Depth-dependent self-annealing behavior of electroplated Cu

The remarkable microstructure evolution of as-electroplated Cu in a few hours at room temperature is generally termed Cu self-annealing, which might induce transitions of the resistivity, internal stress, impurity distribution, and crystallographic defects that govern the physical/chemical characteristics of an entire Cu film. In this study, we performed a cross-sectional investigation of this time-dependent phenomenon to investigate the crystallographic/microstructure transition during the Cu self-annealing procedure. The crystallographic evolution of electroplated Cu, including grain size distribution, crystallographic orientation, and grain boundary (GB) characteristics, with respect to various Cu deposition depths and self-annealing times (t), were investigated using a scanning electron microscope (SEM) combined with an electron backscatter diffraction (EBSD) analysis system. The initiation of Cu grain growth was from the bottom of electroplated Cu (i.e., the substrate side), and the orientation of the newly developed Cu grains correlated with the substrate (Cu) orientation. The bottom-up Cu grain growth accompanying the GB elimination provided a rationalization for the redistribution (out-diffusion) of impurities with t. This knowledge advances our understanding of the overview of the electroplated Cu microstructure evolution during its self-annealing procedure.