Pure Bottom-up filling process for efficient TSV metallization

TSV (Through Silicon Via) is an enabling technology for 3D WLP (Wafer Level Packaging) and 3D integration. TSV is a very hot topic for semiconductor industry today. One of the key processes for TSV is the electroplating process. The quality and rate of electroplating are two critical parameters for TSV filling, which can be significantly improved by Bottom-Up filling with much thinner overburden. Also, bottom up plating is a critical process to thin overburden. In this study, the copper plating of TSVs with the diameter and the depth in the ranges of 2.5-30 μm and 50-300 μm, respectively, was investigated. A nearly 100% bottom up plating recipe was developed in order to achieve void-free and seamless filling. The performance of this plating recipe was evaluated by vertical and top-down cross-sections images of filled TSVs using optical microscopy and X-ray inspection. The influence of the suppressor and cupric ion concentrations on Bottom-Up filling were investigated. Pure Bottom-Up filling can be achieved with a strong enough suppressor and high copper concentration. The strength of suppressor determines the required amount of copper concentration. The influence of diffusion time to different via diameter were also discussed. The copper concentration can be up to 120g/L in Methylsufonic Acid (MSA). The void-free and seamless copper deposition results with via diameter from 2.5μm-25μm or aspect ratio up to 20 can be achieved.