Fabrication of high aspect ratio metallic microstructures on ITO glass substrate using reverse-side exposure of SU-8

This paper describes a simple and inexpensive method to fabricate high aspect ratio metallic microstructures without the requirement of specialized equipments. In the method, a patterned nickel film is deposited on the conductive layer of an ITO glass, which works as an electrode supplying current to the nickel pattern. The nickel pattern electrodeposited serves as both the exposure mask and the seed layer for electroforming of metallic microstructures later on. Conventional contact UV lithography was applied to pattern a thin AZ4620 positive photoresist film coated on the ITO layer of the glass substrate. After development of the photoresist, a nickel film was electrodeposited in the recesses where exposed AZ4620 had been lifted up by using the emerged ITO layer as the conductive electrode. The formed Ni pattern functioned as an exposure mask to pattern a thick SU-8 photoresist coated on it. SU-8 microstructures with high aspect ratio were fabricated with reverse-side exposure. By using the fabricated SU-8 microstructure as a template, and the nickel pattern on the ITO glass substrate as the seed layer, nickel microstructures with high aspect ratio of about 15 and a sidewall slope of 89° were successfully fabricated after removing the SU-8 template in the hot Remover PG followed by a wet etchant.