Micromachining using the high energy flat-top beam of a femtosecond pulse UV laser system: micropillar prefabrication

Abstract

Ablation with ultrashort laser pulses as a surface micromachining tool was studied using a hybrid die-excimer laser system that has high energy per laser pulse (tens of mJ’s), about 600 fs pulse duration and low repetition rate (2 Hz). The effect of ablation on the material microstructure with this high energy pulsed laser system was studied. Micropillars were fabricated by laser ablation using a spot size of hundreds of micrometers. Two methods were tested for micromachining. Multiple laser pulse ablation on a standing sample resulted in a columnar microscturcure around the micropillars. This unwanted structure was avoided by beam scanning, resulting in a rather homogeneous ditch. By HR-EBSD measurement it was found that the heat affected zone is less than 1 ?m , which was confirmed by numerical temperature simulations, too. The dislocation density measured below the specimen surface was unaltered, meaning that no significant crystal degradation occurred. In summary, large-scale micro objects with a diameter in the order of 100 ?m without significant change in the crystalline microstructure below the surface, like large-scale micropillars for compression tests, can be fabricated.