The combination of time-of-Ñight secondary mass spectrometry (ToF-SIMS) and monochromatized x-ray photoelectron spectroscopy (XPS) has proved to be a valuable tool for the analysis of chemically modiÐed polymer surfaces. By applying these techniques in situ, together with a plasma modiÐcation chamber and a Knudsen cell, we have investigated the plasma modiÐcation of polyimide in an oxygen plasma and the Ðrst steps of copper deposition on the untreated and the plasma-modiÐed polyimide substrate. Characterization of the initial stages of copper deposition by XPS and comparison with the untreated and the plasma-modiÐed substrate indicate that, in the case of the untreated substrate, copper binds to the carbonyl group of the repeat unit, whereas after plasma modiÐcation a great number of C-O and C-N functionalities are available as binding sites for the metal overlayer. The molecular ion species identiÐed by ToF-SIMS allow the identiÐcation of speciÐc plasma-induced fragmentation mechanisms and conÐrm the interface reaction mechanisms deduced from the XPS results. The nature and amount of copper-substrate bonds are directly correlated to the adhesion strength of the copper/polyimide interface as measured by the force applied in a standard industrial peel test.