Patterning NiB electroless deposited on glass using an electroplated Cu mask, microcontact printing, and wet etching

We present a method to pattern an electroless-deposited metal layer based on electroplating a mask and patterning this mask using microcontact printing (μCP) and wet etching. This method starts by derivatizing a glass substrate with an amino-functionalized silane, 3-(2-aminoethylamino)propyltrimethoxysilane (EDA-Si) from solution and using the amine functions of the grafted silane to immobilize Pd/Sn colloids from an acidic suspension onto the glass. The Pd/Sn colloids initiate the electroless deposition (ELD) of a 150 nm thick NiB layer onto the glass. The as-deposited NiB has a specific resistivity of 22 μΩ cm and can be covered with 50 nm of an electroplated Cu layer. Microcontact printing a protective monolayer of eicosanethiol (ECT) onto the Cu and etching it selectively with a cyanide-based etch bath defines the pattern of the Cu mask. This pattern is transferred into the NiB underlayer using a sulfuric acid-based wet etch. The ECT monolayer, the Cu mask, and the Pd/Sn residue remaining on the glass were all removed, yielding the NiB structures. Every step was monitored with X-ray photoelectron spectroscopy (XPS) and the NiB structures were characterized using atomic force microscopy (AFM). Although it comprises a large number of steps, this patterning method is simple and yields high-quality NiB patterns. This method generalizes μCP to metals that are not directly printable, and it could be used instead of vacuum-depositing a metal and patterning it using photolithography.