Nano-scale residual stress depth profiling in Cu/W nano-multilayers as a function of magnetron sputtering pressure

Residual stresses in thin films and multi-layered coatings fabricated by physical vapour deposition largely affect their mechanical and thermal reliability during operation in numerous fields of applications. By changing the argon working pressure in between each multilayer planar DC magnetron sputter deposition step, it is possible to control the residual stress distribution within coatings. A combination of FIB-DIC ring-core strain analysis, synchrotron XRD analysis based on the sin2(Ψ) method and micro-cantilever deflection analysis is used to reconstruct the in-plane stress state of multilayer coatings at different deposition pressures, with a residual stress depth profile resolution of 50 nm. A clear transition from compressive to tensile residual stresses is observed with an increase of working pressure, with pronounced stress peaks near the substrate-coating interface. These peak stresses resolved by FIB-DIC ring-core analysis exceed the average XRD stress measurements significantly, thus providing a reasonable explanation for multilayer failure. Experimental results are presented and comprehensively discussed in the context of deposition conditions for different thin film applications.