Chemical metallization of ultrathin polymer insulation film for through-silicon via application

Highlights: • The adhesion between nickel-phosphorus films and polymers is enhanced. • 4-vinylpyridine functional groups are covalently grafted on the polymer surface. • The catalytic performance of palladium can be improved with hydrofluoric acid. • This method has been applied in through-silicon-vias with high aspect ratio. Insulating polymers have attracted much attention in the fabrication of through-silicon-vias (TSVs) for their ease processing procedures and stress buffer properties. However, due to the high aspect ratio of TSVs as well as the chemical and physical inertness of polymers, metallization of polymers is hugely challenging. Herein, an aqueous surface functionalization method aided by diazonium chemistry and the activation process with hydrofluoric acid (HF) have been proved efficient concerning the nickel layer deposition on ultrathin polymethacrylic acid (PMAA) film. 4-vinylpyridine functional groups are covalently grafted on the PMAA surface to enhance the palladium catalysts adsorption by forming stable coordination complexes with PdCl₄^2-. Moreover, by adding a small amount of HF into the traditional acidic palladium chloride activation solution, non-agglomerated atomic palladium with larger catalytic specific surface area can be formed. As a result, a uniform and compact nickel film is obtained with excellent adhesion to PMAA both on planar substrates and in 3-dimensional vias. This facile and efficient approach can be finely applied for the metallization of the polymer insulation layer in TSVs with high aspect ratios, which has a promising application prospect in the microelectronic industry.