Development of Straight, Small-Diameter, High-Aspect Ratio Copper-Filled Through-Glass Vias (TGV) for High-Density 3D Interconnections

With the development of artificial intelligence (AI) and $5 \mathrm{G} / 6 \mathrm{G}$ communication technologies, glass is increasingly recognized for its potential because of its high elastic modulus, adjustable coefficient of thermal expansion (CTE), and low loss in high-frequency information transmission. Effectively managing the thin glass panels in the manufacturing process is still a great challenge, often requiring thicker glass to overcome handlingrelated reliability concerns. At the same time, high interconnect density in through-glass vias (TGVs) is crucial for future highbandwidth and high-performance communication, while straight, smaller TGV via diameters and fine pitch are highly desired. However, the processes involved, such as via etching, metallization, and filling, of straight, small-diameter vias, for deeper via depths with high aspect ratios (AR) become bottlenecks and significant challenges for achieving high-performance glass packaging substrates. Currently, TGVs with a thickness of 400 $\mu \mathrm{m}$ and via diameters ranging from $20 \mu \mathrm{m}$ to $80 \mu \mathrm{m}$, with relatively low aspect ratios, have been widely studied. In this study, we successfully fabricate straight, small-diameter, high AR TGVs with thickness of $300 \mu \mathrm{m}$ and via diameter of $15 \mu \mathrm{m}$ and $20 \mu \mathrm{m}$ using laser modification followed by chemical etching. The TGVs are fully filled with copper through a sequential process of doubleside physical vapor deposition (PVD), electroless plating, and electroplating. After copper filling, chemical mechanical polishing (CMP) is performed to remove excess copper from the panel surface. The results demonstrate the effectiveness of this approach in achieving a record-high TGV aspect ratio (AR=20), along with reliable and well-defined TGV structures..