For the deposition of Ru on TiN films by metal-organic chemical vapor deposition, pretreatment of the TiN film surface with Electron Cyclotron Resonance (ECR) plasma is essential to enhance Ru nucleation. In the present work, the effects of hydrogen, argon and oxygen plasma treatments on Ru nucleation, induced by Metal-Organic Chemical Vapor Deposition (MOCVD), were investigated using scanning electron microscopy, Auger electron emission spectroscopy and X-ray diffraction analyses. Ru nucleation is enhanced with increasing hydrogen or argon ECR plasma exposure time, while it decreases with increasing oxygen ECR plasma exposure time. Hydrogen ions in the hydrogen plasma react with TiN to form Ti and NH 3. Argon ions in the argon plasma remove nitrogen or oxygen atoms from the top surface of the TiN or TiON film during the argon plasma treatment. The highest Ru nucleation density was obtained on TiN when the underlying TiN surface is pretreated with argon ECR plasma.