Combined ToF‐SIMS/XPS study of plasma modification and metallization of polyimide

Abstract

The combination of time-of-flight secondary mass spectrometry (ToF-SIMS) and monochromatized x-ray photoelectron spectroscopy (XPS) has proved to be a valuable tool for the analysis of chemically modified polymer surfaces. By applying these techniques in situ, together with a plasma modification chamber and a Knudsen cell, we have investigated the plasma modification of polyimide in an oxygen plasma and the first steps of copper deposition on the untreated and the plasma-modified polyimide substrate. Characterization of the initial stages of copper deposition by XPS and comparison with the untreated and the plasma-modified substrate indicate that, in the case of the untreated substrate, copper binds to the carbonyl group of the repeat unit, whereas after plasma modification a great number of C–O and C–N functionalities are available as binding sites for the metal overlayer. The molecular ion species identified by ToF-SIMS allow the identification of specific plasma-induced fragmentation mechanisms and confirm 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. Copyright © 1999 John Wiley & Sons, Ltd.