Investigation of atomic-layer-deposited ruthenium nanocrystal growth on $SiO2$ and $Al2O3$ films

The growth of ruthenium (Ru) nanocrystals on the $SiO2$ and $Al2O3$ films has been investigated using atomic layer deposition (ALD) method, indicating that much higher density Ru nanocrystals are grown on the $Al2O3$ film compared with the $SiO2$ film. Ru nanocrystals with a density of $9×1010cm−2$ are obtained on the $Al2O3$ film in the present experiment. The typical nanocrystal height increases with ALD cycles; however, the resulting nanocrystal density decreases for long deposition time (e.g., $600cycles$⁠) on the $Al2O3$ film, going with inferior size uniformity. Postdeposition annealing treatments at both 800 and $900°C$ cause a decrease in the nanocrystal density and an increase in the medial transverse dimension of nanocrystals. Prolonged annealing time at $900°C$ leads to a shrinkage of the medial transverse dimension of nanocrystals due to the formation of ball-like nanocrystals driven by minimizing the total surface energy. X-ray photoelectron spectroscopy analyses reveal metallic Ru nanocrystals surrounded by $RuO2$ which is attributed to Ru oxidation in the air.