Residual Stress, Mechanical Behavior and Electrical Properties of Cu/Nb Thin-Film Multilayers

The effect of compositional wavelength on the residual stress, electrical resistivities and mechanical properties of Cu/Nb thin-film multilayers sputtered onto single-crystal Si substrates was evaluated. Electrical resistivities were measured down to 4 °K using a standard four-point probe measurement system. A differential specimen-curvature technique was used to detennine residual stress, and a mechanical-properties microprobe was employed to obtain hardness and elastic modulus. Characterization techniques included profilometry, Ion-Beam Analysis (IBA) and Transmission Electron Microscopy (TEM). The hardness of the Cu-Nb multilayers increased with decreasing compositional wavelength so that the layered structures had hardness values in excess of either of the constituents and the hardness predicted by the rule of mixtures. A peak in the net residual compressive stress of the multilayers was observed at a compositional wavelength of 100 nm. No resistivity plateau was observed within the composition wavelength range studied.