Synergistic effect of CTA+ and Br- on defect-free TSV filling by Cu electrodeposition

Abstract

Suppressing additives for Cu electrodeposition play a critical role in inducing bottom-up filling in micrometer-scale features such as through-silicon vias (TSVs). This study explores the adsorptive behaviors of cetyltrimethylammonium cation (CTA+) and bromide ion (Br-) and their application to defect-free TSV filling. Electrochemical analyses reveal that both CTA+ and Br- suppress Cu electrodeposition, with only CTA+ exhibiting negative differential resistance (NDR) behavior. The addition of Br- to CTA+ enhances the suppression effect while maintaining the NDR behavior of CTA+. TSV filling experiments demonstrate that the NDR behavior of the CTA+ and Br- combination induces the passive-active transition on the sidewalls of TSVs, which is essential for Cu bottom-up filling. The effects of CTA+ and Br- concentrations on the passive-active transition are also investigated, showing that CTA+ determines the height at which the passive-active transition occurs, while Br- enhances suppression to inhibit Cu growth on the sidewalls in the active region. Based on these behaviors, the optimal CTA+-Br- combination leads to successful bottom-up filling in TSVs. The mechanisms of TSV filling with CTA+ and Br- are suggested based on electrochemical analyses and gap-filling results. The active region at the TSV bottom, formed via selective breakdown of suppressing adsorbates, is filled while effectively inhibiting Cu deposition on the sidewalls, followed by filling the remaining portion of TSVs with vertical Cu growth.