Void-free copper filling of through silicon via by periodic pulse reverse electrodeposition

In this work, the Cu electrodeposition was carried out for the filling of through silicon via (TSV) using an additive-free Cu electrolyte and periodic pulse reverse (PPR) current. It was attempted to understand the filling mechanism by PPR plating and then to explore a potential solution for void-free filling in easy electrolytes. The filling results showed that the void size was continually reduced as decreasing current density. A void-free filling was obtained at low current density. During the Cu growth process, a "V" shape filling structure occurred at the upper of the via and the ratio of this structure increased with the decrease of current density. The electrochemical analyzes results demonstrated that at low current density, the potential during forward deposition was more uniform along the depth, and during reverse pulse the potential difference between the shallow and deep location was larger than that at high current density. This result implied that at low current density the reverse pulse played a strong suppression effect that contributed to the "V" shape growth. A competitive growth model between the bottom reversed "V" structure and the upper "V" structure was proposed to explain the void-free filling mechanism in PPR plating process.