Improvement in ferroelectricity of HfxZr1−xO2 thin films using top- and bottom-ZrO2 nucleation layers

Takashi Onaya,Akihiko Ohi,Takahiro Nagata,Toshihide Nabatame,Naoki Ikeda,Atsushi Ogura,Naomi Sawamoto

doi:10.1063/1.5096626

Abstract

A ferroelectric HfxZr1−xO2 (HZO) thin film crystallized with nanocrystalline top- and bottom-ZrO2 nucleation layers (D-ZrO2) exhibited superior remanent polarization (2Pr = Pr+ − Pr− = 29 μC/cm2) compared to that of similar thin films (12 μC/cm2) crystallized without a ZrO2 nucleation layer (w/o) when the HZO film thickness was 10 nm. Epitaxial-like grain growth of the HZO film was observed on the surfaces of both the top- and bottom-ZrO2 layers, while there was almost no significant difference in the crystal grain size of the HZO film in all samples, as determined by cross-sectional transmission electron microscopy images. Consequently, the ferroelectric orthorhombic, tetragonal, and cubic (O/T/C) phase ratio of the HZO film was significantly increased by using the ZrO2 nucleation layers. It was furthermore confirmed that the 2Pr values were strongly correlated with the O/T/C phase ratio of the HZO film. Therefore, it is clear that the top- and bottom-ZrO2 nucleation layers play an important role in the formation of the ferroelectric HZO film. These results suggest that the HZO film fabrication technique using a nanocrystalline ZrO2 nucleation layer is a promising candidate for next-generation device applications.

Highlights

We previously reported that the 2Pr value (24 μC/cm2) of the TiN/HZO (10 nm)/TiN MFM capacitor, which annealed after TE-TiN deposition, was 2 times higher than that (12 μC/cm2) of the postdeposition annealing (PDA)-treated w/o sample, which annealed before TE-TiN deposition, mainly due to the TiN capping effect.[37]
The 2Pr values of MFM capacitors with a 10-nm-thick HZO film increased in the following order: w/o (12 μC/cm2) < B-ZrO2 (15 μC/cm2) < T-ZrO2 (23 μC/cm2) < D-ZrO2 (29 μC/cm2), while all capacitors showed almost the same Ec value of around 1.2 MV/cm
Epitaxial-like grain growth of the HZO film occurred on the nanocrystalline top- and bottom-ZrO2 layers, while all samples exhibited almost the same grain size of the ferroelectric film

Summary

INTRODUCTION

It has been reported that HfxZr1−xO2 (HZO) thin films exhibit ferroelectricity over a wide composition range of the Hf:Zr ratio, while dopant-free HfO2 and ZrO2 single layers commonly show dielectric- and antiferroelectric-like behaviors, respectively.[1,2,3,4,5,6,7] HZO films have great advantages, such as stable ferroelectricity even in thin regions (∼10 nm), a large bandgap (>5 eV), and compatibility with semiconductor integrated circuit technology.[8,9,10,11,12,13] the highly mature atomic layer deposition (ALD) techniques available for HfO2 and ZrO2 enable the fabrication of conformal films, even on the three-dimensional structures required for next-generation memory devices. In this study, based on these ideas, we prepared MFM capacitors with an HZO film, which was deposited using an Hf/Zr cocktail precursor and crystallized using top- and bottom-ZrO2 nucleation layers, and examined the ferroelectricity and crystallization of the resulting HZO films

EXPERIMENTAL

RESULTS AND DISCUSSION

CONCLUSION