To improve the thermal stability of Mo/Si multilayers, a novel method to form carbide based diffusion barriers, produced by the implantation of Si with CHx+ ions, has been developed. The multilayers were grown by e-beam evaporation, while CHx+ ions were implanted at the Mo/Si interfaces, using a Kaufman ion source with a Ne/CH4 gas mixture. Energies were varied from 300 to 1000 eV. The growth as well as the implantation procedure were monitored by in situ X-ray reflectometry. Auger Electron Spectroscopy was used to characterize the surface composition before and after CHx+ ion implantation. The shift of the Si LVV Auger peak revealed the formation of SiC. Ex situ X-ray reflectometry showed a thermal stability of both the reflectivity and the multilayer period up to 430 K. (c) 2006 Elsevier B.V. All rights reserved.