A novel sampling moire method and its application for distortion calibration in scanning electron microscope

High-resolution scanning electron microscope (SEM) is widely used for microscale material and structure characterization. However, the distortion in SEM imaging causes serious error for the quantitative measurement of optical methods. In previous work, the distortion calibration requires to set up a mathematic model of SEM imaging and then to determine the model parameters by calculation. The distortion filed is hard to directly extract from the SEM image by classic methods. In order to tackle this problem, we developed a direct sampling moire method (DSM) for simple and fast analysis of grating distortion. In DSM, the distortion fields can be directly presented visually through processing a single grating image. The measurement accuracy of DSM was verified by numerical simulation to be better than the classic sampling moire. In the experiment, a standard grating with pitch of 6.5 mu m was used in DSM to calibrate the distortion fields at different magnifications (50 x, 100 x, 150 x, 300 x) in SEM. The fitting results of the calibrated distortion field agreed well with the existing distortion model, which demonstrated the feasibility of DSM for distortion calibration in SEM.