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Micromachining by picosecond laser radiation

Fundamentals and applications

Beckmann, L.H.J.F. ; European Optical Society -EOS-:
Lasers in material processing
Bellingham, Wash.: SPIE, 1997 (Europto series)
ISBN: 0-8194-2517-6
pp.252-258 : Ill., Lit.
Conference on Lasers in Material Processing <1997, München>
Conference Paper
Fraunhofer ILT ()
material processing; micromachining; picosecond laser radiation; pump & probe measurements

Decreasing film thicknesses and sizes of microstructures require an ultraprecise removal of the material and a reduction of the heat-affected zone. For these applications picosecond laser pulses seem to offer new challenges. Because of the short pulse length higher power densities can be reached and rapid heating can possibly lead to an earlier evaporation of the material and to a reduction of the molten zone which resolidifies after the end of the laser pulse at the edges of the processed area. The removal of different materials was investigated using laser pulses with a pulse length of 40 ps produced by a diode-pumped mode-locked Nd:YAG-laser in combination with a regenerative amplifier. The laser radiation was focused to a 7 mu m spot diameter, yielding power densities up to 5x10(exp 12) W/cm2. Pump & probe investigations were used to study the interaction of intense ultrashort laser beams with matter. BY this technique ultrashort processes with time resolution determined by the pul se length of pump and probe pulses can be photographed. The measurements allow a detailed characterization of the material removal including melting, vaporization and fast resolidification and the feedback of the surrounding atmosphere to the processed microstructures. The single-shot removal threshold fluence and the removal rate per pulse for 40 ps laser pulses and a wavelength of 1064 nm were determined for Si3N4-ceramics. Different materials like metals, semiconductors and ceramics were microstructured by picosecond laser radiation yielding structural dimensions smaller than 20 mu m.