Electrochemical and ATR-SEIRAS Investigation of Micro-via Filling Performance of Amino-Functionalized N-Heterocyclic Levelers

This study investigates the feasibility of 2-mercaptopyrimidine (MPD), 2-thiocytosine (TC), and 4,6-diamino-2-thiopyrimidine (DTP) as novel levelers for copper electroplating in micro-via filling applications. Galvanostatic measurements, combined with in situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) and density functional theory (DFT) calculations, were employed to elucidate the adsorption behaviors and interfacial mechanisms of the additives. Results indicate that while all three molecules adsorb onto copper surfaces via Cu-S and Cu-N coordination, TC and DTP form more stable adsorption configurations due to additional amino group interactions. MPD, lacking amino functionality, exhibited significant desorption at negative potentials. Micro-via filling experiments demonstrated that MPD fails to achieve effective leveling, whereas trace amounts (1 mg/L) of TC and DTP enabled bottom-up superfilling with filling efficiencies of 96.6% and 101.5%, respectively. These findings highlight the critical role of amino groups in enhancing adsorption stability and deposition uniformity, offering valuable insights for the molecular design of high-performance electroplating additives.