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

Through hole (TH) filling by electrolytic Cu deposition has become a critical process for high density interconnection technologies associated with three-dimensional packaging. In this study, the morphological and crystallographic evolutions of the electrolytic Cu TH filling with the plating time (t) were investigated using an optical microscope and a field-emission scanning electron microscope equipped with an electron backscatter diffraction (EBSD) analysis system. The Cu deposition rate in the TH was strongly dependent on t, which was established at a moderate rate of ∼0.3 μm/min at t = 40 min-74 min, then dramatically accelerated to ∼4 μm/min at t = 74 min-80 min (termed "fast deposition regime"), and subsequently decelerated in the final plating regime (t = 80 min-100 min). EBSD analyses showed that the electrolytic Cu predominantly possessed high-angle grain boundaries with strong coincidence site lattices atΣ3 (60° rotation at b111>) andΣ9 (38.9° rotation at b101>) for all t examined. Interestingly, the [111]TD (transverse direction) orientation displayed a relatively strong presence in the initial induction regime, while the [111]TD + [101] TD orientations with large grain sizes became dominant in the fast deposition regime (i.e., t = 74 min-80 min), and there was a very low concentration of the [111]TD orientation in the final deposition regime. This research offered a better understanding of the morphological and crystallographic evolutions in each stage of the electrolytic Cu TH filling.