Atomic Layer Deposition of Hafnium–Zirconium-Oxide Films Using a Liquid Cocktail Precursor Containing Hf(dmap)<sub>4</sub> and Zr(dmap)<sub>4</sub> for Ferroelectric Devices
Akihiro Nishida, Tsukasa Katayama, Takashi Endo, Yasutaka Matsuo
Abstract
An Hf x Zr 1– x O 2 (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 ZrO 2 exhibit lower thermal stability than those for HfO 2; 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/cm 2 . Our findings show that FER-1 is a highly useful ALD precursor for industrial HZO production.