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

High aspect ratio (∼15) and ultrafine pitch (∼35μm) 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 ∼20nm) 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 (∼2.4GPa) than that with lower twin density (∼1.8GPa). The electrical conductivity of the electroplated copper (2.2μΩcm) is retained comparable to the pure copper.