dThe effects of nitrogen postplasma treatment on the properties of a Cu/Ta/a-C:F structure were investigated. Interface reactions between Ta and a-C:F were also examined. A strong interaction between Ta and a-C:F at the interface and defluorination of a-C:F film occurred during Th sputter deposition. Ta fluoride was observed at the interface between Ta and a-C:F, which led to adhesion and reliability problems. In order to suppress the reaction at the interface, nitrogen plasma was applied to the as-deposited a-C:F film. The fluorine concentration of the film surface decreases with plasma treatment. As the plasma treatment power increases, the adhesion between Ta and a-C:F film improved. From this study, it was found that nitrogen plasma treatment of a-C:F films is a very effective method for suppression of defluorination of a-C:F film and the interface reaction between Ta and a-C:F film.