Obtaining different orientation relationships for Cu films grown on (0001) α-Al2O3 substrates by magnetron sputtering

Cu films were grown on (0001) alpha-Al2O3 single-crystals by magnetron sputtering. The growth behavior was manipulated by Ar+-ion sputter cleaning of the substrates at kinetic energies between 100 and 500 eV, changing the sputter rate from 0.75 to 1.1 nm/s, and using nominal substrate temperatures of 100 and 200 degrees C, respectively. Polycrystalline Cu films formed on alpha-Al2O3 substrates after an Ar+-ion bombardment at 500 eV, while epitaxial Cu films evolved when Ar+-ion energies of 100 and 200 eV were used. The epitaxial Cu films always consisted of two twin-related growth variants. However, two different orientation relationships emerged which differ by a 30(degrees) in-plane rotation of the (111) oriented Cu films when the deposition rate is changed from 0.75 to 1.1 nm/s. The results will be discussed on the basis of differences in the growth process.