Characterization of a single-crystal silicon micromirror array for maskless UV lithography in biochip applications

Abstract

A single-crystal silicon (SCS) micromirror array (MMA) was designed, fabricated and characterized to achieve stable UV light reflectors for biochip fabrication applications such as peptide synthesis systems. The MMA was optimized for biochip applications, with a simple fabrication process (only three photomasks), a large mirror size (210 × 210 µm2) and appropriate separation (60 µm). All the mirrors in the array (16 × 16) were reliable because silicon was used as the structural material for mechanical and optical parts. The mirror surface roughness was very low, being less than 3.93 nm. The turn-on response time was 104 µs and turn-off time was about 800 µs, including settling time. The measured pull-in voltage for the 256 mirrors had an average of 97.0 V and a standard deviation of 2.1 V. A UV reflection test using standard photoresist, AZ1512, showed that the exposure contrast ratio was about 125. From these characterizations, the MMA was shown to have good performance for a useful light modulator for maskless UV lithography, especially in biochip applications.