The effects of nitrogen incorporation on the properties of atomic layer deposited Ru thin films as a direct-plateable diffusion barrier for Cu interconnect

Abstract

N-incorporated Ru films were deposited by atomic layer deposition (ALD) at a deposition temperature of 270 °C using 1-isopropyl-4-methylbenzene- cyclohexa-1,3-dienyl ruthenium and N2/H2 mixture plasma as the precursor and reactant, respectively. The N content in the ALD-Ru films was controlled by changing the gas ratio [N2 versus the total gas (N2 + H2) flow rates] in the reactant from 0.82 to 1. Secondary ion mass spectrometry depth profiling revealed an increase in N content in the film with increasing gas ratio. The amount of N in the ALD-Ru films had a considerable effect on the film properties, such as resistivity, crystallinity and microstructure. Although the resistivity of the pure ALD-Ru film was ∼ 19 μΩ cm, the N-incorporated ALD-Ru films deposited with a gas ratio of 0.86 (N/Ru: ∼ 0.38) showed a resistivity of ∼ 340 μΩ cm, which increased continuously with increasing gas ratio. X-ray and electron diffraction revealed degradation in film crystallinity and decrease in grain size with increasing N incorporation into ALD-Ru films. Transmission electron microscopy showed that N-incorporated ALD-Ru films formed nanocrystalline and non-columnar grain structures. This is in contrast to that observed in the pure ALD-Ru film, which had a polycrystalline columnar grain structure. The growth rate of a representative N-incorporated Ru film deposited with a gas ratio of 0.86 showed a linear dependency on the number of ALD cycles; growth rate of 0.051 nm/cycle at short incubation cycles of ∼ 3. The step coverage was approximately 98% over the trench structure (aspect ratio: 4.5) with a top opening width of 25 nm. The direct plating of Cu on an optimized N-incorporated ALD-Ru film (5 nm in thickness) was possible. The structure of Cu (80 nm)/N-incorporated ALD-Ru (8 nm)/Si was found to be stable without the formation of copper silicide after annealing at 600 °C for 30 min. © 2014 Elsevier B.V.