STUDY ON INHERENT STRESS OF VAPORIZED Ag FILM ON THE LASER REFLECTING MIRROR

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Ag film on the LASER reflecting mirror is made by PVD such as ion plating or vapor deposition. Measuring the stresses in these two types of Ag films on the glass by X-ray diffracting method, it is appeared that ion plating film has a prioriyt of crystal growth orientation different from vapor deposited film which has random orientation of crystal growth. Then in this study, attention was paid on the vapor deposited Ag films to evaluate the residual stresses by experiments and/or analyzes. Using X-ray diffraction method, residual stresses of two types of Ag vapor deposited films were measured. The one type was Ag film with NaCl substrate. In this case, compressive residual stress less than -70MPa was obtained on the film. The second type, was Ag film without NaCl substrate after separating to each other. The residual stress on the surface of this separated Ag film was less than <plus-minus>20MPa and was almost zero when thickness of film was less than 2.0mum. Similarly, the residual stress on the back surface (substrate side) was about <plus-minus>15MPa and was almost zero when thickness of film was less than 2.0mum. By these measuring results, it became clear that there was some hardened layr within 2.0mum in depth from film/substrate interface such as an inherent strain. Consequently, the residual stresses on the Ag vapor deposited films can be evaluated by compound method of "beam theory" and "inherent stress theory" based on elasticity and its equation for estimation was newly propo