Excimer laser material processing: state-of-the-art and new approaches in microsystem technology

In this paper the current state of the art and new trends in excimer laser processing of polymer materials are presented. Two processing regimes are of general interest: below and above the ablation threshold. The modification of polymer surface can be carried out by laser processing below ablation threshold. This is successfully demonstrated for the fabrication of optical singlemode waveguides in PMMA for the visible optical range and for 1550 nm. The obtained structures reveal absorption losses in the order of 1.4 dB/cm up to 5 dB/cm. Laser exposure using contact masks or direct scanning of planar structures are appropriate methods for the integration of optical waveguides in PMMA sensor devices (Y-branch). Above the ablation threshold excimer laser micromachining is a powerful tool for a rapid manufacturing of complex three-dimensional micro-structures in polymer surfaces with depths between 0.1 μm and 1000 μm and aspect ratios up to 10. Typical application fields are presented in micro-optics, micro-fluidics and rapid tooling. Micro-Laser-LIGA is established in order to fabricate nebulizer membranes, micro-fluidic devices and integrated single mode waveguides. Furthermore, the fabrication of 3d-shapes in metallic mold inserts is successfully demonstrated. Debris formation is completely suppressed. Polymer structuring with a low power short pulse excimer laser with high repetition rates up to 500 Hz is compared to the structuring with a "conventional" high power excimer laser with a repetition rate of about 10-100Hz as well as with a UV-Nd:YAG (1-2 kHz). These "high-repetition-rateexcimer lasers" with relatively small pulse energies but with much shorter laser pulse duration (< 6 ns) provide a significant improvement of pattern quality. Furthermore, the high repetition rate enables a fast material processing which is discussed in detail for several application fields.