Electron backscatter diffraction analysis on the microstructures of electrolytic Cu deposition in the through hole filling process: Butterfly deposition mode

Electrolytic Cu deposits in a through hole (TH) structure are a critical reliability issue for the high density interconnection (HDI) technologies of three-dimensional packaging. In this study, we investigated the butterfly deposition of electrolytic Cu fillings via optical microscopy (OM) and field-emission scanning electron microscopy (FE-SEM) in combination with electron backscatter diffraction (EBSD). The Cu TH filling proceeds through three distinct regimes relative to the plating time (t): (1) the conformal deposition regime (t = 30-40 min), (2) fast deposition regime (t = 40-55 min), and (3) final deposition regime (t = 55-110 min). The EBSD analyses showed that the Cu grains were predominantly oriented with [111]‖TD (TD: transverse direction) in the conformal and fast deposition regimes; however, the [111]‖RD (RD: rolling direction) orientation became dominant in the final deposition regime. Additionally, a large number of high angle grain boundaries (HAGBs) with strong coincidence site lattices (CSLs) existed at Σ3 (60° rotation at 〈111〉) and Σ9 (38.9° rotation at 〈101〉) in the Cu fillings. The microstructural/crystallographic evolutions of the butterfly and other deposition modes (i.e., dogbonding) were compared.