New Strategy for Controlling the Size and Shape of Metallic Features Formed by Electroless Deposition of Copper: Microcontact Printing of Catalysts on Oriented Polymers, Followed by Thermal Shrinkage

This paper describes a new method of reducing the size of the metal features made by electroless deposition and fabricating complex-shaped, patterned surfaces. Microcontact printing (μCP) was used to pattern oriented glassy polymers with palladium colloids, stabilized with tetraoctadecylammonium bromide. These colloids are catalysts for the selective electroless deposition of copper. Annealing of the activated polymer at a temperature slightly above its glass transition temperature led to a shrinkage of the substrate. Immersion of the shrunken substrate in the plating bath yielded the metal features. The maximum shrinkage of the feature size achieved was on the order of a factor of ∼4 in one direction of the oriented polymer and of ∼7 in the perpendicular direction. Control of the extent and direction of shrinkage allowed the fabrication of metal features with sizes and shapes different from those on the polydimethylsiloxane stamp used for the patterning of the substrate and from the draw ratios. Free-standing metal structures were produced by dissolving the substrate after the metal film had reached the desired thickness. Complex-shaped, patterned surfaces could be fabricated by wrapping the activated polymer film around a scaffolding or template; during the annealing, the polymer adapted the shape of the underlying scaffolding. Metalization of the activated, shaped substrate resulted in patterned three-dimensional structures.