Insertion of HfO2 Seed/Dielectric Layer to the Ferroelectric HZO Films for Heightened Remanent Polarization in MFM Capacitors

Abstract

This article highlights the role of HfO2 seed/dielectric insertion layers on the ferroelectric properties of hafnium zirconium oxide (HZO)-based metal-ferroelectric-metal (MFM) capacitors. Maximum remanent polarization ( ${P}_{r}$ ) of $22.1~\mu \text{C}$ /cm2 was achieved when HfO2 seed layer of critical thickness (10 A) was inserted at the bottom of HZO films. However, as the bottom HfO2 seed layer thickness increases from 10 to 200 A, the ${P}_{r}$ was found to decrease. The same critical thickness of HfO2 seed layer when inserted at top of the HZO films was found to give a maximum ${P}_{r}$ of $19.6~\mu \text{C}$ /cm2. The obtained ${P}_{r}$ in both the cases (bottom and top HfO2 seed layer) was found to be better than the reference HZO device ( $17.7~\mu \text{C}$ /cm2). Moreover, increased coercive field $({E}_{c})$ was noticed due to the HfO2 seed layer insertion (1.11 MV/cm for bottom HfO2 and 1.09 MV/cm for top HfO2) when compared with the reference device (1.04 MV/cm). Short pulse switching measurements were carried out on the as-fabricated capacitors, and an enhanced ${E}_{c}$ and interfacial capacitance was observed in case of devices with HfO2 seed layer. The crystal structures, and interfacial layer effect was keenly observed and analyzed for the HZO films with and without the seed layer using grazing incidence X-ray diffraction (GIXRD) and X-ray photoelectron spectroscopy (XPS), respectively. The HfO2 seed layer was found to result in higher o-phase formation, and facilitates the diffusion/migration of oxygen atoms from seed layer to the substrate or vice versa in the HZO capacitors giving rise to enhanced ferroelectricity.