Growth of copper microflowers assisted by electromigration under a low current density and subsequent stress-induced migration

The growth of well-shaped copper (Cu) microflowers assisted by electromigration (EM) and subsequent stress-induced migration (SM) is described. The Cu film is surrounded but not covered by a resist and is pre-stressed by EM under a low current density in air. After finishing the EM pre-stressing, the film has been stored for 6 months in a vacuum at room temperature, and the time-dependent growth of Cu microflowers due to SM is detected. The grown Cu microflowers are about 1-3 μm in size, and the petals are 0.1-1 μm wide and several tens of nanometers thick. The growth mechanism, which is based on atomic diffusion, is discussed. The growth environment is considered to be a key factor in the shape formation of Cu microflowers.