Herein, low-resistivity Ru metal films were fabricated via atomic layer deposition (ALD) using dicarbonyl-bis(5methyl-2,4-hexanediketonato)Ru(II) and O-2 as the Ru precursor and co-reactant, respectively. ALD-grown Ru showed excellent growth characteristics, with high growth per cycle (0.89-1.44 angstrom/cycle), short incubation period (<3 cycles), and good conformality at deposition temperatures of 240-300 degrees C. Polycrystalline Ru films with a dense grain structure were obtained, and the crystallinity and grain size of the Ru metal films increased with increasing deposition temperature. The Ru films contained negligible carbon impurities at all investigated deposition temperatures; however, oxygen-impurity contents of 16, 8, and 3 at% were observed at 240, 270, and 300 degrees C, respectively. Interestingly, despite the presence of significant oxygen impurities, the as-prepared ALDgrown Ru metal films showed a very low resistivity of 13.6-16.5 mu Omega cm. Post-deposition annealing at 400-700 degrees C enhanced the electrical resistivity of the film (to as low as similar to 10.4 mu Omega cm), owing to the increased grain size, dense and smooth surface morphology, and negligible oxygen-impurity content. Modeling of the electron scattering mechanism of the ALD-grown Ru films revealed that the grain size of the films substantially influences the film resistivity, whereas the oxygen impurity in the Ru film had a relatively insignificant effect.