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 6months 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 1–3μm in size, and the petals are 0.1–1μm 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. ► We succeeded in an abundant growth of Cu microflowers through a physical approach. ► We found EM could induce a time-dependent growth of Cu micro materials. ► Growth mechanism based on atomic diffusion for Cu microflowers was investigated. ► We found the growth environment may be a key for a flower-shape formation of Cu.