Selective Electroless Copper Deposition by Using Photolithographic Polymer/Ag Nanocomposite

Abstract

This paper presents a novel, direct, selective, vacuum-free, and low-cost method of electroless copper deposition, allowing additive patterning of nonconductive surfaces. Ag nanoparticles (NPs) synthesized inside a photosensitive polymer are acting as seeds for electroless copper deposition. The resulting copper film surface morphology was studied with scanning electron microscopy. Copper films were shown to display a rough grainlike structure, covering substrate uniformly with good metal-substrate adhesion. Copper thickness was studied as a function of the plating time, temperature, and Ag NPs seed concentration. A maximal copper thickness of ${0.44}\,\pm \,{0.05}~\mu \text{m}$ was achieved when plated at 30 °C with 0.4 M Ag(I). The minimum feature resolution of copper patterns, grown with 0.025- and 0.1-M silver salt, is attained down to ${10}~\mu \text{m}$ . The maximum electrical conductivity of the copper film prepared with 0.025-, 0.1-, and 0.4-M Ag(I) approaches ( ${0.8}\,\pm \,0.1) \times {10}^{{7}}$ S/m, ( ${1.1}\,\pm \,{0.1}) \times {10}^{{7}}$ S/m and ( ${1.6}\,\pm \, {0.4}{)} \times {10}^{{7}}$ S/m, respe- ctively. Electroless copper interconnections and LED circuit on glass substrate were fabricated as a proof of concept demonstrators.