Nano-titania (TiO2) incorporated into polyimide (PI) matrix can significantly enhance the adhesion strength for PI/TiO2 hybrid film and copper system. Surface modifications by various plasma treatments (Ar, Ar/N-2 and Ar/O-2) were also applied in this study to improve the adhesion strength. The Ar/N2 plasma treatment is regarded as the more effective way in promoting the adhesion strength. The maximum adhesion value of 9.53 N/cm was obtained for the PI/TiO2-1 wt% hybrid film with Ar/N-2 plasma treatment. It is enhanced about 10 times as large as pristine PI. Furthermore, by Ar/O-2 plasma treatment, a weak boundary of copper oxide was formed at the interlayer between PI/TiO2 hybrid film and copper which decreases the adhesion strength. The effects of plasma treatment and content of nanosized TiO2 on the adhesion strength between PI/TiO2 hybrid film and copper system were studied. Atomic force microscope and contact angle analyses were used to measure the changes in surface morphology and surface energy as a result of plasma treatment. Besides, the interfacial states of peeled-off polymer side and copper side were investigated by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Based on the result of XPS spectra, the peeled-off failure mode between PI/TiO2 hybrid film and copper was proposed in this study. (C) 2004 Elsevier Ltd. All rights reserved.