Sub-micron surface patterning by laser irradiation through microlens arrays

Microlens arrays (MLA) consist of a series of miniaturized lens that are arranged in certain form of order. The ability of MLA to focus incident light into a series of beam spots makes it useful in various applications such as optoelectronic, optical communications as well as parallel image processing. In this paper the focused laser beams by MLA were used to perform sub-micron patterning by lithographic mean of technique. The patterning process demonstrated is simple and able to produce uniform and repetitive patterns (up to 160,000 patterns in single irradiation) over a large area. Femtosecond laser with ultrashort pulse duration of 100 fs is used to pattern the photoresist. The effects of various exposure parameters such as pulse number and laser fluence on pattern size are studied. It is found that nano-scale patterns can be easily produced by using femtosecond laser due to its ultrashort pulse characteristic and multi-photon adsorption. The patterns generated are then transferred into substrate through reactive ion etching (RIE). Optical microscope and atomic force microscope are used to characterize the patterns created. The potential applications for this novel patterning technique will also be discussed.