Using Digital Image Correlation Method for Measuring Residual Stress in the Nickel Coating of the Specimen

During thin film deposition, the mismatching of thermal expansion coefficients may induce residual stresses in the films, damaging them. The digital image correlation (DIC) method is a nondestructive and noncontact optical testing method for measuring residual stress and is unaffected by the testing environment. Existing methods of measuring residual stress can be used to calculate only the mean thin film residual stress, and no accurate method for measuring full-field residual stress is available. However, thin film rupture or peeling occurs mostly when local residual stress is excessive. In this study, the isotropic properties of thin films are theoretically derived and validated using Stoney’s equation and DIC techniques. Accordingly, this work proposes a DIC-based method for measuring the residual stress of thin films. Nickel thin films were deposited on silicon substrates with the same dimensions using a dual electron-gun evaporation machine; the same set of processing parameters was used for the deposition of all films. To verify the accuracy of the proposed method, the residual stresses that were calculated using that method were compared with a typical residual stress that was obtained using Istar31 software in a three-dimensional profilometer. The results revealed that the error between these two methods was less than 7 %.