The effect of chromium dopant on the microstructure and mechanical properties of sputter-deposited copper films

Cu and Cu(Cr) alloy films were sputtered on Si substrates covered with thermally grown SiO2. Atomic force microscopy, transmission electron microscopy, nano-indentation and four-point probe method were used to characterize the microstructure and properties of films, respectively. It was found that a small amount of Cr refined the Cu grains and decreased the surface roughness of films. After annealing at 450 °C, in contrast to the Cu films with large equiaxed grains, the Cu(Cr) alloy films exhibited a bimodal grain size distribution with fine columnar grains. In addition, high-density twins and preferably oriented columnar grains were found in the Cu(Cr) alloy films. As a result, the hardness and Young's modulus of Cu(Cr) films were much higher than those of Cu films. The final resistivity of the annealed Cu(Cr) alloy films was 2.55 μΩ cm which was close to that of the annealed Cu films.