Compositional dependence of crystallization temperatures and phase evolution in hafnia-zirconia (HfxZr1−x)O2 thin films

Abstract

Polymorphic (HfxZr1−x)O2 (HZO) thin films exhibit ferroelectric, dielectric, and antiferroelectric properties across a wide compositional range due to the existence of orthorhombic, monoclinic, and tetragonal phases. To better understand the phase stability across the HfO2–ZrO2 compositional range, we investigate the structural evolution of HZO thin films in situ via high-temperature x-ray diffraction (HTXRD) for five different compositions [ZrO2, (Hf0.23Zr0.77)O2, (Hf0.43Zr0.57)O2, (Hf0.67Zr0.33)O2, and HfO2]. The real-time monitoring of HZO crystallization reveals a competing driving force between the tetragonal and monoclinic phase stabilities for HfO2-rich vs ZrO2-rich compositions. Additionally, we confirm an XRD peak shift toward lower 2θ with increasing temperature in ZrO2, (Hf0.23Zr0.77)O2, and (Hf0.43Zr0.57)O2 films, which we ascribe to the appearance of a metastable orthorhombic phase during heating. A monotonic trend for the onset crystallization temperature is reported for five compositions of HZO and reveals an increase in onset crystallization temperature for HfO2-rich compositions. Relative intensity fraction calculations suggest a higher fraction of monoclinic phase with increasing annealing temperature for (Hf0.67Zr0.33)O2. This study of phase stability and onset crystallization temperatures offers insight for managing the thermal budget for HZO thin films, especially for temperature-constrained processing.

Metal Nitride Electrode Stress and Chemistry Effects on Phase and Polarization Response in Ferroelectric Hf0.5Zr0.5O2 Thin Films

“…[ 28 ] Hafnium zirconium oxide (Hf 1– x Zr x O 2 , HZO) alloys, in particular, have generated wide interest due to the observation of robust hysteresis behavior with a lower thermal budget compared to most other HfO 2 ‐based ferroelectrics. [ 29,30 ] Zirconium oxide also demonstrates the largest dopant concentration window in which ferroelectric polarization response is observed (≈10–80 at%). [ 9 ] For other dopants, a ferroelectric response is generally observed for concentrations between 1 and 10 at%, excluding lanthanum, [ 31 ] which has been shown to stabilize orthorhombic HfO 2 with doping concentrations up to 20 at%.…”

Urbach‐Energy‐Dictated Spatial Propagation of Electrons in Thermodynamically Tuned Amorphous Zirconia Thin Films

“…[ 9–14 ] Among metal oxides used as an insulator, zirconia thin films can offer a better option in a wide variety of applications owing to their solution processability, acceptable relative permittivity (ε r ), low leakage current density ( J leak ), and high transparency in the visible region. [ 15–17 ] It should be noted that the features of the wide bandgap formation and high bandgap tunability through stoichiometric and morphological manipulations render group IV transition metal oxides such as zirconia, hafnia, and titania considered notably interesting. Therefore, exploring the behavior of electrons, the energy distribution of states, the effects of defects, and relations thereof in zirconia thin films is expected to provide a useful knowledge base for metal‐oxide‐based future electronics.…”

Low-Temperature Dopant-Assisted Crystallization of HfO2 Thin Films

“…Transition metal oxides have been the subject of intense study due to their use in many technologies such as nanoelectronics, sensors, photocatalysis, etc., both in amorphous and crystalline forms. HfO2 can be found in a variety of phases such as cubic, tetragonal, monoclinic, and more recently the orthorhombic [1][2][3][4] . For thin films which are the subject of this proposal, crystallization usually proceeds by nucleation in the tetragonal phase due to the surface energy effect but the monoclinic phase takes over and appears the most dominant 5,6 .…”

“…One should keep in mind that film thickness is an important parameter. HfO2 films with thickness around 100 nm are known to crystallize partially at 250°C and in general, the crystallization onset temperature is inversely proportional to the film thickness 4,5,10,13,30,[44][45][46][47] . For example, Kukli et al demonstrated thicknessdependent crystallization for HfO2 films deposited from tetrakis ethylmethylamino hafnium (TEMAHf) and H2O at 250°C: 5 nm film are amorphous, 30 nm barely crystalline, and for 45nm films the presence of crystallization is evident 48 In this manuscript, we will demonstrate that HfO2 films with thicknesses from 6 to 34 nm deposited at 250-275°C on GaAs oxide surfaces are polycrystalline and contain a variety of crystalline phases.…”