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.

No abstract

A plating process for microvia filling by Cu electroplating, carried out in a plating bath without an accelerator but with a suppressor only, is proposed in this work. The seed layer of microvia used for subsequent Cu-filling plating is Au formed by electroless plating. The surface of the Au seed layer is modified in a solution containing bis(3-sulfopropyl)-disulfide (SPS) and various supporting electrolytes. This pretreatment is similar to the self-assembly monolayer (SAM) of a thiol molecule on a Au substrate. The coverage density of the adsorbed thiolate strongly depends on the presence or the absence of a supporting electrolyte and it crucially determines the filling performance of the plating process. The plating results demonstrate that the thiolate adlayer which is initially formed on the Au seed layer is transferable onto the surface of the plated Cu and then interacts with chloride ions to further facilitate Cu nucleation and growth. According to the results of the filling plating and the electrochemical analysis, an accelerating mechanism of SPS-SAM for copper electrodeposition and its transferring mechanism are proposed in this work

not Available.

The most widely used accelerators for microvia filling by copper electroplating are 3-mercapto-1-propanesulfonate (MPS) and bis(3-sulfopropyl) disulfide (SPS). In this study, a new accelerator, 3,3-thiobis(1-propanesulfonate) (TBPS), which has neither a thiol group (e.g., MPS) nor a disulfide group (e.g., SPS) but rather contains a thioether group and two sulfonic acid groups, was investigated and formulated to perform microvia filling by copper electroplating. The accelerating effect of TBPS on copper electrodeposition and its chemical interaction with chloride ions and H 2 SO 4 were characterized by galvanostatic measurements. Electrochemical analyzes showed that the acceleration of TBPS on copper electrodeposition strongly depended on the chloride ion and H 2 SO 4 concentrations. An optimal copper plating solution composed of CuSO 4 , polyethylene glycol (PEG), TBPS, chloride ions, and H 2 SO 4 was developed and used to perform bottom-up copper filling of microvias. Although TBPS contains a thioether group instead of a thiol group, a trace amount of TBPS can strongly accelerate copper electrodeposition in the presence of proper chloride ion and H 2 SO 4 concentrations.