Atomic Layer Deposition of Ru for Replacing Cu-Interconnects

Abstract

The atomic layer deposition (ALD) of Ru using a metal–organic precursor, tricarbonyl(trimethylenemethane)ruthenium [Ru(TMM)(CO)3] and O2 as a reactant is reported. The high vapor pressure, thermal stability, and relatively small ligands of the precursor facilitate efficient ALD. Typical self-limiting growth and an ALD temperature window of 220–260 °C are observed along with significantly high growth per cycle (GPC) (∼1.7 Å) and short incubation cycles (∼6) at 220 °C. Density functional theory calculations indicate that the high growth rate and self-limiting behavior can be attributed to the characteristics of the trimethylenemethane ligand. The as-grown polycrystalline films (average grain size ∼20 nm and negligible impurities) were evident from plan-view transmission electron microscopy. The variation in film resistivity with increasing film thickness and deposition temperature was investigated with and without annealing. Films deposited at 260 °C show low resistivity (∼12.9 μΩ cm), which further decreases (∼9.8 μΩ cm) postannealing at 500 °C. A thin Ru film is successfully deposited with 100% step-coverage on a dual-trench structure having an aspect ratio of ∼6.3 (minimum width: ∼15 nm). The interfacial adhesion energy measured using the four-point bending test exceeds 7 J m–2, regardless of the dielectric material and annealing treatment. The Ru precursor permits enhanced nucleation and GPC at relatively low deposition temperatures to construct high-quality Ru films with significantly low resistivity using simple, plasma-free techniques, and is suitable for the fabrication of emerging Ru films to replace Cu-based interconnects.