Extremely anisotropic single-crystal growth in nanotwinned copper

By electroplating of nearly unidirectionally <111>-oriented nanotwinned and fine-grained Cu on a Si wafer surface followed by annealing at 400-500 °C for up to 1 h, we grew many extremely large <100>-oriented single crystals of Cu with sizes ranging from 200 to 400 μm. By patterning and annealing the nanotwinned Cu films, we grew an array of <100>-oriented single crystals of Cu with sizes ranging from 25 to 100 μm on Si. In comparison, single-crystal nano-wire growth is a one-dimensional anisotropic growth process, in which the growth along the axial direction is much faster than in the radial direction. We report here a bulk-type two-dimensional crystal growth of an array of numerous <100>-oriented single crystals of Cu on Si. This growth process has the potential for microbump applications in three-dimensional integrated circuit-packaging technology for hand-held consumer electronic products.