Fabrication of three-dimensional micro- and nanoscale features with single-exposure photolithography

We report a technique for fabricating three-dimensional structures from two-dimensional photomasks in a single exposure. Size-dependent transmission properties of apertures in the photomask and exposure energy were used to control polymer feature dimensions. The photomasks were produced by electron beam lithography, and apertures in the photomasks were 0.35-5.5 microm wide and 20-30 microm long. Photomasks were coated with the negative tone photoresist SU-8, and following exposure and postexposure processing, the resulting SU-8 features had widths from 0.35 to 5.5 microm and heights from 1.1 to 10.8 microm. With this technique, nanoscale features were easily coupled to microscale features because they were created in the same photoresist layer with one exposure.