CMSE2015

Laser based microfabrication techniques
Prof. Sigitas Tamulevičius
Institute of Materials Science Kaunas University of Technology, Lithuania
Different techniques and optical setups employing continuous wave as well as pulsed femtosecond lasers in production of microstructures and optical elements will be presented. Features and applications of the direct laser beam writing, interference lithography, laser ablation by direct laser beam as well as by the interference field will be discussed. Today interference or holographic lithography (HL) is emerging as very promising and powerful technique for creating structures with sub-micrometer to nanometer scale periodicities. Currently fabrication of photonic crystals is perhaps the most common HL application. Besides research trends in photonic crystals, HL is shown to be applicable in vast range of areas where regular microstructures are necessary. Holographic lithography (HL) is high throughput technique capable of patterning complex regular structures with sub-wavelength resolution. There have been shown successful attempts where formation of optical sensors, nanowires, porous membranes, broadband membrane reflectors, magnetic dots, nano-fluidic structures and micro lenses arrays was performed employing HL. Examples of fabrication and characterisation methods of two-dimensional periodic microstructures in photoresist with pitch of 1.1-1.2 μm, formed using two-beam multiple exposure holographic lithography technique will be presented. The regular structures were recorded employing different angular positions of the sample in between two and three sequential exposures, providing fringes of various symmetries on thin positive tone photoresist layer spin-coated on floated glass substrates. After exposure and development, the resulting structures were analysed employing optical and scanning electron microscopy. Application of ultrafast pulsed lasers in HL simplifies the surface patterning by integrating different processes utilized in conventional lithography into one direct surface micromachining step. There exists a wide range of HL optical setups but due to the short coherence length of the ultrafast pulsed lasers they are limited to the symmetrical configurations. Such holographic lithography configurations are often based on diffractive optical element (DOE) beam splitters. Rectangular profile phase diffraction gratings have been successfully demonstrated as efficient beam splitters for time resolved four wave mixing technique. In the current presentation DOE were used to produce uniform interference field that was used in structuring of different materials including polymers, diamond like carbon as well as diamond like based nanocomposites.