A method for in situ measurement of the residual stress in thin films by using the focused ion beam

A new method for the in situ measurement of the residual stresses, σR, in thin films, thickness h, is described. It is based on the combined capability of the focused ion beam (FIB) imaging system and of high-resolution strain mapping software (vic-2d). The method can be used for any film material (whether amorphous or crystalline) without thinning the substrate. In the method, a region of the film surface is highlighted and scanning electron images of that region taken before and after a long slot, depth a, is introduced using the FIB. The mapping software evaluates the displacement of the surface normal to the slot, ux, by using naturally occurring features on the film surface. Numerical results relate the displacements to σR. The accuracy of the method has been assessed by performing measurements on thin (sub-micron) films of diamond-like carbon on glass substrates. Independent measurements of the residual stress exist for this system. The new method determines σR to within 5% of the magnitude determined independently. New possibilities enabled by the method are discussed, such as the ability to perform local measurements and to ascertain through thickness gradients.