Interface identification in micro-LED repair applications via depth profiling using femtosecond laser-induced breakdown spectroscopy.

The commercialization of micro light-emitting diode (micro-LED) display technology depends on the efficient transfer of millions of individual micro-LEDs onto display panels with high spatial precision and yield. However, the extremely high pixel density in 4 K and 8 K displays poses a significant challenge for defect-free transfer. To maintain display quality and ensure production viability, it is crucial to develop effective strategies for repairing defective chips. While conventional laser-based repair methods have been widely used, they often fall short due to the lack of real-time monitoring capability, making it difficult to precisely control ablation depth without causing unintended damage to adjacent structures. In this study, femtosecond laser-induced breakdown spectroscopy (fs-LIBS) is proposed as a repair tool, offering simultaneous real-time elemental analysis and high spatial resolution. Custom-fabricated micro-LEDs with multilayer structures were analyzed using fs-LIBS under varying laser pulse energies. Spectral emissions from key constituent elements were successfully detected, and variations in Ga and Au signals enabled identification of the interface between the p-pad and p-contact layers. Depth profiling further confirmed this interface by monitoring normalized intensities of Ga and Au signals during consecutive laser pulses. These results were validated by elemental mapping of the ablation craters using scanning electron microscopy with coupled energy dispersive X-ray spectroscopy (SEM-EDS). This study highlights the potential of fs-LIBS as an effective technique for monitoring micro-LED repair, reducing the risk of peripheral damage, and improving repair precision in micro-LED displays.