Building thick photoresist structures from the bottom up

Micromachining has pushed the limits of photolithography in the vertical direction. We demonstrate a new technique for producing structures in thick photoresists, with excellent contact alignment and high aspect ratios using a standard UV source. In this technique, we exposed the resist from the bottom by defining the mask as part of the substrate. By doing so, we successfully created high aspect ratio and multiple-layer structures. Additionally, the structures have a slight inward taper, a very useful feature for molding. This technique is a new way of thinking about photolithography, allowing novel structures and simplified processing.