Void Free TSV Copper Filling using Single Additive 3-(1-Pyridinio)-1-Propanesulfonate (PPS)

This paper presents our investigation of the influence of the single additive 3-(1-pyridinio)-1-propanesulfonate (PPS) on through silicon via (TSV) filling in 3D packaging. The concentration and current density of the accelerator were varied to study the effects thereof on the TSV filling. Under the same current density and plating conditions, PPS was found capable of supporting the deposition of copper ions at the interconnection and of improving the filling process to obtain void-free TSV interconnections. A PPS concentration of 1 g/L is ineffective and could result in "U"-shaped (conformal) filling. In contrast, a concentration of 5 g/L PPS, the optimal concentration, can achieve "V"-shaped (bottom-up) filling with a filling ratio of 100%, preventing the formation of seams and voids. This result can be understood by considering that the propanesulfonate group (the S part), which is adsorbed onto the surface at the mouth of the TSV, plays an inhibitory role, whereas the pyridinio group (the P part), which is adsorbed onto the surface at the bottom of the TSV, plays the role of an accelerator. Thus, the effect of PPS at the mouth and the bottom of the TSV interconnection is entirely the opposite. In conclusion, the "V" (bottom-up) filling model with a PPS concentration of 5 g/L at a current density of 0.2 ASD for 3 h provides a 100% filling ratio without any seams and voids in the interconnection.