TiNx films sputtered from a TiN target were used as diffusion barriers between Cu thin films and Si substrates. The influence of density on the diffusion barrier property of TiN, films between Cu and Si was investigated. Material characteristics of TiN, films and metallurgical reactions of Cu (100 nm)/TiNx (25 nm)/Si systems annealed in the temperature range 500-800 degreesC for 60 min were investigated by sheet resistance measurements, X-ray diffraction, and cross-sectional transmission electron microscopy. It was found that the TiN0.81 film with a density of 4.99 g cm(-3) can prevent Cu-Si interaction up to 600 degreesC for 60 min. The TiN0.86 film with a higher density of 5.12 g cm(-3) is a more effective barrier to Cu penetration; higher density TiN0.86 film prevents the Cu reaction with the Si substrate for temperature up to at least 800 degreesC for 60 min. When the composition of the film is similar, the film density is the dominant factor which determines the failure temperature. The failure mechanism of TiNx films as diffusion barriers between Cu and Si was also discussed. (C) 2004 Elsevier B.V. All rights reserved.