Unexpectedly large remanent polarization of Hf0.5Zr0.5O2 metal–ferroelectric–metal capacitor fabricated without breaking vacuum

Abstract

We introduce an Atomic Layer Deposition (ALD) technique referred to here as Sequential, No-Atmosphere Processing (SNAP) to fabricate ferroelectric Hf0.5Zr0.5O2 capacitors in Metal–Ferroelectric–Metal (MFM) structures. SNAP involves the ALD of each layer sequentially while maintaining the sample under vacuum process conditions without ambient exposure during the entire sequential deposition processes. We first use plasma enhanced ALD to fabricate 002-textured TiN films and study the degree of texture and quality of the film by X-ray Diffraction (XRD), Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), and transmission electron microscopy. Building upon the textured TiN film, we fabricate MFM capacitors with 10-nm-thick Hf0.5Zr0.5O2 via SNAP deposition and observe an unexpectedly large remanent polarization (2Pr = 54.2 μC/cm2). We report that annealing at T <800 °C and at T = 800 °C results in different ferroelectric behaviors and phases determined by grazing incidence XRD patterns. We infer that the nonpolar tetragonal phase is dominant in films treated at T <800 °C, whereas the polar orthorhombic phase is dominant in films treated at T = 800 °C. Using ToF-SIMS and x-ray spectroscopy depth profiling on MFM capacitors, we observe an increase in the concentration of defects in the Hf0.5Zr0.5O2 layer after annealing. We believe that the absence of the native passive layer between Hf0.5Zr0.5O2 and TiN layers made via SNAP deposition is responsible for the unexpectedly large remanent polarization. In addition, we associate the 002-textured TiN as potentially playing a role in realizing the unexpectedly large remanent polarization.

Role of Oxygen Source on Buried Interfaces in Atomic-Layer-Deposited Ferroelectric Hafnia–Zirconia Thin Films

“…Note that the high carbon concentration found by XPS is not only due to the presence of unreacted ligands from ALD metalorganic precursors, but also accounts for adsorbed hydrocarbons from exposure to the atmosphere. The XPS quantification is consistent with our previous depth profiling XPS work, which suggested ∼20 atom % C on the surface of the film, which decreases to <5 atom % when measured via depth profiling XPS within the MFM stack …”

“…As shown in Figure , HZO-O 2 * possesses a more pronounced TiO x layer than HZO-H 2 O. Given that the bottom TiN used in our MFM capacitors is strongly 001-textured, the inclusion of a TiO x layer may render an “interface-breaking” effect, i.e., a disruption in how the underlying 001-textured TiN may influence the formation of the texture of HZO. The interface-breaking of TiN/HZO in HZO-O 2 * could thus encourage the growth of more energetically favorable HZO {111} planes which have a lower surface energy compared to the {001} planes .…”

“…In addition, the solid solution of HfO 2 –ZrO 2 can give rise to dielectric, ferroelectric, and antiferroelectric properties by simply altering the Hf/Zr ratio. , Alloying HfO 2 films with ZrO 2 has the additional advantage of lowering the crystallization temperature to 370 °C for 30 nm films, which can help to mitigate the appearance of the deleterious nonferroelectric phase (e.g., monoclinic), which often forms at higher temperatures . Here, we focus our attention on the 1:1 Hf/Zr HZO composition, which is reported to have the highest ferroelectric response. , …”

Fabrication of Ferroelectric Gate Thin‐Film Transistors with a Lanthanum‐Doped HZO Gate Insulator and Indium‐Tin‐Oxide Channel via a Solution Process

“…Furthermore, the diffraction peak shifted toward higher angles when the doping concentration of La was increased to 11 at%, suggesting the formation of a t ‐phase. [ 17,18 ] Owing to structural expansion, the diffraction peak shifted back to a lower angle when the doping concentration of La was further increased to 17 and 23 at%; this indicates the formation of a cubic phase. [ 16,17 ] Although a detailed analysis is required to accurately determine the crystalline phases, peak shift observations can be used as a reference for crystalline phase estimations.…”

High-Endurance Ferroelectric (La, Y) and (La, Gd) Co-Doped Hafnium Zirconate Grown by Atomic Layer Deposition

“…It is believed that the ferroelectric behavior arises due to the formation of a noncentrosymmetric orthorhombic Pca 2 1 phase, , where the oxygen ions are able to switch between two stable positions, which correspond to two stable polarization states . The formation of orthorhombic HZO was evidenced by Müller et al It has been found to be favored by the postmetallization anneal, , which induces sufficient strain within HZO to create favorable conditions for the growth of orthorhombic Pca 2 1 with ferroelectric properties. Similar to HfO 2 , the inclusion of dopants with a size larger or smaller than that of Hf and Zr ions, which are responsible for the distortion and internal stress within HZO, can have a beneficial effect on the ferroelectric properties, especially on the endurance .…”