Enhanced Growth in Atomic Layer Deposition of Ruthenium Metal: The Role of Surface Diffusion and Nucleation Sites

Thermal atomic layer deposition (ALD) of metals on metal oxide surfaces is challenging due to nucleation delays caused by few chemisorption sites and poor material transport at the substrate. Here, we investigate ways to enhance the nucleation and growth of ruthenium (Ru) using ALD with the Ru(Cp)(2) precursor and O-2 as a coreactant. We explore the effects of functionalizing the substrate surface with small organometallic molecules, such as trimethylaluminum and diethylzinc, on the nucleation and growth of Ru layers. Our results demonstrate an enhancement effect, which is reflected in higher nuclei density and a larger average diameter of the deposited Ru nanoparticles for the same number of cycles. We hypothesize that the increase in nucleation is attributed to the augmentation of nucleation sites, while the increase in growth can be attributed to the elevated surface diffusivity. As a result, the transport processes on the surface, such as coalescence and nanoparticle diffusion, are enhanced compared to the nonpretreated substrate. We support this conclusion by examining the morphology of the Ru layers using scanning electron microscopy, combining it with a theoretical growth model and gaining insights into the underlying mechanism of the enhancement effect. This study contributes to the understanding of ALD processes and provides insights into how small organometallic molecules can be used to modify surface diffusion, leading to the enhanced growth of thin films.