Atomic layer deposition of ruthenium (Ru) thin films using ethylbenzen-cyclohexadiene Ru(0) as a seed layer for copper metallization

Ruthenium (Ru) thin films were grown on thermally-grown SiO2 substrates using atomic layer deposition (ALD) by a sequential supply of (ethylbenzene)(1,3-cyclohexadiene)Ru(0) (EBCHDRu, C14H18Ru), and molecular oxygen (O2) at deposition temperatures ranging from 140 to 350 °C. A self-limiting film growth was confirmed at the deposition temperature of 225 °C and the growth rate was 0.1 nm/cycle on the SiO2 substrate with a negligible number of incubation cycles (approximately 2 cycles). Plan-view transmission electron microscopy analysis showed that nucleation was started after only 3 ALD cycles and the maximum nuclei density of 1.43 × 1012/cm2 was obtained after 5 ALD cycles. A continuous Ru film with a thickness of ~ 4 nm was formed after 40 ALD cycles. The film resistivity was decreased with increasing deposition temperature, which was closely related to its crystallinity, microstructure, and density, and the minimum resistivity of ~ 14 μΩ-cm was obtained at the deposition temperature of 310 °C. The step coverage was approximately 100% at trench (aspect ratio: 4.5) with the top opening size of ~ 25 nm. Finally, the ALD-Ru film was evaluated in terms of its performance as a seed layer for Cu electroplating.