Mechanical measurement of the residual stress in thin PVD films

Abstract

A practical mechanical bending plate method is proposed to calculate the residual stress present in thin physical vapour deposition films. A thin circular foil of stainless steel is coated with TiN, using an unbalanced magnetron sputtering technique. Sectioning of this foil into narrow strips leads to an easily measurable radius of curvature. With the help of calculations based on the finite element method it is shown that, if the width-to-length ratio is small, the analytical formula of Senderoff is valid. Above a certain width-to-length ratio, serious errors in calculated stress values are introduced using Senderoff. The second part of this paper describes the influences of the deposition parameters of TiN on the residual stress in the coating. An increase of the bias voltage results in a higher compressive stress, varying from −4.2 to −7.2 GPa. Experiments with different substrate materials show that the growth stress is independent of the substrate material. The total residual stress present in the coating increases with a higher magnetron current and a lower working gas pressure. There was excellent agreement between the results of the proposed method and X-ray diffraction (Seemann-Bohlin).