In this work, the effect of tin-doped indium oxide (ITO) film as capping layer on the agglomeration of copper film and the appearance of copper silicide was studied. Both samples of Cu 100 nm/ITO 10 nm/Si and ITO 20 nm/Cu 100 nm/ITO 10 nm/Si were prepared by sputtering deposition. After annealing in a rapid thermal annealing (RTA) furnace at various temperatures for 5 min in vacuum, the samples were characterized by four probe measurement for sheet resistance, X-ray diffraction (XRD) analysis for phase identification, scanning electron microscopy (SEM) for surface morphology and transmission electron microscopy (TEM) for microstructure. The results show that the sample with ITO capping layer is a good diffusion barrier between copper and silicon at least up to 750 degrees C, which is 100 degrees C higher than that of the sample without ITO capping layer. The failure temperature of the sample with ITO capping layer is about 800 degrees C, which is 100 degrees C higher than that of the sample without ITO capping layer. The ITO capping layer on Cu/ITO/Si can obstacle the agglomeration of copper film and the appearance of Cu3Si phase. (C) 2007 Elsevier B.V. All rights reserved.