Recent advances in integrated circuit have been driven by packaging technology. 3D packaging using TSV (Through-Silicon Via) is becoming common in commercial products. TSVs are formed by filling deep holes with a conductive material. Copper is widely used as the conductive material, since filling the deep holes with copper is enabled by bottom-up electrodeposition using a combination of several additives. Suppressors, levelers, and accelerators are well known categories of additive to acid copper sulfate plating solutions. Bottom-up deposition is realized by various additive formulas. Using leveler alone as additive, extreme bottom-up filling has been demonstrated, and levelers are considered to be essential for bottom-up deposition. But the mechanism is not yet clear with multiple additives addition.

Therefore, understanding of additive behaviors is important. Cyclic voltammetry using a rotational disk electrode has been widely used in additive studies, but interpretation of the results is not easy because adsorption occurs simultaneously with deactivation. The history of additive supply onto the plating surface also influences the hysteretic behavior. Recently, we constructed a microfluidic device in which flow cell experiments and rapid switching of the plating solution are enabled. Using the device, characteristic behavior of leveler, strong suppression and rapid deactivation, was directly observed optical microscopically and electrochemically, and difference with levelers and suppressors was clarified. Further, a TSV-like structure with similar dimensions to real TSVs was constructed in a microchannel, and real-time optical observation of bottom-up deposition was demonstrated.

References

1. T. Akita, et al., J. Electrochem. Soc., 166(1), D3058 (2019)
2. M. Tomie, et al., J. Electrochem. Soc., 167, 082513 (2020)
3. T. Akita, Y. Otsuka, M. Hayase, J. Electrochem. Soc., 167, 162515 (2020)