Loading effects mitigation for wet etching of high-aspect-ratio through-glass vias in thick glass

High-aspect-ratio through glass vias (TGVs) are key structures for advanced semiconductor packaging and optical array coupling, showing excellent application potential in emerging technologies such as AI chips and quantum computers. The high aspect ratio, low sidewall taper angle, and smooth via surface enable low-loss transmission of optoelectronic signals. However, existing fabrication techniques struggle to achieve both high aspect ratios and low taper angles. In this study, multilayer coaxial modification was performed inside thick glass substrates using a Bessel ultrafast laser to construct a continuous TGV contour across the entire substrate thickness. The central core within the contour was subsequently removed through wet etching in a hot alkaline solution with a high etching selectivity, thereby completing the TGV structure. To mitigate loading effects during deep-via etching, the laser modification parameters were optimized to further enhance the etching selectivity. Then, etching parameters such as reactor vessels and solution concentration on the deep-via size were systematically analyzed. The Thiele modulus was introduced to quantitatively evaluate the influence of the above strategies on the axial etching rate. The temporal evolution trends of axial and lateral etching rates, etching selectivity, aspect ratio, and taper angle were established. The results show a maximum etch selectivity of 2700:1 and a taper angle below 0.1°. The achievable maximum aspect ratios exceeding 300:1, achieved in the 6 mm thick substrate, demonstrate the feasibility of fabricating high-quality, high-aspect-ratio TGVs in ultra-thick glass.