Uv-laser ablation of HfO2 dielectric layers on SiO2 for mask preparation

The thickness dependence of ablation rates following 193nm UV-laser irradiation of single HfO2 layers on fused silica (SiO2) is investigated using scanning electron microscopy and stylus profilometry to determine quantitatively substrate roughness and ablation depth. Thin dielectric films of the investigated kind build up dielectric mirrors, which are patterned to prepare masks for excimer-laser micromachining. The single pulse ablation thresholds are found to increase approximately linearly with increasing HfO2 thickness and consequently the threshold fluence for obtaining clean ablation of the total HfO2 coating increases exponentially with its thickness. At elevated fluences both ablation of the coating as well as ablation of the substrate are observed. The results provide important quantitative values for a future treatment of more complicated multilayer systems of HfO2/SiO2 bilayers.