Molecular structure impacts of tetrazole derivatives on their diffusion and adsorption behaviors for microvia copper void-free filling

Optimizing a high-quality leveler has become the core task in developing the microvia copper filling technology. In this work, two nitrogen-containing heterocyclic compounds, iodonitrotetrazolium chloride (INT) and thiazolyl blue tetrazolium bromide (MTT) with a similar tetrazolyl group are selected as the levelers to investigated the molecular structure impacts on their microvia copper filling performance. Both INT and MTT inhibit the electroreduction of copper ions. The inhibiting effect of INT is greatly enhanced by convection while MTT is independent of convection, indicating a bottom-up filling performance of INT and a conformal filling performance of MTT. The microvias are supper-filled and poor-filled in electrolytes containing INT and MTT, respectively, as predicted by electrochemical analysis. Molecular dynamic simulation demonstrates that INT adsorbs in a flat orientation with its iodine and nitro group's two oxygen atoms interacting on the Cu(111) plane surface. MTT adsorbs on Cu(111) surface via positively charged tetrazole ring and its adsorption ability is much stronger than that of INT. The weak adsorption ability of INT on copper surface and the slow mass transfer rate result in its convection-dependent adsorption behavior and the excellent microvia copper filling performance.