Photolithography is the standard manufacturing technique used for micro-patterning of electronic circuits, as well as other devices such as micro-electromechanical systems (MEMS) and micro-fluidics. However, these processes typically require the use of sets of expensive hard photo-masks, meaning that if any changes to the desired pattern are required then a new set of masks must be fabricated. As an alternative, mask-free processes have been developed for rapid prototyping, such as laser direct-writing and scanning electron-beam lithography.
We have shown that CMOS-controlled UV-emitting micro-LEDs can be implemented as a part of a mask-free photolithography system . Micro-LEDs emitting at 370 nm approximately match the i-line photolithography wavelength and as such are suitable for exposing standard photoresist. The CMOS control electronics allow for easy control of the spatial pattern used to expose the photoresist, as well as allowing the exposure dose to be very finely tuned. By integrating this UV-emitting CMOS-controlled micro-LED array with a demagnification system and piezoelectric translation stage, feature sizes as small as 500 nm have been exposed in photoresist .
Patterns and continuous features such as trenches can be fabricated by translating the photoresist sample and/or altering the pattern emitted from the micro-LED array.
Recently, we have demonstrated fully operational micro-LED arrays which were fabricated using this mask-free process, illustrating that this µLED-based mask-free photolithography system is capable of realising practical optoelectronic devices .
 D. Elfström et al., “Mask-less ultraviolet photolithography based on CMOS-driven micro-pixel light emitting diodes.” Optics Express, 17(26):23522-23529, 2009.
 B. Guilhabert et al., “Sub-Micron Lithography Using InGaN Micro-LEDs: Mask-Free Fabrication of LED Arrays”, IEEE Photonics Technology Letters, in press.