Structures and Properties of Cu/W Nanostructured Multilayers Deposited by Sputtering

Silicon-supported and polyimide-based Cu/W nanostructured multilayers with modulation period lambda=25 similar to 150 nm and modulation ratio eta=0.5 similar to 2 were deposited by magnetron sputtering. The microstructure, surface topography, mechanical and electrical properties of multilayers were investigated by XRD, SEM, EDS, AFM, microforce testing system, nanoindentor and four point probe method. The results indicate that the structure and properties of multilayers are influenced significantly by lambda and eta. The nanocrystalline structure Cu and W layers of multilayers are of Cu(111) and W(110) preferred orientation, respectively. The interplanar spacing of W(110) decreases and the descending range is correlated positively with 1/lambda or eta, and there is a diffusion intermixing layer on the interface of Cu/W layers. The grain size of the uppermost Cu layer increases with the increasing Cu layer thickness. The critical strain of crack initiation epsilon(c) decreases generally with the increasing lambda or decreasing eta while the yield strength (sigma(0.2), microhardness H and electrical resistivity rho are correlated negatively with lambda or eta. The changed thickness of Cu layer and W layer with the varying lambda or eta is corresponding to the changes in the grain size and the grain boundary density of Cu layer, the volume fraction of W layer and the amount of Cu/W interface, which cause the ability of dislocation motion and electron scattering effects to change, further to change the properties of Cu/W nanomultilayers.