Microstructure and properties of Cu-C pseudoalloy films prepared by sputter deposition

The microstructure and properties of Cu-C pseudoalloy films prepared by RF magnetron sputtering have been investigated. As Cu and C are mutually immiscible, nonequilibrium supersaturated solid solutions of C in Cu with nanocrystalline microstructures were observed in as-deposited films. Upon heating of the films, three major transition events took place. Recovery occurred at approx280-300 deg C, while at approx400 deg C, crystallites started to growth and coalescence, due to the release of strain energies stored during deposition. Annealing at > 600 deg C led to the occurrence of grain growth and altered the microstructure considerably. Although attempts have been made in this study, a possible annealing-induced phase separation could not be unambiguously identified. Yet, the fact of low twin densities and fine grain structures observed in the annealed films suggests that the extensive grain growth was impeded by the presence of carbon. Resistivity and hardness properties correlated well with the film microstructure and were governed by the impurity effect of carbon. Low-carbon Cu-C films yielded relatively low resistivity, attributable to the improved film microstructure. Hardness results indicted the strengthening of films was mainly due to fine structure, presence of carbon, and grain refinement by annealing twins.