A Review of Research Progresses in Through-Glass Via (TGV) Metallization

Through-glass vias (TGVs), as key vertical interconnect structures in 2.5-D/3-D advanced packaging, offer low dielectric loss, low parasitic capacitance, and excellent high-frequency transmission performance. However, several challenges remain in TGV metallization, including (1) incontinuity of seed layers in high aspect ratio TGVs; (2) non-uniform distributions of copper-ion concentration and current density, leading to significant differences in copper deposition rates between the via interior and the via opening; (3) voids, seams, and double bridging caused by excessively rapid deposition at the via opening or poor control of the central bridging position; and (4) low filling rate and resulting high cost. This article reviews the research progress in TGV metallization to address the above issues. Several electroless plating studies were reported to improve the seed layer continuity and uniformity. Adjusting the concentrations of copper ions, chloride ions, accelerators, suppressors, and levelers in the plating bath are the keys to regulating the deposition rates at the via opening, via walls, and via center. Electroplating strategies, including pulsed electroplating and multistage electroplating, can optimize the electric-field distribution inside the vias. Ultrasonic agitation enhances forced convection within the vias and thereby improves mass-transport conditions. In summary, this paper reviews the research progress in TGV metallization, with emphasis on these key challenges and corresponding solutions, and discusses their prospects for high-density interconnects in advanced packaging.