Fabrication of high-aspect-ratio microstructures using excimer laser

Abstract

An excimer laser micromachining system is developed to study the ablation of high-aspect-ratio microstructures. The study examines the ablation efficiency, specifically, the impact of changing major laser operating parameters on the resulting microstructural shapes and morphology. The study focuses on glass, although results on silicon and aluminum are also included for comparison. In ablating grooved structures, the ablation depth has been observed to be linearly proportional to the operating parameters, such as the pulse number and fluence. The results specifically indicate that ablation at low fluence and high repetition rates tends to form a V-shaped cross-section or profile, while a U-shaped profile can be obtained at high fluence and low repetition rate. The ablation rate or ablated volume has then been quantified based on the ablation depth measured and the ablated profile observed. The threshold fluence has also been obtained by extrapolating experimental data of ablation rate. The extrapolation accuracy has been established by the good agreement between the extrapolated value and the one predicted by Beer's law. Moreover, a one-dimensional analytical solution has been adopted to predict the ablated volume so as to compare with the experimental data. The reasonable agreement between the two indicates that a simple analytical solution can be used for guiding or controlling further laser operations in ablating glass structures. Finally, the experimental results have shown that increasing the repetition rate favors the morphology of ablated surfaces, though the effect of repetition rate on ablation depth is insignificant.