Stress reduction mechanism of diamond-like carbon films incorporated with different Cu contents

Cu incorporated diamond-like carbon (Cu-DLC) films were deposited on Si/glass substrate by a hybrid ion beam deposition system, which consists of a direct current (DC) magnetron sputtering of Cu target and a linear ion source. The Cu concentration (from 0.1 to 39.7 at.%) in the Cu-DLC films was controlled by varying the sputtering current. The dependence of residual stress, microstructure and atomic bond structure upon Cu concentration was investigated systematically. Results indicated that the nanoscale Cu particles began to evolve from the carbon matrix in the Cu concentration range of 2.6-7.0 at.%. The residual stress of the Cu-DLC films (less than 0.60 GPa) showed a significant reduction compared with that of the pure carbon film (2.0 GPa). Theoretical calculations revealed that the formation of antibonding between Cu and C and the relaxation of distorted bond angles and bond length accounted for the significant reduction of residual stress caused by Cu incorporation.