Chemical interaction, adhesion and diffusion properties at the interface of Cu and plasma-treated thiophene-based plasma polymer (ThioPP) films deposited by plasma-enhanced chemical vapor deposition (PECVD) were studied. Surface characterization of ThioPP films treated by Ar and O-2 plasma using X-ray photoelectron spectroscopy (XPS), contact angle measurements, and atomic force microscopy (AFM) showed the formation of C=O chemical bonds by O-2 plasma treatment and increase in surface roughness resulting in the decrease of contact angle. The chemical interaction between Cu and plasma-treated ThioPP films investigated by XPS showed the formation of Cu-S chemical bonding resulting in the strong adhesion of Cu on ThioPP films. Diffusion properties of Cu/ThioPP films annealed at 450 degreesC for 1 h were surveyed by current-voltage (I-V) measurement. The slight reduction of Cu diffusion into ThioPP films treated by O-2 plasma compared to that of the samples untreated or treated by Ar plasma is attributed to the formation of new chemical bonding states on the surface of O-2 plasma-treated ThioPP films.