Residual Stress Measurement on Thin Films Using Low Energy Synchrotron Radiation

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Residual stress was measured on sputter-deposited copper (Cu) thin films with a thickness of 0.2 to 3 μm by the x-ray diffraction method using synchrotron radiation. The influence of the surface energy of the substrate on the residual stress of the Cu thin films was studied. Polytetrafluoroethylene (PTFE) was used for the middle layer because it has much smaller surface energy than that of Si. The tendencies of the residual stress against the thin film thickness were very different according to the surface energy of the layer below. The crystallite size of the Cu sputtered on PTFE was smaller than the Cu sputtered on Si. The intrinsic stress calculated using a model proposed by L.B.Freund and Eric Chason [J.Appl.Phys.89,48(2001)] almost agreed with the measured residual stress. It was found that the residual stress of the Cu layer can be estimated by the crystallite size of Cu, which depends on the surface energy of the material of the layer below the Cu film, and the thickness of Cu film.