Inverse analysis of accelerator distribution in copper through silicon via filling

Accelerator distribution along plating surface was estimated by numerical inverse analysis. We demonstrated superfilling of through silicon vias (TSV) by selective accelerator deactivation by a reverse pulse. However, direct measurement of the accelerator distribution after the selective deactivation is difficult. Numerical simulation of shape evolution was developed considering diffusion of cupric ion, accelerator enrichment, acceleration decay and surface diffusion of accelerator. By minimizing the difference between experimental and simulational filling profiles, inverse analysis for estimating accelerator distribution was performed. Obtained accelerator distribution supported our hypothesis on selective accelerator deactivation mechanism, but the estimated accelerator coverage around the TSV bottoms was too large when the acceleration decay was taken into account. Preliminary experimental results with patterned thick resist chips suggested that the acceleration decay around via bottoms was very slow due to depletion of dissolved oxygen.