Determination of the mechanical properties of thin films by digital phase shifting interferometry

A new method for the measurement of internal stress and coefficient of thermal expansion of thin oxide films is presented and investigated experimentally, that combines digital phase shifting interferometry with image-processing technique to improve the accuracy of the conventional interferometric method. The change of the deflection (or curvature) of the coated substrates by the deposited film can be obtained by the phase maps. Using the Zernike polynomial fitting algorithm, a 3-D contour plot is generated from the polynomial coefficients to visualize the deformation of the thin film. Four oxide films prepared by ion beam sputter deposition with a Kaufman-type ion source are investigated for their mechanical properties. The contribution of the proposed method is to increase the sensitivity and accuracy of the temperature-dependence stress measurements.