Investigations of photo-induced decomposition of palladium acetate for electroless copper plating

Photo-induced decomposition of palladium acetate films has been performed by using argon and xenon excimer vacuum ultraviolet (VUV) sources that emit radiation peaking at wavelengths of 126 and 172 nm, respectively. VUV irradiation of a substrate treated with palladium acetate results in the formation of palladium, which acts as a catalyst for subsequent copper plating by means of an electroless bath. A selective copper pattern can thus be formed in a simple process using a contact mask. The surface morphology of films on silicon substrates has been investigated using an atomic force microscope (AFM) and a scanning electron microscope (SEM). Exposure conditions were found to affect the morphology and density of the Pd activation layer. The electrical resistivity of the films, measured by four-point probe, and the adhesion strength of copper on the Pd-nucleated substrate, were both found to be dependent on the thickness of the palladium.