Through-wafer electroplated copper interconnect with ultrafine grains and high density of nanotwins

High aspect ratio (similar to 15) and ultrafine pitch (similar to 35 mu m) through-wafer copper interconnection columns were fabricated by aspect-ratio-dependent electroplating. By controlling the process parameters, ultrafine copper grains with nanoscale twins (twin lamellar width similar to 20 nm) were obtained in the copper columns. Transmission electron microscope reveals that the density of these nanotwins depends on the location along the length of the columns. The highest twin density was achieved at the bottom of the column where the electroplating starts. The presence of higher density of the nanotwins yields significant higher hardness (similar to 2.4 GPa) than that with lower twin density (similar to 1.8 GPa). The electrical conductivity of the electroplated copper (2.2 mu Omega cm) is retained comparable to the pure copper. (c) 2007 American Institute of Physics.