KRF-EXCIMER LASER PRETREATMENT AND METALLIZATION OF POLYMERS

Metal film adhesion to polymers can be improved by pretreatment with U V-laser radiation before metal deposition. Chemical changes associated with irradiation are investigated for polyimide (PI) and polybutylene terephthalate (PET) surfaces. Irradiated surfaces are coated with alu minum films less than or equal to 10 nm in thickness, enabling the eff ects of irradiation on the metal/polymer interface to be studied. Irra diation is done in air with KrF-excimer laser radiation(lambda = 248 n m) at fluences per pulse less than or equal to 600 mJ/cm(2). The thres hold fluence epsilon(t) for material removal is determined by profilom etry measurements of etched features, and the chemical properties of t he polymer and the metal/polymer interface are studied with X-ray phot oelectron spectroscopy (XPS). Aluminum films are thermally evaporated in situ in the XPS spectrometer. Irradiation of PI at fluences near ep silon(t) (41 mJ/cm(2)) results in loss of oxygen and opening of the im ide ring, resulting in doubly bonded nitrogen species. After evaporati on of aluminum the carbonyl (C = O) Cls XPS signal is reduced in inten sity, and both Al-0 and Al3+ are found, the latter being located at th e interface. In comparison to unirradiated areas, irradiated areas hav e more aluminum in total and a higher proportion of interfacial Al3+ s pecies, indicating an increase in the concentration of metal binding s ites. Although for PET the O to C ratio also decreases with irradiatio n at fluences near epsilon(t) (38 mJ/cm(2)), changes in the amounts of Al-0 or Al3+ for irradiated areas in comparison to unirradiated areas are much smaller than for PI and consist mainly of a slight enhanceme nt of Al-0 for films deposited on irradiated surfaces.