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 9×10¹⁰ cm^-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., 600 cycles) 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.