Step-and-scan maskless lithography for ultra large scale DNA chips

A maskless photolithography test bed was constructed to examine the requirements for stepper-based synthesis of Ultra Large Scale DNA chips (ULS-DNA chips). The test bed is based on a microscope optical layout with a 5 × reduction imaging lens and micro/nano controlled staging at the image plane. Spatial light modulation is enabled by a Digital Micromirror Device (Texas Instruments DMD 0.7XGA) and the positioning system is composed of a piezoelectric nano-positioner (nPoint Inc., Madison, WI) mounted on a high precision linear-motor stage (Newport Corp., Irvine, CA). With this test bed we examined the requirements of overlay and alignment in a stepper-based DNA microarray synthesis system. We demonstrated multi-field chip synthesis with a spot size of 3.15 μm at the 5 × reduction. All tests were verified by standard hybridization, and fluorescence microscopy. In addition to our demonstration of step-and-scan lithography for DNA chip synthesis, we drafted and modeled an imaging optic for a production scale tool capable of synthesizing DNA chips containing up to 20 million pixels.