Patterning of SU-8 resist with digital micromirror device (DMD) maskless lithography

Abstract

Digital micromirror device (DMD) based maskless lithography has a number of advantages including process flexibility, no physical photomask requirement, fast turnaround time, cost effectiveness. It can be particularly useful in the development stage of microfluidic and bioMEMS applications. In this report, we describe the initial results of thick resist SU-8 patterning, soft lithography with polydimethylsiloxane (PDMS) and lift-off of Cr features using a modified DMD maskless system. Exposures of various patterns and microfluidic channels reveal that the system is well capable of printing 60 μm thick resist at a resolution as small as a single pixel (less than 13 μm) with an aspect ratio about 5:1. Both negatively and positively tapered sidewalls are achieved by projecting the UV light from front side of the SU-8 coated Si wafer and from the back side of the coated glass, respectively. The positive sidewall has an angle 88o which is ideal to serve as a mold for subsequent PDMS soft lithography. Both SU-8 and PDMS microfluidic devices for biomolecular synthesis were fabricated with this maskless system. In addition, a lift-off process was also developed with the intention to create built-in metal features such as electrodes and heaters.