Measurements of strain during vapour deposition of thin films and multilayers

Zinc selenide (ZnSe), barium fluoride (BaF2) and silver (Ag) single layer and multilayered thin films were deposited by thermal evaporation onto cantilevered substrate Si(100) with native oxide, near room temperature in high vacuum. The macroscopic strain in the film during and after deposition was determined from the change in electrical resistance of a strain gauge glued at the substrate back surface. The intrinsic component of the strain was obtained by subtraction of the apparent thermal component, obtained by measuring the strain in the heating phase of the deposition process. During the deposition, the strain in the film shows a general trend regardless of the growth parameters: initially it is negative with a linear behaviour, then reaches a broad minimum value and increases towards an asynthetic value after vacuum cooling. After deposition ends, residual strain analysis indicates tensile in-plane strain for all the investigated samples. When a multilayer BaF2/ZnSe/Ag/Si(100) is deposited continuously, the evolution of the features of the strain is different for the several layers, but it is same for the corresponding single layers. The BaF2/ZnSe interface strain can be related to the discontinuities in strain measured, during the process associated with the formation of the interface itself. These discontinuities were evaluated for both BaF2 on ZnSe and ZnSe on BaF2.