Selective rear-side ablation of aluminum thin layers with ultrashort-pulsed laser radiation

Abstract

In recent years, several applications for laser ablation of thin metal layers from the fused silica substrate side have been studied. The rear-side ablation is a highly effective ablation method for thin layer structuring and reveals a high structuring quality. Therefore, the present work dealt with the selective rear-side ablation of thin aluminum layers (10–50 nm) on fused silica with ultrashort-pulsed laser radiation (λ = 1028 nm, $$ \tau_{\text{H}} $$ = 0.2–10 ps and w0,86 = 15.2 µm). The influences of pulse duration and layer thickness on the ablation thresholds as well as the incubation coefficients were determined. For layer thicknesses of 30 and 50 nm, a decrease of the ablation threshold with increasing pulse duration was determined. Whereas, the ablation threshold remained constant for layer thicknesses of 10 and 20 nm. Different morphologies were observed depending on the process parameters. The rear-side ablation of aluminum proceeded over the melting phase and no lift-off process had taken place. In addition to experimental investigations, calculations were carried out to determine the theoretical threshold fluences. The theoretical values were compared to experimental data. With the help of these investigations, the quality of the structuring of aluminum layers can be improved.