KrF-excimer laser pretreatment and metallization of polymers

Metal film adhesion to polymers can be improved by pretreatment with UV-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 aluminum films less than or equal to 10 nm in thickness, enabling the effects of irradiation on the metal/polymer interface to be studied. Irradiation is done in air with KrF-excimer laser radiation(lambda = 248 nm) at fluences per pulse less than or equal to 600 mJ/cm(2). The threshold fluence epsilon(t) for material removal is determined by profilometry measurements of etched features, and the chemical properties of the polymer and the metal/polymer interface are studied with X-ray photoelectron spectroscopy (XPS). Aluminum films are thermally evaporated in situ in the XPS spectrometer. Irradiation of PI at fluences near epsilon(t) (41 mJ/cm(2)) results in loss of oxygen and opening of the imide ring, resulting in doubly bonded nitrogen species. After evaporation of aluminum the carbonyl (C = O) Cls XPS signal is reduced in intensity, and both Al-0 and Al3+ are found, the latter being located at the interface. In comparison to unirradiated areas, irradiated areas have more aluminum in total and a higher proportion of interfacial Al3+ species, indicating an increase in the concentration of metal binding sites. Although for PET the O to C ratio also decreases with irradiation 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 enhancement of Al-0 for films deposited on irradiated surfaces.