Atomic layer deposition of nickel oxide films using Ni(dmamp)2 and water

Abstract

A precursor originally synthesized for the chemical vapor deposition of metallic nickel, $\mathrm{Ni}{\left(\mathrm{dmamp}\right)}_2$ ($\mathrm{dmamp}=$ 1-dimethylamino-2-methyl-2-propanolate, -$\mathrm{OC}{\mathrm{Me}}_2\mathrm{C}{\mathrm{H}}_2\mathrm{N}{\mathrm{Me}}_2$ ), has been adopted as a nickel source for the atomic layer deposition of nickel oxide (NiO) using water $\left({\mathrm{H}}_2\mathrm{O}\right)$ as the oxygen source. The precursor is a solid at room temperature, but readily sublimes at 90 °C. The self-limiting atomic layer deposition (ALD) process by alternate surface reactions of $\mathrm{Ni}{\left(\mathrm{dmamp}\right)}_2$ and ${\mathrm{H}}_2\mathrm{O}$ was confirmed from thickness measurements of the NiO films grown with varying $\mathrm{Ni}{\left(\mathrm{dmamp}\right)}_2$ supply times and numbers of the $\mathrm{Ni}{\left(\mathrm{dmamp}\right)}_2\text{-}{\mathrm{H}}_2\mathrm{O}$ ALD cycles. The ALD temperature window for this precursor was found to be between 90 and 150 °C. Under optimal reaction conditions, the growth rate of the NiO films was $\sim 0.8\mathrm{\AA }∕\mathrm{cycle}$ . The NiO films deposited on Si(001) at 120 °C were characterized by x-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy. The x-ray diffraction patterns showed no distinct peaks for NiO, indicating that the films deposited at this temperature were amorphous. X-ray photoelectron spectroscopy analysis showed the films to be stoichiometric with no detectable amount of carbon impurities. For a film with the thickness of 810 Å (with 1000 ALD cycles) the root-mean-square surface roughness was only $\sim 4\mathrm{\AA }$ as measured by atomic force microscopy. To elucidate the ALD mechanism of the Ni precursor with water, a quadrupole mass analyzer was employed with ${\mathrm{D}}_2\mathrm{O}$ as the oxygen source in lieu of ${\mathrm{H}}_2\mathrm{O}$ . Interestingly, unlike the usual ALD fashion, the $\mathrm{Ni}{\left(\mathrm{dmamp}\right)}_2$ precursor does not seem to decompose but only coordinatively bond to the OH-terminated surface when it was introduced. Next, the $\mathrm{Ni}{\left(\mathrm{dmamp}\right)}_2$ -surface species decompose to produce a hydroxylated nickel oxide surface and the alcohol dmampH when water was supplied.