Self-Assembled Monolayers Assisted all Wet Metallization of SU-8 Negative Tone Photoresist

Abstract

The present work investigates the application of a Self-Assembled Monolayer (SAM) on the widely used negative photoresist SU-8. (3-Aminopropyl) trimethoxysilane (APTMS) is employed to form SAMs on the surface of the polymer through wet silanization in ethanol. The treatment process of SU-8 resin surface is optimized to achieve a well-formed, high quality SAM. Wettability measurements, atomic force microscopy (AFM) and infrared (IR) spectroscopy are employed to follow and optimize the silanization process. Following silanization, the resulting SAMs are employed as adhesion layers for electroless plated metallic layers. For this purpose, the superior affinity of APTMS amine terminal groups towards Pd2+ ions is exploited to activate the surface. Metallic coatings such as Cu, Ni–P or Co–Ni–P are thus deposited by mean of autocatalytic deposition. The surface of metallized samples is analyzed using AFM, scanning electron microscopy (SEM) and glow discharge optical emission spectroscopy (GDOES). Finally, Ni–P is deposited on a micropatterned SU-8 surface to demonstrate the potential of the presented metallization approach for microfabrication.