Metalizable polymer thin films in supercritical carbon dioxide

We report an environmentally "green" method to improve adhesion at a polymer/metal interface by using supercritical carbon dioxide (scCO(2)). Spun-cast polystyrene (PS) and poly(methyl methacrylate) (PMMA) thin films on cleaned Si wafers were used for this study. Film thicknesses of both polymer films were prepared in the range of 100 angstrom to 1600 angstrom. We exposed the films to scCO(2) in the pressure-temperature (P-T) range corresponding to the density-fluctuation ridge, where the excess swelling of both polymer films occurred, and then froze the swollen structures by quick evaporation of CO2. A chromium (Cr) layer with film thickness of 300-400 angstrom was deposited onto the exposed film by using an E-beam evaporator. X-ray reflectivity (XR) measurements showed that the interfacial width between the Cr and exposed polymer layers increased by a factor of about two compared with that without exposure to scCO(2). In addition, the large interfacial broadening was found to occur irrespective of the thickness of both polymer films. After the XR measurements, the dewetting structures of the PS/Cr films induced by additional annealing were characterized by using atomic force microscopy, showing improved surface morphology in the exposed films. Contact angle measurements showed that a decrease in interfacial tension with exposure to scCO(2) accompanied the increase in interfacial width.