Accelerator Screening by Cyclic Voltammetry for Microvia Filling by Copper Electroplating

A cyclic voltammetry (CV) screening method is proposed in this work to identify an effective accelerator for the copper superfilling of microvias of a printed circuit board (PCB). Five typical organosulfides are used as model additives to evaluate the performance of the screening method. The five organosulfides are 3-mercapto-1-propanesulfonate (MPS), bis(3-sulfopropyl) disulfide (SPS), 3-mercaptopropionic acid (MPA), 3-mercapto-1-propanol (MPO), and 3,3-thiobis(1-propanesulfonate) (TBPS), where MPS, MPA, and MPO contain a thiol head-group, SPS contains a disulfide group, and TBPS contains a thioether group. MPS, SPS, and TBPS have one or two terminal groups of sulfonates, whereas MPA has a terminal group of carboxylic acid, and MPO has a terminal group of alcohol. The CV screening method revealed that MPS, SPS, and TBPS are accelerators for copper electrodeposition and that MPA and MPO are not. A specific copper deposition peak, specifically, the α peak, that appears in the CV patterns is an indicator for accelerator screening. This study is the first to indicate that TBPS with a thioether group rather than a thiol group can accelerate copper electrodeposition and can be used for the copper superfilling of the microvias of a PCB.