Completely aqueous route for metallization of structural polymeric materials in micro-electro-mechanical systems

A one-step aqueous diazonium-based process has been proved efficient with respect to the covalent grafting of aminophenyl layers onto KMPR photoresist polymer. In contact with acidic palladium chloride solution for only a few minutes, the positively charged protonated aminophenyl groups on the modified KMPR surface can electrostatically immobilize PdCl42- complexes. This KMPR surface functionalized with palladium-aminophenyl complex activators enables initialize the subsequent autocatalytic deposition of nickel (electroless nickel plating) and leads to a formation of adhesive nickel-boron film onto KMPR substrate. Our proposed green chemistry strategy for the metallization of KMPR photoresist polymer via the diazonium reduction suggests an opportunity to benefit from the incomparable physico-chemical properties of KMPR by integrating it within MEMS structures. The obtained 60 nm thick and compact nickel-boron alloy (93:7 by weight), evidenced through SEM, AFM and XPS techniques, can be used as a conductive seed layer for direct electrolytic deposition of copper. Consequently, a vacuum-free process for copper filling of mechanical features etched inside the KMPR layer has been demonstrated.