Manipulating adsorbate configurations in copper electroplated low aspect-ratio via fill in redistribution layers

Abstract

Copper metal is widely electroplated for microelectronic interconnections such as redistribution layers (RDL), pillar bumps, through silicon vias, etc. With advances of multilayered RDL, via-on-via structures have been developed for ultrahigh-density any-layer interconnection, which expects superconformal filling of interlayer low aspect-ratio vias jointly with coplanar lines and pads. However, it poses a great challenge to electrodeposition, because current via fill mechanisms are stemming from middle to high aspect-ratio (>0.8) vias and lacking applicability in low aspect-ratio (<0.3) RDL-vias, where via geometry related electric-flow fields coupling must be reconsidered. In the present work, a four-additive strategy has been developed for RDL-vias fill and thoroughly investigated from additive electrochemistry, in situ Raman spectroelectrochemistry, and quantum chemistry perspectives. A novel adsorbate configuration controlled (ACC) electrodeposition mechanism is established that at weak-convection bilateral edges and lower corners, the adsorbate displays a weakly-adsorbing configuration to assist accelerator-governed deposition, whereas at strong-convection center, the adsorbate exhibits a mildly-adsorbing configuration to promote leveler-determined inhibition. Deposit profiles can be tailored from dished, flat to domed, depending on predominance of leveler over accelerator. This study should lay theoretical and practical foundations in design and application of copper electroplating additives of multiple adsorbate configurations to cope with complicated interconnect scenarios.