Application of ultraviolet depth lithography for surface micromachining

Very thick photoresist layers were patterned by contact ultraviolet (UV) lithography. In a following microelectrodeposition step the generated resist patterns were molded and three-dimensional (3D) microstructures were fabricated directly onto system surfaces. The new technology, called 3D UV-microforming, consists of an advanced resist preparation process, an UV lithographic step, resist development, a molding procedure by electrodeposition, and finally stripping and cleaning for finishing the structures. It enables the low-cost fabrication of a wide variety of microcomponents for many different uses. During resist preparation, layers up to 200 mu m thickness were obtained. By using a standard UV mask aligner as an exposure tool followed by immersion development, thick resist layers up to 100 mu m could be patterned in a single step on preprocessed silicon wafers. Repeated exposure and development were successfully used for structuring resist layers of up to 200 mu m thickness. Using AZ 4000 series photoresist, the resolution is also limited by mechanical stability. For lines and spaces in 15-mu m-thick resist a minimum width of 3 mu m for the resist was found to be necessary to overcome the fabrication process. For thicker layers high aspect ratios of more than 10 as well as steep edges of more than 88 degrees could be fabricated. The resist patterns used were molded by pulse or by direct current electroplating. For microsystem applications some metals and alloys were deposited. Three-dimensional microcomponents were fabricated as samples for demonstrating the new technique. The technique allows the use of materials with interesting properties, ones that could not be provided by standard processes. (C) 1995 American Vacuum Society.