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.