The effect of eigenstrain induced by ion beam damage on the apparent strain relief in FIB-DIC residual stress evaluation

FIB milling using Ga ions is known to be accompanied by implantation, multiplication of material defects, material property modification (e.g. amorphisation), inelastic shrinking/swelling and residual stress generation. These processes affect the reliability of the micro-ring-core method for residual stress evaluation. Safe use of this technique requires formulating approaches that provide quantitative criteria of the method's validity. In the present study this task is accomplished by proposing a numerical model based on eigenstrain. Parametric simulations were performed to identify the extent to which the FIB-DIC micro-ring-core measurements are affected. As an example of a real and relevant material system, the procedure was applied to silicon material. The curvature of an AFM cantilever due to FIB damage was monitored, and the eigenstrain magnitude determined by matching the model to observations. Using the resulting eigenstrain profile, parametric analysis was performed in terms of the pillar radius, and the elastic strain field calculated at the pillar surface that is monitored in the FIB-DIC micro-ring-core method. An important property of the model is its versatility that allows it to be adapted to different milling conditions and geometries to determine the ultimate spatial resolution limits of the FIB-DIC method.