Oxidation and Reduction Characteristics of Sputter-Deposited Cu Thin Films

The oxidation and reduction characteristics of sputter-deposited Cu thin film with a preferred orientation have been studied. It was found that Cu oxide, which is identified as phase, is easily formed by annealing at 200°C in an ambient. The linear relation between thickness and the square root of oxidation time indicates that the oxidation process of Cu films obeys a parabolic rate law at temperatures from 200 to 280°C. The activation energy of the oxidation reaction in the Cu film was 0.89 eV. The oxidized Cu films were reduced by annealing at 300°C. The formed in the Cu metal of a partially oxidized film was reduced at about 5 min, and the sheet resistance decreased to that of an as-deposited Cu film. The sheet resistance of a fully oxidized Cu film decreased with annealing time and saturated after about 10 min. As a result, the preoxidation sheet resistance could not be recovered. This incomplete recovery is due to the formation of voids in the reduced Cu film. Void-free reduced Cu films with low sheet resistance can be obtained by using appropriate temperatures and pressures during the annealing.