Application of the digital phase-shifting method in 3D deformation measurement at micro-scale by SEM

There have been many approaches for three-dimensional (3D) deformation measurement at the macro-scale, but these methods are mostly not applicable to 3D deformation measurement at the micro-scale due to the low resolution. With the broad application of the scanning electron microscope (SEM) at micro-scale measurement, in-situ deformation measurement under SEM has been made feasible. The 3D deformation measurement method based on digital phase shifting and the SEM system is proposed in this paper. In the proposed method, two SEM images of a specimen grating at different tilting angles are required to solve the in-plane and out-of-plane displacement. The digital generated reference grating is superimposed with the SEM images of a the specimen grating at different tilting angles to form the digital moire. Using the digital phase-shifting method, the phase information of the grating at different tilting angles can be acquired. With the derived relationship between the phase of the grating at different tilting angles and the in-plane and out-of-plane displacement, 3D displacement can be obtained. To verify the feasibility and assess the accuracy, a numerical experiment is conducted to reverse the given in-plane and out-of-plane deformation. The proposed method is used to measure the out-of-plane deformation of aluminum film on a soft substrate. The successful results indicate that this method is feasible and has the potential to be applied in 3D deformation measurement at micro-scale.