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

An HfxZr1–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.