Picosecond laser lift-off method for fracture and debonding of copper oxide layer grown on copper substrate

The objective of this work is to investigate the ablative removal behavior of copper oxide under the picosecond laser (pulse duration 12 ps and wavelength 1064 nm) irradiation. For this purpose, a thin CuO layer with a thickness of about 750 nm is synthesized on a pure copper substrate by the dipping method to serve as the target samples for experimental tests. It is shown that, unlike the pure ablation behavior, the removal process of the CuO layer is mainly based on the nonthermal lift-off effect, by which the stripping of the whole piece of oxide films from the substrate can be achieved with a single pulse shot. A minimum fluence required for peeling off the layer is determined to be about 0.11 J/cm(2). Further analyses demonstrate that the entire pop-off of the CuO layer caused by the confined ablation at the interface occurs only if the laser fluences are applied below 0.62 J/cm(2). However, when it comes to the cases at higher fluences, a thin residual layer can be observed remaining on the substrate. To explain this phenomenon, a plausible interpretation with respect to the ablation induced by nonlinear absorption and impact ionization is proposed, which declares that it is the combination of direct ablation and the interface lift-off that ultimately causes such special removal features. In addition, the influence of the oxide film thickness on the debonding threshold and the removal behavior are additionally assessed.