Atomic Layer Deposition of Hafnium–Zirconium-Oxide Films Using a Liquid Cocktail Precursor Containing Hf(dmap)4 and Zr(dmap)4 for Ferroelectric Devices

Abstract

An Hf_xZr_1–xO₂ (HZO) thin film is a promising material for next-generation ferroelectric memory devices. Ferroelectric HZO films are industrially produced using the atomic layer deposition (ALD) technique. However, conventional ALD precursors for ZrO₂ exhibit lower thermal stability than those for HfO₂; thus, the deposition temperature is limited by the Zr precursor processing temperature (320 °C), limiting the quality of HZO. In this study, we developed an ALD precursor for HZO: a liquid homoleptic cocktail precursor referred to as FER-1, which is composed of tetrakis(1-(N,N-dimethylamino)-2-propoxy)hafnium [Hf(dmap)₄] and tetrakis(1-(N,N-dimethylamino)-2-propoxy)zirconium [Zr(dmap)₄] in a 1:1 mol % mixture. Both Hf(dmap)₄ and Zr(dmap)₄ have shown a high thermal stability as high as 371 °C. In addition, these compounds have a similar vapor pressure, similar to the ALD window, and excellent mixture stability. Furthermore, FER-1 exhibits a very clear thermogravimetric curve with no decomposition or residue formation at 10 Torr. Interestingly, the Hf/Zr concentration ratio of the HZO film prepared by using FER-1 was the same as the Hf/Zr concentration ratio in the precursor mixture, demonstrating that the Hf/Zr composition can be easily controlled. The HZO film deposited at 340 °C exhibits ferroelectricity with remanent polarization of 36.9 μC/cm². Our findings show that FER-1 is a highly useful ALD precursor for industrial HZO production.