Physical Mechanisms during fs Laser Ablation of Thin SiO2 Films

Ultra-short pulse lasers can be applied for fast and precise structuring of thin passivating SiO2 films on the surface of high efficient Si solar cells. This single pulse ablation reaction is investigated over the whole reaction time ranging from ps to μs by pump-probe microscopy. Results show ultra-fast reflectivity changes of the Si after 1 ps interpreted as melting and subsequent creation of a gas-liquid-mixture at 10 ps. The generated pressure causes the layer to bulge at 100 ps with velocities up to 1800 m/s and accelerations of 1012 g. The layer disintegrates at around 10 ns.