Investigation of Nitrogen Heterocyclic Compounds as Levelers for Electroplating Cu Filling by Electrochemical Method and Quantum Chemical Calculation

A series of nitrogen heterocyclic compounds (NHCs) bearing different functional groups were investigated as levelers for electroplating Cu microvia filling. The cathodic potential decreased with an injection of 4-amino-6-hydroxy-2-mercapto- pyrimidine (AHMP), 4-hydroxy-2-mercapto-6-methyl-pyrimidine (HMMP), 6-dimethyl-2-pyrimidinethiol (DPT), or 2-mercaptopyridine (2-MP), whlie the cathodic potential increased with an addition of 2-MPD. To evaluate filling performance of a plating solution on an addition of the leveler, the relationship between the super filling capability (SFC) of the plating solution and the Cu stripping quantity was proposed. The SFC was positively associated with the filling performance of the microvias, and the high SFC value was conducive to improve the filling performance of microvia and to reduce thickness of plated Cu film on the surface. Furthermore, the adsorption ability and active functional groups of NHCs were analyzed by quantum chemical calculations. Different from the conventional nitrogen active sites in quaternary ammoniums, the –SH and = S groups in the NHCs were the most active reaction sites for surface adsorption on Cu surface and the adsorption ability of NHCs was negative correlation with energy gap (ΔE). In addition, scanning electron microscope and X-ray diffraction results indicated that the uniformity and brightness of the electroplated Cu film were improved by an addition of AHMP, HMMP, DPT, and 2-MP due to a significant change of the Cu crystalline orientation in plating deposition.