From uniform Cu thin films to 〈1 1 0〉 and 〈1 1 1〉 columns

This paper reports the transition phenomenon from uniform Cu thin films to 〈1 1 0〉 and 〈1 1 1〉 columns. Using magnetron sputtering technique, we deposit a series of Cu films on an SiO2/Si(1 1 1) substrate. Characterizations using the scanning electron microscopy (SEM), the transmission electron microscopy (TEM), and the X-ray diffraction (XRD) reveal the morphology, the crystal orientation and the internal strain of the Cu films and columns. The Cu films are always uniform and 〈1 1 1〉 textured during the early stage of deposition. For higher sputtering power and shorter target-substrate distance, the 〈1 1 1〉 uniform film yields to columns as deposition continues. This transition correlates with the internal strain in the uniform film. At moderate strain, the columns are of 〈1 1 0〉 orientation and they nucleate at the grain boundaries of the uniform film. At even higher strain, the columns are of 〈1 1 1〉 orientation and they form by the breakup of grains in the uniform film. Based on the strain characterization and the column formation mechanism, we suggest that strain energy is the driving force of the transitions from uniform films to columns.