Factors limiting the measurement of residual stresses in thin films by nanoindentation
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Experimental results and finite element simulations are presented to examine whether a recently developed nanoindentation method for measuring residual stresses in bulk, monolithic materials can be applied to thin films. The method is based on indentation with spherical indenters in the elastic-plastic transition regime. Experiments were performed on 7 m copper films and 5 m chromium films deposited on (100) silicon substrates using indenters with radii of 30, 69 and 122 m. The biaxial stresses in the films, which were controlled by processing, were verified by X-ray techniques. Nanoindentation measurement of the film stresses proved difficult due to practical considerations arising from surface roughness, substrate effects and problems in producing an appropriate reference specimen for comparison. Finite element simulations showed that the substrate problems can be alleviated by using an indenter with a radius of the order of (or smaller than) the film thickness. However, the other difficulties pose serious obstacles to the practical implementation of the method to thin film residual stress measurement. 2003 Elsevier B.V. All rights reserved.