Competitive adsorption between suppressor and accelerator in copper methanesulfonic acid bath for electrodeposition

The rapid development of three dimensional packaging makes it necessary to develop smaller and more reliable microbumps. In the electrodeposition process of bump cylinder, the filling quality is largely determined by the combination of additives. In this work, the effect and competitive adsorption between suppressor polyethylene glycol (PEG) and accelerator Bis-(3-sodiumsulfopropyl disulfide) (SPS) were investigated in copper methanesulfonic acid (MSA) plating bath. The results indicated that suppressor inhibited the Cu
⁺
/Cu reduction process in copper deposition by forming PEG-Cl
^-
-Cué passivation film on the electrode surface. And the inhibiting effect was found to reach saturation when suppressor concentration reached above 9 mg/L, due to the coverage limitation of suppressor absorption. When accelerator was added into plating bath with PEG, SPS was supposed to disrupt or displace the adsorbed PEG and to form a bridge (RS-Cu2
⁺
-Cl
^-
) with the electrode metal, which speed up the charge-transfer process. Thus the electrochemical process was converted to be diffusion controlled.