KrF excimer laser micromachining of MEMS materials: Characterization and applications

Conventional photolithography-based microfabrication techniques are widely used to create microscale structures and devices nowadays. However, these techniques are limited to two-dimensional fabrication and also to particular materials. Excimer laser micromachining enables us to overcome those limitations and facilitates three-dimensional (3D) microfabrication. This paper presents a comprehensive characterization study for excimer laser micromachining of micro-electro-mechanical system (MEMS) materials. By using a 248 nm KrF excimer laser and four representative MEMS materials (Si, soda-lime glass, SU-8 photoresist and poly-dimethysiloxane (PDMS)), the relations between laser ablation parameters (fluence, frequency and number of laser pulses) and etch performance such as the etch rates in the vertical and lateral directions, aspect ratio, and surface quality were obtained. The etch rate increased almost linearly for all four materials as the fluence increased but no significant variation in etch rate was observed as the frequency of laser pulses was changed. The etch rate was also inversely proportional to the number of laser pulses. Physical deformation in the laser-machined sites on PDMS and SU-8 was investigated using SEM imaging. In order to demonstrate the 3D microfabrication capability of an excimer laser and the utility of this characterization study, two novel implantable biomedical microscale devices made of SU-8 and PDMS were successfully fabricated using the optimized laser ablation parameters obtained in this study.