Time and Temperature Dependence of Copper Protrusion in Metallized Through-Glass Vias (TGVs) Fabricated in Fused Silica Substrate

In this work the influence of annealing dwell time and temperature, as well as post-annealing thermal processing treatment on copper (Cu) protrusion in Cu through-glass vias (TGVs) were studied. The Cu TGVs were made in Corning HPFS Fused Silica substrate, with a diameter and depth of $50~\mu \text{m}$ and $300~\mu \text{m}$ , respectively. For a constant annealing temperature of 400 °C, the results show a dependence of Cu protrusion with annealing dwell time, which saturates at about 240 min. Additional post-annealing thermal processing treatment, done at 400 °C (60 min dwell time) revealed that when an annealing dwell time ≥ 120 min is used no difference in the amount of Cu protrusion was found between the annealing step and the post-annealing thermal processing step. This indicates that downstream Cu protrusion can be eliminated when an annealing dwell time ≥ 120 min is used. On the other hand, from the temperature – dependent study of the annealing treatment, it was found that downstream Cu protrusion occurrence can be eliminated by performing annealing treatment at 450 °C (60 min dwell time), followed by post-annealing thermal processing treatment of 400 °C (60 min dwell time). Therefore, downstream Cu protrusion from a thermal processing treatment of 400 °C with 60 min dwell time can be eliminated either by using a longer annealing dwell time (120 min) at 400 °C or by increasing the annealing temperature to 450 °C, with a shorter dwell time of 60 min.