Influence of Pulse Duration and Surface Topography on Laser Ablation of Silicon Nitride Layers on Thin Emitters

In this paper, influences of pulse duration and surface topography on laser ablation of silicon nitride layers on thin emitters were investigated. For the first time, the pulse duration dependent threshold fluence and the pulse duration dependent laser-induced damage were studied by using an IR laser system with tunable pulse duration. For all pulse durations, bare silicon was observed in the ablated regions. A linear increase of the threshold fluence with pulse duration was determined. The reason for this is an increase of the probability of multi-photon-absorption (MPA) in silicon at shorter pulse durations. Furthermore, a pulse duration dependent laser-induced damage is observed. Differences in damage characteristics between planar and textured surfaces were also observed. On textured samples losses in the open circuit voltage Voc of at least 40 % were determined. In contrast, on planar samples much lower losses in Voc were determined.