Effects of Accelerator Alkyl Chain Length on the Microvia Filling Performance in Copper Superconformal Electroplating

In addition to the commercialized accelerator bis-(sodium sulfopropyl)-disulfide (SPS), we designed and synthesized two other disulfide compounds, namely, bis-(sodium sulfohexyl)-disulfide (SHS) and bis-(sodium sulfoethyl)-disulfide (SES), to investigate the effect of their alkyl chain lengths on the microvia filling performance. The galvanostatic measurements show that the addition of Cl− to different accelerator-containing solutions leads to the same synergistic effects at a current density of 20 mA/cm2, indicating that the interactions between accelerators and Cl− are independent of their alkyl chain lengths. However, when both Cl− and a suppressor are present, the alkyl chain length in accelerators strongly impacts their anti-suppressor strength, which increases with the growth of the alkyl chain length, reaches a maximum (SPS) and then decreases. A possible adsorption and interaction model was proposed to explain the difference of anti-suppressor effects, and microvia filling plating experiments were carried out to evaluate the effects on the filling performance. It was found that both SES and SPS, which have appropriate molecular lengths and relatively strong antagonistic effects against polyethylene glycol (PEG) and Cl− ensemble, achieved complete microvia filling. For SHS, due to the overlong alkyl chain and weak antagonistic effect against PEG and Cl−, no microvia was completely filled.