Thermal Atomic Layer Deposition (ALD) of Ru Films for Cu Direct Plating

Ruthenium (Ru) thin films were grown on thermally-grown SiO2 substrates by thermal atomic layer deposition (ALD) using a sequential supply of a zero metal valence precursor, isopropyl-methylbenzene-cyclohexadiene Ru(0) (IMBCHRu, C16H22Ru) and molecular oxygen (O2) at substrate temperatures ranging from 185 to 310°C. The growth rate at 185°C was approximately 0.059 nm/cycle but its resistivity was >3000 μΩ cm. When the deposition was done at 200°C, the resistivity was decreased drastically to ∼100 μΩ cm, and the film growth rate increased to 0.075 nm/cycle. An ALD temperature window from 225 to 270°C was observed. A high growth rate of 0.086–0.089 nm/cycle was obtained at this ALD temperature window. The film deposited at 270°C showed a minimum resistivity of ∼30 μΩ cm and a high density of 11.7 g/cm3 and with no impurities in the film, such as oxygen and carbon. At 310°C, the growth rate increased to 0.136 nm/cycle due to a partial decomposition of the precursor. In addition, the film resistivity increased slightly to ∼40 μΩ cm with the incorporation of carbon and the formation of a less-dense film. The step coverage of the ALD-Ru film was dependent on the dimensions of the contact and deposition temperature. At the contact with an aspect ratio of ∼4.6 (top opening diameter: 80 nm), the step coverage was excellent irrespective of the deposition temperature. However, at the contact with an aspect ratio of ∼25, the step coverage of the film deposited at 310°C (or above ALD temperature window) was degraded, even though those prepared within ALD temperature window were ∼100%. Finally, ALD-Ru film was used successfully as a seed layer for Cu electroplating.