High-accuracy micromachining of ceramics by frequency-tripled Nd:YAG-lasers

Ceramics like Si3N4, Al2O3 (sapphire) and ZrO2 and also diamonds can be hardly machined by conventional methods. Short pulse lasers, especially frequency-tripled, diode pumped Nd:YAG-lasers with a high beam quality offer the possibility to ablate these materials with high quality. With a spot size of about 10 mu m, high fluences (> 100 J/cm(2)) can be achieved, so that the materials are vaporised without or with only a small amount of molten material. This technique is applicable for drilling small holes with diameters greater than or equal to 5 mu m (aspect ratio up to 60) and cutting of thin ceramic substrates (thickness < 0.5 mm). The edges are sharp and the face of the cut is very smooth. Furthermore it is possible to ablate three dimensional microstructures. Therefore the laser beam is scanned over the surface and the material is ablated pulse beside pulse. The surface roughness depends on the overlap of the laser pulses, the pulse energy and the scanning strategies. With optimised machining parameters the surface roughness can be reduced to R-a less than or equal to 0.1 mu m. Due to the low ablation rate of around 0.05 mu g / pulse the ablation depth of a single slice can be controlled very precisely. Depending on the material and the machining parameters the depth is in the range of 1 to 10 mu m.