-loss spectroscopy to identify the influence of the electronic states of the oxygen atoms in HfO_2 thin films by comparing HfO_2 samples for different oxygen source pulse time during atomic-layer deposition (ALD). Although all samples by ALD have higher oxygen content in the film than that in the reference stoichiometric HfO_2 sample, variations in the local symmetry of amorphous HfO_2 thin films were significantly affected by oxygen source pulse time. Moreover, leakage currents of high-oxygen content HfO_2 samples with longer O_3 pulse time decreased considerably, compared with those of low-oxygen content HfO_2 samples with shorter O_3 pulse time, in which oxygen-related defects were observed by the V_fb shift under constant voltage stress. After postdeposition annealing (PDA), the electronic structure of oxygen atoms in HfO_2 films was affected by the initial oxidation states in the amorphous HfO_2 films. Furthermore, after PDA, polycrystalline HfO_2 in high-oxygen content samples was mostly of the monoclinic phase, whereas the metastable tetragonal phase was readily formed in low-oxygen content HfO_2.