Influence of Oxygen Content on the Structure and Reliability of Ferroelectric Hf_xZr_1–xO₂ Layers

Abstract

Although some years have passed since the discovery of the ferroelectric phase in HfO 2 and ZrO 2 and their solid solution system Hf x Zr 1−x O 2 , the details of the emergence of this phase are still under investigation. Surface energy contribution, dopant inclusion, residual stress, electric field, and oxygen vacancies have been proposed and studied as potential factors that can influence the phase stabilization. In this work, Hf x Zr 1−x O 2 layers with different Hf/Zr ratios are deposited via atomic layer deposition (ALD) and physical vapor deposition (PVD) and the amount of oxygen that is supplied during deposition is varied. Results are compared for the two deposition techniques for undoped HfO 2 layers. Electrical and structural analysis for the atomic layer-deposited films with different Zr contents and O 2 contents is then performed and the reliability of the films when integrated into capacitors is addressed. The results are correlated to the composition of the layers and a model for layer crystallization is suggested.

Impact of Iridium Oxide Electrodes on the Ferroelectric Phase of Thin Hf0.5Zr0.5O2 Films

“…This minimizes the amount of oxygen vacancies in the film and stabilizes nonferroelectric monoclinic phase portions as observed by GIXRD. [ 21,23 ] These monoclinic phase portions reduce the remanent ferroelectric polarization, which is in good correlation with the wake‐up model published by Pesic et al [ 12 ] The reason for the high depolarization field in films annealed in nitrogen atmosphere is predicted to be a tetragonal interfacial region formed by a high vacancy concentration at the interface. As there is only a slight reduction of the IrO 2 top electrode but no significant change in the oxygen vacancy level as observed in HAXPES, there seems to be limited oxygen out‐diffusion close to the electrode interface with annealing in nitrogen gas.…”

“…[ 11,19–22 ] For pure HfO 2 , the amount of oxygen and oxygen vacancies within the film can significantly influence the stabilization of the crystalline phases. [ 21,23 ] It has been shown that oxygen‐rich films crystallize in the nonferroelectric monoclinic phase (m‐phase), whereas oxygen‐deficient films predominantly form in the tetragonal phase (t‐phase). The stabilization of the ferroelectric orthorhombic phase (o‐phase), however, seems to need a certain amount of oxygen vacancies in between these two extremes.…”

“…[11,[19][20][21][22] For pure HfO 2 , the amount of oxygen and oxygen vacancies within the film can significantly influence the stabilization of the crystalline phases. [21,23] It has been shown that oxygen-rich Thin film metal-ferroelectric-metal capacitors with an equal mixture of hafnium oxide and zirconium oxide as the ferroelectric material are fabricated using iridium oxide as the electrode material. The influence of the oxygen concentration in the electrodes during crystallization anneal on the ferroelectric properties is characterized by electrical, chemical, and structural methods.…”

An Overview of Ferroelectric Hafnia and Epitaxial Growth

“…Materano et al also found that increasing oxygen content in the growth atmosphere promoted the transition to monoclinic phase, whereas the tetragonal and orthorhombic phase were favored under oxygen‐deficient conditions. [ 98 ] Therefore, a lower incubation time reduces the crystallization temperature and larger nuclei are present in the as‐deposited hafnia thin films at room temperature. [ 41 ] Density functional theory (DFT) calculations also verified this correlation that tetragonal and orthorhombic phase formation is suppressed for higher oxygen concentrations in HfO 2 , and monoclinic phase nuclei are formed.…”

Interplay between oxygen defects and dopants: effect on structure and performance of HfO2-based ferroelectrics

“…Despite oxygen being heavily discussed as a key parameter for phase stabilization and reliability control both in traditional perovskite ferroelectrics and in newer HfO 2 -based materials, only lately the effect of the oxygen supply during film deposition has started to be studied systematically by tuning film growth processing parameters. [16][17][18] Within this review, first a general overview of oxygen related defects in oxides is presented. The next section presents the impact of the amount of these defects in terms of oxygen supply during deposition as shown through existing literature reports for undoped HfO 2 and differently doped HfO 2 layers.…”