Tetrazole Derived Levelers for Filling Electroplated Cu Microvias: Electrochemical Behaviors and Quantum Calculations

Three tetrazole derivatives (TDs), 1-(3-Acetamide) phenyl-5-mercaptotetrazole (ACET), 1-Phenyl-5-mercaptotetrazole (PMT) and 1-Methyl-5-mercaptotetrazole (MMT), have been studied as novel levelers for filling electroplated Cu microvia. It is found that the Cu deposition potential decreases with the addition of TDs into the Cu plating solutions, with the lowest deposition potential observed for MMT and the largest deposition potential change (Δη) observed for ACET. The ACET exhibits the strongest convection-dependent adsorption behavior with SPS, Cl−, and OP/OE, and the thickness of copper surface layer can be thinned to ∼15 μm in the ACET concentration range of 1.0 ∼ 10.0 ppm. The electrochemical impedance spectroscopy studies suggest that both the charge transfer resistance (Rct) and the adsorbed layer resistance (Rad) increase with the addition of TDs. Quantum chemical calculations indicate that the energy gaps (ΔE) of TDs correlate negatively with Δη, and the most active reaction sites for surface adsorption are the N3 in the thiol forms and the N4 in the thione forms of the TDs through Fukui functions.