Complete 3D UV microfabrication technology on strongly sloping topography substrates using epoxy photoresist SU-8

Abstract

A complete process of 3D UV depth lithography with electrodeposition was integrated into a complex technology for the fabrication of copper high-aspect-ratio micro coils. Three effects complicated the lithographic processing. A satisfactory adhesion of the resist structures on the copper seed layer could be achieved by application of a MCC Omnicoat TM adhesion layer. Locally uncontrolled crosslinking reactions within the SU-8 were caused by light reflections at strongly sloping topography. They could be avoided either by local removal of the reflecting seed layer or by redesign of the photomask. The SU-8 removal was accomplished by plasma etching followed by lifting off the resist residues in a wet etch step necessary for the removal of the seed layer. Resist structures of a width both of lines and of spaces of 4–4.5 μm were formed at 20 μm thickness, resulting in corresponding copper coils electroplated to a height of 15 μm.