Void-Free Filling of HAR TSVs Using a Wet Alkaline Cu Seed on CVD Co as a Replacement for PVD Cu Seed

The results of a wet alkaline seed deposition process directly on a thin adhesion promoter film, such as chemical vapor deposition (CVD) Co, are presented. This solution has been successfully used for copper plating on blanket and patterned through-silicon-via (TSVs) wafers covered with either silicon oxide/physical vapor deposition (PVD) Ta/CVD Co or silicon oxide/PVD Ti/CVD Co stacks. Such direct plated films were used as seed layers for subsequent copper plating from an in-house-made acidic Cu bath with model additives poly(ethylene glycol) (PEG), bis(3-sulfopropyl) disulfide (SPS), and Janus Green B (JGB). We report the impact of the directly plated stack composition and thicknesses on the integration of the wet alkaline seed in TSVs with width and high aspect ratio (HAR) as high as 8:1. The conformal wet seed layer enables the achievement of a successful void-free filling using an in-house made acidic Cu bath with model additives (SPS, PEG, and JGB).