A rotating ring-disk study of interactions among SPS, cuprous ions, and oxygen
The most common additives in copper plating baths for deep via filling are chloride, polyethylene glycol (PEG), a suppressor, and bis-(3-sulfopropyl)-disulfide (SPS), an accelerant. The copper in acid plating baths is provided by a Cu (II) salt. Cu (I) may be present as well and it influenced the effectiveness of SPS. In this investigation, the interactions among SPS, Cu (I) and oxygen were studied by rotating ring-disk voltammetry. The ring electrode acted as a plating substrate, while Cu (I) was generated at the disk by anodic dissolution of copper. Because Cu (I) is consumed by reaction with oxygen, the experiments were carried out under air, oxygen, or argon atmospheres. When SPS is present in the solution, a sudden kinetic acceleration is observed at the ring during Cu (I) generation at the disk. By comparing the ring deposition rate without and with Cu (I) generation at the disk, it is found that deposition is accelerated by higher levels of Cu (I) and SPS. The result is considered in light of the hypothesis that the true accelerant is formed by homogeneous reaction of SPS and Cu (I).
Networked Digital Library of Theses and Dissertations