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 (O-2) at substrate temperatures ranging from 185 to 310 degrees C. The growth rate at 185 degrees C was approximately 0.059 nm/cycle but its resistivity was > 3000 mu Omega cm. When the deposition was done at 200 degrees C, the resistivity was decreased drastically to similar to 100 mu Omega cm, and the film growth rate increased to 0.075 nm/cycle. An ALD temperature window from 225 to 270 degrees 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 degrees C showed a minimum resistivity of similar to 30 mu Omega cm and a high density of 11.7 g/cm(3) and with no impurities in the film, such as oxygen and carbon. At 310 degrees 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 similar to 40 mu Omega 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 similar to 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 similar to 25, the step coverage of the film deposited at 310 degrees C (or above ALD temperature window) was degraded, even though those prepared within ALD temperature window were similar to 100%. Finally, ALD-Ru film was used successfully as a seed layer for Cu electroplating. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3575163] All rights reserved.