Function of Sulfhydryl (–HS) Group During Microvia Filling by Copper Plating
Shenghao Zhao, Kaining Pang, Xiaojing Wang, Ning Xiao
Abstract
In this work, 3-mercapto-1-propanesulfonate (MPS) with one sulfhydryl (–HS) group and 2,3-dimercapto-1-propanesulfonate (DMPS) with two –HS groups were used as model additives to reveal the function of –HS group during copper plating. Chronopotentiometry was employed to characterize the different electrochemical behaviors of the two model additives. It indicated that DMPS showed stronger accelerating effect than MPS in the plating bath containing Cl − , which could be attributed to its enhanced adsorption caused by two –HS groups. The pre-adsorption and desorption experiments demonstrated the synergistic effects and competitive adsorption between Cl − and the model additives. Moreover, the accelerating mechanism was investigated by cyclic voltammetry combined with rotating ring-disk electrode (RRDE), demonstrating MPS could accelerate the rate-determining step (RDS) of copper deposition only if Cl − was present, whereas DMPS could enhance the RDS whether Cl − existed or not. Finally, microvia filling experiments were carried out to evaluate the filling performance of the two model additives. The results indicated that in the plating bath containing PEG and Cl − , MPS showed good filling performance, while DMPS did poorly. However, after the introduction of JGB, the filling performance of DMPS was greatly improved, which was resulted from the competitive adsorption between DMPS and PEG being balanced by JGB.