High-aspect-ratio electroformed Ni-Co microstructures with improved mold adhesion using a LIGA-like process and a Novolak sublayer

This work relates to a method for increasing the adhesion of polymer resist to electrically conductive substrates which is an important step in the lithographic steps for creating high-aspect-ratio micro structures. Here we are particularly interested in plating Ni-Co into the very tall high-aspect- ratio accurately patterned polymethyl methacrylate (PMMA) micromolds. They were made by deep x-ray lithography for primary or secondary metal structures or metal mold inserts within the framework of the LIGAS process. We investigated the effect of using a Novolak intermediate layer on various substrates to consolidate the adhesion of the relatively weak PMMA-metal interface. Modifying our process by introducing this intermediate Novolak sublayer improved the adhesive properties overall throughout the whole process including the planarization step, leading to a more reliable process with better yield as well an increase in the quality of the Ni-Co parts. The increase of bond resistance to heat and x-rays was evaluated by shear stress measurements.