Light Induced Damage of Silicon Nitride with femtosecond laser

This report focuses on studying optical damage of thin Silicon Nitride (20nm) on Silicon (bulk), and Silicon Nitride (120nm) on Silicon Dioxide (18nm) on Silicon (bulk). These samples are damaged with a 45fs single pulse at 400nm central wavelength (pump) and measured with a 45fs 800nm central wavelength (probe) in a pump-probe setup. For the Silicon Nitride on Silicon sample, it’s found that for pulses below the ablation threshold, there’s likely a crystal/amorphous phase change underneath the Silicon Nitride layer (Silicon or Silicon native oxide). For pulses near the ablation threshold, complete delamination is observed for the Silicon Nitride on Silicon sample. Aditonally, microstructural changes at the center of delamination and at the parts where Silicon Nitride is not yet delaminated is seen with SEM and AFM. For pulses above the ablation threshold, multiple damage regimes with different morphology are identified. In these regimes, Silicon removal is observed with ”pit” morphology, as well as planar delamination. For the Silicon Nitride on Silicon Dioxide on Silicon sample, similar behavior as for the Silicon Nitride on Silicon sample is found for pulses below the ablation threshold. Meaning, a phase change is observed. However, not only the phase of the buried silicon but the silicon nitrate itself can change. For Pulses near the ablation threshold, morphology of bulging and ”donuts” (circular areas where height increases at the edges) are observed. For pulses above the ablation threshold, cascading craters are seen. The thickness of these craters suggest that damage in Si substrate does not play a dominant role (compared to other possible mechanisms) due to Silicon Nitride not being removed from the Silicon substrate upwards.