Growth of highly conformal ruthenium-oxide thin films with enhanced nucleation by atomic layer deposition

Highly conformal and conductive RuO2 thin films were deposited without nucleation delay using atomic layer deposition (ALD) by zero-valent metallorganic precursor, (ethylbenzyl)(1,3-cyclohexadienyl)Ru(0) (EBCHDRu, C14H18Ru) and molecular oxygen (O2) as a precursor and reactant, respectively. RuO2 thin films could be successfully prepared by controlling the process parameters, such as a reactant flow rate, a reactant pulsing time, a precursor pulsing time, and a deposition temperature. X-ray diffractometry, X-ray photoelectron spectroscopy, and secondary ion mass spectrometry analysis revealed that the formation of a RuO2 phase became favorable with increasing both the reactant flow rate and the pulsing time and with decreasing the precursor pulsing time and the deposition temperature. With the optimized pulsing conditions, the RuO2 film deposited at 225 °C had a tetragonal structure and exhibited excellent properties such as the low resistivity of 118 μΩ-cm, the high density of 6.85 g/cm3 close to the bulk value, and the negligible roughness of 0.33 nm. The growth rate of ALD-RuO2 was as high as 0.186 nm/cycle on the SiO2 substrate and the number of incubation cycles was negligible as 2. The film showed excellent step coverage of ∼100% onto 25-nm-width trench structures with an aspect ratio of 4.5. The ALD-RuO2 was highly stable up to annealing at 700 °C in both O2 and N2 ambient. Finally, the ALD-RuO2 film was evaluated as a bottom electrode of a metal-insulator-metal capacitor with a high-k (dielectric constant) ALD-TiO2 dielectric. The dielectric constant of ALD-TiO2 was confirmed to be as high as ∼68. This extremely high dielectric constant was attributed to the formation of a rutile-structured TiO2 film on top of the ALD-RuO2 bottom electrode, as evidenced by high-resolution transmission electron microscopy analysis.