Deep ultraviolet excimer laser processing for the micro via hole on semiconductor package

Moore's law has almost reached the limit of resolution on semiconductor die and, therefore, multidie packaging is one of the alternative solutions. Substrate materials currently use organic build-up films and silicon substrates [through silicon via (TSV)] in applications. But recently, organic films, too, have reached the resolution limit, and TSV is expensive. In this situation, nonalkali glass (glass) and fused silica (SiO₂) substrates are expected to be good alternatives in high-frequency signal transfer applications like 5G telecommunication. But the via holes are hard to process with less defects (tips and cracks) on the glass and SiO₂ substrates. Deep ultraviolet (DUV) excimer laser ablation is expected to have a finer (<10 μm) resolution with a shorter wavelength (248-193 nm) and also hard material processing with a higher photon energy (5-6.4 eV). Therefore, the authors have explored the application of the DUV excimer laser ablation process for a via hole on hard materials like glass and SiO₂ substrates. In this study, they have investigated the via hole quality through the DUV excimer laser ablation process. The results show the possibilities of micromachining on both glass and SiO₂ substrates. The authors have succeeded by achieving a value of <50 μm through the via hole grid aspect ratio of 6 on the glass substrate without any significant defects. As the ablation rate is quite an affordable value, DUV excimer lasers are expected to play a crucial role in the next-generation manufacturing process for semiconductor packages. The authors also investigate the SiO₂ substrate with DUV excimer lasers.