Ti:sapphire Laser Ablation of Silicon in Different Ambients

Titanium-sapphire laser ablation of silicon was investigated in atmospheric air, water and 20% KOH solution. The number of overlapping pulses was tuned between 3 and 1000 by changing the processing time. The ablated surfaces were investigated using scanning electron microscopy, X-ray microanalysis and stylus profilometry. In each ambient, plasma formation was observed during ablation. X-ray microanalysis indicated that the process starts with surface oxidation in case of air and water ambient. With increasing pulse number the surface was roughened, resulting in larger structures. Crater formation was observed in air and in water, with higher etching rate in the latter case. The depth profile of the ablation holes and grooves is rather different for this two ambient. Narrow conical grooves were observed in case of ablation in air, while flat bottom grooves were produced in water. Laser processing in KOH solution did not result in etching, only the native oxide layer was removed. Etching occurred in these areas, if the samples were left in KOH solution for a longer time. on these observations the material removal by fs laser pulses is attributed to evaporation and reactions of Si with radicals in the laser induced plasma, such as atomic or ionic oxygen. The application of KOH introduces K ions or atoms into the laser induced plasma, which may react faster with oxygen than with Si, thus resulting in decrease in etching rate during laser processing.