Measurement of residual stress by slot milling with focused ion-beam equipment

In this paper, the authors present a new approach to residual stress measurement that takes advantage of the combined imaging-milling capabilities of focused ion-beam equipment. The method is based on the measurement of the displacement field originated when a slot of a few microns is milled on the material under study. The fitting of the experimental results with an analytical model together with the independent determination of Young's modulus allows us to find the residual stress of the layer under study. The complete experimental procedure is described and its feasibility is demonstrated on a LPCVD silicon nitride micromachined membrane. Values obtained by this new method show a good agreement with values obtained by a classical method such as the bulge test