Insights into the synergistic effects of safranine in an acidic copper bath on through-hole void-free filling for high-quality electronics interconnection

In this work, we develop a novel safranine (SA)-based acidic sulfate copper electronic plating process for through-hole copper void-free filling for high-quality electronics interconnection, and both the molecule actions and synergistic effects of safranine (SA) are carefully explored. Cyclic voltammetry experiments at rotating rates of 200 r/min and 1200 r/min demonstrate that SA itself can accelerate the electro-reduction of copper ion, heighten the inhibiting effect of polyethylene glycol (PEG) and acceleration effect of bis-(3-sulfopropyl) disulfide (SPS). The addition of SA to the virgin make-up solution (VMS) containing PEG and SPS makes the relative electric charge (∆Q) between the low and high rotating rates be increased from 1.27 ± 0.04–22.53% ± 0.05, indicating the higher copper electronic plating amount at the center than that at the mouth of through-hole. In situ Fourier transform infrared spectroscopy together with theoretical calculations further illustrate that the molecule SA is adsorbed on the copper surface through the N atom in the aromatic ring, PEG and SPS can heighten the adsorption of SA on the Cu surface, and both PEG and SPS both synergistically influence with SA to achieve the void-free copper filling of through-hole.