MANA International Symposium 2025

Semiconductor Materials - 02

Title

Effect of oxidant gas on ferroelectricity of atomic layer deposited HfxZr1-xO2 thin films

Author's photo

Authors

Takashi Onaya, Tomomi Sawada, Toshihide Nabatame,
Kazuhito Tsukagoshi

Affiliations

Thin Film Electronics Group, MANA, NIMS

URL

https://www.nims.go.jp/mana/research/semiconductor-materials/thin-film-electronics.html

Email

ONAYA.Takashi@nims.go.jp

Abstract

Ferroelectric HfxZr1−xO2 (HZO) is a promising candidate material for future non-volatile memory devices because it can be deposited by atomic layer deposition (ALD). However, it has not been clarified how the ALD oxidant gas affects the quality of HZO films. In this study, we investigated the effect of ALD oxidant gas, such as H2O and O2 plasma, for HZO films on ferroelectricity, focusing on its role in the formation of ferroelectric orthorhombic (O) phase.

O2 plasma-based HZO films formed nanocrystals with ferroelectric O phase even after the ALD process due to strong oxidation power and high energy ion/electron bombardment of O2 plasma as shown in Fig. 1, while H2O-based films formed an amorphous structure. After the low temperature annealing at 300°C, the O2 plasma-based film was fully crystallized, and the O phase was formed more in the O2 plasma-based film than the H2O-based film. Consequently, O2 plasma-based film showed 1.2 times higher remanent polarization of 29 µC/cm2 than that (24 µC/cm2) of the H2O-based film as shown in Fig. 2. Therefore, the nanocrystals in the as-grown O2 plas ma-based HZO film could play an important role as nuclei for the crystallization and O phase formation [3,4]. These results indicate that a superior ferroelectricity of HZO films can be obtained by using O2 plasma as an ALD oxidant.

Fig. 1. Cross-sectional TEM image of the O2 plasma-based HZO film without an annealing process.
Fig. 2. Polarization–electric field hysteresis curves of H2O- and O2 plasma-based films after the annealing process at 300°C.

Reference

  1. J. Müller et al., Appl. Phys. Lett. 99, 112901 (2011). DOI: 10.1063/1.3636417
  2. J.-H. Kim, T. Onaya et al., ACS Appl. Electron. Mater. 5, 4726 (2023). DOI: 10.1021/acsaelm.3c00733
  3. T. Onaya et al., Microelectron. Eng. 215, 111013 (2019). DOI: 10.1016/j.mee.2019.111013
  4. T. Onaya et al., APL Mater. 9, 031111 (2021). DOI: 10.1063/5.0035848