Structural influence of nitrogen-containing groups on triphenylmethane-based levelers in super-conformal copper electroplating

Abstract

Leveler is one of the most important additives for super-conformal copper electroplating, which has been widely applied in the fabrication of nanoscale (or microscale) interconnect features in integrated circuits (ICs) and printed circuit boards (PCBs). Because the structure-property relationship of the leveler is not clear, the development of novel leveler with high microvia filling performance is very time-consuming and challenging. In this study, a series of triphenylmethane-based (TPM-based) molecules with different nitrogen-containing groups have been designed, synthesized, and investigated as novel levelers for super-conformal copper electroplating. Their structure-property relationships are investigated by electrochemical analyses, contact angle measurements, and microvia filling electroplating experiments. It is found that the steric hindrance and the type of the nitrogen-containing groups (tertiary amine or quaternary ammonium with counter anions) in a leveler not only affect its adsorption ratio and strength on the copper interface, but also affect its adsorption preference on different copper crystalline plane. In combination with Cl−, polyethylene glycol (PEG, suppressor), and bis-(3-sulfopropyl) disulfide (SPS, accelerator), all TPM-based levelers show excellent microvia filling performances in copper electroplating and their effective concentrations are related to their antagonistic ability against the accelerator SPS.