X-ray diffraction analysis of the structure and residual stresses of W/Cu multilayers

A structural study has been carried out on tungsten layers from W/Cu multilayers (copper plays the role of spacer) prepared by ion beam sputtering. Using X-ray diffraction, three series of W/Cu multilayers were prepared, each one with various tungsten thicknesses (12, 3, 1.5 nm) but with constant nominal copper thickness (1, 0.5, 0 nm). X-ray diffraction measurements reveal that tungsten layers are systematically under strong compressive stress state. Thin film average stress values obtained using curvature method are compressive and lower than those determined from tungsten x-ray diffraction. All the multilayers showed stratification as revealed by X-ray reflectometry diagrams. It has been observed that samples with nominal copper thickness beneath 0.5 nm present two preferential crystallographic orientations: namely {110} and {111}. Moreover, all observed textures present a rotational isotropy in the sample surface plane (fiber-texture). An original {111} tungsten fiber-texture has been evidenced and its presence depends on the interface quality. A correlation between measured stresses, interface oxidation and preferential crystallographic orientations is suggested.