Void formation in Cu-Sn micro-connects

Interfacial voiding of Cu-Sn micro-connects has been identified as a significant reliability challenge due to its impact on the mechanical and electrical stability of interconnections. As critical dimensions decrease, the negative impacts of voiding become more significant. Recent studies have identified incorporated impurities during electroplating as a source of voiding in Cu-Sn micro-connects. Furthermore, electroplating parameters including, current density, electroplating temperature and additive concentration all contribute to interfacial voiding. Typically voided Cu-Cu₃Sn interfaces have been identified as Kirkendall Voids, which are known to form as a result from the imbalance of solid state diffusion fluxes in the Cu-Sn system. Even though diffusion appears to be an enabling mechanism for void formation this paper will suggest that diffusion imbalance alone cannot be the only factor in void formation. This communication intends to explore this concept further by examining different electroplating chemistries and current densities and quantitatively assessing the resulting voiding characteristics as a function of thermal annealing. These results can be used to assess the reliability concerns associated with electroplating in the fabrication of micro-connects.