An improvement of an optical method for in situ measurement of the intrinsic stress in thin films is described. The method presented is based on the well-known beam bending technique using the deflection of a laser beam that reflects itself on a sample. The first new development lies in the evaluation of the bending plate equation. The second uses image processing to determine the deformation of the sample. The method has been applied to pure chromium films on glass substrates to validate the stress measurements. The reproducibility of stress measurement is of about 8%. Results show the great adaptability of the technique to any kind of stress evolution during the physical vapor deposition process and give additional information about the evolution of stress versus film thickness, in comparison with ex situ techniques. Finally, a correlation between stress measurement and microstructure has been carried out.
Chromium layers have been deposited by three PVD techniquesvacuum arc evaporation, vacuum evaporation, and dc magnetron sputteringat substrate temperatures up to 500°C. The samples have been subjected to stress detection by analysis of the stress-induced sample bending, some of them by X-ray stress analysis, too. The subject of the investigations is the explanation of the dependence of the intrinsic film stress on the substrate temperature for each method, and a comparison of the obtained results. The most important difference between the deposition techniques is the average energy of the layer forming species. It is shown that there is a clear correspondence between these energies and the difference in the stress evolution in dependence on the substrate temperature for the different deposition techniques.
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