Investigation of Hydrogen Effect on Ferroelectricity of Atomic Layer Deposited Hf0.5Zr0.5O2 Thin Film

Abstract

Ferroelectrics have retrieved great interest since the discovery of a ferroelectric phase in HfO2.1 Especially, ferroelectric Hf0.5Zr0.5O2 (HZO) thin films have studied for application as a non-volatile memory and field-effect transistor, due to their high scalability and compatibility with CMOS process.2 In our previous work, we have achieved a low thermal budget process (400 °C) by controlling the tensile stress from the TiN electrode during the annealing process.3 Moreover, the TiN electrode can act as a barrier layer against hydrogen diffusion, therefore, the HZO films using the TiN electrodes can prevent degradation of the ferroelectric properties from hydrogen incorporation. However, during the deposition of HZO film using atomic layer deposition (ALD), the choice of oxygen source can affect the residue in the deposited film. When hydrogen-related substances are used as the oxygen source, the ferroelectric properties can be altered by the residues remaining in the HZO film.In this study, we adopted various oxygen sources such as H2O, deuterium oxide (D2O), and O3, for the investigation of hydrogen effect on the ferroelectric properties of the ALD-HZO films. The HZO films were deposited on the TiN bottom electrode by ALD using Hf[N(CH3)2]4 (TDMA-Hf) and Zr[N(CH3)2]4 (TDMA-Zr) as the precursors of Hf and Zr, while H2O, D2O, or O3 as the oxidant. After the TiN top electrode was deposited, rapid thermal annealing was done, and metal-insulator-metal capacitors were fabricated using a Pd/Au hard mask and wet etch process.The HZO films exhibited the formation of a non-centrosymmetric orthorhombic phase which is origin of the ferroelectricity, without consideration for the oxygen sources.4 However, it was confirmed that the ferroelectricity of the HZO film deposited with the oxygen source including hydrogen such as H2O and D2O, was degraded due to the more incorporation with hydrogen. As a result, the ferroelectric polarization of H2O-, and D2O-based HZO was lower than that of O3-based HZO. Simultaneously, the H2O- and D2O-based HZO exhibited higher leakage current than that of O3-based HZO. The results strongly suggest that the suppression of hydrogen incorporation is important to apply ALD-HZO films for next-generation memory application.This work is supported by the National Research Foundation of Korea (NRF) grant (No. NRF-2019R1F1A1059972), Brain Pool Program (No. 2019H1D3A2A01101691), and the Fostering Global Talents for Innovative Growth Program (No. P0008750). 1 T. S. Böscke, et al., Appl. Phys. Lett. 99, 102903 (2011). 2 S.J. Kim, et al., Appl. Phys. Lett. 113, 182903 (2018). 3 S.J. Kim, et al., Appl. Phys. Lett. 111, 242901 (2017). 4 S.J. Kim, et al., JOM 71, 246 (2019). Figure 1