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Micromachining Using an Excimer (248nm) Laser

Choo, Kok Leong
An excimer laser micromachining facility was developed to investigate laser-material interaction. It includes the COMPex 205i excimer laser (manufactured by Lambda Physik) using a krypton fluoride (KrF) (248nm wavelength) is the lasing medium, an 3-axis precision stage, and optical deliver system that includes an attenuator module, a homogenizer, field lens, and a doublet. The system was mounted on a vibration free isolated table. Multipulse, excimer laser micromachining studies ware conducted in air and under water on different workmaterials, including PMMA, borosilicate glass (Corning 0211glass), and silicon. Process parameters, such as pulse frequency, number of pulses, and pulse energy density were varied to optimum conditions for best finish and uniform geometry with minimal surface damage. The laser-ablated surfaces were examined using an optical microscope, MicroXAM laser interference microscope, and a scanning electron microscope (SEM). Threshold fluences (FTH) for ablation in air are 0.53, 2.19 and 2.44 J/cm2 for PMMA, borosilicate glass and silicon, respectively. Presence of thin film water during the ablation process facilitated in the removal of debris giving a clean finishing cut. Photothermal ablation was dominant when the fluence was below the threshold value and pure photochemical above this value. For the case of borosilicate glass, a hump or build-up of about 50 nm is found at low fluence.