Probing the molecular properties of 5-(3-pyridyl)-1H-tetrazole at the electrode/electrolyte interface: Towards void-free copper filling of high aspect ratio through-holes

Void-free filling of high aspect ratio through-holes remains a significant challenge in the fabrication of high-density interconnection PCBs. In this work, a novel tetrazole compound, 5-(3-pyridyl)-1H-tetrazole (TZP), was introduced into an acidic sulfate copper electroplating system. The molecular structure, adsorption behavior and electrochemical properties of TZP were systematically investigated through DFT calculations, MD simulations, electrochemical analyses and in situ Raman spectroscopy. Results reveal that TZP exhibits strong planar adsorption on copper surfaces via combined chemical and physical interactions, facilitated by electron transfer from copper to its LUMO orbital, with an adsorption energy of -958.07 kcal/mol. Electrochemical measurements demonstrate that TZP synergistically enhances the inhibitory effect of PEG while antagonizing the acceleration effect of SPS, thereby creating a deposition gradient favorable for through-holes filling. In situ Raman spectroscopy confirms that TZP adsorbs stably on the copper surface in a horizontal configuration, with PEG promoting its adsorption and SPS inducing configurational changes. Contact angle tests confirm that TZP significantly improves the wettability of the electroplating bath, reducing the contact angle by 17.6°, which facilitates deeper penetration of additives into high-aspect-ratio structures. Practical electroplating experiments validate that the TZP-containing bath achieves complete, void-free filling of through-holes, in contrast to the defective filling observed in the TZP-free bath. Furthermore, TZP induces a preferred (220) crystallographic orientation, and introduces beneficial compressive stress in the copper coating.