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.