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

Abstract

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 ~0.3μm/min at t=40min–74min, then dramatically accelerated to ~4μm/min at t=74min–80min (termed “fast deposition regime”), and subsequently decelerated in the final plating regime (t=80min–100min). EBSD analyses showed that the electrolytic Cu predominantly possessed high-angle grain boundaries with strong coincidence site lattices at ∑3 (60° rotation at <111>) and ∑9 (38.9° rotation at <101>) 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=74min–80min), 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.