Thesis: Real-Time Spectroscopic Monitoring of Microvias Powering the AI Revolution

In cooperation with the Chair of Laser Technology (LLT), the Fraunhofer Institute for Laser Technology (ILT)—Europe’s leading center for contract research and development in the field of laser technology—is offering the opportunity to write a thesis on the topic: »Real-Time Spectroscopic Monitoring of Microvias Powering the AI Revolution«. The explosive growth of artificial intelligence is driving an unprecedented demand for high-density interconnect printed circuit boards. Next-generation AI chips require ever finer microvias to connect increasingly thin copper layers through dielectric substrates. Today, CO₂ lasers are the industrial standard for via drilling, but their minimum feature size is physically limited. Ultrashort pulsed lasers offer a path to significantly smaller vias. However, a critical challenge arises: unlike CO₂ radiation, the 515 nm USP beam couples efficiently into copper, meaning the very copper layer that must be preserved is ablated alongside the dielectric. As copper layers shrink to thicknesses below 5 µm, even a single excess pulse can cause irreversible damage. This thesis addresses this challenge by developing a real-time, in-line endpoint detection system. The plasma generated by each individual laser pulse is spectrally analysed to detect the characteristic copper emission—the instant copper is exposed, the process stops. This enabels damage-free microvia drilling at industrial throughputs.