Abstract
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.
Highlights
Mechanical characteristics like residual stresses, hardness, elastic modulus and, interfacial adhesion are of great importance for advanced coating technologies [1]
Three series of W/Cu multilayers have been deposited by ion beam sputtering on (001) silicon wafers, each one with a different tungsten thickness and a constant copper thickness
For a copper nominal thickness smaller than 0.5 nm, an additional {111} component of texture in tungsten layers is observed. This is the first time that {111} fiber-texture is observed in tungsten thin films
Summary
Mechanical characteristics like residual stresses, hardness, elastic modulus and, interfacial adhesion are of great importance for advanced coating technologies [1]. Studying and tailoring the size effect on elastic constants of polycrystalline thin films require controlling the nanostructure (grain size, residual stresses, texture). Regarding the system studied here, namely W/Cu multilayers, and in spite of the immiscibility of the two materials under condition of thermodynamic equilibrium, physical vapour deposition (PVD) may induce mixing effects. This effect results from the fact that PVD layers are out of equilibrium [7]. Because of the very small diffracting volumes and the need for quantitative strain measurements to study size effects on elastic constants, obtaining textured tungsten is an essential issue. The present paper reports on the evolution of the microstructure and texture in function of the thickness of the spacer and of the tungsten layers
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