Polyimide (PI) materials have attracted much attention as a promising substrate in electronic packaging, on the basis of fact that PI has a low dielectric constant and the good thermal-mechanical and chemical properties. Copper offers a better electromigration-resistant performance and lower thin film resistivity as compared with other interconnects. Copper thin films were deposited on PI substrates by physical vapor deposition (PVD) method. Amorphous TiN film with thickness of 150 nm prepared by PVD was used as a diffusion barrier between Cu on PI. Effect of heat treatment up to 300  on the behavior of TiN diffusion barriers and copper film resistivity were studied. The spectra of AES depth profile indicated that TiN prevented Cu from diffusing into PI from room temperature to 300 . After treatment, the adhesion strength of copper films was measured by the peel test, the adhesion improvement by heat treatment was mainly attributed to the removal of tensile residual stress in copper films.