Mechanical properties of highly (111)-oriented nanotwinned Cu lines

Abstract

Previous paper has reported that nanotwinned copper has very high mechanical strength, reasonable ductility, low electrical resistivity and ability in improving electromigration reliability.([1]-[3]) Based on these advantages, nanotwinned copper (nt-Cu) is becoming a promising application in electronic industries. In the studies of K Lu et al., nt-Cu shows excellent mechanical properties.([4]) The ductility of nanotwinned copper is still limited. In addition, highly (111)-oriented nt-Cu films have been fabricated by electroplating in 2012. ([5]) However, the mechanical properties of the highly (111)oriented nt-Cu films have not been examined. Whether the nt-Cu films can possess higher mechanical strength and maintain reasonable ductility is of interests. To prepare the (111)-oriented nanotwinned copper, we used CuSO4-based electroplating solution with suitable additives. The thicknesses of the electroplated films for tensile tests are 7-20 m. Control specimens without (111) nt-Cu are also fabricated for comparison. In this research, we investigate the effect of nanotwinned structure on mechanical properties. The results indicate that the tensile strength of the nt-Cu films can reach to 700 MPa, which are much higher than the samples without (111) nanotwins. However, the elongation of the (111) nt-Cu was less than 10%.